What is heartworm disease?
Heartworm disease is an infection inside the
bloodstream of animals. It is caused by a worm
called Dirofilaria immitis. This worm is spread
to animals by mosquito bites. Dogs, cats,
ferrets, wolves, coyotes, seals, and sea lions
can all become infected. The disease does NOT
spread directly from animal-to-animal, it is
only spread by mosquito bites. This disease has
been rare in Los Angeles County in the past. It
may be increasing now. Infected dogs and coyotes
are reservoirs for the disease.
Local cases of heartworm
Since the beginning of 2005 until now (Aug 27,
2012), veterinarians in Los Angeles County have
reported 96 cases. Of these, 12 cases were in
cats and 84 in dogs.
In 37% of these cases, the pet
caught the infection in Southern California
(local). In 41% of cases the pet was infected
outside of Southern California (imported). In 23% of cases there was not enough information
about the animal to say where they caught it
(unknown). The graph seen above right
shows these cases by year.
The majority of the cases
(73%) had no symptoms at the time it was
diagnosed. In the other cases, symptoms
included cough (19%), tiredness (12%), and heart
In the past 5 years, several
cases of heartworm disease have been detected in
the area northeast of Downtown Los Angeles (see
cluster of black stars near center of map).
There are more heartworm cases
in the county that are not reported.
The Companion Animal Parasite Council reports
that 176 dogs tested positive for heartworm
in LA County in 2011. See their
map for details.
What are the symptoms of
Animals that are infected with heartworm may
tiredness, problems breathing, coughing, and
heart failure. Infected cats may breathe hard
and be more likely
to vomit. It is important to know that infection
can be present for awhile 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
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.
In 15% of the 96 local cases, treatment was not done.
Untreated animals may be "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.
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
VETERINARIANS: Report a case of heartworm disease by using
this form or by using the
online reporting portal.