Heartworms (scientific name Dirofilaria immitis) are a parasite of dogs and other canids, such as foxes. Cats are more resistant to infection than dogs; their infection rate is only 5–20% of that of the dog. Heartworm disease is a serious and potentially fatal disease in our dogs and cats. These worms may grow up to a foot long and wreak havoc in the heart, lungs and associated blood vessels of affected pets. Blood clots, an embolus (blockage), or heart failure may occur.
Mosquitoes infected with the Heartworm larvae (immature stage) transmit the parasite to the dog (or cat) when they bite. It takes six months for the larvae to mature into the adult heartworm. The worms can live for years in our pets. Signs of heartworm disease may include a mild persistent cough, exercise intolerance, decreased appetite, and weight loss. Treatment includes multiple injections of anti-parasitic drugs.
No longer limited to the South, Heartworms are found in most areas of the United States. There is a low prevalence of Heartworm disease in southern California. Approximately 0.5% of all positive cases of Heartworm in the U.S. are in California (compared to almost 20% in Texas). Of these cases, almost 5% are in Los Angeles County (compared to 32.28% in Sonoma County). But, it’s important to remember, there are likely a significant number of cases that go unreported or undiagnosed.
I recommend annual testing off all dogs for Heartworm via an antigen blood test (tests for substances secreted by adult female worms). It costs only $25 for dogs. Additional testing is necessary if there is a positive result. Detection of heartworms is more difficult (more expensive) in cats. Once you have a negative test, you may begin giving your pet monthly Heartworm preventative.
My advice to clients has always been if you see mosquitoes in your environment, you definitely should keep your dog on monthly Heartworm preventative such as Trifexis, Heartgard, topical Advantage Multi and Revolution, Interceptor, or Sentinel. You must give the preventative every month; if you miss a dose, re-test and then re-start the medication. I advocate preventative therapy in cats in endemic areas (indoor cats can be affected too). I like using the topical Revolution in cats because it also prevents flea infestations, treats and controls hookworms, roundworms, and ear mites.