Heartworms are serious and dangerous canine parasites spread by mosquitoes. When these insects bite your dog they can transmit this parasite which can cause suffering and death. These worms travel to the heart and when mature can be a foot long. Adult heartworms are difficult to treat, so a good prevention program is necessary.

Dogs and cats in the Southeastern US are far more likely to contract this deadly parasite than pets in North Dakota or Montana. If you have not already done so you should get your pets screened. Don’t procrastinate just because mosquito season has passed. Your dog might already be infected.

Dogs get heartworms from female mosquitoes and mosquitoes get them from infected dogs. The parasite can’t complete its life-cycle without both animals. Young larvae called microfilaria live in the bloodstream. There are a total of six developmental stages. L1, L2 develop in infected dogs which become L3 larvae in mosquitoes. This process in mosquitoes takes about 10-14 days.

When an infected mosquito bites a dog it can transmit the L3 larvae into the new host canine. These can now become L4, then developing adults (L5) and finally mature adults (L6). Mature adults reside primarily in the right atrium of the heart. The entire lifecycle can take as long as seven years.

Most dogs with heartworm will be anemic, lack energy or be prone to coughing. They may also have high blood pressure, difficulty breathing and extremely rapid heart rate. Once the disease has reached this stage it is difficult and often dangerous to treat.

Your veterinarian can give you heartworm preventative. This will kill the L3 and L4 larvae and keep them from reaching later stages. This medicine must be administered monthly at regular intervals or L3 and L4 larvae will become adults. Once the next developmental stage is reached the preventative is ineffective.

At this point all is not lost. Your veterinarian can often still treat the problem but it’s tougher. Usually multiple treatments are necessary. Medications required to treat adults come with precautions. Activity should be reduced, for example.

Infected dogs are classed 1-4 with 4 being the worst. These dogs show serious heart problems and killing the adult worms too quickly could hasten death rather than prevent it. Globs of dead heartworms could clog the heart and lungs. Immature larvae are usually attacked first. Your veterinarian can give you more specific information, but this disease is nothing to ignore.

Mosquito season has passed, but heartworm larvae can live in your dog for a long time. However, there’s no need to be paranoid either. If your dog is receiving regular treatments he is safe even if you have another animal with heartworms. They can’t directly pass the parasite. It must go through a mosquito first and regular treatment will combat reinfection.

If some of this confuses you, talk to your veterinarian. That’s always the best policy. Cats and ferrets can also get the disease. Keep that in mind. Heartworm can infect people, but it is rare and the parasites can’t complete their life-cycle in humans, so you don’t have to worry about that.

Ted Manzer teaches agriculture at Northeastern High School.