Heartworm Disease ----------------- Ferrets are susceptible to heartworm disease, a mosquito- transmitted illness seen primarily in dogs. Ferret owners must carefully consider the pros and cons of preventive therapy for this disease. Some ferrets may have adverse reactions to the drug used for heartworm prevention. Furthermore, the average pet ferret is very unlikely to be bitten by an infected mosquito unless it lives in an area of heavy heartworm infection and is often exposed to mosquitoes (is housed outdoors). Most pet ferrets housed exclusively indoors are unlikely to become infected by heartworms and should not require preventive therapy.