Veterinary Public Health

Pet Health Calendar
Contact Information
Veterinary Public Health Program
313 N Figueroa St. Rm 1127
Los Angeles, CA 90012
Tel (213) 989-7060
Fax (213) 481-2375
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Heartworm Disease in Animals in Los Angeles County

What is heartworm disease?
It is an infection in animals caused by a worm called Dirofilaria immitis. This worm is spread by mosquito bites. The adult worms live in the heart and large blood vessels in the chest. Dogs, cats, ferrets, wolves, coyotes, seals, and sea lions can all become infected. The disease does NOT spread directly from animal-to-animal. 

What are the symptoms of heartworm disease?
Infected animals may have tiredness, problems breathing, coughing, and heart failure. Infected cats may breathe hard and be more likely to vomit. Infection can be present for a while in the pet before symptoms appear.

How do you know if your pet is infected with heartworms? The only way to know is by having a blood test for heartworms performed at a veterinary hospital.

What is the treatment for heartworm infection?
Veterinarians treat infected pets by giving medication to kill the worms in the bloodstream. As the worms die, there is a risk of the pet having a bad reaction to the dead worms. Therefore, heartworm disease is treated only under the close supervision of a veterinarian.

Is there any heartworm disease in Los Angeles County?
Yes. Between 2007-2016, veterinarians in Los Angeles County reported 324 cases - in 21 cats and 303 dogs. The majority of the cases (77%) had no symptoms at the time they were diagnosed.


In 28% of these cases, the pet had not traveled outside of Southern California, so they had acquired the infection locally. The graph seen at the right shows these cases by year. The amount of reports received per year increased in 2014 because laboratories began to report cases.

How Can I Prevent Heartworm in My Pet?

1. Mosquito Control. Mosquitoes breed in stagnant water. Stop mosquito breeding by dumping any standing water on your property every 2 days. Mosquitoes feed the most at dawn, dusk and at night, so keep your pet indoors at night. 

2. Heartworm Preventative Medication. Heartworm preventative medications are generally regarded as safe and help prevent infection with additional parasites. Discuss the issue with your pet’s veterinarian.

Untreated animals
In 21%  of the cases in LA County, the animal had not been treated for heartworm infection at the time of the report. Untreated animals may become  "reservoirs" for the disease. This means they can infect mosquitoes, and then the mosquitoes can infect more pets. Infected coyotes can be reservoirs for the disease.

Can humans catch heartworm? 
However human infections with Dirofilaria immitis are very rare.  In most cases, the person has no symptoms, but a small shadow ("coin lesion") may be seen inside the lungs on a chest X-ray.  No cases of human heartworm infection have been reported in LA County.  See articles in blue box below for more information.

Tracking Heartworm in LA County
Heartworm in animals is reportable in LA County.  In 2014, laboratories were required to begin reporting cases, and the reports available increased. Cases are categorized as Confirmed, Probable, or Suspected based on the Heartworm Case Definition for LA County. Of the 257 cases reported between 2005-2015, 51% were Confirmed, 39% were Probable, and 10% were Suspected.

Reporting Heartworm Cases
VETERINARIANS: Report a case of heartworm disease by using this form or by using the online reporting portal.

Invasive Aedes mosquitoes in Los Angeles (LA) County

  • Three new species of drought-resistant mosquitoes 
    are spreading LA County.
    Aedes aegypti - CDC

  • They are black with white stripes, and
    bite in daytime.

  • Two of the new mosquito species have transmitted heartworm in other countries, and therefore may spread heartworm here.

  • The Yellow Fever mosquito and Asian Tiger mosquito are potential vectors for multiple human viruses, such as West Nile, Zika, chikungunya, and dengue. The California Department of Public Health has an interactive map showing places in California where these two mosquitoes have been detected.

  • Your help is needed! Be a mosquito-fighter.

2007-2016 Heartwormn Los Angeles County - graph

2007-2016 Heartworm Los Angeles County Map



American Heartworm Society (find "Pet Owner Resources" at bottom of page)


Heartworm in California Coyotes
2004 - Modeling Distribution of Canine Heartworm, in California Coyotes pdf icon
2003 - Spread of Dirofilaria immitis in California Coyotes

Heartworm Infection in Humans
2010 - Public Health Issues Concerning Widespread Canine Heartworm Disease
2005 - Public Health Aspects of Dirofilariasis in the United States
2002 - Human Dirofilariasis: Uncommon Cause of  Pulmonary Coin-lesion
2001 - Heartworm in a 28 year-old-man in California pdf icon

Last updated: January 17, 2018
Public Health has made reasonable efforts to provide accurate translation. However, no computerized translation is perfect and is not intended to replace traditional translation methods. If questions arise concerning the accuracy of the information, please refer to the English edition of the website, which is the official version.
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