Susceptibility to winter vomiting disease: a sweet matter

Norovirus, the cause of winter vomiting disease, has emerged in recent years to be a major cause of sporadic and epidemic gastroenteritis worldwide. The virus has been estimated to cause >200,000 deaths each year in developing countries. Although the virus is highly contagious, volunteer and field studies have shown that a subset of individuals appears resistant to infections. A single nucleotide mutation (G428A) in the fucosyltransferase gene (FUT2) on chromosome 19 provides strong protection from infection in 20% of the white population. Histo-blood group ABO(H) antigens with terminal fucose are believed to function as receptors for human norovirus in the gastrointestinal tract, but also negatively charged potential receptors have been identified. Norovirus infection is a unique example where a single nucleotide mutation in a fucosyltransferase gene plays a crucial role in susceptibility to one of the most common viral diseases. This review discusses the role of host genetics and carbohydrate structures in susceptibility to winter vomiting disease.

A functional Toll-like receptor 3 gene (TLR3) may be a risk factor for tick-borne encephalitis virus (TBEV) infection

BACKGROUND

Tick-borne encephalitis virus (TBEV) infections may be asymptomatic or cause severe symptoms in the central nervous system. A mutation in the chemokine receptor 5 gene has been associated with increased risk of TBE but explains only a limited number of cases. Investigations of further risk factors are needed.

METHOD

To investigate the importance of the innate immune response, we analyzed 128 TBE patients, 77 patients with aseptic meningoencephalitis (AME) and 135 healthy controls, for 3 mutations: 2 in the Toll-like receptor 3 (TLR3) gene and 1 in the 2'-5'-oligoadenylate synthetase (OAS1) gene.

RESULTS

Although no association was found between the mutation in the OAS1 gene and TBE, the genotype distribution ofrs3775291, a mutation in TLR3, differed significantly between TBE patients and controls; 61%, 32%, and 7% of the TBE patients were carriers of the wild-type, heterozygous, and mutant genotype of rs3775291, respectively. The corresponding percentages among healthy controls (n = 126) were 52%, 29%, and 19% (P = .02), and among AME patients (n = 75) were 47%, 32%, and 21% (P = .009). Additionally, the wild-type rs3775291 allele was more common among TBE patients than among healthy controls (allele frequency, .768 vs .663; P = .01).

CONCLUSION

A functional TLR3 is a risk factor for TBEV infection.

Asymptomatic norovirus infections in Nicaraguan children and its association with viral properties and histo-blood group antigens

BACKGROUND

It has been previously reported that histo-blood group antigens (HBGAs) and particularly secretor status provides protection against symptomatic norovirus infection, but it remains unclear to what extent this includes asymptomatic infections in children.

METHODS

To explore whether HBGAs or certain viral genotypes are associated with asymptomatic norovirus infections in a pediatric population in Nicaragua, we investigated 163 children ≤5 years of age, without a recent history of diarrhea (≤10 days).

RESULTS

Asymptomatic norovirus infections were observed in 11.7% (19/163), with children ≤6 months of age being most frequently infected (16%). Of the 19 norovirus-positive children, 4 (21%) and 10 (53%) were infected with genogroups GI and GII, respectively, and 4 children (21%) were infected with viruses of both genogroups. Most children had ≥10 viral genomes per gram of feces. Nucleotide sequence analysis (15/19) revealed uncommon genotypes, such as, GII.7 (n = 5) and GII.2 (n = 3). An interesting observation was the low frequency of norovirus GII.4 strains among the asymptomatic children. AB blood type, Lewis a (Le) phenotype and nonsecretor genotype (sese) were not found among the asymptomatic children, but they occurred in population controls.

CONCLUSIONS

Frequency of asymptomatic norovirus infections was similar to that observed in symptomatic children from Nicaragua. Norovirus GII.2 and GII.7 were frequently detected but the globally dominating GII.4 was infrequent. Host genetic factors previously observed to be associated with protection against symptomatic norovirus infection were not found in this study.

