Heartworms are parasites that are transmitted by mosquitoes. The mosquito picks up larval stage one (baby heartworms) from the blood of an infected dog. This develops to the third larval stage in the mosquito. The mosquito then passes this larvae to another dog when it bites him/her. Over the next 5-7 months, the larvae migrates through the tissues, eventually developing into larval stage six (the adult heartworm). The adult heartworms live in the pulmonary artery- the artery that leads from the heart to the lungs. They mate and produce offspring called microfilaria that exist in the bloodstream. A mosquito will bite this dog, pick up this stage one larvae, and the cycle begins all over again.
Adult heartworms grow to be 5-7 inches long, and they can live for 3-5 years. They can cause a variety of symptoms and health issues. The most common disease that occurs secondary to heartworm infection is heart disease. Because the worms live in the artery that goes from heart to the lungs, the heart has to work extra hard to pump blood around them. This extra work causes the heart to become enlarged, which will eventually lead to wasting and weakening of the heart muscle. At this point, the heart begins to fail. Heart failure can result in the failure of other organs (i.e the liver, kidneys, etc.) because it cannot pump enough blood to them to keep them healthy. Circulating baby heartworms also cause damage to organ tissue as they pass through them.
Clinical signs of disease often seen/associated with heartworm disease include:
1) Coughing- especially when excited or exercising. This can be secondary to lung inflammation, an enlarged heart pushing on the trachea (windpipe), a blood clot in the lungs, and/or fluids in the lungs (heart failure)
2) decreased energy
3) Swollen abdomen from fluid buildup- when the heart cannot pump blood appropriately, fluid will back up in the body
4) decreased appetite- from organ dysfunction or fluid in the abdomen pushing on the stomach
5) difficulty breathing- same causes as the coughing
6) reddish coloration to the urine- from kidney disease and/or passage of microfilaria (baby heartworms) through the kidneys causing inflammation.
7) sudden collapse or death
An adult heartworm infection can be diagnosed with a simple blood test. This test checks for the presence of female worms. You cannot tell how light or heavy your pet’s worm load is by the result of this test. If your dog has a strictly male infection, this test will be negative. A false negative can also occur with early infection. It takes 7 months from the time your pet is infected with heartworms for them to develop to adult size. For this reason, Effingham Animal Hospital always recommends a retest in 7 months when heartworm prevention doses have been missed. We will recommend certain types of prevention that will be the safest for your positive dog, and may have a weakening effect on the adult worms. We’ll also give you an antihistamine dose for your pet if he/she has missed doses. This should be given an hour prior to the first prevention dose to help prevent any adverse side effects.
There is treatment available for adult heartworm infection in dogs. Lab work and x-rays should be done prior to treatment to make sure your pet is a good candidate. Your pet needs to be on heartworm prevention for 2 months (3 doses total) prior to starting treatment. This allows the larval stage five worms (“teenagers”) an opportunity to grow to adult size. If you begin treatment (which only kills larval stage 6) without doing this, these “teenage” worms may mature after the treatment is complete, resulting in another adult heartworm infection. Your veterinarian will also prescribe a course of an antibiotic to help weaken the worms.
Adult heartworm treatment involves injections into the muscles on your pet’s lower back. He/she will need three injections total- one initially, then one month later he/she will get two injections 24 hours apart. Your pet will need to be strictly confined during this time period (2-3 months total). The heartworms will be dying and decomposing in your pet. Overactivity could result in a clot in the lungs caused by a piece of a heartworm or inflammation. At Effingham Animal Hospital, we prescribe a steroid to be given during treatment to help control inflammation. It will also help with any discomfort the pet may be experiencing from his/her intramuscular injections. If it is not feasible for you to treat your dog for heartworms, keep him/her on monthly prevention to prevent him/her from getting any more heartworms.
A heartworm infection is detrimental to your dog, and treatment is detrimental to your bank account. Heartworms can be easily and inexpensively prevented with a monthly dose of medication. There are preventions available without (more economical) and with (pricier) flea control included. You should start your puppy on prevention at 6 weeks of age, or as soon as you adopt him/her. If your new pet is 7 months of age or older, he/she should be tested for heartworms prior to starting prevention, then retested in 7 months.
At Effingham Animal Hospital, we recommend putting cats/kittens on monthly prevention as well. While it is less likely for them to get adult heartworms (they are not the natural host), they CAN get them, and there is no treatment available for cats. More commonly and most importantly, cats sustain lung damage from the older larval stages even though they die prior to reaching adulthood. A monthly preventative will kill the larvae before they mature to these stages.
In summary, your dog and/or cat should be on a monthly heartworm prevention year round, lifelong. In this hot, humid Georgia climate- we often have 80 degree days in the middle of “winter”- we have to deal with mosquitoes year round- out of the house AND in it. It’s not a question of “if” your pet will get heartworms if not on monthly medication in the south, but “when”. Protect your beloved four legged family member from this horrible- and 100% preventable- disease.
We hope you enjoyed this post! Tune in next week for a new topic!
