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
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 2009-2018, veterinarians in Los Angeles
County reported 521 cases - in 30 cats and 490 dogs. The
majority of the cases (77%) had no symptoms
at the time they were
In 27% 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.
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
In about 20% of the cases in LA
County, the animal had not been treated
for heartworm infection at the time of the
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?
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. In a few cases in the world, a
heartworm has been found in a lump under the
skin of a person. 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 521 cases reported between 2009-2018, 49%
were Confirmed, 39% were Probable, and 13% were
Reporting Heartworm Cases
VETERINARIANS: Report a case of heartworm disease by using
email it in to
firstname.lastname@example.org or fax to 213-481-2375.