Heartworm: The silent killer

Maggee Gardea

Special to Village News

Often unknown for its devastating seriousness, heartworm is one of the most overlooked diseases among pet owners. Although not limited to, heartworm disease is most commonly found in dogs and is contracted through the bite of an infected mosquito. Larvae travel through the bloodstream and eventually reside in the heart and lungs. The larvae then grow into the adult parasite, Dirofilaria immitis.

Heartworm can be fatal and nearly 300,000 dogs are infected yearly. Along with the increased precipitation Fallbrook has experienced, there will be increased breeding amongst mosquitoes and other insects, such as fleas and ticks, so precautionary action is especially important this year.

In addition, families may unknowingly travel to heartworm prone areas where their pets can contract this disease and bring it home to infect other animals in the area.

The amount of worms that live within the infected animal's heart is referred to as the worm burden and can range from 1 to 250 adult worms. Typically adult worms vary from 10 to 12 inches. Once the adult worms have matured and begun mating, the female releases immature worms into the bloodstream of the infected animal. At this point, a mosquito bites the infected animal and is now infected with the immature worms.

The mosquito is a necessary host for the development of the immature worms into larvae that are capable of infecting dogs. Once the mosquito bites another unaffected animal, the larvae are injected under the skin and migrate to the heart, where they develop into adults.

Perhaps one of the greatest dangers of this disease is that the symptoms do not always show. As the disease progresses, the symptoms, along with pets' health, will begin to worsen. Common symptoms include coughing and decreased activity, but in more severe cases will include lost body composition, exhaustion after little activity, worsening cough and signs of heart failure.

More severe cases develop Caval syndrome, a condition where the adult worms interfere with proper blood flow within the heart. Unfortunately, many infected animals show no signs at all and can appear completely healthy.

Because of the often silent symptoms, it is important to test pets yearly for heartworm. There are two types of tests, both of which test the blood for indications of adult worms. It takes approximately five to six months for either test to be able to detect the adult worm. This period is due to the time it takes for the larvae to travel to the heart and lungs and mature into adults.

If a pet is infected with heartworm, there are two treatment options. Melarsomine dihydrochloride, which is Food and Drug Administration approved to kill adult worms is injected into the patient through the back muscles. The second treatment option, Advantage Multi, which is FDA approved is applied topically and used to kill the immature worms. Each of these treatments poses a risk for blood clots and are expensive.

The best way to treat heartworm is through prevention. It is important to note that prevention works to kill larvae before they mature into adult worms, but is not effective after the worm has grown into an adult.

Pets must first be tested for heartworm, and only those that have negative results can use prevention. Giving pet prevention while they are possibly infected can cause the prevention to kill any immature worms; however, it may cause a pet to experience a shock-like reaction and perhaps death. As such, it is a safe option to always have a pet on a preventative.

Maggee Gardea is an employee of Avocado Animal Hospital.