CYTAUXZOONOSIS IN THE CAT
HOW DO CATS GET THIS INFECTION?
Cytauxzoon felis is spread by tick bites. The usually implicated ticks are the American Dog Tick (Dermacentor variabilis) and the Lone Star Tick (Amblyomma americium). Bobcats (and infected domestic cats) 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. The organisms home to the immune cells lining the blood vessels as described above and, if the host lives long enough, the schizonts will eventually produce offspring (the piroplasms). Bobcats do not get sick during this process. It is the local bobcat population that infects the local tick population.
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.
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, a combination of atovaquone and azithromycin yielded a 60% survival rate in experimentally infected cats. Atovaquone, an anti-malarian drug, is not readily available but can be obtained through compounding pharmacies. and another drug, imidocarb, can be used in the meantime. Cats must be hospitalized, supported with intravenous fluids, and have 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. It is yet unknown how this is able to happen. (Different strain of Cytauxzoon, effective medication, and genetics are all theories)
Since mortality is very high with this infection and treatment is still highly investigational, prevention is paramount. 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 it should be noted that there are not nearly as many tick products for cats as there are for dogs. Most canine tick products are toxic to cats and cannot be safely used so meticulous label reading is crucial. Just because a product works on fleas definitely does not mean it also works on ticks and the feline label is needed to ensure safety.
Because new products are being approved and released every year, please visit our tick product comparison chart and look for a product on the list with feline approval.
Page posted: 12/20/2007