TRICHOMONIASIS
Before the Second World War, trichomoniasis was considered in many countries
to be a certain cause of bovine infertility as a consequence of endometritis, pyometra,
early abortion and sterility.
Transmission was exclusively by the venereal route.
In certain countries (Great Britain, Netherlands, France, Cyprus, Czechoslovakia)
the infection has become a clinical rarity and an exceptional laboratory finding
during the past 10-15 years. On the other hand, it remains a serious cause of infertility
in other countries, particularly in dairy herds, poorly supervised herds and
mountainous regions, wherever communal bulls are still used.
The disease has regressed considerably, or even disappeared, wherever breeding
is well supervised, breeding animals are tested, and AI used on a large scale.
In the male, the protozoan parasite Trichomonas foetus colonises solely the
mucosal crypts of the prepuce or penis, without visible signs of infection and
without eliciting the formation of local antibodies, or specific agglutinins in the
blood.
In the female, contamination occurs in about 25% of cases by natural service,
and the parasite may remain in the vagina without penetrating to the uterus. However,
when a cow is inseminated with contaminated semen, the parasite gains direct
access to the uterus, causing death of the embryo either directly or indirectly (from
endometrial lesions); the result is a return to oestrus. If fetal development is more
advanced, abortion or fetal maceration may occur, with accumulation of pus (pyometra),
while the corpus luteum remains active because the endometrial lesions
have upset prostaglandin secretion. Secretion of local antibodies in the vagina may
overcome infection, but is unlikely to protect against a subsequent reinfection.
Clinical diagnosis is derived solely from herd records showing a combination of
many cases of return to oestrus, endometritis, purulent vaginal discharge, abortion
and pyometra. Confirmation of the diagnosis usually rests on direct microscopic
examination of preputial washings from the bull used in the herd, with culture of
the parasite.
Diagnosis can also be confirmed by identifying the parasite in a purulent vaginal
discharge and/or stomach of an aborted fetus.
However, such diagnosis, while easy to interpret, requires correct techniques for
specimen collection (preputial washing during vigorous massage of the preputial
sac), and very rapid examination at the right temperature (37°C), since the parasite
dies in about 6 hours outside the host; at lower temperatures the movement of the
parasite will be diminished or absent altogether. A mobile laboratory capable of
doing the test and setting up a culture on site is essential to guarantee accurate and
reliable results.
Serological diagnosis by the mucus agglutination test is unsatisfactory because of
the poor immunogenicity of the trichomonas, even in the case of local antibodies.
The treatment of infected bulls by repeated applications of ointments containing
acriflavine or trypaflavine has been largely superseded by systemic therapy with
dimetridazole, given by mouth at 50 mg/kg once daily for 4-6 days. This usually
cures most infected bulls and cows. A useful supplementary treatment for females
is the injection of prostaglandin, which re-establishes a normal cycle in the uterine
mucosa by its luteolytic action.
Prophylaxis and eradication of trichomoniasis require the abolition of venereal
contamination by changing to AI. Of course, the bulls selected for AI have to come
from a disease-free herd, and have to be quarantined before reaching puberty.
During quarantine preputial washings should be taken on 2 or 3 occasions for examination
for T. foetus. The bulls must not come into contact with untested cows
used as teasers. These conditions are similar to those required for controlling
campylobacteriosis.
In some European countries, such as Czechoslovakia, any animal found to be
infected is not treated but eliminated (Polak, 1984), although in most countries
dimetridazole is still used. Treated animals should not be used for breeding until 2
or 3 tests on preputial washings during the 2 months after treatment have proved
negative. When a bull at an AI centre is found to be infected, its entire stock of
semen should be destroyed as suspect from the date of the last negative test.
Trichomoniasis is a notifiable disease in Romania, and adult males and females
have to be treated Until repeated laboratory testing has shown that the infection has
been eliminated. It is forbidden to move a bull over 6 months of age away from an
infected premises, except for slaughter. This prohibition is lifted 3 months after the
last known case of trichomoniasis has been cured.
