Feline Tritrichomoniasis

By:  Dawn Skupin

Tritrichomonas foetus is emerging as a fairly new parasite in felines.   The first cases were reported in 1996, where it was found in the intestine and associated with diarrhea in the cat.  T. foetus is a single-celled, flagellated protozoan parasite that reproduces by binary fission and is transmitted by direct transmission from host to host. This protozoan likes the warm, moist and oxygen-deprived conditions inside the colon. 

Until recently, TF was usually associated with venereal trichomoniasis in cattle. There is no known evidence that directly links bovine, (cattle), TF with feline TF.  In fact, veterinarians do not know how T. foetus made its way into the feline population.  While TF is known to be a significant cause of reproductive problems in cattle, (infertility, abortion and endometritis), its role in causing or contributing to reproductive problems in the cat is still unknown.  There has been no evidence of spread from other species or spread via food or water.

Cats/kittens with T. foetus infection can be of any age, sex or breed.  Young cats that are densely housed such as multi-cat households, catteries or animal shelters, seem to be at an increased risk of infection.   Tritrichomoniasis is most common in cats/kittens under the age of 12 months, but can also be found in older cats.  Adult cats appear less likely to develop diarrhea but may serve as a source of infection, a carrier status, to other cats in the household. Most importantly, absence of diarrhea does not mean that a cat is free of infection.  This is particularly true in multicat households where other cats have tested positive for the infection.  Rather, diarrhea may be observed periodically, alternating between severe diarrhea and normally formed stools over a period of months to years.  It is this waxing and waning of the diarrhea that indicates a possibility of TF.

T. foetus primarily colonizes on the surface of the colonic mucosa, leading to chronic large bowel diarrhea.  Without treatment cats remain persistently infected. In fact, if left untreated almost 90% of affected cats will resolve the symptoms within two years.  However, most of these cats will continue to carry the TF organism.  The diarrhea may spontaneously resolve itself, but the cats will often experience recurrent bouts of diarrhea after being exposed to stress.  Left untreated, it is thought many cats develop inflammatory bowel disease later in life.

The primary pathway of infection is thought to be through the litter box where the cats can transfer the parasite from the feces of one cat to the paws of another where they later become ingested during grooming. T. foetus can live for several days in a “Wet” stool. 

Infected cats may or may not have observable symptoms. Cats can experience symptoms of TF anywhere from days to years after exposure. Symptomatic cats present diarrhea with cow-like pie stools.  There is a possibility of mucus or fresh blood present in the stool.  These stools often have a very strong odor.  Although this condition is contagious, it is not considered life-threatening.  

Cats harboring the tritrichomonas organism generally appear healthy but show an increased frequency of defecation with loose to liquid stools.  Fecal incontinence is often observed.  The anal region may appear inflamed and protrude.  A rectal prolapse may occur in some cases, particularly in the case of young kittens.

There are four ways to test for TF.  Diagnosis of tritichomoniasis infection is made by identification of trophozoites on a direct fecal smear examination, fecal culture, PCR analysis of fecal material, or by colonic mucosal biopsy. The disadvantage of a direct fecal smear examination include low sensitivity and possible misdiagnosis of the infection, as Giardia and T. foetus closely resemble each other.  Additionally only fresh warm samples must be used.  Co-infection by T. foetus and Giardia are common.  Treatment for Giardia is not effective for TF.

A direct fecal smear examines feces in a saline solution under a microscope for the presence of trichomonads.  This is poorest detection method as it can only detect only 14% of infected cats.

Fecal culture smears are incubated in a growth medium for T. foetus.  The medium contains antibiotics which suppress unwanted bacterial growth.  The culture is then examined for the presence of TF.  Performed correctly, a fecal culture can detect approximately 55% of infected cats.

A PCR diagnosis has been shown to be the most sensitive method for detecting TF, as it detects both live and dead organisms.  This test can be hampered by intermitted shedding of the parasite by the host.  A PCR test can detect approximately twice as many infected cats as can the fecal culture. 

The fourth method of diagnosis, a routine colon biopsy, is unlikely to find this parasite.  This is the most invasive form of testing and requires identification by a pathologist.  It is suggested that a minimum of six tissue samples from the colon be submitted for identification.  This method of testing is most commonly used when the cat is being tested for chronic colitis.

Fecal sample submission to a lab is a very important part of the testing procedure.  Litter box specimens are the least desirable method of sample collection. Fresh, witnessed stools are preferable.  Do not use stools that are hours old.  The wetter the stool, the longer TF can survive outside of the cat’s body.  Dry or semi-dry samples are not effective when testing for TF.  Another method of sampling is by a rectal swab.  Fecal material does not need to be obtained to test with this method.  This method is not recommended for a PCR test, as it does not gather enough material for the test.  A reasonably good method for testing is using a fecal loop. This needs to be done by someone skilled at using the loop as it can cause serious damage to the colon from improper usage.  The best method of sample collection is through a saline fluid flush.  This is done by inserting a catheter into the colon and infusing approximately 10cc of sterile saline.  It is then gently re-aspirated.  The solution can then be examined directly under a microscope for trichomonads or submitted for PCR analysis.

