Epidemiological Analysis of Porcine Circovirus Type 2 (PCV2) Spatio-temporally of Circulation in Vietnam from 2004 to 2019

Introduction: Porcine circovirus 2 (PCV2) is a causative agent of postweaning multisystem wasting syndrome (PMWS), an epizootic disease that causes significant economic losses to pig producers worldwide, including Viet Nam. However, analyses of which groups of PCV2 strains cause disease in pigs in Viet Nam are still limited, leading to the delay or lack of application of specific vaccine sources to prevent PMWSs in other countries. Method: In this study, we aimed to analyze the geographical and temporal diversity of PCV2 in pig farms across 26 provinces in Vietnam, thus identifying the dominant strain for vaccine production. After samples from North, Central, and South Viet Nam were collected, phylogenetic trees were created to study the molecular genetic/evolutionary relationships, thereby classifying the existing PCV2 strains. The spatiotemporal distribution of strains is shown visually for observation. Finally, an analysis of the important evolutionary differences between the two strains, PCV2d and PCV2b, revealed that these strains were superior in Viet Nam. Results: Our study examined the diversity of PCV2 strains in Vietnam, ranging from the northern to southern regions, and the PCV2d strain was revealed to be the predominant strain. Interestingly, we observed the presence of 2 or 3 different genotypes of PCV2 in the same province and at the same time. We identified the presence of PCV2h, PCV2g, and PCV2e genotypes that had not been previously detected. Furthermore, we identified potential sites of positive selection in the capsid epitopes, which are believed to play a crucial role in evading the host immune system. Conclusions: The results showed that Viet Nam has 5 genotypes, namely, PCV2b, PCV2e, PCV2g, PCV2h and PCV2d—the main causative strains of the disease. The coexistence of strains in the same geographical area was also shown, indicating the importance of preparing vaccines and preventing livestock infection in Viet Nam.