Cytauxzoonosis In the Cat

Cytauxzoonosis usa map

THIS CONDITION IS CONSIDERED UNIFORMLY FATAL IN THE DOMESTIC CAT

bobcat

American Bobcat

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

Feline red blood cells infected with Cytauxzoon felis. The organism is the dot seen inside some of the red blood cells.

Cytauxzoon felis is a single-celled organism that infects both the blood and tissues of the cat. The blood parasite stage is called a “piroplasm” and 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 actually plug blood vessels and cause death in approximately 3 weeks from the time of infection.

 

HOW DO CATS GET THIS INFECTION?

Cytauxzoon felis is spread by tick bites. The usually implicated tick 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.

American Dog Tick

American Dog Tick (Dermacentor variabilis)

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 present in a few days if they are not present 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.

Mycoplasma hemofelis infection

 

Cytauxzoon felis infection

Mycoplasma hemofelis infection

 

Cytauxzoon felis infection

If diagnosis is to be made post-mortem 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 in one study. 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.

PREVENTION

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 on the cat and there is one currently marketed: Frontline. It is important to realize that most canine tick products are toxic to cats and cannot be safely used.

 

Frontline Plus for cats

 

http://frontline.us.merial.com/home/

Page posted: 12/20/07
Page last updated: 3/20/2012