Norovirus gastroenteritis outbreak with a secretor-independent susceptibility pattern, Sweden

Nonsecretors were highly susceptible to norovirus GI.3 in a foodborne outbreak.

Norovirus (NoV) is recognized as the commonest cause of acute gastroenteritis among adults. Susceptibility to disease has been associated with histo-blood group antigens and secretor status; nonsecretors are almost completely resistant to disease. We report a foodborne outbreak of GI.3 NoV gastroenteritis that affected 33/83 (40%) persons. Symptomatic disease was as likely to develop in nonsecretors as in secretors (odds ratio [OR] 1.41, 95% confidence interval [CI] 0.46–4.36 vs. OR 0.71, 95% CI 0.23–2.18, p = 0.57). Moreover, no statistical difference in susceptibility was found between persons of different Lewis or ABO phenotypes. The capsid gene of the outbreak strain shares high amino acid homology with the Kashiwa645 GI.3 strain, previously shown to recognize nonsecretor saliva, as well as synthetic Lewis a. This norovirus outbreak affected persons regardless of secretor status or Lewis or ABO phenotypes.

Genetic basis of host resistance to norovirus infection

Noroviruses have emerged as a major cause of acute gastroenteritis in humans of all ages and are responsible for 200,000 deaths every year, mainly in developing countries. Despite high infectivity and lack of long-term immunity, authentic and volunteer studies have shown existence of inherited protective factors. Recent studies have shown that secretor status controlled by the α1,2-fucosyltransferase gene located on chromosome 19 determines susceptibility to most, if not all, norovirus infections, with individuals homozygous for the G428A nonsense mutation (nonsecretors) representing 20% of the highly protected European population.

The G428A nonsense mutation in FUT2 provides strong but not absolute protection against symptomatic GII.4 Norovirus 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.

Ala67Thr mutation in the poliovirus receptor CD155 is a potential risk factor for vaccine and wild-type paralytic poliomyelitis

Poliovirus infections can be asymptomatic or cause severe paralysis. Why some individuals develop paralytic poliomyelitis is unknown, but a role for host genetic factors has been suggested. To investigate if a polymorphism, Ala67Thr, in the poliovirus receptor, which has been found to facilitate increased resistance against poliovirus-induced cell lysis and apoptosis, is associated with increased risk of paralytic poliomyelitis, poliovirus receptor genotyping was undertaken among Italian subjects with vaccine-associated (n = 9), or with wild-type paralytic poliomyelitis (n = 6), and control subjects (n = 71), using RFLP-PCR and pyrosequencing. Heterozygous poliovirus receptor Ala67Thr genotype was found in 13.3% of the patients with paresis and in 8.5% of the controls (Odds Ratio = 1.667). The frequency of Ala67Thr among the controls is in agreement with earlier published data. It is concluded that the Ala67Thr mutation in the poliovirus receptor is a possible risk factor for the development of vaccine-associated or paralytic poliomyelitis associated with wild-type virus.

Genetic susceptibility to symptomatic norovirus infection in Nicaragua

Host genetic resistance to Norovirus (NoV) has been observed in challenge and outbreak studies in populations from Europe, Asia, and USA. In this study, we have investigated if histo-blood group antigens can predict susceptibility to diarrhea caused by NoV in Nicaragua, Central America, and if this can be reflected in antibody-prevalence and titer to NoV among individuals with different histo-blood group antigen phenotypes. Investigation of 28 individuals infected with NoV and 131 population controls revealed 6% of non-secretors in the population and nil non-secretors among patients infected with NoV, suggesting that non-secretors may be protected against NoV disease in Nicaragua. Surprisingly, 25% of the population was Lewis negative (Le(a-b-)). NoV infections with genogroup I (GI) and GII occurred irrespective of Lewis genotype, but none of the Lewis a positive (Le(a + b-)) were infected. The globally dominating GII.4 virus infected individuals of all blood groups except AB (n = 5), while the GI viruses (n = 4) infected only blood type O individuals. Furthermore, O blood types were susceptible to infections with GI.4, GII.4, GII.7, GII.17, and GII.18-Nica viruses, suggesting that secretors with blood type O are susceptible (OR = 1.52) and non-secretors resistant. The overall antibody-prevalence to NoV GII.3 VLP was 62% with the highest prevalence among blood type B carriers (70%) followed by A (68%) and O (62%). All four investigated individuals carrying blood type AB were antibody-negative. Among secretors, 63% were antibody-positive compared to 33% among non-secretors (P = 0.151). This study extends previous knowledge about the histo-blood group antigens role in NoV disease in a population with different genetic background than North American and European.

