Researchers investigating EBA disease in cattle herds

By Andrew Church
Epizootic Bovine Abortion (EBA), also known as Foothill Abortion, is a disease responsible for reducing calf production on ranches in western and northern Nevada, California, southern Idaho and southern Oregon.

Ongoing research by the University of Nevada's College of Agriculture, Biotechnology, and Natural Resources and the University of California Davis School of Veterinary Medicine has worked to investigate this disease as well as develop strategies to mitigate its damages. EBA is caused by infection through the bite of Ornithodoros coriaceus, a species of tick that cohabits areas used for livestock production.

The pathogen carried by the ticks cause pregnant cows to either abort their calves late in term (six to nine months), or results in the birth of weak calves that die soon after. The prominence of the disease in these regions raises herd death tolls, and is detrimental to livestock producers. In some areas, the estimated loss of life to EBA can be in upwards of 50 to 60 percent of a calf crop. Much like the relationship between malaria and mosquitos, the ticks serve as a vehicle for the transference of the pathogen. When ticks bite the host, the host is infected with the pathogen, causing it to multiply.

Other ticks that bite the infected host will receive the pathogen as well, and continue the cycle. Although it has been known for 40 years that ticks carry the disease, the specific organism responsible for causing EBA was largely unknown until recently. "The EBA pathogen is relatively susceptible and can be treated with antibiotics," said Michael Teglas, assistant professor in the Department of Animal Biotechnology.

"However, most of these cattle are turned out on the range where it is difficult for ranchers to administer treatment." In response to this dilemma, researchers at UNR have initiated several projects to uncover more about EBA, with support from the California and Nevada Cattlemen's Association.

The first of these projects was to establish the correlation between EBA outbreaks and tick-infested regions. To determine whether or not ticks were the culprits, researchers devised a series of "tick traps" to determine if tick populations were present in certain regions of Nevada. Ticks are naturally attracted to carbon dioxide, which is expired by all mammals. Using dry ice as bait (which emits carbon dioxide), researchers were able to record tick populations throughout Nevada.

This research concluded that cases of EBA were limited to regions with a presence of Ornithodoros coriaceus. The second phase of research deals with analyzing immunity and developing strategies towards preventing EBA from occurring. A curious aspect about infected cattle is that they develop a short-term immunity to the disease following an abortion. Using mice as a surrogate host, researchers were able to use the bacteria grown in them to infect a test group of cattle with EBA, and study the effects more closely.

"For a long time the method of transferring EBA to cattle was to collect about 100 ticks and try to put them on test cattle," Teglas said. "Using mice we were able to really improve the effectiveness of our studies." Through these studies, researchers were able to determine the length of time the pathogen lived within the host's bloodstream. In doing so, they gained insight into how long cattle would have temporary immunity to EBA, as well as to the time period in which EBA could be transferred to other ticks.

Additionally, by studying the blood of infected cattle, researchers were able to identify the pathogen itself. "It's taken us a very long time to figure out what this organism is," Teglas said. "At first it was thought to be a virus, or a form of bacteria. In 2005 UC Davis researchers discovered it was a slow-growing intercellular bacteria." Utilizing this knowledge, researchers have developed an experimental vaccine to inoculate against the disease.

While still being tested, the vaccine has been successful in protecting heifers exposed to EBA. "The vaccine is still in the testing phase, but so far we have had no EBA abortions in treated heifers," Teglas said. "We are still testing to make sure there are no adverse effects. It's our policy at UNR to develop treatments that are safe for livestock." According to CABNR, results from this project have already been disseminated to cattle producers through educational programs such as the annual Nevada Cattlemen's Update and University of Nevada Cooperative Extension.