Foothill abortion disease, also known as epizootic bovine abortion (EBA), leads to the loss of 45,000 to 90.000 calves each year in California, Southern Oregon and Northern Nevada, and after more than 50 years of research, scientists have gradually built a better understanding of the unusual biology of the disease pathogen and its vectors.
The pathogen, transmitted by the Pajaroello tick, typically does not cause disease in cows or heifers, but does affect the developing fetus in pregnant females, resulting in abortions or stillbirths.
The bacterium causing the disease has been uncommonly difficult to isolate, culture and characterize, in part because it reproduces very slowly, replicating only about once per day. University of California – Davis, only recently characterized the causative bacterium as Pajaroellobacter abortibovis, in the order Myxococcales, suborder Sorangiineae, family Polyangiaceae and most closely related to Sorangium cellulosum.
According to the researchers, modified Gram staining, combined with transmission electron microscopy, provide strong evidence that the bacterium is gram negative.
The UC-Davis research report, titled “Characterization of Pajaroellobacter abortibovis, the etiologic agent of epizootic bovine abortion,” recently was published in the journal Veterinary Microbiology.
The disease’s vector, the Pajaroello tick or Ornithodoros coriaceus, also is unusual in that it is a soft tick, which remains on its host for just a short time, biting it to feed on blood, then dropping off, in contrast with most ticks that embed into the host’s skin and remain there for days or weeks.
Better understanding of the disease pathogen has led to development of an experimental vaccine to protect against EBA. According to a news release from UC – Davis, vaccine trials to prevent the disease are now in the second year, thanks to a longtime partnership between UC Davis, the University of Nevada, Reno, and the California Cattlemen’s Association. During the first year, some 9,000 heifers throughout California were inoculated with the live vaccine several months before they become pregnant.
UC – Davis veterinary immunologist Jeffrey Stott says 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. “From an efficacy standpoint this is the crème de la crème,” Stott says. He adds that continued studies of the pathogen will improve understanding of maternal-fetal interactions and potentially result in development of a better, second-generation vaccine against foothill abortion disease.
Read more about foothill abortion disease from UC – Davis.