Abstract

Rotavirus gastroenteritis still remains a major cause of morbidity and mortality among young children in developing countries, with 150 000–200 000 deaths occurring annually in sub-Saharan Africa. We reviewed papers published over the last 30 years on the epidemiology of rotavirus diarrhoea among the hospitalized and out-patient children in Kenya. The analysis shows rotavirus prevalence of 6–56% with diarrhoea occurring throughout the year and generally exhibiting distinct peaks during the dry months. Among the common genotype, G1 was the most predominant up to the year 2002 but more recently there has been an emergence of genotype G9 as the most predominant genotype and to a less extent G8. It is important to continue rotavirus surveillance in Kenya to determine accurately the burden of rotavirus disease and the emerging new genotypes. This will assist policy makers in decision making on rotavirus vaccine introduction and determining the impact of the vaccine.

Introduction

Rotavirus gastroenteritis still remains a major cause of morbidity and mortality among infants and young children in both developed and developing countries [1, 2]. It is estimated that ∼600 000 rotavirus-related deaths occur among children of <5 years globally every year due to increased diarrhoea hospitalizations caused by rotavirus [3]. Studies done in Vietnam showed more than double increase from 21 to 56% rotavirus detection rates in children hospitalized with diarrhoea over a period of 15 years (1986–2001) [4, 5]. A similar surveillance done in nine Asian countries showed rotavirus prevalence of 45% in children hospitalized with diarrhoea [6].

Global prevalence of rotavirus derived from several studies conducted throughout the world have shown that rotaviruses account for 15–71% (average, 33%) of acute gastroenteritis requiring hospitalization of infants and young children [7]. Sanitation seems to have less impact on rotavirus infection rates as rotavirus infection occurs both in developed countries with high social economic levels and good sanitation standards as well as developing countries with poor sanitation [1, 8–14]. Nevertheless, mortality is higher in developing countries [8]. Herein, we highlight the epidemiology of rotavirus infection and review the prevalence of rotavirus strains circulating in Kenya.

Rotavirus Strains Classification

On the basis of antigenic and genetic diversities, 15 G types and 20 P types have been identified to date among rotavirus strains of both human and animal origin [2, 15]. In this context, 10 G types and 11 P types have been described in association with human infections, resulting in at least three dozen different G/P combinations [15]. Although, there is a broad diversity of rotavirus types infecting humans, the majority of isolates from children that present with diarrhoea can be classified into the four groups, as follows: P[8]G1, P[4]G2, P[8]G3 and P[8]G4. More recently, however, P[8]G9 and P[6]G9 strains have emerged globally as common G and P type combinations encountered in human infections [15–18].

Rotavirus Epidemiology in Kenya

Rotavirus epidemiological studies done in Kenya over the last 30 years have been conducted in both urban and rural settings. Overall, these studies have in general focused on the occurrence of acute diarrhoea associated with out-patient clinic visits and hospitalizations. These studies show an average prevalence rate of 6–56% [19–21], (Table 1). All four epidemiologically important rotavirus G types (G1–G4) have been detected in Kenya [19, 20, 25], (Table 2). Recent studies have shown that uncommon strains may account for a significant proportion of rotavirus strains detected in Kenyan children who present with diarrhoea [21]. Rotavirus strains with G9-type specificity have been detected in Kenya with increasing frequency in the past [21, 26, 30].

