HOOKWORMS

HOOKWORMS


Hookworms belong to the phylum Nematoda, which contains worms that are round and unsegmented. Members of this phylum are called nematodes. There are thousands of species of nematodes, but only seven are of zoonotic importance in North America. These are Ancylostoma braziliense, A. caninum, A. tubaeformis, Uncineria stenocephala, Toxocara canis, Toxocara cati, and Baylisascaris procyonis.


T. canis, T. cati, and B. procyonis are nematode parasites that are discussed under roundworms.



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ETIOLOGY: PARASITIC


A. braziliense, A. caninum, A. tubaeformis, and U. stenocephala are all capable of infecting dogs and cats. When the immature larvae of these parasites are found in atypical or dead-end hosts, a disease called cutaneous larva migrans (CLM) or creeping eruption develops. The most severe cases of CLM are associated with A. braziliense infection.



HOSTS


A. braziliense is the hookworm of dogs and cats, seen primarily in the southeastern United States. A. caninum is the most common hookworm of dogs in tropical and subtropical areas, A. tubaeformis is the most common hookworm of cats in tropical and subtropical areas, and U. stenocephala is the hookworm of dogs and cats in cooler regions of the United States and Canada. Humans are considered atypical or dead-end hosts.



TRANSMISSION


Adult hookworms are found attached to the wall of the small intestine. They feed on the host’s blood. During the normal life cycle of hookworms, eggs are passed by adult females in dog or cat feces and hatch as larvae on the ground. In 1 to 3 weeks they become infective larvae. The infective larvae are found in shady, moist, sandy soil. The larvae infect the host either by being ingested or by penetrating the host’s skin (Figure 19).


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FIGURE 19 Cutaneous larva migrans.


Larvae that enter the host through minute breaks in the skin migrate to the lungs via the bloodstream. Once in the lungs, they break out of the blood vessels and enter the alveoli, then crawl up the respiratory tree to the trachea, where they cause a mild irritation that makes the host cough. Coughing brings the larvae to the mouth, where they are swallowed and travel to the small intestine, attach to the wall, and mature to adulthood.


If the larvae are ingested, they travel directly to the small intestine. Some of the larvae stay there, and some burrow through the intestinal wall and travel to the lungs through tissues. Once in the lungs, they follow the same path as larvae that penetrated the skin. Some of the larvae that are traveling through tissue encyst and stay in the tissue, until the (female) host becomes pregnant. Near the end of the pregnancy, these encysted larvae become active, and either finish their migration to the lung and on to the intestines, or they travel to the mammary glands, where they congregate and are passed in the milk to the newborn offspring.


If the infective larvae accidentally penetrate the skin of a human through minute breaks, they are unable to penetrate any further than the outer layer of the skin. They cannot penetrate into blood vessels and travel to the lung. Humans are considered atypical or dead-end hosts. Many people are infected by walking barefooted on beaches, where dogs and cats have been allowed to roam freely and contaminate the sand with infected feces.

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Oct 1, 2016 | Posted by in EXOTIC, WILD, ZOO | Comments Off on HOOKWORMS

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