Heartworms, or Dirofilaria immitis, are worm-like parasites that can reach up to a foot in length. While many warm-blooded mammals, including ferrets and cats, can get heartworms, dogs are the main target of heartworms. Heartworms are transmitted by mosquitoes, who leave a larval form of them behind after bites. Adult heartworms travel to the pet's lungs. If untreated, these heartworms cause extreme health issues, which may lead to death.
When a mosquito bites a dog with heartworm, it ingests the microfilaria, or baby heartworms, along with the dog’s blood. These microfilariae mature over the course of about a week within the mosquito, transforming into a larval form of the heartworm. After the larval form is achieved, the mosquito passes it along to other dogs that it bites.
Without the intermediary step of the mosquito, heartworm disease would not spread. Because of the parasite’s reliance on mosquitoes, the disease spreads particularly rapidly during the summertime, when temperatures are warmer.
The best way to handle heartworms is to give your dog a monthly preventative treatment. The American Heartworm Society recommends that preventatives be given year round. This treatment helps stop your dog from getting heartworm disease, but it also helps stop other dogs from getting heartworm.
The preventative treatments do not prevent mosquitoes from biting and transmitting the heartworms; rather, the medications destroy the microfilariae within the dog's bloodstream.
In addition to year-round preventatives, dogs should be given an annual heartworm test, which serves to double check that the preventatives are working and that no doses have been missed. The heartworm test actually checks to see if your dog got heartworm disease the previous year. The tests cannot detect heartworms until they have reached maturity and given birth to microfilaria.
During a heartworm test, vets will take a sample of the dog’s blood and look for either signs of the microfilaria or for antigens that the heartworms give off. A heartworm test is also generally required before starting your dog on a preventative or switching preventative medications.
In the early stages of heartworm disease, there are virtually no symptoms. Heartworm disease has four stages, and as it progresses, the symptoms become more noticeable and disruptive. Some signs of the disease are a cough, a reluctance to exercise, and lethargy. As the disease progresses, dogs may start to bleed from their lungs.
During treatment of heartworm disease, vets will need to destroy the microfilaria, as well as the adult heartworms. Two different course of treatment are necessary for the different stages of heartworms. For the young heartworm, ivermectin-based preventatives can be given. Adult heartworms will require treatment with an adulticide, to kill them off. Since killing off the adult heartworms is a traumatic experience for a dog, a month-long rest period is required after the first treatment, which is an injection of medication into the dog, usually given in a hospital. During the rest period, it is very important for dogs to abstain from all activity. Although trying and expensive, treatment is generally successful.
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Heartworm Disease in Dogs: 5 Things You Should Know
This information is for informational purposes only and is not meant as a substitute for the professional advice of, or diagnosis or treatment by,your veterinarian with respect to your pet. It has, however, been verified by a licensed veterinarian for accuracy.