C. felis spreads without cure

Stillwater, Okla.-It's almost always fatal to domestic cats, and it's spreading.

Cytauxzoon felis, a tick-transmitted disease, has a very high fatality rate without a known cure. Officials say numbers of cases are increasing. This carrier tick species is D. variabilis.

Cytauxzoonosis is making its way north and is being seen with increasing frequency, reports A. Alan Kocan Ph.D., professor in the Department of Veterinary Pathobiology at Oklahoma State University's College of Veterinary Medicine.

Kocan explains, "We have known about it in the southeast and south central part of the country for a number of years. But the number of cases and frequency of cases is increasing fairly dramatically," he says. "It is apparently being recognized more readily now or probably spreading or a combination of the two into other areas. We are seeing it further north than we used to see it," he adds.

Cytauxzoon felis (C. felis) is a tick-transmitted disease. Once a cat is infected, it carries a very high fatality rate without a known cure. The only method of control is tick prevention.

This map outlines the distribution of Cytauxzoon felis in the United States. The most recent state to add to the list is Kansas.

"This is a little protozoan parasite that lives in red blood cells. It appears to be a natural parasite in wild cats like bobcats," he adds.

The increasing incidence of the disease probably has more to do with people choosing to live in more remote areas as anything else, he adds.

On the move

The disease was first described in Missouri in the '70s. It has since moved into Arkansas, Texas, Georgia, Mississippi, Florida and Louisiana. Most recently, Kansas has documented C. felis.

In North America, distribution of the disease is thought to correspond with that of the only known tick vector, Dermacentor variabilis.

The ticks feed on the bobcat, and when they attach to feed on a domestic cat, it "almost uniformly dies from the infection." Bobcats are deemed a free-ranging, long-term asymptomatic carrier of the organism.

Kocan says, "It is an extremely pathogenic organism in domestic cats. The difficulty with the disease is that we are seeing more of it and in more areas."

This pulmonary vessel is from a C. felis infected domestic cat (hemotoxylin and eosin stain, x 200).

Diagnosis on a live animal is also challenging. The problem is we don't have a vaccine or treatment. Even with diagnosis, there is nothing that can be done. That makes it a very difficult case for the veterinarian to manage.

"The parasite causes the cells to enlarge dramatically in size, and this occurs in all blood vessels over a short period of time," he explains. "Essentially what happens is that it occludes the blood vessels, so they can't transport oxygen. It is a kind of asphyxiation that occurs."

Clinical signs start showing up about 2.5 weeks after a tick infects its feline host. Kocan says that clinical signs initially include anorexia and depression, followed by high fever, pallor, icterus, splenomegaly and hepatomegaly. The cat will most likely succumb in four to six days following infection.

Kocan adds, the onset of the disease is so rapid, typically animals don't even have time to develop an immune response before death. This fact has hampered research for either a diagnostic test or vaccine.

Tough diagnosis

Diagnosing C. felis is tough for practitioners because there isn't a serologic test. Part of the problem posed to researchers in developing a test is due to the lack of immune response in infected animals because of the rapid progression of the disease. Most diagnostic tests are based on this immune response, so too are development of vaccines.

A practical way to diagnose C. felis is to take blood and stain it (Wright-Giemsa stained blood films or mononuclear phagocytes containing schizonts from blood films, impression smears or biopsy material).

The problem, Kocan says, is that it is a fairly new clinical entity for some areas, therefore, veterinarians have not had much experience diagnosing the disease. In addition, the disease is on the move, and most practitioners aren't aware it is even in their area.

"It is a relatively new parasite so practitioners who have been out of school more than 10 years, have probably never heard of it," Kocan says.

While universities have attempted aggressive therapies to save infected animals, including complete blood transfusions, no practical and viable treatment options have emerged.

Help on the way?

Research is under way to hopefully develop a diagnostic or vaccine, but research remains in early stages.

Kocan and his research team have received a Morris Animal Foundation two-year grant to study C. felis in greater detail. In fact, the team has identified a geographic area in Arkansas with a reservoir of cats that have survived without treatment. He is interested in finding out why those cats have developed a natural immunity to the disease. If that is determined, additional tests can be created.

"We are looking at exploring why there is a difference in the population of cats; and hopefully we can use that in some type of prevention control or immunization."