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Veterinary Forum April 2007 (Vol 24, No 4)

Expert describes cytauxzoonosis — an ounce of prevention best for this disease with no cure

by Marie Rosenthal

    LAS VEGAS — Cytauxzoonosis, a fatal feline disease, has spread across the South, Sharon Fooshee Grace, DVM, MS, MAg, DABVP, DACVIM, said here at the Western Veterinary Conference.

    "There have been a number of reports indicating that it is on the rise. However, it is not a reportable disease, so there are no hard numbers," she explained. "But there has been an increased recognition of this disease, and the geographic area that is seeing it is expanding."

    Cytauxzoonosis, a tick-borne disease, was first recognized in Missouri in 1973. "In the decade after it was identified in Missouri, it had spread into Arkansas, Oklahoma, Tennessee, Georgia, Ala­bama and Florida."

    Now the disease stretches across the South from the Atlantic Coast to Texas and as far North as Indiana, according to Grace, who is clinical professor in the department of clinical sciences, Mississippi State University College of Veterinary Medicine. "This is not a disease you need to let run its natural course because it is a difficult death.

    "This disease is of increasing concern to us because there is little we can do for the cat once it becomes infected. The best we can do is prevent it," she said.

    "My philosophy with this disease has been to make the diagnosis quickly and give the cat a humane end to its suffering because this is a terrible disease to witness," Grace explained.

    Cytauxzoonosis is caused by the protozoa, Cytauxzoon felis; domestic and wild cats can become infected, and the bobcat is the natural reservoir, she said. Although it is usually fatal in domestic cats, cytauxzoo­nosis is rarely fatal in the bobcat, which usually experiences a transient infection.

    The disease is transmitted by the bite of Dermacentor variabilis, the American dog tick. Despite the vector's name, dogs do not become infected, she said. As one would expect from a tick-borne disease, cytauxzoonosis is seasonal, according to Grace.

    "As soon as the ticks are active in late spring, I start to see cases. Although it is more common in outdoor cats, I would encourage you to put this on your differential list if you live in endemic areas. The first case I diagnosed was in an indoor-only cat," she said.

    There are two phases of the disease: a tissue phase followed by an erythrocyte phase. Because there is no diagnostic test and clinical signs mimic diseases caused by other organisms, such as Mycoplasma and Toxoplasma, cytauxzoonosis is difficult to diagnose early, Grace said.

    Clinical signs

    "How are you going to recognize this?" she asked. "One of the hallmarks that I use to recognize cytauxzoonosis is the presence of an extremely high fever. These cats are so hot they feel like they are on fire. They often will curl up in the cage, and as you stand in front of the cage, you can feel the heat emanating from their bodies."

    Cats suffer lethargy, anorexia and depression, followed in a few days by high fever, dehydration, pallor, lympha­den­opathy, splenomegaly and hepato­megaly. The parasite replicates rapidly within the phagocytes that line the lumen of blood vessels. During the eryth-r­ocyte phase, the cat develops a high fever, and venous blood flow is obstructed, causing vascular collapse and shock. At this point, the cells swell and rupture to release merozoites, which can be picked up on the blood smear.

    However, this pathologic confirmation does little to help change the course of the disease. Most cats die within 24 to 48 hours after the fever spikes. Just before death, the cat's temperature will plummet, she said.

    "One of the problems with this disease is that it is over so fast from the time of infection to death that the cat never has time to mount an immune response," she said. Cats are in such agony that they vocalize, and this vocalization is very distressing to hear. A few cats have survived, she added, but it is rare.

    All cats should receive supportive care, such as intravenous fluids to support tissue perfusion. Heparin may help control the procoagulant state. Sometimes antibiotics are given. Although not approved for use in cats, imidocarb dipropionate is often used. Imidocarb is an antiprotozoan that is approved for use in dogs with Babesia infection.

    "Reports are starting to appear in the literature about using imidocarb dipropionate, which is given as two injections, 3 to 7 days apart," Grace said. The cat should be pretreated with atropine.

    "Some cats have survived. We are not sure if they survived because they have some resistance to the organism, because there is a less virulent strain circulating or because of the drug," she admitted. There are reports that a less virulent form is emerging in Arkansas and Oklahoma — the cats that survived did not have as high a fever as other cats with the disease, she said.

    If the cat does survive, it has lifelong immunity to reinfection, she added.

    There had been an effort to develop a vaccine, but that was abandoned. Instead, experts recommend putting cats in endemic areas on tick prophylaxis.

    "The best thing that you can do is try to prevent this disease, so it is important to educate your client's accordingly. The cat is not going to get a second chance if it gets cytauxzoonosis," Grace said.

    For more information:

    Grace SF. Cytauxzoonosis as an emerging disease. Presented at: Western Veterinary Conference; Las Vegas; Feb. 18-22, 2007.

    Birkenheuer AJ, Le JA, Valenzisi AM, et al: Cytauxzoon felis infections in cats in the mid-Atlantic states: 34 cases (1998-2004). JAVMA 2006;228: 568-571.

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