TRICHOMONOSIS IN CATS
Jody L. Gookin, DVM, Ph.D., DACVIM-Internal Medicine

BACKGROUND:
In general, trichomonads are considered to be nonpathogenic, commensal, and highly susceptible to anti-protozoal drugs.Important exceptions are the Tritrichomonasspp. such as T. foetus, T.suis, and T. vaginalis that are importantveterinary and human pathogens. T. foetusand T. vaginalis cause venerealtrichomonosis in cattle and people, respectively. T. suis is reportedly common in the swine nasal cavity andintestinal tract and is of undetermined pathologic significance. Tritrichomonas foetus and T. suis are considered to be identicalon the basis of morphology, ultrastructural analysis, RAPD analysis, isozymichomogeneity and 16S-like rRNA gene sequence analysis. Experimental infectionsof various hosts with T. foetus or T. suis have revealed little hostspecificity. T.foetus has onlyrecently been reported as a pathogen of cats. The natural history of T. foetus in the feline host and anyrelationship to bovine or swine trichomoniasis needs further evaluation.

The prevalence of T. foetus infection was 31% among 117 cats from 89 cattery ownersattending an international cat show. Evidence of the organism was found infeces from eighteen cat breeds from 17 states and Germany on the basis ofdirect microscopic examination, protozoal culture or PCR. Catteries in which T. foetus was identified had largernumbers of cats with diarrhea and lower number of square feet of facility percat, suggesting that crowding may be a significant risk factor for infection.Proximity of a cattery to agricultural species (pigs, cattle, horses), feedingof raw meat, type of water source, outdoor contact or history of travel werenot identified as significant risk factors for T. foetus infection. Co-infection by T. foetus and Giardia wascommon. Tritrichomonas foetus was notdemonstrated by either direct microscopic examination or protozoal culture offeces from 100 feral cats or 20 healthy indoor cats from geographic regionscomparable to those of naturally infected cats. Thus, T. foetus does not appear to be a component of the normal felineintestinal flora.

PATHOGENESIS:
It is likely that multiple organism, host, and environmental factors are involved in the pathogenesis of diarrhea in cats with T. foetus infection. Pathogenic factors associated with trichomonads include interaction with endogenous bacterial flora, adherence to host epithelium and elaboration of cytotoxins and enzymes. Infection of specific pathogen free cats with axenically cultured T. foetus results in chronic colonization of the terminal ileum, cecum and colon and large bowel diarrhea akin to that observed in naturally infected cats. In naturally-infected cats T. foetus antigen can be demonstrated within the superficial mucus and in contact with the surface epithelium of the cecum and colon. There is also evidence of antigen uptake by surface epithelial cells. Whether long-term infection of cats with T. foetus is a predisposing factor for development of inflammatory bowel disease is unknown. The predominance of young cats from dense housing conditions may reflect an increased opportunity for exposure or enhanced susceptibility to infection because of environmental stress or immunologic immaturity.

SIGNALMENT:
Infected cats are generally young but have ranged in age from 3 mos. to 13 years (median 9 mos.). Of 32 cats described by our institution, 75% were < 1 year of age at the time of diagnosis. Cats are frequently from multiple-cat housing conditions (catteries or shelters). Infections are seen in both non-purebred (sheltered) and purebred cats. Among purebred cats, we have observed numerous geographic foci of infection within the Abyssinian and Bengal breeds. Infection of Pixie Bob catteries has also been reported. Rather than suggesting a specific breed predisposition, infection among purebred cats likely reflects their increased housing density and exposure via travel for purposes of showing and breeding.

