West nile fever and encephalitis
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West Nile Fever and Encephalitis. From Mayoclinic.com. Introduction.

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West Nile Fever and Encephalitis

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West nile fever and encephalitis

West Nile Fever and Encephalitis

From Mayoclinic.com



  • In the summer of 1999, large numbers of crows began dying in New York City. Health officials eventually discovered the cause, but not before four people died of the same disease — West Nile virus, a mosquito-borne illness that mainly affects birds, humans and horses.



  • West Nile virus: A single stranded RNA virus containing an envelope

  • Family flavivirus.

  • Although the exact mechanism of illness is unknown, West Nile virus probably enters the host's bloodstream, multiplies and moves on to the brain, crossing the blood-brain barrier. Once the virus crosses that barrier and infects the brain or its linings, an inflammatory response occurs and symptoms arise.

Virulence factors

Virulence Factors

  • Portal of entery

    • Parenteral rout. Infected mosquito deposits virus under the skin.

Virulence factors1

Virulence Factors

  • Adhesion

    • Hemagglutinin binds to target cells

    • Proteins on the viral envelope called Domain III proteins bind to aVb3 integrin protein on the host cell.

Virulence factors2

Virulence Factors

  • Evading the Immune System

    • Virus blocks the production of interferon (IFN)

Virulence factors3

Virulence Factors

  • Tissue Distruction

    • Destroys tissue in the central nervous system leading to encephalitis.

Mode of transmission

Mode of Transmission

Bridge vector mosquitoes

Maintenance vector mosquito

Bridge vector mosquitoes

  • Amplification of the virus occurs throughout the summer as Culex mosquitoes feed on infected birds.

  • If amplification is significant enough, then bridge vector mosquitoes – (mosquitoes that that bite both humans and birds) become infected in late summer and pose an infection threat to humans.

  • WNV is not transmitted through person to person contact

Reservoir and incubation

Reservoir and incubation

  • Reservoir

    • Birds (Jays and Crows)

  • Transmission vector

    • Mosquitoes from the genus Culex

  • Incubation period

    • 3-14 days

  • Signs and symptoms

    Signs and Symptoms

    • Most people infected with the West Nile virus have no signs or symptoms.

    • About 20 percent of people develop a mild infection called West Nile fever. Common signs and symptoms of West Nile fever include:

      • Fever

      • Headache

      • Muscle aches

      • Backache

      • Lack of appetite

      • Nausea, vomiting and diarrhea

      • Skin rash

      • Swollen lymph glands

    Signs and symptoms cont

    Signs and Symptoms cont

    • In less than 1 percent of infected people, the virus causes a more serious neurological infection,

      • inflammation of the brain (encephalitis) or of the brain and surrounding membranes (meningoencephalitis), and paralysis.

    • Signs and symptoms of these diseases include:

      • High fever

      • Severe headache

      • Stiff neck

      • Disorientation or confusion

      • Stupor or coma

      • Tremors or muscle jerking

      • Signs and symptoms of Parkinson's disease

      • Convulsions

      • Partial paralysis

    Risk factors

    Risk Factors

    • Among those more likely to develop severe or fatal infections are:

      • Adults over 50 years old.

      • People with immune systems weakened by long-term steroid use, chemotherapy drugs or anti-rejection drugs following transplant surgery.

      • Pregnant women.

      • People with certain genetic mutations.

    Screening and diagnosis

    Screening and diagnosis

    • Blood sample.

      • Serological screening for anti-West Nile virus IgM antibodies



    • Most people recover from West Nile virus without treatment.

    • Those who develop encephalitis or meningitis may only need supportive therapy with intravenous fluids and pain relievers.

    • Currently, researchers are investigating interferon therapy as a treatment for encephalitis caused by West Nile virus.

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