Stopping a Course of Medicine Early Is How a Curable Illness Turns Resistant
Learn the symptoms and control of cholera, typhoid and tuberculosis, then AIDS, chicken pox and hepatitis, then malaria, amoebiasis and sleeping sickness, then ascariasis, taeniasis and filariasis.
Why does a patient who feels better still have to finish the tablets?
A person with tuberculosis begins treatment and within a few weeks feels considerably better. The cough eases, the fever settles, the appetite returns. The medicine is clearly working, and there are months of it still to take.
Stopping now is one of the most damaging things that patient can do — and not only to themselves.
The medicine kills the weakest bacteria first. Within a few weeks the great majority are gone, which is exactly why the patient feels well. What is left is the hardiest fraction: the ones that survive longest, resist best and are slowest to be killed.
Stop the treatment at that point and those are the bacteria that multiply back. The illness returns, and it returns as a population descended entirely from the toughest survivors — an infection that the same medicine no longer controls.
So an incomplete course does not merely fail to cure. It selects for resistance, and the resistant strain is then passed on to other people, who get an illness that was treatable and is no longer.
That is the single most useful idea in this chapter, and it applies well beyond tuberculosis. Every disease on this page has symptoms you can learn and control measures you can carry out, and in almost every case the control turns out to be simpler and cheaper than the treatment.
This page covers the second part of the ICSE Class 9 Biology chapter on health and hygiene: the bacterial diseases cholera, typhoid and tuberculosis; the viral diseases AIDS, chicken pox and hepatitis; the protozoan diseases malaria, amoebic dysentery and sleeping sickness; and the helminthic diseases ascariasis, taeniasis and filariasis.
Stopping now is one of the most damaging things that patient can do — and not only to themselves.
The medicine kills the weakest bacteria first. Within a few weeks the great majority are gone, which is exactly why the patient feels well. What is left is the hardiest fraction: the ones that survive longest, resist best and are slowest to be killed.
Stop the treatment at that point and those are the bacteria that multiply back. The illness returns, and it returns as a population descended entirely from the toughest survivors — an infection that the same medicine no longer controls.
So an incomplete course does not merely fail to cure. It selects for resistance, and the resistant strain is then passed on to other people, who get an illness that was treatable and is no longer.
That is the single most useful idea in this chapter, and it applies well beyond tuberculosis. Every disease on this page has symptoms you can learn and control measures you can carry out, and in almost every case the control turns out to be simpler and cheaper than the treatment.
This page covers the second part of the ICSE Class 9 Biology chapter on health and hygiene: the bacterial diseases cholera, typhoid and tuberculosis; the viral diseases AIDS, chicken pox and hepatitis; the protozoan diseases malaria, amoebic dysentery and sleeping sickness; and the helminthic diseases ascariasis, taeniasis and filariasis.
What are the symptoms and control of cholera, typhoid and tuberculosis?
Two of these three spread through contaminated water and the third through the air, and the difference decides the whole control strategy.
Cholera — caused by Vibrio cholerae, spread by contaminated water and food.
- Symptoms: sudden severe watery diarrhoea, painless and profuse, with stools like rice water; vomiting; severe dehydration with sunken eyes, a dry tongue and loose skin; muscle cramps; very little urine; a weak pulse and cold clammy skin. Death can follow quickly, and it is caused by the loss of water and salts rather than by the bacteria themselves
- Control: drink boiled or chlorinated water; sanitary disposal of faeces; wash hands with soap; cover food; kill flies; give oral rehydration solution immediately to replace the lost water and salts; antibiotics; vaccination; isolate the patient and disinfect the articles used
Typhoid — caused by Salmonella typhi, spread by contaminated water and food.
- Symptoms: a continuous fever that rises in a step-ladder fashion over about a week; headache and body ache; loss of appetite; constipation followed later by diarrhoea; a coated tongue with foul breath; rose-coloured spots on the abdomen; an enlarged spleen; and great weakness. A serious complication is perforation of the intestine
- Control: boiled water and hygienically prepared food; sanitary latrines; TAB vaccination; antibiotics; disinfect the patient's stools and urine; and identify and treat carriers — people who harbour the bacteria without being ill themselves and who must be kept away from handling food
Tuberculosis — caused by Mycobacterium tuberculosis, spread by droplet infection through coughing, sneezing and spitting.
- Symptoms: a persistent cough lasting more than two or three weeks, sometimes with blood-stained sputum; chest pain; an evening rise of temperature with night sweats; loss of weight and appetite; and increasing weakness. It attacks the lungs chiefly, but can also affect the bones, joints, intestine, lymph nodes and brain
- Control: BCG vaccination; do not spit in public; cover the mouth while coughing; live in well-ventilated, sunlit rooms and avoid overcrowding; good nutrition; screen the patient's contacts; and complete the full prescribed course of antibiotics
Notice the carrier problem in typhoid, because it is genuinely awkward. A carrier has no symptoms at all and is not ill, yet passes the bacteria in the faeces and urine. So a perfectly healthy-looking cook can be the source of an outbreak, and no amount of isolating the sick would stop it.
That is why control of typhoid requires the water supply and hand-washing rather than only the treatment of patients — the source may not be a patient at all.
And tuberculosis is the disease on which completing the course matters most, for the reason this page opened with. A question asking why tuberculosis treatment must be continued for months even after the patient feels well wants the resistance argument, and it is the most important sentence in this section.
Cholera — caused by Vibrio cholerae, spread by contaminated water and food.
- Symptoms: sudden severe watery diarrhoea, painless and profuse, with stools like rice water; vomiting; severe dehydration with sunken eyes, a dry tongue and loose skin; muscle cramps; very little urine; a weak pulse and cold clammy skin. Death can follow quickly, and it is caused by the loss of water and salts rather than by the bacteria themselves
- Control: drink boiled or chlorinated water; sanitary disposal of faeces; wash hands with soap; cover food; kill flies; give oral rehydration solution immediately to replace the lost water and salts; antibiotics; vaccination; isolate the patient and disinfect the articles used
Typhoid — caused by Salmonella typhi, spread by contaminated water and food.
