Rotaviruses are identified as an important cause of gastroenteritis requiring hospitalization and causing several deaths in Asian and African children [20, 21]. In our study, 54 (35%) out of 154 samples of patients suspected with gastroenteritis were ELISA positives (26 male vs 28 female). This result showed that there was no significant difference in the detection of RVA to sex and implies that RVA affects both male and female children. Conversely, in the age group, we found that 51.8% of RVA positive cases were attributed to the age group of 6 to 11 months in agreement with the studies conducted in surrounding countries such as the Democratic Republic of Congo (DRC) were 54.3% of children were infected in this group of age [22]; but in contrast to those in Rwanda where it was mostly children aged 12 to 24 months who have been most affected by RVA infection [24]. However, children aged 24 to 59 months were the least infected and accounted for 9.2% of cases. This result can be explained by the role of the immune memory that is built up by repetition of infections and provides a natural immunity that reduces or eliminates severe forms of RVA diarrhea [23]. We also showed that children under 2 years of age were the most RVA infected and represented approximately 90% of cases. These data corroborate those of others sub-Saharan countries that also reported a high incidence of RVA diarrhea in the under-2 age group [22, 25].
We found a highly cases of children testing positive for RVA gastroenteritis in the dry months compared to rainy months. This finding is common in s several Africa countries of sub-Saharan [22, 26],.
Before the introduction of the Rotavirus vaccine into the vaccination program in the Congo, stool samples were collected from children received in 4 hospitals with different localizations (north, center and south) at Brazzaville. About 45.4% of pre-vaccination samples were positive. This prevalence is similar to those previously reported in a study conducted in south of Brazzaville and in some neighboring countries such as the Central African Republic (located in northern Congo), with a prevalence of 46.4% and 45% respectively [15, 26]. The data reported in this study are lower than those reported in DRC where an average prevalence of 61% was reported between 2009 and 2012 [22]. However, in Gabon, between 2010 and 2011, only 27% of prevalence rate was reported in the same study population [25].
Just after the introduction of the Rotavirus vaccine, we found prevalence rates of 16% and 4.7% in the cities of Brazzaville and Pointe-Noire, respectively. Compared with the pre-vaccine period, a very marked decrease in cases of RVA related diarrhea was observed. Indeed, a 29.4% reduction in RVA cases was reported during the post vaccination period. In the city of Pointe-Noire, only 4.7% of children were confirmed infected with RVA. These data may suggest the positive impact of Rotavirus A vaccine in the prevention of RVA diarrhea. The same tendency to drastically reduced RVA cases has also been reported in other countries such as Rwanda (51 to 55%), Malawi (48.2%) and South Africa (44.9 to 65.4%) one to four years after vaccine introduction [27, 28, 29]. Similarly, the reduction of 86%, 96%, and 92%, respectively in the age groups of 6–11, 12–23, and 24–35 was reported [30].
We observe a certain temporal distribution of the RVA genotypes in this study. Indeed, before the introduction of the vaccine, the genotypes G1 of the VP7 gene, represented 81% of isolates, followed by G9 with only 2%. Cases of mixed infection have also been identified between G1G2 and G1G9 in proportions of 6% and 2%, respectively. Regarding the VP4 gene, the predominantly P genotype was P[8] with 79.6% and mixed infections P[6]P[8] with 6% of cases. Rare genotypes such as G8, G10 and G12 previously identified in Brazzaville by Mayindou et al [15] and in other sub-Saharan countries [31] were not reported in the current study. This difference between works conducted in Brazzaville may be related to the duration of sample collection as well as the sample size. After the introduction of the vaccine, genotypes G1 remains predominant; however, there is an emergence of rare genotypes such as G8 and G12. Regarding P type, P[8] has been detected in the majority of cases. It has been characterized an unusual P[4]P[6] mixed genotype. Overall, the genotypic distribution of the strains that we report, have also been identified in other studies before or after introduction of vaccination [22, 32].
The P[6] genotype was reported in several studies of RVA infection and further identified P[6] genotype associated with a wide range of RVA genotypes both asymptomatic and symptomatic infection [32, 33]. In our study, we report in the pre-vaccine group, 7% of patients with a mixed P[6]P[8] genotype and 20% of P[4]P[6] genotype after vaccine introduction. These genotypes have also been reported in DRC [22].
In this study, we report the predominance of the genotypes combination G1P[8] (75.92%). In the previous report in RoC conducted between 2012 and 2013, this genotype was detected in 49.3% of cases [15]. Similarly, the G9P[8], G1G2P[8] P[6] and G1G9P[8] genotypes were detected at low prevalence prior to introduction of vaccination. The high prevalence of the G1P[8] genotype has also been reported in previous studies in other African countries [34].
In the period following the introduction of the vaccine, the presence of genotypes G8P[8], G1P[4]P[6] and G12P[8] was observed. However, given the small sample size and the number of positive results obtained after vaccination, it is difficult to compare the distribution of genotypes in the two groups of the study. Nevertheless, studies in Eastern and Southern Africa [32] found no difference in the detection of RVA strains before and after the introduction of vaccination. The uncommon genotypes such as G8P[8] and G12P[8] detected in this study have increasingly been identified in several African and Asian countries [35, 36] and those incidence were interesting features in this part of study and suggesting a greater diversity among Congolese RVA infections. The mixed infections with the unconventional strain G1P[4]P[6] detected in the first time in RoC was previously identified in Kenyan children with diarrhea [37]. Those unusual combinations of G and P type that are reported in several developing countries as a cause of diarrheal disease in young children were certainly due to reassortment between human and animal RVA strains circulating in population [38].
In addition, the identification of RVA strains such as G1P[8], G1P[4]P[6], G8P[8] and G12P[8] in four vaccinated children with Rotarix can be explained by several factors such as the fact that Rotavirus vaccines do not completely protect children against RVA gastroenteritis, as shown by several post-vaccination studies [27, 28, 29].
Limits Of Study
The study was conducted during six months of the year and only two cities were included, the results obtained did not represent the national burden. We also consider the fact of using ELISA as a limit as because of the relatively low sensitivity compared to molecular techniques there is the possibility of having false negative results. Also, a multiplex RT-PCR used for RVA genotyping are a bond with load viral and primers sequences, however, presence of mutations into gene sequences and the low viral load can induce some cases of false negatives and untippable strains.