Trictrichomonas foetus

Recognition of the Trictrichomonas foetus as an important enteric parasite of cats first occurred in the mid-1990s.  Since then reports from several regions of the world have established that the parasite is an important pathogen in these hosts.  The trophozoites of Tritrichomonas foetus lives in the ileum and large intestine on the mucosal surface or sometimes in the crypts.  They can cause significant diarrhea.  The parasite and disease are seen most commonly in young cats, especially if overcrowded and/or stressed.  Laboratory diagnosis is based on parasite detection in direct smears of faeces, culture of faeces in selective media, and PCR.  Currently there is no effective treatment.  Tritrichomonas foetus has recently been reported from the uterus of a cat in Norway with uterine pathology.  The question  of possible transmission of T. foetus between cats and cattle and vice-versa has not yet been fully resolved.

 

In cattle

The flagellate protozoan Tritrichomonas foetus infects the genital system of cattle and what is believed to be the same species occurs in the intestinal tract of pigs (previously known as T. suis) and cats, although recent research indicates that cattle and cats each have their own genotype of the parasite.  In cattle the parasite has a direct life cycle and the trophozoites (the only known life cycle stage) are transmitted venereally.  The major problem caused by T. foetus in cattle is abortion which usually occurs during the first half of pregnancy.  Bulls act as carriers for T. foetus and once they acquire the parasite they remain infected for life.  Diagnosis of T. foetus in bulls is by culture of a preputial scraping and identification of the parasite either by microscopy (with which sensitivity and especially specificity may be problematic) and/or PCR.  Similar tests can also be applied to placental fluids and to the stomach contents of aborted foetuses.  Control of trichomoniasis in cattle can be difficult and depends on management strategies to detect and cull infected bulls and cows BEFORE introduction to a herd or breeding.  There are no effective treatment or vaccines approved in Canada for either bulls or cows.  Currently there is no evidence for natural transmission of T. foetus between cattle and cats.  Other than a case report with an uncertain identification of the parasite, Tritrichomonas foetus is not known to be zoonotic.

Phylum: Parabasalia
Class: Trichomonoda
Order: Trichomonadida
Family: Trichomonadidae

All known members of the Class Trichomonadida are parasitic, and most have only a trophozoite stage (no cyst) in their life cycles. The taxonomy within the Class is not yet fully established, particularly at the species level, but molecular approaches are proving helpful.

Tritrichomonas foetus is a flagellate that in cats inhabits the colon. Tritrichomonas foetus in cats seems to be the same organism as that causing abortion and reproductive losses in cattle, but more work is required to establish a definitive identification for the species. Organisms from the two hosts may prove to be genetically and biologically distinct, and there may prove to be several genotypes, each with their own characteristics, including host specificity. Close relatives of T. foetus that have a role in human health include Trichomonas vaginalis and Pentatrichomonas hominis. A less close relative is Giardia.

 

In cattle

Tritrichomonas foetus causes abortion and reproductive losses in cattle and GI disease (primarily large bowel diarrhea) in cats. Recent research indicates that cattle and cats each have their own genotype of T. foetus, but there may prove to be several genotypes, each with their own characteristics, including host specificity. Also, the organism previously described as T. suis in pigs is now believed to be T. foetus. Close relatives of T. foetus that have a role in human health include Trichomonas vaginalis and Pentatrichomonas hominis. A less close relative is Giardia.

Tritrichomonas foetus has only a trophozoite stage in its life cycle. Trophozoites are pear-shaped and measure up to approximately 25 µm by 15 µm with a nucleus at the broad (anterior) end and an adjacent sausage-shaped parabasal body. Three anterior flagellae arise from the broad end and a fourth, posterior, flagellum lies along the outer edge of the undulating membrane before extending posteriorly. In liquid medium, the trophozoites move with a characteristic tumbling motion. The flagellae and internal structures can usually be seen in stained and mounted specimens.

 

In cattle

Tritrichomonas foetus has only a trophozoite stage in its life cycle. Trophozoites are pear-shaped and measure up to approximately 25 µm by 15 µm with a nucleus at the broad (anterior) end and an adjacent sausage-shaped parabasal body. Three anterior flagellae arise from the broad end and a fourth, posterior, flagellum lies along the outer edge of the undulating membrane before extending posteriorly. A spine-like axostyle protrudes from the posterior end of the parasite. In liquid medium, the trophozoites move with a characteristic tumbling motion. The flagellae and internal structures can usually be seen in stained and mounted specimens. In some cultures, a "round form" (diameter 15 to 20 μm) is also seen.

Tritrichomonas foetus has been recovered from cattle, pigs and cats in several parts of the world, and may occur in other mammals. The understanding of host range will change as more is learned of the detailed taxonomy of the parasite. A recent study reported a prevalence of 31% among cats at an international cat show in the US.

