Ancylostoma caninum 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. caninum nematodes can penetrate the human skin (causing cutaneous larval migrans), they do not develop any further. Occasionally, A. caninum larvae may migrate to the human intestine, causing eosinophilic enteritis, and they have also been implicated as a cause of diffuse unilateral subacute neuroretinitis.
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. caninum in dogs 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 puppies 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.
According to Zajac and Conboy (2006), the most important mode of transmission of A. caninum to dogs is transmammary (i.e., via puppies nursing from infected mothers), followed by ingestion of third-stage larvae from the environment or from paratenic hosts (i.e., intermediate hosts in the parasite's life cycle that are not essential to parasite development) and, rarely, by direct skin penetration by larvae.
Mieszczanek and Wedrychowicz (1999) developed a simple genetic test using the polymerase chain reaction (PCR) on DNA from hookworm eggs to distinguish two of the most common hookworms inecting domestic dogs, Ancylostoma caninum and Uncinaria stenocephala, in living hosts.
Ancylostoma caninum is found worldwide, with its distribution in North America extending north to southern Canada (Zajac and Conboy 2006).
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