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Deadly Tick-borne Disease Not as Fatal as Once Thought

By Kelley Weir

Researchers at the University of Georgia uncovered some surprising data in a recent Morris Animal Foundation–funded study of cytauxzoonosis, a tick-borne disease that affects cats. Once thought to be 100 percent fatal, research has found that, at least for some cats, the severity of the disease is lessening.

Cytauxzoonosis causes severe illness, and in most infected cats, the course of disease is rapid. Supportive care and antiprotozoal drugs have had inconsistent therapeutic results and limited success in treating cytauxzoonosis. In the past, nearly all cats died of the initial clinical illness within one week, but recently some cats have survived without veterinary care, which suggests the existence of a less fatal strain of Cytauxzoon felis, the pathogen that causes this disease.

C. felis was first detected in 1973 in Missouri, then throughout the southeastern and south-central United States. Wild bobcats have been identified as a natural host of the parasite, and although often not clinically affected themselves, infected bobcats serve as a reservoir for the parasite, which is then transmitted by ticks to domestic cats. Research now indicates that some cats can harbor the parasite without showing symptoms.

“Our latest findings suggest that asymptomatically infected pet cats that are carriers of the C. felis parasite may serve as additional reservoirs for infection and thus greatly increase the risk of exposure for other domestic cats,” says lead investigator Dr. Holly Brown from the University of Georgia.

With Foundation funding, Dr. Brown and her team evaluated how the disease spreads and whether cats who recover from the infection still harbor the parasite. They determined that clinically healthy cats may still be able to spread the disease, and this area should be investigated further.

“In our study we detected a significant population of asymptomatic C. felis–infected animals, including cats that survived acute cytauxzoonosis, cats that cohabited with those previously diagnosed with infection and feral cats in endemic regions,” Dr. Brown says.

In comparing historical blood and tissue samples from infected cats, both cats that died and cats that survived, the scientists determined that some unique parasitic strains are more pathogenic than others, which supported their hypothesis that the parasite may be genetically adapting to cause less severe disease in domestic cats. They also discovered that disease severity varied depending on the geographical location of the cat.

The good news for cats and their owners is that owners can now feel more confident that treatment will ensure their pet’s survival.

“Previously, cytauxzoonosis carried such a poor prognosis that euthanasia was recommended for most infected cats. In light of our findings, the consideration to pursue treatment is supported,” says Dr. Brown.

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