Table 1

Prevalence of Rotavirus infection in Kenya for the period 1975–2005

Area of study Year of study Detection assay No. tested Age (years) Percent positive with rotavirus References 
KNH, Nairobi 1975–76 Culture 160 <6 41 [22
KNH, Nairobi 1994 ELISA 153 <5 22 [23
KNH, Nairobi 1981–83 ELISA/PAGE 36 <5 39 [24
KNH, Nairobi 1987 ELISA 98 neonates [20
KNH, Nairobi 1989–91 PAGE 278 <1 33.8 [19
IDH, Nanyuki, Kitui 1991–94 ELISA 1431 <6 24,22,13 [25
KNH, Nairobi 1996–99 ELISA 538 <5 17.3 [26
KNH, Nairobi 2000 Dako, IDEIA 382 <5 56.2 [27
Karen, Nairobi 1999–2000 Dako, IDEIA 207 >5 14 [28
Karen, Nairobi 2001–02 Dako, IDEIA 119 <5 11 [29
Maua, Meru 2004–05 Dako, IDEIA 135 <5 18 [21
Area of study Year of study Detection assay No. tested Age (years) Percent positive with rotavirus References 
KNH, Nairobi 1975–76 Culture 160 <6 41 [22
KNH, Nairobi 1994 ELISA 153 <5 22 [23
KNH, Nairobi 1981–83 ELISA/PAGE 36 <5 39 [24
KNH, Nairobi 1987 ELISA 98 neonates [20
KNH, Nairobi 1989–91 PAGE 278 <1 33.8 [19
IDH, Nanyuki, Kitui 1991–94 ELISA 1431 <6 24,22,13 [25
KNH, Nairobi 1996–99 ELISA 538 <5 17.3 [26
KNH, Nairobi 2000 Dako, IDEIA 382 <5 56.2 [27
Karen, Nairobi 1999–2000 Dako, IDEIA 207 >5 14 [28
Karen, Nairobi 2001–02 Dako, IDEIA 119 <5 11 [29
Maua, Meru 2004–05 Dako, IDEIA 135 <5 18 [21

KNH, Kenyatta National Hospital; IDH, Infectious Diseases Hospital; PAGE, Polyacrylamide gel electrophoresis; NR: Not reported; ELISA, Enzyme linked immunosorbent assay. Dako, IDEIA: commercial rotavirus-detection enzyme immunoassay kit (IDEIA™, DAKO Diagnostics, UK).

Table 2

Percentages of rotavirus strain with specific VP7 genotype/serotype circulating in Kenya from 1980–2005

Year of study No. tested Technique/ assay G1 G2 G3 G4 G8 G9 Predominant stain type References 
1982–83 16 FFN 43.7 25 12.5 G1 [31
1989–91 95 ELISA 28 13 – – G1 [19
1989–91 317 RT-PCR 23.3 17 0.6 41.6 – – G4 [25
1996–99 456 RT-PCR 27 11 16 – <1 G1 [26
2000 20 RT-PCR 70 – – 10 15 G1 [30
1999–2000 23 RT-PCR 17.4 34.8 8.7 8.7 4.35 G3 [28
2001–02 13 RT-PCR 62.5 25 12.5 G1 [27
2004–05 17 RT-PCR 17.4 – – – 29.4 47.1 G9 [21
Year of study No. tested Technique/ assay G1 G2 G3 G4 G8 G9 Predominant stain type References 
1982–83 16 FFN 43.7 25 12.5 G1 [31
1989–91 95 ELISA 28 13 – – G1 [19
1989–91 317 RT-PCR 23.3 17 0.6 41.6 – – G4 [25
1996–99 456 RT-PCR 27 11 16 – <1 G1 [26
2000 20 RT-PCR 70 – – 10 15 G1 [30
1999–2000 23 RT-PCR 17.4 34.8 8.7 8.7 4.35 G3 [28
2001–02 13 RT-PCR 62.5 25 12.5 G1 [27
2004–05 17 RT-PCR 17.4 – – – 29.4 47.1 G9 [21

FFN, fluorescence focus neutralization; RT-PCR, Reverse transcriptase polymerase chain reaction; ELISA, Enzyme linked immunosorbent assay; No. tested, Number of samples tested.

Seasonality of Rotavirus Infection in Kenya

In Kenya rotavirus diarrhoea occurs throughout the year [31], but seasonal peaks are observed during the dry seasons (January–March and June–September) [32, 33]. This is in contrast to other regions of Africa like southern Africa (South Africa, Madagascar, Zambia and Zimbabwe) where rotavirus occurs during the autumn and winter and which overlap with the dry seasons and in northern Africa (Egypt and Morocco) where rotavirus occurs in autumn and winter seasons but not in dry seasons [34, 35] and in Tunisia it occurs predominantly in the cool, dry season [36]. The rotavirus season in West Africa occurs during the dry cool months (January–February and July–September) [37].

