Cytauxzoonosis in Cats
THIS CONDITION IS CONSIDERED UNIFORMLY FATAL IN DOMESTIC CATS
What is Cytauxzoon Felis?
Cytauxzoon (pronounced “sight-oz-o-un”) felis is a blood parasite first recognized in Africa as a parasite of antelopes and other ruminants. It was then recognized in the U.S. in 1976, not as a livestock infection but as a feline one, affecting and killing cats from forested areas. Initially there was concern that livestock were soon to be next as this was a ruminant infection as far as anyone knew but research showed only cats could be infected. It appears that in the U.S. the natural host of this infection is the bobcat, where most of the time the infection is minor, and it is only the domestic cat for whom infection is a disaster.
Cytauxzoon felis is a single-celled organism that infects both the blood and tissues of a cat. The blood parasite stage is called a piroplasm and it is fairly easy to recognize when a blood sample is examined under a microscope. This phase of the parasite’s life cycle is not particularly harmful; it is the tissue stage, called a schizont, which causes the trouble. The cat’s immune system recognizes it as an invader and launches a massive attack. Cells called macrophages consume schizonts in large numbers to destroy them but there are so many macrophages swollen with consumed schizonts that they plug blood vessels and cause death approximately 3 weeks from the time of infection.
How do Cats get this Infection?
Cytauxzoon felis is spread by tick bites. The tick usually implicated is the American Dog Tick (Dermacentor variabilis). Bobcats carry the Cytauxzoon piroplasms in their blood, ticks feed on the bobcats, and then drop off and molt to their next life stage. They are still carrying the Cytauxzoon piroplasm when they attach onto their next host, and if that next host is a domestic cat a lethal infection results.
CATS CANNOT BE INFECTED WITHOUT A TICK BITE.
How is Diagnosis Made?
The cat typically has a fever, with or without jaundice, and is brought to the veterinarian for evaluation. In most cases the piroplasms are fairly obvious when the blood sample is evaluated. Because the tissue phase of the infection with the schizonts comes first and the blood infection with piroplasms comes after, it is possible that at the time the blood is tested no piroplasms are yet present. Because of the rapid progression of the infection, piroplasms will likely be seen in a few days if they are not at first so sometimes a second blood evaluation is needed.
Because piroplasms sometimes have variable sizes, they are sometimes mistaken for Mycoplasma hemofelis, a much more treatable infection.
Cytauxzoon organisms are larger and have a thick “dot” on their ring-shape.
If diagnosis is to be made post-mortem (after death), it is usually easy to find the schizonts in many body tissues.
Is There any Treatment at all?
In one study diminazine aceturate treatment was able to save several cats. Another study has reported success in one cat using imidocarb diproprionate. Cats must be hospitalized and their blood anti-coagulated so as to prevent inappropriate clotting and vessel clogging with schizont-laden macrophages.
A milder strain of Cytauxzoon felis seems to have emerged in west Arkansas and east Oklahoma where a number of cats have survived without treatment (as do most bobcats). These cats continue to have piroplasms in their blood but seem to have no effect from this.
The most effective prevention is to keep the cat indoors where there is no tick exposure. The next best prevention is to use a tick control product; speak to your veterinarian about what is best for your cat. It is important to realize that most canine tick products are toxic to cats and cannot be safely used.
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