June 22, 2024


Heartworm illness is a deadly infection that causes severe lung disease, heart failure, organ damage, and death in dogs, cats, and ferrets. Dirofilaria immitis, a parasitic worm, is the cause. 

The worms are transmitted via a mosquito bite. The dog is the definitive host, which means the worms grow up, mate, and create offspring while living within the dog. 

The mosquito serves as an intermediate host, which means that the worms spend a brief time inside the mosquito before becoming infective (able to cause heartworm disease). 

The adults of the worms are termed “heartworms” because they dwell in an infected animal’s heart, lungs, and blood vessels.

Adult female heartworms discharge their offspring, called microfilariae, into the bloodstream of an infected dog. When a mosquito bites a microfilariae-infected dog, the mosquito also becomes sick. While living inside the mosquito, the microfilariae develop into infective larvae over the next 10 to 14 days, depending on the environmental conditions. 

white and brown cockerspaniel

To become infective larvae, microfilariae must pass through a mosquito. When an infected mosquito bites another dog, the infective larvae pass through the bite wound to the dog. In a freshly infected dog, it takes roughly 6 to 7 months for infective larvae to grow into adult heartworms. The lifecycle is completed when adult heartworms mate and the females discharge their young into the dog’s bloodstream.

Is Heartworm Contagious? 

Heartworm disease is not contagious, which means that a dog cannot contract it by being near an affected dog. The only way to contract heartworm disease is to be bitten by a mosquito.

Adult heartworms have the appearance of cooked spaghetti strands, with men reaching 4 to 6 inches in length and females reaching 10 to 12 inches. The amount of worms living inside an infected dog is referred to as the worm burden. The typical worm burden in dogs is 15 worms, although it can range from 1 to 250. Heartworm can live up to 5 to 7 years inside a dog.

Can A Vet Cure Heartworms? 

A veterinarian will utilize blood tests to check for heartworms in a dog. Antigen tests detect specific heartworm proteins, known as antigens, secreted into the dog’s bloodstream by adult female heartworms. The heartworm proteins can be discovered in a dog’s bloodstream 5 months after being bitten by an infected mosquito. Antigen tests can reveal infections with one or more adult female heartworms in most cases.

Adult heartworm infection is indicated by the presence of microfilariae in the bloodstream. Microfilariae can be found in a dog’s circulation about 6 months after an infected mosquito has bitten it (because it takes about that long for the heartworms to develop from infective larvae into adults that mate and produce microfilariae). Another test detects microfilariae in a dog’s circulation.

Labrador Retriever, Dog, Pet, Tongue Out

Before initiating heartworm prophylaxis, all dogs over 7 months should be tested for heartworms. Heartworms can live and thrive within a dog that appears healthy on the exterior. If a dog with heartworms is not tested before starting a preventive, it will stay infected with adult heartworms until it becomes sick enough to display symptoms. Heartworm preventatives do not kill adult heartworms. Giving a heartworm preventive to a dog with adult heartworms can also be dangerous or fatal. If microfilariae are present in the dog’s bloodstream, the preventative may cause them to die rapidly, resulting in a shock-like reaction and death.

Heartworm illness is commonly visible in dogs with high worm burdens, who have been affected for a long time, or who are particularly active. The number of worms residing inside the dog (the worm burden), the length of time the dog has been contaminated, and how the dog’s body reacts to the presence of heartworms all influence the severity of heartworm illness. The dog’s activity level influences the severity of the disease and the onset of symptoms. Heartworm disease symptoms may be difficult to detect in dogs with low worm burdens, who have just been affected, or who are not very active.

Let us know in the comments if you have ever heard of heartworms before… 

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