UC Davis Koret Shelter Medicine Program

According to the American Heartworm Society, it is best to treat a dog for the heartworms first, wait 6 months to allow the lungs to recover and then perform surgery.  It should be noted that it can take 4-5 months for the dead worms and all of their remnants to be removed from the vasculature in a heavily infected dog and it is the dead worms that cause the majority of the pathology associated with heartworm infections.  For infected dogs, the risk of surgery may actually be the same or even lower prior to treatment than after treatment if an adequate recovery time is not permitted.

Waiting for this recovery is not usually practical in the world of animal sheltering and thus a compromise has been suggested.  For class 1 dogs (asymptomatic) surgery should be done prior to treatment.  For class 2 dogs (mild symptoms) a tapering dose of glucocorticoids +/- doxycycline should be administered over the 4 weeks prior to surgery to help reduce inflammation.  For class 3 dogs (moderate to severe signs) surgery should be done 6 months after treatment. For a full description of heartworm disease classes please see The American Heartworm Society website.

There is a chapter on heartworm disease, authored by C. Thomas Nelson of the American Heartworm Society, in the textbook Infectious Disease Management in Animal Shelters that should be referenced in your protocols. 

Thank you for raising this important question and we hope this information has been useful.

Cindy
 
Cynthia Karsten, DVM
Resident, Koret Shelter Medicine Program
Center for Companion Animal Health
UC Davis School of Veterinary Medicine
www.sheltermedicine.com
www.facebook.com/sheltermedicine