Amoebiasis — a Protozoan of the Large Intestine

Amoebiasis, also called amoebic dysentery, is caused by the protozoan Entamoeba histolytica, which lives in the large intestine of humans. The typical symptoms are constipation, abdominal pain and cramps, and stools that carry excess mucus and blood clots.

The way it spreads is worth noting. Houseflies act as mechanical carriers — they pick up the parasite from the faeces of an infected person and deposit it on food and food products, contaminating them. The main source of infection, therefore, is drinking water and food contaminated by faecal matter, which is exactly why clean water and covered food matter so much.

Ascariasis and Filariasis — Two Worm Diseases

Some diseases are caused by helminths, the parasitic worms. Ascariasis is caused by Ascaris, the common roundworm, an intestinal parasite. Its symptoms include internal bleeding, muscular pain, fever, anaemia and blockage of the intestinal passage. The eggs of the worm pass out with the faeces of infected people and contaminate soil, water and plants; a healthy person then picks up the infection through contaminated water, vegetables and fruits.

Filariasis, better known as elephantiasis, is caused by the filarial worms Wuchereria (W. bancrofti and W. malayi). These worms live for years in the lymphatic vessels, usually of the lower limbs, and cause a slowly developing chronic inflammation there; the genital organs are often affected too, leading to gross deformities. The worms are transmitted from person to person through the bite of female mosquito vectors.

Ringworm — a Fungal Infection of the Skin

Ringworm is one of the most common infectious diseases and, unlike the others above, it is caused by fungi — those of the genera Microsporum, Trichophyton and Epidermophyton. The main symptoms are dry, scaly lesions on the skin, nails and scalp, accompanied by intense itching.

Heat and moisture help these fungi grow, so they thrive in skin folds such as those in the groin or between the toes. Ringworm is generally picked up from soil, or by using the towels, clothes or even the comb of an infected person — which is why sharing such personal items is best avoided.

Prevention and Control

Guarding against these diseases comes down to three kinds of measures. Personal hygiene means keeping the body clean and consuming clean drinking water, food, vegetables and fruits. Public hygiene means proper disposal of waste and excreta, and periodic cleaning and disinfection of water reservoirs, pools and tanks — measures that matter most for food- and water-borne diseases like amoebiasis and ascariasis.

For diseases spread by insects, such as filariasis and malaria, the key is vector control: not letting water stagnate in and around homes, cleaning household coolers, using mosquito nets, introducing fish like Gambusia that feed on mosquito larvae, spraying insecticides in ditches and swamps, and fitting doors and windows with wire mesh. These steps have become all the more important given the spread of the vector-borne (Aedes mosquito) diseases dengue and chikungunya in many parts of India.

Quick Recap

  • Amoebiasis — Entamoeba histolytica in the large intestine; constipation, cramps, stools with mucus and blood; houseflies are mechanical carriers; spreads by faecally contaminated food and water.
  • Ascariasis — Ascaris (roundworm), an intestinal parasite; internal bleeding, muscular pain, fever, anaemia, intestinal blockage; eggs in faeces contaminate soil, water and plants.
  • Filariasis (elephantiasis) — Wuchereria (W. bancrofti, W. malayi); chronic inflammation of the lymphatic vessels (usually lower limbs) and genital organs; spread by female mosquito vectors.
  • Ringworm — fungi Microsporum, Trichophyton, Epidermophyton; dry scaly lesions with intense itching; thrive in heat and moisture; spread via soil and shared towels, clothes and combs.
  • Prevention — personal hygiene, public hygiene and vector control (no stagnant water, mosquito nets, Gambusia fish, insecticides, wire mesh); dengue and chikungunya spread by Aedes mosquitoes.

Solved Examples — Section 4

Q1. Name the causative organism of amoebiasis and the organ it affects.

Answer: Amoebiasis is caused by the protozoan Entamoeba histolytica, which lives in the large intestine of humans.

Q2. How do houseflies contribute to the spread of amoebiasis?

Answer: Houseflies act as mechanical carriers — they transfer the parasite from the faeces of an infected person to food and food products, contaminating them.

Q3. Which worm causes ascariasis, and how does a healthy person acquire it?

Answer: Ascariasis is caused by Ascaris, the roundworm. Its eggs pass out in faeces and contaminate soil, water and plants; a healthy person is infected through contaminated water, vegetables and fruits.

Q4. What causes filariasis, and which part of the body is chiefly affected?

Answer: It is caused by the filarial worms Wuchereria (W. bancrofti and W. malayi), which cause chronic inflammation of the lymphatic vessels, usually of the lower limbs (and often the genital organs).

Q5. Ringworm is caused by which group of organisms, and what conditions favour their growth?

Answer: Ringworm is caused by fungi of the genera Microsporum, Trichophyton and Epidermophyton. Heat and moisture favour them, so they thrive in skin folds like the groin and between the toes.

Q6. Give one control measure suited to a water-borne disease and one suited to a vector-borne disease.

Answer: For a water-borne disease like amoebiasis, ensure clean drinking water and proper disposal of excreta. For a vector-borne disease like filariasis, control the mosquitoes — avoid stagnant water, use mosquito nets and introduce Gambusia fish that eat the larvae.