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Running head: WEST NILE VIRUS
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West Nile Virus
Nick Kurek
Ferris State University
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Abstract
West Nile Virus [WNV] is a reemerging disease. It is an emerging disease in the United States
where it has spread from an initial appearance in the New York City area in 1999 to become
endemic in the continental United States. It is necessary for clinicians and the general population
to be aware of WNV. This paper explores WNV. Transmission, clinical presentation, diagnosis,
treatment, means of possible prevention of acquisition, an analysis of current literature, and a
look at factors that may actual promote the emergence of WNV will be discussed. The author
leaves the reader pondering reality.
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West Nile Virus
We live in a dangerous world. A seemingly insignificant thing, such as a mosquito bite,
could potentially be fatal and/or have life altering consequences. Mosquitoes, while necessary
for the food chain, carry many diseases. West Nile Virus [WNV] is one of them.
WNV is technically a reemerging infectious disease. Veenema (2013) defines
reemerging as “infections that have been known but demonstrate a marked increase in incidence
or geographic range” (p. 430). While WNV is not a new disease globally, it is relatively new in
the United States and certainly of concern. Anderson & Harrington (n.d.) inform us that while
we have known about the WNV since the late 1930’s, it first appeared in the United States
during the summer of 1999 in the New York City area. Kilpatrick, Kramer, Jones, Marra, &
Daszak (2006) state “WNV has caused repeated large-scale human epidemics in North America
since it was first detected in 1999” (para.1). WNV has spread across the continental United
States with cases having been reported in all 48 continental States (Anderson & Harrington,
n.d.). The National Institute of Allergy and Infectious Diseases [NIAID] (2010) has WNV in its
list of 20 emerging and re-emerging infectious diseases.
The Centers for Disease Control and Prevention [CDC] (2013) informs us that there has
been 1.5 million reported WNV infections in the United States since the first in 1999. WNV
continues to spread across the country and in Michigan. In its most current report, the Michigan
Department of Community Health [MDCH] received 104 reports of WNV from 2007 – 2011
with the highest annual total of 34 cases being reported in 2011 (Michigan Department of
Community Health Bureau of Disease Control, Prevention, and Epidemiology Reportable
Infectious Diseases in Michigan, 2007–2011, p. 96).
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Transmission
What is WNV? The MDCH states “WNV is a single-stranded RNA virus of the
Flaviviridae family (flavivirus)” (Michigan Department of Community Health Bureau of Disease
Control, Prevention, and Epidemiology Reportable Infectious Diseases in Michigan, 2007–2011,
p. 95). WNV is a zoonotic (spread from animals to humans), vector borne disease. The Virginia
Department of Health (2013) informs us that a vector borne disease is “the term commonly used
to describe an illness caused by an infectious microbe that is transmitted to people by bloodsucking arthropods (insects or arachnids)”. The CDC (2013) states:
Vector-borne diseases are among the most complex of all infectious diseases to prevent
and control. Not only is it difficult to predict the habits of mosquitoes, ticks and fleas, but
most vector-borne viruses or bacteria infect animals as well as humans. WNV which is
primarily a disease of birds, is a good example.
WNV is definitely an example of a vector borne disease. In fact, Kilpatrick et al (2006)
state “WNV is now the dominant vector-borne disease in North America”.
It is important to realize that not every mosquito carries WNV. The MDCH (2007-2011)
states “In areas where WNV is actively circulating, less than 1 in 100 mosquitoes will be
infected”; however, once a mosquito is infected, it remains infective and can subsequently infect
people for its life span (Michigan Department of Community Health Bureau of Disease Control,
Prevention, and Epidemiology Reportable Infectious Diseases in Michigan, 2007–2011, p. 95).
Unfortunately, like most viruses there can be multiple routes of transmission. WNV is
usually acquired from being bitten by an infected mosquito. There have been “a very small
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proportion” of cases where it has been spread from “blood transfusions, organ transplants,
exposure in a laboratory setting, and from mother to baby during pregnancy, delivery, or
breastfeeding” (CDC, 2013).
Clinical Presentation
People get bit by mosquitoes all the time. It is very possible to be infected with WNV
and not know it. The CDC (2013) states “70-80% of those who become infected with WNV do
not develop any symptoms”. This implies that the vast majority of people who are infected may
not even realize it and may even potentially transmit it to others.
