Ancylostomatoidea - Hookworms
Male and female Ancylostoma caninum recovered from a dog. Adults males are usually 10-12 mm in length, and the females average 14-16 mm in length. Prepatent period varies by route of transmission and can be as short as 2 weeks when larvae are ingested or as long as 4 weeks when larvae are acquired by dermal penetration.
In situ photo of Ancylostoma caninum found on necropsy of a dog. Infected dogs may present with anemia from blood loss due to worm feeding, skin lesions associated with penetration of third-stage larvae, diarrhea associated with fourth-stage larvae damaging the small intestine, and/or hemorrhagic pneumonitis associated with larval migration.
The buccal cavity of the hookworm of cats. Although very similar to the stoma of adult Ancylostoma caninum, the teeth on the ventral margin of Ancylostoma tubaeforme are slightly larger. Infection with this species is the result of skin penetration or ingestion of third-stage larvae, or ingestion of paratenic hosts with larvae encysted in tissues.
A parasite of cattle and zebu, Bunostomum phlebotomum may be found in the small intestine feeding on blood. Penetration of larvae may cause cattle to stamp their feet and lick their legs, and heavy infections with adults may lead to diarrhea, anemia, and hypoproteinemia. In calves this manifests as marked weakness, emaciation, and submandibular edema.
Egg of Uncinaria stenocephala. This hookworm infects dogs (rarely cats) in cooler temperate regions, including the northern US, Canada, and Europe. Eggs resemble those of Ancylostoma spp. in that they are elliptical, thin-shelled, and contain morulae in fresh feces, but Uncinaria eggs are slightly larger (71-92 X 35-58 µm).
Goat lungs showing classic Muellerius capillaris lesions. Adult worms of this genera live in the alveoli and pulmonary parenchyma of sheep and goats. There, they form nodules that turn a greyish color, a result of the degeneration of accumulated leucocytes and necrotic pulmonary tissue. Despite this, hosts generally show no apparent clinical signs.
Neurologic signs of a goat infected with Parelaphostrongylus tenuis. When Parelaphostrongylus tenuis infects a host other than the white-tailed deer, the larvae migrate aberrantly, usually causing damage to the dorsal horns of the grey matter of the spinal cord. Small ruminants are particularly susceptible to neurologic disease due to aberrant migration of Parelaphostrongylus tenuis.
Adult Stephanurus dentatus excised from cysts in the perirenal fat surrounding the ureter of a pig. Adults are usually found in cysts that communicate with the ureter through which they pass their eggs. The eggs leave the host via urine. Host infections may be acquired through ingestion of third-stage larvae, ingestion of a paratenic host, or from dermal penetration by the third-stage larvae. The larvae then migrate extensively through the organs.
Strongyloidea - Large and Small Strongyles
Large buccal cavity of an adult Chabertia ovina. This parasite is found in the colon of sheep, goats, and cattle throughout the world and feeds on the granular layer that it digests with esophageal secretions. Blood feeding is incidental and may be a cause for frank blood in the feces of the host.
Nodules formed by Oesophagostomum columbianum in the colon of a sheep. Oesophagostomum columbianum is a parasite of the colon of sheep, goats, camels, and wild antelope. Their larvae encyst anywhere from the pylorus to the colon to complete their development and become adults that attach in the colon. Frequently, the larval nodules become abcesses that are filled with caseous material.
With the exception of Nematodirus spp., eggs of Trichostrongyloidea species have this typical morphology. They are elliptical, have a thin shell, and are approximately 65-100 X 35-50 µm, depending on the species. In fresh feces eggs contain morulae which develop to first stage larvae within eggs in the environment.
Larva of Ollulanus tricuspis. Third-stage larvae are approximately 500 µm and have a tricuspid tail similar to that of the adult female (2nd and 4th stage larvae also have this type tail). Adults and larvae are found in the stomach of domestic cats and other felids. Diagnosis is based on the identification of larvae or small adults (1 mm) in vomitus using the Baermann test.