Why Animal Humane Society transports and treats heartworm positive dogs

August 15, 2019

There’s no disease more expensive and painful to treat yet easier to prevent. No disease more commonly vilified by pet owners and as frequently misunderstood. There’s no disease that seals the fate of more shelter dogs or that more rescue organizations are unable or unwilling to take on. It’s been found in all 50 states, Canada, Europe, South America, and the Caribbean. It’s heartworm disease.

Animal Humane Society takes in more than 22,000 animals each year — more than every other rescue organization and municipal shelter in the Twin Cities combined. We’re fortunate to have resources that no other shelter in Minnesota has: a team of more than 20 veterinarians, an in-house pharmacy and surgery suite, and the ability to treat hundreds of dogs with heartworm disease each year.

Leading the pack

The majority of animals who arrive in our care come from local owner surrenders and strays found in our community. Successful spay and neuter efforts continue to reduce the homeless pet population in Minnesota. Meanwhile, the number of Minnesotans hoping to adopt is growing. Animal Humane Society’s transport program not only helps adopters find a new pet, it furthers our commitment to helping animals in need, no matter where they are. And most of the animals transported to AHS are coming from overcrowded southern shelters where heartworm disease is more prevalent.

2016 Heartworm map

2016 Heartworm incidence map, American Heartworm Society

It's lifesaving work — and not just for the animals that are transported north. When AHS takes in an animal from an overcrowded source shelter, it frees up the space and resources needed to care for another animal in that community — an animal who may not have otherwise been given a chance.

The benefits don’t stop there. We’re actively partnering with southern shelters to provide education, share resources, and even deliver free medical supplies.  

Each month, we take in between 600 and 800 dogs from partner shelters. AHS isn’t the only animal welfare organization in Midwest with a transport program, but we are one of the only shelters with the expertise, resources, and willingness to take in dogs that test positive for heartworm. In 2019, we took in 350 dogs with heartworm — more than any other shelter or rescue group in Minnesota. According to the ASCPA most Minnesota shelters will open their doors to 1-2 heartworm positive dogs per transport. At AHS, we allow up to 10% of every transport to consist of heartworm positive dogs.

“In many of those southern shelters, more than 80% of adult dogs are heartworm positive,” says Dr. Graham Brayshaw, Chief Veterinarian at Animal Humane Society. “Transporting just a few of these dogs to Minnesota frees up significant resources in those communities, allowing them to focus on reducing overpopulation and preventing the needless euthanasia of animals with treatable conditions. Every heartworm positive dog we take in will help those source shelters save more lives.

Meet Tiff


Tiff, a gentle yellow Lab, was abandoned in the Mississippi Delta region. She was rescued and brought to a shelter in Mississippi, where shelter staff discovered Tiff was infected with heartworm. The shelter had no way to treat it. At just a year old, Tiff’s fate was grim — until AHS agreed to take her in.

By the time the sweet, young dog arrived in Minnesota, she was suffering from grade four heartworm, the most severe grade of the disease. We started treatment immediately.

Now, Tiff is heartworm free. She has a long life ahead of her, and a loving new home to spend it in.

But not every shelter is willing or able to transport dogs with heartworm. To understand why, you need to know a bit more about heartworm disease — what it is, what it isn’t, and more importantly, how it’s spread.

Understanding heartworm

Heartworm is an internal parasite that’s transmitted through the bite of an infected mosquito. Just one bite is enough to spread the disease. After being bitten, heartworm larvae begin to develop in the tissue of your pet. If your dog is on a monthly heartworm preventative, the active ingredients will kill larvae and prevent them from growing into adult worms. Without preventatives, the larvae develop and move into your dog’s blood stream, eventually making their way to his heart.

Adult heartworms look like strands of spaghetti and can reach up to 12 inches in length. Left untreated heartworms can cause heart and lung damage, organ failure, and even death. Unfortunately, treatment is costly, painful, and time intensive.

A painstaking treatment

At a private vet clinic, heartworm treatment can cost upwards of $1,000 — or more for large dogs. Treatment often requires up to a month of pre-op antibiotic therapy before it can begin. After, an arsenic substance is injected deep into a dog’s muscle tissue to kill the adult worms — it’s a painful process that often leaves dogs uncomfortable and sore. Thirty days later, the injection is repeated.

Lee-lah came to AHS on a transport from the south.

Unfortunately, treatment doesn’t end there. As the worms die they must dissolve in the dog’s body — a process that takes up to eight weeks. During this time, dogs must remain on a strict exercise restriction. If a dog becomes too active, serious complications can occur.

This painstaking treatment process explains why many shelters can’t take on the burden of treating more than a handful of heartworm positive dogs at a time. It’s too costly — both financially and in terms of resources and time. So why take on the expense? Because, when the medical care is provided, dogs with heartworm aren’t just treated, they’re cured.

As experts in shelter medicine, we’ve refined a treatment approach that works for the unique needs and challenges of a busy animal shelter. Utilizing heartworm preventatives along with antibiotics, a shorter timeframe between injections, and a committed group of foster volunteers, we’ve successfully treated thousands of dogs while limiting their stay in shelter. We’re incredibly proud of these efforts. But not all animal lovers are proponents of this lifesaving work.

Is it worth the risk?

A lack of resources isn’t the only obstacle heartworm positive dogs face. Some shelters and rescue groups refuse to transport the sick canines. Our neighbors in Wisconsin, for example, have banned the transport of heartworm positive dogs entirely — in fear the disease will spread.

It’s important to remember that heartworm disease isn’t spread from dog to dog. It can only be spread by mosquitoes, and thanks to our long, cold winters, the window in which mosquitoes can transmit heartworm is quite narrow. Additionally, AHS is doing even more to limit potential transmission.

By starting treatment immediately, we ensure that Microfilaria — the baby worms that are transmitted to mosquitoes — are killed as soon as possible after each dog arrives in Minnesota. In fact, some dogs receive this first step of treatment before they make their journey north. This greatly reduces any risk that a heartworm positive dog from the south could spread the disease.


We’re also breaking down barriers so every pet owner in our community can access heartworm prevention. Preventatives are highly effective, but they can be a hardship for some pet owners to obtain. Animal Humane Society Veterinary Centers offer cost-effective products and services to animal lovers, with additional discounts based on income, so that all families can protect their pets and limit the spread of disease.

It’s important to note that heartworm seems to be on the rise in large, urban cities. Some critics are blaming shelters (like AHS) that offer transport programs. However, incidence rates are calculated by the average number of cases per clinic — without regard to population. “Anywhere that you have denser populations of people and animals, you’ll see more instances of disease,” says Dr. Brayshaw. “It’s not that heartworm disease is more prevalent in metropolitan areas now, it’s simply proportional to the number of people and pets living in these areas.” As the population of people and pets grows, the number of heartworm cases will naturally grow along with it.

There’s no way to completely eradicate the spread of heartworm, but the risk is low, and we do everything within our power to limit it even further.

Doing the most good


To cure a heartworm positive dog from the south is to give that dog her life back. It’s the ultimate second chance — and second chances are what we’re all about.

“Our focus is always on doing the best we can for animals” says Dr. Brayshaw. “For us, heartworm disease is just one small part of the whole landscape of animal welfare that we work in. And we don’t want this one small thing to get in the way of so much good.”

It’s a huge undertaking, but we’re lucky enough to have the resources to help these dogs thanks to our supporters.

Animal lovers in our community have ensured we don’t have to choose between helping an injured dog in our own backyard or a sick stray many states away. An animal in need is an animal in need — and dogs with heartworm disease will always have a place at Animal Humane Society.