Viral Encephalitis

1. Viral Encephalitis John Nuara, Salwa Touma, Kelly Wines Microbiology and the Control of Infectious Diseases April 22, 2003

2. Kelly • Introduction • Transmission • Outbreaks • Reservoir

3. 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

4. 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)

5. Alphavirus Surface • Spike-like structures on virion surface • Spikes are used to attach to susceptible animal cells • RNA-containing viruses

6. Most encephalitides are transmitted by mosquitoes Other types are transmitted by ticks Transmission of Arbovirus

7. 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

9. 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

10. 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.

11. Most Common Types of Arboviral Encephalitis in the US • Eastern equine encephalitis • Western equine encephalitis • La Crosse encephalitis • St. Louis encephalitis • West Nile encephalitis

12. 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

13. 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

14. Eastern Equine Outbreaks in US

15. 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

16. 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

17. Western Equine Outbreaks in US

18. La Crosse encephalitis (LAC) • Bunyavirus • Transmitted by the tree-hole mosquito • Principal vertebrate hosts • Eastern chipmunks • Gray Squirrels • Red Foxes

19. 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%

20. La Crosse Outbreaks in US

21. 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

22. 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

23. 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

24. St. Louis Outbreaks in US

25. 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

26. 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

27. West Nile Outbreaks in US

29. Mosquito Breeding Grounds

30. Discarded Tires

31. Lakes and Ponds

32. Trash

33. Plants are natural incubators

34. Salwa • Structure • Pathogenesis • Symptoms • Diagnosis

35. John • Treatment • Prevention • Genetic Engineering • Weaponization