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)
