Foothill abortion vaccine awaits approval

May 25, 2012

With expenses and the cost of maintaining a ranch constantly on the rise, obtaining a calf from every mother cow becomes increasingly important to an operation’s bottom line. For decades, however, ranchers in the foothill regions surrounding California’s Sierra Nevada mountains have taken elevated abortion rates and reduced calf crops as a matter of course. These often devastating economic losses are the result of Epizootic Bovine Abortion, an abortive disease commonly known as foothill abortion. However, relief may be in sight for ranchers in the afflicted area. According to researchers at the University of California, Davis (UC Davis) School of Veterinary Medicine, a long awaited vaccine for the disease is completing the development phase, and USDA approval now represents the final hurdle before it can be made available.

Foothill abortion is a bacterial infection resulting from the bite of the Pajaroello (pa-ha-WAY-lo) tick, a soft shelled tick that makes its home in dry dirt around trees, brush and rocks. These areas are also favored as bedding areas by cattle and wildlife, providing the tick with ample opportunity to feed. Once infected, a cow exhibits no outward symptoms. However, without a functioning immune system, an unborn calf is a prime target for the as yet unnamed bacteria carried by the tick. Cattle that are infected between 30 and 200 days gestation will typically abort sometime during the third trimester. While some infected cows do carry their calves to full term, these calves are born very weak, and normally do not survive. Once gestation has reached 6.5 months, fetal calves have developed sufficient immunity to prevent the disease from taking hold, and are unaffected.

The disease has plagued California ranchers for decades, costing producers in that state $6.4 million annually. It is estimated that foothill abortion results in a 10-15 percent abortion rate in that state, resulting in the loss of 45,000-90,000 calves per year.

The disease was first observed by ranchers in the 1930s and ’40s, and the connection with the presence of Pajaroello ticks was established in the 1960s. Since that time, however, progress on a reliable means of combating the disease has been difficult. Unlike most biting ticks, which remain on cattle for an extended period of time, the Pajaroello tick feeds for only 10 or 20 minutes before dropping off. In addition to rendering insecticides virtually useless, this behavior also made scientific examination of the bacteria nearly impossible. It was not until the mid 1990s that biologists were able to successfully culture it in a laboratory. Following this discovery, however, work on the disease has progressed steadily. Led by UC Davis immunologist Jeff Stott, a team of researchers at UC Davis, as well as the University of Nevada in Reno, began closing in on a vaccine in 2007. According to UC Davis extension veterinarian John Maas, a workable solution may finally be at hand. “What we’ve got is a vaccine that appears to work very well,” says Maas. “The trials continue to look very good.”

The vaccine, says Maas, is a cultured version of the disease-causing bacteria, and is essentially an improvement on a management practice utilized by area ranchers for years. Researchers studying the disease observed that, once bitten, cattle developed an immunity to the pathogen that lasted one to three years. This immunity occurred whether the cow had actually aborted or not. Armed with this knowledge, afflicted ranchers have been able to reduce the severity of outbreaks by exposing their open cattle to tick infested areas, effectively inoculating those cattle that are successfully bitten prior to breeding. The new vaccine, which is cultured in mouse tissue, utilizes this same practice, but in a more uniform fashion. “This is more standardized, because you make sure that everyone gets ‘bit’” explains Maas. “Even in herds where they do a good job exposing their young animals before breeding, you still oftentimes get a 10-15 percent abortion rate. The problem is only about 5 to 15 percent of the ticks are infected; they’re not all carriers.”

The vaccine is currently undergoing USDA’s approval process, a step that Maas says may not have been necessary a few years ago. “We used to have a biologics division within the California Department of Food and Agriculture that would approve vaccines like this,” he explains. “If they were still around, we’d have had that by now.” When budget problems forced the closure of that division, approval was turned over to USDA, which has a lengthier process. “It’s hard to know,” says Maas, “but, hopefully, it’s just a year or two away. Maybe less, if everything goes well.” There are other loose ends that will need to be addressed as well. For example, the scope of the approval is not yet known. “We don’t know if this will be approved for just California, or for the entire region,” says Maas. “When you get outside of just a few states, you really don’t have [the disease].” Although it primarily affects the California foothills, foothill abortion also occurs with some regularity in Nevada and southeast Oregon, and has been observed as far east as the Jarbidge region in Idaho.

Spread by wildlife and livestock, the tick can potentially inhabit any arid environment with adequate cover. “This tick doesn’t make it in western Oregon or Washington,” says Maas. “It’s a dry environment tick.”

Once the vaccine is approved, a system of manufacture and distribution must also be developed. Due to the regional nature of the disease, Maas indicates that pharmaceutical companies have shown little interest in taking on the project. Compounding the issue, as a live bacteria, the vaccine must also be stored cold, either in dry ice or liquid nitrogen.

Finally, because the vaccine is made from the infectious bacteria, it can only be administered to open cattle. “If you give it to a pregnant animal between 30 days and 6.5 months gestation, she’s going to abort in 100 days,” says Maas. “So it’s going to be for open cattle.” Just as with the earlier management method, the period of time a cow will retain immunity is unknown. In previous discussions, Stott has indicated that this vaccine is intended as a ‘stop gap’ measure, and that work will continue towards a vaccine that works against the bacteria at the genetic level.

Stop gap or not, for many ranchers in California’s Sierra foothills, the vaccine represents a potential light at the end of the tunnel, and a workable solution for a disease that has plagued their operations for decades, say researchers. — Jason Campbell, WLJ Correspondent