Trichomoniasis

Species

Feline
Tritrichomonas foetus (most prevalent)
Pentatrichomonas hominis
Must be differentiated by careful morphological comparisons or PCR (most commonly done by the latter method)

Canine
Pentatrichomonas hominis (most prevalent)
Tritrichomonas foetus
Must be differentiated by careful morphological comparisons or PCR (most commonly done by the latter method)

Pentatrichomonas hominis may or may not be associated with clinical disease.  The remainder of this guideline focuses on the pathogenic T. foetus.

Life Cycle

• The parasite lives in the host’s descending colon and cecum and divides by longitudinal binary fission. 
• Although the trophozoites do form pseudocysts, there is no resistant cyst stage that lives outside the host for extended periods.  Pseudocysts also appear to undergo asexual binary fission within the cyst.

Stages

Culture of feces increases the number of organisms, thereby facilitating detection.

• Trophozoites are found in loose or diarrheic feces. 
• Pseudocysts form when the flagella and undulating membrane are internalized under adverse environmental conditions (i.e. too hot, too cold); recent work suggests adverse conditions may not be required for pseudocysts to form.

Disease

• Many cats are asymptomatic carriers and are free of any clinical signs even though they may test positive by PCR or other methods. Most infected cats, although beset with chronic loose stools, often remain active, playful, and do not lose weight.
• Both infection and disease is most common in cattery cats.
• The most common clinical sign is chronic diarrhea, which can last weeks, months or years.  The diarrhea may contain blood and/or mucus and is often accompanied by large bowel inflammation and fecal incontinence.
• Diarrhea may resolve only to relapse months later. 
• Age of onset is between 0-24 months, averaging 9 months.
• Research has shown that most cats have spontaneous resolution of diarrhea (which can take up to two years) as well as clearance of T. foetus from feces and decreased colonic inflammation.
• Infection of the urogenital tract even in cats with long-standing colonic infections is very rare

Prevalence

• A survey of 117 cats from 89 catteries revealed the prevalence of T. foetus at 31% among cats (36 out of 117) and catteries (28 out of 89) based on results of fecal smear examination, fecal culture, or PCR diagnosis.  Among catteries where T. foetus was identified, they were more likely to have had a recent history of diarrhea, an historical diagnosis of coccidia infection in adult cats, and less square feet of housing per cat.
• A recent survey looking at T. foetus infections in the pet cat population found that of 173 cats sampled nationwide, 17 were positive for this parasite.  Of the positives, 9 were co-infected with either one or more of the following: Giardia (5), Cryptosporidium sp. (1), Cystoisospora sp. (2).  One of the positives was also diagnosed with FIP.  All cats positive for T. foetus had a history of diarrhea. 
• From surveys for T. foetus in the US and around the world, it would appear that T. foetus is more common in cats that are housed in large groups such as catteries.  Some work suggests that the disease appears more commonly in long-haired cat breeds and in cats <1 year of age.
• Tritrichomonas foetus has been observed via microscopy and identified by PCR as T. foetus in the feces of a few dogs.  Of 17 dogs with fecal samples positive for trichomonads, 17 were infected with P. hominis, 1 with only T. foetus, and one had an infection with both agents.

Host Associations and Transmission Between Hosts

• The route of transmission is most likely fecal-oral.
• This organism has been identified by some researchers using molecular methods as being very similar or identical to that present in cattle.  However, other researchers have concluded that it is different in certain genetic characteristics, and have noted that the cat genotype has not been isolated from the cattle when examined by these methods.  Cross-transmission studies between cats and cattle suggest there are differences in pathology between the two host-adapted strains. 
• Others assert that T. foetus of cattle is the same species as Tritrichomonas suis of the nasal cavity and colon of pigs.

Prepatent Period and Environmental Factors

• Details involving the definitive life cycle, mode of transmission, and full range of hosts are unknown.  In a recent experimental infection of cats with feline isolates of T. foetus, organisms were recovered from feces beginning 15 days post-infection. 
• Recent work shows T. foetus can survive for short periods of time outside the host for varying periods of time in water (30 to 60 minutes), cat urine (>180 minutes), dry  (30 minutes) and canned (120 to 180 minutes) cat food, and on filter paper (15 minutes).  Survival was not documented for even short periods on cat litter. 
• Slugs have been shown to serve as transfer hosts with the potential of maintaining infections and shedding organisms in their feces on food items or passing the infection if ingested.

Site of Infection and Pathogenesis

• In experimentally infected cats, T. foetus was found predominantly in the cecum; however, organisms were additionally recovered from the ileum and descending colon. 
• All intestinal samples taken from experimentally infected cats showed an increase of lymphocytes and plasma cells in the mucosa.  There was also an increase in the presence of crypt abscesses and mucus production. 
• A study involving naturally infected cats showed mild to moderate lymphoplasmacytic and neutrophilic colitis, crypt epithelial cell hypertrophy, hyperplasia, loss of goblet cells, crypt microabscesses and an attenuation of superficial colonic mucosa.

Diagnosis

• Diagnosis of T. foetus may be achieved via observation of organisms in a direct fecal smear, after culturing in media, or via PCR.
• Tritrichomonas foetus is pear-shaped, 10-25um long and 3-15um wide.
  • The organisms bear 3 anterior flagella, one posterior flagellum, and an undulating membrane that is approximately ¾ the length of the cell. 
• Culture of feces for T. foetus can be performed using Diamond’s TYM media or the commercially available InPouch™ TF – Feline Tritrichomonas foetus Test (Biomed Diagnostics White City, Oregon).
• Polymerase chain reaction (PCR) assays are also available, and are especially important when differentiating between T. foetus and P. hominis.
• Tritrichomonas foetus is often misdiagnosed as Giardia spp., but the movement of the organism is quite different.  Tritrichomonas foetus movement is jerky and random while Giardia movement resembles a “falling leaf” and seems more deliberate.

Treatment

• There is no approved treatment for feline or canine trichomoniasis, however, several drugs have demonstrated efficacy against feline T. foetus in the research laboratory.
  • Ronidazole (30-50mg/kg, BID, for 14 days) is currently considered the treatment of choice.  In some cats, a reversible neurotoxicity similar to that seen with metronidazole has been reported.  
  • Metronidazole (30-50 mg/kg, BID, for 3-14 days) has been used in the past as has tinidazole, but clearance of infections appears less common than when ronidazole is used.
  • Resistance to ronidazole and metronidazole have been reported using the feline isolates both clinically and in culture systems.
• Home remedies including the use of prescription diets, plain turkey and rice, yogurt, slippery elm, pumpkin, glutamine, frequent bathing and litter box changes did not consistently lessen diarrhea.
  • However, cats do sometimes improve with careful dietary management.

Control and Prevention

• It is best to keep infected cats away from other cats, limiting contact as much as possible and not allowing them to share a litter box.

Public Health Considerations

• Tritrichomonas foetus is not considered a zoonotic agent

Selected references:

• Gookin JL et al.  2004.  Prevalence of and risk factors for feline Tritrichomonas foetus and Giardia infection. J Clin Microbiol 42: 2707-2710.
• Rosado TW et al.  2007.  Neurotoxicosis in 4 cats receiving ronidazole. J Vet Intern Med 21: 328-331.
• Rosypal AC et al.  2012.  Survival of a feline isolate of Tritrichomonas foetus in water, cat urine, cat food and cat litter.  Vet Parasitol 185: 279-281.
• Stockdale HD et al 2009.  Tritrichomonas foetus infections in surveyed pet cats.  Vet Parasitol 160: 13-17