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Control of trichomoniasis: Control at the state and farm levels (Proceedings)

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Aug 01, 2010

Trichomoniasis, or "trich," is a disease that can cause devastating reductions in the percentage of cows exposed to a bull that successfully calve.1,2,3 The disease is caused by a protozoan parasite, Tritrichomonas foetus and the organism is transmitted by the act of mating.4 Infected bulls seldom exhibit any symptoms, while infected cows will most commonly have early embryonic loss (generally day 20 to 90 of gestation), and occasionally pyometra or abortion of larger fetuses. In infected herds, ranchers will often notice that a high percentage of cattle are still showing estrus 60 days or more into the breeding season. The number of cows that calve can be reduced by 20% to 40% and the mean calving date will be later than in non-infected herds.

Infection in the cow occurs primarily by exposure to an infected bull at breeding. Initial infection of the female does not cause rapid conception failure, rather the pregnancy progresses to about 20 to 90 days, at which time the embryo/fetus dies and is resorbed or aborted. A period of infertility may last for another two to six months as a result of the infection. Cows that are infected with Trichomonas foetus typically clear the infection within a few months. Immunity, however, is not permanent and the cow is subject to re-infection in subsequent breeding periods. Occasionally an open cow will fail to clear the infection or a pregnant cow will remain infected through pregnancy and deliver a normal calf. These chronic carrier conditions in females are rare, but of concern, because these females can serve as a source of infection to bulls in the following breeding season; or be a route of introduction to a herd that purchases a chronically-infected cow.

Bulls contract the organism by breeding an infected cow. Because most cows will clear the infection within a few months, the female most likely became infected during the present breeding season from exposure to an infected bull. The trich organism colonizes the penile crypts and prepuce, but does not produce any symptoms in infected bulls. Bulls less than 4 years of age tend to clear the infection, while those 4 years of age and older are often infected for life; and no legal treatment is available to clear infected bulls. Although young bulls tend not to become permanent carriers, they can still spread the infection to susceptible females during the period that they are infected.

Testing for trichomoniasis: Sample collection and handling

Because adult bulls are chronically infected with the organism (vs. females and young bulls that are temporarily infected), smegma samples obtained from the prepuce/penis are most commonly used to establish a herd diagnosis (infected or non-infected herd) and to classify individual bulls as infected or non-infected. A positive test result from cervical mucus samples taken from females with pyometra can also be used to establish a herd as being infected. The samples are cultured in a growth media that supports the growth of flagellated protozoa. The transport and culture media commonly used in the U.S. today is the InPouch™ TF (biomed Diagnostics Inc., San Jose, CA). Historically, a variety of media have been used with Diamond's media being used in many earlier investigations of Trichomoniasis.

In bulls, the preferred sample is from the glans penis. This can be obtained by using a sterile insemination pipette and performing a vigorous back and forth scraping motion along the glans while applying negative pressure with an attached 10 ml syringe. A separate pipette and syringe should be used for each animal. The preferred sample from females is the cervical mucous or uterine secretions. These samples can be collected by applying negative pressure with a syringe attached to a sterile insemination pipette, while the pipette is positioned within the open cervix or positioned to collect fluid from the vaginal floor.

The handling and/or shipping of the inoculated media samples is one of the most critical steps in Trichomoniasis diagnosis. When using the InPouch™ TF, inoculate the sample into the small upper chamber of the pouch, flush out the pipette. If the pouches are to be shipped, the samples should be left in the upper chamber and not pressed into the lower chamber until they arrive at the lab. This allows them to be handled freely but then once at the lab, the inoculation of the lower chamber can be completed and the pouch maintained upright from then on. In-Pouch TF media can be transported by commercial carrier, but this must be by overnight express/one-day delivery and the inoculated media should be kept at 65° F to 75° F until it is incubated. It is especially important to avoid overheating or freezing. Ship the inoculated pouches in insulated containers (no ice) that will protect the samples from extreme temperatures because Trichomonads are very susceptible to either freezing or overheating. It is important to arrange shipping so the samples arrive at the laboratory or clinic that will perform the testing within 30 hours of collection. For both culture and PCR, preputial samples should be cultured as soon after collection as possible. Storing preputial samples for even 24 hours may result in a loss of approximately 10% in diagnostic sensitivity, with longer delays causing more drastic declines. If the culture will be performed on-site, squeeze or "squeegee" the liquid down into the lower chamber. Carefully express air bubbles out of the lower chamber to maintain the anaerobic environment. Roll the top of the plastic pouch down to the top of the lower chamber and fold the wire strips across to hold and seal it. Don't stir or mix the content and keep the packet upright at all times once the lower chamber is inoculated.