A ProMED-mail post
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International Society for Infectious Diseases
Date: 29 Mar 2010
Source: Kob.com [edited]
A deadly sexually transmitted disease (STD) affecting cattle has
popped up in New Mexico, prompting the state's livestock board to take
action.
The STD is causing concern for ranchers who depend on their herds to
reproduce.
"The name of the disease is bovine trichomoniasis, which is a
reproductive disease that affects cattle, and it causes abortions in
the cows," said Sandra Barraza, Chaves County's extension officer.
There is no cure for trichomoniasis, commonly known as "trich."
Veterinarian John Wenzel has talked to some ranchers in Roswell and
says the number of cases is growing.
"In the years 2008 and 2009, the number of calves tested at the
veterinary diagnostic lab greatly increased, almost doubled," Wenzel
noted.
Once the disease is in a herd, the results can be economically
devastating, easily wiping out half of expected calves. It's also hard
for ranchers to spot the signs.
"There really is no way to tell; usually, most livestock producers
figure out there's a problem when they have a low live-calf percent,
but by that time, it's too late. They've already lost those calves for
the year," noted Barraza.
The New Mexico Live Stock Board is trying to slow the spread of the
disease and handed down new requirements last month [February 2010],
including testing bulls for the STD.
Animals that test positive for the STD are usually slaughtered, but
officials say the meat poses no risk to anyone.
[Byline: Taryn Bianchin]
--
Communicated by:
ProMED-mail
[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. 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 percent 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, and more frequent diagnosis.
_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.
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. Unlike many other protozoan organisms, _T. foetus_ is
incapable of forming cysts and cannot survive outside the host for any
length of time. 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.
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.
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. Some cows can carry
the organism through the gestation period and well into the postpartum
period.
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. 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.
There is no consistent observable sign to help with the diagnosis of
the disease. Unfortunately, there is no good 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.
By itself, vaccination will not clear up a trichomoniasis problem.
Currently, one killed whole-cell vaccine is available for use in the
U.S. (Trich Guard or Trich Guard V5-L, Fort Dodge Laboratories). These
products, when used according to label directions, show effectiveness
in the female but none whatsoever in the bull. It is important to
realize that the vaccines will not prevent transmission of _T. foetus_
or infection with the organism but it will limit duration of infection
and result in more pregnancies being carried to term. Vaccine is best
used in situations where bulls cannot be tested or removed, when
desirable management practices cannot be employed, or in other
high-risk situations.
Portions of this comment have been extracted from
- Mod.TG]
....................................................tg/msp/jw
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