Managing the Transport of Heartworm-Positive Dogs to Increase Lifesaving

In striving to become no-kill, shelters invariably come up against the challenge of finding positive outcomes for “challenging” animals. In regions plagued by mosquito activity, like the south, heartworm-positive dogs often end up in that category even though the disease is treatable. Most of these dogs shouldn’t be difficult to save, but when shelters are overwhelmed with heartworm-positive dogs and under-resourced to treat them, transport programs are vital.  

Shelters, rescues, and veterinarians in regions rarely faced with managing the illness are understandably leery of bringing in dogs who might transmit heartworms to other dogs in the area, and who require time-consuming and expensive treatment. Yet vets who have been working in heartworm-prevalent states know that the disease can be managed.  

It’s important that we find ways to help organizations understand the process of transporting and treating heartworm dogs safely and efficiently, so that more of them can be saved. 

Reducing Transmission Risk  

Heartworm is transmitted by mosquitos that have picked up some of the microfilaria swimming around in the bloodstream of a dog positive for the disease. Those microfilaria mature through a few stages so that they can pass on the illness when that mosquito bites other dogs. However, there are multiple things that can be done by shelters sending heartworm-positive dogs that will end the life cycle and prevent transmission on the receiving end.  

Though we’d prefer dogs got preventative before they became infected, it’s better late than never. Ideally, one of the following options should be administered prior to transport, but if that isn’t possible then they should be administered as soon as possible upon arrival: 

• A single dose of a moxidectin product like Advantage Multi will eliminate most immature heartworms.  
• Heartgard used in conjunction with an insecticide labelled to kill and repel mosquitoes (like Advantix) is also effective.  
• Shelters may also choose to administer a macrocyclic lactone preventative like ivermectin along with a dose of an isoxazoline insecticidal product such as Nexgard. The added benefit of the latter product is that it kills mosquitoes after they feed, thus stopping further environmental transmission. 

Choosing Transport Candidates 

Once a dog tests positive for heartworm, the severity of the disease can be presumed based on clinical signs. Mild cases can be asymptomatic or have a cough, whereas moderate cases have exercise intolerance and abnormal lung sounds in addition to a cough. Severe cases have all these symptoms, plus labored breathing, fainting episodes and fluid accumulation in the abdomen.  

Ultimately, the best candidates for transport are dogs who are three years or younger and are showing no symptoms of infection. Though older dogs with mild symptoms can be transported, receiving shelters should understand there is risk that they have long-standing or repeat infections if they live in a heartworm-prevalent area and have never had preventative.  

While the veterinary standard in private practice is to do further diagnostic testing prior to treatment, no test or combination of tests can accurately determine the number of worms present in an individual dog—and thus the extensiveness of the illness. In fact, vast numbers of heartworm adulticide treatments have been performed without the benefit of extensive diagnostic testing in shelters and private clinics across the country. Since shelters often are operating on slim budgets, foregoing such testing will save time, staff, and financial resources. 

Treating Heartworm-Positive Dogs 

If it’s possible for the sending shelter to begin treatment prior to transport, it should. It’s not practical, however, to expect source shelters to complete treatment before transporting any heartworm-positive dog. That would be ideal, but it’s unrealistic given the volume of heartworm dogs and the capacity constraints that drive the need for transport in the first place. 

Initial steps recommended by the American Heartworm Society (AHS) include the use of doxycycline and heartworm prevention for positive dogs. Doxycycline is effective against Wolbachia organisms, a symbiotic bacteria harbored inside heartworms. Eliminating these organisms will reduce microfilaria; it also weakens adult worms and prevents larval stages of heartworms from developing into adults. Dogs treated with doxycycline likewise have less pulmonary pathology associated with the death of worms during treatment. 

Because heartworm disease is endemic in areas of the country where other infectious disease is often prevalent (distemper, parvo), additional strategies to mitigate the risk of infectious disease during transport should be employed prior to beginning the protocol.  

The AHS-recommended heartworm treatment involves a three-injection melarsomine protocol for all dogs regardless of severity of infection. This protocol has shown 98% efficacy and a decreased risk of complications. If the sending shelter opts to start melarsomine injections, it should wait two to four weeks to transport dogs long-distance (though the decision whether to transport depends on the environment and its ability to hype up the dog).  

The details of the melarsomine protocol and a video walking you through the injections are  contained in our manual but the protocol involves a series of deep intramuscular injections given over a period of roughly four weeks. The first injection is given 60 days (or longer) after the first dose of heartworm prevention. The second injection is given four weeks after the first, and the third injection is given the following day on the opposite side.  

Prednisone is also dispensed after the first two injections to reduce the risk of post-treatment complications. Since many dogs experience pain following melarsomine injections, preemptive pain control is recommended. 

Recovering Heartworm Patients Successfully 

Safe, successful treatment also requires a well-managed recovery period, and that means dogs should begin strict activity restriction at the time of the first injection and continue for four to six weeks after each injection. A month is typically acceptable for asymptomatic dogs, though longer restriction is recommended for dogs demonstrating significant clinical signs.  

All told, this means eight to 10 weeks of restricted activity—and ideally, this will occur in a foster or adoptive home. In fact, the full treatment for heartworms can be administered within a willing foster or adoptive home, and the dog will further benefit from not having to spend any more time in a shelter. 

Fostering a heartworm-positive dog undergoing treatment is appealing to many people because the timeline is well-defined and even large, rambunctious dogs must be restricted. Trazodone can be used for very active dogs who aren’t super cooperative with being restricted to a crate for such a lengthy period. 

Treatment failures are uncommon with the three-injection protocol, though reinfection can occur if the dog doesn’t continue receiving preventative medication. It takes several weeks to months for dead heartworms to break down and receiving shelters should understand that recently treated dogs will continue to test positive for an extended period following treatment (even though no live worms are present). Some dogs will test negative within three to six months after treatment; some may remain positive longer. If a dog tests positive earlier than nine months, do not retreat but re-test at nine months.  

Changing Attitudes About Heartworm 

Even if shelters are receptive to accepting heartworm-positive dogs, some states have restrictions that make transport not possible. No matter if it’s a state, a shelter, or an individual vet, there will continue to be resistance if those of us who recognize that heartworm prevention, transmission, and treatment is well within our purview don’t force change.  

But to advocate for change, shelter vets need to be involved at a national, state, or even local decision-making level—and a big challenge in this profession is that most shelter vets don’t feel represented by organized veterinary medicine. Therefore they don't participate in the American Veterinary Medical Association or their state or local Veterinary Medical Association. 

If we don’t have a voice in those organizations, we can't impact change. When it comes to heartworm, we can come in with the scientific data that proves this approach, which is also what the American heartworm Society stands behind.  

The reason to effect change now isn’t simply due to the need for transports as a lifesaving option for these dogs. In theory dogs can become heartworm positive in literally any state.  

Sure, shelters in cooler climates probably won’t see heartworm in 20% of their dog population like southern shelters do, but odds are good that they will start seeing some. Understanding how to cut down transmission risk and treat the disease will mean they’ll be ready to help those dogs, too. Since vets play a vital role in the journey to no-kill 2025, that’s something we should all want. 

Erin Katribe, DVM, MS 
Best Friends Animal Society Medical Director 

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