Heartworm Disease: What You Need to Know

In dogs, cats, and ferrets, heartworm illness causes severe lung disease, heart failure, organ damage, and death. It is driven by a parasitic worm called Dirofilaria immitis. Mosquito bites are responsible for the spread of worms. The dog is the definitive host, which implies that the worms grow, reproduce, and mate only within the dog. The mosquito serves as an intermediary host, where the worms dwell briefly before becoming infective (able to cause heartworm disease). Adult worms reside in the heart, lungs, and blood vessels of infected animals.

What is the heartworm’s life cycle?

The heartworm parasite’s life cycle is complicated, requiring an intermediary host in the mosquito before infecting the dog. Mosquitoes are the vectors of heartworm transmission. Up to 30 different mosquito species can spread heartworms.


A female mosquito bites an infected dog during a blood meal, swallowing microfilariae. Microfilariae mature in the mosquito’s intestines for 10-30 days before entering its mouthparts. They are infectious larvae that can mature in a dog at this stage. When a mosquito bites a dog, infectious larvae enter the body.

Where can you find heartworm disease?

Canine heartworm disease is present around the world. It was once restricted to the United States’ southern and southeast areas. The highest number of documented cases remains within 150 miles of the Gulf of Mexico and Atlantic Ocean coasts and along the Mississippi River and its tributaries. However, the disease is spreading rapidly and has already reached the United States, including California, Oregon, and Washington.

What is the mode of transmission of heartworm disease?

Due to the requirement of an intermediary host in the mosquito for transmission, the disease is not transmitted directly from dog to dog. Thus, disease transmission happens concurrently with mosquito season, which extends throughout the year in many parts of the United States. The number of infected dogs and the length of the mosquito season closely correlate with the incidence of heartworm disease in a specific area.

What effect do heartworms have on your dog?

In most cases, dogs do not show clinical signs of sickness for several years. As a result, the illness is most usually diagnosed in dogs between two and eight. The disease is uncommon in puppies under one year, as it takes approximately five to seven months for microfilariae to mature into adult heartworms following infection. Regrettably, the disease is frequently advanced by the time clinical signs show. That is why it is always important to take your dog to the best vet simi valley has available on a regular basis. 

How is heartworm illness diagnosed?

In most cases, simple blood tests can diagnose heartworm infection. Additional testing is frequently required to determine treatment safety in heartworm-positive dogs. One or more of the following tests before initiating treatment is recommended.


Serology of adult heartworm antigens. This test necessitates the collection of a blood sample. For additional information, read “Heartworm Disease Testing in Dogs.” X-rays of the chest (X-rays). Radiographs are frequently recommended before initiating medication for heartworm infection to determine the extent of heart and lung damage. Examinations (complete blood cell count, serum biochemistry). Blood testing prior to heartworm therapy may be recommended to assess heartworm-associated organ damage. Visit this page to learn more on other veterinary procedures for your dog. 

How is heartworm disease treated?

Melarsomine dihydrochloride is an arsenic-based drug that the FDA has approved to treat adult heartworms in dogs. It is thoroughly injected into the back muscles of dogs with stable class 1, 2, or 3 heartworm disease. Advantage Multi for Dogs (imidacloprid and moxidectin) is another FDA-approved drug that is intended to eradicate microfilariae from a dog’s bloodstream. Visit ParkAnimalHospitalSimi.com to learn more about emergency vet situations. 

Prevention Is Always Better Than Cure

The FDA has licensed numerous products for the prevention of heartworms in dogs. All of these drugs mandate a prescription from a veterinarian. The majority of products are administered monthly, either by a topical liquid applied directly to the skin or through an oral pill. Chewable and non-chewable oral pills are available. A single product is injected under the skin every six to twelve months, and a veterinarian can only administer the injection.