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WNV Testing - MNIT Experience

Understand the importance of WNV testing through MNIT's research findings and testing algorithm. Learn about the efficacy of current testing methods and the prevalence of WNV infections.

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WNV Testing - MNIT Experience

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  1. WNV Testing - MNIT Experience • Marek Nowicki • Research Director CTDN Medical Advisory Board January 25th, 2011

  2. Kinetic of a Typical WNV Infection

  3. 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

  4. 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

  5. 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.

  6. 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!

  7. 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.

  8. Current MNIT WNV Algorithm

  9. WNV Assays * Clinical or with confirmed WNV(+)s or (-)s CDC specimens ** With background subtraction

  10. 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?

  11. Thank you! • Questions? ....................

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