The Disease

• What is it?
• How do you get it?
• Clinical Symptoms
• Laboratory Diagnosis
• Treatment/Recovery
• Statistics

What is it?

Encephalitis is an inflammation of the brain, caused by bacterial or viral infections. Inflammation occurs when bacteria or viruses are able to cross from the blood into the central nervous system (CNS).

How do you get it?

West Nile virus normally affects wild birds. Sometimes, however, the virus can be passed to mammals, including humans.

Birds and mammals get the disease in the same way: through the bite of a mosquito carrying the virus. The mosquitoes become infected when they take blood from birds that are infected with the virus. This infected blood is then introduced directly into other birds and mammals when the mosquito takes another blood meal.

Infection in humans occurs in the same manner – through the bite of a mosquito carrying the virus. The virus is NOT transmitted person-to-person or animal-to-person.

West Nile virus is seasonal, due to its dependence on mosquitoes for transmission. In temperate climates, the virus is only active in the summer months when mosquitoes are most prevalent. In warmer climates, you can be exposed to the virus year-round.

Clinical Symptoms

Most cases of West Nile encephalitis are asymptomatic or result in mild flu-like symptoms. The groups at greatest risk for severe infections are the very young, the elderly and people with weakened immune systems. In the New York City outbreak, the four individuals who died from viral encephalitis were over the age of 68.

Symptoms of the West Nile encephalitis:

• Mild cases: sudden fever, headache, vomiting, stiff neck and back, drowsiness, double vision, inability to coordinate muscle movements, convulsions
• Severe cases: focal paralysis, intractable seizures, coma and death
• After effects can include: deafness, epilepsy and dementia
• Incubation period: 3-12 days following a bite from a disease-carrying mosquito

*Doctors should watch for: confusion, altered consciousness, and fever during a clinical examination

For detailed information about CSF evaluation, EEG, and Imaging studies, link to Medscape: Diagnosis and Management of Viral Encephalitis

Laboratory Diagnosis

If a patient is suspected of having viral encephalitis, a full microbiological examination is required, including: serologic studies, viral cultures, and examination by PCR (polymerase chain reaction).

For more info,link toMedscape: Diagnosis and Management of Viral Encephalitis

Various enzyme-linked immunosorbent assays (ELISA) can be used for antibody detection.

Early in the infection, specific monoclonal antibodies (Mabs) can be used.

Virus identification can be helpful for determining viruses in serum, cerebrospinal fluid and mosquitoes. Commonly used assays include: Mabs for use in IFA assays, Mabs with high avidities for binding in complex protein mixtures, and PCR tests.

For more info, link to the CDC: Info on Arborial Encephalitides

Treatment/Recovery

There are no specific anti-viral drugs for West Nile encephalitis. Instead, supportive therapy is used which deals with the problems that can arise in severe cases of the disease. Therapy can consist of antipyretics to reduce fever (eg. Tylenol), IV fluids, anti-convulsants, and other supportive measures to deal with swelling in the brain, loss of automatic breathing activity, bacterial infection. etc.

In babies and seniors, the prognosis for encephalitis can be fatal. In other age groups, recovery can be slow. Patients with severe cases of encephalitis should be kept in a skilled nursing unit and assessed regularly for level of consciousness and potential complications.

Statistics

Mortality rate: 3% to 15% (higher in younger and older age groups)

No cases were recorded in the USA prior to September 1999.

No reliable data are available regarding numbers of cases of the West Nile virus world-wide.