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west nile virus
encephalitides
arboviruses
west nile virus
Birds are no
longer needed to test for West Nile. This is the fifth year
that the virus will be monitored within Cabarrus county. It is
now considered to be an established virus and not one that is
spreading into this county. The same species of birds are
sensitive to the disease and that is something to keep in mind when
finding a dead bird. The crow, cardinal, blue jay and raptors
have a higher mortality rate then other bird species do. There
are many species of birds that are able to carry the WNV but few of
these will die from it. The virus is either maintained within
the bird or it is suppressed by the bird's immune system. If
the virus is able to amplify then the mosquito is then able to pick
up the virus in the bloodmeal that it takes from the bird.
WNV was first identified in the US in
1999 in New York City. The virus established itself
within the avian population making birds its primary host. It
was then subject to the birds migratory paths allowing it to spread
to the different states across the nation. Since 1999, the
virus has spread across the US. WNV amplifies
within birds and then is transferred to other animals by mosquitoes.
This natural cycle sometimes takes a detour by infecting animals
that are unable to amplify the virus. These are referred to as
dead-end host; such as humans and horses. The dead-end
host will feel the effects of the virus but a mosquito will be
unable to transfer the virus from it to another host. So
infection of humans is undesirable for the virus as it ensures
certain doom. Other confirmed dead-end hosts include human,
horse, dog, squirrel, cat, rabbit, black bear, aquarium seal,
alligator, bovine, sheep, goat, llama, alpaca, emu, deer, chipmunk,
bat, skunk and others. Most of these animals rarely show
symptoms or their species is mildly effected by the virus.
Early detection is key in monitoring the virus and its impact on
public health and the environment.
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References & more info:
NIAID
CDC
arboviruses
The word arbovirus comes from the
condensed term: arthropod-borne virus. Arthropod being an
animal with a segmented body, jointed appendages and an exoskeleton
such as mosquitoes, ticks and spiders. These viruses are found
all over the world. In the US the main arboviruses regarding
mosquitoes, other than WNV, are LAC, WEE, SLE, EEE (see below for
more detail). The majority of infections are asymptomatic or
result in flu-like symptoms. Only a small percentage of
infected people develop encephalitis. Encephalitis is a
swelling of the brain which can lead to temporary or long term
damage or even death.
For the most part, humans and domestic animals are dead-end hosts
that end the transmission cycle of the virus; there is not enough
viral concentration in the blood of the host to continue the cycle.
To minimize exposure to these diseases, adequate personal protection
and education is essential.
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References & more info:
CDC
encephalitides-
lacrosse encephalitis/(LAC)
LAC is mostly found
in the mountain counties of North Carolina.
It is under reported due to the misdiagnosis of
many cases. There is no treatment for LAC, only management of
its symptoms. LAC has a host reservoir of chipmunks and tree
squirrels.
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References & more info:
CDC
western equine encephalitis/(wee)
WEE is also an alpha virus. It
is a leading cause of encephalitis in horses and humans in north
America. If affects mainly the western states including
western Canada. The virus infects most songbirds via the
mosquito species that breed in stream and irrigation drainage
waters. The virus can also infect other mammals as well.
Most cases are asymptomatic or just mild sickness. Clinical
cases include fever, headache, nausea, vomiting, anorexia and
malaise.
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References & more info:
CDC
st.louis encephalitis/(sle)
SLE is the most common
mosquito-transmitted disease to humans in America. It is a
flavivirus that causes about 200 fatalities a year
nationwide. Humans are
exposed to SLE though inclusion in the mosquito-bird transmission
cycle. As with many encephalitides, SLE is under-diagnosed.
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References & more info:
CDC
malaria
Malaria kills around 1 million
children
every year worldwide. Malaria is caused by the parasite
Plasmodium which is transferred to people by mosquitoes.
The parasite enters the salivary glands of the mosquito where it is
then injected into the next host.
This disease is a major problem in the countries of Africa, Central
& South America, Asia and the Indonesian Islands. Symptoms
include fever, shivering, headache, joint pain and vomiting.
Severe cases progress to convulsions, coma and even death.
Local transmission of malaria occurred in
northern Virginia in August of 2002. There were 2 cases,
one a 19 year old and the other a 15 year old. There both were
diagnosed and confirmed with malaria. Both people have fully
recovered after the malaria was identified and treated for.
Both patients had not been exposed through international travel,
blood transfusion, organ transplant or needle sharing. They
did live 1/2 mile from each other and less then 10 miles from
Washington Dulles International Airport. Mosquito testing
identified Anopheles quadrimaculatus and Anopheles
punctipennis as positive with the same strain of P.vivax
as the patients Finding a positive pool of mosquitoes in the
midst of active cases is very unusual. Anopheles mosquitoes
must be infected with the P.vivax parasite between 1-2 weeks
before being able to infect other people. Yet only have a life
span of about 4 weeks. This only allows a small window to trap
positive mosquitoes.
In 2003,
Palm Beach County Florida recorded 7 cases of locally acquired
malaria. All were the same strain of P.vivax and are
thought to originate from the same single source. All patients
were men with a mean age of 35 and all engaged in outdoor activities
and live within 10 miles of the Palm Beach International Airport.
Mosquitoes trapped in that area were all negative for the parasite.
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References & more info:
WHO
CDC
reports
CDC
PHPM
NPIC
USGS |
