Detection of African Swine Fever Virus from Wild Boar, Singapore, 2023.

We detected African swine fever virus (ASFV) from a wild boar in Singapore. In <72 hours, we confirmed and reported ASFV p72 genotype II, CD2v serogroup 8, and IGR-II variant by using a combination of real-time PCR and whole-genome sequencing. Continued biosurveillance will be needed to monitor ASFV in Singapore.

Development of Differentiating Infected from Vaccinated Animals (DIVA) Real-Time PCR for African Horse Sickness Virus Serotype 1.

African horse sickness (AHS) is a highly infectious and often fatal disease caused by 9 serotypes of the orbivirus African horse sickness virus (AHSV). In March 2020, an AHS outbreak was reported in Thailand in which AHSV serotype 1 was identified as the causative agent. Trivalent live attenuated vaccines serotype 1, 3, and 4 were used in a targeted vaccination campaign within a 50-km radius surrounding the infected cases, which promptly controlled the spread of the disease. However, AHS-like symptoms in vaccinated horses required laboratory diagnostic methods to differentiate infected horses from vaccinated horses, especially for postvaccination surveillance. We describe a real-time reverse transcription PCR-based assay for rapid characterization of the affecting field strain. The development and validation of this assay should imbue confidence in differentiating AHS-vaccinated horses from nonvaccinated horses. This method should be applied to determining the epidemiology of AHSV in future outbreaks.

Overexpression of the nucleocapsid protein of Middle East respiratory syndrome coronavirus up-regulates CXCL10.

Middle East respiratory syndrome coronavirus (MERS-CoV) causes respiratory diseases in humans and has a high mortality rate. During infection, MERS-CoV regulates several host cellular processes including antiviral response genes. In order to determine if the nucleocapsid protein of MERS-CoV (MERS-N) plays a role in viral-host interactions, a murine monoclonal antibody was generated so as to allow detection of the protein in infected cells as well as in overexpression system. Then, MERS-N was stably overexpressed in A549 cells, and a PCR array containing 84 genes was used to screen for genes transcriptionally regulated by it. Several up-regulated antiviral genes, namely TNF, IL6, IL8, and CXCL10, were selected for independent validation in transiently transfected 293FT cells. Out of these, the overexpression of MERS-N was found to up-regulate CXCL10 at both transcriptional and translational levels. Interestingly, CXCL10 has been reported to be up-regulated in MERS-CoV infected airway epithelial cells and lung fibroblast cells, as well as monocyte-derived macrophages and dendritic cells. High secretions and persistent increase of CXCL10 in MERS-CoV patients have been also associated with severity of disease. To our knowledge, this is the first report showing that the MERS-N protein is one of the contributing factors for CXCL10 up-regulation during infection. In addition, our results showed that a fragment consisting of residues 196-413 in MERS-N is sufficient to up-regulate CXCL10, while the N-terminal domain and serine-arginine (SR)-rich motif of MERS-N do not play a role in this up-regulation.

A cross-clade H5N1 influenza A virus neutralizing monoclonal antibody binds to a novel epitope within the vestigial esterase domain of hemagglutinin.

The sporadic outbreaks of highly pathogenic H5N1 avian influenza virus have raised public health concerns. Monoclonal antibodies (MAbs) against hemagglutinin (HA) have been increasingly used successfully for therapeutic purposes. Previously, MAb 9F4, generated against clade 1 H5N1 HA, was observed to have cross-clade neutralizing efficacy and inhibited viral entry by preventing the pH-mediated conformational change of HA. Furthermore, mouse-human chimeric MAb 9F4 was found to retain high degrees of neutralizing activity. In this study, through escape mutant generation and in-silico prediction, it was revealed that MAb 9F4 binds to a novel epitope in the vestigial esterase sub-domain of HA comprising at least three non-continuous amino acid residues, arginine (R) at position 62, tryptophan (W) at position 69 and phenylalanine (F) at position 79, which interacted with MAb 9F4 in a conformation-dependent manner. Binding and neutralization studies suggested that R62 is the critical residue for MAb 9F4 binding whereas W69 and F79 seem to cooperate with R62 to stabilize the epitope. Mutation of either R62 or W69 did not affect replicative fitness of the virus in vitro. Interestingly, MAb 9F4 retained neutralizing efficacy against a clade 2.3.2.1a H5N1 virus consisting of an arginine to lysine substitution at position 62 in HA.

Understanding bat SARS-like coronaviruses for the preparation of future coronavirus outbreaks - Implications for coronavirus vaccine development.

