Worms, fungi and prevention

Ascaris, the common round worm, is an intestinal parasite that causes ascariasis: internal bleeding, muscular pain, fever, anaemia and blockage of the intestinal passage.

Ascaris eggs leave in the faeces of an infected person and contaminate soil, water and plants; a healthy person is infected through contaminated water, vegetables and fruits.

Wuchereria (W. bancrofti and W. malayi), the filarial worms, live for many years usually in the lymphatic vessels of the lower limbs and cause a slow, chronic inflammation called elephantiasis or filariasis. Genital organs are often affected too, with gross deformities. Female mosquito vectors carry the worms by their bite.

Ringworm, one of the most common infectious diseases, is caused by fungi of the genera Microsporum, Trichophyton and Epidermophyton. It shows as dry, scaly lesions on the skin, nails and scalp, with intense itching.

Heat and moisture favour these fungi, so they thrive in skin folds such as the groin and between the toes. Ringworm is picked up from soil or from an infected person's towels, clothes or comb.

Personal hygiene (a clean body, clean drinking water, food, vegetables and fruit) and public hygiene (disposal of waste and excreta, periodic cleaning and disinfection of reservoirs, pools, cesspools and tanks, and hygienic public catering) matter most for food- and water-borne diseases: typhoid, amoebiasis and ascariasis.

For air-borne diseases such as pneumonia and the common cold, one must also avoid close contact with infected persons and their belongings.

For vector-borne malaria and filariasis, the key step is to control the vectors and their breeding places: no stagnant water near homes, cleaning household coolers, mosquito nets, Gambusia fish in ponds to eat mosquito larvae, insecticide in ditches, drains and swamps, and wire mesh on doors and windows. Aedes mosquitoes spread dengue and chikungunya.

Vaccination eradicated smallpox, and has largely controlled polio, diphtheria, pneumonia and tetanus. Antibiotics and other drugs treat many infectious diseases.