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. Infected
are reservoirs for the disease.
What are the symptoms of
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
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
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
Between 2005-2014, veterinarians in Los Angeles County reported
187 cases - in 15 cats and 172 dogs. The
majority of the cases (74%) had no symptoms at the time it was
In 32% of these cases, the pet had not traveled
outside of Southern California, so it has
acquired the infection locally. The graph seen upper right
shows these cases by year.
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
In 15% of the 100 cases in Los Angeles
County, the animal was not treated.
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
Can humans catch heartworm?
Humans can potentially get infected if they are
bitten by a mosquito that is carrying the worm.
However human infections with Dirofilaria
immitis are very rare. In most cases, the
person has no symptoms, but small shadows ("coin
lesions") may be seen inside the lungs on a chest
X-ray. No cases of human heartworm infection
have been reported in our county.
See articles in
blue box below for more information.
Tracking Heartworm in LA County
Heartworm in animals is reportable in
Los Angeles County. The reports help track
trends in this disease. 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 187 cases reported between 2005-2014, 53%
were Confirmed, 41% were Probable, and 6% were
Reporting Heartworm Cases
VETERINARIANS: Report a case of heartworm disease by using
this form or by using the
online reporting portal.