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Running head: EMERGING INFECTIOUS DISEASE
Emerging Infectious Disease
Keri Foster
Ferris State University
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Abstract
Emerging infectious diseases are of growing concern as they account for many deaths. West Nile
Virus (WNV) is one of these diseases that not only causes death but also provides challenges to
the public health system. By gaining a clear understanding of the factors involved with this
disease and gaining knowledge of the steps needed to prevent and control it could reduce the
threat of future human epidemics. This paper provides relevant and evidence-based facts to
supply the public with pertinent information.
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Emerging Infectious Disease
An emerging disease is one that has appeared in a population for the first time or that has
previously existed but is increasing in incidence and geographical areas (WHO, 2013).
Understanding how these diseases spread is of great importance. They cause a great concern for
the population since they can cause severe illness and death. One emerging infectious disease
that continually provides challenges to the public health system today is West Nile Virus
(WNV). “In 2011, WNV was the most common cause of neuroinvasive arboviral disease in the
United States” (Lindsey, et al., 2012, pg. 511). Arboviral diseases are viral diseases transmitted
by blood feeding arthropods, primarily mosquitoes and ticks, and “are among the most important
of the emerging infectious disease public health problems facing the world at the beginning of
the third millennium” (Gubler, 2006, pg. 1). This research paper provides relevant and evidencebased information to provide the reader with a clear understanding of the severity of this
emerging disease, in hopes to reduce the transmission rate in relation to its unpredictable path.
Descriptive Summary
Imperative factors of WNV including information on transmission/isolation, clinical
presentation, diagnosis, and therapy are important to the population and organizations that
participate in surveillance or control of the disease. Surveillance for WNV involves a
continuous, systematic data collection that analyzes health related data needed to monitor and
clarify the epidemiology to set priorities and to inform the public of policies and strategies
implemented to decrease transmission of this infectious disease (WHO, 2013).
Transmission/Isolation
A crucial aspect is to understand the spread and isolation of WNV to avoid transmission.
WNV is transmitted primarily through the bites of infected mosquitos categorizing this virus as
an arthropodborne virus or often called an arbovirus as recently described (Lindsey, et al., 2011).
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Humans can become infected with WNV when bitten by mosquitos that carry blood from their
infected hosts, typically infected birds and small animals (Lindsey, et al., 2011). Today,
scientists have identified more than 138 bird species and more than 43 mosquito species that are
capable of transmitting WNV (NIAID, 2012).
WNV can also be transmitted from person-to-person through blood transfusions, organ
transplants, intrauterine, and infected mothers who are breast feeding. “Presumptive WNV
infections were identified in 137 blood donors through routine screening of blood supply, of
these, one subsequently developed neuroinvasive disease and 32 developed nonneuroinvasive
disease” (Lindsey, et al., 2011, pg. 510). In 2002, the first intrauterine case was reported where a
child of a mother that was infected with WNV was born with several abnormalities (Gould &
Fikrig, 2004). Because of these transmission routes pregnant women should take precautions to
reduce the risk of contracting WNV. Also, in 2002, “WNV was identified in an organ donor and
four transplant recipients” (Gould & Fikrig, 2004). It has since been found in several additional
cases in relation to organ transplantation.
WNV was first isolated in 1937, in the West Nile district of Uganda through the serum of
a febrile woman (Gould & Fikrig, 2004). Following its original isolation, several outbreaks of
mild illnesses have developed in many countries. Since the 1990’s the frequency of WNV and
the severity of outbreaks have drastically increased. In 1999, a cluster of encephalitis cases were
identified in New York City causing seven human fatalities and hundreds of deaths among birds
and horses (Gould & Fikrig, 2004). By the end of 2003, WNV had spread to all but two of the
lower 48 states causing the number of cases to increase and has since been on the rise (Gould &
Fikrig, 2004). As of September 2012, the number of human cases increased to 3,142 in 45 states
within the United States including 1,630 resulting in neuroinvasive disease and 134 deaths
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(Petersen & Fischer, 2012). This proves that WNV is a major concern for the population today
as the incidence and the geographical routes are increasing.
