Quick Summary
- Bacterium causing foothill abortion disease named after tick that carries it
- Without harming the cow, bacteria cause fatal immune response in the fetus
- Collaboration with ranchers leads to successful cattle vaccine trials
After more than 50 years of research, the tick-borne bacterium responsible for one of the most troubling and economically devastating cattle diseases in the Western United States has been named and genetically characterized by researchers at the University of California, Davis.
鈥淭his is a most unusual bug, a 鈥楻ipley鈥檚 Believe It or Not鈥 bacterium, and the tick that carries it is equally bizarre,鈥 said veterinary immunologist Jeffrey Stott, who has led the effort to develop a preventive vaccine for the malady that western ranchers know all too well as 鈥渇oothill abortion disease.鈥
Using an electron microscope, Stott and colleagues physically examined the bacterium in tissue sections taken during postmortem exams of aborted calves. They then characterized it by partially sequencing three of its genes and named it 鈥Pajaroellobacter abortibovis,鈥 recognizing the Pajaroello tick that carries the bacterium as well as its abortion-inducing impact on infected cows and their fetuses.
The findings of this study are reported in the Aug. 30 issue of the journal Veterinary Microbiology, .
The disease, which occurs in California鈥檚 coastal mountains and the foothill regions of California, Southern Oregon and Northern Nevada, annually results in the death of an estimated 45,000 to 90,000 unborn calves.
Vaccine trials to prevent the disease are now in the second year, thanks to a longtime partnership between 新澳门六合彩内幕信息 Davis, the University of Nevada, Reno, and the California Cattlemen鈥檚 Association. During the first year, some 9,000 heifers throughout California were inoculated with the live vaccine several months before they become pregnant.
Ranchers鈥 foothill nemesis
Ranchers in California and neighboring states have struggled with foothill abortion disease at least as far back as the 1940s. While the disease seemed to have little impact on the health of the pregnant cows grazing in the foothills, it resulted in their calves being aborted, stillborn or born so weak that they soon died.
In the 1980s, 新澳门六合彩内幕信息 Davis School of Veterinary Medicine researchers found evidence that the infected cow fetuses were producing an immune response to an unidentified microbe. Between 2000 and 2010, Stott and colleagues identified the microbe as a member of the genus Myxococcus and developed techniques to grow the live bacteria in laboratory mice. Cells from such mice were eventually used to develop the vaccine.
Slow-growing bacteria resist culturing
鈥淭his bacterium is like no other animal pathogen ever described,鈥 Stott said. 鈥淚t probably replicates only once per day, which explains why we were unable to cultivate it using standard laboratory techniques.鈥
He noted that the bacterium also has a much smaller genome than the most closely related, characterized bacterium, indicating that Pajaroellobacter abortibovis has probably lost some of its genetic material as it evolved.
Not your everyday tick
The Pajaroello tick is as intriguing as the disease-causing bacteria it carries, Stott said. Unlike more common ticks that burrow their way into the skin of people and animals to feed, the Pajaroello is a soft-bodied tick and does not embed itself in its hosts.
Instead, the Pajaroello lives in the decomposing plant litter at the base of trees, shrubs and rocks, and is attracted to cattle by the carbon dioxide the animals give off. Only once every few months, the tick makes the effort to pierce the cow鈥檚 skin and feed on its blood for about 20 minutes.
Native peoples of the U.S. reportedly feared the bite of the Pajaroello more than the bite of rattlesnakes, believing that a second bite by the tick would be fatal to a person. Cows, on the other hand, can have a local response to tick bites but appear to have minimal systemic reaction.
鈥淚f the bacteria that cause foothill abortion are transmitted to cows by a tick bite or experimental injection, they don鈥檛 cause an inflammatory response 鈥 probably in part because the bacteria replicate so slowly,鈥 Stott said.
Unfortunately, cows鈥 developing fetuses are not so lucky.
Deadly to fetuses
鈥淚t turns out that once the bacteria get into the cow鈥檚 tissue, they travel to the cow鈥檚 uterus,鈥 Stott said. 鈥淚n cows and other ruminants, no antibodies are passed between the mother and the fetus, so the fetus is immunologically naive and thus very vulnerable.鈥
As the fetus matures, it begins to develop an immune system, eventually triggering an immunological response to the presence of the bacteria.
鈥淭he fetus essentially destroys itself and usually dies about four months after the cow is infected,鈥 Stott said.
By that time, the rancher has lost the productive use of the cow for the season as well as the potential market value of the calf, which might be as much as $2,000 in today鈥檚 market.
Provides model of maternal-fetal interaction
The current vaccine appears to be more than 95 percent effective in preventing the infection in pregnant cows and their fetuses and may provide lifetime immunity for the vaccinated cows.
鈥淔rom an efficacy standpoint this is the cr猫me de la cr猫me,鈥 Stott said.
He hopes that further studies of the bacteria鈥檚 disease-causing mechanisms will provide a valuable model for studying the biology of maternal-fetal interactions and for developing an even better, second-generation vaccine against foothill abortion disease.
Collaborators and funding
In addition to Stott, collaborators on the study included lead author Roxann S. Brooks, formerly in Stott鈥檚 laboratory and now at the U.S. Department of Homeland Security; as well as 新澳门六合彩内幕信息 Davis researchers Myra T. Blanchard, Kristin A. Clothier, Scott Fish and Mark L. Anderson.
Funding for the study was provided by the U.S. Department of Agriculture and the California Cattlemen鈥檚 Association. Pfizer Animal Health provided a scholarship, which in part supported Roxann Brooks鈥 D.V.M. and Ph.D. studies.
Media Resources
Jeffrey Stott, School of Veterinary Medicine, 530-752-2543, jlstott@ucdavis.edu
Pat Bailey, News and Media Relations, 530-219-9640, pjbailey@ucdavis.edu