USAMRIIDUSAMRIID

Michael Turell, Kirti Dave, Maria Mayda, Zahra Parker, Russell Coleman, and Daniel Strickman US Army Medical Research Institute of Infectious Diseases, Fort

Detrick, MD; VecTOR Test Systems, Inc., Thousand Oaks, CA; Walter Reed Army Institute of Research, Silver Spring, MD; US Army Medical

Materiel Development Activity, Fort Detrick, MD; US Department of Agriculture, Agriculture Research Service, Beltsville, MD

Evaluation of novel dipstick assays for the detection of Rift Valley fever virus (RVFV) in mosquitoes

Opinions, interpretations, conclusions, and recommendations are those of the author and are not necessarily endorsed by the U.S. Army.

Research was conducted in compliance with the Animal Welfare Act and other federal statutes and regulations relating to animals and experiments involving animals and adheres to principles stated in the Guide for the Care and Use of Laboratory Animals, National Research Council, 1996. The facility where this research was conducted is fully accredited by the Association for the Assessment and Accreditation of Laboratory Animal Care International.

Overview of RVFV

POTENTIAL FOR BECOMING ESTABLISHED IN NORTH AMERICA

Many North American mosquito species are potential vectors of RVF virus

Ample supply of susceptible domestic vertebrate hosts (cattle, goat, sheep)

Role of deer, horses, rodents, etc. is not known

AVAILABLE DIAGNOSTIC ASSAYS

Research Laboratory based• RT-PCR• ELISA• Infectious virus assays (cell culture)

Commercially available• None

Negative control

Positive “Control” line

“Test” line

RVFV-infected mosquito

Schematic side view of test strip

<3

<3

3.5

7.9

<3

<3

6.18.1

7.0

8.1

GenomeEquivalents

Sample number Dipstick CT Value Virus titer247 0 29.4 0

250 0 29.2 0

261 0 29.3 0

262 0 29.1 0

265 0 28.9 0

270 0 28.9 0

267 0 28.2 1

253 0 28.6 1.7

251 +/- 27.8 1.8

260 0 30.2 2

269 0 28.6 2.5

255 0 27.8 2.8

266 0 26.9 3

248 +/- 29.3 3.3

268 0 27.9 3.3

264 0 25.5 3.7

256 0 25.4 3.8

257 0 25.5 4

233 0 24.8 4.2

240 +/- 23.4 4.2

243 + 23.0 4.3

254 +/- 23.7 4.3

235 ?? 24.0 4.5

236 + 27.1 4.6

252 ?? 25.2 4.7

258 0 25.4 4.7

244 0 25.3 5

246 + 25.2 5.1

239 +++ 22.8 5.2

271 +/- 24.6 5.2

234 +++ 22.3 5.3

241 ++ 21.9 5.3

242 ++ 25.3 5.5

238 +++ 21.7 5.6

237 +++ 21.1 5.7

249 ++ 21.2 5.8

263 ++ 20.2 6

259 ++ 21.3 6.2

Sensitivity of the dipstick based on the amount of infectious virus present

TiterNumber tested Negative Positive ?

>5.0 10 0 9 (90%) 1

4.5-5.0 5 2 1 (20%) 2

<4.5 22 18 0 (0%) 4

Sensitivity of the dipstick based on the CT (RT-PCR) value

CT value

Number tested Negative Positive ?

<23 25 2 23 (92%) 0

23-25.3 12 4 3 (25%) 5

>25.3 35 31 2 (6%) 2

RVF D-1 RVFWNSLE VEE JE D-2 D-3 D-4

Specificity

Dengue 1-4Japanese encephalitis La Crosse St. Louis encephalitisVenezuelan equine encephalitis West Nile Yellow fever

Strains of RVFV tested

OS-1 MauritaniaRhod 2269/74 ZimbabweAr-B 1976 Central African Republic21445 KenyaZH501 Egypt

Strain Where isolated

Summary

• The newly developed dipsticks for RVFV are about as sensitive as the VecTest ® West Nile virus dipstick

Summary

• The newly developed dipsticks for RVFV are about as sensitive as the VecTest ® West Nile virus dipstick

• The RVFV dipstick detected virus in nearly all samples containing 105 plaque-forming units of virus.

Summary

• The newly developed dipsticks for RVFV are about as sensitive as the VecTest ® West Nile virus dipstick

• The RVFV dipstick detected virus in nearly all samples containing 105 plaque-forming units of virus.

• There was a strong correlation between the infectious virus assay titer and the CT value