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 • 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
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
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
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
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
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)
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
Dude, where’s my blood meal?
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)
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
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
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)
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
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
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
Questions?
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.
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
