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A modified liquid phase (LP) blocking ELISA used to assess type O foot-and-mouth disease virus antigenic variation in
R A Lunt1, W Linchongsubongkoch, L J Gleeson
1CSIRO Australian Animal Health Laboratory, Geelong, Vic., Australia.
Abstract:
A selection of type O foot-and-mouth disease (FMD) viruses isolated in Thailand between 1986 and 1989 were compared to the reference viruses O1 Thailand 1960 (O BKK/60) and O Nakorn Pathom 1965 (O NPT/65) using a liquid-phase blocking ELISA (LP ELISA) to derive serum titres and associated r values. Interpolation techniques were used to increase the precision for estimation of r values through a more accurate estimation of serum titres at predicted equivalent levels of antigen input. Mean r values were 0.45 (for 56 field viruses) relative to O BKK/60 reference virus and 0.56 (for 51 field viruses) relative to O NPT/65. While only two viruses showed considerable difference (r < 0.20) to a reference virus (O BKK/60), 41% and 31% gave r values less than 0.4 for O BKK/60 and O NPT/65 respectively. This indicated antigenic differences between reference and field viruses which may result in a reduction in vaccine efficacy.
Insights
Foot-and-mouth disease (FMD) viruses in Thailand showed antigenic differences from reference strains. This suggests current vaccines may offer reduced efficacy against circulating FMD virus types.
Area of Science:
- Veterinary Virology
- Immunology
- Epidemiology
Background:
- Foot-and-mouth disease (FMD) poses a significant threat to livestock globally.
- Type O FMD viruses are endemic in Southeast Asia, including Thailand.
- Monitoring antigenic drift in FMD viruses is crucial for vaccine effectiveness.
Purpose of the Study:
- To assess the antigenic relationship between field strains of type O FMD virus isolated in Thailand (1986-1989) and established reference strains.
- To evaluate potential reductions in vaccine efficacy due to antigenic variations in circulating FMD viruses.
Main Methods:
- Liquid-phase blocking enzyme-linked immunosorbent assay (LP ELISA) was employed to compare field and reference FMD virus strains.
- Serum neutralization titres and associated 'r' values were calculated to quantify antigenic similarity.
- Interpolation techniques were utilized to enhance the precision of 'r' value estimations.
Main Results:
- Mean 'r' values indicated antigenic differences between field isolates and reference viruses (O BKK/60 and O NPT/65).
- A significant percentage of field viruses (41% vs. O BKK/60, 31% vs. O NPT/65) exhibited 'r' values below 0.4, suggesting notable antigenic divergence.
- Only two viruses showed substantial differences (r < 0.20) to the O BKK/60 reference strain.
Conclusions:
- Antigenic differences exist between the studied type O FMD field viruses and reference strains used in Thailand.
- These antigenic variations may compromise the efficacy of existing FMD vaccines.
- Continuous antigenic surveillance of FMD viruses is essential for maintaining effective disease control strategies.