Heartworm is a mosquito-borne parasite that can infect dogs, cats, ferrets and other mammals, even the occasional human. Infection can cause serious illness and death. Heartworms grow to about a foot in length and can live in your pet’s lungs, heart and blood vessels. Only a mosquito bite can spread heartworm infection.
Dogs are the most natural host for heartworms, which can multiply within a dog’s body and can cause permanent damage even after successfully removed. Cats are less affected by heartworms, and most of these worms will not reproduce in your cat. Nonetheless, even immature heartworms can precipitate respiratory disease in cats.
Heartworm in dogs can be prevented and treated with medicine, but be aware that the treatment drugs for dogs can’t be used on cats, so that prevention is the only option for felines. It takes about 6 months for a mosquito-borne heartworm larva to mature into an adult heartworm, and the parasite can live for up to 7 years in dogs and 3 years in cats.
Heartworm infection has been diagnosed in all 50 states. Since you can’t guarantee that your pet will never be bitten by an infected mosquito, preventative medicine is recommended for all your dogs and cats. The American Heartworm Society recommends you get your pet tested for heartworm every 12 months and receive heartworm preventative 12 months a year.
Prevention is much easier, cheaper and safer than treatment. Preventative medicines are quite effective when administered regularly in the proper amounts. Your veterinarian will be happy to discuss the alternative preventatives with you and prescribe the one that’s best for your particular pet. There are three types of heartworm preventatives:
Oral: A monthly chewable tablet can be administered to prevent heartworm. These tablets typically contain either ivermectin or milbemycin. A daily tablet containing diethylcarbamazine is no longer used. A side benefit of some oral medications is their ability to prevent whipworms, hookworms and roundworms. Some tablets also contain flea medicine that prevent production of live eggs. The only caution regarding oral preventatives is to make sure your pet swallows the whole pill rather than spitting it out. Some pets are allergic to the flavoring in a chewable product, but your vet can provide an alternative if necessary.
Topical: A monthly dose of liquid medicine applied to the back of your pet’s neck is effective in preventing heartworm. The formulations may also protect against fleas, mites, roundworms, hookworms and other parasites. Some pets might not like having the medication applied to their skin and will try (unsuccessfully) to rub it off. The medication may be toxic if ingested, so if you have multiple pets that lick one another, segregate them after treatment, and from young children who might touch the treatment spot.
Injection: The drug moxidectin can be injected by your vet for up to six months of effective treatment. It prevents heartworm and hookworm in dogs, but can’t be used on cats. Only a specially trained veterinarian can administer this injection. Speak to your vet for more information.
If your veterinarian diagnoses heartworm infection in your dog, treatment proceeds in a number of steps:
Confirmation: Your vet will perform a second test to confirm the infection. This is important to prevent unnecessary treatment that is both expensive and complex.
Rest: You should prevent your dog from exercising after the infection is confirmed, because exercise can increase the damage caused by heartworms. Your veterinarian will explain how to limit your dog’s activity.
Stabilization: It might be necessary for your vet to administer therapy to your dog to stabilize it before treatment is given. This process can take several months if the infection is severe or if your dog has other serious conditions.
Treatment: Your vet will administer treatment, usually in a multi-step protocol. The veterinarian will select the best drug for your dog and monitor your pet’s improvement. Your vet will need to watch out for complications, which can occur even when the infection level is mild.
Follow-up: After your veterinarian judges the treatment complete, your dog will be regularly tested. You will need to ensure that your pet receives periodic preventative treatment for the rest of its life.
Even though there isn’t a suitable treatment medicine for cats, your vet will still monitor the cat’s symptoms and administer good care to help your cat survive the infection. Your vet might choose to administer small doses of prednisolone to reduce inflammation. In severe cases, you cat might need intravenous fluids, antibiotics and other drugs to counteract symptoms. In some cases, cats can have heartworms surgically removed.
Dr. Paul has a strong interest in avian and exotic animal medicine and surgery, as well as small animal internal medicine and surgery.
He has provided services for numerous breeders, kennels, aviaries, and mini zoos.