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Christopher Rehm, DVM

Making the Case for Heartworm Prevention in Cats

Elizabeth Clyde Druin, DVM
Owner, Clyde's Animal Clinic, Matton, Illinois

Making the Case for Heartworm Prevention in Cats

While they are harder to diagnose than dogs,While they are harder to diagnose than dogs,cats get heartworm disease, too

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Q. You’re a big believer in heartworm prevention in cats. What has driven that belief?

A. I saw my first feline heartworm case more than 25 years ago. The cat had died suddenly, so I performed a necropsy and found two adult heartworms in the heart. Back then, there were no preventives for cats, and veterinarians and owners were largely unaware of the problem. Today, awareness is higher and we have several products to choose from, which makes compliance easier. But we still have a long way to go.

Tackling Tough Conversations

AHS 18 Winter Bulletin PDF

About Heartworm Treatment Costs

Christopher Rehm, DVM
President, AHS; Owner, Rehm Animal Clinics of Mobile and Baldwin Counties Mobile, Alabama

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Q. Breaking the news to an owner that a dog has heartworms and needs treatment isn’t easy, and explaining the costs can compound the difficulty. How do you justify the cost of treatment to a client who has trouble paying for it?

A. No question, heartworm treatment is expensive. In my southern Alabama practice, I work with many clients and rescue groups with limited resources, so I understand how difficult it can be to discuss these costs with clients. My approach is to explain that I’m recommending what’s best for the pet’s long-term health. Beyond eliminating heartworm infection, the disease caused by damage to the cardiopulmonary system can be long-term. The treatment protocol we use can make a difference in minimizing disease over time.

The Wrath and Aftermath of Hurricanes

AHS 18 Winter Bulletin PDF

What are the Implications for Heartworm Infection?

by Clarke Atkins,DVM, DACVIM

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Q. Historically, what do we know about the connection between devastating storms and heartworm incidence?
A. While high winds associated with hurricanes may reduce mosquito populations for a short period of time, resultant standing water and non-functioning mosquito abatement programs allow extensive mosquito blooms. Hurricanes also cause destruction, evacuation and financial misery in affected areas. Because of reduced care or abandonment (an estimated 250,000 dogs were abandoned in New Orleans alone after Hurricane Katrina), massive numbers of dogs miss doses of heartworm preventive and suffer exposure to mosquitoes 24 hours a day. In heavily endemic heartworm areas, where many dogs are already infected with heartworms, the result can be a heartworm epidemic.

The AHS Guidelines: 2018 Updates

AHS Jul 18 Summer Bulletin PDF

Guidance on Prevention, Testing and Treatment

by Tom Nelson, DVM

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While heartworms are a tough opponent, knowledge is a powerful weapon. To arm veterinarians with the most up-to-date and comprehensive information about heartworm management, the American Heartworm Society (AHS) created guidelines on heartworm prevention, testing and treatment, as well as heartworm epidemiology and biology. Guideline revisions are published as needed, based on sound principles of heartworm management. The 2018 guidelines include the following recommendations.

The AHS Protocol vs. “Slow Kill”

AHS Jul 18 Summer Bulletin PDF

by Andrew Moorhead, DVM, MS, PHD, DIP

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Heartworm treatment can be time consuming and expensive, causing some clients to balk when presented with a treatment plan. Because heartworm is both serious and progressive, I advise clients that treatment is no place to cut corners.

Q. What is the rationale for the steps involved in the American Heartworm Society (AHS) heartworm treatment protocol?

A. The AHS protocol starts with administration of a macrocyclic lactone (ML) drug on Day 1 and Day 30 of treatment, along with oral doxycycline at 10 mg/kg BID on days 1–30.

  • Giving the ML eliminates any juvenile stages of worms that might be present. Melarsomine is not labelled for treatment of worms less than 4 months or age
  • Administering doxycycline eliminates Wolbachia bacteria. This bacteria plays a key role in heartworm pathogenesis, and eliminating Wolbachia signifi- cantly reduces inflammation and worm mass, thus decreas- ing the severity of pulmonary thromboembolisms (PTE).
  • Glucocorticoids should also be given as needed to control clinical signs of PTE.

Why Don’t Clients Give Heartworm Preventives?


While pet numbers in the U.S. are increasing, the number of annual heartworm preventive doses sold in the U.S. is declining. I believe this is a frightening trend, especially considering that the average number of heartworm cases per veterinary clinic rose by 21% between 2013 and 2016.1

I recently researched medication adherence in human patients2 in order to better understand why people don’t take their own medications. In the process, I learned that the reasons my clients don’t give pets heartworm preventives as directed are similar to the reasons they skip their own cholesterol, diabetes and blood pressure medications.


Relocate Dogs—Not Heartworms

by Brian A Digangi, DVM, MS, DABVP

Q. The American heartworm Society (AHS) and the Association of Shelter Veterinarians (ASV) recently released a set of best practices for transporting dogs. Why?

A. The AHS and ASV saw a need for heartworm-specific transport recommendations to guide veterinarians and animal shelters. Heartworm disease has become more widespread in the U.S. over the past several decades, due in part to the increased movement of heartworm-positive dogs to regions where heartworm disease was once uncommon. When mosquitoes feed on a microfilaremic dog, they become heartworm vectors capable of transmitting heartworms to unprotected pets.

Is it Negative or Not? The Role of Heat Pretreatment in Heartworm Testing


by Brian A Digangi, DVM, MS, DABVP

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Veterinarians today are fortunate to have several point-of-care heartworm tests. In the majority of cases, these D. immitis antigen tests meet practitioners’ needs for speed and accuracy. However, when test results conflict with clinical expectations, the added step of heat pretreatment (HPT) of the sample should be considered.

Q. What can cause a “no antigen detected” result when the patient is infected?

A. Patient-side diagnostic tests rely on the presence of soluble heartworm antigen for the detection of heartworm infection. In cases where soluble antigen is bound to endogenous antibodies, forming an insoluble unit in the bloodstream known as an “immune complex,” the antigen is essentially blocked from detection. This blocking has been linked to several factors:

AHS Survey Finds Increase In Heartworm Cases

AHS Jul 18 Summer Bulletin PDF

Is heartworm incidence up or down in your practice area?

by Christopher J Rehm, DVM

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The latest American Heartworm Society Heartworm Incidence Survey has uncovered both challenges and opportunities for veterinarians in practice. On one hand, heartworm incidence has inched upwards in the three years since the AHS survey was last conducted. On the other hand, the power to reverse this upward trend is, quite literally, in our hands.


April is Heartworm Awareness Month


APRIL IS HEARTWORM AWARENESS MONTH and the ideal time to discover the many resources available from the American Heartworm Society (AHS). Our goal: to arm you with the knowledge and tools you need to defeat this serious parasite.

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RT @AHS_Think12: Thinking about slow kill as a protocol in your practice? In this mini-lecture, veterinary cardiologist Dr. Clarke Atkins s…

by Heartworm Society