This mysterious cause of abortion in cattle was first recognized in foothill regions of coastal and central California, but also occurs in southern Oregon, parts of Nevada and Arizona. 

The pathogen causing death of the fetus is transmitted by bites of a soft-bodied tick (Ornithodoros coriaceus) that inhabits these regions. Jeff Stott, a professor in the University of California, Davis’ School of Veterinary Medicine, has spent more than 40 years studying this disease and the ticks that cause it.

The tick that transmits this disease is different from ticks on dogs, horses or cattle.  It lives in arid regions, burrowing into the ground where deer or cattle bed. If the tick hasn’t taken a blood meal for a month or so, it crawls out of the ground, locates an animal lying there, and attaches briefly to engorge with blood.

Ticks need 30 minutes

Unlike hard-bodied ticks that stay on the host for days or weeks, these ticks only need 30 minutes of attachment to fill with blood. Then they drop off the animal and burrow back into the ground.

“The tick was identified as the vector in the 1980’s but it wasn’t until 20 years ago that we finally identified the oddball bacteria causing abortion, recently named Pajaroellobacter abortibovis,” says Stott.

“It lives in these ticks and replicates maybe once every few days, whereas most bacteria multiply rapidly, so this one is difficult to culture. The only known naturally-susceptible animal is a bovine fetus that does not yet have an immune system.  If we intentionally infect a pregnant heifer, about the earliest we see an abortion is about 100 days later. Cattle abort about 3 to 5 months after being bitten by the tick,” he explains.

Some ranchers in tick-infested regions reduced abortions by changing breeding season to avoid overlapping the susceptible gestation period with tick exposure, or only using tick-infested pastures after cows were past 6 months pregnant. 

Exposed animals usually have immunity for several years, so some ranchers exposed their yearling heifers to tick-infested pastures before breeding, to develop immunity before they were bred. The alternate approach was to delay exposure of pregnant heifers until the last months of gestation. A better solution would be a vaccine to provide the needed immunity.

Stott worked with ranchers in California, Oregon and Nevada, and in collaboration with University of Nevada, Reno. 

“We also received inquiries from people outside these regions who wanted to vaccinate heifers so they could bring cattle into these areas as immune before breeding or as immune pregnant cows or heifers. That market had been thwarted by foothill abortion because if anyone brings a naïve herd into these regions the cattle abort -- not at a rate of 20 to 50% like resident animals, but upwards of 85%,” he explains.

Vaccine developed

After nearly 10 years of developing and testing a vaccine to prevent this abortion-causing infection, researchers found a company to make and market it. Many companies were initially interested until they realized it would just be a regional market.

The vaccine was eventually granted a conditional license by USDA, and became commercially available in September, 2020 from Hygieia Biological Laboratories of Woodland, Calif.

Jenna Chandler, Hygieia’s product manager for this vaccine, previously worked with the researchers who developed and tested it. She tells producers that if they aren’t sure whether they’d benefit from use of this vaccine or might have questions about it, they should contact their local veterinarian. This vaccine must be sent to and administered by a veterinarian; it is a live vaccine that must be kept frozen in liquid nitrogen.

“Producers can order the vaccine directly from Hygieia,” she says. “They tell us how many doses they want, when they need it, and who their veterinarian is. We deliver the vaccine by courier, to their veterinarian,” she explains. Producers should order it well ahead of when they plan to use it; the courier has a circuit for delivery to veterinarians, so if the courier was in your area last week it may be a month or so before he is out there again.

“The foothill vaccine can be given at the same time as routine vaccines for replacement heifers, but on the opposite side of the neck, to prevent any interactions.  Generally it is given at the same time as Bangs vaccination, since a veterinarian is already on the farm to administer that one,” she says. This is a good age to vaccinate heifers, since the foothill vaccine must be given well ahead of breeding.

“This is a very potent vaccine and we advise that it not be handled by women who are pregnant or might become pregnant. The vaccine is to be given only to weaned heifers 6 months of age and older, and not currently pregnant. It must be given at least 60 days before breeding,” she says. The animal needs to build immunity. If given too soon before breeding, the vaccine bacteria can affect the developing embryo--and the fetus would be aborted a few months later.

Eventually this vaccine will become important for more producers than just ranchers in regions inhabited by the tick. 

“Producers and purebred breeders who may not be affected in their own state may want to ship cattle to affected areas,” says Chandler. “We’ve had calls from people telling us they are getting a load of heifers from Colorado or South Dakota or some other state.  Those heifers would be completely naïve with no immunity, and vulnerable to infection.  Unless they are vaccinated before being bred, this would be a disaster,” 

Will open markets

This vaccine will open up more markets for breeders in other states, with opportunity to sell heifers to ranchers in regions that have this disease.

“There are also some ranchers who can’t run cattle on certain leases or pastures in tick areas without huge losses,” she says. “The vaccine will open up new areas for grazing, because now there’s a way to manage this problem in their herds.”

One question producers ask is if vaccine vials come in any other size than the 30-dose vials currently in use. “That vial costs $800 (about $26 per dose), and needs to be used all at once, within 4 hours of opening, so the company is considering doing some smaller vial sizes,” she says. A producer might only have 20 heifers to vaccinate, or 50, so a 30-dose vial doesn’t come out evenly. 

Some people ask if animals would have adverse effects from vaccination if they’ve already been exposed to the infection, but there are none. In nature the animal would be bitten every now and then by a tick, and repeatedly exposed—simply getting another “booster” in immunity. Because of this situation, the vaccine only needs to be given once, to heifers, to make sure they have immunity before becoming pregnant. 

“The UC Davis studies have shown that vaccine immunity lasts about 3 years,” she says. “If you are vaccinating that animal, it is obviously because she is in foothill country or being sent to foothill country, and she will continue to have natural exposure to the bacteria through tick bites, which act as a booster.”

The exception might be in fringe areas where tick exposure is low or sporadic.  Occasionally you a cow might not get natural exposure for a few years and no longer has much immunity.

Field trials show that you can vaccinate adult cows (not just heifers) if they are vaccinated when open, at least 60 days prior to their next breeding. This would be recommended if a person is bringing adult cows into a tick-infested area, or where cows might need to be periodically boostered in a fringe area with sporadic tick exposure.

[Heather Smith Thomas is a freelance writer based in Salmon, Idaho.]