Human Health and Disease
Health and common diseases
Name the pathogen, symptoms and spread of common diseases.
Health is not just the absence of disease. It is a state of complete physical, mental and social well-being. It depends on our genes, on infections, and very much on our lifestyle: what we eat and drink, whether we rest and exercise, and our habits.
Diseases that spread from person to person are infectious. They are caused by pathogens: bacteria, viruses, fungi, protozoans and worms (helminths). The common ones:
| Disease | Pathogen | How it spreads; signs |
|---|---|---|
| Typhoid | Bacterium Salmonella typhi | Contaminated food and water. Sustained high fever (39-40 °C), weakness, stomach pain, loss of appetite; can perforate the intestine. Confirmed by the Widal test. |
| Pneumonia | Bacteria Streptococcus pneumoniae, Haemophilus influenzae | Droplets or sharing utensils. Infects the air sacs of the lungs, which fill with fluid; fever, chills, cough; lips and fingernails may turn grey or blue. |
| Common cold | Rhino viruses | Droplets, or touching contaminated objects. Infects the nose and respiratory passage, not the lungs. Lasts 3-7 days. Antibiotics do not work on viruses. |
| Malaria | Protozoan Plasmodium | Bite of the female Anopheles mosquito. |
| Amoebiasis | Protozoan Entamoeba histolytica | Food and water contaminated by houseflies carrying faeces. Constipation, cramps, stools with mucus and blood. |
| Ascariasis | Roundworm Ascaris | Eggs in contaminated water, vegetables and fruit. Internal bleeding, muscular pain, fever, blocked intestine. |
| Filariasis (elephantiasis) | Worm Wuchereria | Mosquito bite. Long-lasting swelling, mostly of the legs, due to blocked lymph vessels. |
| Ringworm | Fungi Microsporum, Trichophyton, Epidermophyton | Towels, combs, soil. Dry, scaly, itchy patches on skin, nails and scalp; grows in warm, moist folds of skin. |
Malaria in more detail. Infected mosquitoes inject Plasmodium in a form called sporozoites. They multiply first in the liver, then in red blood cells, which burst. Each burst releases a toxin, haemozoin, causing a bout of chill and high fever that recurs every three to four days. Plasmodium falciparum causes the most serious form, malignant malaria. When a mosquito bites an infected person, the parasite completes its development inside the mosquito, ready to infect someone else.
Prevention:
- Personal hygiene: clean body, clean drinking water, clean food.
- Public hygiene: proper disposal of waste and sewage, clean water supplies, cleaning tanks and pits.
- Controlling vectors: removing stagnant water where mosquitoes breed, spraying insecticides, using mosquito nets, and introducing fish such as Gambusia into ponds, which eat mosquito larvae.
- Vaccination: vaccines have controlled many diseases. Smallpox has been eradicated completely, and polio, diphtheria, pneumonia and tetanus have been largely controlled.
For bacterial diseases, antibiotics are a powerful cure. They do not work on viruses.
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