Intestinal parasites

Protozoa

Giardia

Direct fluorescent antibody assay (DFA) is often the standard against which other tests for Giardia are measured (). The Merifluor® Cryptosporidium/Giardia assay uses a fluorescein isothiocyanate (FITC)-labelled monoclonal antibody directed against cell wall antigens of Giardia cysts in the stool. A positive result is indicated by apple green fluorescence of the cyst (). Morphological identification is facilitated by the fluorescent appearance of the cysts or oocysts; however, a fluorescent microscope is necessary to perform this test. Enzyme immunoassays are relatively simple to perform and do not require morphological identification of the cyst or oocyst. A capture (polyclonal) antibody adsorbed to the bottom of a micro-well is used to detect the presence of Giardia-specific antigen (GSA) in the faeces. An in-house Giardia SNAP test (Idexx Laboratories) is also now commercially available.

Treatment: Metronidazole is moderately effective in the dog, with a reported efficacy of 67%. The drug appears to be effective in cats, although neurological adverse effects are occasionally seen in dogs at the higher recommended dose of 50 mg/kg p.o. q24h for 5-10 days. Metronidazole is administered at 25 mg/kg p.o. q12h for 5 days in cats. Albendazole (25 mg/kg p.o. q12h for 5 days for cats) is also effective, but may cause leucopenia in some animals and it should not be used in early pregnancy. Fenbendazole is not approved for use in the cat in the USA but is licensed in the UK. If is effective in both dogs and cats when used for 3-5 days at 50 mg/kg p.o. q24h.

Vaccination: A vaccine is available in the USA, but as infection is readily diagnosed and treated and many infected dogs are asymptomatic, the merit of vaccination against giardiasis has not been convincingly demonstrated. Indeed the vaccine does not prevent infection but only reduces shedding of trophozoites or cysts. Thus routine vaccination for Giardia is not recommended in household dogs. The vaccine may have application in breeding kennels where large numbers of dogs are housed in close proximity to one another.

Cryptosporidium

Cryptosporidium can cause chronic diarrhoea in cats and dogs, although it is usually considered a self-limiting infection. Detection by faecal flotation is difficult as the organism is very small. Acid-fast staining of faecal smears and immunoassays aid detection.

Treatment: Eradication of this parasite has proven difficult and many putatively effective drugs are toxic in cats or dogs. The macrolide, tylosin, is not effective for eradication of Cryptosporidium. Azithromycin is used in humans for management of cryptosporidiosis and can be administered at 7-10mg/kgp.o.q12hfor7day$ in dogs and cats. The aminoglycoside, paramomycin, is potentially nephrotoxic and ototoxic and should preferably not be used. Nitazoxanide may also be effective ().

Toxoplasma

For information on Toxoplasma see BSA VA Manual of Canine and Feline Infectious Diseases.

Tritrichomonas foetus

Tritrichomonas foetus is considered a cause of mild cofitis in some animals, particularly cats.

Nematodes

Whipworms

Animals acquire Trichuris vulpisintection () by ingesting ova. The adult worms burrow into the colonic and caeca) mucosa and may cause inflammation, haematochezia and intestinal protein loss. Cats rarely acquire whipworms. Severe infection may cause hyponatraemia and hyperkalaemia, mimicking hypo-adrenocorticism.

Faecal flotation showing Trichuris vulpis ova (darker appearing biperculate ova) and Ancylostoma caninum ova.

Diagnosis: T. vulpis should always be considered in dogs with evidence of colonic disease. A faecal cen-trifugation flotation should allow recognition of the biperculate ova; however, intermittent shedding has been well documented in dogs, and animals with a negative faecal flotation should be empirically treated.

Treatment: Fenbendazole is a broad spectrum anthelmintic that is remarkably safe. The drug is administered orally at 50 mg/kg q24h for 5 consecutive days, and the regime is repeated at 3 weeks and 3 months following initiation of therapy.

Roundworms

Roundworms are common in dogs (Toxocara canis and Toxascaris leonina) and cats (Toxocara car/and Toxascaris leonina). In young puppies and kittens common clinical signs include diarrhoea, failure to thrive, a poor haircoat and a ‘pot bellied’ appearance. Vomiting is occasionally observed when the round-worms gain access to the stomach.

Diagnosis: The large ova (approximately 80 u.m) with a characteristic thick wall are easy to appreciate on faecal flotation.

Treatment: Piperazine and pyrantel are safe in puppies and kittens (see Chapter 28). The treatment should be repeated at approximately 3 weeks. Fenbendazole is also an effective anthelmintic and can be administered to newborn puppies at 100 mg/kg for 3 days to kill more than 90% of prenatal larvae. Puppies should be routinely treated every 2 weeks, starting at 2 weeks of age, until 8 weeks.

Hookworms

Ancylostoma spp. are voracious blood suckers, where the worms live in the small intestinal lumen and attach to the mucosa. Dogs are infected when they ingest ova or by transcolostral transmission. Puppies and occasionally kittens can have life-threatening blood loss or iron-deficiency anaemia, melaena, haematochezia and failure to thrive.

Uncinariaspp. are not blood suckers, but can cause both profuse diarrhoea and interdigital dermatitis due to transdermal larval migration.

Diagnosis: Faecal flotation should be positive as the worms produce a large number of eggs.

Treatment: Fenbendazole, pyrantel and milbemycin are all effective in the dog.