Heartworm disease is caused by parasites known as Dirofilaria immitis. Dogs are infected when they are bitten by infected mosquitos. The immature worms grow into adults in the dog's body and cause damage to the heart and blood vessels. By the time a dog shows symptoms of the disease, the harm has already been done. Treatment is possible, but it can be risky and there may be ongoing damage to the heart. This is one disease where prevention is definitely better than cure.
Protecting dogs from heartworm disease involves giving them medication that kills the larvae that have infected the dog before they can mature and cause problems. It's still possible for a dog to become infected with heartworm while being given preventative medication; first, because pet parents may forget to give the drug as directed, and second, because heartworms are becoming resistant to some commonly used medications. This means it's essential that pet parents treat their dogs regularly and don't overlook a dose, which may allow some larvae to survive. It's also important that yearly heartworm tests be conducted to see if dogs have become infected in spite of being given the preventative treatment.
To help protect dogs from heartworm in spite of the potential failings of using oral preventatives, scientists from University of Georgia College of Veterinary Medicine have been investigating a double defense protocol. They are treating dogs with a heartworm preventative as well as a topical pesticide that kills mosquitos as soon as they come in contact with it. In the study, 32 dogs were divided into four groups of eight. All dogs were exposed to mosquitos known to carry heartworm that were resistant to milbemycin, a commonly used heartworm preventative.
One group of dogs was the control group and received no heartworm preventative or topical insecticide. All of these dogs became infected with heartworm. A second group was treated with monthly milbemycin, but because the heartworms were resistant to this drug, these dogs also acquired heartworm infection. The third group had a topical insecticide applied that helped to prevent the mosquitos from biting the dogs, and only three of these eight dogs were infected with heartworm. The last group was treated with both milbemycin and the topical insecticide and none of these dogs tested positive for heartworm. This suggests that killing mosquitos before they have the opportunity to bite and infect a dog can be an important part of controlling heartworm disease.
Heartworm in dogs can be treated, but it can be a long, drawn-out, and expensive process. It can also leave affected dogs with long-term health issues. Because the incidence of heartworm in the United States is a constant concern, particularly in the southern states, something more than just monthly preventative medication needs to be done. The University of Georgia study shows that a multimodal approach to preventing heartworm infection in dogs is essential and indeed effective in stopping the spread of the disease. This approach should take the form of reducing mosquito populations by removing any areas of standing water that could potentially be breeding sites, killing mosquitos before they can bite a dog, and administering drugs to prevent larvae growing into adults.