The severe acute respiratory syndrome coronavirus (SARS-CoV) first emerged in 2003, causing the SARS epidemic which resulted in a 10% fatality rate. The advancements in metagenomic techniques have allowed the identification of SARS-like coronaviruses (SL-CoVs) sequences that share high homology to the human SARS-CoV epidemic strains from wildlife bats, presenting concrete evidence that bats are the origin and natural reservoir of SARS-CoV. The application of reverse genetics further enabled that characterization of these bat CoVs and the prediction of their potential to cause disease in humans. The knowledge gained from such studies is valuable in the surveillance and preparation of a possible future outbreak caused by a spill-over of these bat SL-CoVs.

Memory T cell responses targeting the SARS coronavirus persist up to 11 years post-infection.

Severe acute respiratory syndrome (SARS) is a highly contagious infectious disease which first emerged in late 2002, caused by a then novel human coronavirus, SARS coronavirus (SARS-CoV). The virus is believed to have originated from bats and transmitted to human through intermediate animals such as civet cats. The re-emergence of SARS-CoV remains a valid concern due to the continual persistence of zoonotic SARS-CoVs and SARS-like CoVs (SL-CoVs) in bat reservoirs. In this study, the screening for the presence of SARS-specific T cells in a cohort of three SARS-recovered individuals at 9 and 11 years post-infection was carried out, and all memory T cell responses detected target the SARS-CoV structural proteins. Two CD8(+) T cell responses targeting the SARS-CoV membrane (M) and nucleocapsid (N) proteins were characterized by determining their HLA restriction and minimal T cell epitope regions. Furthermore, these responses were found to persist up to 11 years post-infection. An absence of cross-reactivity of these CD8(+) T cell responses against the newly-emerged Middle East respiratory syndrome coronavirus (MERS-CoV) was also demonstrated. The knowledge of the persistence of SARS-specific celullar immunity targeting the viral structural proteins in SARS-recovered individuals is important in the design and development of SARS vaccines, which are currently unavailable.

Substitution at aspartic acid 1128 in the SARS coronavirus spike glycoprotein mediates escape from a S2 domain-targeting neutralizing monoclonal antibody.

The Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) is the etiological agent for the infectious disease, SARS, which first emerged 10 years ago. SARS-CoV is a zoonotic virus that has crossed the species barriers to infect humans. Bats, which harbour a diverse pool of SARS-like CoVs (SL-CoVs), are believed to be the natural reservoir. The SARS-CoV surface Spike (S) protein is a major antigenic determinant in eliciting neutralizing antibody production during SARS-CoV infection. In our previous work, we showed that a panel of murine monoclonal antibodies (mAbs) that target the S2 subunit of the S protein are capable of neutralizing SARS-CoV infection in vitro (Lip KM et al, J Virol. 2006 Jan; 80(2): 941-50). In this study, we report our findings on the characterization of one of these mAbs, known as 1A9, which binds to the S protein at a novel epitope within the S2 subunit at amino acids 1111-1130. MAb 1A9 is a broadly neutralizing mAb that prevents viral entry mediated by the S proteins of human and civet SARS-CoVs as well as bat SL-CoVs. By generating mutant SARS-CoV that escapes the neutralization by mAb 1A9, the residue D1128 in S was found to be crucial for its interaction with mAb 1A9. S protein containing the substitution of D1128 with alanine (D1128A) exhibited a significant decrease in binding capability to mAb 1A9 compared to wild-type S protein. By using a pseudotyped viral entry assay, it was shown that the D1128A substitution in the escape virus allows it to overcome the viral entry blockage by mAb 1A9. In addition, the D1128A mutation was found to exert no effects on the S protein cell surface expression and incorporation into virion particles, suggesting that the escape virus retains the same viral entry property as the wild-type virus.

A simple methodology for conversion of mouse monoclonal antibody to human-mouse chimeric form.

Passive immunotherapy has mainly been used as a therapy against cancer and inflammatory conditions. Recent studies have shown that monoclonal antibody-(mAb-) based passive immunotherapy is a promising approach to combat virus infection. Specific mouse mAbs can be routinely generated in large amounts with the use of hybridoma technology but these cannot be used for therapy in human beings due to their immunogenicity. Therefore, the development of chimeric and humanized mAbs is important for therapeutic purpose. This is facilitated by a variety of molecular techniques like recombinant DNA technology and the better understanding of the structure and function of antibody. The human-mouse chimeric forms allow detailed analysis of the mechanism of inhibition and the potential for therapeutic applications. Here, a step-by-step description of the conversion process will be described. The commercial availability of the reagents required in each step means that this experimentation can be easily set up in research laboratories.