Resumen de Epidemiologia molecular de brots de gastroenteritis per norovirus i d’hepatitis a: de la seqüència consens a la quasiespècie
Human norovirus (HuNoV) and hepatitis A virus (HAV) are two of the most relevant enteric viruses from public health and food safety perspectives. HuNoV cause sporadic and epidemic acute gastroenteritis worldwide and HAV is the main cause of acute hepatitis.
The overall objective of the present thesis was to expand knowledge about the epidemiology and molecular characterization of outbreaks caused by HuNoV and HAV occurring in Catalonia, by analyzing consensus sequences obtained by Sanger and viral quasiespecies obtained by NSG. The thesis is structured into four articles. In the first two studies, Sanger consensus sequencing was used to characterize the circulating strains of HuNoV associated with outbreaks during a 3-year period. Of all outbreaks of possible viral etiology, 76% were due to HuNoV, and 15 different genotypes were identified. In addition, the emergence of the new Genogroup II genotype 4 variant was confirmed. The role of food handlers (FHs) and health-care workers (HCWs) was also evaluated for most outbreaks, by analyzing the incidence of infections, and by characterizing the levels and the duration of excretion of HuNoV in feces. Attack rates among FHs and HCWs in outbreak scenarios were similar, but the percentage of asymptomatic infections was significantly greater among FHs, with no differences in the duration or levels of excretion between symptomatic and asymptomatic infections.
In the other two studies, NGS protocols were developed for HuNoV and HAV to analyze viral quasiespecies within infected hosts and between linked patients. These protocols constitute an excellent tool for the future characterization of outbreaks, since they provide a huge amount of variant strains circulating in a short time. Overall, we found that viral diversity was host-specific, and for HuNoV, a higher variability was observed in asymptomatic subjects, suggesting their contribution to the propagation of minor variants in the population. In the HAV study, viral populations from patients of Barcelona of MSM 2016-2017 outbreak were analyzed and we found positive pressure of viral antigenic variants in vaccinated subjects, highlighting the importance of adhering to good vaccination practices to avoid as much as possible the emergence of vaccine escape mutants.
