‘Bobcat fever’ may not be a well-known cat disease, but if your cat lives in the Southern or South-Central United States, you certainly need to know what it is. If this nasty infection does strike a cat your quick action is the only thing that might save its life.
‘Bobcat Fever’ is actually a parasite transmitted by ticks. The particular villain is the Lone Star tick; a notorious carrier of disease and not just Bobcat Fever.Amblyomma americanum – to give this pest its technical name – has in recent years been spreading across the USA and putting many cats at risk in once safe areas. The tick will also aggressively attempt to attach itself to humans; but with humans the effects of a bite are a nasty rash with a resemblance to (but without the later symptoms of) a debilitating illness called Lyme’s disease.
For cats the tick’s bite can be deadly. Dr. Leah Cohn, veterinarian at the University of Missouri, calls Bobcat Fever the ‘Ebola virus for cats’ for good reason. As she points out: ‘The disease acts very quickly and can kill a cat less than a week after it begins to show signs of being sick, so it is important to get treatment from a veterinarian as soon as the cat appears ill.’
The natural reservoir host from which the ticks spread the disease is indicated by the name – the bobcat. (Although mountain lions, that is, cougars, are also known to carry the parasite). Though the parasite is endemic in some bobcat populations, it can infect other felines, from small domestic cats to fully-grown tigers. Healthy outdoor cats are most at risk because they are more likely to be bitten by an infected tick than a cat which lives indoors. Indoor cats are not completely safe, because though the disease does not affect dogs or humans, both have been known to carry ticks indoors and thus subsequently infect a cat.
What exactly is bobcat fever and how does it cause a cat to become ill?
The disease is mostly seasonal, and is most active between April and September. This is because Bobcat Fever is caused by a parasite calledCytauxzoon felis (C. felis) which infects the ticks which are most active at this time. The actual bugs are tiny single-celled organisms called protozoa, and they travel from the tick to the cat by the tick’s bite. This means that the infection is by tick and only by tick. Once it has been cleared of ticks an infected cat cannot infect another cat directly.
Once the parasite enters the cat’s body, it targets cells called macrophages which play an important role in the body’s immune response. Once infected with the protozoa, macrophages expand, turning into so-called ‘giant cells’. Those cells quickly clog the blood vessels, and the consequent restricted blood flow rapidly results in multi-organ failure. The parasites mature through different stages and in each stage they can infect different cells. So, for example, in the blood the parasite can also infect red blood cells, making their shape signet-like (such cells are known as erythrocytic piroplasms). Infected red blood cells can be a useful diagnostic tool since erythrocytic piroplasms can be quickly detected under a microscope with a blood smear.
Symptoms of ‘Bobcat Fever’
Early symptoms of ‘Bobcat Fever’ are quite generic and can mislead an owner into thinking that the cat is just ‘a bit under the weather’. These initial signs include sluggishness and a loss of appetite. But once the onset of the infection starts in earnest, the cat will start to deteriorate rapidly.
At this time symptoms may include a high temperature accompanied by dehydration, jaundice, an enlarged liver and spleen, pale mucus membranes and respiratory distress. The early symptoms of the disease are seen within 5-10 days after a tick bite. It only takes a few days for the disease to progress to the final stages and if not treated almost inevitably causes death.
Diagnosis and treatment
A blood test is definitely the quickest way to detect the parasite. If the C. felis protozoa have entered the red blood cells, a veterinarian can quickly detect this. Sadly not all cats will have this useful diagnostic feature. However, most infected cats will have a decreased level of both white and red blood cells and a correspondingly increased level of liver enzymes, which are an early symptom of liver damage. For more accurate diagnosis, the veterinarian can take samples from infected organs and tissues. Blood samples can also be sent off for more detailed analysis by polymerase chain reaction (PCR). PCR is also useful for ruling out other infections which yield similar symptoms, particularly Mycoplasma haemofelis (an illness formerly known as Haemobartonella felis).
Prior to the last five years, the only available treatment for C.felis infection was imidocarb dipropionate, an antiparasitic drug which was not particularly effective. Only 25% of cats treated with imidocarb dipropionate survived a Bobcat Fever infection.
Recent studies by Leah Cohn and her colleagues (ref 1) have shown that a combination of the anti-malarial drug atovaquone and an antibiotic called azithromycin increases the survival rate of infected cats to 60%. Although 60% is still relatively low, it is considerably better than the previous 25%.
All sick cats require aggressive supportive care, intravenous of fluids, nutritional support, anti-pain treatment, and occasionally a blood transfusion as well. An accurate diagnosis of cytaux and early treatment are critical. Once the disease is well advanced, treatment is less likely to be effective.
Prevention is by far the best way to keep the cats safe from C. felis.
All outdoor cats should have topical tick treatment applied year round in this area of the country. We can help you with the best options. It should also be remembered that no treatment can protect a cat 100% because though tick treatments discourage bites, they cannot completely prevent them. Therefore people with cats in an area where ticks carry C. felis need to stay vigilant for the early signs of infection.
1. Cohn, L.A.; Birkenheuer, A.J., Brunker J.D., Ratcliff E.R., Craig, A.W. (2011).“Efficacy of Atovaquone and Azithromycin or Imidocarb Dipropionate in Cats with Acute Cytauxzoonosis”. J Vet Intern Med 25 (1): 55–60.