- Symptoms: a continuous fever that rises in a step-ladder fashion over about a week; headache and body ache; loss of appetite; constipation followed later by diarrhoea; a coated tongue with foul breath; rose-coloured spots on the abdomen; an enlarged spleen; and great weakness. A serious complication is perforation of the intestine
- Control: boiled water and hygienically prepared food; sanitary latrines; TAB vaccination; antibiotics; disinfect the patient's stools and urine; and identify and treat carriers — people who harbour the bacteria without being ill themselves and who must be kept away from handling food
Tuberculosis — caused by Mycobacterium tuberculosis, spread by droplet infection through coughing, sneezing and spitting.
- Symptoms: a persistent cough lasting more than two or three weeks, sometimes with blood-stained sputum; chest pain; an evening rise of temperature with night sweats; loss of weight and appetite; and increasing weakness. It attacks the lungs chiefly, but can also affect the bones, joints, intestine, lymph nodes and brain
- Control: BCG vaccination; do not spit in public; cover the mouth while coughing; live in well-ventilated, sunlit rooms and avoid overcrowding; good nutrition; screen the patient's contacts; and complete the full prescribed course of antibiotics
Notice the carrier problem in typhoid, because it is genuinely awkward. A carrier has no symptoms at all and is not ill, yet passes the bacteria in the faeces and urine. So a perfectly healthy-looking cook can be the source of an outbreak, and no amount of isolating the sick would stop it.
That is why control of typhoid requires the water supply and hand-washing rather than only the treatment of patients — the source may not be a patient at all.
And tuberculosis is the disease on which completing the course matters most, for the reason this page opened with. A question asking why tuberculosis treatment must be continued for months even after the patient feels well wants the resistance argument, and it is the most important sentence in this section.
What are the symptoms and control of AIDS, chicken pox and hepatitis?
All three are viral, so none of them can be treated with an antibiotic — and their routes of spread are completely different from one another.
AIDS — Acquired Immuno Deficiency Syndrome, caused by HIV, the Human Immunodeficiency Virus.
- How it spreads: unprotected sexual contact with an infected person; transfusion of infected blood or blood products; sharing contaminated needles and syringes; and from an infected mother to her child during pregnancy, at birth or through breast milk
- How it does NOT spread: shaking hands, hugging, sharing food or utensils, using the same toilet, mosquito bites, coughing or sneezing. This matters as much as the list above, because the fear of casual contact causes real harm to patients and prevents nobody from being infected
- Symptoms: the virus destroys the helper T-lymphocytes, so the body's immunity collapses. There is a long period with no symptoms, then persistent fever, night sweats, severe loss of weight, chronic diarrhoea and swollen lymph nodes — and then repeated infections that a healthy body would resist easily, such as tuberculosis, pneumonia and fungal infections, together with certain cancers
- Control: use only screened blood for transfusion; use disposable needles and syringes; safe sexual practice; testing and treatment of infected pregnant women; and education and awareness. Antiretroviral drugs control the virus and prolong life, but there is no vaccine and no cure
Chicken pox — caused by the varicella virus, spread by droplet infection and by contact with the fluid from the blisters or with contaminated articles.
- Symptoms: mild fever, headache and body ache, then a rash that appears first on the trunk and spreads outwards. Each spot passes from a flat red mark to a raised fluid-filled blister and then to a scab, with intense itching — and spots at different stages are present at the same time
- Control: isolate the patient until the last scab has fallen; do not share clothes, towels or bedding; disinfect the patient's articles; vaccination; soothing applications and antiviral medicine to relieve the symptoms; and avoid scratching, which leaves scars and admits bacteria
Hepatitis — inflammation of the liver caused by hepatitis viruses, and commonly called jaundice.
- How it spreads, and this is the part that carries the marks: hepatitis A and E spread through contaminated water and food — the faecal-oral route; hepatitis B and C spread through infected blood, needles and sexual contact, and from mother to child
- Symptoms: fever, loss of appetite, nausea and vomiting, pain in the upper right abdomen, yellowing of the skin, eyes and nails, dark yellow urine, pale stools, and extreme weakness
- Control: boiled water and hygienic food for A and E; screened blood and disposable syringes for B and C; sanitary disposal of waste; vaccination against hepatitis A and B; rest, a light low-fat diet and no alcohol
Now the point that makes hepatitis worth studying carefully. It is the same organ disease — an inflamed liver, with the same yellowing and the same weakness — reached by two completely different routes.
So the question "how do you prevent jaundice?" has two answers, and which one applies depends entirely on the type. Boiling the water is useless against hepatitis B, and screening blood is useless against hepatitis A.
A question that asks for the prevention of hepatitis without specifying the type expects both routes to be named — and that is exactly the kind of distinction an examiner sets, because a student who has learnt the disease as a single entry gets half of it wrong.
AIDS — Acquired Immuno Deficiency Syndrome, caused by HIV, the Human Immunodeficiency Virus.
- How it spreads: unprotected sexual contact with an infected person; transfusion of infected blood or blood products; sharing contaminated needles and syringes; and from an infected mother to her child during pregnancy, at birth or through breast milk
- How it does NOT spread: shaking hands, hugging, sharing food or utensils, using the same toilet, mosquito bites, coughing or sneezing. This matters as much as the list above, because the fear of casual contact causes real harm to patients and prevents nobody from being infected
- Symptoms: the virus destroys the helper T-lymphocytes, so the body's immunity collapses. There is a long period with no symptoms, then persistent fever, night sweats, severe loss of weight, chronic diarrhoea and swollen lymph nodes — and then repeated infections that a healthy body would resist easily, such as tuberculosis, pneumonia and fungal infections, together with certain cancers
- Control: use only screened blood for transfusion; use disposable needles and syringes; safe sexual practice; testing and treatment of infected pregnant women; and education and awareness. Antiretroviral drugs control the virus and prolong life, but there is no vaccine and no cure
Chicken pox — caused by the varicella virus, spread by droplet infection and by contact with the fluid from the blisters or with contaminated articles.
