Transcript Viral Encephalitis

Viral Encephalitis
John Nuara, Salwa Touma, Kelly Wines
Microbiology and the Control of Infectious Diseases
April 22, 2003
Kelly




Introduction
Transmission
Outbreaks
Reservoir
Introduction to Viral Encephalitis


Inflammation of brain tissue caused by a viral infection
Can have acute viral encephalitis or post-infectious
encephalomyelitis


Acute viral encephalitis is caused by direct viral infection of neural cells
Post-infection encephalomyelitis follows infection with various viral
agents
Primary Cause



Arboviruses are the most common causes of viral
encephalitis
Arbovirus stands for arthropod-borne viruses
There are 3 virus families associated with encephalitis



Togaviridae (Alphavirus) – most common
Flaviviridae (Flavavirus)
Bunyaviridae (Bunyavirus)
Alphavirus Surface



Spike-like structures on
virion surface
Spikes are used to attach
to susceptible animal
cells
RNA-containing viruses
Transmission of Arbovirus

Most encephalitides are
transmitted by
mosquitoes
Other types are
transmitted by ticks

Transmission cont..



Infection occurs when
the infected arthropod
takes a blood meal
Most cases of arboviral
encephalitis occur from
June – September, when
arthropods are most
active
In warmer parts of the
country, cases can occur
year-round
Other Causes








Herpes simplex, type 1 (HSV-1) and type 2 (HSV-2)
Enteroviruses – viruses that typically occur in the GI tract
Coltivirus
Measles
Mumps
Rabies
Rubella
Lymphatic choriomeningitis virus
Other Cause cont...





Cytomegalovirus
Epstein-Barr virus (EBV)
Human immunodeficiency virus (HIV)
Varicella-zoster virus (VZV)
Influenza A and B
* Viruses are not the only cause of encephalitis; bacteria, fungus, parasites,
toxins, and allergic reactions can also cause it.
Most Common Types of Arboviral
Encephalitis in the US





Eastern equine encephalitis
Western equine encephalitis
La Crosse encephalitis
St. Louis encephalitis
West Nile encephalitis
Eastern Equine Encephalitis (EEE)




Alphavirus
Mosquito-borne
First identified in the 1930’s
Found
Eastern Seaboard
 Gulf Coast
 Some inland Midwestern area


Most common during warm months
Eastern Equine Encephalitis cont..



153 confirmed cases in US since 1964
One-third of infected individuals die; many
others suffer permanent brain damage
In addition to humans, EEE virus can also
produce severe disease in horses, some birds,
and puppies
Eastern Equine Outbreaks in US
Western Equine Encephalitis (WEE)





Alphavirus
Mosquito-borne
First isolated in 1930’s from the brain of a horse
with encephalitis
Found mainly in western parts of US
Most common in June and July
Western Equine Encephalitis cont..




639 confirmed cases in US since 1964
Usually causes a mild infection in people
Children <1 yr. often suffer permanent
complications
3% of infected individuals die
Western Equine Outbreaks in US
La Crosse encephalitis (LAC)



Bunyavirus
Transmitted by the tree-hole mosquito
Principal vertebrate hosts
Eastern chipmunks
 Gray Squirrels
 Red Foxes

La Crosse Encephalitis cont..





Discovered in La Crosse, Wisconsin in 1963
Since then, the virus has been identified in
several Midwestern and Mid-Atlantic states
Approximately 75 new cases of LAC are
reported per year
Most cases occur in children <16 yrs.
Fatality ratio <1%
La Crosse Outbreaks in US
St. Louis Encephalitis (SLE)



Flavavirus
Mosquito-borne
Discovered in St. Louis, Missouri in 1933



1095 reported cases
201 deaths
During the same year, human SLE epidemics also
occurred in



Kansas City, Missouri
St. Joseph, Missouri
Louisville, Kentucky
St. Louis encephalitis cont..

In hindsight, the first known SLE epidemic actually
occurred in 1932 in Paris, Illinois





38 reported cases
14 deaths
Since 1933, there have been at least 41 outbreaks in US
Since 1964, there have been 4, 478 reported human
cases; with an average of 128 cases/yr.
Outbreaks occurs intermittently


Up to 3,000 cases during large outbreaks
20 in other years
St. Louis Encephalitis cont..




Outbreaks most commonly occur in the late summer or
early fall; year-round in milder climate (such a St. Louis)
Can occur throughout most of the US
Less than 1% of SLE viral infections are clinically
apparent, and most remain undiagnosed
Clinical disease most often occurs in children and
elderly


7% children die
30% elderly die
St. Louis Outbreaks in US
West Nile Virus





Flavavirus
First isolated in the West Nile Province of Uganda in
1937
First epidemic occurred in Israel in the 1950s
Primarily affects individuals in Africa, the Middle East,
western Asia, and Europe
In late August and September 1999, there was an
outbreak in New York City and neighboring counties


Outbreak was initially attributed to St. Louis Encephalitis
Most likely introduced to North America through
international travel of infected persons to New York or by
imported infected birds
West Nile Virus cont..





The virus can infect people, horses, many birds, and
some other animals
Infection usually occurs in the late summer or early fall
Most people who become infected with West Nile
Virus have either no symptoms or only mild ones.
A small percentage (<1%) of patients will develop
more severe diseases from infection, including West
Nile Encephalitis
Infections are most common in children and the elderly
and as many as 10% of infected individuals will die
West Nile Outbreaks in US
Mosquito Breeding Grounds
Discarded Tires
Lakes and Ponds
Trash
Plants are natural incubators
Salwa




Structure
Pathogenesis
Symptoms
Diagnosis
John




Treatment
Prevention
Genetic
Engineering
Weaponization