Human Caliciviruses: a study of viral evolution, host genetics and disease susceptibility

Abstract: The viruses described in this thesis are the norovirus and sapoviruses, which belong to the family of human caliciviruses and are known to cause gastroenteritis in humans. Gastroenteritis has emerged as a global health problem and is based on the large number of infected considered as one of the most common diseases today. According to estimates of the World Health Organization (WHO), gastroenteritis causes over five times more pediatric deaths compared to pediatric deaths caused by HIV/AIDS worldwide. Norovirus, the cause of the famous “winter vomiting disease”, is alone responsible for more than 200 000 deaths each year in children less than 5 years of age.The mechanism for emergence and evolution of new human calicivirus strains, as well as protective immunity in the human population is poorly understood. The main focus for this thesis was to elucidate the possible correlation between human calicivirus evolution, host genetics and disease susceptibility. One of the main findings presented in this thesis is the documentation of in vivo capsid gene evolution and quasispecies dynamics during chronic NoV GI.3 infection (Paper 1). In paper II, we reported that the G428A nonsense mutation in the FUT2 gene provides strong but not absolute protection against symptomatic GII.4 NoV infection. In my last two papers (Paper III and IV), we were the first to investigate host genetic susceptibility factors during authentic SaV infection.To summarize, the results presented in this thesis show that the success of human calicivirus infection probably is determined by a delicate interplay between virus evolution and susceptibility of the host, both genetically and immunologically.