Part One of "The Heartworm Story" is dated May 18 below this post.
A Cautionary Tale: A friend skipped the winter months giving heartworm preventative in a high risk geographic area. She didn't know she was in such a high risk area and she thought she was being safe and kind to her dogs by giving them a break from heartworm preventative for a few months out of the year. Saving a few dollars occurred to her too. One of her dogs tested positive for heartworm and the treatment was $1,200.00. Now her dogs are on monthly, year-round heartworm prevention.
Despite good diagnostic tests and preventatives, Heartworm disease is increasing.
States with the most reported cases are: parts of VA, CA; all the southeastern states of NC, SC, GA, Fl; the Gulf Coast states AL, MS, LA, AR, TX and the midwestern states MO, IN, IL and MI, WI
One of the big problems with heartworm disease, besides the fact that it will kill your dog, is that your dog can show no signs or symptoms of the disease until he or she is heavily infected. The symptoms are a persistent cough, lethargy, loss of appetite, and weight loss. But once these symptoms appear, there may be a heavy infestation of heartworms. That is not good news.
If your dog is not on heartworm preventative or has been on and off intermittently—it might take several tests at different times to determine if she/he is positive. Here’s why—tests won’t reveal a positive until there are female adult heartworms and takes about 7 months after infection. So…if your dog was not on preventative from November through March, for example, if he is infected in November he might not show positive for heartworm until June. Or if he got infected in March he may not show positive until October.
Facts ("Epidemiology" if your working on your vocabulary):
- The infective 3rd stage larvae need steady 24 hour daily temperatures above 64˚ for 1 month.
- Intermittent temps below 57˚ retard larvae maturation even if the temp rises during the day
- At 80˚ it takes 10-14 days for microfilariae to develop to the infective stage. So clean out those gutters, tires, buckets, etc. lying around outside!
- Peak months are July and August
- Favorable year round conditions exist in Florida and the Gulf States
- Heartworm transmission is limited to 6 months or less (Canada) above the 37th parallel.
- Below the 37th parallel, that’s the Virginia/North Carolina state line, the transmission time is much shorter.
I’ll spare you the gross and graphic illustrations of heartworms, but here is where you can see some microscopic images of heartworms.
So why does our vet and the Heartworm Society recommend year round monthly heartworm treatment? Because we mess up--we forget, we are late, we don’t have or want to spend the money, or for some of us, we think it will be a cold winter, we don't want to give our dogs chemicals or poisons, or we don’t think our dogs are at risk. And because the geographic area is spreading as is the rise in positive cases.
If you want all the details of treatment, The Heartworm Society has a detailed explanation under the “Veterinary Resources” section. Melarsomine, (trade name Immiticide) is an arsenic based drug injected deep into a back muscle. During treatment you must be absolutely vigilant about restricting your dog’s exercise—only leash walks until treatment is complete.
Recently researchers discovered a parasite called Wolbachia that lives symbiotically inside heartworms. Can you believe it? First Myra the mosquito transmits the heartworm microfilariae, then they discover there is a bacteria that lives symbiotically inside the heartworm! Treating the dog with the antibiotic doxycycline seems to sterilize the female heartworm. One of the risks of treating dogs for heartworm and the reason the dog is restricted from exercise is the sudden kill off of worms can block the flow of blood through the lungs, causing embolism and shock. The recommendation now is to treat with doxycycline before starting the Immiticide treatment. It kills the Wolbachia and weakens the heartworms, which seems to reduce the risk of embolism and shock.
Now you know more than you ever wanted to know about Heartworm disease. Don’t worry, there’s more, but I’ll save that for another day. Our next topic will be on the preventatives, what's safe for your dog, shortcut dos and don'ts, and how to save some money.