|
| |
|
San Joaquin Experimental Range
- Research Bulletin -
|
Bovine Trichomoniasis:
General Information, Diagnosis and Control
by
Michael W. Thomas, D.V.M.
and
Wallace M. Harmon, Ph.D.
CATI Publication #940301
© Copyright March 1994, all rights reserved
Introduction: Importance of
Trichomoniasis
Bovine trichomoniasis is a reproductive disease of cattle which can have
significant economic impact to cow-calf operations and other cattle
enterprises. Venereal transmission of the causative organism,
Tritrichomonas foetus, can cause one of the most commonly
recognized diseases leading to decreased reproductive efficiency in
cattle.1,2 An infected cow becomes
subject to early embryonic death, abortion, pyometra and transient infertility.
In some regions of North America, South America and Australia where open
range beef operations are common, as many as 50% of the herds can be
infected. Although the organism has been known to cause reproductive
problems for over 100 years, there has been an increased awareness of the
disease in the past few years because of the economic impact, required testing
in some areas,3 and more frequent
diagnosis.
The economic impact of trichomonas infection is severe. In beef operations,
and even sometimes in dairies, the calf crop can be reduced up to 50
percent4 depending on the percentage of
bulls infected and the susceptibility of the cows in the herd. In addition to the
obvious loss from fewer calves, further losses include an extended breeding
season or a later calving dates with a shorter growing period for calves, due to
increased number of repeat breeders. These combined losses can result in as
high as 35 percent decrease in economic return per cow in an infected
herd.4
Characteristics of the Causative Organism
Tritrichomonas foetus is a flagellated protozoan which inhabits the
reproductive tract including the prepuce and distal penis in bulls and the
vagina and uterus in cows. It is a motile organism approximately twice the
size of a white blood cell. Protozoa are single celled organisms which are
structurally more complex than bacteria but with many similar biologic
characteristics including multiplication by binary fission. The organism can
be identified in liquid medium under low power (100x) where it is recognized
by its characteristic jerky-tumbling motion. No stains are needed to identify
the living organism. Once seen under a microscope, trichomonads are hard to
mistake for other organisms. Under higher magnification, structures of
locomotion including three anterior flagella, a single posterior flagellum and
an undulating membrane can be seen (Figure 1).
Transmission
Transmission of T. foetus is from infected bull to susceptible cow or
from infected cow to susceptible bull during breeding. Infection presumably
occurs by rubbing off organisms from the preputial
membrane.6
Unlike many other protozoan organisms, T.
foetus is incapable of forming cysts and cannot survive outside the host
for any length of time.5 Thus, direct
venereal contact is necessary for transmission of the infection. Rarely, dirty
equipment along with unsanitary technique for genital examination can be a
possible means of transmission.2
Bulls are long-term carriers of the infection. They carry the infection in the
folds of the penis or in the fornix area of the prepuce. Younger bulls are less
likely to become permanent carriers than are older bulls, but may still transmit
the organism to susceptible females. Yearling bulls, even so called "virgin"
bulls have been found by several investigators and practitioners to be culture
positive on occasion.6
Cows are also potential sources of new infections and maintaining the
organism in a herd. Usually they only harbor the organism for a few heat
cycles after infection or pregnancy loss. Sexual rest of at least 4 months has
been prescribed for infected cows.7
Some cows can carry the organism through the gestation period and well into
the postpartum period. Skirrow8 found
2 of 40 infected cows from 2 herds that carried the infection through the entire
gestation and for up to 9 weeks postpartum. Such a 'carrier cow' presents a
problem when trying to control the disease and offers at least partial
explanation for the persistence of infected animals when control measure have
concentrated on eliminating positive bulls.
Although not likely, transmission is possible by artificial insemination using
frozen semen. The organism does not normally inhabit the urethra but could
be found in the semen if infectious preputial fluid drained into the artificial
vagina at the time of semen collection. A few trichomonads can survive the
dilution techniques and freezing and thawing along with the sperm.9 Transmission with artificial insemination
(AI) is not likely with proper technique and because reputable semen
companies regularly test their bulls. In fact AI is a recommended method of
dealing with an infected herd.
