Heartworm
Disease
Dogs are considered the definitive host for heartworms (Dirofilaria immitis).
However, heartworms may infect more than 30 species of animals
(e.g., coyotes, foxes, wolves and other wild canids, domestic cats
and wild felids, ferrets, sea lions, etc.) and humans as well.
When a mosquito carrying infective heartworm larvae bites a dog
and transmits the infection, the larvae grow, develop, and migrate
in the body over a period of several months to become sexually
mature male and female worms. These reside in the heart, lungs,
and associated blood vessels. Even as immature adults, the worms
mate and the females release their offspring (microfilariae), pronounced:
(micro fil ar ee), into the blood stream. The time elapsed from
when the larvae enter the dog until the minute offspring can be
detected in the blood (pre-patent period) is about six to seven
months. The male heartworms (four to six inches in length) and
the females (10-12 inches) become fully grown about one year after
infection, and their life span in dogs appears to be at least five
to seven years. |
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Preventive
Measures Internal
Parasites
External
Parasites
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Impact
Microfilaremia, the presence of heartworm offspring in the blood of the host,
is relatively common in dogs. However, not all heartworm infections
result in such offspring circulating in the blood. These are known
as occult heartworm infections and may be the result of a number
of factors such as single sex heartworm infections, host immune
responses affecting the presence of circulating offspring (microfilariae)
and most significantly, the administration of heartworm preventives.
Clinical Signs Associated
with Canine Heartworm Disease
Early Infection
No abnormal clinical signs observed
Mild Disease
Cough
Moderate Disease
Cough, exercise intolerance, abnormal lung sounds
Severe Disease
Cough, exercise intolerance, dyspnea (difficulty breathing), abnormal lung sounds,
hepatomegaly (enlargement of the liver), syncope (temporary loss of consciousness
due to poor blood flow to the brain), ascites (fluid accumulation in the abdominal
cavity), abnormal heart sounds, death
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