West Nile Virus. By Chimnonso Onuoha

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1 West Nile Virus By Chimnonso Onuoha Family: Flaviviridae Genus: Flavivirus Etiologic agent- Japanese encephalitis Antigenic Complex Etiological Agent and Characteristics WNV is an arbovirus in the family Flaviridae. Its spherical, enveloped capsid has a diameter of approximately 50 nm that contains single-stranded RNA that encodes the capsid. It also has an envelope, and pre-membrane proteins, as well as 7 nonstructural proteins that aide in its viral replication. The virus has two genetic lineages: lineage 1 strains are found in North America, Europe, Africa, Asia, and Australia; lineage 2 strains are found in sub-saharan Africa and Madagascar(5). Transmission Mosquitoes, primarily of the species Culex, become infected when they feed on infected animals, primarily birds, which circulate the virus in their blood for a few days. The virus eventually gets into the mosquito's salivary glands. Later, when mosquitoes bite another host, the virus may then be injected into humans and animals, where it can multiply and cause illness. An unremarkably proportion of human infections have occurred through organ transplant, blood transfusions and breast milk. There is ONE reported case of trans-placental (mother-to-child) WNV transmission. To date, no human-to-human transmission of WNV through casual contact has been documented, and no transmission of WNV to health care workers has been reported when standard infection control precautions have been put in place. However, transmission to laboratory workers has been reported(3). Reservoirs Birds are the natural reservoir while it is maintained in nature in a mosquito-bird-mosquito transmission cycle (2). Identifying Tests The primary diagnostic test is the antibody test which measures IgM antibodies that are produced after the initial infection. A capture enzyme-linked immunosorbent assay (ELISA) test then follows. These antibody samples come from blood or the cerebrospinal fluid taken during a lumbar puncture/ spinal tap.

2 In most cases the test is positive following a mandatory wait of 8 days after the early onset of symptoms as they may prove inconclusive or false negative if tested when symptoms first occur. A second test is the plaque reduction neutralization test or PRNT which is the most specific test for the arthropod-borne flaviviruses. It can be used to help distinguish false-positive results in an IgM antibody test. Additional Tests: IgG antibody sero-conversion (or significant increase in antibody titers) in two serial specimen collected at a one week interval by enzyme-linked immunosorbent assay (ELISA); neutralization assays viral detection by reverse transcription polymerase chain reaction (RT-PCR) assay Virus isolation by cell culture (5). History of the disease 1937, Uganda: the virus is identified Name derived from location it was discovered Early 1950s&60s, Mediterranean Basin: The epidemiology and ecology of WNV was first characterized 1951, Isreal: The first recognized epidemic of WNV occurred in the small town outside of Haifa, where a total of 123 cases with no fatalities occurred among 303 inhabitants. Young children represented the majority of cases. During this outbreak the various clinical features associated with infection were first described in detail, with the main symptoms being fever, headache, myalgias, anorexia, abdominal pain, and vomiting; lymphadenopathy, angina, and diarrhea were somewhat less common , Egypt: Several large outbreaks led to a further understanding of the ecology, epidemiology, and clinical characteristics of WNV. 1951, upper Nile Delta region: Studies included serosurveys among humans and animals; isolation and identification of virus vectors; experimental infection of birds, equines, arthropods, and humans; and ecologic assessments. This study studies allowed understanding of the various clinical and epidemiologic aspects of the virus. 1999, New York : September WNV outbreak (4) Signs and Symptoms

3 Mild infections are common with the West Nile virus. Infection is either asymptomatic in around 80% of infected people, or can lead to West Nile fever or severe West Nile disease. About 20% of people who become infected with WNV will develop West Nile fever. Symptoms include fever, headache, tiredness, and body aches, nausea, vomiting, occasionally with a skin rash (on the trunk of the body) and swollen lymph glands. More severe infections are less common the symptoms of severe disease (also called neuro invasive disease, such as West Nile encephalitis or meningitis or West Nile poliomyelitis) include headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis. Patients may also experience difficulty walking, muscle weakness, fatigue, insomnia, as well as long-term effects after severe illnesses. Memory loss, depression, irritability, and confusion are the most prevalent residual effects. Symptoms in children are the same as symptoms in adults but children may also complain of headache,fever, and lethargy. Most cases of West Nile virus infection are mild, the prognosis for recovery is generally good. In severe cases, death-rates are highest in the elderly or those with a compromised immune system(3). Virulence Factors The most useful virulence factor is the presence of a protein coat which allows it to invade cells undetected. In addition, WNV comes in two strains which are found in two hemispheres of the Earth. This allows it to spread twice as fast. In addition, due to warmer wetter environments created by global warming proliferation of the veto mosquitoes has also come to pass. Finally, the lack of an established vaccine does not allow for bodily resistance before contraction of the virus (5). Prevention / Control A) Mosquitoes control is usually left up to local governments. The type of control methods used by a program depends on the time of year, the type of mosquitoes to be controlled, and the habitat structure. Methods can include elimination of mosquito larval habitats, application of insecticides to kill mosquito larvae, or spraying insecticides from trucks or aircraft to kill adult mosquitoes. B) Control of larval breeding sites through source reduction, water management, and chemical and biologic control methods would be essential. If the situation worsened then chemical spraying to control adult vector mosquitoes would need to be implemented.

