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Development and evaluation of one-step rRT-PCR and immunohistochemical methods for detection of Rift Valley fever virus in biosafety level 2 diagnostic laboratories |
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| Authors: | Drolet Barbara S Weingartl Hana M Jiang Jieyuan Neufeld James Marszal Peter Lindsay Robbin Miller Myrna M Czub Markus Wilson William C |
| Affiliation: | a United States Department of Agriculture, Agricultural Research Service, Arthropod Borne Animal Diseases Research Unit, Manhattan, KS, USA b National Centre for Foreign Animal Disease, Canadian Food Inspection Agency, Winnipeg, Manitoba, Canada c Department of Medical Microbiology, University of Manitoba, Winnipeg, Canada d National Microbiology Laboratory, Public Health Agency of Canada, Winnipeg, Manitoba, Canada e University of Wyoming, Laramie, Wyoming, USA, previously at Arthropod-Borne Animal Diseases Research Unit, Unites States Department of Agriculture, Manhattan, KS, USA f Faculty of Veterinary Medicine, University of Calgary, Alberta, Canada |
| Abstract: | Rift Valley fever virus (RVFV) is a zoonotic insect transmitted virus endemic to Africa and the Arabian Peninsula. Infection causes abortions and high mortality in newborn ruminants. The overall human infection rate is <1%; however, fatality rates in those with severe clinical disease have been reported as high as 29%. The potential of RVFV as a bioterrorism agent and/or being accidentally introduced into North America is widely recognized. Currently, regional veterinary biosafety level 2 (BSL-2) diagnostic laboratories lack safe, modern, validated diagnostic tests to detect RVFV. An existing one-step real-time RT-PCR (rRT-PCR) assay was modified for quick virus inactivation for use in BSL-2 laboratories, evaluated on serum and tissue samples from experimentally infected lambs and calves, and compared to virus isolation. Viremia was detected in all inoculated sheep with titers reaching 106.5 plaque forming units/ml, or up to 1010 viral RNA copies/ml. Viremia in calves was lower and not detected in all inoculated animals; however, all animals became transiently febrile and were infected as determined by rRT-PCR of tissues. Virus was isolated from rRT-PCR-positive liver and/or spleen in 33% of lamb and 41% of calf samples between 2 and 7 days post inoculation. For RVFV antigen detection, reagents are typically produced at BSL-3Ag or BSL-4 conditions and require inactivation and safety testing for use outside of containment. In this study, antiserum against recombinant RVFV-nucleocapsid (N) was produced to develop an immunohistochemical (IHC) assay which was subsequently evaluated on formalin fixed lamb and calf tissues at BSL-2 laboratory conditions. Antigen was detected by IHC in 79% of rRT-PCR-positive sheep and 70% of rRT-PCR-positive calf tissues tested. Once validated and approved by national regulatory agencies, these assays can be safely produced and distributed to regional diagnostic laboratories, providing capacity for early detection of RVFV in suspected ruminant samples. |
| Keywords: | Rift Valley fever virus Real-time RT-PCR Immunohistochemistry Bovine Ovine |
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