Helminthiases

worm diseases; worm infestations; diseases resulting from the infestation of animals or man with worms (helminths). Helminthiases are widespread throughout the world.

Helminthiases in man. Human beings may become infested with helminths belonging to the trematodes (digenetic flukes), cestodes (tapeworms), and nematodes (round-worms). Human beings and animals sometimes become infested with acanthocephalans (proboscis or thorn-head worms). Depending on the species of helminth, helminthiases are classified as trematodiases, cestodiases, nematodiases, and acanthocephaliases. The helminthiases most commonly found in man include opisthorchosis and fascioliasis (both trematodiases); diphyllobothriasis, hymenolepiasis, taeniasis, and echinococcosis (all cestodiases); and ascariasis, enterobiasis, ancylostomiasis, trichinosis, dracunculiasis, and trichuriasis (all nematodiases). Some helminthiases are common to man and animals (the so-called helminthozoonoses).

Ascariasis, trichuriasis, and some other diseases develop after the consumption of vegetables, fruits, and greens contaminated by the soil. Dirty hands may also be responsible for contamination. (The eggs or larvae of the helminths that cause these diseases reach the infestation stage in soil.) Taeniasis, cestodiasis, opisthorchosis, trichinosis, and other diseases, which are caused by helminths whose larvae are formed in the body of an intermediate host, develop after the consumption of raw or inadequately cooked meat, fish, and other foods. The larvae of certain helminths (for example, filiariae) enter the body through the bites of blood-sucking insects, and the larvae of other helminths (ancylostomes, schistosomes) are capable of actively penetrating the skin.

The course of a helminthiasis varies with a number of factors, including the species of parasite, the number of helminths entering the body, their location, and the condition of the patient. The pathogenic effect of helminths in the body consists of sensitization and subsequent development of allergic reactions, toxicity, mechanical injury to tissues that promotes the penetration of an infection into the body, and absorption of blood and some food, especially vitamins. The introduction of helminths may make the host immune to subsequent infestations.

Helminthiases are diagnosed mainly by finding the eggs or larvae of parasitic worms in the patient’s feces. Immunological methods of diagnosis have been developed for several helminthiases. Treatment depends on the species of helminth that caused the disease. Preventive measures that can be taken by the individual include careful washing of vegetables and fruits, keeping hands clean, and cooking meat and fish adequately. Systematic dehelminthization is also done.

Helminthiases in animals. Farm, game, and wild animals are parasitized by over 2,000 species of helminths belonging to the flat, round, and proboscis worms. These diseases occur all over the world and inflict great economic damage by lowering animal productivity and by killing animals. Helminths may parasitize most organs and tissues, causing diseases that vary in severity and outcome. Depending on the classification of the helminths, helminthiases of animals are divided into trematodiases, cestodiases, nematodiases, and acanthocephaliases. The trematodiases of domestic animals that have the most practical significance are fascioliasis, dicroceliasis, and paramphistomiasis of ruminants. The most important cestodiases are monieziasis, avitellinosis, thysanieziosis, echinococcosis and coenurosis of sheep, and cestodiasis of dogs and waterfowl. Among the nematodiases the most significant are ascariasis of swine, dogs, furbearing animals, horses, and birds, dictyocauliasis of ruminants, and strongylosis of sheep. The most important acanthocephaliases are macracanthorhynchosis, polymorphosis, and filicolliases of waterfowl. Pond fish culture is greatly harmed by such fish helminthiases as bothriocephaliasis, philometrosis, liguliasis, dactylogyrosis, sanguinocolosis, diplostomatosis, and gyrodactyliasis.

Helminthiases can be controlled by general measures, including improvement of the feeding and maintenance of animals, setting aside isolated pastures for young animals, biothermal sterilization of manure, and cultivation of pastures. Prevention of animal helminthiases also involves veterinary anthelmintic measures such as preventive and therapeutic dehelminthization of animals and dehelminthization of the environment.