Peer Review #2 of "Molecular serotyping of Haemophilus parasuis isolated from diseased pigs and the relationship between serovars and pathological patterns in Taiwan (v0.1)"

Abstract

Background: Haemophilus parasuis (H. parasuis) is the etiological agent of Glässer's disease, and causes severe economic losses in the swine industry. Serovar classification is intended as an indicator of virulence and pathotype and is also crucial for vaccination programs and vaccine development. According to a polysaccharide biosynthesis locus analysis, H. parasuis isolates could be classified by a molecular serotyping assay (except for serovars 5 and 12). The aim of this study was to identify H. parasuis isolates from diseased pigs in Taiwan by using a molecular serotyping assay and to analyze the relationship between serovars and pathological patterns. Methods: From August 2013 to February 2017, a total of 133 isolates from 277 lesions on 155 diseased animals from 124 infected herds serotyped by multiplex PCR and analyzed with pathological data. Results: The results showed that the dominant serovars of H. parasuis in Taiwan were serovars 5/12 (37.6%), 4 (27.8%) and 13 (15%) followed by molecular serotyping non-typable (MSNT) isolates (13.5%), which are differentiated on a genetic basis. Nevertheless, the serovar-specific amplicons were not precisely the same sizes as previously indicated in the original publication, and MSNT isolates appeared with unexpected amplicons or lacked serovar-specific amplicons. Furthermore, most H. parasuis isolates were isolated from nursery pigs infected with porcine reproductive and respiratory syndrome virus. The percentage of lung lesions (30.4%) showing H. parasuis infection was significantly higher than that of serosal lesions. Discussion: Collectively, the distribution of serovars in Taiwan is similar to that found in other countries, but MSNT i solates remain due to genetic variations. Furthermore, pulmonary lesions may be optimum sites for H. parasuis isolation, the diagnosis of Glässer's disease, and may also serve as points of origin for systemic H. parasuis infections in hosts.