Vaccine released for foothill abortion

After decades of research and trials, a vaccine preventing foothill abortion has been granted a conditional license by the USDA Center for Veterinary Biologics. The vaccine is being marketed by Hygieia Biological Laboratories of Woodland, CA.

Foothill abortion, formally named epizootic bovine abortion (EBA), is caused by a bacterium carried by the Pajaroella tick. The tick doesn’t embed itself on an animal like other ticks, but comes out of the soil when cattle bed down, feeds for 15-20 minutes, and then drops off.

Many Pajaroella ticks are infected with the bacteria, named Pajaroellobacter abortibovis after the tick and the bacterium’s abortion-causing impact. After feeding, the tick passes the bacteria onto the animal. The bacterium isn’t strong enough to impact adult animals with an immune system, which is why it only causes a fetus to abort.

Jenna Chandler, Hygieia EBA product manager, told WLJ this makes it difficult to diagnose foothill abortion in an animal, as an affected female doesn’t show any symptoms of sickness. But if she is pregnant, it takes about four months to cause mortality, depending on when she was infected.

The tick exists throughout “scrubby areas” like the Foothills of California, and throughout southern Oregon and western Nevada. The tick is unlikely to be found in irrigated pasture as it prefers dryer areas.

“They noticed as early as the 1920s that cattle pastured in these kind of scrubby Foothill areas were prone—first-calf heifers, usually—to abort their fetuses and they couldn’t figure out why,” Chandler said. “Now we know that it’s due to this bacteria spread by the tick.”

Chandler also noted the disease is often called the “disease of first-calf heifers” because once the heifer has been bitten, they develop an immune response and won’t experience an abortion again.

Ordering the vaccine

The vaccine has been granted conditional licensure by the USDA, not full licensure, but producers are still able to order the vaccine through Hygieia. The vaccine is only able to be administered by a veterinarian, so Hygieia will deliver the vaccine to a producer’s vet and not directly to the producer.

The current price for the vaccine is $800 for a vial of 30 doses. Chandler recommends giving Hygieia 30-60 days’ notice before the vaccine is needed, as it must be kept in liquid nitrogen and delivered by a courier.  

After vaccination, producers must wait at least 60 days to initiate breeding, as the vaccine is giving the animal the bacteria, and breeding too soon will cause an abortion. Current research shows the immunity from the vaccine lasts around two to three years, and the heifer should be boosted naturally by getting bit by the tick afterward.

The development process

The development process of the vaccine has stretched all the way back to the 1950s, to researchers at University of California (UC), Davis, School of Veterinary Medicine. The university has partnered with the University of Nevada, Reno, and later the California Cattlemen’s Association (CCA), to further expand understanding of the disease and develop trials. A decade of vaccine trials have been conducted to ensure the safety and efficacy of a vaccine.

Dr. Jeffrey Stott, lead researcher at the UC Davis Veterinary School, has worked on the development process since 1985. Stott told WLJ the disease was just “too complex for yesterday’s technology.” Although still unable to grow the bacteria in culture, researchers discovered it could be grown in immune-deficient mice.

The cells are harvested from the immune-deficient mice, and then frozen down to liquid nitrogen temperatures—the same approach you would use to cryopreserve embryos and semen, hence why the vaccine must be stored in liquid nitrogen, Stott said. A 2-cc dose is then given subcutaneously after diluting for a four-hour maximum.

Stott said around 100 ranches participated in producer trials for the vaccine, through the help of CCA. Ranchers would request a vaccination date and time, and then the UC Davis lab would make arrangements to go out and vaccinate their heifers. Around three to four hours after being vaccinated, ranchers would check to make sure there was no immediate type of systemic response to the vaccine.

Producers would then check the animals after the 90-day withholding period, typically when preg-checking. All the pregnancy data was collected and sent to USDA, as well as any animals that died or anything that happened to the animals in the 90 days.

Stott recalled one of the first five ranches involved in the trials typically lost 50-60 percent of their calves off their replacement heifers every year due to the disease. One of the difficulties of calving in the tick-plagued areas is it’s difficult to find aborted fetuses in the dry country, especially with scavenging wildlife around.

“People that spring calve bring them in in the fall, and all they know is they’ve got a bunch of open animals,” Stott said. “What do you do? You can’t afford to sell them, especially if they’re replacement heifers.

“You don’t know which ones are immune to foothill abortion and which ones are just not conceiving and should be marketed. It’s impossible to distinguish, so it pretty much means you have to carry your replacement heifers over for a second year, and hope they breed.”

Stott noted producers will often try to get their heifers exposed to the tick naturally before they breed, which may not be the most efficient use of property and permits. He also reiterated the importance of not vaccinating pregnant animals, or turning out to breed too soon after vaccination, as it will result in an abortion. — Anna Miller, WLJ editor