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Heartworm, a serious and often fatal disease of
dogs, cats, and other species of mammals, is
preventable. And, with the beginning of the mosquito
season, to help raise public awareness, April is
being recognized as Heartworm Prevention Month. The
American Heartworm Society has issued the following
informative article:
Most pet owners wouldn't knowingly put their pet at
risk of becoming infected with a potentially deadly
disease, yet according to the American Heartworm
Society (AHS), millions of pet owners who fail to
protect their dog from heartworm infection are doing
so everyday.
Heartworm is a life-threatening canine parasite
transmitted by mosquitoes that affects dogs in all
48 of the contiguous states and Hawaii. While
research shows that
America's
dog owners are familiar with the threat caused by
heartworm disease, adherence to the proper
administration of traditional heartworm
preventatives remains a serious problem for dog
owners and veterinarians.
According to a recent
Gallup
survey of 18,000 veterinary clinics nationwide, only
55 percent of U.S. dog-owning households are on a
heartworm preventative. And, for dogs who are on a
preventative, studies indicate that one in three dog
owners missed giving the monthly heartworm
prevention dose by more than a month, and 20 percent
of those who missed a monthly dose eventually
stopped giving the heartworm preventative
altogether, leaving their dog vulnerable to
potential infection.
With more than 240,000 dogs and 3,095 cats testing
positive for heartworm infection nationwide in 2001,
pet owner noncompliance to heartworm prevention
creates a serious problem that is putting America's
pets at risk.
What is Heartworm
Disease?
Canine heartworm disease is a potentially deadly
infection, caused by worms (Dirofilaria
immitis) that may grow to be
14-inch-long adults. These worms live in the right
side of the heart and arteries and of the lungs.
Dogs of any age and breed are susceptible to
infection. Heartworm infection can cause potentially
serious damage to these arteries, eventually leading
to heart failure, and in severe cases, damage other
organs such as the liver and kidneys. In extreme
cases, a dog can be infected with several hundred
heartworms. Cats are also susceptible to the
disease, but do not contribute significantly to
spreading the infection.
Coinciding with mosquito season, heartworm disease
is spread by mosquitoes that become infected with
microfilariae
while taking a blood meal from an infected dog. The
microfilariae mature into the infective larval stage
within the mosquito. When the mosquito then bites
another dog, cat, or susceptible animal, it then
passes the
larvae
into the animal's blood stream through the bite
wound, resulting in heartworm infection. It then
takes a little over six months for the infective
larvae to mature into adult worms that can live for
five to seven years in the dog.
Heartworm Disease is
Preventable
Because heartworm disease is completely preventable,
the AHS recommends that pet owners take steps now to
talk to their veterinarian about how to best protect
their pets from this dangerous disease. According to
the AHS, heartworm prevention is safe, easy, and
inexpensive compared to treating a dog or cat after
worms have matured into adults. While treatment for
heartworm disease is possible, it is a complicated
and expensive process, taking weeks for infected
animals to recover.
There are a variety of options for the prevention of
heartworm infection in dogs, including an injectable
administered by your veterinarian that provides
protection for six months, daily and monthly tablets
and chewables and monthly topicals. For cats, there
are monthly chewables, and a topical solution. All
of these methods are extremely effective, and when
administered properly on a timely schedule,
heartworm infection can be completely prevented.
Founded during the Heartworm Symposium of 1974, the
American Heartworm Society was formed to facilitate
and encourage the generation and dissemination of
information about heartworm disease and encourage
adoption of standardized procedures for its
diagnosis, treatment and prevention. The Society
stimulates and financially supports research, which
furthers knowledge and understanding of the disease.
Its headquarters are located in Batavia, Ill.
Source: PetEducation.com
Frequently Asked Questions:
What causes the death of a dog due to heartworm
disease?
Heartworm disease may cause a combination of medical
problems within the same dog including dysfunction
of the lungs, heart, liver and kidneys. The worms
are found in the right side of the heart and in the
major vessels that bring blood to and from the right
chambers, where they cause inflammation and
interfere with blood flow. This primarily causes
pulmonary thromboembolisms (clots in the lungs) and
congestive heart failure. It can also lead to liver
or kidney failure. Death can be caused by one or a
combination of these problems.
