The first published description of heartworm in dogs appeared
more than 100 years ago in an issue of "The Western Journal
of Medicine and Surgery." Heartworm in cats was first described
in the early 1920's. Since then, naturally acquired heartworm
infection in cats and dogs is identified as a worldwide clinical
problem. Despite improved diagnostic methods, effective preventives
and increasing awareness among veterinary professionals and
pet owners, cases of heartworm infection continue to appear
in pet dogs around the world. The diagnosis of the disease is
still complex and elusive in cats.
What do we know about it?
Heartworm disease is a serious and potentially fatal condition
caused by parasitic worms living in the arteries of the lungs
and in the right side of the heart of dogs, cats and other species
of mammals, including wolves, foxes, ferrets, sea lions and
(in rare instances) humans. Heartworms are classified as nematodes
(roundworms) and are but one of many species of roundworms.
The specific roundworm causing heartworm in dogs and cats is
known as Dirofilaria immitis. Until recently canine heartworm
disease was considered to be a problem only in warm climates,
but in the past few years it has been found in almost all areas
of the United States and Canada. Since dogs travel widely with
their owners, and infected dogs can carry heartworms for several
years, heartworm disease may be a problem anywhere in the nation.
Heartworm infection is transmitted by mosquitoes. When a mosquito
bites an infected dog, it takes up blood which may contain microfilarae.
These incubate in the mosquito for about two weeks, during which
they become infective larva. Then, when the mosquito bites another
dog, the infective larvae are passed into the second dog, infecting
it. The infective larvae migrate through the tissues of the
body for 2-3 months. They develop into several stages called
L1, L2, and L3 stages. The L1 stage only lasts for 1-2 days.
The L2 and L3 stages last for approximately two months. They
then enter the heart where they reach adult size approximately
3 months after infecting your pet.
The mosquito is the only natural vector of transmission for
canine heartworms, and about 70 species are capable of carrying
the disease. As you might expect, heartworm infection is more
common in areas where mosquitoes are numerous, and outdoor dogs
constantly exposed to mosquitoes are the most frequent victims.
How can I find out if my dog has heart disease?
Your veterinarian is your dog's healthcare expert. Regular
veterinary visits are important for early detection of health
Your veterinarian may ask you for specific information about
your dog before performing a thorough physical examination.
If indicated, blood and urine tests, X-rays, an EKG or other
tests may be ordered. Regular testing is important for early
detection of heart disease in dogs.
"Too often, dog owners do not take their dogs to visit
the veterinarian until they are displaying severe signs of heart
failure, and by then it may be too late," says Dr. Bicknese.
"When heart disease is detected in your dog, your veterinarian
can recommend a schedule of regular visits and discuss a treatment
plan that can help."
Can dogs with heart disease be treated?
Yes. Although there is no cure for most heart disease in dogs,
new treatments are available. Success of treatment depends on
various factors, but early detection is always best. By following
your veterinarian's recommendations, you can help your dog live
a longer, more comfortable life.