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West Nile Fever PowerPoint PPT Presentation

West Nile Fever

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West Nile Fever

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West nile fever l.jpg

West nile fever

Dr.T.V.Rao MD

Dr.T.V.Rao MD

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West nile virus is an Arthropod-Borne virus

  • Transmitted by mosquitoes

  • Can infect people and other animals

  • Similar to some other viruses(a Flavivirus, in the Japanese Encephalitis Antigenic Complex – e.g. similar family to Yellow Fever, St. Louis encephalitis virus)

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West Nile Virus (WNV) before 1996

  • First discovered in 1937 in the West Nile district of Uganda

  • Mild feverish illness

  • Severe illness, like meningitis or encephalitis, was rare

  • Wide distribution in Asia, Eastern Europe, Africa

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West nile fever virus belongs to Flaviviridae

  • West Nile fever virus is in the family Flaviviridae. It is found in both temperate and tropical regions, having been first identified in the West Nile sub-region in the East African nation of Uganda in 1937.

Dr.T.V.Rao MD

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The virus is a

  • Flaviviridae

    • Flavivirus

      • Single stranded RNA virus

  • 2 genetic lineages

    • Linage 1

      • 3 clades (1a, 1b, 1c)

  • Infects humans, birds, mosquitoes, horses, and other mammals

Dr.T.V.Rao MD

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Dr.T.V.Rao MD

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Dr.T.V.Rao MD

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WNV Human Infection “Iceberg”

For every case of illness

involving the brain or spinal


~150 total infections

~10% fatal

(<0.1% of total infections)




Very crude estimates


“West Nile Fever”



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“arbovirus” - derived from phrase “arthropod-borne.”


Infects birds, humans, other vertebrates (Africa, E. Europe, W. Asia, Middle East.)

Closely related to St. Louis encephalitis virus found in US.

What is West Nile Virus?

Dr.T.V.Rao MD

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Animals too get infected and spread the disease

  • Although found mainly in birds, West Nile Virus has been identified in other animals such as horses, cats, bats, chipmunks, skunks, squirrels, and domestic rabbits. As the virus multiplies in the animal's system it crosses the blood-brain barrier and eventually resulting in inflammation of the brain.

Dr.T.V.Rao MD

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Wild and domestic birds - primary host.

Spreads from birds to man and other animals via mosquitoes feeding on an infected bird and then biting another host.

Mosquitoes that transmit WNV and SLE usually prefer to bite birds.

Human infections with these mosquito-borne viruses are very rare and can be prevented by taking simple measures to avoid mosquito bites.

West Nile Virus

Dr.T.V.Rao MD

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An electron micrograph of the West Nile virus. West Nile virus is a Flavivirus commonly found in Africa, West Asia, and the Middle East.

Dr.T.V.Rao MD

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Current trends in spread of west nile fever

  • The virus has been described in Africa, Europe, the Middle East, west and central Asia, Oceania (subtype Kunjin), and most recently, North America. Recent outbreaks of WN virus encephalitis in humans have occurred in Algeria in 1994, Romania in 1996-1997, the Czech Republic in 1997, the Democratic Republic of the Congo in 1998, Russia in 1999, the United States in 1999-2000, and Israel in 2000. Epizootics of disease in horses occurred in Morocco in 1996, Italy in 1998, the United States in 1999-2000, and France in 2000. In the U.S. through September 2000, West Nile virus has been documented in Connecticut, Maryland, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, the District of Columbia and most recently Florida.

Dr.T.V.Rao MD

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Mosquito Vectors

Nearly 50 species of mosquitoes capable (at least in the lab) of transmitting WNV

Culex tarsalis feeding

  • Important vectors vary by geography, e.g.

    • Culex tarsalis(western states)

    • Culex pipiens(Midwest, and elsewhere)

    • Culex quinquefasciatus(south)

  • Different behaviors – some fly very long distances

  • Feeding habits, infection rates, breeding areas all important

Dr.T.V.Rao MD

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Incidental hosts

Humans, horses, and other animals

Amplifying hosts



Culex spp., Aedesspp.,Ochlerotatus spp.

Dr.T.V.Rao MD

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Dr.T.V.Rao MD

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Species Affected

Center for Food Security and Public Health, Iowa State University, 2011

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  • Primary mosquito vector

    • Culex spp.

  • Tick vectors

    • Asia, Russia

    • Role in transmission not clear

Dr.T.V.Rao MD

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Human Transmission

  • Direct contact

    • Infected birds, tissues

  • Laboratory acquired

  • Blood transfusions

    • Screening implemented in 2003

  • Organ transplants

  • Trans placental transmission

  • Breast feeding

Dr.T.V.Rao MD

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Disease in Humans

  • Incubation: 2 to 14 days

  • Many WNV infections asymptomatic

  • Two forms of disease

  • West Nile fever

    • Most common form

    • Resembles influenza

    • Most infections resolve in 2 to 6 days

    • Persistent fatigue can occur

Dr.T.V.Rao MD

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Disease in Humans

  • West Nile neuroinvasive disease

    • Occurs rarely

      • Progression of West Nile fever

    • Can be severe and life-threatening

    • Three syndromes

      • Encephalitis

      • Meningitis

      • Acute flaccid paralysis

    • Persistent neurological dysfunction may occur

Dr.T.V.Rao MD

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Clinical presentation of west nile fever

