Drought increases rabies outbreaks

Aug 19, 2011

Reports of rabid animals are on the increase in Texas this year. By mid August, 51 positive rabid animals, approximately 82 percent skunks, had been reported in the Panhandle and south Plains surpassing the number of cases reported in 2010 in the same area. With activity on the rise, Dr. James Alexander, regional zoonosis control veterinarian for the Texas Department of State Health Services, recently spoke to veterinarians and animal control officials about the region’s rabies situation at a meeting held in Lubbock, TX.

"The drought has definitely increased the occurrence we are seeing of rabid animals. When water becomes scarce, wildlife will migrate toward human activity where there’s always plenty of food and water," explained Alexander. "Wildlife exposure to communities has increased with urbanization. Often, people may live on the edge of a city or on small properties of about two or three acres. Folks will leave food out for their pets in these suburbs and small towns, basically creating a ‘skunk convention’ as they and other animals come searching for the food they’ve found readily available."

"Our records show that increases of rabid animals typically follow a five- to seven-year cycle. As the number of rabid animals increases, more of the reservoir population is exposed to rabies, which eventually results in a major die-off. When that happens, the decreased population means fewer animal will congregate to spread the disease until the population builds back up after a few years. In our region, the primary vector of rabies is the skunk. The next most common species affected by rabies this year in our region are cats and horses. For the first time since before 1996, there have been four confirmed rabid horses in Region 1.

Feral cats have become a significant issue as far as human exposure to rabies this year. Four rabid cats have been confirmed and all four were feral in origin. Three of those cats exposed a total of five humans. Feral cats serve as an excellent ‘bridge’ to transmit rabies between skunks and humans. Feral cat colonies, including barn cats, should be vaccinated and neutered or eliminated, especially when rabies is active in an area. As a result of the increasing numbers of feral cats, that species has surpassed dogs as the most common non-wildlife species affected by spillover from the skunk reservoir statewide. Cats and raccoons are currently tied at 22 confirmed cases while there have been only seven cases of rabies confirmed in dogs across Texas this year.

Alexander’s review of the disease helped explain the fundamentals behind the protocol for management of human or animal exposure to rabies. "Rabies lives in the central nervous system and its associated fluids, but it is found mainly in the saliva. People need to be aware of this when handling tissues. However, it is not in the blood. The virus enters the body when saliva gets through the skin, primarily by bites into the muscle where the virus replicates for several days. Other possible routes of entry include saliva contact with a fresh cut or abrasion or by contact with mucous membranes of the eyes, nose or mouth.

Once it’s in the body, it then spreads to the central nervous system along the nerve tracts, ultimately reaching the brain. Once the virus reaches the brain, it then migrates to the salivary glands where it is ready to be spread to another victim. The time between the appearance of the virus in the saliva and the development of symptoms is less than 10 days. That’s the reasoning for the 10-day quarantine period for rabies suspects when a bite occurs from a dog, cat or domestic ferret," explained Alexander. "A rabid animal may not be symptomatic when it bites or otherwise exposes someone to saliva, but clinical signs of the disease will appear within the 10-day quarantine if that animal is infected with rabies. Wildlife involved in bites need to have their brains submitted for rabies testing when possible."

"Generally, the closer the bite is to the brain, the quicker the development of the neurologic disease. Livestock may have longer incubation periods if they are bitten on the leg and the virus has farther to travel to reach the central nervous system. It can take three weeks or longer in some cases but that time frame can be difficult to ascertain because, oftentimes, livestock exposure goes unseen."

Alexander’s district encompasses many rural communities. He described behaviors that can be associated with rabies in livestock, especially considering that many symptoms mimic other diseases. Mammals infected with rabies can demonstrate altered behavior ranging from extreme, unprovoked vicious attacks, self mutilation and abnormal libido, to roaming or isolation from a herd.%u3000They may conversely exhibit depression, paralysis and excessive salivation from inability to swallow.

Historically, the disease was called ‘hydrophobia,’ fear of water, but that appears to occur only in humans due to paralysis of throat muscles, creating a choking sensation if drinking is attempted. This is generally not seen in animals, which often will try to drink but can’t.

