Heartworm disease is a serious and potentially fatal disease affecting pets, particularly dogs, who are a natural host for heartworms. Animals get heartworms from the bite of infected mosquitos.
Heartworm disease is caused by foot-long worms (heartworms) that live in the heart, lungs and associated blood vessels of affected pets, causing lung disease, heart failure, and damage to other organs in the body.
Consistent use of monthly preventive medications is the best option. We also recommend annual screening for heartworms and larvae. If heartworm disease is present, treatment should be administered as early in the course of the disease as possible.
No one wants to hear that their dog has heartworms, but the good news is that many infected dogs can be successfully treated. We will work with you to battle this serious disease using a multi-modal approach that draws on the latest research.
The goal of any heartworm treatment is to improve the dog’s clinical condition and to eliminate all life stages of the heartworms with minimal post-treatment complications. Clinical signs of heartworm disease should be controlled as much as possible before administering an adulticide. This may require administration of steroids (cortisone), diuretics (“water pills”), vasodilators, heart medications, and fluid therapy. As long as exercise is restricted, treatment for dogs that are not showing clinical signs is usually not a problem. Treating a dog with moderate to severe heartworm disease, especially if there is significant illness, may be challenging.
Melarsomine dihydrochloride is the only adulticidal drug approved by the FDA for heartworm treatment. The American Heartworm Society (AHS) recommends a three-dose protocol: one intramuscular (IM) injection into the lumbar muscles (between L3 and L5) followed at least one month later by two IM injections of the same dose 24 hours apart. This protocol is safer and more effective compared to previous heartworm treatment protocols.
Exercise restriction during the recovery period is essential for minimizing heart and lung complications. As worms die as a result of adulticidal treatment, they decompose and worm fragments can lodge in the pulmonary arteries and capillary beds in the lung lobes. These worm fragments can block blood flow and cause thromboembolism (clots). Increased activity or exercise during heart worm treatment causes an increase in blood flow throughout the body, increasing the likelihood of thromboembolism (clots) and right-sided heart failure.
Tapering anti-inflammatory doses of steroids can help to control clinical signs of pulmonary thromboembolism (clots in the lungs), which can be severe after adulticide therapy, if infection is heavy and pulmonary arterial disease is extensive. Prednisone is the steroid of choice that is dosed twice daily for the first week and once daily for the second week, followed by every other day for one to two weeks.
- Doxycycline (Antibiotic):
Microfilaria, which are parasites responsible for heartworm disease harbor intracellular gram-negative bacteria called Wolbachia. Wolbachia have also been implicated as a component in the pathogenesis of filarial diseases. Doxycycline, an antibiotic, reduces Wolbachia numbers in all stages of heartworms. The American Heartworm Society recommends administration of doxycycline twice daily for four weeks before administration of melarsomine. Minocycline, an alternative antibiotic, given at the same dosage regimen may be a viable alternative during periods of doxycycline shortage.
- Macrocyclic Lactones (Heartworm preventatives):
In addition to adult heartworms, a heartworm-positive dog likely harbors juvenile stages of heartworms. Juvenile stages (worms less than four months old) might not be susceptible to either the MLs (heartworm prevention) or melarsomine (heartworm treatment) which creates a gap in the treatment. The susceptibility gap can be minimized by administering an ML preventive for two months prior to administering melarsomine. This will reduce new infections, eliminate existing susceptible larvae, and allow older worms (between two and four months of age) to mature to a point where they would be more susceptible to melarsomine.
- Macrocyclic Lactone/Doxycycline:
In cases where adulticide therapy is not possible or is contraindicated, the use of a monthly heartworm prevention medication along with doxycycline for a four-week period might be considered. An antigen test should be performed every six months and the dog not be considered clear of infection until two consecutive heartworm tests, six months apart, have been obtained. If the dog is still heartworm positive after one year, repeat the doxycycline (antibiotic) therapy. Exercise should be rigidly restricted for the duration of the treatment process.
For Additional Information
The American Heartworm Society provides excellent information on the prevention and treatment of heartworm disease in both cats and dogs.
If at any time, you have questions about your pet’s treatment, do not hesitate to contact us.
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