Heartworms were first recognized in the United States in 1847 and have since been known as one of the most devastating parasites that can infect dogs. Treatment is long, difficult and expensive, and heartworm infections can end in death if not diagnosed early enough. Symptoms usually don't develop until the disease has progressed significantly. Thus, it's important to recognize the causes and symptoms as soon as possible.
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Transmission
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Most dog parasites are transmitted through stool or parasites left behind in the ground. However, heartworms can only be transmitted by mosquitoes. Mosquitoes suck blood from infected dogs and become infected themselves. They then transmit the heartworms to the next dogs with which they come in contact. If neighboring dogs have heartworms, it is more likely that your dog will contract the illness, but only if mosquitoes are present.
Heartworm Larvae
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Heartworms begin their life as tiny larvae that are laid in the heart of infected dogs. They live in the bloodstream. These larvae are small enough to be sucked into the mosquito when it bites the dog. The larvae live in the mosquito for two or three weeks, where they grow large enough to migrate to the mosquito's mouth. Once in the mouth, they are passed into another dog, where they can grow to maturity. Larvae can live in the dog for up to two years. They can't mature unless they are passed to a mosquito and then returned to a dog host.
Adult Heartworms
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Once they have returned to a dog host, the larvae spend about three months maturing and migrating to the dog's heart, where they grow into adults up to 14 inches long. Adult heartworm can live five to seven years and lay larvae every six to seven months. A severely infected dog can have hundreds of heartworms living in the right side of its heart and the major blood vessels that connect the heart and lungs. This can obstruct blood flow between the heart and lungs in severe cases.
Symptoms
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Heartworm has few symptoms, so most owners don't recognize their dog is ill until it is severely infected. Symptoms include weight loss, decreased appetite, lethargy and coughing. Heartworm can be diagnosed with a blood test and is often identified in routine exams because it causes a heart murmur, which can be heard through a stethoscope.
Prevention
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Heartworm prevention is easy, so if you live in an area with mosquitoes, veterinarians recommend year-round preventative medication. The most common medication is Ivermectin, but there are many varieties of prevention and many prevent against other parasites such as fleas, worms and ticks. Heartworm prevention doesn't kill adult worms, but it kills larvae and prevents them from developing into harmful adults. If your dog has already contracted heartworms, consult your veterinarian before giving preventive medication as it can cause severe problems in infected dogs.
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