Does the age of a dog have anything to do with
better success in treatment for heartworm disease?
The age of the dog is just one factor to consider
when treating a dog for heartworms. Older dogs with
long-term heartworm infections may have damaged
lungs, hearts, livers, and kidneys that could
potentially complicate heartworm treatment. But if a
dog has moderately healthy organs and is
exercise-restricted, he should have a successful
treatment regardless of age.
Does a mother dog produce antibodies for puppies, so
that they are immune from heartworm infection?
No, there is no maternal transfer of protection
against heartworms. If puppies are exposed to
mosquitoes carrying infective larvae, they can be
infected. In areas with year-round potential for
infection, puppies should be started on heartworm
preventive by eight weeks of age. In areas where
there is minimal risk of heartworm infection during
the colder months, the puppy should be started in
early spring / summer, as indicated by your
veterinarian.
My cat goes outside daily. Should I put her on
heartworm prevention medication?
The prevalence of feline heartworm infection is
generally 5-15% of that found in the local dog
population. If heartworms are found in dogs in your
area, you should consider putting your cat on a
heartworm preventive. Your veterinarian will know
the risk in your area and can guide you on whether a
preventive is indicated.
My cat never goes outside. Should I put her on
heartworm prevention?
Both indoor cats and outdoor cats may develop
heartworms if exposed to mosquitoes carrying the
infective larvae. The prevalence of feline heartworm
infection is generally 5-15% of that found in the
local dog population. If heartworms are found in
dogs in your area and mosquitoes get into your
house, you should consider putting your cat on a
heartworm preventive. Your veterinarian will know
the risk in your area and can guide you on whether a
preventive is indicated. The American Heartworm
Society is recommending administration of a
preventive year-round for the following reasons: (1)
activity against some common intestinal parasites,
(2) increased compliance, and (3) retroactive
efficacy as a safeguard for inadvertent missed
doses.
Are heartworms more common in certain areas of the
United States?
Heartworms have been found in dogs native to all 50
states. The highest infection rates in dogs are
observed within 150 miles of the Atlantic and Gulf
coasts and along the
Mississippi River
and its major tributaries.
Is there an effective natural prevention for
heartworm?
No, there is no natural prevention for heartworms.
Is it OK to have surgery on a heartworm positive
dog?
If the surgery can be postponed, it would be better
to treat the dog for the heartworms first.
What are the signs of heartworm disease in cats?
Signs of heartworm disease in cats can be very
non-specific. Signs which may be seen include
intermittent vomiting, coughing, asthma-like
attacks, and lack of appetite or weight loss. Sudden
acute signs of collapse and death may also occur.
How often should I have my cat tested for
heartworms?
Although serology tests are becoming more sensitive,
we are not yet totally satisfied with our ability to
diagnose heartworms with these tests alone. We
recommend testing prior to starting a preventive to
establish a baseline reference prior to initiating
chemoprophylaxis.
My dog tested positive for heartworms. What does
this mean?
That means your dog actually has heartworms in the
right chambers of its heart or pulmonary arteries.
If left untreated, they could begin to cause
heartworm disease if the process has not already
started. Most all dogs can be successfully treated
and rid of heartworms if they are detected prior to
causing severe heartworm disease. In asymptomatic
dogs, less than 1 % would likely have any
significant problem from treatment.
What is the treatment for heartworm disease? Why is
it so expensive?
Adult heartworms are killed using a drug called an
adulticide that is injected into the muscle. A
series of injections is given. Treatment may be
administered on an outpatient basis, but ordinarily
hospitalization is recommended. When the dog is sent
home, exercise should be limited to leash walking
for the duration of the treatment period, which can
last from one to two months. This will decrease the
risk of blocked blood flow through the lungs by dead
worms. The expense of treatment is affected by
several factors, such as the cost of the drug, the
pre-treatment tests and multiple office visits.
How long does it take before heartworm infection can
be detected by blood tests?
