Animal House: Heartworm Disease Updates

Animal House: Heartworm Disease Updates

During a conversation with Dr. Howard Acree of Cedar Hills Animal Hospital, the question came up regarding the necessity to continue monthly heartworm treatment for my senior dog Sylvia, 17. Sylvia is in excellent health for her age but only enjoys brief walks outdoors due to anxiety caused by her near-total blindness. Staying indoors limits her exposure to the mosquitoes that carry heartworm disease, which prompted the discussion.

Dr. Acree assured me that monthly heartworm prevention medication is still necessary year-round for all dogs, even indoor dogs and especially in Florida. He said heartworm-infected mosquitoes could survive Florida’s mild winters and fly inside homes through open windows, doors, or into cars or garages to infect unprotected pets. It only takes one mosquito bite to transmit microscopic heartworm larvae, causing heartworm disease. Dr. Acree began his veterinarian practice in 1987 and is a former Veterinarian of the Year, honored by the Florida Veterinary Medical Association.

Because heartworm disease is found in every state, with consistently high numbers of cases throughout the U.S., heartworm prevention, early detection and treatment is an ongoing scientific focus of veterinarian research. Heartworm experts strive to reduce the number of confirmed cases while improving diagnosis accuracy, prevention choices, treatment options and safety. The American Heartworm Society (AHS) provides regular disease prevention updates that explain how mosquitoes transmit heartworms, how to prevent and treat the disease, and what pet owners must know to protect pets.

At the 17th Triennial Heartworm Symposium presented by AHS in New Orleans last September, 40 speakers from three continents convened to present their heartworm research and related clinical topics. This international symposium comprised the latest scientific data on all aspects of heartworm disease.

“Heartworm disease continues to be one of the most common and costly diseases confronting the veterinary profession,” said veterinary cardiologist and triennial symposium co-chair Dr. Marisa Ames. “The fact that heartworm incidence remains far too high — year after year — makes it clear that veterinarians need forward-thinking innovations and practical approaches to this disease.”  Ames is an associate professor of medicine and epidemiology at the UC Davis School of Veterinary Medicine.

New approaches presented at the symposium included tactics learned from managing malaria, where the mosquitoes — instead of pets — could be treated in the future. Treatment of the favored host pest would prevent them from carrying or transmitting live heartworms.

Speakers stressed the importance of better information for pet owners about heartworm disease in cats, which can be fatal. Cat owners need to know how often indoor or outdoor, homeless, and feral cats are diagnosed with heartworm disease and that it can be fatal. There was also an emphasis on developing more accurate diagnostic protocols for feline heartworm disease.

Speakers also noted that climate change has contributed to the heartworm disease crisis. Historically, traditional winter freezing temperatures throughout the mid and northern U.S. reliably killed mosquito populations. Now dramatically fluctuating winter temperatures allow mosquitoes to survive.

Urban sprawl has also contributed to the robust heartworm population by creating “heat islands.” Urbanized areas experience higher temperatures than undeveloped land. Paved surfaces, rooftops, buildings and infrastructure absorb and re-emit the sun’s heat far more than natural landscapes such as forests, grasslands and water. The “heat islands” create perfect year-round survival zones for mosquitoes to breed and spread heartworms even during colder weather.

Untreated heartworm disease can be fatal to dogs, cats and ferrets. When an uninfected mosquito bites a heartworm-infected animal, it becomes infected, ensuring the continuous cycle and spread of heartworms. Heartworm-infected mosquitoes bite pets and transmit microscopic heartworm larvae into the pet’s bloodstream. The heartworm larvae travel to the heart, lungs, and blood vessels, where they live and mature. They can grow up to 12″ long and continuously breed.

Prevention treatments, oral, injectable, or topical prescription products, are necessary for indoor and outdoor pets and may include other ingredients to protect against fleas, ticks, and parasites. Monthly heartworm prevention medications can be safely given to puppies and kittens at eight weeks old. Pets must have the proper amount of heartworm prevention medication circulating in their bloodstream to kill heartworms. Heartworm prevention medication will not kill adult heartworms.

