Protozoa

By | 2011-08-04

Balantidium coti

Balantidium coli is primarily a pathogen of sheep. Only one case report of natural infection in the dog has ever been published. In another report, a total of 375 fecal samples of 56 mammalian species belonging to 17 families of 4 orders were examined for the detection of Balantidium coli. B. coli organisms were detected in several animal species, but not in dogs or cats.

Entamoeba histolytica

Two isolated case reports of colitis in dogs and one in cats are associated with recovery of Entamoeba histolytica from the feces. E. histolytica can be recovered from the feces of healthy dogs and cats, but it appears to be of low pathogenicity in dogs and cats.

Giardia

Giardia: Cause

Giardia spp. are protozoal parasites that primarily infect the small intestine of dogs and cats. The cecum and colon are only occasionally colonized by Giardia. All mammalian isolates are currently classified as Giardia lamblia, although some nomenclature systems use the name G. duodenalis or G. intestinalis. Recent DNA sequence technology suggests that one or two distinct Giardia genotypes can be isolated exclusively from dogs, and a distinct genetic group can be isolated from cats. It is not clear whether differences in pathogenicity exist between these genotypes. Giardia species have a worldwide distribution. Because Giardia is maintained in nature primarily by fecal-oral transmission, more cases are associated with crowded and unsanitary conditions. A recent study showed a prevalence in the dog of 7.2%.

Pathophysiology of Giardia

Giardia spp. are found on the surface of enterocytes, where the trophozoites attach to the brush border of the epithelium. Specific histologic changes have not been reported, but persistence of infection may promote apoptosis and inhibition of re-epithelialization.

Clinical examination

Although infected animals may remain asymptomatic, clinical signs such as acute or chronic diarrhea, weight loss, or even acute or chronic vomiting may develop. Although Giardia cysts and trophozoites have been found in the feces of dogs with both small bowel and large bowel diarrhea, Giardia infection is primarily a problem of the small intestine.

Diagnosis of Giardia

Giardia infections can be diagnosed by demonstrating motile trophozoites on fresh fecal smears or cysts by zinc sulfate sedimentation. Commercial enzyme-linked immunosorbent assay (ELISA) kits have also been used to detect Giardia antigen in fresh fecal samples. Enzyme-linked immunosorbent assay assays may be slightly more sensitive and specific than a single zinc sulfate concentrating technique in diagnosing Giardia infections in dogs. A direct immunofluorescent antibody test has been used in the diagnosis of Giardia infections in humans, but it has not yet been validated in the dog. Duodenal aspirates during gastrointestinal endoscopy appear to be ineffective in diagnosing Giardia infection.

Treatment of Giardia

Metronidazole, ipronidazole, fenbendazole, albendazole, and a praziquantel, pyrantel pamoate, febantel combination have all been used in the treatment of Giardia infections with varying levels of success. A Giardia vaccine has been shown to be effective in prevention and therapy in dogs, but efficacy has not yet been established in cats.

Prognosis of Giardia

The prognosis for long-term health and recovery is generally very favorable.

Isospora cants, Isospora ohioensis, Isospora felis, Isospora neorivoha

The Isospora species are the most common coccidial parasites of dogs (Isospora canis and Isospora ohioensis) and cats (Isospora felis and Isospora neorivoha). The coccidia are primarily parasites of the small intestine, but Isospora ohioensis may induce cecal and colonic pathology in puppies and young dogs. Sulfadimethoxine (50 mg / kg orally, once a day for 10 days) or sulfatrimethoprim (15 to 30 mg / kg orally, once a day for 5 days) may be used where clinical signs warrant treatment.

Tritrichomonas foetus

Tritrichomonas foetus: Cause

Tritrichomonas foetus is a flagellated protozoan parasite that is an important venereal pathogen in cattle. T. foetus has also been identified as an intestinal pathogen in domestic cats from which intraluminal infection of the colon leads to chronic large bowel diarrhea. Infected cats are usually young and frequently reside in densely populated housing such as catteries or animal shelters. Cats often have a history of infection with Giardia spp.; these infections are subsequently identified as trichomoniasis after failure to eradicate the organisms with standard antiprotozoal treatment (e. g., metronidazole or fenbendazole).

Pathophysiology

After experimental inoculation in cats, Tritrichomonas foetus organisms have been shown to colonize the ileum, cecum, and colon, reside in close contact with the epithelium, and are associated with transient diarrhea that is exacerbated by coexisting cryptosporidiosis.

Clinical examination

Infected animals have clinical signs that are consistent with chronic colitis-type diarrhea.

Diagnosis of Tritrichomonas foetus

Diagnosis of trichomonosis in cats is made by direct observation of trichomonads in samples of freshly voided feces that are suspended in physiologic saline (0.9% NaCl) solution and examined microscopically at x200 to x400 magnification. Tritrichomonas foetus can also be grown from feces via incubation at 37° C. in Diamond’s medium. The sensitivity of direct examination of a fecal smear for diagnosis of T. foetus in naturally infected cats is unknown but is suspected to be poor. A commercially available culture system that is sensitive and specific for culture of Tritrichomonas foetus will improve the diagnostic outcome. These kits are most useful when inoculated with less than or equal to 0.1 g of fresh feces at 25° C. More recently, a single-nested tube polymerase chain reaction technique has been developed that is ideally suited for diagnostic testing of feline lecal samples that are found negative by direct microscopy and by definitive identification of microscopically observable or cultivated organisms.

Treatment of Tritrichomonas foetus

At this time the origin of the infection in most cats is unknown, and no effective antimicrobial treatment exists for Tritrichomonas foetus infection. Metronidazole and fenbendazole may improve clinical signs but generally do not resolve infection. Nitazoxanide eliminates shedding of Tritrichomonas foetus and Gryptosporidium oocysts, but diarrhea and oocyst shedding recur with discontinuation of treatment. A series of cats that were treated with paromomycin for Tritrichomonas foetus infection subsequently developed kidney failure. Consequently, paromomycin should probably not be used in cats.

Prognosis of Tritrichomonas foetus

The prognosis for eradication of the organism is not encouraging at this time.