4 Mosquito-Proof Your Home Install or repair screens on windows and doors to keep mosquitoes outside. Help reduce the number of mosquitoes around your home by emptying standing water from flowerpots, gutters, buckets, pool covers, pet water dishes, discarded tires, and birdbaths on a regular basis. Avoid Mosquito Bites 1. Use insect repellents when you go outdoors. Repellents containing DEET, picaridin, IR3535, and some oil of lemon eucalyptus and para-menthane-diol products provide longer-lasting protection. 2. When weather allows, wear long sleeves, long pants, and socks when outdoors. Mosquitoes may bite through thin clothing, so spraying clothes with repellent containing permethrin or another EPA-registered repellent will give extra protection. Don't apply repellents containing permethrin directly to skin. Do not spray repellent on the skin under your clothing. 3. Take extra care during peak mosquito biting hours. Take extra care to use repellent and protective clothing from dusk to dawn or consider avoiding outdoor activities during these times(1). Vaccine/Treatment There is no specific treatment for West Nile virus infection. Intensive supportive therapy is directed toward the complications of brain infections. Anti-inflammatory medications, intravenous fluids, and intensive medical monitoring may be required in severe cases. Two vaccines are available for vaccinating equines: an inactivated WNV vaccine and a recombinant vaccine that uses canarypox virus to express WNV antigens. Although, there is no specific remedy for the viral infection an inactivated vaccine is being studied for human. A DNA vaccine that elicits expression of WNV E and prm antigens has been used in mice, horses, and birds. Vaccination of crows with Kunjin virus, a subtype of WNV, protected against WNV, and a DNA vector, which elicited expression of attenuated Kunjin virus, provided protective immunity against WNV in mice(5). Current Outbreaks

5 Local incidence cases- Between 1999 and 2001, 18 of the 149 reported confirmed cases of human WNV in the U.S, resulted in death. In of 4,156 reported cases were resulting in deaths. In 2003 there were 9862 reported cases that resulted in 264 deaths and 30% of those cases being severe. The incidence levels between dropped to reported cases with 100 deaths. Global incidence cases- Since the first WNV was identified in 1937 it has been confirmed in Africa, Western Asia, the Middle East, and the Mediterranean region of Europe. The incidence levels for these countries is not well recorded because there is no technology to implement programs that record the incidence levels of viruses and diseases. There is however cases reported by the CDC in Canada, Israel and Romania. From of the 2300 reported cases in Canada resulted in deaths. Israel had 33 in 400 confirmed cases result in death. In 2000 Romania had fatality rate of 10% in the 500 reported cases between 1996 and 1997 (6). Citation 1. Cunha, John. West Nile Encephalitis. MedicineNet. n.p., 15 Nov 201. Web. 5 May Campbell, Grant. West nile virus. Ncbi.nlm.gov. Pubmed, Sept Web. 5 May west Nile Virus. Who.int.WHO. July Web. 5 May Sejvar, James J. West Nile Virus: An Historical Overview. The Ochsner Journal 5.3 (2003): Print. 5. Hayes EB, Sejvar JJ, Zaki SR, Lanciotti RS, Bode AV, Campbell GL. Virology, pathology, and clinical manifestations of West Nile Virus disease. Emerg Infect Dis. 8 Aug Web.6 May DOI: /eid b 6. Caren Chancey, Andriyan Grinev, Evgeniya Volkova, and Maria Rios, The Global Ecology and Epidemiology of West Nile Virus, BioMed Research International, vol. 2015, Article ID , 20 pages.10 Aug Web. 6 May doi: /2015/376230