Symptoms of Heartworms in Dogs

Heartworms in dogs are parasites that are transmitted through mosquitoes. These parasites are known as Dirofilaria immitis, but are called heartworms, as they lodge in the heart. An infection with heartworms is severe in dogs. Unfortunately, the symptoms are subtle and may pass unnoticed. The worms can affect cats and other wild animals, in addition to dogs.

Stages of Development of Heartworms

Heartworms are transmitted through mosquitoes. They have several life stages, and when they reach adulthood they infect the heart of the host. The mosquito passes the larval heartworms to the host and the larva develops for 1 week under the skin of the host, after which it will migrate to the muscles, chest and stomach of the dog. This stage lasts up to 2 months.

4 months after the mosquito bite, the immature heartworms will enter the blood flow and migrate to the heart, lodging in the pulmonary artery. Here, the worms will grow and mature. The females can reach up to 12 inches in length, while males can grow 9 inches long.

The worms require up to 7 months to reach adulthood. This period is also known as the prepatent period.

When the worms mature, they will reproduce, giving birth to microfilariae. The microfilariae will circulate in the bloodstream of the host and if the host is bitten by a mosquito, it will become a carrier, being able to infect other animals.

Symptoms of Heartworms in Dogs

Unfortunately, the dog will show no clinical signs during the first 6 to 7 months after the infection. The prepatent stage cannot be diagnosed.

In exceptional cases, a heartworm larva can accidentally end up in the eye, brain or leg arteries of the dog, in which case there will be blindness, confusion and lameness in the limbs.

After the worms reach adulthood, the dog may still present no symptoms. Some dogs may display lethargy; if the infection is more severe, the dog will show symptoms such as:

  • Dry coughing, especially after exercising; in advanced cases of heartworms, the dog will cough up blood
  • Tiredness; the dog will spend more hours sleeping and sitting
  • Early exhaustion after physical exercise
  • Vomiting
  • Lack of appetite; however, some dogs may enjoy a healthy appetite, even if infected
  • Weight loss, resulting from the lack of appetite
  • Fainting and sudden collapse
  • Difficulty in breathing
  • Depression; the dog will not show interest in activities

If the condition is not detected, the heartworm infection will advance and cause congestive heart failure.

Treatment Options

Heartworms can only be detected after the prepatent period. 6 or 7 months after the contracting of larvae, the heartworm antigens will be present in the blood.

The treatment of heartworms contains an arsenic based compound that is meant to eliminate the worms. Surgery may also be recommended if the infection is advanced.

Prevention of Heartworms

While you cannot prevent your dog being bitten by mosquitoes, you can get some medication that may prevent the development of heartworms. Typically dogs get ivermectin or Heartguard.