Download West Nile encephalitis

West Nile Fever and
Encephalitis
From Mayoclinic.com
Introduction
• 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.
Etiology
• 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 bloodbrain barrier. Once the virus crosses that barrier and
infects the brain or its linings, an inflammatory response
occurs and symptoms arise.
Virulence Factors
• Portal of entery
– Parenteral rout. Infected mosquito deposits
virus under the skin.
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 Factors
• Evading the Immune System
– Virus blocks the production of interferon (IFN)
Virulence Factors
• Tissue Distruction
– Destroys tissue in the central nervous system
leading to encephalitis.
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
• Birds (Jays and Crows)
• Transmission vector
• Mosquitoes from the
genus Culex
• Incubation period
• 3-14 days
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:
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Fever
Headache
Muscle aches
Backache
Lack of appetite
Nausea, vomiting and diarrhea
Skin rash
Swollen lymph glands
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:
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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
• 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
• Blood sample.
– Serological screening for anti-West Nile virus
IgM antibodies
Treatment
• 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.