As with most diseases there is an incubation period from infection to manifestation of
symptoms. Those who do develop WNV symptoms usually start to feel sick and exhibit
symptoms 3 to 14 days after being infected (Goodman & Livingston, 2012). The majority of
people who develop WNV symptoms experience a relatively mild form. The CDC (2013) states:
About 1 in 5 people who are infected will develop a fever with other symptoms such as
headache, body aches, joint pains, vomiting, diarrhea, or rash. Most people with this type
of West Nile virus disease recover completely, but fatigue and weakness can last for
weeks or months.
While most cases of WNV are relatively mild, there are cases that become severe.
Goodman & Livingston (2012) inform us “approximately 1 in 150 infected persons develop
severe disease with serious symptoms”. WNV can have lifelong consequences. Murray et al
(2010) that “WNV is capable of long-term persistence in patients, particularly in the presence of
chronic clinical symptoms” (p.3). WNV may even result in death. The CDC (2013) states:
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Less than 1% of people who are infected will develop a serious neurologic illness such as
encephalitis or meningitis (inflammation of the brain or surrounding tissues). The
symptoms of neurologic illness can include headache, high fever, neck stiffness,
disorientation, coma, tremors, seizures, or paralysis. Serious illness can occur in people
of any age. However, people over 60 years of age are at the greatest risk for severe
disease. People with certain medical conditions, such as cancer, diabetes, hypertension,
kidney disease, and people who have received organ transplants, are also at greater risk
for serious illness. Recovery from severe disease may take several weeks or months.
Some of the neurologic effects may be permanent. About 10 percent of people who
develop neurologic infection due to West Nile virus will die.
Diagnosis
Usually, the WNV mimics flu-like symptoms and passes in a short period of time. Many
people do not seek care unless they develop severe symptoms. This is important to note as it
may definitely skew the number of cases in that there may be a more wide spread incidence;
however, many may simply not be reported due to the mild symptoms experienced.
It is when symptoms become severe and progress that people present to clinicians for
treatment. An accurate history is an essential part of the assessment. Many of the symptoms
previously discussed will be present. In contemplating a differential diagnosis, the CDC (2013)
recommends:
WNV should be considered in any person with a febrile or acute neurologic illness who
has had recent exposure to mosquitoes, blood transfusion, or organ transplantation,
especially during the summer months in areas where virus activity has been reported. The
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diagnosis should also be considered in any infant born to a mother infected with WNV
during pregnancy or while breastfeeding.
Unfortunately, some people may not be able to give nor have family available to provide
a history. Clinically, the manifestation of WNV may be similar to other viral infections and may
not necessarily be readily diagnosed. The CDC (2013) states:
Less than 1% of infected persons develop neuroinvasive disease, which typically
manifests as meningitis, encephalitis, or acute flaccid paralysis. WNV meningitis is
clinically indistinguishable from viral meningitis due to other etiologies and typically
presents with fever, headache, and nuchal rigidity. WNV encephalitis is a more severe
clinical syndrome that usually manifests with fever and altered mental status, seizures,
focal neurologic deficits, or movement disorders such as tremor or Parkinsonism. WNV
acute flaccid paralysis is usually clinically and pathologically identical to poliovirusassociated poliomyelitis, with damage of anterior horn cells, and may progress to
respiratory paralysis requiring mechanical ventilation. WNV poliomyelitis often presents
as isolated limb paresis or paralysis and can occur without fever or apparent viral
prodrome. WNV-associated Guillain-Barré syndrome and radiculopathy have also been
reported and can be distinguished from WNV poliomyelitis by clinical manifestations
and electrophysiologic testing.
As with many diseases, initial routine blood work may not be specific enough to lead to
diagnosis. Specific blood tests provide the definitive diagnosis of WNV. Quest Diagnostics
(2012) states:
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The IgM antibody capture enzyme-linked immunosorbent assay (MAC–ELISA) is the
most conclusive laboratory method for diagnosis of WNV infection of the CNS. Quest
Diagnostics currently offers an IgM MAC–ELISA, an IgG ELISA, and a real-time
polymerase chain reaction (PCR) assay for WNV. The methods can be performed using
CSF or blood (ie, serum/plasma) samples. A nucleic acid amplification test is also
available for donor testing.
