Pteropine orthoreovirus (PRV), potentially of bat origin, is reported to be a causative agent of emerging respiratory tract infections among humans in Southeast Asia. We evaluated the efficacy of serologic assays using the major outer capsid and cell attachment proteins (CAP) of PRV strains in the screening, confirmation and identification of three groups of human PRV infections; Indonesian/Japanese, Indonesian/Hong Kong and Malaysian strains. The different serologic assays were tested using rabbit polyclonal antisera raised against these proteins of selected PRV strains, and validation was carried out using sera from a Miyazaki-Bali/2007 PRV-infected patient and the patient's contacts. The results of this study showed that rabbit polyclonal antisera raised against the CAP of the Miyazaki-Bali/2007 PRV strain showed the highest reactivity to the Miyazaki-Bali/2007 PRV and to a lesser extent, cross-reactivity with the HK23629/07 and Melaka PRVs, respectively. Neutralization activity against the Miyazaki-Bali/2007 PRV was observed using rabbit anti-Miyazaki-Bali/2007 PRV CAP (320) but not with rabbit anti-HK23629/07 (<20) and Melaka (<20) PRV CAP. This lack of cross-neutralization, suggests the potential for human reinfection with different strains. The use of sera collected from contacts of the Miyazaki-Bali/2007 PRV-infected patient suggested that human-to-human infections with PRV are unlikely. Previously reported cases of PRV infections among human have been mild. However, the expanding geographic distribution of these viruses, of which its virulence remains unknown, warrants close monitoring to enable the development of prevention and control strategies in the event that a change in virulence occurs.
Owing to genotype-specific neutralizing antibodies, analyzing differences in the immunogenic variation among dengue virus (DENV) genotypes is central to effective vaccine development. Herein, we characterized the viral kinetics and antibody response induced by DENV type 2 Asian I (AI) and Asian/American (AA) genotypes using marmosets (Callithrix jacchus) as models. Two groups of marmosets were inoculated with AI and AA genotypes, and serial plasma samples were collected. Viremia levels were determined using quantitative reverse transcription-PCR, plaque assays, and antigen enzyme-linked immunosorbent assay (ELISA). Anti-DENV immunoglobulin M and G antibodies, neutralizing antibody titer, and antibody-dependent enhancement (ADE) activity were determined using ELISA, plaque reduction neutralization test, and ADE assay, respectively. The AI genotype induced viremia for a longer duration, but the AA genotype induced higher levels of viremia. After four months, the neutralizing antibody titer induced by the AA genotype remained high, but that induced by the AI genotype waned. ADE activity toward Cosmopolitan genotypes was detected in marmosets inoculated with the AI genotype. These findings indicate discrepancies between heterologous genotypes that influence neutralizing antibodies and viremia in marmosets, a critical issue in vaccine development.
A Japanese man suffered from acute respiratory tract infection after returning to Japan from Bali, Indonesia in 2007. Miyazaki-Bali/2007, a strain of the species of Nelson Bay orthoreovirus, was isolated from the patient's throat swab using Vero cells, in which syncytium formation was observed. This is the sixth report describing a patient with respiratory tract infection caused by an orthoreovirus classified to the species of Nelson Bay orthoreovirus. Given the possibility that all of the patients were infected in Malaysia and Indonesia, prospective surveillance on orthoreovirus infections should be carried out in Southeast Asia. Furthermore, contact surveillance study suggests that the risk of human-to-human infection of the species of Nelson Bay orthoreovirus would seem to be low.