CLINICAL FINDINGS:
Feline T. foetus infection is characterized by a waxing and waning large bowel diarrhea that occasionally contains fresh blood and mucus. Diarrhea is semi-formed to cow-pie in consistency and malodorous. In very young cats and with poor housing conditions, the anus may appear edematous, erythematous and painful; involuntary dribbling of feces or rectal prolapse may be seen. In general, cats otherwise maintain good health and body condition. A consistent feature of T. foetus diarrhea is improved fecal consistency and disappearance of trichomonads during administration of antimicrobial drugs with return of diarrhea containing trichomonads shortly after drugs are discontinued. Misdiagnosis of Giardia is common in cats having T. foetus infection. Cats diagnosed with Giardia on the basis of direct fecal smear examination and that fail to respond to appropriate antimicrobial therapy should be closely re-evaluated for the possibility that the observed trophozoites were T. foetus.

PATHOLOGIC FINDINGS:
Hematologic and serum biochemical analysis results from cats with T. foetus infection are invariably normal. Coexisting enteric infection by recognized feline pathogens (e.g. Giardia, Cryptosporidium, or internal parasites) is not a consistent feature. Infected cats usually test negative for FeLV antigen and FIV antibody. Histopathologic changes in colonic mucosal biopsies from infected cats have been consistent with mild to severe lymphoplasmacytic colitis. Because trichomonads are non-invasive and extremely fragile, they are rarely preserved in intestinal biopsy specimens from infected cats although immunohistochemistry may be used to enhance their detection.

DIAGNOSIS:
Direct Fecal Smear Examination:

Diagnosis is made by observation of trophozoites in feces diluted with saline solution and examined under a coverslip using a 20 or 40x objective. Lowering the microscope condenser to increase contrast may enhance visualization. Trichomonad trophozoites must be distinguished from those of Giardia. Giardia trophozoites have a concave ventral disc and motility reminiscent of a ¡§falling leaf¡¨. In contrast, trichomonads are spindle-shaped, have an undulating membrane that courses the entire length of the body and possess a jerky, forward motility. Tritrichomonas foetus can be difficult to reliably distinguish from non-pathogenic intestinal trichomonads such as Pentatrichomonas hominis on the basis of light microscopic appearance as the two organisms differ in appearance only by the number of anterior flagella.

Fecal samples should be freshly voided and diarrheic. Detection of trophozoites can be improved by collecting samples using a fecal loop and by examination of multiple fecal smears. Trichomonads will not survive refrigeration and are not observed after fecal flotation or sedimentation. Survival of trophozoites in feces can be extended from 0 to 4 days by removal of adherent litter and dilution of the sample with normal saline to avoid desiccation (3 ml 0.9% saline per 2 g of feces). Concurrent antibiotic therapy will diminish the number trophozoites present in feces, a fact that should be considered in cats with negative fecal smear results. The sensitivity of direct fecal smear examination for diagnosis of trichomoniasis is low (2% in cats with experimentally induced infection and 14% in cats with spontaneous disease).

Fecal Protozoal Culture

If repeated direct microscopic examination results are negative for trophozoites, feces may be cultured in-house using a commercially-available system marketed for diagnosis of T. foetus infection in cattle (In PouchTM TF, Biomed Diagnostics, San Jose CA). For diagnosis of feline T. foetus, pouches should be inoculated with 0.05 g (about the size of a peppercorn) of freshly voided or loop-collected feces and incubated at room temperature (25¢XC) in an upright position. Prior to microscopic examination, pouches are tapped against a bench-top to dislodge adherent organisms and then placed within a manufacturer-provided clamp that allows the pouch to be mounted onto the stage of a light microscope. Pouch contents should be examined every other day for motile trophozoites using a 20 or 40x objective and discarded if still negative after 12 days. Fecal culture using In PouchTM TF has a detection limit of >= 1000 T. foetus organisms/0.05 g feces and is superior to direct fecal smear examination for diagnosis of T. foetus infection. Neither Giardia nor P. hominis organisms can survive in In PouchTM TF for longer than 24-hr and thus positive cultures are strongly suggestive of T. foetus infection. Strictly speaking however, the types of trichomonads potentially hosted by cats and the specificity of In PouchTM TF with regard to these other types of trichomonads is unknown. Positive In PouchTM TF cultures do not preclude the possibility of coinfection with P. hominis or Giardia.