Diagnosis
There is no consistent observable sign to help with the diagnosis of the
disease. Lesions in an aborted fetus may lead to a presumptive
diagnosis,10 but confirmation of the
diagnosis requires demonstration of the organism in the tissue or most
frequently in culture. Herd or individual diagnosis of bovine trichomoniasis
in bulls or cows depends on the accurate demonstration of Tritrichomonas
foetus in culture. Two cultivation techniques have been successfully
employed with consistent results: in vitro Diamond's medium, specifically
prepared for culture of T. foetus,11
and the InPouch TF® culture
system (BioMed Diagnostics, San Jose, CA). The latter is a plastic pouch
convenient for uses in the field containing a proprietary medium with a 12-15
month shelf life. Other diagnostic techniques including serological methods
and DNA probes lack the sensitivity needed for effective diagnosis at this
time.12
Reliability of the culture techniques depends on proper collection and handling
of the specimen. In either case it is recommended that the specimen is directly
deposited into the culture medium in the field rather than using a transport
medium such as lactated Ringer's as this may result in up to 20 percent of
positive samples being lost.6 Proper
collection of the specimen requires understanding the areas that the organism
is likely to inhabit and consistent technique. (See Insert: Procedures for identifying trichomonads)
Disease Mechanisms
Although much has been learned in recent years, the exact disease-causing
mechanism induced by T. foetus infection is not known. Other than
protozoan-induced abortion, the pathogenic processes result in rather
insignificant problems such as unnoticeable or slight signs of inflammation in
the bull and transient vaginitis, cervicitis, and possible endometritis in the
cow. T. foetus is generally considered an organism of limited ability
to invade tissues and this would make it easy to explain the apparent lack of
irritation in the prepuce of the bull. Recent microscopic documentation with
specialized techniques has demonstrated the organism deep in the tissues of
the placenta and the fetus.8 The
inflammation is mild, however, and the exact abortive mechanism and timing
of abortion is not understood and many questions on specific mechanisms
remain unanswered.
Treatment
Unfortunately, there is no therapeutic agent for treating bovine trichomoniasis. In the past ipronidazole was used, but it was never approved
for use in cattle and is no longer available. Other related compounds do not
seem to be as effective as ipronidazole, and they likewise are not approved for
use in cattle and/or are not available. Although the possibility exists for new
therapeutic agents, control of this disease has to be by other means at the
present.
Immunology
Cows are better than bulls in mounting an effective immune response to
T. foetus infection. In the cow, parasites seem to provoke a mild
inflammatory response that is associated with either early or late termination
of pregnancy. Although it is often considered as though it were only a
disease symptom, inflammation is mediated by immune mechanisms and can
be an important effective immune response. In T. foetus infection, it
might bring the infection to a close, perhaps simply by flushing organisms
out of the reproductive tract. Carrier cows, on occasion, may be important in
the maintenance of infection in herds. In these cases, the immune or flushing
mechanisms have apparently not successfully destroyed or expelled the
organism.
Typical antibody in immune cows appears in the mucus secreted primarily by
the uterine endometrium. Immune globulins of the IgG class have been
found in these secretions. IgG antibodies could protect the cow by a number
of mechanisms of action including preventing attachment of the organism to
vaginal or uterine epithelial cells, immobilization or by lysis of the
parasite.13 In other infectious diseases
this antibody class is commonly found in the blood, not in secretions. Unlike
this more usual immune response, circulating antibody has not been detected
in cows infected with T. foetus. A practical consequence of this
peculiarity is that no serological test has been developed for diagnosis.
Since infection in bulls seems to provoke neither disease nor an immune
response, bulls, once infected, are the important hosts for parasite
maintenance in a herd. As noted, young bulls are less likely to be infected,
and, thus, a source of infection, than are older animals. This correlation of
prevalence with age, however, almost certainly has nothing to do with
immunity. Instead, it seems likely to be a consequence of differential
susceptibility to infection. Older males, with deeper furrows or folds in the
mucosal coverings of penis and prepuce, are simply more likely to retain
organisms in the more protective environment of these folds than are younger
animals.
