Do you recommend skipping a month or two of heartworm prevention in the winter?
I recommend using heartworm prevention every 30 days, year round. There are several reasons for this: Virginia has mild weather and mosquitoes are unpredictable; heartworm prevention actually “back kills” heartworm instead of truly preventing heartworm; most heartworm preventives also prevent against some common intestinal parasites which are infective all year long.
Heartworms (Dirofilaria immitis) are spread by infected mosquitoes. Several different species of mosquito carry Dirofilaria immitis. The mosquitoes transmit heartworm larvae from infected dogs into the bite wound of healthy dogs while feeding.
The larvae develop in tissues then migrate to the heart and lungs where they mature into adult worms. The adult worms then produce microfilariae (baby heartworms) that travel through the bloodstream. Heartworm disease can be fatal in dogs if left untreated.
The entire heartworm life cycle takes about 6 and 1/2 months with approximately 6 months of it occurring in the dog. Common signs of heartworm infection range from no symptoms at all to coughing, exercise intolerance and difficulty breathing.
Heartworm treatment is expensive and can have side effects. Sometimes, treating heartworm still leaves behind residual disease in the heart and/or lungs depending on how severe the infection and how long it has been left untreated. Therefore, it is much easier to prevent by giving your pet prevention every 30 days.
“Back killing” means the heartworm preventive will kill any heartworm infection transmitted in the last 30 days. The preventive kills the immature heartworms in dogs today, but won’t have any effect on heartworm larvae introduced tomorrow.
It is important to use year-round heartworm prevention in cats as well. Cats can also get heartworm disease with prevalence in Virginia of 6-10%. And of these heartworm positive cats, 25% are indoor only. Heartworm disease isn’t quite the same in cats as most damage occurs in the lungs.
Heartworm testing in cats is not as reliable as in dogs and there is no treatment for cats with heartworm, only symptoms can be controlled. Therefore, prevention is key.
There are different ways to prevent heartworm, including oral and topical preparations. The most common parasites covered as a prevention (not treatment) in heartworm medications are roundworms and hookworms. These parasites are potentially zoonotic (transmissible to people). This is another reason it is important to use heartworm preventive all year.
Roundworms can infect people by accidentally ingesting roundworm eggs (found in soil or other contaminated objects).
In people, roundworms migrate through the body, causing damage as they go. They can damage the lungs, heart, liver and brain.
They can also cause impaired vision or blindness. In the United States alone, roundworm infection in people is in excess of 10,000 cases per year according to the Center for Disease Control. In dogs and cats, roundworms can cause diarrhea, vomiting, weight loss, poor appetite, and abdominal distention.Hookworms can infect people by the larvae penetrating the skin or by accidentally ingesting infected soil or other fomites.
Hookworms also cause damage as they migrate through humans. These parasites usually migrate just below the surface of the skin causing itchiness and rashes although they can penetrate deeper into the body affecting internal organs.
In dogs and cats, hookworms can cause anemia, diarrhea or constipation, decreased appetite, weight loss and even death.
Certain preventives may also include ingredients that help prevent whipworm, fleas and/or ticks.
Whipworms are parasites that will not infect humans, however they are very difficult to get rid of once in the environment. Whipworms can cause large bowel diarrhea, weight loss and anemia.
Please discuss your pet’s lifestyle with your veterinarian to determine the best option for you and your family.