Treatment
There is no cure for WNV. The CDC (2012) states “although various drugs have been
evaluated or empirically used for WNV disease, none have shown specific benefit to date”.
There is no specific treatment for WNV. Treatment of those infected with WNV is directed at
managing symptoms and providing supportive care (Goodman & Livingston, 2012).
Prevention
While WNV cannot be treated as yet, its spread may be prevented or at least controlled
through mosquito management. Even though mosquitoes carry many diseases, they are a
necessary member of the food chain and we cannot simply eradicate them. We can attempt to
control the mosquito populations and protect ourselves from them. CDC (2012) states:
No WNV vaccines are licensed for use in humans. In the absence of a vaccine,
prevention of WNV disease depends on community-level mosquito control programs to
reduce vector densities, personal protective measures to decrease exposure to infected
mosquitoes, and screening of blood and organ donors. Personal protective measures
include use of mosquito repellents, wearing long-sleeved shirts and long pants, and
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limiting outdoor exposure from dusk to dawn. Using air conditioning, installing window
and door screens, and reducing peridomestic mosquito breeding sites, can further
decrease the risk for WNV exposure. Blood and some organ donations in the United
States are screened for WNV infection; health care professionals should remain vigilant
for the possible transmission of WNV through blood transfusion or organ transplantation.
Any suspected WNV infections temporally associated with blood transfusion or organ
transplantation should be reported promptly to the appropriate state health department.
It is important to note that in the CDC’s recommendation, the community and each
individual are encouraged to take and are provided with measures to enhance their own safety
and decrease potential for acquisition. Awareness is essential. We can decrease our chances of
acquiring WNV by following the CDC’s advice. Personal protection as outlined by the CDC
may not always be followed; however, it is necessary to be cognitive of it especially if we are
going to be in areas heavily populated with mosquitoes. Prevention starts with awareness and
each individual’s actions or inactions. Veenema (2013) informs us that increases in infectious,
vector borne diseases can be attributed to “standing pools of water from increased rainfall which
become a rich breeding ground for mosquitoes” (p. 432). Something as simple as maintaining
our properties and ensuring that there is not standing water lying for mosquitoes to breed in can
make a huge difference.
Analysis
Upon a rather thorough review of current available literature, it is quite evident that the
government and government funded researchers are aware of and concerned with WNV and its
potential. WNV has essentially exploded across the United States in a matter of a relatively few
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years. The majority of the sources all drew from the CDC. Many provided the exact same or
very similar yet differently worded overviews as well as transmission, diagnosis, treatment, and
prevention criteria. Essentially most of the basic information was taken from the CDC and
regurgitated in slightly different words. This is understandable as it simply is what it is.
Factors that may Promote WNV
WNV is a vector-borne disease. Veenema (2013) informs us that the climate changes in
the United States as well as the world are affecting and will continue to affect us (chapters 18 &
26). The scary thing is that with global warming and climate changes, there is a high potential
for increased incidences and exposures of WNV and other vector-borne viruses and diseases.
Kilpatrick, Meola, Moudy, & Kramer (2008) summarized:
Both viral evolution and temperature influence the distribution and intensity of
transmission of WNV, and provides a model for predicting the impact of temperature and
global warming on virus transmission.
Conclusion
In today’s global society viruses and diseases are not necessarily specific to a particular
region as in years past and are becoming increasingly found throughout the world wherever the
climate can support them. It is somewhat reassuring that WNV usually is relatively mild in
manifestation; however, it can potentially have lifelong consequences and in some cases may
even be fatal. We are lucky to have recognized WNV and be aware of what we can do to protect
ourselves. There will always be a certain amount of exposure/risk; however, we need to attempt
to minimalize it as best we can.
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The fact that most cases of WNV are mild leads one to question the accuracy of data.
How many folks have had WNV and simply thought it was the flu? How many folks simply do
not go to the doctor? How many clinicians have misdiagnosed mild cases? This is important to
note as it definitely skews the number of actual cases. It is totally plausible and most likely that
WNV and perhaps even a number of other viruses and diseases are more prevalent and wider
spread than previously thought.
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References
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Bradley, C. A., Gibbs, S. E. J., & Altizer, S. (2008). Urban land use predicts west Nile virus
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