The vaccine commonly in use in cows against T. foetus is
administered by intramuscular injection. It is not surprising, then, that it
provokes a transitory circulating antibody response.14 More important, however, is the cow's response
to vaccination by antibody secretion in the reproductive tract. Because this
response, which must be the effective one, is also transitory, care must be
taken to follow the vaccination protocol established by the manufacturer so
that antibody is available in the reproductive tract in high titer at the
appropriate time in the infection process.10
Parasites like T. foetus, are often successful even though they provoke an
immune response. T. foetus , like some other parasites, may cope
with the immune response directed against it by masking itself in host
protein. It is perhaps ironic that the protein used by T. foetus for
antigenic disguise is the antibody itself.
Corbeil1
has demonstrated that bovine IgG can be bound to
the surface of this organism in a non-antibody specific way. As such it could
be an effective barrier to the usual antigen-antibody reaction necessary for an
effective immune response.
Practical Control Measures
In 1949, Bartlett15 defined two basic
principles of control of trichomoniasis in cattle: 1) keep from breeding
susceptible cows to infected bulls, and 2) keep from breeding susceptible
bulls to infected cows. Most practical control measures still rely on these two
principles. Except for the introduction of a new vaccine for immunization
with the T.foetus organism and the increased emphasis on culturing
and culling positive bulls, little has changed in the past few years in regards to
control programs for trichomoniasis. Even with a vaccination program, other
aspects of a complete program should be followed. In 1985, BonDurant6 gave some good advice for practical control.
Some of the following suggestions are patterned on what he recommended.
These practical suggestions may help reduce the losses from this disease. The
suggestions are for naturally bred herds in range situations, but some of the
suggestions apply to other management situations.
1. Good fences make good neighbors and prevent problems. Keep fences
in good repair and make note of any co-mingling of the herd with
neighboring herds. If common grazing lands are used, keep bulls out of
these areas if possible.
2. A breeding season with a limited exposure to bulls (i.e. 90 day breeding
season) should be used. In the event of an outbreak it is much easier to
identify the problem if the time of exposure to the bulls is reasonably
tight. If the breeding season is extended or year-round, the disease will
be more difficult to control and to identify animals carrying the organism.
3. Replace old bulls with young bulls, keeping the average bull age as
young as possible.
4. Culture all new bulls coming into the herd regardless of age. It is
essential that the veterinarian be comfortable with the diagnostic
collection procedure and has some confidence in his ability to isolate and
identify the organism. On many occasions culture can be done at the
same time as breeding soundness examinations. All bulls should also be
checked before shipping to other areas, 3-4 weeks before the breeding
season begins and 2-3 weeks after the bulls are taken from the cows at
the end of the breeding season.
5. Cull open cows at pregnancy check time and any others that abort or
have a noticeable discharge. Check the aborted fetus and any discharge
for T.foetus . Although most cows clear themselves within the
first few estrus cycles after abortion or early embryonic death, it has ben
shown that cows can carry the infection throughout the pregnancy and
well into the post-partum period. This "carrier cow" can re-introduce the
organism into the bulls.
6. Vaccinate cows against the T.foetus organism. A commercial
vaccine containing inactivated T.foetus and a proprietary
adjuvant is available for use in a control program. Controlled trials with
this product have shown to significantly reduce the abortion losses when
bred to infected bulls. It does not appear that the vaccine prevents
infection of the cow with T.foetus, rather it limits the duration of
the infection and thus prevents the pathologic effect of the organism by
causing the cow to rid her system of the infection before damage is done
to the fetus.14
7. Use artificial insemination if it can be administered effectively with
proper personnel for insemination and estrus detection. Check the source
of the semen to see if bulls at that facility are tested for trichomoniasis.
8. Control other reproductive disease like campylobacteriosis (vibriosis)
with an appropriate vaccination program. Conscientious vaccination for
diseases like vibrio will make it easier to spot a trichomoniasis problem.
Vaccinate females before the breeding season. Males can also be
immunized.
Procedures for indentifying
trichomonads16
Changes in calving rates or calving intervals may indicate a trichomoniasis
problem. Concentrate diagnostic efforts in the bull battery, in open cows, and
in cows with a uterine discharge. All bulls should be checked on a regular
basis. But checking is especially important before the breeding season
begins, whenever new bulls come into the herd, after the breeding season
ends and if return heats or open cows are observed. After the breeding
season, it is important to give the bulls about two weeks of rest from breeding
before taking diagnostic samples.
Specimen collection technique is important regardless of the nutrient medium
used for culturing. Use a dry infusion pipette with a 20-cc syringe for both
bulls and cows. In the bull, direct the pipette to the distal penis in the sheath.
