Rabies – in cattle?A K-State veterinarian discusses how common the viral disease can be in the cow herd.
December 31, 2015
When rabies is mentioned, it often conjures classic images from movies of an infected animal running rabid. While this viral disease seems far from concern, particularly in domestic animals, recent events suggest it is a bigger problem than traditionally thought.
The most commonly diagnosed domestic carrier of rabies in the Midwest is cats; however, in Kansas, there has been a recent increase in cattle confirmed with rabies.
"In Kansas the past two years, cattle have been the most common domestic species we've diagnosed with rabies," said Gregg Hanzlicek, director of production animal field investigations for the veterinary diagnostic laboratory at Kansas State University. "This year, we have 13 confirmed bovine cases. Last year there were nine."
Hanzlicek said that in the state, the skunk is the most likely carrier that spreads the disease to domestic animals such as dogs, cats, horses and cattle. Those species then will show the clinical signs of rabies.
“Once the rabies is in the brain, it will get 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, we believe all of the organs that have nerves are basically infected with the virus. Therefore, an animal thought to be rabid should not be salvaged.” Gregg Hanzlicek, director of production animal field investigations for the veterinary diagnostic laboratory at Kansas State University
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For producers who are interested in where rabies has been located in Kansas, the veterinary diagnostic laboratory's website, http://www.ksvdl.org, has a tab called "Disease Trends" that showcases the number of recent rabies cases, by species within each county.
"Producers can use that map to see the specific cases of different diseases throughout the state," Hanzlicek explained. "It is updated every Monday morning, and it shows in the state, county-by-county, what species and the number of that species have been confirmed with several important diseases including rabies."
How infection occurs
The rabies virus is spread through the saliva of a positive animal, Hanzlicek said. Being bitten by a positive animal is the primary way the virus is spread. However, other methods of spreading the disease are saliva from a positive animal getting into an open wound, or saliva from a positive animal getting into a mucus membrane—the eyes, gums or lips—of another animal or human.
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," Hanzlicek said, adding that 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.
"Lets say an animal is bitten on its back leg," Hanzlicek said. "Rabies will travel through the nerves of the back leg to the spinal cord, and then from the spinal cord, it will go to the brain. When it gets into the brain is when we start seeing the clinical signs."
He said an animal that is bitten on the nose, as it is believed most cattle are, 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.
"Once rabies is in the brain, it will get into the salivary glands," Hanzlicek said. "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, we believe all of the organs that have nerves are basically infected with the virus. Therefore, an animal thought to be rabid should not be salvaged."
Clinical signs of infection
Hanzlicek said that behavioral changes alone are not definitive for rabies. Other possible signs include anorexia, head pressing, bellowing (rabid cattle many times exhibit a unique vocalization), continually trying to defecate, unproductive defecation and unexplained rear-limb lameness.
"There are many different clinical signs, but we say if an owner sees one of his or her animals acting strangely, behavior wise, rabies has to be on the list to rule out," Hanzlicek said.
He noted that there are two forms of rabies, furious form and dumb form.
"The furious form is the form we remember from the movies, where the dog becomes rabid," Hanzlicek said. "The infected animal will attack inanimate objects, such as tractors, feed bunks and fences. They will also attack animate objects, including other animals and humans. We do see cattle with the furious form, but it is more rare than the dumb form."
"With the dumb form, they act like they are not aware of their surroundings. They are quiet. They stand off, and they may head press. Often, they will start drooling at the mouth and have difficulty swallowing, and they might become slightly bloated."
Often when producers see abnormal salivation or trouble swallowing, they think something is stuck at the back of the throat, Hanzlicek said. 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.
What to do when suspecting infection
Hanzlicek stressed that 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 I am a producer, and I see a behavioral change in one of my animals, I will put rabies on the list of possible causes and call a veterinarian," Hanzlicek said. "Veterinarians can help identify rabies, but also most veterinarians are vaccinated for rabies. They know what precautions to take to avoid contamination when examining the rabies suspect animal."
Therefore, let the veterinarian look into the mouth of a potentially infected animal; don't personally do those examinations. Unfortunately, the only way to definitively diagnose rabies is in a deceased animal, where a specific portion of the brain is required for testing, he said. Veterinarians are trained to sample the appropriate portion of the brain for a diagnosis.
There are effective rabies vaccinations available for humans, dogs, cats, horses and cattle. Hanzlicek recommends that producers who show cattle consider vaccinating those cattle for rabies. If those show animals contract rabies, there is more of a chance of exposure to humans.
"While it isn't always practical to vaccinate the whole cow herd, some herds in Kansas have started due to the number of skunks that are present in their area," he said. "However, there are certain states where rabies is more prevalent than in Kansas, and veterinarians in some states do recommend all cattle receive the rabies vaccine."
–K-State Research and Extension