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Heartworms, one of the most dangerous parasites in domestic animals, are particularly insidious because they often show no signs at all until the infected animal usually a dog is heavily infested and severely ill. In fact, according to the American Heartworm Society, most dogs show no physical indications of infection until the disease has progressed to the point where treatment is no longer feasible.
In other words, when signs of heartworm become visible, it is usually too late to treat the dog for the disease. The best way to diagnose heartworms in dogs is through a blood test done by your veterinarian. A blood sample taken by the vet is examined through a microscope for the presence of microfilaria immature heartworms. If microfilaria are present, it means that your dog has adult heartworms in his heart muscle and must be treated for them. The treatment is a long, involved process, and can be dangerous to your dog, so prevention is extremely important. To understand how important routine heartworm preventative is to your dog's health and to the health of other dogs in your area you need to understand what heartworm is, how it spreads and how it affects your dog.
What Heartworm Is
Heartworms are parasitic round worms that live primarily in the heart muscle of dogs, though there is a growing incidence of heartworms being found in other animals including cats, wolves, foxes, skunks and ferrets. They can grow as long as fourteen inches. A single heartworm can eventually kill your dog, though infected dogs may have up to 300 adult worms living inside their hearts. A heartworm can live for up to seven years, and produce millions of microfilaria in its lifetime.
Microfilaria are also present a danger to your dog. The microscopic worm larvae live in your pet's bloodstream and travel through his circulatory system. When they are present in large numbers, they can clog tiny capillaries and impair circulation, causing multiple problems.
The signs of heartworm infestation vary with the number of worms, the location of worms, the length of time the worms have been present and the amount of damage done to the heart, lungs, liver and kidneys from the adult worms and the microfilariae.
Adult worms cause damage by clogging the heart and the major blood vessels leading from the heart. Their presence keeps the heart valves from working properly, and reduces the blood supply to the lungs, liver and kidneys. This leads to a malfunction of these organs, including cirrhosis of the liver.
The most obvious signs of heartworm infection are a chronic soft, dry cough, shortness of breath, low stamina, weakness, listlessness and nervousness. Because heartworms impair circulation and interfere with the delivery of oxygen to the body, these signs are most obvious after exercise. A dog with advanced heartworm infestation may even faint after or during vigorous exercising.
A vet may notice other signs of heartworm infestation on examination. He or she may hear abnormal heart and lung sounds, or note congestive heart failure symptoms. The abdomen and legs may swell from fluid accumulation, and the dog may lose weight or be anemic. Infected dogs may die suddenly during exercise or excitement from congestive heart failure.
How Heartworm Spreads
Heartworm is spread from one infected dog to another by mosquitoes. The cycle starts when a mosquito takes a blood meal from an infected dog. The blood that the mosquito ingests is infested with microfilaria immature heartworms. That microfilaria will live in the mosquito's digestive system over the next two to three weeks, maturing there. When they are mature, they move from the digestive system to the mouth parts of the mosquito. The next time that the mosquito takes a blood meal, the microfilaria which are now called infective larvae are deposited on the skin of the animal. From there, they burrow into the skin until they reach a blood vessel and are carried through the bloodstream to the heart where they settle in to mature into adults. Within two to three months, the larva will be a sexually mature adult, and start producing microfilaria which is released into the bloodstream to start the cycle all over again.
Heartworm Prevention What dogs should be protected
Because heartworm is spread by mosquitoes, it is most common in states where the mosquito population is high but it has been reported in all 50 states. In states that have a mosquito problem year round, all dogs should be treated with heartworm preventative each month. In other states, dogs should be tested for heartworm at the start of mosquito season and if they are not infected, should be treated with heartworm preventative monthly through mosquito season.
