Feline heartworms(HWs) are a parasite more commonly thought of in dogs but has been seen with an increased frequency in this areaís cats. The regional prevalence parallels that in dogs but at a lower rate (roughly 5 to 20% that seen in dogs). While this parasite, which is spread by mosquitoes, affects outdoor cats more frequently, indoor cats are also at risk- accounting for up to 1/3 of diagnosed cases. Once established, the adult HWs live 2-3 years before being eliminated by the catís own immune system.
While most feline infections are comprised of 6 or less worms (usually only 1-2), even light infections are capable of producing severe disease with potentially life-threatening consequences. This is due in part to cats smaller body size as well as the way their bodies respond to the parasite. Some cats may be asymptomatic and never show any signs until the HW parasite is cleared naturally by the catís own body. Other cats may develop more chronic signs including difficulty breathing(48%), a cough (38%), persistent (possible intermittent) vomiting, poor appetite, weight loss, and lethargy. Acute clinical signs include sudden onset of breathing difficulties, seizures, blindness, collapse, or death.
Physical examination of the HW positive cat may be normal or reveal lung/heart abnormalities due to the parasiteís influence on these 2 organs. The work-up on a possible HW patient include a CBC, chemistry profile, urinalysis, and HW antigen and antibody blood test. These last 2 tests in particular can indicate exposure and/or current infection with the HW. Unfortunately, in cats, false negatives are quite frequent due to the immaturity of the worms, low worm burdens, and single-sex infections. Chest Xrays can also show a number of characteristic changes. Other tests including an EKG and ultrasound may also be used to determine a catís HW status.
Treatment of the HW positive cat depends, in part, on the severity of the clinical signs.
The current treatment of adult HWs is off label and carries significant risk of severe complications. Therefore, the mainstay of treatment is corticosteroids to reduce the inflammation associated with the worms and, by doing so, decrease clinical signs. A bronchodilator may also be used if further respiratory support is needed. Prevention of HWs is the logical and easiest approach.
A monthly HW preventative is recommended, both for indoor and outdoor cats. Two options are available. Interceptor is a flavored tablet which is given monthly by mouth to eliminate immature HWs while also controlling 2 intestinal parasites (roundworms and hookworms). It is available in 3 weight specific sizes for kittens 9 weeks, and older. The second option is a topical product called Revolution, which is effective against fleas, HW's, hookworms, roundworms, and ear mites.