The Emerging Predominant Genotypes in Kenya

Available data indicate that all the major global human rotavirus genotypes (G1, G2, G3, G4 and G9) were detected in Kenya and the major P genotypes (P[4], P[6] and P[8]) were detected during the period 1996–99 and 1999–2002 (Table 2). In 1996–99 studies, P[8] was the predominant P genotype but there was an apparent shift during 1999–2000 when P[6] was predominant (Table 3). Majority of the genotypes of rotavirus circulating in Kenya during the period 1975–2002, were similar to those common in other part of the world i.e. G1–G4. However, it is apparent that the emerging VP7 genotypes (G8 and G9) are replacing the most common G genotypes (G1–G4) as observed during the period 2004–05 (Table 2).

Table 3

Percentages of rotavirus Strain with specific VP4 genotype circulating in Kenya from 1996–2000

Year of study No. tested Detection assay P[4P[8[P6] P[9Predominant stain type References 
1996–99 00 RT-PCR 47 27 – P[8[26
1999–2000 23 RT-PCR 8.7 26.1 65.2 P[6[28
Year of study No. tested Detection assay P[4P[8[P6] P[9Predominant stain type References 
1996–99 00 RT-PCR 47 27 – P[8[26
1999–2000 23 RT-PCR 8.7 26.1 65.2 P[6[28

RT-PCR, Reverse transcriptase polymerase chain reaction; No. tested, Number of samples tested.

Emerging New Rotavirus Strains in Kenya

One interesting finding in these studies is the diminishing of the common genotypes G3 and G4 which are being detected in low frequency while the predominance of the emerging genotypes (G8 and G9) has been confirmed during a recent study [21].

The emergence of G9 strains as an important cause of gastroenteritis in Kenya [21, 30], and the increase in global divergence of rotavirus strains in other parts of the world [38–40], emphasize the need for continual surveillance of rotavirus strains, more so, in developing countries such as Kenya, where new vaccines are likely to have the greatest impact. The information generated by rotavirus strain surveillance is important for the development of more efficacious vaccines and also for the evaluation of the potential benefit of these vaccines in reducing <5 year child mortality and morbidity in Kenya.

Available Rotavirus Vaccines and Their Possible use in Kenya

Given the importance of rotavirus infection and related cause of acute childhood diarrhoea and gastroenteritis, and the fact that improved hygiene conditions have failed to significantly decrease the incidence of rotavirus-associated diarrhoea, a vaccine against rotavirus appears to be the best option [41]. The first human rotavirus vaccine to be licensed (RotashiedR by Wyeth Lederle Vaccines, Philadelphia, PA) was withdrawn from the market few months after being introduced in the childhood immunization schedule in the United States of America due to an apparent association with intestinal intussusception [42]. Recently, two new rotavirus vaccines [Rotarix™ by GlaxoSmithKline (GSK) Biologicals, Rixensart, Belgium and RotaTeq™ by Merck Vaccines, Whitehouse Station, NJ] have been developed and clinical trials have been conducted in Latin America, Europe and North America [43–46]. Clinical trials with these new vaccines are on going in five African countries.

Future Perspective

Although the major global genotypes G1–G4 were detected during the period 1975–2002 (Table 2), there has been an occurrence of divergent rotavirus strains such as G9,G8 and G8/G9 mixed infections in Kenya and this has also been reported in other parts of Africa [21, 17, 26]. These emerging strains may pose challenges to the efficacy of the new rotavirus vaccines in Africa. Thus, additional surveillance data are needed to detect the unusual and new strains that may be circulating at the time of new rotavirus vaccine introduction in African children.

Conclusion

This review highlights the epidemiological features of rotavirus infection in Kenya and underscores the importance of an effective and safe rotavirus vaccine which may lead to reduction of rotavirus diarrhoea morbidity and mortality among the infants and young children in a developing country such as Kenya. There is optimism across the region as we wait for the immunogenicity and efficacy trial data of the new rotavirus vaccines being tested in Africa.

Acknowledgements

J.M.M. and A.D.S. are founder members of the African Rotavirus Network (ARN). N.M.K. and J.O.N. are members of the African Rotavirus Network. None of the authors have associations that could pose conflicts of interest. The results of this study were presented at the Virology Africa symposium held on November 8–11, 2005 in Cape Town, South Africa. We acknowledge support from World Health Organization and the African Rotavirus Surveillance Network.

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