AHS Board Speaks Out

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.

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.

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.

STEPHEN JONES, DVM

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.

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.

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:

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.

CHRISTOPHER J. REHM, DVM

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.

CHRIS DUKE, DVM

Q. I’m a big believer in heartworm prevention, but I find myself repeating my “heartworm 101” lecture over and over to clients. Is it worth it?

TOM NELSON, DVM

Q. While the American Heartworm Society (AHS) recommends year-round heartworm prevention for dogs and cats, many veterinarians and owners take a seasonal approach. What is the AHS’ rationale?