Heartworm disease is a parasitic disease that is transmitted (in the microscopic stage) by mosquitoes to their dog, cat and other animal hosts. The microscopic worm larve grow up in the animal host's heart to become long, spaghetti-like (round) worms that cause heart and lung damage.
According to the American Heartworm Society, "When the mosquito then bites another dog, cat, or susceptible animal, the larvae are deposited on the skin and actively migrate into the new host. For about 2 months the larvae migrate through the connective tissue, under the skin, then pass into the animal's venous blood stream and are quickly transported to the arteries of the lung. It takes a total of approximately six months for the infective larvae to mature into adult worms that begin producing offspring, microfilariae. Adult heartworms can live for five to seven years in the dog." (read more)
Left untreated, they can cause death in the host animal. This is definitely a disease that is much easier to prevent, by giving a monthly heartworm preventative, than to treat.
Information gathered about heartworms, prevention and treatment has grown considerably over the last 20 years. In this interview, Dr. Wallace Graham, 2011 president of the American Heartworm Society, brings us up to date on the latest heartworm incidence reports, treatment guidelines and prevention of heartworm.
1) Q: How have pet infection rates changed in the last 10 years in the US?
Dr. Graham: The American Heartworm Society (AHS) tracks trends in heartworm incidence using data from clinic heartworm testing and numbers of heartworm-positive dogs and cats in clinics across the country. Based on our Heartworm Incidence Surveys conducted every three years, (2001, 2004, 2007, 2010), heartworm infection is a problem in every state in the continental US.
It is surmised that weather patterns impact mosquito populations, thereby having some bearing on the transmission of heartworms. Although the 2010 incidence map indicates that the new infections are more densely located due to the generally dry year that 2010 was, the actual number of cases reported showed little change.
Unfortunately, heartworm prevention administration has been declining over most of this time, beginning before the economic downturn.
2) Q: What are the current recommendations for heartworm testing and prevention? What about pets who do not travel and live in non-mosquito areas?
Dr. Graham: The AHS recommends twelve months of prevention for every pet and yearly testing. Certainly, some pets are at higher risk than others but the risk is zero for very few. The cost of prevention is minor compared to costly treatment and strict, lengthy cage confinement, while the upside benefits (including decreasing the potential for zoonosis by most preventive products) are so great, there is little to argue against the use of preventives.
3) Q: Are heartworms becoming resistant to some preventatives?
Dr. Graham: We have no studies that show that any population of heartworms is resistant to current preventives, when used as prescribed.
That being said, there are some preliminary studies that have the scientific community's attention and that indicate the need for further study. I am certain that there are studies under way that will help shed light on this topic. As soon as more information is available, AHS will help disseminate it as widely as possible.
4) Q: What are the current "best practices" for heartworm treatment in dogs? Cats?
Dr. Graham: Please refer to heartwormsociety.org and visit our Veterinary Resources section for current veterinary guidelines on canine heartworm patients and feline heartworm patients.
5) Q: Could you comment on the heartworm adulticide shortage?
Dr. Graham: We recommend that veterinarians follow the AHS endorsed interim management plan to ensure the health and safety of their patients. While the following is a brief summary, veterinarians are advised to visit heartwormsociety.org for the complete plan.
The goals of the interim plan endorsed by AHS include:
- Reduce potential pathology from the infection
- Maintain the health of the heartworm-positive dog until it can be appropriately treated
- Prevent additional heartworm infection of the dog
6) Q: For veterinary professionals - could you please tell us more about "Heartworm University" and the current call for samples of microfilaria and/or heartworms for a genetic study?
Dr. Graham: New information about heartworm disease, including its diagnosis, prevention and treatment, is flowing in volumes compared to the trickle of information we had during most of the 1990s.
Heartworm University brings the latest information we have as an industry, along with nationally recognized speakers, to veterinarians who practice in heartworm-endemic areas. Attendees are involved in interactive learning sessions in courses ranging from controversial issues to recent developments in disease pathophysiology, diagnostics, screening and testing, treatment protocols, prevention strategies, and pet owner counseling.
Along with AHS developments, a veterinary researcher has put out a call to veterinarians in the collection of heartworm samples to better understand the genetic differences among heartworm populations around the country. More information on this genetic survey sampling and how to provide assistance can be found on heartwormsociety.org
Thank you, Dr. Graham, for taking the time to answer these important questions about heartworm awareness.
About Dr. Graham
Dr. Wallace E. Graham, Jr. founded Wooldridge Creek Animal Hospital in 1982. Since then, Dr. Graham and staff have continued a tradition in compassionate Veterinary care in Corpus Christi and surrounding areas.
Learn More: About The American Heartworm Society
