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West Nile Virus

West Nile Virus. Focus on clinical aspects of human infection. Jo Hofmann, MD State Epidemiologist for Communicable Disease Washington State Department of Health. Overview and learning objectives. Review: Clinical features of human West Nile virus (WNV) infections

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West Nile Virus

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  1. West Nile Virus Focus on clinical aspects of human infection Jo Hofmann, MD State Epidemiologist for Communicable Disease Washington State Department of Health

  2. Overview and learning objectives • Review: • Clinical features of human West Nile virus (WNV) infections • Routes of WNV transmission in humans • Learning objectives • Describe symptoms of the most common illness associated with WNV infection • Identify the most common route of virus transmission • Describe two new methods of surveillance for WNV infections

  3. WNV infection: clinical syndromes • West Nile fever • Mild infection • West Nile neuroinvasive disease • Meningitis • Encephalitis • Acute flaccid paralysis (AFP) • Polio-like syndrome • Movement disorders • Involuntary muscle spasms • Parkinson’s-like syndromes • Other neurological manifestations

  4. Fatal WNV infection: <0.1% of all infections 10% of WNND 1/150 of all infections cause West Nile neuroinvasive disease (WNND) <1% WNND Very crude estimates ~20% West Nile fever ~80% No symptoms Human infection with WNV

  5. Washington State Department of Health West Nile virus infections, by age group & clinical category -- United States, 2003 Source: Hayes, N. 5th Nat’l Conf. on West Nile Virus, 2004

  6. West Nile fever • Self-limited illness with sudden onset • Fever, headache, muscle aches, fatigue • Nausea, vomiting • Rash, swollen lymph nodes • Symptoms can be debilitating, may persist for weeks • Does not progress to West Nile neuroinvasive disease

  7. West Nile neuroinvasive disease • The disease formerly known as West Nile meningoencephalitis • Rarest WNV infection • Neurological symptoms occur 1-2 days after onset of fever • WNND includes • Meningitis - stiff neck, headache, abnormal cerebrospinal fluid • Encephalitis - confusion, seizures • Acute flaccid paralysis (AFP)

  8. West Nile virus-associated acute flaccid paralysis (AFP) • Rare, cases seen during outbreaks • Symptoms look like poliomyelitis (polio) • Asymmetrical weakness (left > right, etc.) • No sensory symptoms • Abnormal cerebrospinal fluid • Affects young, healthy patients compared with other WN neuroinvasive disease • Fever, headache may be absent • May occur with or w/o meningitis or encephalitis

  9. Dude, where’s my blood meal?

  10. Newly described routes of WNV transmission • Transfusion of blood, platelets, fresh frozen plasma • Organ transplantation • Perinatal exposure (infected mother to newborn) • Breastfeeding • Occupational exposure (laboratory accidents, alligator and poultry farming)

  11. WNV infections following transfusion • First recognized in 2002 • >60 suspected cases investigated; 23 cases confirmed following transfusion from 16 infected donors • Sources: red blood cells, platelets, and plasma • Nationwide screening of blood donations began July 2003 – new method of surveillance for WNV infections

  12. Screening the blood supply • Asking donors about symptoms • Screening donations with nucleic acid amplification test (NAAT) – detects virus • Contaminated products destroyed, donors contacted • Blood banks report infected blood products to state health departments • 6.2 million units screened in 2003 – >1000 donors infected with WNV reported

  13. Confirmed and probable transfusion-associated WNV infection, 2003 • Occurred in epicenter of outbreak • Three in Texas • One each in Nebraska, Iowa, Kansas • Onset of symptoms during peak of outbreak: August through October • Average age of cases 63 years • Five developed WNND (encephalitis)

  14. Perinatal transmission of WNV • First described in U.S. in 2002 • Several children born to mothers with confirmed WNV infection • Some with neurological defects • A large series of cases from 2003-2004 still being investigated • CDC has on-line reporting site for registry of pregnancy-associated cases

  15. Coming soon: web-based reporting WNV infection during pregnancy: Healthcare providers report on-line States/local HD informed when their providers report Providers contacted for follow-up and specimens needed for testing For now: Call state/local health department or CDC @ 970-221-6400

  16. Summary • Most WNV infections are asymptomatic • Most common illness is West Nile fever • The most common route of transmission is through the bite of an infected mosquito • Transfusion and pregnancy associated cases • Screening of blood donors and web-based reporting of pregnancy associated cases are new surveillance methods

  17. Questions?

  18. References • Interim guidelines for the evaluation of infants born to mothers infected with West Nile virus during pregnancy. MMWR 2004;53:154-7 • Transmission of West Nile virus from an organ donor to four transplant recipients. New Engl Jour Med 2003;348:2196-2203. • Possible West Nile virus transmission to an infant through breast-feeding - Michigan 2002. MMWR 2002; 51:877-8.

  19. References • Petersen LR, Marfin AA. West Nile Virus: a primer for the clinician. Ann Intern Med 2002;137:173-9. • Investigations of West Nile virus infections in recipients of blood transfusions. MMWR 2002;51:973-4. • Neurologic manifestations and outcome of West Nile virus infection. JAMA. 2003;290:511-5. • CDC WNV clinical guidance website: http://www.cdc.gov/ncidod/dvbid/westnile/clinical_guidance.htm

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