Due to new scientific information about heartworm resistance, testing, and treatment, the American Heartworm Society (AHS) is re-thinking the guidelines that veterinarians must follow when testing pets.
 
It has long been suspected that heartworms are becoming more difficult to treat due to the parasites building a resistance and improper drug administration by pet owners. According to new research, this is no longer speculation – there is evidence to support it. Thus, the AHS is straining the importance of proper drug administration and other preventative measures now more than ever.
  
Heartworm Prevention
In the past, the AHS' guidelines focused on diagnosing, preventing, and treating heartworms, respectively. However, the guidelines have been revised such that prevention now takes a front-seat to diagnosing and treating, as this is the only way around the parasites potentially becoming immune to the drugs. It's now recommended that any animal that is prone to heartworms is given preventative care all year-round.
 
New Testing
Antigen testing has been considered the most sensitive way to diagnose heartworms in an asymptomatic dog, or to confirm that heartworms are present when the dog is showing symptoms. However, the new research shows that this type of testing has a 7.1% false negative rate. To address this issue, the AHS is now suggesting that both antigen testing and microfilaria testing both be performed during a screening in order to ensure the most accurate results. This will help to become aware of the issue, and begin combating by using heartworm treatments on the dogs, sooner.
 
Proper Heartworm Treatment
Pet owners should begin a heartworm prevention program when the dog reaches 6 to 8 weeks of age, and it is currently being recommended that dogs stay on a treatment plan year-round – previously, it was said only to be necessary to put the dogs on prevention during certain months. This must continue for the dog's entire life.
 
There are many different brands of heartworm drugs, which include ingredients like ivermectin (for Ivomec and Heartgard), milbemycin oxime (for Interceptor), and selamectin (for Revolution). Which drug you choose will depend upon whether your dog is heartworm-free, in the early stages of heartworm, or in an emergency stage. It also depends on the breed.
 
It's important to administer the drug exactly as suggested on the packaging. Most only need to be administered once per month and come in the form of chewable tablets or liquids. If you miss a month of administering the drug, start again immediately the next month and have a screening performed within six months.