- Symptoms: mild fever, headache and body ache, then a rash that appears first on the trunk and spreads outwards. Each spot passes from a flat red mark to a raised fluid-filled blister and then to a scab, with intense itching — and spots at different stages are present at the same time
- Control: isolate the patient until the last scab has fallen; do not share clothes, towels or bedding; disinfect the patient's articles; vaccination; soothing applications and antiviral medicine to relieve the symptoms; and avoid scratching, which leaves scars and admits bacteria
Hepatitis — inflammation of the liver caused by hepatitis viruses, and commonly called jaundice.
- How it spreads, and this is the part that carries the marks: hepatitis A and E spread through contaminated water and food — the faecal-oral route; hepatitis B and C spread through infected blood, needles and sexual contact, and from mother to child
- Symptoms: fever, loss of appetite, nausea and vomiting, pain in the upper right abdomen, yellowing of the skin, eyes and nails, dark yellow urine, pale stools, and extreme weakness
- Control: boiled water and hygienic food for A and E; screened blood and disposable syringes for B and C; sanitary disposal of waste; vaccination against hepatitis A and B; rest, a light low-fat diet and no alcohol
Now the point that makes hepatitis worth studying carefully. It is the same organ disease — an inflamed liver, with the same yellowing and the same weakness — reached by two completely different routes.
So the question "how do you prevent jaundice?" has two answers, and which one applies depends entirely on the type. Boiling the water is useless against hepatitis B, and screening blood is useless against hepatitis A.
A question that asks for the prevention of hepatitis without specifying the type expects both routes to be named — and that is exactly the kind of distinction an examiner sets, because a student who has learnt the disease as a single entry gets half of it wrong.
What are the symptoms and control of malaria, amoebic dysentery and sleeping sickness?
All three are caused by protozoa, and each is named in practice by the route it takes rather than by the parasite.
Malaria — caused by Plasmodium, transmitted by the bite of an infected **female Anopheles mosquito.
- Symptoms: attacks of fever in three stages — a cold stage with shivering and a violent chill, a hot stage with high fever, headache and a burning sensation, and a sweating stage as the temperature falls and the patient is left exhausted. The attacks recur at regular intervals, every second or third day depending on the species, and there is anaemia, an enlarged spleen and increasing weakness
- Control: destroy the mosquito and its breeding places — remove stagnant water, spray oil on standing water, introduce larvivorous fish, spray insecticide, fill in ditches; prevent the bite — mosquito nets, screens, repellents, full-sleeved clothing; and treat patients promptly with antimalarial drugs, which reduces the reservoir of parasites available to the next mosquito
Amoebic dysentery, or amoebiasis — caused by Entamoeba histolytica, which lives in the large intestine. Spread by contaminated water and food, by flies, and by infected food handlers.
- Symptoms: frequent loose stools with mucus and blood; griping pain in the abdomen; a repeated urgent desire to pass stools; flatulence, nausea, loss of appetite and weight; and weakness. A serious complication is an abscess of the liver
- Control: boiled water and clean food; sanitary latrines; wash hands with soap; kill flies and cover food; wash raw vegetables thoroughly; and treat both patients and cyst passers, who pass the infective cysts without being ill
Sleeping sickness — caused by Trypanosoma, transmitted by the bite of the tsetse fly.
- Symptoms: fever, headache, joint pain, swollen lymph nodes and a sore at the site of the bite. Later the parasite reaches the brain and nervous system, producing confusion, a disturbed sleep pattern with sleepiness by day and sleeplessness by night, difficulty in speech, personality change, and eventually coma
- Control: control the tsetse fly — clear the bush in which it breeds, set traps, spray insecticide; wear protective clothing; and screen and treat infected people early. It does not occur in India; it is found in parts of Africa
Now the pattern across the three, and it is worth stating because it is how the control measures are remembered.
- Malaria is a mosquito problem, so you attack the mosquito
- Amoebiasis is a water and food problem, so you clean the water and the hands
- Sleeping sickness is a fly problem, so you clear the bush the fly breeds in
In none of the three is the parasite itself the primary target. Treating patients matters, and in malaria it genuinely reduces transmission — but the measure that prevents the disease at scale is always aimed at the route, not at the organism.
And notice the cyst passer in amoebiasis, which is the same awkward problem as the typhoid carrier: a person with no symptoms who is nevertheless infective. So in both diseases, isolating the visibly ill is not enough**, and that is why the water supply and hand-washing do the real work.
Malaria — caused by Plasmodium, transmitted by the bite of an infected **female Anopheles mosquito.
- Symptoms: attacks of fever in three stages — a cold stage with shivering and a violent chill, a hot stage with high fever, headache and a burning sensation, and a sweating stage as the temperature falls and the patient is left exhausted. The attacks recur at regular intervals, every second or third day depending on the species, and there is anaemia, an enlarged spleen and increasing weakness
- Control: destroy the mosquito and its breeding places — remove stagnant water, spray oil on standing water, introduce larvivorous fish, spray insecticide, fill in ditches; prevent the bite — mosquito nets, screens, repellents, full-sleeved clothing; and treat patients promptly with antimalarial drugs, which reduces the reservoir of parasites available to the next mosquito
Amoebic dysentery, or amoebiasis — caused by Entamoeba histolytica, which lives in the large intestine. Spread by contaminated water and food, by flies, and by infected food handlers.
