Epidemiology Of Diseases- Ascariasis and Ancylostomiasis
Ascariasis (Roundworms)
The roundworm lives in the upper part of small intestine. It resembles and ordinary earthworm. The male measures upto 20 cm and the female up to 45 cm in length. The female lays eggs in large numbers which are passed in the faeces. They contaminate the soil or vegetables. Given optimal conditions, the egg takes about 10 days to become embryonated or infective. When the infective eggs are ingested, they reach the intestine where they hatch into larvae. The larvae penetrate the intestine and migrate to liver and lungs and then travel up to the trachea to pharynx to be swallowed by the human host. They reach the small intestine where they become sexually mature in about 6 to 10 weeks.
Problem In India
Roundworm infestation is widespread in India. In certain parts of the country like UP and Bihar, 30 to 50 percent of population are known to be infested.
Clinical features
The infestation is often symptomless. the parasite robs the human host of his nutrition and thus contributes to poor nutritional status, especially in children. The toxic body fluids of the parasite may produce such symptoms as urticaria. Heavy infestation can cause abdominal pain. At times the parasite may cause intestinal obstruction in children. Diagnosis is made by finding ova on microscopic examination of stool samples.
Epidemiological factors
(1) Age: Highest incidence is generally found in pre-school children. (2) Soil conditions: The eggs survive better in clay soil than in sandy soil (3) Human habits: The habit of open air defecation causes soil pollution and favours the spread of the disease (4) Mode of transmission: By ingestion of infective eggs from contaminated food or drink. (5) Incubation period: About 2 months- this is the time taken between ingestion of infective eggs ans the release of eggs by the female worm.
Prevention and control
Three kinds of action can be considered. (1) TREATMENT: The drugs of choice are piperazine and mebendazole. Chemotherapy should be aimed at the most heavily infected section of the population mainly small children or the most vulnerable (under nearest children). But drug treatment has no preventive value unless supplemented by sanitation measures. (2) SANITATION MEASURES: Use of sanitary excrete should be promoted in rural areas. Efficient sewage disposal offers the best approach for control of ascariasis on a long-term basis. (3) HEALTH EDUCATION: This should be directed towards raising the standards of personal and domestic hygiene that is hand washing with soap and water after defecation and before eating food; washing of vegetables before eating them raw and protection of food from flies.
Ancylostomiasis (Hookworms)
There are 2 types of hookworms- Ancylostoma dudenale and Nector americanus. They are found attached to the mucosa of the small intestine particularly in the jejunum. Each worm measures about 8 to 10 mm in length. Adult A. dudenale and N. americanus are believed to survive for on an average of one and four years respectively. The worms are passed in the faeces by infested persons.
The female parasite lays eggs which are passed in the faeces. A single female may lay 10000 2 20000 eggs per day. The eggs hatch into lava outside the human body in the soil where they grow and develop into infective larvae. When a person walks bare foot on contaminated soil, the infective lava penetrate the skin and enter the human host. They pass into the lymph and blood stream and reach the lungs; they travel up the trachea and the pharynx from where they are swallowed. The larvae finally reach the small intestine where they developed into sexually mature worms and start laying eggs in about 6 weeks.
Problems In India
It has been estimated that about 45 million people in India are infested with hookworms. The disease is highly endemic in Assam (tea garden of India) Kerala, West Bengal, certain parts of Uttar Pradesh, Bihar, Odisha and Andhra pradesh.
Clinical features
Hookworms occur in the small intestine, particularly jejunum. They cause small ulcers in the intestine and cause chronic blood loss. The ill effects of hookworm infestation are iron deficiency anaemia, oedema, heart failure, general disability, loss of body resistance and capacity for sustained hard work.
Epidemiological factors
(1) AGE: In endemic areas, the highest prevalence is in the age groups of 15 to 25 years. (2) SOIL CONDITION: Since hookworm larvae develop in the soil, the soil must be favorable. That is, the soil must be porous and contain moisture and organic matter. A temperature of 25 to 30 degree Celsius is considered favourable for its development. (3) HUMAN HABITS: The habit of open air defecation causes soil pollution and favours the spread of disease. The habit of walking barefoot results in transmission. (4) MODE OF NUTRITION: Infective lava from soil enters the human host by piercing through the skin of bare feet.(5) INCUBATION PERIOD: 6 weeks.
Prevention and control
(1) CHEMOTHERAPY : The drug of choice is mebendazole. It will remove both hookworms and roundworms. In areas where heavy hookworm infections are prevalent, community oriented chemotherapy may be necessary. The control of hookworm anaemia needs treatment with iron and folic acid. (2) SANITATION MEASURES : Use of sanitary excrete should be promoted in rural areas. This will prevent soil pollution. Efficient sewage disposal is the best approach for control of intestinal parasites. (3) HEALTH EDUCATION : This should be directed towards use of sanitary latrines, wearing shoes for personal prophylaxis and hand washing before eating food. In short, hookworm infection could be best controlled by improving sanitation health education and the wearing of shoes.
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