Protozoal Causes: Neospora caninum and Trichosomiasis
Neospora caninum
This parasite which is harboured by dogs occurs worldwide and is a common cause of abortion in dairy cattle; it also occurs in Kenya/East Africa. - Pups born from infected dogs show signs of paralysis.
In cattle sporadic abortion most commonly occurs between 4 and 6 months of gestation. Abortion storms have been observed and repeat abortions in affected cows have also been reported. Stillbirth can also occur. Occasionally infected calves are born alive; they are underweight, weak and often show signs of paralysis. Sometimes the paralysis develops as late as 4 weeks after birth. - Usually the aborted foetus is decomposed, cows are not clinically ill and the placenta is not retained.
Transmission to cattle is via feed contaminated with dog faeces. Transmission from cow to cow does not occur.
There is no safe treatment and no vaccine.
Strict hygiene to prevent contamination of feed by dogs' faeces is the only prevention. Strictly keep dogs out of feeding areas and pastures.
Trichomonas fetus (Trichomoniasis)
Trichomoniasis is a venereal protozoal infection of cattle caused by Trichomonas foetus. It occurs without fever and is contagious. Trichomoniasis is confined to the reproductive tract of the cow and the penis sheath of the bull. The disease occurs worldwide.
Mode of spread
The infection is spread through mating or through the use of contaminated insemination instruments or stockmen's hands.
T. foetus infection is confined to the reproductive tract, where it can invade most parts. Infection normally lasts about 3 months. There is usually a mild inflammation of the vagina shortly after infection but significant changes do not normally take place until 50-60 days after infection when strong inflammation of the vagina and uterus, accumulation of pus in the uterus and early abortion may take place.
Abortions are often undetected and the main feature observed is often a failure of cows to hold to service.
Infection in the male is usually confined to the surface of the prepuce and penis and is usually so mild it is not clinically apparent.
Signs of Trichomoniasis
- Cows may have a more than normal watery vaginal discharge about 2 weeks after coital infection
- Abortion may occur in early or late in pregnancy
- After abortion the placenta is often retained and there may be pus in the uterus.
- The foetus has no specific lesions.
- Inflammation of the uterus and pyometra ? a pus filled uterus
- There is irregular heat and the cow may stop coming into heat altogether
- Cows eventually clear themselves of infection and the uterus is usually normal 2-6 months after infection
Bulls show no symptoms but once infected tend to remain permanent carriers.
Diagnosis
Trichomoniasis can be suspected in any breeding cattle if there is a history of reproductive failure characterized by repeated returns to service, a lower than expected pregnancy rate, a wide range of gestational ages and cases of early abortion and pyometra.
Laboratory diagnosis is possible and can be made from a foetus, placental fluids, uterine contents, or via mucus taken from the vagina or from sheath washings from carrier bulls.
Diseases with similar symptoms
The disease must be differentiated from Vibriosis which it resembles.
Prevention and Control
The simplest control method involves ceasing to breed cows for at least 3 months, by which time they will have eliminated the infection, and to carry out examination of the cervical mucus using the vaginal mucus agglutination test.
Use of a clean bull either for natural mating or artificial insemination is also a control method.
Recommended treatment
The majority of infected cows and heifers recover completely and clear the infection and so they are not normally treated.
In bulls treatment using various Imidazoles has been used but none is both safe and effective. Ipronidazole is probably the most effective but can cause sterile abscesses at the injection site. In addition bulls are probably susceptible to re-infection after successful treatment.
Resistance to Ipronidazole may also be a concern. The biggest problem, however, is that the success of treatment is measured by repeat sampling which may mean that the individual bull can never be definitely said to be negative. Therefore it is better to slaughter the bulls and replace them with virgin bulls or to test and cull positive bulls.
Re-infection is prevented by exposing only uninfected (clean) bulls to uninfected (clean) cows. Clean cows are assumed to be those with calves at foot and virgin heifers.