- Symptoms: frequent loose stools with mucus and blood; griping pain in the abdomen; a repeated urgent desire to pass stools; flatulence, nausea, loss of appetite and weight; and weakness. A serious complication is an abscess of the liver
- Control: boiled water and clean food; sanitary latrines; wash hands with soap; kill flies and cover food; wash raw vegetables thoroughly; and treat both patients and cyst passers, who pass the infective cysts without being ill
Sleeping sickness — caused by Trypanosoma, transmitted by the bite of the tsetse fly.
- Symptoms: fever, headache, joint pain, swollen lymph nodes and a sore at the site of the bite. Later the parasite reaches the brain and nervous system, producing confusion, a disturbed sleep pattern with sleepiness by day and sleeplessness by night, difficulty in speech, personality change, and eventually coma
- Control: control the tsetse fly — clear the bush in which it breeds, set traps, spray insecticide; wear protective clothing; and screen and treat infected people early. It does not occur in India; it is found in parts of Africa
Now the pattern across the three, and it is worth stating because it is how the control measures are remembered.
- Malaria is a mosquito problem, so you attack the mosquito
- Amoebiasis is a water and food problem, so you clean the water and the hands
- Sleeping sickness is a fly problem, so you clear the bush the fly breeds in
In none of the three is the parasite itself the primary target. Treating patients matters, and in malaria it genuinely reduces transmission — but the measure that prevents the disease at scale is always aimed at the route, not at the organism.
And notice the cyst passer in amoebiasis, which is the same awkward problem as the typhoid carrier: a person with no symptoms who is nevertheless infective. So in both diseases, isolating the visibly ill is not enough**, and that is why the water supply and hand-washing do the real work.
What are the symptoms and control of ascariasis, taeniasis and filariasis?
All three are caused by worms, and the route of entry — swallowed or injected — decides everything about the control.
Ascariasis — caused by Ascaris lumbricoides, the roundworm, living in the small intestine. Spread by swallowing its eggs in contaminated water, food or soil, often on unwashed raw vegetables or from unwashed hands.
- Symptoms: abdominal pain, nausea, loss of appetite, anaemia and malnutrition because the worm consumes the host's food, restlessness, diarrhoea or constipation. A heavy infestation can block the intestine. The migrating larvae pass through the lungs and cause cough and fever, and worms may be passed in the stool
- Control: sanitary latrines and proper disposal of faeces; boiled water; wash raw vegetables and fruit thoroughly; wash hands with soap before eating; do not use untreated sewage as manure; cut the nails short and avoid putting fingers in the mouth; and deworming medicine
Taeniasis — caused by Taenia solium, the tapeworm, living in the small intestine. Spread by eating undercooked pork containing the larval cysts; the beef tapeworm is contracted the same way from beef.
- Symptoms: abdominal pain, alternating hunger and loss of appetite, indigestion, loss of weight, anaemia and weakness, and segments of the worm passed in the stool. The dangerous complication comes if the eggs are swallowed: the larvae then encyst in the muscles, the eye and the brain, a condition called cysticercosis, which causes fits
- Control: cook meat thoroughly; inspect meat before sale; sanitary latrines, so that pigs cannot feed on human faeces and pick up the eggs; boiled water; wash hands; and treat infected people with anthelmintic drugs
Filariasis, also called elephantiasis — caused by Wuchereria bancrofti, transmitted by the bite of an infected **female Culex mosquito. The adult worms lodge in and block the lymphatic vessels.
- Symptoms: recurring fever with pain and inflammation of the lymph nodes and vessels; then swelling of the legs, arms, scrotum or breasts as lymph accumulates behind the blockage, with the skin over the swelling becoming thick, rough and hard — which is the appearance that gives the disease its common name. The swelling is disfiguring and, once established, permanent
- Control: control the Culex mosquito, which breeds in dirty stagnant water — clean the drains, remove standing water, spray insecticide; prevent bites with nets, screens and repellents; mass administration of antifilarial medicine in affected areas; treat patients; and careful hygiene and care of the affected limb
Now the classification that makes these three easy to hold together.
- Ascariasis and taeniasis enter through the mouth — one by swallowing eggs, the other by eating undercooked meat. So both are prevented by food and water hygiene and by sanitary latrines
- Filariasis enters through a mosquito bite. So it is prevented by vector control, exactly like malaria, and hygiene in the kitchen does nothing for it
And there is a sting in the tail of taeniasis that is worth noticing. Eating the undercooked meat gives you the adult worm in the intestine, which is unpleasant but treatable. Swallowing the eggs gives you larvae encysted in the muscles and the brain, which is far more serious.
So a person carrying the adult worm is a danger to others and to themselves — the eggs they pass can be swallowed by anybody, including by the patient through their own unwashed hands. That is why sanitation and hand-washing matter even after the meat has been cooked properly**, and it is the detail that turns this from a list of symptoms into a piece of reasoning.
Ascariasis — caused by Ascaris lumbricoides, the roundworm, living in the small intestine. Spread by swallowing its eggs in contaminated water, food or soil, often on unwashed raw vegetables or from unwashed hands.
- Symptoms: abdominal pain, nausea, loss of appetite, anaemia and malnutrition because the worm consumes the host's food, restlessness, diarrhoea or constipation. A heavy infestation can block the intestine. The migrating larvae pass through the lungs and cause cough and fever, and worms may be passed in the stool
- Control: sanitary latrines and proper disposal of faeces; boiled water; wash raw vegetables and fruit thoroughly; wash hands with soap before eating; do not use untreated sewage as manure; cut the nails short and avoid putting fingers in the mouth; and deworming medicine
Taeniasis — caused by Taenia solium, the tapeworm, living in the small intestine. Spread by eating undercooked pork containing the larval cysts; the beef tapeworm is contracted the same way from beef.