It takes seven months from the time a dog is bitten
by infected mosquitoes until a blood test can
accurately detect the presence of adult female
worms.
My dog has heartworms. I can’t afford to treat him.
Are there any alternatives?
There is only one drug (melarsomine - Immiticide®)
approved by the FDA for the treatment of heartworms.
Research has shown that ivermectin, the active
ingredient in several heartworm preventives, has the
ability to slowly kill young adult heartworms. This
generally requires more than a year of continuous
monthly administrations and may take more than two
years before heartworms are eliminated completely.
The older the worms are when first exposed to
ivermectin, the slower they are to die. In the
meantime, the infection persists and continues to
cause disease. Therefore, long-term continuous
administration of ivermectin generally is not a
substitute for conventional treatment.
My dog was treated for heartworm three months ago
and his heartworm test is still positive. Should I
retreat as my vet recommends?
It can take four or more months for all the remnants
of the dead worms to be cleared from the dog.
Testing to see if the dog is clear should not be
done until at least six months following treatment.
Can heartworm larvae spread to puppies through the
mother’s bloodstream?
Microfilaria (embryos) can spread to puppies from
the mother’s bloodstream, but these can not develop
into adult heartworms. Microfilaria must first pass
through a mosquito where they are transformed into
infective larvae. These microfilaria are eliminated
from the puppies when they are placed on heartworm
preventives.
Why do dogs need to be blood tested before starting
heartworm medication?
Before starting a preventive program, all dogs that
could possibly be infected with mature heartworms
should be tested. Giving heartworm preventives to
dogs having heartworms can lead to severe reactions
that could be harmful or even fatal to the dog.
Puppies under seven months of age can be started on
heartworm preventives without first testing. That is
because it can take up to six and one half months
after being bitten by infected mosquitoes before the
dog will test positive. The puppy should be tested
four to seven months after starting heartworm
preventive to detect any infection acquired during
the first few months of life.
Is there a vaccine for heartworm disease?
At this point in time, there is not a commercially
available vaccine for the prevention of heartworm
disease in dogs or cats. However, there are research
scientists looking at this possibility. There are a
variety of pharmaceutical products administered
either orally or topically that effectively prevent
the development of heartworm disease in dogs and
cats.
I heard that the heartworm prevention medication is
toxic to certain breeds of dogs, particularly
collies. Is this true?
One of the most used heartworm preventive
medications is based on ivermectin. This medication
when used orally at the heartworm preventive dose (6
mcg/kg) is completely safe for all breeds of dogs. A
few dogs of the Collie breed were found to be
sensitive to ivermectin when administered in
exaggerated doses equal to 16 times the dose
recommended for prevention of heartworm disease.
My dog has heartworms. My vet started her on monthly
prevention before he started treatment. Is this OK?
In most cases, it is the preferred approach! By
starting the prevention program you are ensuring
that your dog will not get a new heartworm
infection, while being treated for the existing
heartworm disease. Further, you are helping to keep
your dog from being a source of heartworm larvae
(microfilaria) for mosquitoes to pick up and
eventually infect other dogs. Your vet’s approach
may make the treatment of the existing infection
more effective and is in agreement with the
recommendations of the American Heartworm Society.
I heard that certain heartworm prevention
medications will also protect against intestinal
parasites. Are these medications much stronger and
will they hurt my dog?
Certain heartworm preventive products are also
effective in removing specific intestinal (and
external) parasites and are labeled for such uses.
The ability of these products to remove several
species of parasites is not due to being stronger,
that is they do not contain more of the active drug
used to prevent heartworm disease. They either
contain a single active ingredient that is effective
against several parasites including developing
heartworm or a combination of ingredients to achieve
control of many different parasites. The products
have been tested and meet the same safety
requirements as the heartworm prevention only
products.
My vet said my dog has heartworm disease and is in
the 4th stage. What is a stage?
Stage or class is used to describe the severity of
the disease and determine the best way to treat the
dog with the disease. The class of the disease a dog
has can also help predict the chances of a
successful treatment or prognosis. The stages or
classes run one through four. Unfortunately, the 4th
stage or class four disease is the most severe and
the most difficult to treat. Such cases generally
require a surgical procedure to remove the worms
from the heart and major blood vessel bringing blood
into the heart before any further treatment can be
attempted. You should discuss your dog’s condition
and prognosis with your veterinarian immediately.