 

In cattle

Tritrichomonas foetus has been recovered from cattle, pigs and cats in several parts of the world, and may occur in other mammals.  Recent research indicates that cattlem and cats each have their own genotype of T. foetus, and understanding of host range will change as more is learned of the detailed taxonomy of the parasite. In recent years T. foetus has been recognized as a significant cause of reduced productivity in beef cattle in areas of the Canadian prairies, particularly on community pastures in Saskatchewan. Carefully designed control measures have helped to greatly reduce the losses.

As far as is known, Tritrichomonas foetus has only a trophozoite stage and transmission is by direct contact, including by ingestion in cats and venereally in cattle. In cats the organism lives in the ileum, caecum and colon, mostly close to the mucosal surface but also occasionally in the mucosal crypts

 

In cattle

As far as is known, Tritrichomonas foetus has only a trophozoite stage, which multiplies by longitudinal binary fission. Transmission is by direct contact, primarily venereally in cattle. In bulls, the parasite lives in the  crypts of the preputial mucosa . In cows, it is thought that most organisms remain in the lumen of the reproductive tract (vagina, uterus and oviduct), although they have been identified by immunohistochemistry in placental tissue and in fetal lung tissue and abomasum. How the parasites made their way to these locations remains a mystery.

 

Little is known of the epidemiology of Tritrichomonas foetus in cats. Young, densely housed cats seem to be most commonly infected and affected clinically. It is assumed there are carrier cats that act as a source of infection for others, and transmission from mothers to kittens may be important for maintenance of the parasite in cat populations. The significance of possible host-switching (for example from cats to cattle and vice versa) is not known.

 

In cattle

Almost all transmission of T. foetus among cattle occurs at coitus. It is believed that 100-200 viable organisms can establish infection in a naïve heifer or cow.

Bulls are the primary reservoirs for T. foetus and once they acquire the parasite should be considered persistently infected. Transient infections can occur in bulls of all ages, and may be more frequent in bulls less than four years of age. This may be because younger bulls are more able to clear the parasite, and/or because they are less likely than older bulls to breed infected cows that have aborted and that are open towards the end of the breeding season. It is very risky, however, to assume that any infected bull will clear the parasite, and all bulls with T. foetus should be culled.  Bulls acquire the parasite from infected cows and heifers, and can then transmit it to uninfected females. Tritrichomonas foetus is usually cleared spontaneously from cows and heifers within a few months of infection, with or without abortion, but in a very few animals will persist for longer periods. Once infected, most cows are immune to re-infection, at least for the breeding season in which they were infected. The parasite is not believed to survive more than transiently outside its mammalian hosts, although it can be transmitted by artificial insemination and by gynaecological examination.

Transmission of T. foetus is facilitated in cattle management systems that co-mingle cows and heifers from several farms with bulls, some or all of which are potentially infected but have not been tested for the parasite.

Trophozoites of T. foetus damage the mucosa of the large intestine by mechanisms that have not yet been determined. Typical lesions include lymphocytic-plasmacytic colitis, epithelial cell hypertrophy in the crypts, and disruptions of the surface epithelium. Where these lesions are particularly severe, organisms can invade the lamina propria and deeper layers of the intestinal wall.  Tritrichomonas foetus has recently been reported from the uterus of a cat in Norway with uterine pathology.

The characteristic clinical sign of feline tritrichomoniasis large bowel diarrhea. Cats in shelters and purebred show cats are more often infected than house cats, but infection is believed to be more common than is clinical disease. Because there are currently no effective treatments for T. foetus, the infection in cats often becomes chronic, often lasting months before the parasite disappears spontaneously.

 

In cattle

In bulls, infection with T. foetus is usually asymptomatic. In heifers and cows, the most common presenting clinical sign is early embryonic death and abortion (at 1 to 16 weeks, most commonly around 8 to 9 weeks) resulting from placentitis and affecting a proportion of animals bred to one or more infected bulls. Infection does not always result in abortion; some pregnant cows do not abort but clear the infection. Rarely a normal calf will be delivered at full term to a cow that is still infected. Other, less commonly observed, clinical signs in females include longer oestrus cycles following an early abortion, uterine discharge and pyometra. The means by which T. foetus causes abortion and the other clinical signs are not fully understood.

History and clinical signs are often helpful.  In addition, three laboratory techniques are used to detect T. foetus in feces: a) direct smear and visualization of the trophozoites (the least sensitive); b) fecal culture in the In Pouch™ TF Feline; and c) PCR (the most sensitive). The infection has not yet been recognized with sufficient frequency in western Canada for any of these techniques to have been widely applied.