- Symptoms: abdominal pain, alternating hunger and loss of appetite, indigestion, loss of weight, anaemia and weakness, and segments of the worm passed in the stool. The dangerous complication comes if the eggs are swallowed: the larvae then encyst in the muscles, the eye and the brain, a condition called cysticercosis, which causes fits
- Control: cook meat thoroughly; inspect meat before sale; sanitary latrines, so that pigs cannot feed on human faeces and pick up the eggs; boiled water; wash hands; and treat infected people with anthelmintic drugs
Filariasis, also called elephantiasis — caused by Wuchereria bancrofti, transmitted by the bite of an infected **female Culex mosquito. The adult worms lodge in and block the lymphatic vessels.
- Symptoms: recurring fever with pain and inflammation of the lymph nodes and vessels; then swelling of the legs, arms, scrotum or breasts as lymph accumulates behind the blockage, with the skin over the swelling becoming thick, rough and hard — which is the appearance that gives the disease its common name. The swelling is disfiguring and, once established, permanent
- Control: control the Culex mosquito, which breeds in dirty stagnant water — clean the drains, remove standing water, spray insecticide; prevent bites with nets, screens and repellents; mass administration of antifilarial medicine in affected areas; treat patients; and careful hygiene and care of the affected limb
Now the classification that makes these three easy to hold together.
- Ascariasis and taeniasis enter through the mouth — one by swallowing eggs, the other by eating undercooked meat. So both are prevented by food and water hygiene and by sanitary latrines
- Filariasis enters through a mosquito bite. So it is prevented by vector control, exactly like malaria, and hygiene in the kitchen does nothing for it
And there is a sting in the tail of taeniasis that is worth noticing. Eating the undercooked meat gives you the adult worm in the intestine, which is unpleasant but treatable. Swallowing the eggs gives you larvae encysted in the muscles and the brain, which is far more serious.
So a person carrying the adult worm is a danger to others and to themselves — the eggs they pass can be swallowed by anybody, including by the patient through their own unwashed hands. That is why sanitation and hand-washing matter even after the meat has been cooked properly**, and it is the detail that turns this from a list of symptoms into a piece of reasoning.
Exam tip
Exam tip: pathogen, symptoms, control — three parts, every time
Give the causative organism by name for every disease. Vibrio cholerae, Salmonella typhi, Mycobacterium tuberculosis, HIV, varicella, Plasmodium, Entamoeba histolytica, Trypanosoma, Ascaris lumbricoides, Taenia solium, Wuchereria bancrofti.
Cholera kills by DEHYDRATION — give rice-water stools, vomiting, cramps and sunken eyes, and name oral rehydration solution first among the measures.
Typhoid has a STEP-LADDER fever, rose spots on the abdomen and an enlarged spleen. Name TAB vaccination and the carrier problem.
Tuberculosis is AIR-BORNE — a cough of more than two or three weeks, blood-stained sputum, evening rise of temperature, night sweats, weight loss. Name BCG and say the full course must be completed to avoid resistance.
For AIDS give both lists — how it spreads and how it does not. Say the virus destroys the helper T-lymphocytes and that there is no vaccine and no cure.
Chicken pox has spots at DIFFERENT STAGES together, and the patient stays isolated until the last scab falls.
Hepatitis has TWO routes — A and E by contaminated water and food, B and C by blood, needles and sexual contact. Name both or lose half the marks.
Malaria has THREE stages — cold with shivering, hot with high fever, sweating as it falls — recurring at regular intervals. Name the **female Anopheles.
Amoebic dysentery gives stools with MUCUS AND BLOOD and can cause a liver abscess; name the cyst passer.
Sleeping sickness is spread by the TSETSE FLY and reaches the brain, disturbing the sleep pattern.
Ascariasis is caught by swallowing EGGS; taeniasis by eating undercooked PORK; filariasis from the female Culex.
Cysticercosis comes from swallowing tapeworm EGGS, not from the meat — say which one when asked.
And group the control measures by route: food and water hygiene for the swallowed ones, vector control for malaria and filariasis, and ventilation and BCG** for tuberculosis.
Cholera kills by DEHYDRATION — give rice-water stools, vomiting, cramps and sunken eyes, and name oral rehydration solution first among the measures.
Typhoid has a STEP-LADDER fever, rose spots on the abdomen and an enlarged spleen. Name TAB vaccination and the carrier problem.
Tuberculosis is AIR-BORNE — a cough of more than two or three weeks, blood-stained sputum, evening rise of temperature, night sweats, weight loss. Name BCG and say the full course must be completed to avoid resistance.
For AIDS give both lists — how it spreads and how it does not. Say the virus destroys the helper T-lymphocytes and that there is no vaccine and no cure.
Chicken pox has spots at DIFFERENT STAGES together, and the patient stays isolated until the last scab falls.
Hepatitis has TWO routes — A and E by contaminated water and food, B and C by blood, needles and sexual contact. Name both or lose half the marks.
Malaria has THREE stages — cold with shivering, hot with high fever, sweating as it falls — recurring at regular intervals. Name the **female Anopheles.
Amoebic dysentery gives stools with MUCUS AND BLOOD and can cause a liver abscess; name the cyst passer.
Sleeping sickness is spread by the TSETSE FLY and reaches the brain, disturbing the sleep pattern.
Ascariasis is caught by swallowing EGGS; taeniasis by eating undercooked PORK; filariasis from the female Culex.
Cysticercosis comes from swallowing tapeworm EGGS, not from the meat — say which one when asked.
And group the control measures by route: food and water hygiene for the swallowed ones, vector control for malaria and filariasis, and ventilation and BCG** for tuberculosis.
Did you know
Why oral rehydration solution saves more lives than antibiotics in cholera
Cholera is caused by a bacterium, and antibiotics do kill it. So the obvious treatment for cholera is an antibiotic.
The treatment that actually saves the patient is a glass of water with a little salt and sugar dissolved in it.
The reason is in what cholera does. The bacterium settles in the intestine and produces a toxin that makes the intestinal wall pour out water and salts at an enormous rate. That is the watery diarrhoea, and it is not a side effect — it is the whole disease.
