Heartworm disease is a serious and potentially fatal disease in dogs and cats. It is
caused by a worm called Dirofilaria immitis.
Heartworms are found in the heart and large adjacent vessels of infected dogs. When
the worms infect a cat, they may go to several parts of the body.  The female worm is 6
to 14 inches long and 1/8 inch wide; the male is about half the size of the female. A
severely infected dog may have as many as 300 worms.
Adult heartworms live in the heart and pulmonary arteries of infected dogs. They have
been found in other areas of the body, but this is unusual. They survive up to 5 years
and, during this time, the female produces millions of young (microfilaria). These
microfilaria live in the bloodstream, mainly in the small blood vessels. The immature
heartworms cannot complete the entire life cycle in the dog, a mosquito is required to
complete the heartworm life cycle. The microfilaria are therefore not infective (cannot
grow to adulthood) in the dog, although they do cause problems, and spread the
disease.
As many as 30 species of mosquitoes can transmit heartworms. The female mosquito
bites the infected dog and ingests the microfilariae during the feeding. The microfilariae
develop further for 10 to 30 days in the mosquito and then enter the mouth parts of the
mosquito. The microfilariae are then called infective larvae and are now able to grow to
adulthood when they enter a dog.
When fully developed, the infective larvae enter the bloodstream and move to the heart
and adjacent vessels, where they grow to maturity in 2 to 3 months and start
reproducing, thereby completing the full life cycle.  
The disease is not spread directly from dog to dog. An intermediate host, the mosquito,
is required for transmission. Spread of the disease therefore coincides with the
mosquito season. The number of dogs infected and the length of the mosquito season
are directly correlated with the incidence of heartworm disease in any given area.
Canine heartworm disease occurs all over the world. In the United States, it was once
limited to the south and southeast regions. However, the disease is spreading and is
now found in most regions of the United States and Canada, particularly where
mosquitoes are prevalent, IE- near rivers and in places that have warm winters.
It takes a number of years before dogs show outward signs of infection. Consequently,
the disease is diagnosed mostly in 4 to 8 year old dogs. The disease is seldom
diagnosed in a dog under 1 year of age because the young worms (larvae) can take up
to 7 months to mature following establishment of infection in a dog.  Because visibly
signs may not show up until there has been too much damage it is important to test
yearly, even when on prevention.
Most dogs infected with heartworms do not show any signs of disease for as long as
two years. Unfortunately, by the time signs are seen, the disease is well advanced. The
signs of heartworm disease depend on the number of adult worms present, the location
of the worms, the length of time the worms have been present, and the degree of
damage to the heart, lungs, liver, and kidneys from the adult worms and the
microfilariae.
The most obvious signs are: a soft, dry, chronic cough, shortness of breath, weakness,
nervousness, listlessness, and loss of stamina. All of these signs are most noticeable
following exercise, when some dogs may even faint.
Destruction of lung tissue leads to coughing. Cirrhosis of the liver causes jaundice,
anemia, and general weakness because this organ is essential in maintaining a healthy
animal. The kidneys may also be affected and allow poisons to accumulate in the body.
Severely infected dogs may die suddenly during exercise or excitement.
Adult worms cause disease by clogging the heart and major blood vessels leading from
the heart. They interfere with the valve action in the heart. By clogging the main blood
vessels, the blood supply to other organs of the body is reduced, particularly the lungs,
liver and kidneys, leading to malfunction of these organs.
Young worms: Microfilariae circulate throughout the body but remain primarily in the
small blood vessels. Because they are as wide as the small vessels, they may block
blood flow in these vessels. The body cells being supplied by these vessels are
deprived of the nutrients and oxygen normally supplied by the blood. The lungs and liver
are primarily affected.

Testing:        
The first step in heartworm prevention is a simple blood test to check for the presence
of heartworms.  The heartworm prevention available in nearly 100% effective, but there
is still a small chance that infection may occur.  There is also the possibility that your pet
may not swallow the whole dose, or may even spit it out when you are not looking.  This
makes it important to test yearly to make sure there is no infection, even when on
prevention year round.
There are two kinds of heartworm tests that we use, a Microfilariae test, where the
blood is run through a filter and is inspected under a microscope to find any of the
microfilariae.  There is also an Antigen test, which runs the blood through a chemical
process to detect adult heartworms.  This is the more accurate of the two tests.

Prevention:
Once your pet has been found to be free of heartworms, it should be started on
heartworm prevention.  Puppies should be started on heartworm prevention at 4-6
weeks of age.  However, they cannot be tested for heartworms until they are 6 months-
testing prior to 6 months of age runs the risk of a false negative due to the incubation
period.
Now days most all heartworm prevention is given monthly, in a single dose.  Care
should be taken to make sure that your pet consumes the complete tablet.  It is also
important that the pervention be given at monthly (30 day) intervals.  If the interval
exceeds 30 days the effectiveness is reduced and re-medication is recommended.  
Prevention We Offer:
Heartgard Plus- this preventative protects you pet against heartworms, as well as the
intestinal parasites roundworm and hookworm.  It is available in different dosage
strengths for different weights.  Each comes in a carton with 6 chewable beef jerky type
treats.  This is an advantage if you pet is picky about what they eat.  It also includes
stickers to put on your calender to remind you when the pills are due.
Interceptor-This preventative protects against heartworms, as well as the intestinal
parasites roundworm, hookworm, and whipworm.  It is available in dosage strengths for
different weights.  Each comes in a dispenser card with 6 pills and also includes
stickers for you calender.
Sentinel-This preventive protects against heartworms, the intestinal parasites
hookworm, roundworm, and whipworm, and also prevents flea eggs from hatching.  It is
available in dosage strengths for different weights and is sold in packages containing 6
pills.
Revolution- This is a topical (applied to the skin) preventative that protects against
heartworm, fleas, ticks, ear mites, and sarcastic mange.  It comes in dosage strengths
for different weights and is sold in packages containing 3 ampules

Heartworm Treatment:
Dogs that have tested positive for heartworms must undergo a dangerous and costly
treatment to kill the parasites.
      Dogs must have bloodwork and chest X-rays done before treatment to make sure
that they are healthy enough for the treatment.
      The first part of the treatment consist of two injections 24 hours apart.  This section
of the treatment kills only the adult worms in the heart.
      Dogs must be rested for 4-6 weeks after this first treatment.  If they get excited or
exercise, the dying worms will move into the lungs and impair the dog's breathing.
      After the rest period, the second part of treatment is started.  The drug
administered kills the microfilariae in the blood.
      A microfilarial heartworm test is done one week later.  This test will be negative if
the treatment was successful.  The dog should then be put on heartworm preventative.
      In 4-6 months an antigen heartworm test is done.  If this test is negative, the
treatment was successful in killing the adult worms.
To avoid putting your dog through this intense treatment, it is important to keep your
dog on preventative for the entire year.  Warm weather months have an abundance of
mosquitoes, and in cold weather mosquitoes try to find protected areas in your house
or doghouse.  Thus, even dogs kept mainly indoors can become infected.
Heartworms and Prevention