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Heartworm Disease (HWD) is probably one of the
least understood and most commonly underestimated conditions in pets
today. Because it is a silent killer, with actual symptoms not
appearing until the late stages of the disease, prevention is many
times neglected. Pet owners, in an effort to save money on their
pets’ health care, oftentimes refuse heartworm testing and
prevention in favor of treating less life-threatening, but more
obvious conditions such as fleas and ticks.
While there are some areas of the United
States where HWD prevention is not necessary, HWD is a major problem
in the Southeast, East, Mississippi River Valley and California. In
the northern states, heartworm "season" is shorter, but
the disease is a very real threat nonetheless.
The first step in understanding the risks to
your pet is understanding the disease itself. How is it spread? How
does it affect pets? How can it be treated and prevented? These are
all questions that must be addressed before a pet owner elects to
postpone HWD testing and/or prevention.
HWD is carried by mosquitoes and is caused by
the parasite Dirofilaria immitis. It affects both dogs and
cats. For transmission of HWD to take place, a mosquito sucks blood
containing microscopic baby worms from an infected animal. The baby
worms develop in the mosquito and become infective in about 2 weeks.
This infective larval stage is then passed on to another animal via
another mosquito bite. The baby heartworms mature in the infected
animal 3 to 4 months later when they migrate to the heart and
pulmonary arteries. Here they may live as long as 7 years and reach
lengths of up to 12 inches. If these mature worms consist of both
males and females, reproduction occurs. This results in microscopic
baby worms circulating in the blood, thus completing the lifecycle.
Damage to the heart and lungs of the infected
animal can be severe, even though mild infestations may produce no
symptoms. The first signs of HWD are usually coughing, weight loss
and tiring easily during exercise. Later stages of the disease are
characterized by heart failure, with severe coughing and difficulty
in breathing. If a pet reaches this stage of HWD, its life is in
danger.
Your veterinarian can test for HWD in his/her
clinic or hospital. While one blood test can reveal the presence of
the baby worms, another identifies proteins produced by adult female
worms. X-rays can also be diagnostic. Testing for HWD should be done
yearly on all dogs over 6 months of age.
After a pet is found not to have HWD, the
veterinarian usually prescribes a HWD preventive. The most popular
preventives are easily administered, monthly medications that are
extremely safe when given according to your veterinarian’s
instructions. In areas where HWD is a major problem, preventive is
given year-round. In other areas, prevention is used from very early
spring until 1 to 2 months after the first hard frost. Your
veterinarian can also advise you in this respect.
If your dog tests positive for HWD, the
treatment can be painful and risky, as well as costly. A
hospitalization usually is required once the dog is deemed healthy
enough to undergo the treatment, which consists of a series of
injections. The drugs used to kill adult heartworms can cause
irritation at the injection site and also have potential to damage
the liver and kidneys. As the adult heartworms die, they can produce
a serious reaction in the lungs 1 to 3 weeks after the treatment.
Many times, other drugs must be given to reduce lung inflammation
and coughing. It is very important that the patient be kept
extremely quiet, avoiding all exercise and excitement for at least 1
month after treatment. If this is not done, the risk for heart
failure and death is high.
As you can see, the old adage that "an
ounce of prevention is worth a pound of cure" holds true where
HWD is concerned. It is far easier, less costly and better for the
pet to prevent HWD than to treat a dog that has it. As there is no
approved treatment for cats infected with HWD, prevention is the
only choice. Your veterinarian can provide valuable advice and
information about HWD, allowing you to make the best decision for
your pet with his/her health in mind.
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