Genetic basis of antigenic variation of SAT3 foot-and-mouth disease virus

Foot-and-mouth disease (FMD) continues to be a major burden for livestock owners in endemic countries and a threat to FMD-free countries. The epidemiology and control of FMD in Africa is complicated by the presence of five clinically indistinguishable serotypes. Of these the Southern African Territory (SAT) type 3 has received limited attention, likely due to its restricted distribution and it being less frequently detected. We investigated the intratypic genetic variation of the capsid-coding region of 22 SAT3 viruses and confirmed the geographical distribution of four topotypes. The antigenic cross-reactivity of 12 SAT3 viruses against reference antisera was assessed by performing virus neutralization assays and calculating the r1-values, which is a ratio of the heterologous neutralizing titre to the homologous neutralizing titre. Interestingly, cross-reactivity between the SAT3 reference antisera and many SAT3 viruses was notably high (r1-values > 0.3). Moreover, some of the SAT3 viruses reacted more strongly to the reference sera compared to the homologous virus (r1-values > 1). An increase in the avidity of the reference antisera to the heterologous viruses could explain some of the higher neutralization titres observed. Subsequently, we used the antigenic variability data and corresponding genetic and structural data to predict naturally occurring amino acid positions that correlate with antigenic changes. We identified four unique residues associated with a change in cross-reactivity, with two sites that change simultaneously. The analysis of antigenic differences is critical for surveillance and proper vaccine selection for effective control or the design of vaccine antigens tailored for specific geographic localities, using reverse genetics

Inherent biophysical stability of foot-and-mouth disease SAT1, SAT2 and SAT3 viruses

Foot-and-mouth disease (FMD) virus (FMDV) isolates show variation in their ability to withstand an increase in temperature. The FMDV is surprisingly thermolabile, even though this virus is probably subjected to a strong extracellular selective pressure by heat in hot climate regions where FMD is prevalent. The three SAT serotypes, with their particularly low biophysical stability also only yield vaccines of low protective capacity, even with multiple booster vaccinations. The aim of the study was to determine the inherent biophysical stability of field SAT isolates. To characterise the biophysical stability of 20 SAT viruses from Southern Africa, the thermofluor assay was used to monitor capsid dissociation by the release of the RNA genome under a range of temperature, pH and ionic conditions. The SAT2 and SAT3 viruses had a similar range of thermostability of 48–54 °C. However, the SAT1 viruses had a wider range of thermostability with an 8 °C difference but with many viruses being unstable at 43–46 °C. The thermostable A-serotype A24 control virus had the highest thermostability of 55 °C with some SAT2 and SAT3 viruses of similar thermostability. There was a 10 °C difference between the most unstable SAT virus (SAT1/TAN/2/99) and the highly stable A24 control virus. SAT1 viruses were generally more stable compared to SAT2 and SAT3 viruses at the pH range of 6.7–9.1. The effect of ionic buffers on capsid stability showed that SAT1 and SAT2 viruses had an increased stability of 2–9 °C and 2–6 °C, respectively, with the addition of 1 M NaCl. This is in contrast to the SAT3 viruses, which did not show improved stabilisation after addition of 1 M or 0.5 M NaCl buffers. Some buffers showed differing results dependent on the virus tested, highlighting the need to test SAT viruses with different solutions to establish the most stabilising option for storage of each virus. This study confirms for the first time that more stable SAT field viruses are present in the southern Africa region. This could facilitate the selection of the most stable circulating field strains, for adaptation to cultured BHK-21 cells or manipulation by reverse genetics and targeted mutation to produce improved vaccine master seed viruses.The Vaccine Initiative (ESCP) in South Africa.http://www.elsevier.com/locate/virusres2020-04-15hj2019BiochemistryGeneticsMicrobiology and Plant PathologyVeterinary Tropical Disease

An external quality assessment feasibility study; cross laboratory comparison of haemagglutination inhibition assay and microneutralization assay performance for seasonal influenza serology testing: A FLUCOP study

Introduction: External Quality Assessment (EQA) schemes are designed to provide a snapshot of laboratory proficiency, identifying issues and providing feedback to improve laboratory performance and inter-laboratory agreement in testing. Currently there are no international EQA schemes for seasonal influenza serology testing. Here we present a feasibility study for conducting an EQA scheme for influenza serology methods. Methods: We invited participant laboratories from industry, contract research organizations (CROs), academia and public health institutions who regularly conduct hemagglutination inhibition (HAI) and microneutralization (MN) assays and have an interest in serology standardization. In total 16 laboratories returned data including 19 data sets for HAI assays and 9 data sets for MN assays. Results: Within run analysis demonstrated good laboratory performance for HAI, with intrinsically higher levels of intra-assay variation for MN assays. Between run analysis showed laboratory and strain specific issues, particularly with B strains for HAI, whilst MN testing was consistently good across labs and strains. Inter-laboratory variability was higher for MN assays than HAI, however both assays showed a significant reduction in inter-laboratory variation when a human sera pool is used as a standard for normalization. Discussion: This study has received positive feedback from participants, highlighting the benefit such an EQA scheme would have on improving laboratory performance, reducing inter laboratory variation and raising awareness of both harmonized protocol use and the benefit of biological standards for seasonal influenza serology testing.publishedVersio

Genetic basis of antigenic variation of SAT3 foot-and-mouth disease viruses in Southern Africa

Foot-and-mouth disease (FMD) continues to be a major burden for livestock owners in endemic countries and a continuous threat to FMD-free countries. The epidemiology and control of FMD in Africa is complicated by the presence of five clinically indistinguishable serotypes. Of these the Southern African Territories (SAT) type 3 has received limited attention, likely due to its restricted distribution and it being less frequently detected. We investigated the intratypic genetic variation of the complete P1 capsid-coding region of 22 SAT3 viruses and confirmed the geographical distribution of five of the six SAT3 topotypes. The antigenic cross-reactivity of 12 SAT3 viruses against reference antisera was assessed by performing virus neutralization assays and calculating the r1-values, which is a ratio of the heterologous neutralizing titer to the homologous neutralizing titer. Interestingly, cross-reactivity between the SAT3 reference antisera and many SAT3 viruses was notably high (r1-values >0.3). Moreover, some of the SAT3 viruses reacted more strongly to the reference sera compared to the homologous virus (r1-values >1). An increase in the avidity of the reference antisera to the heterologous viruses could explain some of the higher neutralization titers observed. Subsequently, we used the antigenic variability data and corresponding genetic and structural data to predict naturally occurring amino acid positions that correlate with antigenic changes. We identified four unique residues within the VP1, VP2, and VP3 proteins, associated with a change in cross-reactivity, with two sites that change simultaneously. The analysis of antigenic variation in the context of sequence differences is critical for both surveillance-informed selection of effective vaccines and the rational design of vaccine antigens tailored for specific geographic localities, using reverse genetics.Biotechnology and Biological Sciences Research Council (BBSRC), Department for International Development and Medical Research Council (UK).https://www.frontiersin.org/journals/veterinary-science#pm2021BiochemistryGeneticsMicrobiology and Plant PathologyProduction Animal Studie