The disease has been described as being either ‘furious rabies,’ where the affected animal or person acts in an aggressive or agitated fashion, or ‘dumb rabies,’ where mild symptoms can imitate other diseases and syndromes.

"In cattle, we tend to see both types. Rabid cattle will charge people, horses, other cattle or inanimate objects such as a barn door. ‘Dumb rabies’ signs can be vague, appearing like other syndromes. When rabid cattle can’t swallow, they salivate profusely, standing with their necks outstretched. The temptation when you see a cow that has difficulty swallowing is to stick your arm in her mouth to see if she has a stick or a bone lodged in her throat . . . Or check for woody tongue. Those would certainly be the common problems associated with those symptoms," said Alexander. "Cattle may vocalize with a characteristic bellow. Other signs seen include straining with their heads down, weakness, wobbliness and decreased milk production."

"We tend to see more of the ‘dumb form’ of rabies in horses, which includes excessive salivation and difficulties chewing and swallowing," Alexander stated. "These symptoms can occur with many equine disease syndromes. Although horses can’t vomit, they may appear to be regurgitating or choking. Human exposure happens when someone examines the mouth of a horse which appears to be having problems eating, drinking or salivating excessively. They might make unusual sounds described as howling or barking."

Alexander added that rabid horses may be found agitated, restless, uncoordinated, head pressing or stargazing. They can appear colicky, stretch out, paw, get up and down repeatedly or kick at their belly.

Extreme abnormal behavior changes seen in horses include charging and viciously biting at whatever and whomever they are attacking. Horses’ unprovoked aggression can be directed toward non-living objects. They’ll demonstrate self mutilation by biting at themselves or exhibit the classic ‘fly biting’ syndrome commonly seen in rabid dogs appearing to snap at flies—but there are no flies present.

%u3000"We don’t see many cases of rabid sheep or goats; however, that may reflect the lack of access to observe range animals. The aggressive ones are usually the ones that get noticed," said Alexander. "They can demonstrate the same neurologic issues seen with other livestock, such as increased libido, fixed stares and salivation. Sheep will pull their wool out obsessively, creating sores."

Rabies in pigs is uncommon and Alexander reasons that the thickness of their hide plus their fat layer prevent the rabies virus from penetrating into the muscle where it can multiply. Rabid pigs will sometimes eat their young.

As with their livestock counterparts, rabid cats and dogs exhibit either behavioral or systemic signs of rabies. In regards to the increasing feral cat population, Alexander depicted scenarios that he receives reports on frequently.

"People will describe a frightened or aloof barn cat that suddenly becomes friendly. Then these cats become exceedingly aggressive, sometimes charging anything or anybody around the barn," illustrated Alexander.%u3000

"Another situation we get reports on is the rabid skunk that shows up with a kitten or puppy in its mouth. Unfortunately some folks try to rescue that kitten or puppy by pulling it out of the skunk’s mouth, resulting in their exposure to the virus. Often, part of a litter survives a skunk attack and a person will decide to nurse them back to health, only to be exposed to rabies a few weeks later when the animal becomes rabid."

Considering that rabies can look like other diseases, Alexander emphasized that veterinarians are challenged when diagnosing these animals. History of exposure or bite from wild or unvaccinated animals can be key.

Texas allows vaccination of livestock and horses by owners and producers. However, the length of quarantine or post-exposure management may be altered when vaccines are not administered by veterinarians.

Alexander’s district has reported four positive cases of rabies in horses so far this year, surpassing previous records. He anticipates there will be more. Approximately half of reported rabid animals have exposed other animals. Approximately one-fourth of reported rapid animals have exposed humans. In light of the increased number of rabid horses, Alexander recommends that animals at risk be vaccinated against rabies, for their protection as well as their owners.

"Horses live in the same place as skunks, so they are at risk of becoming infected with the virus. Since the value of horses has dropped, some people may think it isn’t worth the cost of getting a vaccination. But they need to be aware that the cost of handling and disposal of a dead horse far exceeds the price of a vaccine. I recommend to people to get their horses, show stock, high-dollar breeding stock and dogs and cats vaccinated against rabies," Alexander emphasized.

Regardless of species, rabies is always fatal. Local animal control, veterinarians and public health officials should be contacted with questions or concerns about animals showing potential signs of rabies. — Ginger Elliott, WLJ Correspondent