Evidence of Drug-Resistant Heartworm Found in Louisiana


Parasite prevention is still an important part of your pet’s health regimen. By: SkitterPhoto

Heartworm infection and tick-borne diseases are on the rise across the country. Parasites are getting more sinister. It’s getting harder to control and prevent these infections.

A recent report out of Louisiana has identified a drug-resistant strain of heartworm, meaning the heartworm preventatives we have relied on for years do not work on this particular strain.

A lovely Louisiana Labrador named Maddie, supposedly on monthly preventative, presented with a drug-resistant strain of heartworm. Maddie’s blood was sent to the Department of Infectious Diseases at University of Georgia. The lab confirmed the Lab’s infection, naming the strain Metairie-2014.

How This Happened

This story should not be alarming but thought-provoking. Heartworm resistance is still very rare. The vast majority of dogs who take a monthly heartworm preventative like Heartgard or Interceptor will not develop a heartworm infection.

But more drug resistance is likely to occur. Usually, when we begin to document a handful of resistant cases, there are more cases on the horizon.

1. Endemic Locations

To date, true drug-resistant heartworm infections have only been documented in the Mississippi Delta, an area where the disease is endemic and there are extremely high rates of transmission by mosquitoes.

Veterinarians have been discussing resistant strains for years, without a lot of concrete evidence or epidemiological data. The Metairie-2014 strain is now proof.

2. No Mosquito Protection

A heartworm-infected mosquito must bite your dog and transmit the heartworm microfilaria into their body. The oral heartworm preventatives then kill this very early stage of heartworm in your dog.

But if you also protect your dog from getting bitten by the mosquito in the first place, your dog is doubly protected. A product such as Advantage Multi offers this double protection.

3. Improper Administration of Preventative

Your dog must receive a monthly preventative every month and on time to get the most effective protection. Living in an endemic or warm climate area means it is imperative to give year-round heartworm protection.

4. Excessive Exposure to Mosquitoes

Mosquitoes are more prevalent at certain times of day and in certain areas, such as around lakes and ponds. Keeping your dog or cat inside in the early morning and at dusk, for example, and away from mosquito breeding grounds — like standing water — helps.

5. Mosquitoes in the House

Poor screens, open doors and the wrong kind of lighting can invite mosquitoes into your home. Do everything you can to keep mosquitoes out of the house.

Always check your dog for ticks after playing in a grassy or wooded area. By: Andy_van_Dyk

Don’t Be Blasé About Beastly Bugs

It never ceases to amaze me how blasé or lackadaisical some folks can be about parasites, their pets and themselves. Since we live in a first-world country, many Americans don’t think of parasitic infections as a part of daily life.

We tend to believe parasitic infections only occur in the poorest peoples in tropical areas. If this narrow and inaccurate attitude extends to our pets, people will not take parasite control, heartworm preventative and tick control seriously.

To prevent heartworm and tick-borne disease, preventatives should be used year-round.

But many people don’t think like this — they need to see the first tick on their beloved pooch before they think about tick prevention. Or worse, they have to hear about a person getting Lyme disease or suffer an embedded tick in their own arm before they are propelled to take action and use prevention for their pet.

The same goes for heartworm. It often takes the first day in June when my Northeast area gets hit with the first night of swarming mosquitoes to make some of my clients think about heartworm prevention.

The Staying Power of Parasites

Parasites have 2 ideas in their conniving little beings: to stay alive and to infect more hosts. They put their sneaky, sadistic parasitic thinking caps on and figure out ways to become resistant to our drugs, infect more vectors and travel to more areas.

Heartworm and tick-borne diseases are 2 prime examples of how inventive parasites can be. Heartworm infection used to be found in only certain states but now is found in all 50. In the endemic area of the Mississippi, the crafty worms are mutating to become drug-resistant.

Lyme disease, Ehrlichia and anaplasmosis — all tick-borne diseases — are also increasing in prevalence each year. Warmer temperatures are another risk factor for all these infections, and the global warming trend is not reversing.

Here are some heartworm signs to watch out for in dogs:

Out of Sight, Out of Mind

The term “heartworm” doesn’t mean a lot to some folks. I’ve even been told by clients that they don’t believe in heartworms. Like fake news, they think heartworm disease is a fake or minor disease made up by vets to make money. Well, let me share this gross-out story with any nonbelievers out there.

When I was a young vet, an old dog patient of mine with a serious heartworm infection and cancer was suffering. His human asked me to euthanize him and then asked for a necropsy to document the cancer. After the euthanasia, she said her goodbyes and left. I performed the autopsy within a few hours.

After documenting the hemangiosarcoma (cancer) in the abdomen, I looked at the heart. Upon cutting into the heart, what seemed like thousands of live heartworms wriggled and spewed out of the interior chambers — the heart was literally bursting with heartworms. My poor technician screamed. I remained calm but knew I’d be having some nightmares in the future.

That necropsy still comes to mind frequently when a client tells me they don’t think heartworm prevention is all that necessary. Although I would never wish my necropsy experience on anyone, perhaps my story will make everyone take heartworm and parasite prevention more seriously. An ounce of heartworm prevention is worth a pound of difficult, sometimes impossible cure.


This pet health content was written by a veterinarian, Dr. Debora Lichtenberg, VMD. It was last reviewed Jan. 10, 2018.

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