Heartworm and your pets

in Animals & Pets

Heartworm is a disease of dogs and cats, it rarely causes illness in cats but can be a significant problem in canines.
Is it endemic in Gibraltar? 

Cases of heartworm are few and far between, therefore it is not a disease that isn’t yet endemic in our local pet population but things might be changing!!

I have had my first case of heartworm in a local dog that has only left the territory once to be kenneled in Spain about 3 years ago.

This is a worrying turn of events so the advice has to change.

Heartworm, Dirofilariaimmitis, is a parasite where the adults live in the right ventricle and pulmonary arteries of the heart. The female worm once fertilised releases its offspring, tiny juvenile worms, microfilariae into the blood stream. These microfilariae circulate around the body where they reach peripheral capillaries under the skin. They can circulate in the blood for up to 2 years.

Mosquitoes that may happen to feed on the animal will take on this parasite along with the blood that it imbibes. Once in the mosquito the parasite goes through a development phase before migrating to the mosquito’s salivary glands. This development can only occur when the ambient temperature is over 14 degrees centigrade. Once the mosquito is carrying the microfilariae it will infect any further dog or cat that it feeds on. When an animal is infected the microfilariae migrate to the muscles where they go through another phase of their development before finally entering the circulatory system to reach their final destination, the pulmonary artery and right ventricles. The final development stage into an adult occurs here with females measuring up to 30 cm in length. The whole process of infection to fertile adults in the heart, the pre-patent period, is between six and seven months.

Diagnosis of this disease is a fairly simple affair; historically it could only be diagnosed by taking a blood sample from a peripheral blood vessel and then examining the sample microscopically. This method unfortunately can lead to a lot of false negatives for many reasons so we do not rely on this method now. Blood samples are now tested directly for parasite antigen and/or antibody and these tests are extremely reliable.

Heartworm can be a fatal disease with dogs presenting with clinical signs of congestive heart failure. However the symptoms might be varied, weight loss, anaemia, weakness, anorexia, ascites(fluid in the abdomen).

In cats symptoms might be more subtle, asthma type symptoms, weight loss, but often the only symptom is sudden death/ collapse. 

With advances in medicine there are various alternatives now to treat this illness with a complete resolution of the disease. As long as the illness is diagnosed early enough. However treatment is a longwinded process taking several months and can prove to be quite expensive. In rare cases there can be an anaphylactic reaction when treated so prevention is by far the preferred option.

Prevention can take one of three routes:

  • An annual vaccination against heartworm. Before the vaccine available often caused allergic reaction but the new products on the market are a lot safer
  • Ectoparasite treatment to prevent the infected mosquito biting your pet. These work but there one has to be careful. You must use effective collars and spot-on treatments but the owner must remember to keep applying the products and be aware that is the animal is washed or bathes regularly there will be a reduction in protection
  • There are monthly tablets that can be administered that kill any microfilaria if infected by a mosquito 

Personally where there is high risk to your pet I would advise using two of the options listed above, best to ‘be sure to be sure’.


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