Human nematode parasites


Nematodes are helminths that are elongated, wormiform, pseudocoelomates and are commonly known as roundworms because of their cylindrical body, which is different from other helminths that are flat worms. They are very common and widely distributed free living as well as parasitic animals. Parasitic nematodes are found in a variety of plants and animals and cause various diseases.

Whip Worm (Trichuris trichiura). The intestinal infection by whip-worms causes nausea, vomiting, constipation, headache and fever and in severe infections may cause anaemia and eosinophilia. The adult worms are thin and small, with posterior end broad resembling the handle of a whip. Male is curved on the posterior side while female is straight. Eggs are released along with faeces and infection is direct by ingesting contaminated food.

Thread Worm(Strongyloides stercoralis). Thread worm infection causes nausea, dizziness and bloody diarrhea. Sometimes vomiting, cough and fever may also occur. The worms are long and thread-like found in the intestine and lay thousands of eggs which pass outside with faeces. The larvae hatch in soil and are capable of free existence by feeding on organic debris. But larvae can also penetrate through the sole of feet and become parasitic. They travel through the circulation, reaching lungs, trachea and then swallowed along with sputum. Upon reaching intestine they molt to become adults.

Trichinia Worm (Trichinellaspiralis). Symptoms of disease are nausea, vomiting, muscular pain, oedema and fever. This worm is common in western countries. The worm is found in intestine where it produces juveniles that penetrate the intestinal mucosa to enter blood circulation. Larvae through the blood reach muscles, where they coil and get encysted and become dormant. Infection to the carnivorous animal takes place by eating the encysted larvae along with flesh.

Hook Worm (Ancylostoma duodenale).  The American species of hook worm is called Necatoramericanus. Symptoms include gastrointestinal disturbances, anaemia, weakness, dizziness, headache and nervous disorders. The adults are 3-5 cm long, female being straight and male curved on the posterior end. The worm carries a hook on the anterior end to anchor on the intestinal villi. Eggs are released in intestine and excreted through stools. Larvae hatch in soil, feed on debris and become infective. The soil bound larvae penetrate through the skin of feet and get into the blood circulation. They reach intestine via the lung, trachea land swallowed sputum route and molt to become adult. 

Guinea Worm (Dracunculus medinensis).This worm is also called fiery serpent and occurs in desert areas of Indo-African region. Adult female is 30-40 cm long while male is about10 cm long. Female after mating migrates to the cutaneous tissue of hands and feet which normally come in contact with water. When people go to water bodies to fetch water the female worms release juveniles in water. The larvae penetrate the body of Cyclops, a crustacean commonly found in freshwater in arid areas. Humans get infected by drinking water that contains infected crustaceans.

Pin Worm (Enterobius vermicularis). Pinworm infection is common in children and unhygienic adults. Symptoms include loss of appetite, sleeplessness, bed-wetting, grinding of teeth, nausea and vomiting. The worm is found in large intestine and migrates to anal area to lay eggs. Eggs are sticky and cause itching, resulting in their transfer to hands and clothes and eventually to different places in the house including food items. Man gets direct infection by consuming food and water contaminated with eggs.