 Heartworm disease
Heartworm is a parasitic disease that can affect any dog regardless of age, sex
or habitat. It is found in virtually all parts of the United States and many parts
of Canada. Heartworm is spread by mosquitoes, and tends to have a higher incidence
in areas heavily populated by mosquitoes. Dogs are considered the most common host
for heartworms, however heartworms may also infect more than thirty species of animals
(including coyotes, foxes, wolves, domestic cats, ferrets) and even humans, though
transmission from animal to human (zoonotic infection) is extremely rare.
What are heartworms?
 Heartworms are parasites that live in the blood of a dog’s heart
and adjacent blood vessels. They can grow from four to twelve inches in length,
reach maturation one year after infection and live for approximately five to seven
years. Adult heartworms living in the heart produce offspring, known as microfilariae,
which circulate in the animal’s blood. When a female mosquito bites an infected
animal, it sucks out the blood containing the microfilariae. When the mosquito bites
another pet, the infected larvae are transmitted. In many cases the infected dog
will not show symptoms in the early stages.
Heartworm is the most serious common parasite for dogs because it stresses the dog’s
heart by restricting blood flow and also damages other internal organs. The heart
may enlarge and become weakened due to an increased workload, and congestive heart
failure may occur. Left untreated, the disease can be fatal to dogs.
Blood screening tests can verify the presence of heartworms. Radiographs and x-rays
are used to detect the disease in its later stages. Prompt detection prevents needless
suffering.
Heartworm treatment and prevention
The good news is that most dogs with heartworm can be successfully treated, usually
with drugs (adulticide, microfilaricide) that kill adult heartworms and their offspring.
But prevention is the best cure – it’s safer, less expensive, and better for
your pet!
There are a variety of options for preventing heartworm infection, including an
injectable, monthly topicals and monthly chewable tablets. Preventative medications
are extremely effective and when given properly, on a regular basis, can completely
prevent your pet from contracting heartworm. But remember, year-round heartworm
protection is as good as your diligence in remembering to give your pet the prescribed
medication, as directed by your veterinarian!
Canine heartworm symptoms include:
- Difficulty breathing
- Coughing
- Fatigue, a dog that tires easily
- Listlessness
- Weight loss
- Rough hair coat.
 Ask your veterinarian
Because of the regional and climate-dependant nature of the heartworm cycle, it
is crucial to consult your veterinarian before giving any medication to your pet.
Your veterinarian is your best reference, with expert knowledge of the heartworm
cycle and transmission patterns in your region, along with the individual health
and activity profile of your dog. Before starting a preventive program, all dogs
that could possibly be affected with mature heartworms should be tested as preventive
medicines may cause severe reactions in dogs that are already hosts to adult heartworms.
A dog that is on a preventive medicine should be tested routinely to ensure on going
protection – especially when a dose has been missed or forgotten.
Can you catch heartworm and other parasites from your
pet?
Mosquitoes transmit heartworm, not pets. Humans are unnatural hosts for heartworm – therefore
cases of infection are rare. Many heartworm preventative medicines for pets do eliminate
other parasites such as hookworms, whipworms and roundworms, which are more commonly
seen in humans. Parasitic infections that can be transmitted from animals to humans
are known as parasitic zoonoses:
1. Hookworms
In dogs, hookworm infection occurs through ingestion or skin penetration of hookworm
larvae found in the stools or soil contaminated by feces of an infected animal.
The larvae then develop and migrate to the intestines where they hook onto the intestinal
wall and feast on the host’s blood. The larvae of hookworms can penetrate the skin
and infect humans through contact with soil or sand contaminated by feces of host
dogs or cats. In a human host, the hookworm larvae do not migrate to the intestines
and become blood-sucking adults as they do in pets. Instead, they move around under
the skin and eventually die causing an inflammatory skin reaction known as cutaneous
larva migrans, or “creeping eruptions”. It is important to keep your pet free of
hookworms with good hygiene, preventive medication and regular veterinary check
ups. Also, keep stray dogs and cats out of sandboxes and gardening areas.
2. Roundworms
Roundworms are parasitic worms that are round in shape, live in the dog’s intestines
and consume partially digested food. Unlike hookworms, they do not attach to the
intestinal wall, but literally swim in their food. Adult worms resemble spaghetti
and may come out in the feces or vomit of an infected dog. Transmission to dogs
is through eggs in feces, eating a prey animal that is a host (usually rodents),
mother’s milk, or in utero. In dogs, roundworms cause diarrhea, vomiting and in
extreme cases pneumonia and intestinal obstruction. In humans, roundworms can cause
a serious condition known as visceral larva migrans. Most victims are children who
are infected when putting contaminated fingers into their mouths. Once ingested,
the roundworm larvae, though not in its usual host, tries to complete its lifecycle.
The roundworm gets lost in the human body, usually in the eye, dies and generates
an inflammatory reaction that can cause blindness. Proper hand washing can prevent
infection.
Pet deworming of puppies and preventive medication will reduce environmental contamination.
3. Whipworms
The only way a dog can contract whipworms is by ingesting the eggs. When a dog walks
on ground infected by eggs, they are picked up on the paws and travel into the mouth
when he licks his paws or any contaminated toys or food bowls. Whipworm eggs can
survive extreme exterior conditions for months and even years. Within one to three
months after the eggs are swallowed they hatch in the dog’s intestine, attach to
the wall and begin to suck blood and lay eggs. In dogs, whipworm can cause diarrhea,
weight loss and in some cases, anemia. Whipworm infection in humans is extremely
rare.
Be safe, not sorry
Children are more prone to contracting zoonotic parasites, as they tend to kiss
and play more readily with pets. Parasite larvae are shed in the pet’s feces and
may contaminate soil and sand. When children play in the contaminated areas and
place their fingers in their mouths this allows the eggs to be ingested, causing
infection. Hookworm larvae are capable of infecting a host through penetration of
the skin. Be sure to pick up feces promptly and avoid eating while playing with
your pet. Frequent hand washing, as well as good general hygiene for people and
dogs, is recommended. Routine check ups by your veterinarian – including a
diagnostic test for worms and heartworm – as well as a physical exam along with
medical prevention, will not only keep your dog healthy but will reduce any risk
to you and your family.
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