Dog Heartworm:

Canine heartworms

What is the heartworm?

Heartworm (Dirofilaria immitis) is a large worm – the adult worm can be up to 14 inches long lives in the right side of the heart and pulmonary arteries of an infected dog. Dogs acquire heartworm infection through bites from infected mosquito with heartworm larva.
In the pulmonary arteries of an infected dog, the worm generates an inflammatory response. Presence of a lot of worms reduces the capacity of the heart and this heart must work extra hard to compensate the deficit.

Heartworms Lifecycle

During the initial stage, termed Microfilariae, female worms generate baby worms (larvae) directly after mating with adult males in the infected heart. These larvae, known as microfilariae, enter the circulatory system, awaiting ingestion by a mosquito during a blood meal. The mosquito acts as a vector usually transmitting the microfilariae to a new host. Heartworm hosts may include domestic dogs, coyotes, foxes, or occasionally other animals such as cats, ferrets, or rarely humans. Microfilariae can persist within the host dog for up to two years before perishing from old age. Moreover, they have the potential to be transmitted across the placental barrier to puppies from infected mothers.
Inside the infected mosquito: Within the mosquito, the microfilariae undergo development over several weeks. The microfilariae progress from L2s to L3s, the stage capable of infecting a new dog. This transmission typically occurs through the vulnerable skin of the dog’s nose, which is susceptible to mosquito bites. Inside the infected dog: When an infected mosquito bites a dog, the L3 larvae are not directly deposited into the bloodstream. Instead, they mature into L4 larvae within 1-2 weeks, residing in the skin until advancing into the L5 stage, known as young adults. Subsequently, these young adults migrate to the heart and pulmonary arteries, where they mature further and mate approximately five to seven months after initially entering the host. Consequently, testing puppies less than five months of age for adult heartworm antigen is typically ineffective.

Canine Heartworm Cycle

Heartworm disease Signs

A mild persistent cough, decreased appetite, exercise intolerance, fatigue after moderate activity, and weight loss. If you notice one or more of these symptoms contact your veterinarian or call our veterinary clinic in Newmarket Aurora area at 905-898-1010 even you already dewormed your dog. Deworming usually does not include medicine that can be effective against Heartworm.

Prevention and treatment

Heartworm preventive Medication such as Ivermectin, selamectin, and milbemycin based will kill microfilariae (fisrt stage larvae). However they have little effect (L5, young adult heartworms) or no effect against Dirofilaria immitis (adult heartworms). Veterinarians could use IMMITICIDE (melarsomine dihydrochloride) to kill adult heartworms.