Helminths

By | 2011-07-24

Helminthic infestation is common in dogs and cats. Some species are pathogenic in large numbers, and others are nonpathogenic.

Roundworm Ascarids

Toxocara canis and Toxascaris leonina are found in dogs, and Toxocara can and Toxascaris leonina are found in cats. T. canis can be transmitted across the placenta and T. canis and T. cati through the milk. Infection is also caused by ingestion of the ova or of other hosts, such as rodents. The adult nematodes live in the small intestine. Migrating juvenile T. canis can cause hepatic, pulmonary, and occasionally ocular damage. T. canis presents a public health problem (i. e., visceral and ocular larva migrans).

Clinical Findings

Roundworms most often cause disease in young animals, and common signs are diarrhea, weight loss, or failure to thrive. A poor haircoat and a potbelly may be evident in puppies or kittens. Intestinal obstruction and perforation have been described in severe cases.

Diagnosis

Almost all puppies can be presumed to have T. canis infection. The diagnosis is made by fecal flotation.

Treatment

A wide range of anthelmintics is effective against roundworms (Table 222-10). Treatment should be repeated at 2- to 3-week intervals in affected animals. Young animals should be routinely wormed at 2, 4, 6, 8, 12, and 16 weeks of age and then at least at 6-month intervals. It is important to ensure proper hygiene to stop reinfection or spread. T. canis can be controlled by administering fenbendazole to pregnant bitches at an oral dosage of 50 mg / kg given daily from day 40 to 2 days after whelping.

Hookworms

Ancylostoma caninum is the most important hookworm of dogs and is associated with blood loss and hemorrhagic enteritis. Ancylostoma tubeforme is the most common hookworm in cats but is less pathogenic. Ancylostoma braziliense occurs in dogs in the southern United States.

Uncinaria stenocephala is the hookworm of dogs in western Europe, although it also occurs in the northern United States and in Canada. Infection is most commonly reported in kenneled dogs, particularly greyhounds, and can be acquired prenatally, during lactation, by ingesting larvae, by migration of larvae through the skin, and by ingestion of a paratenic host.

Clinical Findings

Diarrhea, weakness, pallor, vomiting, dehydration, poor growth, and anemia are common in puppies with A. caninum infection. The infection can cause a rapid and fatal anemia or a more chronic iron deficiency anemia. U. stenocephala does not suck large quantities of blood and cause anemia, although severe infestations may be associated with diarrhea. Larval migration of U. stenocephala causes pedal pruritus.

Diagnosis

The diagnosis is made by demonstrating ova in feces.

Treatment

Appropriate anthelmintics are detailed in Table Common Anthehnintic Medications for Dogs.For Ancylostoma infection in anemic puppies, pyrantel pamoate has been suggested as the treatment of choice because it acts very rapidly and is comparatively safe. Anemic puppies may require blood transfusion and supportive care. Monthly administration of milbemycin or ivermectin plus pyrantel pamoate has been approved for the prevention or control of hookworm in dogs.

Common Anthehnintic Medications for Dogs

Drug Dosage Usual Formulation Spectrum Of Activity
Nematode Cestode
Piperazine 83.2-300 mg / kg Tablet Yes No
Pyrantel 5 mg / kg Paste Yes No
Selamectin 6 mg / kg monthly Topical Spot-on Yes No
Fenbendazole 20-100 mg / kg for 1-3 days Granules, paste, suspension Yes Toenia sp.
Mebendazole 50 mg / kg for 2 days Tablet Yes Taenia, Echinococcus spp.
Nitroscanate 50 mg / kg Tablet Yes

(not Trichuris sp. )

Taenia, Dipylidium caninum, (Echinococcus) spp.
Pyrantel, febantel, praziquantel (combination) 1 tablet / 10 kg Tablet Yes Taenia, Echinococcus spp., D. caninum
Pyrantel, febantel (combination) 1 mL / kg Suspension Yes Taenia sp., D. caninum
Dichlorophen 200 mg / kg Tablet No Taenia sp., D. caninum
Praziquantel 5 mg / kg Injection, tablet No Taenia, Echinococcus spp., D. caninum

 

Tapeworms

Dipylidium caninum is the most common tapeworm infecting dogs and cats in the United States and Europe. Fleas are the intermediate host. Echinococcus granulosus is a tapeworm that uses dogs as definitive hosts, but humans and sheep are intermediate hosts. E. granulosus infection is not associated with clinical signs in dogs but is an important zoonosis. Various other Taenia spp. are also common in dogs and cats.

Clinical Findings

Heavy infestations of D. caninum are only rarely associated with diarrhea, weight loss, and failure to thrive. There are usually no clinical signs except “rice grains” (proglottids) in the perineal area or feces.

Diagnosis

A diagnosis of D. caninum infection is made by demonstrating characteristic egg capsules, contained in proglottids, obtained from the perineal area or feces.

Treatment

Treatment of D. caninum infection involves adequate flea control (the animal and the environment) and administration of an appropriate anthelmintic (see Table Common Anthehnintic Medications for Dogs). E. granulosus and other Taenia spp. are best controlled by routine administration of praziquantel (see Table Common Anthehnintic Medications for Dogs).

Strongyloides sp.

Strongyloides stercoralis is a small nematode that may cause hemorrhagic enteritis in young puppies. Infective larvae are ingested, transmitted transmammary or through penetration of the skin, and after migration through the lung develop in the small intestine.

Clinical Findings

Signs of hemorrhagic enteritis occur in young puppies.

Diagnosis

Fecal evaluation using the Baermann technique or demonstration of motile first-stage larvae in smears of fresh feces helps differentiate larvae from Filaroides and mature hookworms.

Treatment

Infection is treated with thiabendazole or possibly fenbendazole or ivermectin (see Table Common Anthehnintic Medications for Dogs).