Heartworm

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Heartworm disease is caused by a mosquito and flea bites that transmits the parasitic worms to dogs. It is a serious and possibly deadly disease. There are no symptoms of heart worm infection in the early stages and is therefore hard to diagnose. Symptoms appear as the number of heart worms gradually increases over a period of months or years. 

Heartworm has always been thought to affect dogs residing in tropical areas, however more cases show that more numbers of dogs being infected by heartworm in the southern area are increasing? 

 

What is Heartworm?

Heartworm, or dirofilaria immitis, is an actual worm that resides in a dog’s heart. The parasites can grow between six and twelve inches long, and an infected dog may host more than a hundred worms which can spread to the lungs and large vessels in the circulatory system. As the parasites mature, they block the blood flow and can lead to anaemia (reduced haemoglobin) or heart failure. 

Heartworm is carried by mosquitoes and fleas in tropical and semi-tropical climates such as Northern Territory and Queensland, but occurrences are not limited to those areas. As dog owners travel (taking southerly vacations in winter months, for example), they expose their pets to the disease, and northern mosquitoes can acquire the parasites as larvae from infected dogs. Cases of this parasite have now been reported throughout all states of Australia, and the parasite can affect all Dog Breeds. 

Once a dog is bitten by an infected mosquito, the worms may not reproduce for up to nine months, leaving no visible symptoms of infection. Because of this, dog owners who travel frequently should take all preventative measures to protect their pets even if there is no indication of a parasite’s presence. Furthermore, this problem can also affect cats, so owners should take precautions with all their pets. 

 

What areas are prone to Heartworm?

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

However, the spread to southern temperate areas such as Adelaide 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:

      • N.E.Suburbs 10 - 15%
      • Western suburbs close to 0%
      • Eastern bayside suburbs 2 - 3%

While the prevalence of heartworm disease in South Australia is low, it is reasonable to suggest preventive treatment for heartworm disease is responsible for preventing outbreaks seen in other states.

 

How does my dog become infected with Heartworm?

Your dog is bitten by a mosquito or flea which is carrying infected larvae from its previous host (another k9) which was infected with heartworm.

 

Are there any treatments for Heartworm?

Although it is a serious condition, this infection can be treated. Because diagnosis is not typically made until adult worms have become prevalent, treatment usually involves hospitalisation. Injections can kill the worms living in the dog’s heart, but they must be administered with care because the powerful drugs can also damage the animal’s liver and kidneys. Blood tests can ascertain both the success of the treatment as well as potential damage to other organs. 

After adult worms are destroyed, additional injections are required to kill the heartworm larvae in the dog’s bloodstream to prevent re-infection. Supplementary treatment may also be necessary to help repair the parasite's damage to the heart and lungs, and the animal may be susceptible to pulmonary infections for some time afterwards. 

 

What preventative treatments are there for Heartworm?

The best cure for heartworm is its prevention, sparing the dog a prolonged ordeal. Both daily and monthly tablets are available that destroy larvae before it reaches maturation, therefore preventing the worms from lodging in the dog’s heart. These preventative measures must be given to dogs throughout warm seasons (spring, summer, and fall), or year-round for animals living in or regularly visiting warm climates. Before travelling to a location with a higher probability of worm infection, consult your veterinarian for appropriate precautions. Furthermore, avoid exceptionally swampy parks or areas of long grass that will harbour elevated mosquito populations. 

The preventative drugs can be exceedingly dangerous for animals already infected with heartworm, and dog owners should always have their pets tested before beginning a preventative program. 

 

What are the symptoms of a dog infected with heartworm?

Heartworm symptoms are not typically noticeable until adult worms begin to clog the animal’s circulatory system, which may be several months after the initial infection. Potential symptoms include:

      • Anaemia, characterized by pale gums, excessive sleep, weight loss, and lethargy 
      • Coughing as worms settle in the lungs 
      • Lack of energy or easy exhaustion because the heart is overworked
      • Weight loss even without reduced appetite
      • Weakened immune system leading to frequent minor illnesses
      • Fainting spells due to reduced blood flow

 heartworm lifecycle

How long can my dog be affected before realise?

Heart worms take 6 to 7 months to reach the adult stage. Adult heart worms can grow up to 12 inches in length and remain in the dog's heart for approximately 5 to 7 years. Once in the pulmonary artery the worms increase greatly in size and begin reproducing daily by the thousands.

 

Summary

Spread through mosquito and flea bites, heartworm is a parasitic infection that disrupts an animal’s circulatory system, eventually leading to life-threatening complications. Treatment can be extensive, but prevention is a simple matter of regular tablets. Though this disease can affect any dog breed anywhere in the country, it is more prevalent in warmer climates where pest populations are higher. By becoming familiar with the disease, its symptoms, and possible treatments, dog owners can take adequate measures to protect their pets and preserve their healthy, active lifestyles.

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