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WNV Testing - MNIT Experience Marek Nowicki Research Director CTDN Medical Advisory Board January 25th, 2011 Kinetic of a Typical WNV Infection Rationale for Testing • Why WNV NAT? • • • How big is the bottom of the WNV “iceberg”? Only 0.1 - 1% of WNV infections symptomatic! Why EIA for IgM anti-WNV? • Am. J. Trop. Med. Hyg., 72(3), 2005, pp. 320-324: “PERSISTENT SHEDDING OF WEST NILE VIRUS IN URINE OF EXPERIMENTALLY INFECTED HAMSTERS” • • • Emerging Infectious Disease Vol. 11, No. 8, August 2005:” West Nile Virus Detection in Urine” J Infect Dis. (2010) 201 (1): 2-4:”Persistent Infection with West Nile Virus Years after Initial Infection” J Infect Dis. (2011) 203 (3): 344-347:”West Nile Virus RNA Not Detected in Urine of 40 People Tested 6 Years After Acute West Nile Virus Disease Initial Algorithm • Cross-reactivity between related arboviruses (WNV, SLEV. DV etc) • IgM class significantly more specific than IgG antibodies • Need for confirmatory testing i.e. Western Blot and/or PRNA Results (Presented at American Transplant Congerss 2010 and accepted for 2011ATC ) •Total tested: 867 (381 N.Cal., 75 C.Cal., 411 S.Cal.) •84 donors were reactive for IgG and/or IgM anti-WNV •Initial reactivity* confirmed using algorithm developed by Viral and Rickettsial Disease Laboratory, CA DHS Richmond, CA: 38 specimens were not confirmed (3 viruses-) 4 were anti-WNV + (2 from N. Cal and 2 from S Cal.) 27 were anti-Dengue virus+ 3 were anti-St. Louis Encephalitis virus+ 11 “indeterminate”* 5 untypable or QNS 0 positive for WNV RNA **The “indeterminate” samples are those with titer (typically 1:40) to one virus, which is too low to satisfy the four-fold criterion for a positive identification; Of these eleven, 9 show such a titer against DEN, 1 to WNV, and 1 to SLE + DEN. Real-Time WNV Testing Results (ATC 2010) •Since June 1, 2009 we tested 471 donors from 2 OPOs (LS & NDN). •Both OPO’s elected to screen their donors yearlong. •FDA approved EIA for IgM anti-WNV (Focus Technologies, Los Angeles), •WNV Procleix NAT (Chiron) for WNV RNA •No anti-WNV+ or WNV RNA+ donors so far •= no false positives! Conclusions • The epidemiology of WNV in the US Western States is changing due to vector control measures and emergence of immune individuals. • It is difficult to predict before the WNV season, which region will be affected by the virus. • Testing algorithm involving IgM anti-WNV testing and NAT offers an affordable and convenient (TAT<5hrs) safeguard against WNV infection with no loss of donors due to false positive results. Current MNIT WNV Algorithm WNV Assays Assay Specificity Sensitivity NAT 100% 100% (Procleix, Chiron) IgG EIA (Focus Diagnostics) IgM EIA (Focus Diagnostics) 99%* 100%** * Clinical or with confirmed WNV(+)s or (-)s CDC specimens ** With background subtraction 97.3%* 93.2%** Proposed Study • Study population: CTDN donors (08-10) • Objective(s): • prevalence of WNV viremia? • Prevalence of viremia and recent infections? • Seroprevalence of 3 major arboviruses? Thank you! • Questions? ....................