Vaccination with Rift Valley fever virus live attenuated vaccine strain
Smithburn caused meningoencephalitis in alpacas |
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Authors: | Tasneem Anthony Antoinette van Schalkwyk Marco Romito Lieza Odendaal Sarah J. Clift A. Sally Davis |
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Affiliation: | Provincial Veterinary Laboratory, Department of Agriculture, Western Cape Government, Capetown, South Africa;South Africa Agricultural Research Council–Onderstepoort Veterinary Institute, Onderstepoort, South Africa;Department of Paraclinical Sciences, University of Pretoria, Onderstepoort, South Africa;Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, KS, USA |
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Abstract: | Rift Valley fever (RVF) is a zoonotic, viral, mosquito-borne disease that causes considerable morbidity and mortality in humans and livestock in Africa and the Arabian Peninsula. In June 2018, 4 alpaca inoculated subcutaneously with live attenuated RVF virus (RVFV) Smithburn strain exhibited pyrexia, aberrant vocalization, anorexia, neurologic signs, and respiratory distress. One animal died the evening of inoculation, and 2 at ~20 d post-inoculation. Concern regarding potential vaccine strain reversion to wild-type RVFV or vaccine-induced disease prompted autopsy of the latter two. Macroscopically, both alpacas had severe pulmonary edema and congestion, myocardial hemorrhages, and cyanotic mucous membranes. Histologically, they had cerebral nonsuppurative encephalomyelitis with perivascular cuffing, multifocal neuronal necrosis, gliosis, and meningitis. Lesions were more severe in the 4-mo-old cria. RVFV antigen and RNA were present in neuronal cytoplasm, by immunohistochemistry and in situ hybridization (ISH) respectively, and cerebrum was also RVFV positive by RT-rtPCR. The virus clustered in lineage K (100% sequence identity), with close association to Smithburn sequences published previously (identity: 99.1–100%). There was neither evidence of an aberrant immune-mediated reaction nor reassortment with wild-type virus. The evidence points to a pure infection with Smithburn vaccine strain as the cause of the animals’ disease. |
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Keywords: | alpacas live attenuated vaccine meningoencephalitis Rift Valley fever virus Vicugna pacos |
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