Ancylostoma braziliense is related to the main nematode worms known as human hookworms, A. duodenale and Necator americanus. In contrast to these two species, however, although A. braziliense nematodes can penetrate the human skin (causing cutaneous larval migrans), they do not develop any further. Cutaneous larval migrans (also known as "creeping eruption" or "ground itch") is a zoonotic infection (i.e.,an infection transmitted from non-human animals to humans) caused by hookworm species that do not use humans as a definitive host. The condition results from migrating larvae that cause an intensely itchy track in the upper dermis and is most commonly caused by A. braziliense and A. caninum (the normal definitive hosts for these species are dogs and cats).
The normal life cycle for A. braziliense is very similar to the cycle for human hookworms in humans: Eggs are passed in the stool and under favorable conditions (moisture, warmth, shade) larvae hatch in 1 to 2 days. The released rhabditiform larvae grow in the feces and/or the soil and after 5 to 10 days (and two molts) they become filariform (third-stage) larvae that are infective. These infective larvae can survive 3 to 4 weeks in favorable environmental conditions. On contact with the animal host, the larvae penetrate the skin and are carried through the blood vessels to the heart and then to the lungs. They penetrate into the pulmonary alveoli, ascend the bronchial tree to the pharynx, and are swallowed. The larvae reach the small intestine, where they establish themselves and mature into adults. Adult worms live in the lumen of the small intestine, where they attach to the intestinal wall. Some larvae become arrested in the tissues, and serve as source of infection for pups via transmammary (and possibly transplacental) routes. Humans may also become infected when filariform larvae penetrate the skin. In a human host, the larvae cannot mature further, but may migrate aimlessly within the epidermis, sometimes as much as several centimeters a day. Some larvae may persist in deeper tissue after finishing their skin migration. (Source: Centers for Disease Control Parasites and Health Website)
Ancylostoma braziliense has a mainly tropical and subtropical distribution; in the United States it occurs in the Gulf Coast region (Zajac and Conboy 2006).
Ancylostoma braziliense is a species of hookworm belonging to the genus Ancylostoma. It is an intestinal parasite of domestic cats and dogs. Severe infection is often fatal to these pets, especially in puppies and kittens. The infection is particularly endemic in the southern United States. It is most often confused with the hamster hookworm Ancylostoma ceylanicum because of their uncanny resemblance.
A. braziliense larvae can cause accidental infection in humans called cutaneous larval migration or creeping eruption, which produces severe itching in the skin. It is the most common skin infection in tropical region, particularly along the beaches of the Caribbean.
Discovery and history
When A. braziliense was described by Gomes de Faria in 1910, and A. ceylanicum by Arthur Looss in 1911, the two species were regarded as synonymous because of their apparent similarities in almost all respect. Especially in 1913, comparison of specimens from human, dog, cat and lion infections in India led to the conclusion that they were definitely of the same species. In 1915 Gomes de Faria realised that the two were distinct species based on their anatomical structures. Till 1921 the two hookworms were accepted as a two valid species. However, in 1922 Gordon made an exhaustive comparison from specimens collected in Brazil, South Africa and India, and his conclusion was that there were no significant distinction. Other parasitologists were also convinced of this so that the two names were again considered synonymous. In 1951 Biocca made an elaborate study on different hookworms in the collection of London School of Hygiene and Tropical Medicine, the Liverpool School of Tropical Medicine and personal collections. He finally identified the defining characters between the two for classifying them as distinct species, which eventually gained general acceptance.
A. braziliense is endemic in the southern United States. It is also found in a number of subtropical regions around the world, including Central and South America, South Africa, and southern Asia. In southern Asia, infection is confined to Indonesia, Borneo, and Malaysia.
Ancylostoma braziliense eggs are passed into the environment through the faeces of cats and dogs. The eggs incubate on warm, moist soil. They hatch into larvae. The infective juvenile penetrate the skin of the host. At this stage, the larvae are present in the epidermis, hair follicles, and glands of the skin, sometimes extending to sebaceous glands where they form coils. Then they migrate to the heart and lung by moving along the blood circulation. In the lungs, the juveniles enter the alveoli and are propelled by cilia up the respiratory tract. From this, the host swallow them and deposit them in the small intestine. They get attached to the intestinal mucosa via the buccal capsule. Here they undergo two successive to become sexually mature individuals.
It can cause "creeping eruption" or "ground itch". It occurs when the larvae from the faeces of cats and dogs accidentally penetrate the human skin, causing severe itching and skin eruption. In fact it is the most common ailment of tropically acquired dermatitis, particularly along the beaches of the Caribbean. However, humans are not the natural definitive hosts, and therefore, a dead-end for the parasites, and the larvae die after few month without further development.
Diagnosis and treatment
Most benzimidazoles are effective. Mebendazole, triclabendazole and fenbendazole are commonly used. Ivermectin and pyrantel pamoate are also effective. The combination of ivermectin 6 μg/kg and pyrantel pamoate at 5.0 mg/kg is 100% efficacious against adult worms in dogs. Human infection in case of cutaneous larva migrans is treated with oral thiabendazole at 500 mg in 4 daily dose.
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