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Heartworm Update 2008

Disease Overview. Heartworm disease is caused by a mosquito-borne parasite called Dirofilaria immitis. This parasite infects dogs, ferrets, wolves, coyotes, seals sea lions and, occasionally, cats. Heartworms live inside in the large blood vessels leading from the heart into the lungs. Animals may become infected when bitten by mosquitoes that are carrying the parasite. Mosquitoes pick up the parasite when they bite an animal that has an active infection. Infection can be present for awhile before symptoms appear. Clinical signs may include tiredness, problems breathing, coughing, and heart failure.

Human Health Risk. Human infections with Dirofilaria immitis are rare, and most commonly have involved for the formation of nodules in the lungs or under the skin. To learn more about human infections see this posting from the American Veterinary Medical Association click here, and see links to articles below.

Local Data. The amount of heartworms in local mosquitoes may increase or decrease over time. Heartworm disease was not reportable in LA County until recently, and is still not reportable in most other regions, so it is not truly known how common the parasite has been locally. A 2004 study found heartworms in coyotes throughout California, primarily in mountainous regions. The study estimated the prevalence of heartworms in Southern California coyotes to be approximately between 5-20%, and to vary from location to location. To read the abstract of this study click here. To read more about heartworm in California coyotes see links to articles below.

Current data is primarily from reports from Los Angeles County veterinarians. A few spontaneous reports from Orange County were also included. A total of 31 local cases in dogs have been reported; 28 from LA County, and 3 from Orange County. The cases were diagnosed between 2005-2008, with all cases involving dogs. Approximately 7 cases were reported per year. The average age of these dogs was 5 years.
Nineteen (61.3%) of these cases, were “imported,” meaning the dog was infected while out-of-state or while in Central or Northern California. Eight (25.7%) of the cases were “local”, or infected while in Southern California. In four cases the location where infection was contracted was unknown.

Nineteen (61.3%) of the cases had no outward clinical signs, seven cases (22.5%) had fatigue, seven (22.5%) cases had a cough, and three (9.6%) of cases presented in heart failure.

Heartworm cases have been reported from all over Los Angeles County. Not all cases are visible on the map: in cases where more than one dog in the home was infected, only one marker appears.
 

Recommendations.

Mosquito Control. Help reduce mosquito breeding by dumping any standing water on your property every 48 hours. Mosquitoes feed the most at dawn, dusk and at night, so it is best to keep your dog indoors at night.

Consider Heartworm Preventative Medication. It is unknown if the local risk of heartworm infection is increasing. In many other parts of the United States heartworm infection risk is high, and pets (particularly dogs) routinely become infected if they do not receive preventative medication. Heartworm preventative medications are generally regarded as safe and some help prevent infection with additional parasites. Discuss the issue with your dog’s veterinarian.

For downloadable version of graph and map click here (pdf).

Report a case of heartworm disease by using this pdf form or by using the online reporting portal.

More Information
American Heartworm Society (find "Pet Owner Resources" section at bottom of main page)

Scientific Articles - Heartworm in California Coyotes
2004 - Modeling the Distribution and Abundance of the Non-native Parasite, Canine Heartworm, in California Coyotes.(abstract)
2003 - Reconstructing the Spread of Dirofilaria immitis in California Coyotes (fullt text, pdf)
1998 - Increasing prevalence of canine heartworm in coyotes from California (full text, pdf)

Scientific Articles - Heartworm Infection in Humans
2005 - Public Health Aspects of Dirofilariasis in the United States (abstract)
2002 - Human Pulmonary Dirofilariasis: Uncommon Cause of  Pulmonary Coin-lesion (abstract)
2001 - Heartworm in a 28 Year-old-man in California (full text, pdf)
 

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