No Place for Worms in the Heart! Know About Heartworms in Cats

Dr Bhaskaran Ravi Latha
Dr A Sangaran
Dr ST Bino
She has a special place in your heart, but do you know what’s in your cat’s heart? Hope it’s not worms and disease! Know more about heartworm in cats and how you can prevent it.
 
Heartworm is a disease in cats that results in severe lung disease, heart failure, and also causes other organs to be damaged. It is caused by Dirofilariaimmitis, commonly called “heartworm”. Filarial nematode infections are among the neglected parasitic infections of felines as far as the Indian subcontinent is concerned. Many infections go unnoticed due to lack of awareness about this disease and improper diagnosis. Change in climatic factors, urbanisation, and transport of cats from exotic locations has resulted in a sharp rise in the cases of heartworm infection. Cats are relatively resistant to heartworm infection as compared to dogs. However, recent studies in cats with heart and respiratory diseases indicate that their susceptibility is far greater. The adult heartworm is found in the cardiovascular system of cats. It is mainly found in right ventricle and pulmonary artery but in cases of heavy infections it may be seen in right atrium and posterior venacava.
 
In hot & humid weather
Heartworm disease has a worldwide distribution, found in tropical and temperate regions of the world. In India, it has been reported in states where the weather is hot and humid. Heartworm infection is transmitted by mosquitoes, mainly by Genus Culex, Aedes and Anopheles.Culex mosquitoes are the major vectors. Adult female heartworms residing in the heart of cat’s release microfilaria (first larval stage)in the blood stream. Mosquitoes take up the microfilaria during blood feeding and further development occurs in the mosquito. The infective third larval stage is then injected into a healthy cat when the mosquito feeds upon. In cats, the disease is more severe as compared to dogs. There is rapid pulmonary enlargement and very high levels of eosinophilic response. The pulmonary arteries are narrowed, thrombus formation in the arterial branches due to the blood clots and worms result in occlusion of the arterioles.
 
It might be hard, but don’t give up!
Occasionally, the severity of the disease can be fatal and cause sudden death. This is due to a reaction within the lungs to the young heartworms, or to a reaction to dead or alive heartworms entering the pulmonary arteries and obstructing the flow of blood to the lungs. However, immature worms cause real damage in the form of a condition known as Heartworm Associated Respiratory Disease (HARD). Even a small number of worms are potentially life threatening in cats.
 
Look out for these signs
Most cats seem to tolerate heartworm infection for a prolonged period without or only with transient clinical signs. Clinical signs depend on the severity of disease and the duration of infection. Common clinical signs of heart worm infection in cats include –

• Intermittent vomiting
•  Diarrhoea
•  Dyspnea
•  Tachypnea
•  Ataxia
•  Coughing
•  Asthma-like attacks and gagging
•  Difficulty in walking, fainting, seizures 

When cats show clinical signs suspected for heartworm disease such as respiratory distress, they should be immediately taken for consultation with a veterinarian and appropriate treatment should be given.
 
Early diagnosis for a better recovery
Diagnosis is based on history, clinical signs, physical examination, and by detection of microfilaria in blood.Early diagnosis of the infection is important for improving the chances for a better recovery. If a cat has once developed heartworm disease, it will be highly susceptible to repeated heartworm infections. Both outdoor and indoor cats are at equal risk. Mosquito control is very important. Cats should be kept indoors during periods of high mosquito activity. Doors and windows should be closed with well-fitting screens or insecticide treated nets to prevent entry of mosquitoes. Mosquito repellants and traps can be used. If diagnosis is done at the right time, your feline friend will be fine in some days! And now that you know about heartworm in cats, your level of responsible pet parenting has surely gone up a notch.
(Dr ST Bino Sundar, Dr A Sangaran, and Dr Bhaskaran Ravi Latha are from Department of Veterinary Parasitology,Madras Veterinary College, Tamil Nadu Veterinary and Animal Sciences University, Chennai,
Tamil Nadu).