The Norovirus Puzzle Characterization of human and bovine norovirus susceptibility patterns

Abstract: Winter vomiting disease is caused by norovirus (NoV) and affects millions of people every year resulting in 200.000 deaths among children in developing countries. It was observed early that not all individuals exposed to the norovirus became ill. The reason for this is now recognized to be dependent upon the secretor status of an individual. The secretor status determines the ability of an individual to express histo-blood group antigens (HBGA) on mucosa and in saliva. A non-secretor is unable to express HBGAs due to a mutation in a gene called FUT2. In this thesis, I have investigated the antibody prevalence and titer in humans in Sweden and Nicaragua to the most common GII NoV and the correlation to secretor status, Lewis status and ABO. I found that secretors had significantly higher antibody prevalence and titer to GII NoV than non-secretors suggesting that non-secretors are less prone to be infected by the GII NoV. In Nicaragua, I also found several different NoV strains circulating at the same time. The NoVs have been circulating and evolving in the human population for some time and the same individuals seems to be infected over and over again with the same virus. This suggests that there is no long-term immunity present but possibly short-term immunity, which would make it very difficult to produce a vaccine against NoV. However, recent studies have shown the possibility of using virus like particles as a vaccine candidate and have demonstrated long-term immunity.The bovine NoV (boNoV) cause gastroenteritis in cattle and are closely related to the human NoV. The possibility of zoonotic transfer to humans is currently being investigated. I found that 26% of Swedish blood donors have antibodies to the boNoV suggesting that they have been exposed to the virus. The human NoV has been observed to be able to infect and cause disease in cattle, could the boNoV do the same in humans? To date, no boNoV strain has been found in humans. The proposed receptor structure for boNoV is the ?Gal epitope, which is present in many mammals like cow, pig, horse, sheep and rabbit but not in humans. This indicates that humans are not at risk for boNoV infection because we lack the proper receptor structure. However, recombinations between different NoV strains have been demonstrated and the possibility of more than one receptor being present has been suggested. I found that aa position 365-379 on the boNoV capsid seems to be important for binding to erythrocytes. In this thesis, I hope to add some new pieces to the Norovirus Puzzle.