Veterinarian Column: Heartworm prevention in dogs

by スタッフAlice’s Dog & Cat

If you visit a veterinary hospital in the spring for rabies or vaccinations, won't they recommend heartworm testing and purchasing preventative medicine? I'm sure there are many people who take tests and purchase preventive medicines just as they are told to do at the veterinary hospital. This time, we will answer pet owners' questions about heartworms, such as the necessity of testing and prevention, and the types of preventive drugs.

◎ Filariasis

Canine heartworm disease is a disease in which heartworms transmitted by mosquitoes infect the heart and pulmonary arteries of dogs. Symptoms vary depending on the number of infestations, but include respiratory symptoms such as coughing and ascites accumulation due to poor circulation. If the parasite moves from the pulmonary artery to the right ventricle, right atrium, or vena cava, resulting in a condition called vena cava syndrome, there is a risk of sudden death.

◎ Treatment method

Currently, there are no deworming drugs for adult worms on the market, so the general treatment is to wait until the adult worm's lifespan. It is difficult to remove adult worms with surgery.

Therefore, it is important to take preventative measures to prevent adult parasitism.

◎ Prevention period

Start time: 1 month after mosquitoes start flying

When to finish: 1 month after the mosquitoes are gone

The period of protection depends on the period of mosquito activity and therefore varies by region. In Tokyo, prevention is recommended from May to early December .

◎ Why is prevention necessary even if mosquitoes are gone?

It is important to administer preventive medicines one month after the mosquitoes have disappeared.

When a dog is bitten by a mosquito, heartworm larvae enter the dog's body. Once inside the dog's body, the larvae repeatedly shed their skin and grow under the dog's skin and muscles. By administering preventive drugs at this time, the larvae will be dewormed all at once. If you forget to take your medication, the grown heartworms will travel to your heart. Preventive drugs are not effective against heartworms that have moved to the heart or pulmonary arteries. It is important to remember to administer it once a month.

Why is a test necessary before administering preventive drugs?

If your dog is infected with heartworms and the infected adult heartworms have given birth to larvae, administering a preventive drug will kill a large number of larvae in the dog's body, causing the dog to go into shock. Because it can happen.

◎ Types of heartworm medicine

Differences depending on the type of parasite that can be prevented

① Only for heartworm prevention

Advantages: cheap

Disadvantages: Fleas and ticks require other methods of prevention.

②Things that can prevent heartworms and parasites such as fleas and ticks

Advantages: One dose can prevent several types of parasites.

Disadvantages: Expensive compared to ①

Differences in administration methods


Advantage: Cheap. Safe to use even for dogs with allergies.

Disadvantages: Dogs may realize it's medicine and won't eat it, so you may have to shove it deep into their throats to get them to drink it.

②Chewable type

Advantages: Good palatability.

Disadvantages: If you have food allergies, you may not be able to use it. If the dog won't eat, it will be difficult to administer the medication.

③Spot type (type that drips onto the skin)

Advantage: Can be easily administered to pets who dislike oral medication.


Advantages: One injection is effective for one year, so there is no need for medication. Prevents missed doses.

Disadvantages: Pain during injection. The dose of the drug is determined by body weight, so it cannot be used during the growing period.

It is important to remember to take heartworm prevention once a month. Recently, preventive medicines are sold online, but in order to use preventive medicines safely, it is best to undergo a test before administering them. When it gets cold in December , the mosquitoes disappear, so it's easy to forget about preventive measures, so be careful not to forget that the last preventative measure is important.