Collect the specimen by scraping the mucosa of the distal penis and the fornix
area while applying suction with the syringe. In the cow use the same
technique in the anterior vagina. The mucus in the anterior vagina may be
thick and some persistence may be required to get the mucus into the pipette.
If the InPouch TF test is used, open the pouch by tearing off its top. Using
the pipette, place the specimen into the upper chamber. As the pipette is
introduced into the upper chamber, draw a small volume of the liquid medium
into the pipette. Move the medium back and forth to rinse the mucus from the
pipette. Then deposit the liquid into the upper chamber . Fold the top of the
pouch down several times to the middle of the pouch. This introduces the
specimen into the lower chamber. The wings of the pouch are then folded to
seal the pouch for incubation.
Incubate at 37°C with the pouch in a vertical position to
concentrate the organisms at the bottom. Cultures are usually examined
microscopically at 24, 48, and 72 hours of incubation. Apply the plastic
viewing clamp provided by the manufacturer to the bottom of the pouch (do
not open the pouch). The clamp serves as a microscope slide. View the
specimen at a magnification of 100x. Trichomonads are recognized by their
jerky movements.
References
1. Corbeil LB, Hodgson JL, Jones DW, et
al. 1989. Adherence of Tritrichomonas foetus to bovine vaginal
epithelial cells. Infect. Immun. 57:2158-2165.
2. Goodger WJ, Skirrow S. 1986.
Epidemiologic and economic analysis of an unusually long
epizootic of trichomoniasis in a large California dairy herd. JAVMA. 189:772-776.
3. Idaho Animal Health Regulation 187 - Trichomoniasis. By Provision of Title 25, Chap. 2, Idaho
Department of Agriculture, Bureau of Animal Health, Boise, Idaho.
4. Rae DO. 1989. Impact of
Trichomoniasis on the Cow-Calf Producers Profitability. JAVMA
194:771-775.
5. Fernandez CF. 1989. Survival of
Tritrichomonas foetus in the Environment. Unpublished data on
file, CSU-Fresno.
6. BonDurant RH. 1985. Diagnosis,
Treatment and Control of Bovine Trichomoniasis. Compend. Cont.
Ed. Pract. Vet. 7:S179-S188.
7. Fitzgerald PR, Bovine Trichomoniasis.
1986. In: Veterinary Clinics of North America, Food Animal
Practice. Vol. 2 Philadelphia, WB Saunders Co, pp 277-283.
8. Skirrow SZ. 1987. Identification of Trichomonad-Carrier Cows. JAVMA. 191:553-554.
9. Clow-Collum N. 1989. Survivability of
T. foetus in Frozen Bovine Semen. Unpublished data on file, CSU-
Fresno.
10. Rhyan JC, Stackhouse, LL, Quinn WJ.
1988. Fetal and Placental Lesions in Bovine Abortion due to
Tritrichomonas foetus. Vet Pathol. 25:350-355.
11. Kimsey, PB. 1986. Bovine Trichomoniasis. In: Current Veterinary Therapy in
Theriogenology 2. Edited by DA Morrow. Philadelphia, WB
Saunders, Inc, pp 275-279.
12. Appell LH, Mickelsen WD, Thomas MW,
Harmon WM. 1993. A Comparison of Techniques used for the
Diagnosis of Tritrichomonas foetus Infections in Bulls. Agri-
Practice. 14:2.
13. Aydintug MK, Widders PR. 1990.
Antibody Enhances Killing of Tritrichomonas foetus by the
Alternative Bovine Complement Pathway. Infect Immun 59:944-
948.
14. Hall MR, Kvasnicka WG, Hanks D. et al.
1993. Improved Control of Trichomoniasis with Tritrichomonas
foetus Vaccine. Agri-Practice 14:1.
15. Bartlett DE. 1947.
Trichomonas foetus and bovine reproduction. Am J Vet
Res. 8: 343-352.
16. Borchardt, KA, Thomas, MW,
Norman, BB, Harmon, WM. 1992. Evaluation of a new
culture method for diagnosing Tritrichomonas foetus
infection. Veterinary Medicine. Feb. 1992.
{ page top }
{
CATI ,
SJER - Research Publications
}
|