WNV Testing - MNIT Experience

Marek NowickiResearch 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(Procleix, Chiron)

100% 100%

IgG EIA(Focus Diagnostics)

99%*97.3%*

IgM EIA(Focus Diagnostics)

100%** 93.2%*** Clinical or with confirmed WNV(+)s or (-)s CDC specimens** With background subtraction

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