Clinical Presentation
While most people infected with WNV have no signs or symptoms others may present
with features such as fever, headache, and fatigue with occasional skin rashes on the trunk of the
body, swollen lymph nodes, and eye pain. Symptoms are usually mild and are referred to as
West Nile Fever (Mayo Clinic, 2012). However, it is possible to acquire serious infections
including inflammation of the brain (encephalitis), inflammation of the membranes surrounding
the brain and spinal cord (meningitis), inflammation of both the brain and the surrounding
membranes (meningoencephalitis), inflammation of the spinal cord (West Nile poliomyelitis), or
a sudden weakness in the arms, legs, or breathing muscles (acute flaccid paralysis) (Mayo Clinic,
2012). The symptoms leading to these serious infections include high fever, severe headache,
stiff neck, disorientation or confusion, stupor or coma, tremors or muscle jerking, lack of
coordination, convulsions, and partial paralysis or sudden muscle weakness (Mayo Clinic, 2012).
According to the Centers for Disease Control and Prevention (CDC) approximately only
20% of infected people develop symptoms of West Nile Fever and approximately one in 150
people infected will develop severe illness (2004). The symptoms of West Nile Fever usually
last for a few days while the symptoms of severe illness can linger for weeks with the effects
such as, muscle weakness, potentially causing permanent damage (Mayo Clinic, 2012). The
mild symptoms of West Nile Fever will usually resolve on their own while other symptoms will
require medical attention.
Diagnosis
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“Preliminary diagnosis of WNV is often based on the patient’s clinical features, places
and dates of travel, activities, and epidemiologic history of the location where infection
occurred” (NIAID, 2012, para. 1). Confirmed diagnosis of WNV involves specific medical
testing. A physician can perform one of the following tests to confirm the presence of the virus;
Laboratory Tests.
A serum blood test may be completed to check for antibodies. These are immune
system proteins that attack foreign substances, such as viruses, in relation to WNV (Mayo
Clinic, 2012). These antibodies can be produced early in an infected person. Your
physician may also check for a positive ribonucleic acid (RNA) test as this is also an
indicator of WNV (Mayo Clinic, 2012).
Lumbar Puncture (spinal tap).
A lumbar puncture is the most efficient diagnostic method to determine severe
disease. The IgM antibody to WNV can be detected from collected CSF as long as it is
within 8 days of the onset of illness and is determined by using the IgM antibody capture,
enzyme-linked immunosorbent assay (MAC-ELISA) test, an important tool used for
routine diagnosis (CDC, 2004). The fluid sample may also show an elevated white cell
count signaling an infection that the immune system is fighting along with the findings of
antibodies.
Brain Tests.
If there is suspicion of neuroinvasive disease, tests can be performed to detect the
level of inflammation or damage. A scan completed to test the brain’s activity, an
Electroencephalography (EEG), a scan performed to detect brain inflammation, a
Magnetic Resonance Imaging (MRI), or a scan that uses x-rays to create detailed images
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of structures inside the body, a Computed Tomography (CT) are tests used in some cases
(Mayo Clinic, 2012).
Therapy
Most individuals that contract WNV go without symptoms; however, The Mayo Clinic
identified two different types of therapy to assist with the treatment of symptoms that may
develop. One is supportive therapy consisting of over-the-counter medications that can be used
to relieve pain from mild headaches and muscle aches acquired from West Nile Fever (Mayo
Clinic, 2012). For more severe symptoms including, the neuroinvasive features, hospitalization
may be needed so the patient can receive intravenous fluids and medications to prevent other
types of infections and to provide comfort to those infected.
