The impact of spontaneous mutations of Enterovirus 71 (EV-A71) on virulence.

• Main Author: Mandary, Madiha Bibi
• Format: Thesis
• Published: 2020
• Subjects: QR355 Virology
• Online Access: http://eprints.sunway.edu.my/2427/

EV-A71 is the main etiological agent for numerous outbreaks of hand, foot and mouth disease (HFMD) in Asia. EV-A71 commonly infect infants and young children below the age of six. Clinical manifestations include the presence of vesicles on the hands, feet as well as ulcers in the mouth. However, EV-A71 has been linked to severe neurological complications such as acute flaccid paralysis, brainstem encephalitis, cardiopulmonary failure and death. The lack of an FDA approved vaccine against EVA71 calls for a need to develop treatments against EV-A71. Presently, the underlying basis for virulence of EV-A71 remains unsolved and the question whether there are molecular determinants for plaque size and virulence remain unknown. Plaque morphology in cell lines are markers for growth capability and the ability to cause cytopathic effects have been used to assess the viral fitness and attenuation. In this study, the naturally occurring plaque size variants within the wild type population of EV-A71 differed in their in vitro virulence. Two EV-A71 plaque variants (EVA71/BP and EV-A71/SP) from the wild type population of EV-A71 subgenotype B4 strain 41 were isolated. There was a significant size difference between the two EVA71 plaque variants and the two EV-A71 plaque variants displayed very different growth kinetics properties in terms of their rates of RNA replication and infectivity in RD and Vero cells when compared against the parental wild type strain. The presence of four novel mutations in the VP1 (I97L, N104S, S246P and N282D) of the EVA71/BP variant and three novel mutations in the VP1 (I97T, N237T and T292A) of the EV-A71/SP variant could account for varying levels of in vitro virulence observed in this study. The three mutations in the EV-A71/SP variant were attributed to its reduced binding ability in contrast with the EV-A71/BP variant and the EV-A71/WT strain. This would significantly reduce the RNA replication and infectivity of the small plaque variant. Lastly, homology modelling of the 3D VP1 structure of the big and small plaque variants revealed structural differences when compared to the parental wild type strain. In addition, it was demonstrated that the EV-A71/SP variant contained an altered GH loop and a smaller hydrophobic pocket that was attributed to the lower binding efficiency of the EV-A71/SP variant. The data collectively indicated that EV-A71/BP and EV-A71/SP variants differed in terms of their in vitro virulence. The differences in amino acid substitutions in the two EV-A71 plaque variants were reflected in the differences observed in folding of the VP1 capsid protein via computational modelling and the cell-receptor binding based on the viral binding assay. The role of each amino acid on the plaque size and virulence should be further investigated by site directed mutagenesis. Hence, these data can potentially serve as a basis for the rational design of a broad spectrum live attenuated vaccine (LAV) to prevent infections by different EV-A71 genotypes and subgenotypes.