So the patient is not killed by the bacteria. The patient is killed by losing water and salts faster than they can be replaced, and that can happen within hours. Blood pressure falls, the kidneys stop, and the circulation fails.
An antibiotic shortens the illness and reduces how long the patient stays infective, both of which are genuinely useful. What it cannot do is put back the water. And by the time it has killed the bacteria, an untreated patient may already have died of dehydration.
Oral rehydration solution goes directly at the thing that kills. Water to replace the volume, salt to replace the sodium and chloride, and a measured amount of sugar — because glucose helps the intestine absorb sodium, so the salt goes in faster with the sugar present than without it.
It is made from ingredients found in every kitchen, needs no refrigeration, needs no doctor, needs no needle, and can be given by a family member. And it works.
There is a wider lesson in this for reading any disease. The question "what is the cause?" and the question "what is killing the patient?" can have different answers — and the treatment has to address the second. Cholera's cause is a bacterium and its danger is dehydration. Tetanus's cause is a bacterium and its danger is a toxin, which is why the treatment is an antitoxin rather than an antibiotic alone.
Treat the mechanism, not the label — and in cholera the mechanism is a tap left running.
The treatment that actually saves the patient is a glass of water with a little salt and sugar dissolved in it.
The reason is in what cholera does. The bacterium settles in the intestine and produces a toxin that makes the intestinal wall pour out water and salts at an enormous rate. That is the watery diarrhoea, and it is not a side effect — it is the whole disease.
So the patient is not killed by the bacteria. The patient is killed by losing water and salts faster than they can be replaced, and that can happen within hours. Blood pressure falls, the kidneys stop, and the circulation fails.
An antibiotic shortens the illness and reduces how long the patient stays infective, both of which are genuinely useful. What it cannot do is put back the water. And by the time it has killed the bacteria, an untreated patient may already have died of dehydration.
Oral rehydration solution goes directly at the thing that kills. Water to replace the volume, salt to replace the sodium and chloride, and a measured amount of sugar — because glucose helps the intestine absorb sodium, so the salt goes in faster with the sugar present than without it.
It is made from ingredients found in every kitchen, needs no refrigeration, needs no doctor, needs no needle, and can be given by a family member. And it works.
There is a wider lesson in this for reading any disease. The question "what is the cause?" and the question "what is killing the patient?" can have different answers — and the treatment has to address the second. Cholera's cause is a bacterium and its danger is dehydration. Tetanus's cause is a bacterium and its danger is a toxin, which is why the treatment is an antitoxin rather than an antibiotic alone.
Treat the mechanism, not the label — and in cholera the mechanism is a tap left running.
Exam relevance
Why does NEET keep returning to disease and its causative organisms?
Because Human Health and Disease asks for the same four facts about each disease — organism, transmission, symptoms, prevention — and that makes it one of the most systematically examinable chapters in the syllabus.
This is the foundation for Class 12 Biology Human Health and Disease, examined in NEET. That chapter covers almost every disease on this page with the same causative organisms named in the same way: Salmonella typhi for typhoid, Plasmodium for malaria, Entamoeba histolytica for amoebiasis, Wuchereria for filariasis, Ascaris for ascariasis, and HIV for AIDS. Match-the-column questions pairing a disease with its causative organism are the single most predictable item in the chapter, and the italicised names on this page are exactly what those questions test.
The malarial life cycle is examined in full. Class 12 traces Plasmodium through both hosts — sporozoites entering the human, multiplication in the liver, the red blood cell stage that ruptures the cells and causes the chill and fever, the gametocytes taken up by the mosquito, and fertilisation and development inside the mosquito's gut. So the three-stage fever described here is explained there by the synchronised rupture of red blood cells, and the mosquito is identified as the definitive host while the human is the intermediate host. That host terminology is a common trap.
AIDS is covered in detail and is heavily examined. Class 12 gives the retrovirus nature of HIV, the reverse transcriptase enzyme, the infection of helper T-lymphocytes and macrophages, the ELISA test for diagnosis, and the antiretroviral treatment. The transmission list and the does-not-spread list on this page are both examined, and questions on how HIV is not transmitted appear precisely because the misconception is so widespread.
The helminths reappear with their life cycles. Class 12 covers Ascaris and its soil-transmitted eggs, and filariasis with the lymphatic blockage described here. The distinction between contracting the adult worm from meat and contracting cysticercosis from the eggs is examined for the tapeworm, and it is the reasoning point this page makes.
Immunity supplies the treatment side. Class 12 covers active and passive immunity, vaccination, antibodies, and antibiotic resistance — which is the formal version of the argument this page opens with. Questions on why a full course of antibiotics must be completed are answered by selection of resistant strains, and the same chapter covers why antibiotics do not work on viruses, which is why none of the three viral diseases here can be treated with one.
Vector control connects to the previous part of this chapter and to ecology. The mosquito genera, the breeding habitats and the use of larvivorous fish as a biological control agent are all examinable, and biological control appears again in Class 12 Microbes in Human Welfare.
Public health appears as applied biology. Oral rehydration and the reasoning behind it, and the importance of sanitation over treatment, belong to the preventive side of the chapter — and the carrier and cyst passer ideas are examined as the reason isolation alone fails.
What the questions look like. For board work, expect name the causative organism, the symptoms and the control measures of a named disease, state how a named disease spreads, and give two preventive measures. Every disease answer wants all three parts, and the organism must be named. For NEET, expect disease-to-organism matching, the malarial life cycle with host terminology, HIV structure and diagnosis, and antibiotic resistance.
How board and competitive emphasis differ. A board paper rewards the symptoms listed with the control measures. A competitive paper assumes both and asks which host is definitive, which enzyme HIV carries, or which stage of the parasite is infective.
