April is National Heartworm Awareness Month
Heartworm disease is a serious
and potentially fatal disease that is widespread in pets. Heartworms live in
the heart, lungs and blood vessels of affected pets. This causes severe lung
disease, heart failure and damage to other organs in the body. Heartworms also
live in other mammal species such as wolves, coyotes, foxes, sea lions and even
humans in some rare cases.
Dogs are a natural host
for heartworms, which means the worms that live inside your pet mature into
adults, mate and produce offspring. Dogs have been known to harbor several
hundred heartworms in their body. Long
lasting damage to the heart, lungs and arteries can affect the quality of life
long after the parasites are gone.
Cats are an atypical host
for heartworm. If they do become infected, most of them do not survive into the
adult stage. They generally only have 1-3 worms, which means that damage can
occur. Immature heartworms can cause
damage in the form of a condition called heartworm associated respiratory
disease (HARD). The medication used to treat dogs for heartworm disease can’t
be used in cats.
How
is heartworm transmitted from one pet to another?
This is where the mosquito
comes into play. The adult female heartworms that are living in coyotes, foxes,
wolves, or dogs produce microscopic baby worms called microfilaria. These baby
worms circulate in the blood stream. When the mosquito takes a blood meal from
the infected animal, it picks up the baby worms which mature into “infective
stage” larvae over the period of 10-14 days. The mosquito then bites a dog, cat
or wild animal, in which the infective larvae are deposited on to the surface
of the animal’s skin. These larvae enter
the new host within the wound left behind by the mosquito. It then takes 6
months for the larvae to mature into adult heartworms. Once mature, heartworms
can live for 5-7 years in dogs and 2-3 years in cats
Signs
and symptoms
Early
stages of the disease may not be noticeable in your pet. The longer they are
infected, the higher the chance is for symptoms to occur.
Signs
for dogs may include: Persistent cough, reluctance to exercise, fatigue after
moderate activity, decreased appetite, and weight loss. As heartworm disease
progresses, heart disease may develop. The longer the disease is present and
the more worms your pet has can cause blockages of blood flow within the heart
that can lead to cardiovascular collapse which is life threatening. Unless your
pet has emergency surgery to remove the worms from the heart, few dogs survive.
Signs
of heartworm in cats can either be subtle or very dramatic. Symptoms may
include: Coughing, asthma like attacks, periodic vomiting, loss of appetite or
weight loss. Unfortunately, in some cases, the first sign of symptoms is sudden
collapse or sudden death.
Is
your pet at risk for heartworm disease?
Heartworm
disease is spreading to new regions of the country each year. Even if you live
in a place that doesn’t have a high incidence, you may travel with your pet not
realizing that where you are going does have a higher incidence of heartworm.
Also, stray, neglected and animals traveling to your area may be carrying it.
For example, when hurricane Katrina hit, 250,000 pets, many of which were
infected with heartworms were adopted out and shipped to all different parts of
the country.
How
and when should you test your pet?
We use
an in house blood test that can detect the heartworm antigen. We recommend
testing your pet at 6 months of age and then yearly after that. It takes at
least 6 months to show positive on the test. We recommend yearly after that.
If your pet has not
been on heartworm prevention, the recommendation would be to test prior to
prevention. You may be wondering why we recommend yearly testing if your pet is
on prevention? We need to make sure the prevention they are on is working.
Preventatives are highly affective, but giving one dose late or skipping could
be the difference if your pet becomes heartworm positive. The National
Heartworm Association is recommending year round prevention to be given.
Heartworm
disease is harder to detect in cats than dogs, because they don’t always have
adult heartworms. We can antigen test for it, but the veterinarian may also
take an x-ray or use an ultrasound to look for heartworms. Prevention is the
best way to go for cats, especially since there is no approved treatment for
them.
My
pet tested positive, now what do I do?
Not all dogs
have microfilaria circulating in their bloodstream or have been on heartworm
prevention drugs that kill microfilaria. We will perform an occult heartworm
blood (ELISA) test to detect antigens (proteins) given off by adult female
heartworms. Any dog that tests positive for heartworm disease will have
additional testing done. We will perform chest x-rays to evaluate the size of
your pets heart and see if there are any changes to their lungs. If heart
failure is suspected, the Doctor may recommend an echocardiogram to make sure
there is no other reason for heart failure to be occurring. Some laboratory
testing will be done as well to check other internal organs as well. If other
disease processes are found, those would be treated first since heartworm
treatment can adversely affect the kidneys and liver.
The treatment used in
dogs is an adulticide such as Immiticide. There are 2 different dosing schedules
available:
1 1. 2 intramuscular injections are given 24
hours apart. This way kills 90-95% of adult heartworms usually in 2-3 weeks.
2. Dogs with right sided heart failure or
changes in their lungs on x-rays are administered the Immiticide in split
doses. This method kills fewer heartworms with each injection which limits the
risk of worsening lung problems or acute death. With this treatment, 1 intramuscular
injection is given, the pet is rested for 4-6 weeks, then 2 injections given 24
hours apart.
This
form of treatment is not recommended in cats because killing of the adult
heartworms can be fatal if too many die at once. Cat’s lungs can’t handle more
than 1-2 heartworms dying at once.
Products that have
ivermectin such as heartgard can be used to slowly kill some of the adult
heartworms if the product is given for at least 18 months. We do not recommend
this method because if your dog is too active, you risk pulmonary embolism and
sudden breathing problems. We only use this method if there are other health
concerns going on at the same time.
Baby microfilaria can
be treated after the adult heartworms have been treated. This is an oral form
of ivermectin that we give, while your pet is hospitalized for the day so we
can monitor. This kills a large number of microfilaria within 2-8 hours after
the medication is given.
All pets are kept quiet
for 6 weeks following treatment to prevent any pulmonary embolisms or acute
death. 4-6 months out, we will run some additional testing to make sure the
heartworm disease has cleared. If your pet remains positive, the treatment
would be repeated.
Prognosis
Most
dogs do well with treatment and are able to be started on prevention after
treatment is complete. We have several types of preventions available depending
what works best with your lifestyle. If your pet has kidney, liver, or lung
changes problems during the treatment, prognosis is guarded if the problems
persist after treatment. Some dogs are able to return to normal activity, but
may not have the same energy level they had before. Dogs with right sided heart
failure may have a poor prognosis because of the treatment and may need
treatment for the rest of their lives.
Preventions
We have different preventions available. We offer monthly chewables, monthly topicals or a 6 month injection available.