Feline trichomoniasis  may be misdiagnosed and is probably under diagnosed.  Trichomonad numbers in feces fluctuate.  Consequently, trichomonads may not be observed if low numbers are being shed. Currently there are no diagnostic tests available that will detect 100% of TF cases.  If the test results are positive, the cat has T. foetus.  Importantly, negative test results can never be used to eliminate the possibility of this infection.  It is usually easier to prove an infection exists in a cat than to prove a cat no longer has an infection.

In the past it was thought that several different antibiotics resolved T. foetus.  These antibiotics included commonly used drugs such as, metronidazole, fenbendazole, albendazole, sulfadimethoxine,  furazolidone, tylosin, enrofloxacin, amoxicillin clindamycin, paromomycin and erythromycin, just to name a few.  However these drug effects were probably overestimated since 88% of the cats will resolve their diarrhea spontaneously.  Approximately 57% of the cats that spontaneously resolve their diarrhea will have normal stools but will still be infected and carriers of the disease.  Success of treatment has varied and is not 100% effective in all cases.  Additional factors such as overall health of the cat and its housing environment are contributing factors that influence the outcome of the treatment. 

The only drug that is felt to be reliable against T. foetus is Ronidazole.  This drug is NOT LICENSED for use in cats and is NOT APPROVED for veterinary use in the United States.  It is a poultry antibiotic.  Like metronidazole, the taste of this antibiotic is particularly bitter and therefore it is not recommended to be administered as an oral liquid.  Ronidazole must be compounded to a suitable size for a cat and put in a capsule for administration.  Ronidazole is to be administered at a rate of 30-50mg/kg orally twice daily for two weeks.  At this dosage, the drug is capable of resolving diarrhea and eliminating the infection of TF in cats. 

Gloves should be used when handling Ronidazole as it is considered a potential carcinogen.  Care must be taken when cleaning the litter boxes of cats on Ronidazole also.  Ronidazole is banned for use in food-producing animals due to the carcinogenic potential to humans.

The most common side effect in cats from treatment with Ronidazole is neurotoxicity.  This means Ronidazole should not be used as a trial drug to see if the animal responds to treatment.  It should only be used with cats that have a confirmed diagnosis of Tritrichomonas.  A clinical study revealed that some cats will exhibit reversible neurological toxicity from Ronidazole.  Most of the side effects have been observed when the dosage is administered at a rate of 50mg/kg.  It is possible in all dosage ranges and cats should be monitored for any signs of nystagmus, ataxia, seizures, twitching, and behavior changes.  Ronidazole should be discontinued immediately in the cats exhibiting signs of neurotoxicity.  Even after Ronidazole is stopped the symptoms of neurotoxicity can continue to worsen for the next few days before slowly subsiding.

Ronidazole should not be administered to cats that are systemically ill.  Cats with T. foetus infection generally do not act sick.  This drug should not be administered to nursing queens because it is not known if the drug can be passed in the milk to young kittens.  It should not be given to very young kittens, under the age of 12 weeks, because the kitten may be at higher risk for neurotoxicity.  Finally, Ronidazole should not be given to pregnant queens because of the possibility of birth defects or neurotoxicity that could happen to unborn kittens. 

While some cases may appear to be resistant to Ronidazole, it is probably more than likely that the cats are being re-infected by other cats from within the colony of cats that are asymptomatic carriers.  If the cat’s infection is resistant to Ronidazole, a higher dose, more frequent administration, or a longer duration of drug treatment WILL NOT WORK and will greatly increase the possibility of neurotoxicity in the cat.  At this time, there are no other alternative treatment options available.  One must remember that even though a test has been given to a cat that is supposedly negative for the organism, it is not necessarily 100% correct. 

It is not possible to fully confirm that an infection has been eradicated, as a negative test does not rule out the possibility of the infection.  Experts recommend a PCR test in one to two weeks after treatment and again at 20 weeks following treatment.  Long-term prognosis for infected cats is good, and that they will eventually overcome the infection.  However this is a slow process and requires repeated testing because if just one cat in the colony does not respond to treatment, it will re-infect the entire colony of cats again!

T. foetus is a relatively fragile organism whose life span outside of the body is normally less than one hour, although it can live for several days in wet, moist feces.  Unlike Giardia, T. foetus cannot form a cyst and does not like the presence of oxygen.  If TF dries out, or if it is refrigerated or if it experiences temperatures above 105 degrees it will die.  Consequently, it is fairly easy to eliminate the organism from a cat’s environment.

Although not proven, it is thought that T. foetus can be zoonotic in nature, and may be able to infect humans.  Thoroughly washing hands after handling cat litter pans, litter scoops and feces is important even if the cats are not suspected to have the disease.  Cat scratches and bites should always be washed immediately with soap and water.  Additionally, disinfection of animal bedding is recommended in an effort to stop the spread of the infection to other cats, and prevent humans from being infected by direct contact with cat feces on bedding material.

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