The single trap that costs the most marks. Treating hepatitis as one disease with one route. Hepatitis A and E travel by contaminated water and food; hepatitis B and C travel by blood, needles and sexual contact — so boiling the water prevents one pair and does nothing for the other. The defence is to write the type letters whenever you write the word hepatitis, because a prevention answer that names only one route is answering only half the question, and the examiner chose that disease precisely because it splits.
This is the foundation for Class 12 Biology Human Health and Disease, examined in NEET. That chapter covers almost every disease on this page with the same causative organisms named in the same way: Salmonella typhi for typhoid, Plasmodium for malaria, Entamoeba histolytica for amoebiasis, Wuchereria for filariasis, Ascaris for ascariasis, and HIV for AIDS. Match-the-column questions pairing a disease with its causative organism are the single most predictable item in the chapter, and the italicised names on this page are exactly what those questions test.
The malarial life cycle is examined in full. Class 12 traces Plasmodium through both hosts — sporozoites entering the human, multiplication in the liver, the red blood cell stage that ruptures the cells and causes the chill and fever, the gametocytes taken up by the mosquito, and fertilisation and development inside the mosquito's gut. So the three-stage fever described here is explained there by the synchronised rupture of red blood cells, and the mosquito is identified as the definitive host while the human is the intermediate host. That host terminology is a common trap.
AIDS is covered in detail and is heavily examined. Class 12 gives the retrovirus nature of HIV, the reverse transcriptase enzyme, the infection of helper T-lymphocytes and macrophages, the ELISA test for diagnosis, and the antiretroviral treatment. The transmission list and the does-not-spread list on this page are both examined, and questions on how HIV is not transmitted appear precisely because the misconception is so widespread.
The helminths reappear with their life cycles. Class 12 covers Ascaris and its soil-transmitted eggs, and filariasis with the lymphatic blockage described here. The distinction between contracting the adult worm from meat and contracting cysticercosis from the eggs is examined for the tapeworm, and it is the reasoning point this page makes.
Immunity supplies the treatment side. Class 12 covers active and passive immunity, vaccination, antibodies, and antibiotic resistance — which is the formal version of the argument this page opens with. Questions on why a full course of antibiotics must be completed are answered by selection of resistant strains, and the same chapter covers why antibiotics do not work on viruses, which is why none of the three viral diseases here can be treated with one.
Vector control connects to the previous part of this chapter and to ecology. The mosquito genera, the breeding habitats and the use of larvivorous fish as a biological control agent are all examinable, and biological control appears again in Class 12 Microbes in Human Welfare.
Public health appears as applied biology. Oral rehydration and the reasoning behind it, and the importance of sanitation over treatment, belong to the preventive side of the chapter — and the carrier and cyst passer ideas are examined as the reason isolation alone fails.
What the questions look like. For board work, expect name the causative organism, the symptoms and the control measures of a named disease, state how a named disease spreads, and give two preventive measures. Every disease answer wants all three parts, and the organism must be named. For NEET, expect disease-to-organism matching, the malarial life cycle with host terminology, HIV structure and diagnosis, and antibiotic resistance.
How board and competitive emphasis differ. A board paper rewards the symptoms listed with the control measures. A competitive paper assumes both and asks which host is definitive, which enzyme HIV carries, or which stage of the parasite is infective.
The single trap that costs the most marks. Treating hepatitis as one disease with one route. Hepatitis A and E travel by contaminated water and food; hepatitis B and C travel by blood, needles and sexual contact — so boiling the water prevents one pair and does nothing for the other. The defence is to write the type letters whenever you write the word hepatitis, because a prevention answer that names only one route is answering only half the question, and the examiner chose that disease precisely because it splits.
Key takeaways
Bacterial, viral, protozoan and helminthic diseases: quick revision
- Cholera — Vibrio cholerae, by contaminated water and food. Severe painless watery diarrhoea with rice-water stools, vomiting, dehydration, sunken eyes, cramps. Control: boiled water, sanitation, oral rehydration solution, antibiotics, vaccination, isolation. It kills by loss of water and salts.
- Typhoid — Salmonella typhi, by contaminated water and food. Step-ladder continuous fever, headache, coated tongue, rose spots on the abdomen, enlarged spleen; complication intestinal perforation. Control: boiled water, sanitary latrines, TAB vaccine, antibiotics, and finding carriers who have no symptoms.
- Tuberculosis — Mycobacterium tuberculosis, by droplet infection. Persistent cough over two or three weeks, blood-stained sputum, evening rise of temperature, night sweats, weight loss. Control: BCG, do not spit, ventilation and sunlight, avoid overcrowding, nutrition, and complete the full course of antibiotics.
- An incomplete course selects for resistance — the medicine kills the weakest bacteria first, so stopping early leaves the hardiest to multiply.
- AIDS — HIV. Spreads by unprotected sexual contact, infected blood, shared needles, and mother to child. Does not spread by handshakes, hugging, shared food, toilets, mosquitoes or coughing. It destroys the helper T-lymphocytes, so immunity collapses and ordinary infections become severe. Control: screened blood, disposable needles, safe practice, treating infected mothers, awareness. No vaccine and no cure.
- Chicken pox — varicella virus, by droplets and by blister fluid. Mild fever, then a rash from the trunk outwards, with flat marks, blisters and scabs present together. Control: isolate until the last scab falls, no shared clothes or bedding, disinfection, vaccination, avoid scratching.
- Hepatitis — inflammation of the liver, commonly jaundice. A and E by contaminated water and food; B and C by blood, needles and sexual contact. Fever, nausea, right upper abdominal pain, yellow skin, eyes and nails, dark urine, weakness. Control: boiled water for A and E; screened blood and disposable syringes for B and C; vaccination against A and B; rest and a low-fat diet.
- Malaria — Plasmodium, by the bite of the female Anopheles. Three stages — cold with shivering, hot with high fever, sweating as it falls — recurring at regular intervals, with anaemia and an enlarged spleen. Control: destroy the mosquito and its breeding water, larvivorous fish, oil on standing water, nets and repellents, prompt treatment.
