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Researcher Seeks to Find Vaccine for Tick-Transmitted Disease Deadly to Cats

Dr. Adam Birkenheuer, an associate professor of internal medicine at the North Carolina State University College of Veterinary Medicine, is the recipient of a grant from the Morris Animal Foundation that supports his continued research into Cytauxzoonosis, a life-threatening disease of domestic cats that is similar to malaria in humans.

Fine-needle aspirate, spleen, cat, Cytauxzoonosis, Wright-Leishman stain. Large macrophage with innumerable Cytauxzoon felis merozoites.

Dr. Birkenheuer and Dr. Leah Cohn, professor of  internal medicine at the University of Missouri College of Veterinary Medicine, developed the drug combination that effectively treats Cytauxzoonosis, or “bobcat fever.” The drug therapy involves an antibiotic and an anti-protozoal drug that is similar to those used to treat malaria.

Cytauxzoonosis is caused by the parasite, Cytauxzoon felis, found in ticks carried by host bobcats. The most common symptoms of infection are lack of energy and appetite, usually accompanied by a profound fever. Some cats develop a yellow discoloration of the skin and the whites of the eyes.

Without treatment, 97 percent of cats with Cytauxzoonosis die. Newer treatments pioneered by NC State and the University of Missouri have improved survival rates to 60-85%.

According to Dr. Birkenheuer, C. felis was first discovered in Missouri in the mid-1970s and for years was only documented in the south central region of the U.S. Prior to the late 1990s the disease had never been reported in North Carolina. The geographic distribution of the parasite has spread rapidly since its discovery, and cytauxzoonosis has been diagnosed in 35 of the states in the continental United States. 

“Between 1998 and 2004 we saw a series of 34 cases from North and South Carolina and Virginia that were diagnosed by the Vector Borne Disease Diagnostic Laboratory at the NC State College of Veterinary Medicine and the State Animal Disease Diagnostic Laboratories,” says Dr. Birkenheuer. “We reported this surge in cases in the Journal of the American Veterinary Medical Association as we went from having never seen this deadly disease to times where we saw several cases a week. 

“There are a couple of reasons we believe we are seeing this increase in Cytauxzoonosis,” continues Dr. Birkenheuer. “One is the change in the distribution of the tick species that can transmit the infection to domestic cats. There are two species of ticks that can transmit the infection from bobcats to domestic cats, Dermacentor variabilis and Amblyomma americanum. Amblyomma americanum is a tick species that aggressively feeds on just about any mammal and has a geographic distribution that is rapidly expanding north and east. The other is that some cats survive the infection and can act as a reservoir leading to the infection of more cats.”

Dr. Birkenheue’s team has been deciphering the Cytauxzoon felis genome sequence and identified about 4,300 protein-coding genes, each of which represents a possible protective antigen.

The best protection against Cytauxzoonosis is to keep cats indoors and use a treatment that is approved to kill ticks on cats (some canine products can be toxic to cats). The use of anti-tick products alone may not guarantee the prevention of infection. A veterinarian should be consulted immediately if an owner detects any signs of the disease in the pet.

Testing for the disease is relatively simple and the veterinarian can usually make the diagnosis by examining a blood smear or performing a cytologic examination of infected tissues like lymph nodes, liver, or spleen. In some cases a DNA test can be used to confirm infection.

North Carolina veterinarians are expected to see more cases of Cytauxzoonosis as the weather warms and the tick season approaches. The  mild winter may mean an increased number of ticks early in the season. Veterinarians may contact Dr. Birkenheuer at if they have questions about diagnosing or treating a patient with cytauxzoonosis. 

The MAF-funded project will also help train at least two DVM/PhD graduate students who are preparing for careers in animal health.