Study on Foot and Mouth Disease Virus Vaccine Strain Selection of Ethiopian Isolates
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Date
2012-04-30
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Addis Ababa University
Abstract
This study was conducted at National Veterinary Institute (NVI) on foot and mouth disease viruses of known serotypes and topotypes identified and characterized ./i•om samples collected from cattle and swine, at different times from different parts of Ethiopia. The study was designed with the aim of selecting appropriate vaccine strains that can provide a broad spectrum cross protection against the circulating serotypes or strains by assessing the serological or antigenic match between the candidate vaccine strains and field isolates of 0, A, and SAT2. The study was done by two-dimensional virus neutralization assay to determine the serological or antigenic relationship 'rl' value between the candidate vaccine strains and field isolates. A total of 21 serotype 0 , 7 serotype A, and 8 serotype SAT2 FMD viruses were used for the study including candidate vaccine strains. The study findings revealed that out of 19 serotype 0 field isolates tested for vaccine match with antisera raised against candidate vaccine strains, 0-ETH/58/2005 and 0-ETHl38/2005, all (J 00%) were found to be antigenically similar with vaccine viruses with 'rl' values above the cut-off point (0.3)(with mean 'rl' value of 0.83 and 0.84, respectively), indicating that both these vaccine strain candidates can confer protection for serotype 0 field viruses circulating in the country. Of the 5 serotype A field strains tested, 4 (80%) match serologically with antisera raised against candidate vaccine strains, A-ETHl6/2000 and AETHl7/2008 with 'rl ' value greater than the cut-off point (mean 'r1 ' value of 0.58 and 0.70, respectively). But 1 serotype A field virus, A-ETHI13/1981 showed significant antigenic variation with vaccine strains with 'r 1' value below the cut-off point (r 1 value: 0.14 and 0.25 for AETHl6/2000 and A-ETHl7/2008, respectively). Furthermore, the 'r1' value obtained by serological matching between 6 SAT2 serotype field isolates and two vaccine strain candidates, SAT2-ETHl64/2009 and SAT2-ETHI76/2009, revealed that the vaccine strains can protect field viruses circulating in the country (Mean 'r1' value: 0.70 and 0.76, respectively). In general, the overall assessment of antigenic relations between the candidate vaccine strains and circulating field isolates tested showed better matching. The protection level of the selected vaccine strains against the challenge by field viruses should be supported by potency testing or animal
challenge.
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Keywords
'r l' value, Ethiopia, field isolates, FMD Virus, vaccine matching, vaccine strains.