In this novel study, we have for the first time identified evolutionarily conserved capsid residues in an individual chronically infected with norovirus (GGII.3). From 2000 to 2003, a total of 147 P1-1 and P2 capsid sequences were sequenced and investigated for evolutionarily conserved and functionally important residues by the evolutionary trace (ET) algorithm. The ET algorithm revealed more absolutely conserved residues (ACR) in the P1-1 domain (47/53, 88 %) as compared with the P2 domain (86/133, 64 %). The capsid P1-1 and P2 domains evolved in time-dependent manner, with a distinct break point observed between autumn/winter of year 2000 (isolates P1, P3 and P5) and spring to autumn of year 2001 (isolates P11, P13 and P15), which presumably coincided with a change of clinical symptoms. Furthermore, the ET analysis revealed a similar receptor-binding pattern as reported for Norwalk and VA387 strains, with the CS-4 and CS-5 patch (Norwalk strain) including residues 329 and 377 and residues 306 and 310, respectively, all being ACR in all partitions. Most interesting was that residues 343, 344, 345, 374, 390 and 391 of the proposed receptor A and B trisaccharide binding site (VA387 strain) within the P2 domain remained ACR in all partitions, presumably because there was no selective advantage to alter the histo blood group antigens (HBGA) receptor binding specificity. In conclusion, this study provides novel insights to the evolutionary process of norovirus during chronic infection.

In November 2004, 116 individuals in an elderly nursing home in El Grao de Castellón, Spain were symptomatically infected with genogroup II.4 (GII.4) norovirus. The global attack rate was 54.2%. Genotyping of 34 symptomatic individuals regarding the FUT2 gene revealed that one patient was, surprisingly, a non-secretor, hence indicating secretor-independent infection. Lewis genotyping revealed that Lewis-positive and negative individuals were susceptible to symptomatic norovirus infection indicating that Lewis status did not predict susceptibility. Saliva based ELISA assays were used to determine binding of the outbreak virus to saliva samples. Saliva from a secretor-negative individual bound the authentic outbreak GII.4 Valencia/2004/Es virus, but did not in contrast to secretor-positive saliva bind VLP of other strains including the GII.4 Dijon strain. Amino acid comparison of antigenic A and B sites located on the external loops of the P2 domain revealed distinct differences between the Valencia/2004/Es and Dijon strains. All three aa in each antigenic site as well as 10/11 recently identified evolutionary hot spots, were unique in the Valencia/2004/Es strain compared to the Dijon strain. To the best of our knowledge, this is the first example of symptomatic GII.4 norovirus infection of a Le(a+b-) individual homozygous for the G428A nonsense mutation in FUT2. Taken together, our study provides new insights into the host genetic susceptibility to norovirus infections and evolution of the globally dominating GII.4 viruses.

We describe the genetic diversity of sapovirus (SaV) in children in Nicaragua and investigate the role of host genetic factors and susceptibility to SaV infections. Our results indicate that neither ABO blood group, Lewis phenotype, nor secretor status affects susceptibility to SaV infection in Nicaragua.

Background. Sapovirus (SaV) infections are increasing globally but there is no information available regarding factors determining susceptibility to SaV infections in the Caucasian population.

Methods. Saliva samples were collected from 64 individuals with sapovirus gastroenteritis in Denmark between October 2008 and November 2010. These were genotyped for the FUT2 G428A nonsense mutation (secretor status) and phenotyped for ABO and Lewis histo-blood groups.

Results. We found that neither secretor status nor Lewis phenotype, were associated with susceptibility to symptomatic infection with SaV. However, individuals of histo-blood groups B and AB had significantly lower risk to be infected (OR 0.18, p≤0.01 and OR 0.10, p<0.05, respectively). For 39 of the 64 SaV positive samples viral strains were genotyped and 41%, (16/39) belonged to genotype GI.2, 10% was GI.1 (4/39), 2.5% was GI.5 (1/39), 8% was GII.1 (3/39), 5% was GII.4 (2/39), 18% was GIV (7/39) and 15.5% was GV (6/39).

Conclusion. This is the first report investigating the role of host genetic factors in SaV susceptibility in the Caucasian population. We found a reduced risk of infection in individuals with blood group B (and AB), but no association to the FUT2 G428A nonsense mutation determining secretor status nor to the Lewis status.