Hartworm
The adult worms are found in the heart and adjacent blood vessels of infected dogs.
The female worm is 2.5 to 5.5 cm long while the male is about half the size. One dog may have as many as 300 worms. The female produces millions of young (microfilaria) which live in the bloodstream. These are taken up by a mosquito when it feeds and develop into infective larvae within the mosquito which are then injected back into another dog.
Transmission by mosquitoes is essential and the worms cannot be transmitted directly from dog to dog. It takes a number of years before dogs show outward signs of infection. Consequently, the disease is diagnosed mostly in 4 to 8 year old dogs, when the disease is usually well advanced. The disease is seldom diagnosed in a dog less than 1 year of age because the young worms (larvae) take up to 7 months to mature following establishment of infection.
Disease
Adult worms cause disease by clogging the heart and major blood vessels. This affects the action of the heart and also the circulation to other major organs. The main clinical signs are a cough, weakness, lethargy and shortness of breath especially at exercise. In advanced cases the dog will suffer congestive heart failure with fluid accumulation in the abdomen and legs and sudden death.
Diagnosis
Diagnosis can be confirmed by blood tests, but a whole range of other diagnostic procedures are necessary to determine the extent of organ damage and so the likely response to treatment.
Treatment and control of heartworm
The treatment of dogs with advanced infections is not without risk. However, there are effective medications that can be used as a routine control measure to prevent the disease reaching this stage. The control of mosquitoes is also of value. It is strongly advised that all dogs are treated regularly in areas where heartworm occurs.
In addition, dogs going on holiday to these areas should be treated during their stay. Your veterinarian will be able to advise.
