Heartworm or Dirofilariosis is a widespread and potentially deadly parasitic disease that can be observed everywhere around the world.
The causative agent of the disease are worms that live and persist inside the heart, the associated blood vessels, and the the lungs causing organ dysfunctions, heart failure, severe lung disease and anemia.
The worms inside the dog’s body mature in time developing into adult forms and eventually the parasites reproduce and create offspring.
This makes the dogs ‘natural hosts’ for the disease. The illness is silent and in the initial stages of the diseases there is absence of any obvious symptoms.
When the disease is left untreated the chances of severe organ damage are high. Because of this owners are advised to make heartworm tests from time to time and use proper preventative medications following veterinarian prescription.
The disease is vector-borne which means that the only possible way to be transmitted from one animal to another is by an intermediate organism, in this case the mosquito.
As we mentioned before the heartworm lifecycle happens inside a dog’s organism, but also in wolves, foxes and coyotes. If you carefully read the previous part you are probably aware that a direct contact with an infected animal won’t do your dog any harm.
When a mosquito attaches on an infected animal’s skin and connects with its bloodstream while sucking the blood meal, the insect picks up the offspring of the heartworms.
These microscopic children are called microfilaria. Once inside the mosquito the microfilaria starts maturing and reaching an infective stage for about 10 to 14 days.
After the infective larvae of heartworm is fully developed inside the mosquito, the next time the insect takes a blood meal from an animal it will automatically infect the organism. The mosquito deposits the infective larvae on the animal’s skin and by sucking the dogs’ blood it leaves a bite wound through which the parasite enters the bloodstream and causes infection.
In about half a year the infective agent will develop into mature heartworm with a life-span of 5-7 years.
Symptoms of Heartworm Disease
The early stage of the disease is asymptomatic or there a few insignificant signs. During progressed stages of the disease the dogs become reluctant to physical activities, experience series of persistent coughing, and lose their appetite and weight. In cases of extreme parasite invasions the development of heart failure, cardiovascular collapse and swollen abdomen as a result of excess fluid are are frequently observed.
Treatment, Therapy and Prevention
Treating clinical heartworm in dogs is a bit tricky so the best option for dog owners is prevention. Dogs should be annually tested for heartworm at the vet clinic.
The preventative treatment can start when the puppies are under 7 months of age. If started early there is no need for a heartworm test prior to the initial treatment. If the treatment starts when the dog is over 7 months of age, a diagnostic test must be made before, and two times after the treatment.
Antibiotics may be prescribed because of a bacteria found living inside the heartworms. When the heartworms die, they release a bacteria known as Wolbachia, which contributes to an inflammatory response to the dog’s body. It is believed that the presence of Wolbachia may cause the body to cause an immune response that could worsen the heartworm disease and cause lung and kidney inflammation seen in dogs with this condition.
Many veterinarians begin treatment by prescribing doxycycline. The heartworm treatment only kills adult worms, so veterinarians may prescribe a monthly heartworm preventive to kill the smaller larvae before initiating adult heartworm treatment.
The administration of corticosteroids may also be given as a preventive which also helps reduce inflammation.
The treatment for heartworm disease takes at least 60 days to complete and consists of a series of drug injections that kills the worms; an organic arsenical compound that is injected into the dog’s lumbar, or back, muscles.
On the days injections are given, your dog must stay in the hospital for observation to make sure it doesn’t have any serious reactions to the treatment. Your veterinarian may also prescribe a tapering dose of steroids for a period of time following the injections.
To follow up on treatment, your dog should be retested after six months to ensure that all of the larvae, microfilariae and adult worms are gone. Dogs who remain heartworm positive after six months may need to repeat treatment to kill the remaining worms.
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