Anticipating rotavirus vaccines: epidemiology and surveillance of rotavirus in South Africa.

Rotavirus infection is associated with acute infantile gastroenteritis in infants and young children globally. In South Africa, rotavirus infection has been shown to be associated with approximately one-quarter of all diarrhoeal admissions to hospital. Rotavirus infection predominantly occurs in infants less than 12 months of age (75%) and has a peak of shedding during the cooler, drier months of the year. A secondary peak during the spring has been observed. Multiple infections with rotavirus and at least one other microbial agent are common. The circulating VP7 serotypes and VP4 genotypes have been determined in various regions of South Africa and show a geographic specific distribution. A decade previously, P[8]G1 or G4 strains predominated, and P[4]G2 strains occurred in an epidemic pattern in one region. More recently, rotavirus strains with P[6] genotype have become common and novel VP7/VP4 genotype combinations are occurring across the country. G9 strains have been reported from Cape Town to Vendaland. The circulating rotavirus types observed in this study add to the knowledge of the natural history of rotavirus infection and provide the groundwork to consider future vaccine strategies.

Epidemiology of astrovirus infection in Zaria, Nigeria.

Astrovirus has been shown to be an important aetiological agent associated with gastroenteritis in children, although few studies have been conducted in Africa. In this study, stool specimens were obtained from 375 young children less than 5 years of age with acute gastroenteritis presenting at Ahmadu Bello University Hospital, and from a control group of 122 children without diarrhoeal illness. The specimens were examined for the presence of human astroviruses using a monoclonal antibody-based ELISA (Astrovirus IDEIATM, Dako, UK). Negative staining electron microscopy was performed on specimens to confirm the presence of astrovirus particles. Astrovirus was detected in 6.7 per cent (25/375) of the diarrhoeal stools compared to 5.7 per cent (7/122) of the control specimens. Astrovirus seemed to infect older children and more than half the children were between 1 and 4 years of age (15/25). Only four children were less than 6 months old. A winter peak of shedding was observed.

Prevalence of unusual human rotavirus strains in Ghanaian children.

Sixty-seven rotavirus-positive fecal samples, collected between January and April 1999, from children with diarrhea in the Upper East Region of Ghana were examined for rotavirus VP7 and VP4 types. Sufficient viral RNA could be obtained from 46 (68.7%) of the samples and all the isolates had short electrophoretic pattern and typed as subgroup I rotaviruses by subgroup ELISA. Three rotavirus strains with G8 specificity were identified for the first time in Ghana. G and P typing by PCR identified two distinct strains, P[6]G2 (50%) and P[6]G8 (4.3%). Eighty-two percent of the isolates (n = 38) were of the "putative" neonatal P[6] genotype. Two of these G8 isolates carried the VP4 P[6] genotype whereas the third could not be assigned a P type. Mixed infections of G1, G2, G3 and G8 were detected amongst the stool samples. The presence of these unusual strains, especially the high incidence of G2 rotavirus strains in Ghana, reinforces the need to put in place a surveillance system for the detection of new and exotic rotavirus strains, that will provide information on the spread of these strains in West Africa as well as useful data for the formulation of the next generation of rotavirus vaccines.

South African G4P[6] asymptomatic and symptomatic neonatal rotavirus strains differ in their NSP4, VP8*, and VP7 genes.

Over the past decade, a G4P[6] strain has been found to be circulating in different neonatal wards in the Pretoria area. This endemic strain was associated with both asymptomatic and symptomatic infection, providing the opportunity to undertake a molecular study of some of the putative "virulence" genes. The genes encoding NSP4, VP8*, and VP7 of two asymptomatic and two Symptomatic strains were sequenced and compared with ST3. Within each of these genes, amino acid substitutions unique to South African strains were recorded. Four conserved amino acid differences between asymptomatic and symptomatic strains at aa 82 (serine to leucine), aa 114 (aspartic acid to glutamic acid), aa 138 (proline to threonine), and aa 169 (leucine to serine) were identified within the NSP4 gene. The hypervariable region of VP8* exhibited 10 specific amino acid differences (at aa 73, 78, 98, 111, 116, 142, 145, 167, 169, and 188) between asymptomatic and symptomatic strains, while three amino acid substitutions within VP7 were noted. These changes to VP7 occurred within the glycosylation site at aa 70 (leucine to serine), at antigenic region A (aa 96, asparagine to threonine), and at aa 318 (aspartic acid to glycine). It may be speculated that these changes are specific to G4P[6] strains. Furthermore, the observed substitutions may also be particular to South African strains. NSP4, VP8*, and VP7 have been associated with virulence and the amino acid substitutions within these genes correlate with both asymptomatic and symptomatic infection observed in neonates.

VP6 subgroup and VP7 serotype of human rotavirus in Zaria, northern Nigeria.

A survey of rotavirus infection in infants and young children with acute diarrhoea was undertaken in Zaria, northern Nigeria during 1997 and 1998. In total, 375 faecal specimens were collected from children aged between 1 and 60 months and 122 specimens from age-matched control children without diarrhoea. Fourteen specimens were collected from neonates in the University Teaching Hospital. Rotavirus antigen was detected in 61 diarrhoeal and four control specimens; four neonates were shedding rotavirus. Polyacrylamide gel electrophoresis of the viral genome showed the presence of five strains of rotavirus with long RNA electropherotypes and one short pattern. The rotavirus VP6 subgroup was determined by monoclonal antibodies specific ELISA and showed that subgroup II strains predominated (72 vs. 9.8 per cent), while eight strains could not be subgrouped and three did not react at all. Examination of the VP7 serotype showed G1 and G3 strains circulating at similar levels (29 and 25 per cent), but no serotype G2 nor G4 strains were identified. G1/G3 'mosaic' virus strains circulated commonly (10 per cent).

Comparative studies of human rotavirus serotype G8 strains recovered in South Africa and the United Kingdom.

Epidemiological studies on the VP7 serotype prevalence of human rotaviruses in South Africa and the United Kingdom identified several strains which could not be serotyped as G1-G4 by monoclonal antibodies. Further analysis of these strains with a G8-specific monoclonal antibody and with probes for human rotaviruses confirmed them as G8 rotaviruses. These G8 strains exhibited a high degree of sequence identity when compared with each other and with other rotavirus G8 strains. Five South African strains were further characterized as VP6 subgroup I, but with a long RNA electropherotype, which is similar to the G8 strains previously isolated in Finland. In the UK strains, one was VP6 subgroup II with a long RNA electropherotype (similar to the Italian G8 strain). The other two were subgroup I with a short RNA electropherotype. None of these strains exhibited the super-short RNA electropherotype described in the prototype G8 strains recovered from Indonesia (69M).