However, this won’t detect the early stages of infection by microfilariae or an established infection by a few adults. Heavy burdens of heartworm will be visible on an ultrasound scan of the heart or chest x-ray. How can you tell if your pet has heartworm? In severe cases, the high number of worms can precipitate a fatal condition called disseminated intravascular coagulation, where the clotting system is activated all over the body leading to formation of numerous clots ( 1). This can be a cause of sudden death or other symptoms depending on where the clot blocks a blood vessel. Clots, or even smaller worms, in the heart can break off and block blood vessels in other parts of the body, usually the lungs. The presence of the worms in the circulatory system can increase the chances of clot formation. The majority of cats don’t show symptoms but are at risk of sudden death ( 2). These signs can be difficult to detect in animals which don’t do much exercise. Abdominal swelling caused by a build up of fluid.A reduced ability to exercise or tiring more easily than normal.Dogs with heartworm show similar symptoms to those in heart failure and might have one or more of the following signs: Symptoms develop gradually and are more severe with higher numbers of worms. As a result, dogs with only a few adult worms might not show symptoms but continue to be a source of infection for others in the area. Heartworm symptoms are mainly due to the physical obstruction of blood flow that they cause. You can discuss the risk to your pets with your own local vet based on a number of known factors such as the prevalence of mosquitoes in your area, outdoor exercise and living in a rural area. However, it’s important to stress that even indoor-only animals could become infected ( 5). Queensland and New South Wales are considered to be areas of higher risk whereas rates in South Australia are low ( 4,5).ĭogs and cats living in rural areas are more at risk of infection than their urban counterparts ( 6). Since then, infection rates have reduced dramatically but there isn’t very much information about the current rates of infection in dogs and cats in Australia. In the 1970s and 1980s, before preventative treatment was widespread, heartworm was present in every Australian state with infection rates of between 5% and 77% depending on the area ( 3). However, you can’t catch heartworm directly from your dog, since the worm must be transmitted by a mosquito. There are rare cases of humans being infected by Dirofilaria immitis. Cats are considered dead-end hosts, meaning that adult worms produce much fewer microfilariae ( 1,2). This period between initial infection and production of new microfilariae can be up to eight months in cats.Īdult heartworm can survive for up to five years in dogs and two years in cats. The larvae take three to six months to develop to adults and begin releasing microfilariae, starting the life cycle again. When the mosquito next feeds, they are injected into the new host’s skin, from where they penetrate the veins and travel to the heart. Once they’ve finished the next stage of development, the larvae migrate to the mosquito’s mouth. The microfilariae develop inside the mosquito for between eight to thirty days, depending on the temperature. When a mosquito takes a blood meal from the host they often take up a few microfilariae as well. These larvae are called microfilarie and travel in the blood vessels all around the body. After mating, the females release larvae into the blood stream. Heartworm is transmitted from dog to dog by mosquitoes.Īdult worms live in the right side of the heart and the arteries which carry blood to the lungs. The effects can be severe, even fatal, so a well-managed prevention protocol is essential in high-risk areas. Heartworm mainly affects dogs and wild canids, such as dingoes, but can also infect cats and ferrets. Heartworm is a parasitic worm, Dirofilaria immitis, which lives in the heart and circulatory system of its host.
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