 

In cattle

The history and clinical signs (especially abortions – which may not be obvious, and an unusually high proportion of open or late calving cows and/or heifers) are very helpful. Diagnostic testing for the parasite is most often directed at bulls. The most reliable methods are based on the collection, culture and examination of material from the penis and prepuce. The method most commonly used in western Canada involves collecting a scraping from the mucosa of the penis and prepuce using an artificial insemination pipette, culturing the scraping in a (not expired) commercial culture kit (InPouch™ TF System) at 37C for seven days, and examining the culture microscopically every other day for typical organisms. Between sampling and culture, the kits should be kept at room temperature, NOT refrigerated, and in the dark. Some veterinarians prefer Diamond’s medium to InPouch™ TF for culture, but it is not currently available as a kit. Kits available for diagnosing T. vaginalis in women are not suitable for T. foetus diagnosis.

In some jurisdictions, the protocol required to detect infection with T. foetus depends on a single test on a bull after a period of sexual rest.  In other jurisdictions, however, two or three tests are required over several weeks because recovery of the organism from some bulls can be intermittent. A single test on infected bulls has been shown to have a sensitivity of greater than 90%, which is improved slightly by a second test. With an experienced observer, examination of the cultures for flagellated organisms with a typical rolling movement should have good specificity (>95%). This can be improved by the use of phase contrast microscopy, or by the examination of wet mounts or of stained slides of the organisms taken from the cultures, or by PCR. The last is available in several veterinary diagnostic laboratories in western Canada. T. foetus-like organisms have been recovered occasionally from virgin bulls, but at least two reports using PCR has demonstrated that these are a different species. The validity of testing samples pooled from several bulls (often 5-10) from a group is being assessed, as is the use of PCR (including qPCR) on samples direct from the bull and held in PBS (without culture) and on cultured samples. The use of pooled samples has the potential to reduce the cost of testing and surveillance.

Diagnostic testing is less often applied to cows and heifers, primarily because of lower test sensitivity. Samples for culture can be collected from foetal abomasal contents, pyometra fluid or scrapings or washings from the anterior vagina. The sensitivity of these test procedures in cows and heifers is approximately 80%, and the specificity is as for bulls. The use of PCR or other confirmatory techniques will improve specificity.

One of the key issues related to the use of culture techniques for the diagnosis of T. foetus is accurate identification of any organisms cultured from the test sample. Tritrichomonas foetus is one of a several flagellates that live in cattle and it is possible that morphologically similar organisms, normally found in the GI system or in the prepuce, may contaminate preputial samples. It is very important, therefore, when collecting the samples to remove any fecal material from around the prepuce (without washing, particularly with a disinfectant, that may reduce parasite viability) and, if inexperienced in culture examination or the finding is unusual in the animal being sampled, to consider the use of a confirmatory test.

There are no drugs approved in Canada for the treatment for Tritrichomonas foetus in cats, and none of those tried (extralabel) has been found to be effective.

Because so little is known about the parasite’s epidemiology, it is difficult to recommend effective control measures. The high prevalences reported in shelters and among purebred show cats suggest that avoidance of overcrowding, good environmental hygiene and minimizing stress may be helpful.

 

In cattle

There are no reliably effective treatments for T. foetus in either bulls or cows, and none are approved in Canada. Vaccines are available for administration to cows to improve calving rates, but none are marketed in Canada.

Successful control of T. foetus in cattle once it is established depends on implementation of an effective testing program, which in Canada usually targets bulls, and changing management systems to minimize transmission. For example, test-positive bulls should be culled. If testing is not possible, or if there are concerns about the accuracy of the testing, then culling bulls over four years of age, or even all bulls, should be considered. Keeping younger, untested bulls is the least desirable control option because if they become infected they will remain so for life. Open cows should be culled, or at least excluded from community pastures, and they should not be housed with bulls outside the breeding season. The breeding season should be shortened to reduce opportunities for transmission and to make it easier to detect late breeders. Infected and uninfected bulls should not be kept together because of the slight risk of bull-to-bull transmission. And if there is any possibility of new introductions into a herd being infected with T. foetus, or of the recipient herd already containing infected animals, all the new introductions, especially the bulls, should be tested before being mixed with other animals.

Tritrichomonas foetus is not known to be zoonotic, although there is a single case report of infection with an organism described as T. foetus in the CSF and urine of a person who had been given an allogenic peripheral blood stem cell transplant. According to the authors of the report, however, it is possible that the parasite in this case may have been T. mobilensis or another trichomonad.

 

 

Payne PA et al. (2009)  The biology and control of Giardia and Tritrichomonas foetus.  Veterinary Clinics of North America Small Animal Practice 39: 993-1007.

Stockdale HD et al. (2006) Feline trichomoniasis: an emerging disease? Compendium on Continuing Education for the Practicing Veterinarian 28: 463-471.

Foster DM et al. (2004) Outcome of cats with Tritrichomonas foetus infection. Journal of the American Veterinary Medical Association 225: 888-892.

 

In cattle

Stromberg B et al. (2006) Gastrointestinal nematode control programs with emphasis on cattle. Veterinary Clinics of North America Food Animal Practice 22: 543-565.