A deletion in the chemokine receptor 5 (CCR5) gene is associated with tickborne encephalitis

Tickborne encephalitis (TBE) virus infections can be asymptomatic or cause moderate to severe injuries of the central nervous system. Why some individuals develop severe disease is unknown, but a role for host genetic factors has been suggested. To investigate whether chemokine receptor CCR5 is associated with TBE, CCR5Delta32 genotyping was performed among Lithuanian patients with TBE (n=129) or with aseptic meningoencephalitis (n=76) as well as among control subjects (n=134). We found individuals homozygous for CCR5Delta32 (P= .026) only among patients with TBE and a higher allele prevalence among patients with TBE compared with the other groups studied. CCR5Delta32 allele prevalence also increased with the clinical severity of disease.

Host genetic resistance to symptomatic norovirus (GGII.4) infections in Denmark

A total of 61 individuals involved in five norovirus outbreaks in Denmark were genotyped at nucleotides 428 and 571 of the FUT2 gene, determining secretor status, i.e., the presence of ABH antigens in secretions and on mucosa. A strong correlation (P = 0.003) was found between the secretor phenotype and symptomatic disease, extending previous knowledge and confirming that nonsense mutations in the FUT2 gene provide protection against symptomatic norovirus (GGII.4) infections.

Mendelian resistance to human norovirus infections

Noroviruses have emerged as a major cause of acute gastroenteritis in humans of all ages. Despite high infectivity of the virus and lack of long-term immunity, volunteer and authentic studies has suggested the existence of inherited protective factors. Recent studies have shown that histo-blood group antigens (HBGAs) and in particular secretor status controlled by the α1,2fucosyltransferase FUT2 gene determine susceptibility to norovirus infections, with nonsecretors (FUT2−/−), representing 20% of Europeans, being highly resistant to symptomatic infections with major strains of norovirus. Moreover, the capsid protein from distinct strains shows different HBGA specificities, suggesting a host–pathogen co-evolution driven by carbohydrate–protein interactions.

A nonsense mutation (428G-->A) in the fucosyltransferase FUT2 gene affects the progression of HIV-1 infection

BACKGROUND

The human FUT2 gene encodes the alpha(1,2)fucosyltransferase that determines secretor status. Homozygous for the nonsense mutation are called non-secretors and are unable to express histo-blood group antigens in secretions and on mucosal surfaces. In this study we have investigated the importance of the FUT2 fucosyltransferase activity on the progress of HIV-1 infection.

METHODS

Swedish blood donors (n = 276), 15 long-term non-progressors (LTNP) and 19 progressors were genotyped with respect to the nonsense mutation 428G-->A in the FUT2 gene. In addition 265/276 blood donors and 19 progressors with rapid or expected progression rate were Delta32 CCR5 genotyped.

RESULTS

Of 276 blood donors 218 (79%) were found to be secretor positive (se+), either homozygous (se+/+) wild type (30%) or heterozygous (se+/-) (49%) and 58 (21%) were homozygous non-secretors (se-/-). Five LTNP (33%) were found to be secretor-positive (se+/+, se+/-) and 10 (67%) se-/-. Of the 19 individuals with normal HIV-1 progression 15 (79 %) were found to be secretor positive and four (21%) were non-secretors. No frequency differences were found in the Delta32 CCR5 allele among the groups studied.

CONCLUSION

Strong association (P < 0.001) was observed between the nonsense mutation 428G-->A in the FUT2 gene and a slow disease progression of HIV-1 infection.