- Amoebic dysentery — Entamoeba histolytica in the large intestine, by contaminated water and food and by flies. Loose stools with mucus and blood, griping pain, urgency, weight loss; complication a liver abscess. Control: boiled water, sanitary latrines, soap, kill flies, wash vegetables, treat cyst passers.
- Sleeping sickness — Trypanosoma, by the tsetse fly. Fever, swollen lymph nodes, then the brain is affected — confusion, disturbed sleep pattern, speech difficulty, coma. Control: clear the fly's breeding bush, traps, insecticide, protective clothing, early treatment. Not found in India.
- Ascariasis — Ascaris lumbricoides in the small intestine, by swallowing eggs in water, food or soil. Abdominal pain, anaemia and malnutrition, possible intestinal blockage, cough from migrating larvae. Control: sanitary latrines, boiled water, wash raw vegetables, wash hands, no untreated sewage as manure, deworming.
- Taeniasis — Taenia solium in the small intestine, from undercooked pork. Abdominal pain, weight loss, anaemia, segments passed in the stool. Swallowing the eggs instead causes cysticercosis in muscle, eye and brain, with fits. Control: cook meat thoroughly, meat inspection, sanitary latrines so pigs cannot reach human faeces, hand-washing.
- Filariasis (elephantiasis) — Wuchereria bancrofti, by the female Culex. The worms block the lymphatic vessels, giving recurring fever and then permanent swelling of legs, arms, scrotum or breasts with thick rough skin. Control: clean the drains and dirty stagnant water where Culex breeds, nets and repellents, mass antifilarial medicine, limb care.
- Group the control by route: food and water hygiene for the swallowed diseases, vector control for malaria and filariasis, and ventilation with BCG for tuberculosis.
Take any disease on this page and produce its organism, its route, two symptoms and two control measures in under a minute — if all four come out, this chapter is finished.
- Typhoid — Salmonella typhi, by contaminated water and food. Step-ladder continuous fever, headache, coated tongue, rose spots on the abdomen, enlarged spleen; complication intestinal perforation. Control: boiled water, sanitary latrines, TAB vaccine, antibiotics, and finding carriers who have no symptoms.
- Tuberculosis — Mycobacterium tuberculosis, by droplet infection. Persistent cough over two or three weeks, blood-stained sputum, evening rise of temperature, night sweats, weight loss. Control: BCG, do not spit, ventilation and sunlight, avoid overcrowding, nutrition, and complete the full course of antibiotics.
- An incomplete course selects for resistance — the medicine kills the weakest bacteria first, so stopping early leaves the hardiest to multiply.
- AIDS — HIV. Spreads by unprotected sexual contact, infected blood, shared needles, and mother to child. Does not spread by handshakes, hugging, shared food, toilets, mosquitoes or coughing. It destroys the helper T-lymphocytes, so immunity collapses and ordinary infections become severe. Control: screened blood, disposable needles, safe practice, treating infected mothers, awareness. No vaccine and no cure.
- Chicken pox — varicella virus, by droplets and by blister fluid. Mild fever, then a rash from the trunk outwards, with flat marks, blisters and scabs present together. Control: isolate until the last scab falls, no shared clothes or bedding, disinfection, vaccination, avoid scratching.
- Hepatitis — inflammation of the liver, commonly jaundice. A and E by contaminated water and food; B and C by blood, needles and sexual contact. Fever, nausea, right upper abdominal pain, yellow skin, eyes and nails, dark urine, weakness. Control: boiled water for A and E; screened blood and disposable syringes for B and C; vaccination against A and B; rest and a low-fat diet.
- Malaria — Plasmodium, by the bite of the female Anopheles. Three stages — cold with shivering, hot with high fever, sweating as it falls — recurring at regular intervals, with anaemia and an enlarged spleen. Control: destroy the mosquito and its breeding water, larvivorous fish, oil on standing water, nets and repellents, prompt treatment.
- Amoebic dysentery — Entamoeba histolytica in the large intestine, by contaminated water and food and by flies. Loose stools with mucus and blood, griping pain, urgency, weight loss; complication a liver abscess. Control: boiled water, sanitary latrines, soap, kill flies, wash vegetables, treat cyst passers.
- Sleeping sickness — Trypanosoma, by the tsetse fly. Fever, swollen lymph nodes, then the brain is affected — confusion, disturbed sleep pattern, speech difficulty, coma. Control: clear the fly's breeding bush, traps, insecticide, protective clothing, early treatment. Not found in India.
- Ascariasis — Ascaris lumbricoides in the small intestine, by swallowing eggs in water, food or soil. Abdominal pain, anaemia and malnutrition, possible intestinal blockage, cough from migrating larvae. Control: sanitary latrines, boiled water, wash raw vegetables, wash hands, no untreated sewage as manure, deworming.
- Taeniasis — Taenia solium in the small intestine, from undercooked pork. Abdominal pain, weight loss, anaemia, segments passed in the stool. Swallowing the eggs instead causes cysticercosis in muscle, eye and brain, with fits. Control: cook meat thoroughly, meat inspection, sanitary latrines so pigs cannot reach human faeces, hand-washing.
- Filariasis (elephantiasis) — Wuchereria bancrofti, by the female Culex. The worms block the lymphatic vessels, giving recurring fever and then permanent swelling of legs, arms, scrotum or breasts with thick rough skin. Control: clean the drains and dirty stagnant water where Culex breeds, nets and repellents, mass antifilarial medicine, limb care.
- Group the control by route: food and water hygiene for the swallowed diseases, vector control for malaria and filariasis, and ventilation with BCG for tuberculosis.
Take any disease on this page and produce its organism, its route, two symptoms and two control measures in under a minute — if all four come out, this chapter is finished.