That sound – the buzz of a mosquito. The little insect with the mighty bite is an unwanted but familiar summer visitor. Although Tucson’s drier climate may lessen the numbers, mosquitoes and their breeding grounds are still an issue. They are annoying, and they can deliver a deadly problem to your dog, cat or ferret.
Adult heartworms in the heart of a deceased pet. Courtesy American Heartworm Society
A certain species of mosquito is the transport of choice for dirofilaria immitus, a threadlike roundworm. The mosquito bites an infected animal such as another dog, coyote, or fox. The insect becomes an intermediate host, meaning the immature form of the worm, also called microfilaria will live inside the mosquito for a short period of time before transferring to a definitive host. The mosquito bites another animal and transfers the microfilaria, where they mature into adult heartworms and reproduce, moving from the bloodstream to major organs. Adult heartworms can grow up to a foot long, and they live in the lungs and blood vessels of an animal as well as in the heart. Left untreated, they can cause potentially deadly heart, lung, and other organ damage.
Veterinarians typically divide heartworm infection into four stages, based on the age and health of the dog and the severity of the heartworm infestation:
- Stage 1 – Young and overall healthy dogs that test positive for heartworm, but are showing no symptoms of infestation, and very little change on X-rays.
- Stage 2 – Heartworm disease is apparent on X-rays. The animal may be coughing, but it shows little to no other symptoms.
- Stage 3 – X-rays show damage to organs, and animal has weight loss, coughing, and labored breathing.
- Stage 4 – The dog is in shock and at a critical stage. Typical heartworm treatment is no longer an option, although surgical removal might be attempted.
“The only FDA approved medication to kill adult heartworms is melarsomine, which is an organic arsenic,” explains Dr. Amy Kranch of Encanto Pet Clinic. “This medication has to be administered 3 times during a 30-day period. Dogs undergoing treatment must be cage rested/exercise restricted for 4 months to try and prevent complications. Complications include pulmonary thrombo-embolism, which is potentially life-threatening, pain at the injection site and (rarely) allergic reactions. In some heavily infected dogs, the adult worms must be surgically removed.”
2013 Heartworm Cases in United States – photo courtesy of American Heartworm Society
Heartworm disease has been diagnosed in all 50 states. According to data provided by IDEXX Laboratories and ANTECH Diagnostics, there were 103 positive cases of heartworm in Pima County in 2014. Nine positive cases where reported in March 2015 alone, with a total of 20 cases in Pima County this year.
Heartworm antigen tests detect certain proteins that are released into the blood by adult female heartworms. The test can detect infections of female adult worms over 7 months old.
Microfilaria may be found in a dog’s bloodstream 6 to 7 months after it has been bitten. Veterinarians look for microfilaria by looking at a sample of blood under the microscope. If they are present the veterinarian knows that your pet either has an early heartworm infection or that there are adult heartworms that have mated and produced offspring.
Heartworm infection is most commonly diagnosed in dogs; however, cats and ferrets are also at risk. Currently there is no treatment for heartworm infection in cats, other than surgically removing the adult heartworms, so prevention is important.
Cats can be infected with heartworms, so keep them safe with testing and preventative. Image Courtesy American Heartworm Society.
The American Heartworm Society and Encanto Pet Clinic recommend that pet owners “Think 12.” Have your pet tested annually for heartworm disease and give monthly heartworm preventative 12 months a year. It takes at least 6 months for a dog to test positive for heartworms after initial infection so puppies under 6 months of age can be started on monthly heartworm preventative without testing for heartworms. It is important to follow up with a heartworm test at 1 year of age and then once yearly. Dogs over 6 months of age must be tested before safely starting monthly heartworm preventative.
We know that sometimes the toughest part about heartworm prevention is remembering to give monthly preventatives, but it is important and we want to help you. Sign up here to receive monthly email reminders. If treatment has been missed please call Encanto Pet Clinic for further recommendations before giving the next dose of heartworm preventative.
So you have been diligent about giving preventative treatment. You are absolutely sure your dog has not spit out or vomited up the medication at any time. Do you need to have your dog tested annually? The answer is yes. Although heartworm preventative is very effective if given once monthly as directed it is not fool proof. The preventatives kill the microfilaria in the dog’s blood, but not the adult heartworms. If there are few heartworms present there is a possibility of a negative antigen test. Dr. Tim Ireland states that if your dog has previously tested negative and you have purchased Heartgard® from your veterinary clinic, Merial® will help pay for the treatment if your dog gets heartworm while on year-round preventative. Ask the staff at Encanto Pet Clinic for more information on the guarantee.