Download WNV Testing - MNIT Experience

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? ....................