Helminthology

Helminths of companion animals

Author: E VOLKER SCHWAN

Nematodes

Hookworms (ancylostomosis)

Ancylostoma

General

Ancylostomosis of dogs and cats is caused by the nematodes Ancylostoma caninum, Ancylostoma braziliense and Ancylostoma tubaeforme . The genus name derives from the Greek words ‘ankylos ’ (= bent) and ‘stoma ’ (= mouth), which, like the common name ‘hookworm ’, are descriptive terms referring to their dorsally bent (‘hook posture ’) anterior end. Hookworms are medium-sized, with a length of 5-25 mm. They have a large buccal capsule, which is armed with teeth. The posterior end of the males terminates in a strongylate bursa. The spicules are equal. The female ’s caudal end tapers gradually and the vulva is located in the posterior third of the body.

Male Ancylostoma caninum worms are 10- 13 mm long and the female worms 14-21 mm long. Both are about 0.5 mm wide. The worms have a large buccal capsule, which is armed with 3 pairs of ventral teeth. Spicules are equal and measure 800-950 μm in length.

Male Ancylostoma braziliense are 5-8 mm long and the females 7-11 mm long. Both are about 0.3 mm wide. The worms have a large elongated buccal capsule armed with 2 pairs of ventral teeth, of which the lateral ones are large and the medial ones small. Spicules are equal and measure 700-1 000 μm in length.

Ancylostoma tubaeforme closely resembles A. caninum but is smaller. Male worms are 9.5-11.0 mm long and female worms 12- 15 mm long. Both are about 0.4 mm wide. Their spicules are larger than those of A. caninum and measure 1 100-1 700 μm in length.

As for all hookworms, the small intestine is the site of predilection of the three species in their definitive hosts.

The eggs of the ancylostomatids of dogs and cats are of the strongylid-type. They are oval, thin-shelled, contain 4-8 blastomeres when laid, and measure 55-95 by 32-58 μm. The eggs of the three species are indistinguishable.

Hosts

  • Ancylostoma caninum: In addition to dogs, the definitive host range includes sylvatic canids, and some of the sylvatic felids, ursids, procyonids and mustelids.
  • Ancylostoma braziliense: In addition to dogs and cats, the definitive host range includes sylvatic canids, felids and mustelids.
  • Ancylostoma tubaeforme: In addition to cats, the definitive host range includes a wide range of sylvatic felids.

Distribution

Ancylostoma caninum is mainly encountered in subtropical and tropical areas, but its range extends into the temperate zones of all continents. Ancylostoma braziliense is found exclusively in tropical and subtropica l areas, while Ancylostoma tubaeforme has a cosmopolitan distribution.

Transmission

All hookworm species have a direct life cycle. Eggs are shed with the faeces and –depending on the environmental temperature and humidity –there is typically a pre-parasitic development from egg to free-living L1, L2 and then finally, a sheathed infective L3, in as few as 4-5 days. Free-living infective larvae can remain viable for 3-4 months in damp soil.

There are various modes of infection for dogs and cats that vary depending on the species of hookworm involved:

  • Percutaneous infection (A. caninum, A. braziliense, A. tubaeforme)
  • Transmammary (lactogenic) infection (A. caninum)
  • Infection by predation on paratenic hosts (A. caninum, A. braziliense, A. tubaeforme)
  • Infection by ingestion of free-living infective larvae (A. caninum, A. braziliense, A. tubaeforme)
  • Autoinfection (A. caninum)

Ancylostoma caninum: Following percutaneous infection, infective larvae follow a blood-tracheal migration route. However, when larvae are ingested orally –for example during transmammary ingestion, ingestion of free-living larvae or ingestion of paratenic hosts, –there appears to be no larval migration. The larvae remain in the intestinal tract and develop directly in the small intestine. Transmammary infection in dogs is regarded as the most important mode of infection.

Infection induces immunity with the result that larvae acquired by older dogs largely adopt a somatic migratory route. These larvae do not develop further and eventually become arrested in the musculature and fat tissue. Arrested larvae remain viable for several years and are reactivated during pregnancy. Reactivated larvae are the source for transmammary infection of litters and autoinfection of bitches. Also, in paratenic hosts, larvae do not develop further and become arrested during the course of their somatic migration. Depending on the mode of infection, the prepatent period is 15-26 days.

Ancylostoma braziliense: Little is known about the modes of infection in dogs and cats. The prepatent period is 13-27 days.

Ancylostoma tubaeforme: Percutaneous infection and infection by ingestion of paratenic hosts and free-living infective larvae appear to be equally important. The prepatent period is 19-22 days.

Socio-economic importance

With the Toxocara spp., A. caninum and A. tubaeforme are the most common and important nematodes of young dogs and cats, and, as the main causes of clinical verminosis, deworming programmes in cats and dogs focus mainly on these two species.

Ancylostoma braziliense is only mildly pathogenic and is of lesser importance.

All hookworm species of dogs, cats and other domestic animals have zoonotic implications and they are one of the causes of cutaneous larva migrans in humans. Cutaneous larva migrans is also colloquially known as ‘creeping eruption ’, ‘plumber ’s itch...

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