Heartworm Frequently Asked Questions
1.
How is my pet exposed? Heartworm
is a mosquito borne parasite that is transmitted during the time an infective
mosquito is feeding. It is not
actually transmitted by the bite of the mosquito, rather, the infective stages
to the pet break out of those portions of the mosquito’s mouthparts that are not
inserted into the pets skin. The
larvae are covered by the fluid that leaks out of the mosquito when the
infective stages of the heartworm breaks out of the mosquito and the infective
larvae enter the dog through the hole made in the dog’s skin by the piercing
portions of the mosquito’s mouthparts.
2.
Do all mosquitoes transmit heartworm?
No. Within a given
geographic area, only a few of the many species of mosquitoes present are
significant vectors. This is due to
several factors. a)
The Mosquito has to support development of the worms to the infective
stage. Some species of mosquitoes
will not allow the worm to develop in their cells and the worms die.
b) The mosquito has to be willing to feed on mammals.
Many mosquitoes are bird feeders and will only reluctantly, if at all,
feed on mammals. In Northern
California, Aedes vexans, Aedes sierrensis, and Aedes dorsalis
are thought to be the major vectors. One
of the pieces of information that will be obtained by this control program is
the identity of field caught adult mosquitoes carrying the infective stage.
3.
How do I determine if my pet is infected? There are blood tests available for pets that can detect the
presence of substances released from the surface of adult worms or detect the
actual microfilariae in the blood. Both
tests should be run on the blood sample from a dog. There are also tests that can be used to detect antibody
produced by cats against the developing adult worm.
4.
Are all pets at equal risk of becoming infected?
No. In
California there are 7 different plant climate zones, each with different
temperature ranges. There are also
great differences in habitats in California, some of which are not favorable for
vector mosquito production. Dogs at
greatest risk of infection in California are those that live in the foothill
plant climate zone of either the coast range or the Sierra Nevada mountain
range. This includes areas with
65cm of rainfall or more per year and elevations between 400 and 3000 ft.
Dogs kept outside day or night or all the time, not receiving preventive
medicine for heartworm living in the foothill plant climate zones are at
greatest risk of infection. Next at
risk are the outdoor, non prophylacted dogs living in the upper Sacramento
Valley along the Sacramento, Feather, and American Rivers or their tributaries. This is followed by the outdoor, nonprophylacted dogs living
in the intermediate valleys plant climate zone, which include much of the region
between the mountains of the coast range.
In these three areas, prevalence in dogs varies from 14 to 174 infected
dogs per 1,000 examined or 1.4 to 17%. These
figures are based upon prevalence data collected on over 75,000 dogs examined
from 1983 through 1999 in Northern California.
At least risk of infection are dogs in the coastal plant climate zone of
the San Francisco Bay Area kept always indoors, with no travel out of that area.
5.
Why should I spend money to prevent the infection? There are two good reasons.
a) Heartworm infections
produce damage to the heart, lungs and kidneys of pets. Much of this damage may be irreversible even if the pet is
treated for the adult worms and microfilariae.
The damage done to those vital organs will reduce the dog’s exercise
tolerance and shorten its life expectancy, thus limiting its value as a family
companion. b) The cost of prevention is much cheaper than the cost of
treatment. The cost of medical care
associated with treating a dog for heartworm infection can reach 750 to 1,000
dollars. Preventive medicine that
is 99% effective in preventing infection and requires the owner to give
the pet a single dose of the drug per month costs $54 a year for a medium sized
dog. In ten years, therefore,
prevention will cost the dog owner $540. This
is $210 to $460 less than the cost of treating the dog just once.
6.
What are the domestic animals most susceptible to infection? Dogs are the domestic pet most involved in general.
In areas of high prevalence in dogs, i.e. the foothill plant climate
zones of California, outdoor cats are at increased risk of infection.
Infections in horses have been reported but appear to be rare even in
areas where dogs are highly infected. Cows,
goats, sheep and pigs are even less susceptible than horses.