The Rabies Risk

Vaccination strategies for livestock to keep producers, veterinarians safe

When cattle are exposed to rabies, there’s typically a small economic price compared to, for example, the millions of dollars bovine respiratory disease (BRD) costs the industry each year. However, infected cattle can infect producers, veterinarians and any other humans in direct contact. The disease is almost always fatal for people, and rabies treatment is expensive and painful.

“Rabies usually shows up as single incidents,” says Gregg A. Hanzlicek, DVM, Ph.D., director of production animal field investigations for the veterinary diagnostic laboratory at Kansas State University. “However, the No. 1 domestic species found to be rabid in Kansas for the past two years is the bovine. Typically, we thought of cats as being the top domestic species, but cattle are significantly exposed to the disease.”

In 2015, Kansas confirmed 13 bovine cases, and nine in the previous year.

Livestock risk

Rabies is typically transmitted through reservoir animals, or those wild animals that contract the virus and interact with livestock, like skunks. The disease is transferred through saliva – typically through a bite – but can occur when saliva from an infected animal enters an open wound or mucus membrane like the eyes, gums or lips. Those species then will show the clinical signs of rabies.

“Cattle are curious,” Hanzlicek says. “They’re likely to approach a skunk if it gets in a pen with a herd of cattle.”

The disease can infect all domestic animals such as dogs, cats, horses and cattle. The time between infection and the onset of clinical signs varies, he added. It can range from as early as a few weeks to as late as a few months after infection.

Many animals will start to carry the virus in their saliva before they start to show clinical signs. The rabies virus is different than most other viruses, because it does not enter the bloodstream. Rather, the rabies virus travels through the nerves from the point of infection, Hanzlicek says.

If an animal is bitten on the nose – as it is believed most cattle are – it will start showing clinical signs earlier than an animal bitten on the back leg. This is because the virus has less distance to travel to the brain. This accounts for the time variation between being infected and showing clinical signs, he notes.

Once rabies is in the brain, it gets into the salivary glands. Then every time that animal bites another animal or human, it is going to spread the virus to those individuals. Toward the end of the disease, scientists believe all organs with nerves are infected with the virus. Therefore, an animal thought to be rabid should not be salvaged, Hanzlicek says.

Signs of rabies

There are two forms of rabies, furious form and dumb form. The furious form is the classic rabid animal that attacks objects, other cattle and even humans. Cattle are more likely to exhibit the dumb form, which is characterized by quiet behavior. All animals are thought to go through both forms before death although both types of behaviors may not be noticed.

“Any time there is a change in behavior, either more aggressive or more somber, consider rabies,” Hanzlicek says. “A lot of times cattle will vocalize frequently, some will try to urinate multiple times, others will act like it’s a limb lameness.”

Often when producers see abnormal salivation or trouble swallowing, they think something is stuck at the back of the throat, he says. This can lead to human exposure to rabies, because producers will reach into the mouth of the cow or the calf to see if there is some object present. While they are doing so, they are exposed to the saliva that contains the rabies virus.

Other possible signs include anorexia or head pressing.

2014 Domestic Rabies Cases

Diagnosis

There is no treatment for rabies. Once an animal shows clinical signs, typically within four to five days that animal will get progressively worse and die.

If rabies is suspected, Hanzlicek recommends taking a cell phone video of the animal and sending it to the local veterinarian. Veterinarians can determine if a case is suspected and are trained to protect themselves from infection.

Also, most veterinarians are vaccinated for rabies. They know what precautions to take to avoid contamination when examining the suspected rabid animal, he notes. The only way to definitively diagnose rabies is in a deceased animal, where a specific portion of the brain is required for testing. Veterinarians are trained to sample the appropriate portion of the brain for a diagnosis.

Rabies can mimic other neurological problems, such as brain abscess or trauma, says Andy Bennett, DVM, with the Veterinary Professional Services Team at Merial, Inc. Veterinarians are prepared to handle themselves carefully and are typically vaccinated in case of a positive rabies case.

Prevention

As dangerous as rabies can be, the good news is that there are vaccines almost 100 percent efficacious, which is rare for vaccines, Bennett says.

“Vaccination is an easy and economical way to prevent disease,” Bennett says. “With high cattle prices, the economic loss can be significant, but the real concern is human safety.”

Rabies vaccines labeled for livestock require an annual vaccination. For dogs and cats, rabies vaccines have an extended duration of immunity. However, the research has not been performed in livestock, he says.

The cost of adding another vaccination is a factor when considering protocols, Bennett notes. He recommends valuable animals that are in close contact with humans be vaccinated, such as: purebred animals, bulls, dairy cows and high-value beef heifers or cows used for embryo transfer.

“In these animals, you’re protecting the genetic potential and dollar investment – not to mention the people that handle these animals on a regular basis,” he says. “If you’re having a rabies outbreak in your area, you might consider vaccinating a larger group of animals.”

In addition, Bennett strongly recommends vaccinating show animals that will be around children.

“I’ve had kids that participated in the county livestock fair, and the question has come up: Should we mandate that these livestock, these show animals, be vaccinated for rabies? We’re protecting animals but also protecting our families,” he notes.

¹ Monroe B, et al. Rabies surveillance in the United States during 2014. JAVMA(248);7:777-788.