Information provided by the Mayo Clinic on December 18, 2012 describes an additional
therapy that is being investigated by scientists. A type of immune cell therapy called interferon
therapy is being explored as a treatment for encephalitis caused by WNV (Mayo Clinic, 2012).
“Some research shows that people who receive interferon may recover better that those who
don’t receive the drug, but more study is needed” (Mayo Clinic, 2012, pg. 5). Currently there is
no cure for WNV nor is there a vaccine available for humans. However, according to the Mayo
Clinic, work to develop a human vaccine is under way (2012).
Analysis of Evidence
“The WNV has spread throughout much of the Americas since its initial identification in
New York City in 1999, but the United States has been by far the hardest-hit American country”
(Petersen & Fischer, 2012, pg. 1282). Hundreds of cases have been reported in all states except
Maine with central United States being most heavily affected. More than 13,000 cases of
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neuroinvasive disease have been reported through 2011 and it is estimated that 2 to 4 million
infections with 0.4 to 1 million resulting illness have occurred (Petersen & Fischer, 2012).
According to the CDC, in 2011 alone there were 712 WNV cases reported from 238
counties in 43 states and the District of Columbia which included 486 (68%) neuroinvasive and
226 (32%) nonneuroinvasive cases (Lindsey, et. al., 2012). “Extrapolating from the 486 WNV
neuroinvasive disease cases reported, an estimated 13,600-34,000 cases of nonneuroinvasive
febrile disease might have occurred in 2011; however, only 226 (1%-2%) nonneroinvasive
disease cases were reported” (Lindsey, et. al., 2012, pg. 513). Of the 486 with neuroinvasive
disease 273 (56%) had encephalitis, 183 (38%) had meningitis, and 30 (6%) had acute flaccid
paralysis with 28 (93%) of the 30 patients with flaccid paralysis also had encephalitis or
meningitis (Lindsey, et. al., 2012). From the 712 reported cases 547 individuals ended up being
hospitalized with a report of 43 deaths (Lindsey, et. al., 2012). According to Lindsey, et. al., the
national incidence of WNV with neuroinvasive disease is 0.16 per 100,000 populations which is
consistent with incidence rates during 2008-2010 (2012).
Of the 712 cases of WNV reported, the highest rates were in the District of Columbia
(1.62), Mississippi (1.04), Nebraska (0.76), and Arizona (0.76) (Lindsey, et. al., 2012). There
were 5 states that reported 51% of neuroinvasive disease cases including California (110 cases),
Arizona (49 cases), Michigan (32 cases), Mississippi (31 cases), and New York (28 cases)
(Lindsey, et. al., 2012). According to the Medical Laboratory Observer, as of mid-September,
nearly 700 cases of WNV had been reported in the United States with almost half of those cases
in Texas, with approximately 60% involving neuroinvasive diseases, causing 26 deaths (2012).
It is estimated that “neuroinvasive disease has a mortality rate of approximately 10% in the
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nation and is frequently associated with long-term functional impairment, particularly among
patients with encephalitis or paralysis” (Petersen & Fischer, 2012, pg. 1283).
Since there are no antibiotics to treat WNV infections and there is currently no
vaccination to protect against this disease it is suggested by the CDC that certain steps are taken
to avoid the possibility of contracting this infection. They advise that individuals use mosquitorepellant products containing an EPA-registered active ingredient such as N,N-Diethyl-metatoluamide (DEET), Picaridin, oil of Lemon Eucalyptus or p-menthane-3,8-diol (PMD), which is
the synthetic version, or IR3535, especially in areas where mosquito activity is increased
(NIAID, 2012). They also recommend wearing long sleeves and pants when mosquitos are most
active or to consider staying indoors during those hours and to make sure your home has good
screens on windows and doors to keep mosquitoes out (NIAID, 2012). An additional step to take
to decrease the change of obtaining WNV is to get rid of mosquito breeding sites by emptying
standing water that may be within surrounding areas of your home. Some of these areas may
include water in flower pots, buckets, tire swings, children’s pools, pet dishes, and bird baths
(NIAID, 2012).