Fecal samples can also be cultured in antibiotic-fortified, modified Diamond¡¦s medium. Such cultivation requires shipment of feces to a research laboratory, preparation and maintenance of sterile medium, and 37¢XC incubation and is not commercially available. There is minimal evidence to suggest that modified Diamond¡¦s medium culture provides any greater diagnostic sensitivity than in-house fecal culture using In PouchTM TF.

Polymerase Chain Reaction

A sensitive and specific single-tube nested PCR based on amplification of a conserved portion of the T. foetus internal transcribed spacer region (ITS1 and ITS2) and 5.8S rRNA gene from feline feces has been described. The PCR test is superior to fecal culture for diagnosis of naturally infected cats and is commercially available at the College of Veterinary Medicine, North Carolina State University.

Exclusion of Coexisting Disease

Coexisting systemic or enteric disease should be excluded in cats with trichomonas infection. Studies of experimental feline infection suggest that coexisting intestinal infection (e.g. cryptosporidiosis) worsens clinical signs of diarrhea and increases the shedding of T. foetus organisms. Further diagnostic evaluation of infected cats may include: CBC, serum biochemical analysis, urinalysis, tests for FeLV, FIV and feline enteric coronavirus, fecal flotation, Giardia-specific antigen testing, fecal IFA for Cryptosporidium, fecal Gram stain for Clostridia, and colonic mucosal biopsies. Commercial ELISA kits to detect fecal Giardia-specific antigen do not cross react with T. foetus.

THERAPY
Pentatrichomonas hominis is reportedly exquisitely responsive to treatment with metronidazole at the dosages effective for Giardia. An effective antimicrobial treatment for feline T. foetus infection has not been identified. Attempts to identify an effective treatment for economically-important bovine trichomoniasis have failed, so specific therapy for feline infection in the near future seems unlikely.

Cats infected with T. foetus have failed treatment with recommended (and in many cases higher) dosages of numerous antimicrobial drugs including metronidazole, fenbendazole, albendazole, sulfadimethoxine, trimethoprim-sulfadiazine, furazolidone, tylosin, enrofloxacin, amoxicillin, clindamycin, paromomycin, and erythromycin. Furthermore, in vitro studies of feline T. foetus in culture have revealed multiple drug resistance (e.g. to paromomycin, furazolidone, metronidazole, anisomycin, azithromycin, ciprofloxacin, chloroquine, doxycycline, tinidazole, and clotrimazole). Although nitazoxanide inhibited growth of T. foetus in culture, rapid resistance to the drug was acquired in vivo. In contrast to prior reports, paromomycin is not an effective treatment for T. foetus infection and has precipitated acute renal failure in infected cats.

Despite their failure to eradicate the infection, some cats have improved fecal consistency while receiving antimicrobial drugs. This may be related to a dependence of trichomonads on endogenous bacterial flora and host secretions for acquisition of essential nutrients. Prolonged use of antibacterial drugs has not been uniformly useful for long-term control of diarrhea and may delay the onset of clinical remission.

In a study of long-term outcome in 26 cats with diarrhea and T. foetus infection, clinical signs resolved a median of 9-months after the onset of diarrhea (range, 4 months to 2 years). Relapses of diarrhea were common and associated with dietary change, medical treatments unassociated with T. foetus infection, and travel. On the basis of fecal PCR, T. foetus was undetectable in >50% of cats when tested 2-5 years after diagnosis. Thus, cats with T. foetus may have a good long-term prognosis for spontaneous resolution of disease.

PUBLIC HEALTH CONSIDERATIONS
In light of the poor host specificity of T. foetus and the intimate association between infected cats and their human companions, the potential for zoonotic transmission should be considered. Only a single case of human infection with T. foetus appears in the literature. The infection presented as epididymitis and meningoencephalitis following immunosuppression and peripheral blood stem cell transplantation.

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