What you don't know about heartworm disease can hurt your dog or cat
By Kim Campbell Thornton
You've probably seen a dusty jar of long, spaghettilike worms in your veterinarian's office. They're heartworms (Dirofilaria immitis), and they are deadly to dogs and cats. The internal parasites make themselves at home in the heart and lungs, causing heart failure and lung disease and potentially migrating to the brain, eye and spinal cord. Here are seven things you might not know about heartworm disease:
1. Heartworms are transmitted by more than 70 species of mosquitoes. Some of these mosquitoes don't need standing bodies of water to reproduce. They thrive in small areas, such as downspouts, gutters and flowerpots and adapt well to cold weather.
2. The incidence of heartworm disease is rising. Between 2013 and 2015, the Companion Animal Parasite Council saw a 166 percent increase in reported positive heartworm cases. That's because nationwide, only about 35 percent of dogs are on preventive medication, says C. Thomas Nelson, DVM, who practices in Anniston, Alabama, and is a spokesperson for the American Heartworm Society. On the West Coast, it's only 16 to 18 percent. In the Southeast, where heartworms are especially prevalent, it's about 26 percent.
3. Heartworm disease has been found in pets in all 50 states. "Owners carry their dogs with them a lot," says parasitologist John W. McCall, Ph.D., professor emeritus in the department of infectious diseases at the University of Georgia College of Veterinary Medicine. "They go from the north to the south, and they just don't really think that they're going into an area where there's mosquitoes. Many owners don't even know heartworm is transmitted by mosquitoes."
4. Cats can get heartworm disease. They are not as susceptible as dogs, but the worms can cause more serious problems in cats. Larvae in the lungs lead to what's called heartworm-associated respiratory disease (HARD), which has signs similar to feline asthma. It's worse if worms manage to develop to the adult stage.
"The clinical signs associated with the presence of a couple of adult worms in the cat's pulmonary artery are usually very severe, ranging from acute respiratory distress to sudden death as a result of severe inflammation and pulmonary embolism," says Romain Pariaut, DVM, an internal medicine specialist and associate professor of cardiology at Cornell University College of Veterinary Medicine in Ithaca, New York.
5. Preventive medication is recommended year-round for dogs and cats in all areas. One reason is because mosquitoes are more widespread. Another is that longer bouts of warm weather and shorter bouts of cold weather mean mosquitoes are seen year-round in most areas.
6. Heartworms are becoming resistant to preventive products. Bacteria, viruses and parasites such as heartworms eventually become resistant to drugs used against them, McCall says. The current drugs have been used for almost 30 years.
"We don't really know how much of a problem it is," he says, "but the longer we use the products, the more likely it is to occur."
7. Experts recommend combining preventive with a dog-safe mosquito repellent. Even though preventive medication is highly effective, it's not failproof, especially in areas where heartworms have become resistant. Based on a study McCall did using Vectra 3D, which repels and kills mosquitoes, combining heartworm preventive with the topical parasiticide was 100 percent effective in blocking transmission of microfilariae (immature heartworms) from dogs to mosquitoes -- a necessary part of the heartworm lifecycle -- and more than 95 percent effective in repelling and killing mosquitoes for 28 days after treatment.
"If the dog is treated, the mosquito can't bite the dog and it can't transmit the infective larvae to the dog," McCall says. "It will pretty much keep the dog protected, even when there's a high degree of resistance." The product is not safe for use on cats, but cats who live with dogs who are protected share the benefit.
Fever can have
Q: My dog had her teeth cleaned, and all went well with a couple of extractions. A week or so later, she wouldn't eat, and when we took her to the vet, she had a 104-degree fever. We tried a couple of different antibiotics, which didn't reduce the fever, so we were referred to a specialty hospital. They tested for everything, and she wasn't getting better. The vets kept her overnight and gave her fluids and super antibiotics, but she would not consistently eat and every test came back negative.
Long story short -- and $10,000 later -- my vet took an X-ray of her mouth and discovered an abscess in the jaw. He removed the tooth, cleaned out the abscess, gave her antibiotics and away she went. Why is it so hard to find the cause of a fever like this? -- via email
A: What an ordeal! I really feel for you. I can tell you that it's a real diagnostic puzzle when fever is the only significant sign on examination. My colleague Kenneth R. Harkin, an internal medicine specialist at Kansas State University College of Veterinary Medicine, spoke on this subject in January at the North American Veterinary Conference in Orlando, Florida. He says that figuring out the cause of a fever of unknown origin -- also called a cryptic fever -- becomes challenging when routine diagnostic tests don't pinpoint the problem.
As you discovered, the cost of testing (and hospitalization) can skyrocket as veterinarians seek other answers. Inflammation is the most common cause of fevers, Dr. Harkin says. Among the many possible inflammatory or infectious diseases that could cause fever are acute pancreatitis, pyelonephritis, lupus, immune-mediated polyarthritis and leptospirosis. Dogs with a recently discovered heart murmur may have bacterial endocarditis. Certain cancers can cause fever as well, including lymphoma, leukemia and liver cancer. All of these can be easily missed because abnormalities in the lab work can be subtle.
I'm glad your dog's fever was successfully resolved. -- Dr. Marty Becker
Do you have a pet question? Send it to firstname.lastname@example.org or visit Facebook.com/DrMartyBecker.
homes permit pets
-- TigerPlace, a retirement community in Columbia, Missouri, is a pet lover's dream. Residents can keep their animals with them and benefit from an animal care staff that helps walk, feed and care for the pets as needed. Allowing pets and providing pet-care services is a growing trend at retirement communities. TigerPlace, with 90 residents, is operated in collaboration with the Sinclair School of Nursing at the University of Missouri. Rebecca Johnson, director of the Research Center for Human-Animal Interaction at MU's College of Veterinary Medicine, says pets encourage people to walk, decrease loneliness and promote social interactions with other people.
-- Prehistoric best friend? Scientists in Siberia are studying the mummified remains -- including skin, hair, internal organs and stomach contents -- of two unusually well-preserved puppies thought to have died in a landslide more than 12,000 years ago. Amazingly, the brain of one is intact, the first-ever completely preserved brain of a Pleistocene canid. DNA tests on the first puppy, found five years ago, confirm dog rather than wolf ancestry, but the genetic makeup of ancient dogs and wolves is similar. The pups' genomes will be further evaluated in the hope of learning more about canine domestication and evolution.
-- A veterinarian at the University of Wisconsin School of Veterinary Medicine is working with physicians to test a new delivery method for a canine melanoma vaccine, according to an article by David Wahlberg in the Wisconsin State Journal. David Vail, DVM, is testing a modified tattoo gun with multiple punctures, which may induce a stronger immune reaction than a single injection. The canine melanoma vaccine, an immunotherapy approach that works to prevent the skin cancer from spreading, was approved in 2010 and is currently injected intramuscularly. If the new approach works in pet dogs, it could also benefit humans. -- Dr. Marty Becker, Kim Campbell Thornton and Mikkel Becker
ABOUT PET CONNECTION
Pet Connection is produced by a team of pet-care experts headed by "The Dr. Oz Show" veterinarian Dr. Marty Becker and award-winning journalist Kim Campbell Thornton. They are affiliated with Vetstreet.com and are the authors of many best-selling pet-care books. Joining them is dog trainer and behavior consultant Mikkel Becker. Dr. Becker can be found at Facebook.com/DrMartyBecker or on Twitter at DrMartyBecker. Kim Campbell Thornton is at Facebook.com/KimCampbellThornton and on Twitter at kkcthornton. Mikkel Becker is at Facebook.com/MikkelBecker and on Twitter at MikkelBecker.