The Truth About Heartworms
by Dr. Jean Hofve
Heartworms are a potentially deadly parasite carried by mosquitoes. It has a fairly complicated lifestyle that involves incubation in and transmission by mosquitoes.
Heartworm Life Cycle
Tiny heartworm larvae, called microfilaria, circulate in the blood, and are sucked up by the mosquito when it feeds on an infected host animal. Once inside the mosquito, the larvae must develop through more stages before they can cause infection. For that to occur, outside temperatures must remain above 57 degrees F, day and night, for a minimum of 8 days. The warmer the temperature, the faster the larvae will mature. If the temperature drops below that critical level, larval development will stop; but the larvae don’t die—development will re-start at the same point when the weather warms back up.
Larvae reach their infective stage in 8 to 30 days (the latter being the entire lifespan of the average mosquito). In dogs, heartworm’s natural host, the larvae migrate to the heart and eventually develop into adult worms, reproduce, fill the blood with microfilaria, and pass them on to the next mosquito. The maturation process takes 6-7 months.
Once in the bloodstream, the microfilaria migrate to the right side of the heart and attach there, where they can grow into adulthood. It takes microfilaria about 6-7 months to mature into adults and start reproducing. Clinical signs (coughing, tiring easily) are not typically seen before that. Adult worms can live up to 7 years in the dog.
In cats, adult worms can develop, but they cannot reproduce; they take about 9 months to mature, and they tend to live only a year or two. However, adult heartworms are about a foot long, so it only takes 1 or 2 to fill up a cat’s tiny heart and cause serious problems. Most larvae will not mature in a cat; its immune system will kill them. However, the larvae can cause inflammation in the lungs as they migrate; this condition can mimic asthma or bronchitis.
Except for a the warmest parts of the U.S. (mainly in the southeast), heartworms are a completely seasonal problem. There is no reason to give heartworm medicine to most pets year-round (except to make money for those who make and sell it!).
In many areas of the country (northern and mountain states, for instance), such warm temperatures simply don’t exist for most of the year, and sustained warm temperatures don’t occur until at least June. In fact, only in Florida and south Texas is year-round heartworm transmission possible. Within 150 miles of the Gulf Coast, heartworm risk exists 9 months out of the year. In the rest of the country, heartworm transmission is possible between 3 and 7 months out of the year. Hawaii and Alaska have each had a few cases of canine heartworm, but the incidence in those states is very low.
Heartworm preventative drugs do not kill adult heartworms, but they do kill microfilaria up to a certain stage of development. Currently it is believed that larvae under 6 weeks old are affected. This means that in order to prevent heartworms from reaching adulthood, the preventative can be given up to 6 weeks after the mosquito bite and still work. The recommendation is to give the drugs every 30 days, purportedly because once-a-month dosing is easier for most people to remember (coincidentally, it also sells more drugs). Preventatives should be given starting 4-6 weeks after the earliest possible infection date and continue 4-6 weeks past the last possible infection date. In most states, protection should be continued through November or December. In southern Texas and Florida, year-round preventatives may be needed. Local conditions may vary from year to year.
Only Natural Pet HW Protect Herbal Formula is a natural product intended for use as a preventative to be used during mosquito season as part of a comprehensive heartworm control program. The formula was designed with two objectives, using herbs that work together to reduce the likelihood of mosquito bites to lower your pet’s risk of becoming infected, and to help eliminate existing larvae-stage parasites in the bloodstream. This tincture was developed to help prevent heartworm infestation using extracts of herbs well known for their mosquito repelling properties, and others well known for their anti-parasitic properties. Using an insect repellent like Only Natural Pet Herbal Defense Spray may also help prevent heartworms by keeping mosquitoes away from pets when they are outside.
An herbal approach to heartworm prevention is not like a traditional heartworm pharmaceutical preventative, which chemically kills all heartworm larvae, but it may be an effective and more natural method to prevent heartworm infection. Consistent dosing is essential for proper protection, along with heartworm testing at least every 6 months.
The key points to remember about heartworm can be summed up as follows:
- The temperature needs to stay above 57 degrees for 8 to 30 days.
- A mosquito has to bite a dog that already has microfilaria in its bloodstream.
- That mosquito has to then bite your dog or cat 8-30 days later.
- You must give the heartworm preventative medication within 6 weeks of mosquito bite to kill microfilaria in the blood and prevent the larvae from growing to adulthood.
Read the full version of this article on our website