  • Many who are bitten by infected mosquitoes show no symptoms of West Nile fever, and are ultimately unaffected by the virus. However, approximately 20 percent of those who are infected will develop West Nile fever which, at a mild level, produces symptoms such as fever, headaches, body aches, swollen lymph nodes and a skin rash

Dr.T.V.Rao MD

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Similar to other meningitis from viruses

Fever, headache, meningismus (neck stiffness, light bothering eyes)

White blood cells in the cerebrospinal fluid

Headache may be quite severe

Most people improve, though persistent headache, fatigue common

WNV Meningitis

Dr.T.V.Rao MD

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West Nile Encephalitis

  • West nile virus is a more serious form of the virus that affects people primarily in the late summer or early fall. However, it can be transmitted year-round in the southern climates where temperatures are milder. There is no vaccine available for the West Nile Virus however several companies are working to develop one.

Dr.T.V.Rao MD

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Out come of west nile virus infection

  • The West Nile virus produces one of three different outcomes in humans. The first is an asymptomatic infection; the second is a mild febrile syndrome termed West Nile fever; the third is a neuroinvasive disease termed West Nile meningitis or encephalitis.

Dr.T.V.Rao MD

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Diagnosis in Humans

  • Serology

    • Serum or CSF

    • IgM capture ELISA

      • Cross reactions possible

    • Plaque neutralization test

  • Detection of virus, antigen, or nucleic acids

    • RT-PCR

    • Immunohistochemistry

Dr.T.V.Rao MD

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Based on high index of clinical suspicion and obtaining specific laboratory tests

Consider WNV, or other arboviral diseases such as St. Louis encephalitis, (esp. in adults >50 years) w/ unexplained encephalitis or meningitis (esp. in summer or early fall).

The local presence of WNV enzootic (bird, mosquito, vet) activity or other human cases should further raise suspicionon.

Recent travel history also important.

Diagnosis of WNV Infection

Dr.T.V.Rao MD

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Testing obtained through local or state health departments and increasingly through private labs

Public health laboratories usually perform an IgM antibody capture enzyme-linked Immuno-Sorbant assay (MAC-ELISA).

W/ this test virus-specific IgM can be detected in nearly all CSF and serum specimens from WNV-infected patients at time of clinical presentation


Dr.T.V.Rao MD

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Serology helps in diagnosis

  • Serum IgM antibody may persist for + 1 yr., so physicians must determine whether the antibody is result of a previous WNV infection and unrelated to the current clinical presentation.

Dr.T.V.Rao MD

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Treatment in Humans

  • No specific therapy

  • Supportive care

  • Therapies in clinical trials

    • Interferon

    • Antisense nucleotides

    • IV immunoglobulin

    • Antiviral drugs

Dr.T.V.Rao MD

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Prevention of west nile fever

  • Despite the fact that it is fairly easy to avoid contracting West Nile fever, few people take the simple steps needed to protect themselves.

Dr.T.V.Rao MD

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  • Mosquitoes are primarily nocturnal insects and usually feed at dusk and dawn; however, some species will bite during the day, especially if you disrupt their watery habitat while hiking through the forest.:

Dr.T.V.Rao MD

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WNV—Personal Protection

  • Use mosquito repellent

    • DEET (skin or clothing)

      • Up to 50% concentration

    • Permethrin (clothing)

  • Wear long sleeves, pants

  • Emphasize protection at times of high mosquito activity (dawn/dusk) or stay indoors

  • Protect your house and yard

    • Use/ fix screens

    • Air-conditioning

    • Empty water (breeding sites)

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Goals in prevention

  • Only veterinary WNV vaccines are currently on the market. Equine WNV vaccines in the USA led to a significant decrease in the number of severe clinical signs associated with WNV infections among horses, and the first veterinary vaccine was also licensed in Europe. There is no human vaccine available to date, neither is a specific treatment to counteract WNV caused disease. Hence, at the moment the only way to prevent an infection with WNV is to avoid mosquito bites. There is also a high demand for novel diagnostic tools that minimize cross-reactivity with other flaviviral infections.

  • The development of safe and efficient vaccine candidates for the protection of humans and of innovative diagnostic systems are major goals of the West Nile Shield Project.

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Fda initiatives

  • To prevent transmission during medical procedures, the U.S. Food and Drug Administration (FDA) has issued guidelines to blood banks to help blood centres determine which potential donors should be excluded from giving blood. A new test to detect West Nile virus went into use by U.S. blood banks in July 2003.

  • FDA has also cleared a test that will be used in the diagnosis of West Nile virus Infection in people.

Dr.T.V.Rao MD

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Prevent the mosquito bites the only real option

  • After getting sick, recovery can take a long time, but most people do improve

  • Avoiding getting bitten by mosquitoes is the only way to prevent WNV

  • There is no treatment, but people are working very hard to develop one

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  • Programme Created by Dr.T.V.Rao MD for Medical and Health Workers in the Developing World

  • Email

  • [email protected]

Dr.T.V.Rao MD

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