Can heartworm larvae spread to kittens through the
mother’s bloodstream?
No. Heartworm larvae are transmitted from one animal
to another only by the bite of a mosquito carrying
the infective stage of the larvae. Occasionally,
microfilariae circulating in the blood of a pregnant
dog can cross the placenta and get into the blood of
puppies in utero, but this has never been reported
in cats. And even when this occurs in dogs, it is of
no consequence, as the microfilariae do not develop
further in the puppies. So, they die in the puppies
within a year unless they are taken up in the bite
of a mosquito.
Is heartworm contagious from dog to dog?
No. Heartworm can be transmitted from animal to
animal only by the bite of a mosquito carrying the
infective stage of the larvae. However, if there is
an infected dog with microfilariae circulating in
the blood susceptible mosquitoes and noninfected
dogs or other susceptible animals in the same area,
the mosquitoes can bite the infected dog and
transmit the infection to the other animals.
Can people get heartworm disease from a mosquito
bite?
Yes, it is possible. Fortunately, people are not
natural hosts for heartworms. However, a few people
are susceptible enough for the larvae (usually only
one) to grow and migrate to their heart and lung
arteries. In this case, the larvae usually die
before they get old enough to produce microfilariae.
The worms die slowly, and as they are dying, the
person’s body produces a wall around the worm. Most
people (over 50%) infected with a heartworm or two
never have symptoms, but some people (33%) will have
chest pains, some (20%) will have a cough, and fewer
(15%) will have a fever. Only about 1% will have the
severe signs of spitting up blood or difficulty in
breathing. Most people that are diagnosed with
heartworms are “smokers.” When the physician sees
the white spot (called a “coin lesion”) on the chest
X-Ray, they don’t want to take the risk that it is a
primary lung cancer, so they do painful surgery to
remove the affected lung tissue, only to find a
dying worm. Unfortunately, there is no reliable
diagnostic test for heartworm in humans.
Can children get heartworm disease by playing with
and being licked by a dog with heartworm disease?
No. Heartworm disease is transmitted only by the
bite of a mosquito that is carrying the infective
stage of the parasite.
I heard that yearly tests for heartworms are not
recommended anymore. Is this true? How often should
I have my dog tested?
Annual testing for heartworm infection is now highly
recommended. Even though heartworm preventives,
particularly monthly oral and topical formulations
and the injectable product, are essentially 100% in
preventing infection when administered according to
instructions on the label, animals on heartworm
prevention occasionally test positive for
heartworms. This apparent lack of efficacy is
usually due to owner compliance failure, travel or
relocation of the animal to an area of active
heartworm transmission, or unknown (or misdiagnosed)
prior infection. Annual testing gives owners peace
of mind in knowing that their pet is free of
heartworms, and in cases where the animal is
infected, it assures them of early diagnosis of
infection and maximal benefits from heartworm
adulticide therapy.
I have missed two months of heartworm prevention for
my dog. Should I worry?
Monthly heartworm preventives kill the heartworm
larvae that accumulate in the dog’s body during the
month prior to dosing. In addition, these
formulations have an additional month of safety-net
(reach-back, retroactive) efficacy when dosing is
resumed. The extended efficacy of these preventives
is a safeguard in the event of inadvertent delay or
omission of a regularly scheduled dose and does not
justify lengthening the recommended interval of
administration. If the lapse in administration of a
monthly formulation or the injectable product is
three to six months, dosing should resume
immediately and the dog should be tested for
possible infection seven to 12 months later. The
reason for testing seven months later is that
heartworms must be about seven months old before the
infection can be diagnosed.
With daily heartworm preventives, if the gap in
administration is less than two months, one to two
doses of a monthly preventive should restore
protection. If the lapse in administration is three
to six months, switch to a monthly preventive
immediately and test the dog seven to 12 months
later.
Source: American Heartworm Society--www.heartwormsociety.org.
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