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Heartworm disease, as the name suggests, are worms that infect the heart! The dog is the most important host, but other mammals may also be susceptible eg: cats, ferrets,and sea-lions. The heartworm infection is transmitted dog-to-dog by infective mosquitos which act as vectors for the disease. Heartworm can be the cause of serious illness due to damage to the heart and lungs and if left untreated, can even be fatal.

DISTRIBUTION AND PREVALENCE

In Australia, the prevalence of heartworm disease is highest in subtropical/tropical areas ( Darwin up to 100%, Brisbane 34% ) and northern temperate areas ( Sydney 25% ).

However, the spread to southern temperate areas such as Melbourne has occurred due to a number of factors: firstly, the movement of dogs that are not on preventative medication into and out of endemic heartworm areas and, secondly, the geographic distribution of suitable mosquito vectors has increased as they become more resistant to the cold.

Studies in Melbourne undertaken two years ago revealed a prevalence of approximately 5%.

This figure is made up of:
North Eastern suburbs 10 - 15%
Eastern bayside suburbs 2 - 3%
Western suburbs 0% (close to)

LIFECYCLE

Adult heartworm live in the heart and the surrounding blood vessels supplying the lungs. These adults reproduce and release tiny larvae called microfilaria into the bloodstream. These microfilaria are subsequently taken up by a feeding mosquito and undergo an essential maturation whilst in the mosquito. When the mosquito takes a blood meal from the next dog, the dog is innoculated with the infected larve, which migrates through the body’s tissues ( approx. 100 days ) to reach the heart and surrounding blood vessels. Here they mature fully to complete the lifecycle.

DIAGNOSIS / TREATMENT

An infection is diagnosed by blood test performed by a veterinary surgeon.

A dog diagnosed with heartworm disease can be treated. It usually involves hospitalisation and carries a certain amount of risk depending on the physical health of the patient. This is definitely a disease where prevention is better than treatment

PREVENTION

There are a variety of drugs on the market designed to prevent heartworm disease. Some are given daily and some monthly. We recommend starting pups at 8 weeks of age. If animals are older than 8 weeks of age but less than 6 months of age, then a blood test should be performed after 6 months of preventative medication.

If animals are older than 6 months, a blood test should be performed before starting medication and another after 6 months of preventative medication.

CONCLUSIONS

While the prevalence of heartworm disease in Victoria is low, it is reasonable to suggest the rapid response to heartworm disease is responsible for averting the outbreaks seen in other states.

The heartworm story is complicated and we recommend you contact your local clinic to assess the prevalence in your area.

Please feel free to contact The Lost Dogs´ Home veterinary clinic or raise questions at your next visit.