Ancylostoma ceylanicum
Ancylostoma ceylanicum is a parasitic roundworm belonging to the genus Ancylostoma. It is a hookworm both of humans and of other mammals such as dogs, cats, and golden hamsters. It is the only zoonotic hookworm species that is able to produce symptomatic infections in humans, with the majority of cases being in Southeast Asia.
Discovery and history
Since the description of Ancylostoma ceylanicum by Arthur Looss in 1911, and A. braziliense by Gomes de Faria in 1910, the two species were considered synonymous because of their apparent similarities in almost all respects. In 1913, comparison of specimens from human, dog, cat and lion infections in India led to the conclusion that they were definitely identical. In 1915 Gomes de Faria described the anatomical structures and concluded that the two were distinct species. Until 1921 A. ceylanicum was accepted as a valid species. However, in 1922 Gordon made an exhaustive comparison from specimens collected in Brazil, South Africa and India, and he failed to identify any distinction. Other parasitologists also became convinced that the two names were synonymous. In 1951 Biocca made an elaborate study of 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.Structure
The adult hookworms are white and about 6–10 mm long. They are generally stouter than A. braziliense. The anterior end is bent dorsally, which gives the body a characteristic "hooked" or J-shaped appearance, hence the common name hookworm. Females have a tapered narrow posterior end, while males have a feathery posterior end owing to their copulatory bursa. Hookworm species are not easily distinguished from the gross appearance. The key diagnostic feature is the appearance of their mouths. Unlike other hookworms, A. ceylanicum has a mouth with cutting plate with a sharp dorsal end that looks like a tooth and a less distinct sharp ventral end.Life cycle
The Infective larvae quickly undergo moulting to shed their sheath either upon ingestion by the host or upon burrowing into the host's skin. If ingested, they pass through the stomach into the intestine and attach themselves to the mucosa. If they have burrowed through the skin, they invade the subcutaneous blood vessels, are carried to the lungs, and then move to the intestine via trachea, oesophagus and stomach. In either case, the larvae develop into the final 3rd stage in the intestinal wall. The 4th stage larvae appear in 47 hours after oral infection. The 5th stage immature worms appear 6 days after infection. They reach sexual maturity on and after 2 weeks after infection.Unlike the hookworms Necator americanus and Ancylostoma duodenale, A. ceylanicum can competently infect and thrive within not only human hosts but other mammalian hosts as well. Because it may primarily infect non-human mammals, and infect humans only opportunistically when its mammalian hosts are in close contact with people, A. ceylanicum is termed a zoonotic hookworm. This same trait makes A. ceylanicum a uniquely useful hookworm, since it can be studied in the laboratory while infecting golden hamsters, unlike most or all strains of N. americanus or A. duodenale, and thus can also be used as a test organism for possible drugs or vaccines aimed at preventing human infections.