Clinicians in the Veterinary Teaching Hospital at North Carolina State University’s College of Veterinary Medicine are advising cat owners and their veterinarians about an increase in a deadly tick-transmitted infectious disease that without proper treatment has a mortality rate close to 100%.
The disease, Cytauxzoonosis, is related to malaria and 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.
According to Dr. Adam Birkenheuer, assistant professor of internal medicine, 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.
“Between 1998 and 2004 we saw a series of 34 cases from North and South Carolina and Virginia that were diagnosed by the NC State Vector Borne Disease Diagnostic Laboratory here at the CVM 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 in the Veterinary Teaching Hospital.”
The disease seems to occur in “hotspots” with some households having several cats acquiring the infection. The majority of cases seen at the Veterinary Teaching Hospital (VTH) have come from Pittsboro, Southern Pines, and coastal North Carolina from Morehead City down to the Southport area. Pet owners and veterinarians should be aware that these are not the only affected areas and VTH cases have come from other parts of the Triangle including Wake Forest, Rolesville, and eastern Raleigh.
“There are a couple of reasons we believe we are seeing this increase in Cytauxzoonosis,” says 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.”
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.
Up until recently, most veterinarians have been taught that this disease is 100% fatal and that there is nothing that can be done. Recently in collaboration with the University of Missouri, NC State clinicians performed a clinical trial evaluating a new treatment. With this new treatment patients at the VTH have had survival rates approaching 85%. The results of the trial should be published soon. CVM researchers with the Center for Comparative Medicine and Translational Research and researchers at the University of Missouri have sequenced the parasite genome and hope to use this information to develop a vaccine and additional novel treatments.
“We are very excited about the results of the clinical trial, but this is still a very serious illness that often requires a week or more of hospitalization but after treatment these cats return to live a completely normal life,” says Dr. Birkenheuer. “In fact they seem immune to re-infection after recovery.”
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.
Fine-needle aspirate, spleen, cat, Cytauxzoonosis, Wright-Leishman stain. Large macrophage with innumerable Cytauxzoon felis merozoites.
Updated July 21, 2010