If an animal tests positive for heartworms, the goal is to first stabilize the pet’s overall health and any symptoms before treatment. Then the veterinarian will administer the FDA-approved medication determined to be safest for that pet based on its physical condition, stage of heartworm disease, age and other contributing factors. Heartworm disease medication kills all parasitic adults and immature heartworms carried by infected mosquitoes.

Once a dog is infected with adult heartworms, the veterinarian may administer one of the FDA-approved arsenic-containing drugs, like injectable Melarsomine. Arsenic-containing drugs quickly kill adult heartworms but are dangerous treatments that pose risks to pets and can have side effects.

Some veterinarians consider doxycycline safer because it is less toxic with fewer side effects than arsenic-based heartworm treatments. Doxycycline is a  slower process that gradually eliminates all heartworms. However, the additional time required by doxycycline to eliminate heartworms, permits internal damage to continue. This delay causes some veterinarians to reject this treatment option except in specific cases.

Pets are monitored during heartworm treatment for possible side effects. After heartworm treatment, the pet should be re-tested for heartworms before resuming monthly heartworm preventive medication to ensure successful treatment.

Some pets never show signs of heartworm disease until its advanced stages, while in others, there are noticeable symptoms: persistent cough, tiredness after mild activity, labored breathing and decreased appetite. If untreated, heartworm disease damages the pet’s heart, lungs, liver, and kidneys, eventually causing death.

Overheating must be avoided during heartworm treatment and recovery, and exercise restriction is necessary to minimize cardiopulmonary complications. Research has documented a direct correlation between the pet’s activity level and the severity of heartworm disease, according to the AHS.

If a pet tests positive for heartworms, discuss treatment options with your veterinarian. If you foster or consider adopting a heartworm-positive dog or cat, discuss care and treatment with the agency representatives. Pets in foster care receive all veterinarian treatment free from their shelter clinic until they are adopted.

Pets with heartworm disease that receive proper veterinarian treatment and care can recover and live normal lives with low chances of any long-term effects, according to the U.S. Food & Drug Administration Center for Veterinary Medicine (FDA) and the AHS. Heartworm disease is not contagious between pets.

Current guidelines from the AHS also recommend that using an Environmental Protection Agency (EPA) registered mosquito repellent can increase protection from heartworms by repelling mosquitoes. Additionally, pet owners should remove any standing water to eliminate mosquito breeding sites and restrict outdoor walks to daylight hours, avoiding prime mosquito feeding periods.

There is no FDA-approved treatment for killing adult heartworms in cats or pet ferrets, but heartworm prevention medication treatment is available. Pet owners should consult their veterinarian regarding the best options for these pets.

Although cats are susceptible to heartworm disease, they naturally resist infection, unlike dogs. However, because of complications with diagnosing and treating heartworm infection in cats and ferrets, misdiagnosis or failure to diagnose is common.

Due to their smaller size and other factors, cats can become acutely ill even from a single-worm infection. They may never show any clinical signs of heartworm disease, and even a small number of heartworms can cause severe disease and are potentially life-threatening.

The FDA warns pet owners that heartworm prevention medications require a veterinarian’s prescription. Internet sites or stores that sell these medications without a prescription are not legitimate sources for heartworm prevention medication. They could be selling dangerous products with toxic ingredients of unknown origin that could harm pets.

At a pet’s annual veterinarian check-up and vaccination visit, there should always be a yearly heartworm blood test done on all dogs seven months and older. Annual testing ensures that any infection is detected and treatment can begin to minimize harm to the pet. If the pet is negative for heartworms, the vet will provide the prescription for monthly prevention medication.

Experts remind pet owners that no drug is 100% effective and even one missed monthly dosage could result in an infection, especially for pets living in heartworm-hotspot, Florida. The sunshine state is ground zero for heartworm disease that has reached epidemic-confirmed case rates throughout the warm, temperate Southeastern U.S.  Unfortunately, some isolated pockets of drug-resistant heartworms have also emerged here.

The AHS invests hundreds of thousands of dollars annually in heartworm research and provides updated recommendations. The society publishes free current guidelines for Canine and Feline Prevention, Diagnosis & Treatment of Heartworm Disease on its website.

By Julie Kerns Garmendia
Resident Community News

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