Promoting Factors
Through research, it was determined that the main risks of contracting WNV are
generally promoted through environmental and societal factors. “Amplification of WNV
depends on several critical factors that are differentially influenced by the weather, including the
numbers and distributions of susceptible birds and vector mosquitos and the rate of virus
replication in mosquitoes” (Petersen & Fischer, 2012, pg. 1282-1283). There are other factors as
well as the weather that increase the risk of WNV. According to the Mayo Clinic, these factors
include time of year, geographic region, time spent outside, age, and health (2012).
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Time of Year
Most cases in the United States occur during the months of July and September. In 2011
there was a significant increase during these months with a peak incidence in late August,
reporting 663 (93%) cases (Lindsey, et. al., 2012). In other years the peak incidence has
occurred in late August and early September with the onset of symptoms beginning anywhere
between July and September.
Geographic region
“WNV has been reported in most of the United States, but Midwestern and Southern
states have recently had the highest incidence rates” (Mayo Clinic, 2012). Prior to WNV
appearing in the United States it was present in areas such as Africa, parts of Asia and the
Middle East. It also ranges into the Western Hemisphere and has continued to expand into
Canada, Mexico, and the West Indies (Gould & Fikrig, 2004).
Time spent outside
“If you work or spend time outdoors, you have a greater chance of being bitten by an
infected mosquito” (Mayo Clinic, 2012, pg. 3). Several cases of WNV infection due to
occupational exposure have been reported. According to the CDC, in 2002, exposure of
laboratory workers occurred through accidental inoculation and two cases were reported in
workers at a turkey-breeding farm in Wisconsin.
Age
“While prevalence rates are fairly uniform across age-groups, rates of neurological
disease increase substantially with age, as does the clinical: subclinical infection ratio” (Gould &
Fikrig, 2004, pg. 8). Also, according to Gould and Fikrig, “advanced age is the main risk factor
for death, with individuals more than 70 years of age at particularly high risk” (2004, pg. 8).
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Mayo Clinic reports that adults older than the age of 50 are at a higher risk of developing WNV
infection. (2012). The median age of patients with WNV was 57 years and the median age of
patients who died was 74 years (Lindsey, 2012). Increased incidence rate among the elderly is
unknown but it is believed to be related to a decreased capacity of these individuals to develop a
protective immune response.
Health
Those with a weakened immune system are at a higher risk for contracting WNV (Mayo
Clinic, 2012). Examples of conditions that weaken the immune system include Human
immunodeficiency virus (HIV), organ transplants, or recent chemotherapy. Also, individuals that
are affected by chronic diseases such as cancer, diabetes, heart disease, and alcoholism are at a
greater risk for developing symptoms and the more serious health effects including encephalitis,
meningitis, or acute flaccid paralysis.
Focal and sporadic cases of WNV continue to cause severe illness in substantial numbers
of people in the United States. Due to the long-term unpredictability and the rapid development
of outbreaks related to WNV, timely national surveillance is required to control these incidences
and geographical distributions. Therefore, prevention of WNV depends on community and
household efforts to reduce mosquito densities. It is unfortunate that regardless of the reported
cases, the prevalence of WNV for years to come is unpredictable, causing concern for the
population.
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Reference
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Gould , L. H., & Fikrig, E. (n.d.). West Nile Virus: A growing concern. (2004). The Journal of
Clinical Investigation, 113(8), 1102-1107. doi: 10.1172/JCI21623
Gubler, D. J. (2006). Human arbovirus infections worldwide. Annals of the New York Academy
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Huang, C., Slater, B., Rudd, R., Parchuri, N., Hall, R., Dupuis, M., & Hindenburg, A. (2002).
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(2012). West Nile virus disease and other arboviral diseases - United States, 2011.
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