Lethargic dog lying in grass
Spring is finally here and the great outdoors is calling to you and your pets. But warmer weather comes with a downside: pests that can cause disease. At the top of the list are mosquitoes because they can give your pet heartworm disease — a potentially deadly condition — with just one bite!

Heartworms know how to get around: Mosquitoes are basically the heartworm airline, and dogs and cats are their mobile homes. According to the American Heartworm Society, heartworm has been diagnosed in all 50 states, even those with cold climates.

The good news is that heartworm disease is preventable in both cats and dogs. Here’s what you need to know to help keep heartworms and other harmful outdoor pests at bay this summer.

Wandering Worms

Heartworm disease is spread by mosquitoes and is acquired in the same way by both cats and dogs: When a mosquito bites a dog that already has heartworms, the mosquito becomes infected and can pass the tiny heart­worm organisms to other animals it bites.

Heartworm disease also occurs in cats, but because there are no good treatment options available for cats, prevention is particularly important for our feline friends.

Heartworm disease can affect both indoor and outdoor pets. Mosquitoes can easily get inside your home and it only takes one bite to infect your pet. Don’t assume that your cat is protected because she never goes outside — heartworm infections have been found in indoor-only cats who were most likely infected by mosquitoes that got into the house.

Signs of Heartworm Disease

Once an animal is bitten by an infected mosquito, it can take several months for signs of the disease to appear, and some pets show no signs of infection at all. During this time, the heartworms mature and travel throughout the host animal’s body. At maturity, they live in the blood vessels between the heart and lungs (and can extend into the heart itself) and can grow to nearly a foot long. As their numbers and size increase, heartworms can interfere with and damage your pet’s vital organs, potentially causing death.

Animals with heartworms may cough, seem tired and have difficulty breathing. In many pets, signs (if they appear at all) do not appear until the disease is advanced. In dogs, heartworm disease most commonly affects the heart and lungs, and over a dozen worms may be present. In cats, heartworm disease most commonly affects the lungs. Although cats with heartworm disease usually have fewer than six heartworms, just one heartworm can be fatal for your feline.

The only way to know for sure if your dog is infected with heartworms is to have your veterinarian obtain a blood sample from him and test it. The American Heartworm Society recommends yearly testing for dogs. Diagnosis in cats is often made by using X-rays and ultrasound in conjunction with blood tests.

If your dog tests positive for heartworm disease, your veterinarian will explain the different treatment options available. Early diagnosis and treatment are preferred, because the chance of complications increases if the disease is allowed to progress. In some complicated cases, surgery to remove the worms may be necessary.

Unfortunately, there is no approved treatment for cats diagnosed with heartworm, making prevention especially important for these pets.

Prevention is Key

Fortunately, heartworm disease is preventable in both cats and dogs. Approved medications are safe and effective when administered properly. They are also easy to give and available in several varieties — pills, chewables, topicals and injections. Cats can be started on preventive medication without pre-testing to determine heartworm status, but dogs should be tested prior to starting any type of heartworm preventive. Talk with your veterinarian about the option that best suits you and your pet. And if you have never had your dog tested, don’t put it off any longer!

Other Pesky Parasites

Dogs and cats should also be tested at least annually for parasites other than heartworms, including hookworms and roundworms, all of which can cause unpleasant gastrointestinal problems in your pet. If your pets go outside, ask your vet if they should be tested even more frequently because they are more likely to come in contact with birds, rodents, dirt or water that might be contaminated with worm eggs.

If your pet has parasites, your veterinarian may prescribe a deworming medication. Today’s dewormers are safe, effective and easy to administer. Fortunately, many heartworm medications also protect against other parasites. In some cases, the range of protection can be the determining factor when deciding which preventive is best for your pet. Talk to your vet about your options.

Giardia is another pest that can make your pet feel bad. Giardia organisms can be passed in the feces of infected animals, so food, soil and water (stagnant water or even freshwater sources) can become contaminated. Under the right conditions, Giardia cysts can remain infective in the environment for months, so talk to your vet about your pet’s exposure risk. Giardia is treatable with medication, but some pets need to be treated more than once.

Finally, no list of outdoor pests would be complete without fleas and ticks. More and more diseases in dogs, cats and people are being associated with bites from ticks and fleas. Talk with your veterinarian about flea prevention options for your dog or cat.

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