How a Mosquito Bite Passes Malaria From Person to Person

Health is more than the absence of disease. It is shaped by the genes we inherit, the infections we meet and the way we live — and many infections can be prevented once we understand how they spread.

This part covers what health means, protozoan and worm diseases such as malaria, bacterial, viral and fungal diseases such as typhoid and dengue, and the ways to prevent them.

Health is a state of complete physical, mental and social well-being, and it depends on three groups of factors — genetic disorders inherited from parents, infections caused by pathogens, and lifestyle, including diet, rest, exercise and habits.

Factors affecting health:

- Genetic disorders — deficiencies a child is born with, inherited from parents
- Infections — diseases caused by pathogens such as bacteria, viruses, fungi, protozoans and worms
- Lifestyle — food and water, rest and exercise, and habits such as smoking or drinking

Achieving good health:

- A balanced diet and personal hygiene
- Regular exercise
- Awareness of diseases, vaccination, proper waste disposal and control of vectors

Infectious and non-infectious diseases. Diseases that pass from one person to another, such as the common cold, are infectious; others, such as cancer, are non-infectious.

An everyday example. Daily yoga and a balanced thali of dal, vegetables and grains support both physical and mental well-being.

The substance. Mental and social well-being count as much as physical health — a person free of infection may still not be healthy.

Malaria is caused by Plasmodium protozoans carried by female Anopheles mosquitoes, amoebiasis by Entamoeba histolytica in contaminated food and water, ascariasis by the roundworm Ascaris whose eggs contaminate soil, water and food, and filariasis by Wuchereria worms spread by female Culex mosquitoes.

Malaria:

- Species — Plasmodium vivax, P. malariae and P. falciparum; malignant malaria from P. falciparum is the most serious and can be fatal
- In humans — sporozoites injected by an infected **female Anopheles multiply in liver cells and then attack red blood cells, which burst
- Bursting releases the toxin haemozoin, causing chills and high fever recurring every three to four days
- In the mosquito — parasites taken up with blood form gametes that fuse in its gut; the resulting sporozoites collect in its salivary glands, ready for the next bite

Amoebiasis** — Entamoeba histolytica, a protozoan living in the large intestine; causes constipation, abdominal pain, cramps and stools with mucus and blood; houseflies carry the parasite to food.

Ascariasis — the intestinal roundworm Ascaris; eggs pass out in faeces and contaminate soil, water and plants; symptoms include internal bleeding, muscular pain, fever, anaemia and blockage of the intestine.

Filariasis (elephantiasis) — Wuchereria bancrofti and W. malayi live in lymphatic vessels, causing chronic inflammation and gross swelling, often of the legs; spread by **female Culex mosquitoes.

An everyday example. Stagnant water in coolers, tyres and pots during the monsoon breeds the mosquitoes that spread malaria and filariasis.

The substance. Only female mosquitoes bite and spread these diseases**, because they need blood to develop their eggs.

Typhoid is caused by Salmonella typhi and confirmed by the Widal test, pneumonia by bacteria such as Streptococcus pneumoniae and Haemophilus influenzae, common cold by rhinoviruses, dengue and chikungunya by viruses carried by Aedes mosquitoes, and ringworm by fungi such as Microsporum, Trichophyton and Epidermophyton.

Bacterial diseases:

- Typhoid — Salmonella typhi enters the small intestine through contaminated food and water and spreads in the blood; causes sustained high fever of 39 to 40 °C, weakness, stomach pain, constipation, headache and loss of appetite; intestinal perforation can be fatal; confirmed by the Widal test
- Pneumonia — infects the alveoli, which fill with fluid; causes fever, chills, cough and headache, and in severe cases the lips and fingernails turn grey to bluish; spreads through droplets and shared utensils

Viral diseases:

- Common cold — rhinoviruses infect the nose and respiratory passage but not the lungs; causes nasal congestion, sore throat, cough and headache for 3 to 7 days
- Dengue and chikungunya — viruses spread by Aedes mosquitoes, which breed in clean stagnant water

Fungal disease:

- Ringworm — dry, scaly, intensely itchy lesions on skin, nails and scalp; heat and moisture help the fungi grow in skin folds; spreads from soil or through shared towels, clothes and combs

An everyday example. Street food washed in unclean water can carry Salmonella typhi, which is why typhoid spreads more where sanitation is poor.

The substance. Common cold viruses do not infect the lungs, whereas pneumonia attacks the alveoli directly.

Communicable diseases are prevented through personal hygiene, public hygiene with clean water and proper waste disposal, avoiding contact with infected people, controlling vectors such as mosquitoes, and vaccination, supported by modern medicines.

Personal hygiene:

- Keeping the body clean
- Drinking clean water and eating hygienic food, with vegetables and fruits washed well

Public hygiene:

- Proper disposal of waste and excreta
- Periodic cleaning and disinfection of water reservoirs and tanks

Vector-borne diseases such as malaria, filariasis, dengue and chikungunya:

- Remove stagnant water near homes and clean household coolers regularly
- Use mosquito nets and screens on doors and windows
- Release fish such as Gambusia, which eat mosquito larvae, into ponds
- Spray insecticides in ditches, drains and swamps

Vaccination and medicines:

- Vaccination and immunisation have eradicated smallpox and largely controlled polio, diphtheria, pneumonia and tetanus
- Antibiotics and other drugs treat many infections

An everyday example. Municipal teams fogging neighbourhoods during the monsoon target the adult mosquitoes that spread dengue and malaria.

The substance. Removing stagnant water prevents several diseases at once — malaria, dengue and chikungunya all depend on mosquitoes that breed in it.