COLUMBIA — Leah Cohn, professor of veterinary internal medicine, and Adam Birkenheuer, of North Carolina State University, have discovered a drug combination that effectively treats cytauxzoonosis, or "bobcat fever," a fatal tick-borne disease affecting domestic cats.
Cohn, who has been working on cytauxzoonosis for nearly a decade, and Birkenheuer based their new combination therapy on the knowledge that it had been used successfully in other species with protozoan diseases. The therapy consists of two drugs, an antibiotic and an anti-protozoal drug that is similar to those used to treat malaria.
"It is a commercially available drug, but it is very expensive because it is an anti-malaria drug," Cohn said. "A full liter bottle can cost up to $1,000, but it would treat a lot of cats."
In Cohn and Birkenheuer's study, 60 percent of infected cats survived with the treatment. Previously, the disease was treated with an anti-protozoal drug that was never investigated to determine its efficacy, Cohn said. Veterinarians also used intravenous fluids, pain-relievers, feeding tubes and blood transfusions to lessen the effects of the disease, but the survival rate was only 25 percent.
"The disease is just absolutely horrible," Cohn said. "Not only do they die and die quickly, but they die a horrible death."
The symptoms, which are vague in the early stage of infection, include lethargy and fever. However, the disease wreaks havoc internally. The protozoa affect macrophage cells, cells involved in immune system responses, causing them to expand and clog blood vessels, Cohn said. This constricts blood flow and leads to organ failure. The parasite can also change form and enter different cells, such as red blood cells.
Cytauxzoonosis, a seasonal disease, is most common in the south-central United States. It is also especially prevalent in Springfield, where three cases a week are not uncommon from April to September, when the weather is most conducive to the ticks that spread it from bobcats to house cats.
Ellen Ratcliff, veterinarian at the Fair Grove Veterinary Service, located 14 miles north of Springfield, has been dealing with cytauxzoonosis since she graduated from veterinary school 11 years ago. Ratcliff assisted Cohn and Birkenheuer with their research by using their treatment and recording the results, allowing them to see how the treatment worked in practice.
“When I first got out of veterinary school, pretty much every cat I saw (with the disease) died,” Ratcliff said. “Last year, I think we treated 25 cats, and the majority of them went home.”
There is no way to track the disease, Cohn said. It doesn’t affect humans or food animals, and it is only transmitted by ticks or blood transfusions.
“I tell people all the time that the only way to really prevent this is to keep the cats inside,” Ratcliff said. “The odds of inside cats getting ticks are very, very slim.”
During the next year, Cohn plans to look at more potential therapies for cytauxzoonosis to see if they will be effective in treating the disease.
“Sixty percent of cats survive, but that means 40 percent die,” Cohn said.
Zac March, director of eLearning for the University of Missouri System, lost two cats to the disease last year.
"We had one of our cats, one that pretty much rarely went outside, come down with very lethargic symptoms," March said. "The next day was even worse. On the third day, we took her to the veterinary school, and that's when Dr. Cohn diagnosed her with this disease and said that the prognosis wasn't good."
Cohn treated the cat, Jolene, but they just missed the window, March said. A month later, their other indoor cat, Ivan, started showing the same symptoms.
"We went through extreme measures to try to save him, but we lost him in five days," March said. "It seemed very unreal to my wife and I."
Despite the tragedy of losing two cats in such a short time span to a seemingly rare disease, March has a positive attitude regarding Cohn's work.
"It's very encouraging to know that Dr. Cohn is on the verge of having good treatment for cats," March said. "It's very promising for cat owners."