Heartworms

• Roundworms

• Hookworms

• Tapeworms

• Heartworms

Dirofilaria immitis in cats

Although cats are susceptible hosts for heartworms, they are more poorer hosts for this infection than are dogs. Furthermore, feline heartworm infection is more elusive to diagnose than in dogs and can be easily missed due to the different behaviour of heartworms in this host.

 

How Heartworms are Transmitted

Heartworms are transmitted by mosquitos. When an infected mosquito bites a cat, it passes it the worms’ larvae that start to migrate until they reach their final site (heart and pulmonary arteries); here they grow to maturity (macrofilariae). If worms of different sex are present, they start producing larvae (microfilariae ) which are released into the bloodstream.

When a mosquito bites an infected cat, it picks up these larvae and can transmit the infection to other cats.

 

Disease

Cats living in heartworm risk areas frequently become infected but parasites do not develop to the adult stage. Furthermore, most heartworm infections in cats are light and consist of 1-2 adult worms, often of the same sex. Thus microfilariae seldomly occur. The life span of adult parasites is quite short. Other than for dogs, where a test for microfilariae is an easy diagnostic tool, a definite diagnosis of heartworm infection in cats can often be obtained only by the application of haematological and serological tests in conjunction with thoracic radiography and echocardiography.

 

Treating Heartworm Infection

Testing cats before administration of a worming treatment or re-testing during preventive anthelmintic treatment is recommended. However, if an antibody test is used, it might show a positive result in sensitised animals exposed to 3rd-4th stage larvae: it will demonstrate that the cat is exposed to a heavy risk of infection and reinforces justification for recommending prevention. Since microfilaremia in cats is uncommon, transient if present and below concentration levels that might trigger an adverse reaction to microfilaricidal preventive drugs, pretesting for microfilariae is unnecessary in healthy cats.

Most heartworm preventative anthelmintics have the potential to control a range of other worms and so an appropriate product may be chosen to control other nematodes and cestodes as necessary. In addition, treatment can be extended throughout the year to ensure the continued control of non-seasonal parasites such as Echinococcus spp. and Toxocara spp., where necessary.

 

Dirofilaria repens in cats

D. repens can infect both cats and dogs. Most infections are asymptomatic, though cold, not painful nodules containing the adult parasites can be found on the skin surface of infected animals. Seldom, in case of heavy infection or in sensitised animals, light to severe infection of the skin can be observed. Most cases of zoonotic Dirofilaria infections in Europe are caused by this species.