Rotavirus infection is the most common cause of diarrhea in children aged <5 years worldwide. It is responsible for some 600,000 deaths annually and approximately 40% of hospitalizations due to diarrhea in children in that age group. Each year around 75,000 hospitalizations and nearly 15,000 deaths in the Region of the Americas are attributable to rotavirus. While the incidence of rotavirus infection in developed and developing countries is similar, 80% of deaths occur in developing countries.
In 2003, between 1986 and 2000, each year rotavirus caused 111 million episodes of infantile diarrhea requiring strictly home care worldwide, 25 million medical visits, 2 million hospitalizations, and an average of 440,000 deaths (1). This means that by 5 years of age, almost all children have experienced an episode of rotavirus diarrhea: 1 out of 5 children has been taken for a medical consultation; 1 out of 65 has been hospitalized, and 1 out of about 293 has died. A more recent study estimates that from 2000-2004, child deaths from rotavirus rose to 600,000 or more around the world (2). In Latin America, each year an estimated 10 million children suffer from the disease, 2 million are taken for a medical consultation, 75,000 must be hospitalized, and 15,000 die (3).
What is Rotavirus
The genus rotavirus belongs to the Reoviridae family. It is a double-stranded ribonucleic acid (RNA) virus with 11 segments. Seven principal rotavirus groups have been identified, labeled A through G. However, only the A, B, and C groups infect humans, and the A group is the most important.
The viral particle consists of three concentric layers of protein around the genome (see figure below). The outside protein layer of the virus particulate consists of two superficial viral proteins: VP4 and VP7. Rotavirus classification by serotype is based on the antigenic specifications of these two proteins. Both the VP7 (type G for glycoprotein) and VP4 protein (type P for protease sensitivity) elicit the production of neutralizing antibodies and are involved with protective immunity. There are 15 G serotypes and 14 P serotypes. In the G serotypes, a precise correlation can be made between serotype and genotype. However, such a correlation is not found in the P serotype. There are 20 P genotypes [numbered 1 to 20 in brackets], for example P. The genes coding the G and P antigens are added independently, allowing various combinations of G and P to be observed.
Four strains are predominant worldwide (including Latin America): G1P, which is responsible for the majority of infections; G2P, G3P, and G4P. In addition to these four, others have been described with serotypes G5, G8, and G9. Serotype G9 is considered to be the world’s 5th-most-important serotype (1).
Who is at risk
Young children <5 years of age are at greatest risk of contracting and dying of rotavirus. Nearly every child is infected with rotavirus at least once before the age of five, with the first infection usually ocurring before age three (6)
Direct fecal-oral contact is considered the most significant rotavirus transmission mechanism. The virus is highly infectious and very stable in the environment: it can survive for hours on hands and even days on hard surfaces, and it remains stable and infectious in human stool for up to 1 week. Individuals with rotavirus excrete significant quantities of viral particles before they begin showing symptoms of the disease, throughout the course of the diarrhea and, in one-third of the cases, up to 1 week after the symptoms disappear. Many people excrete the virus without experiencing diarrhea.
Person-to-person transmission through the hands appears to be responsible for the virus spreading in closed environments, such as homes and hospitals. Transmission between children in day-care centers is caused by direct contact and through contaminated food and/or toys.
Stools generally contain 100 billion viral particles per milliliter, and the infectious dose is between 10,000 and 10 million viral particles. Although rotavirus has been identified in several species of animals, both wild and domestic, animals do not appear to play a significant role as reservoirs or in transmission to human beings.
Distribution and Seasonality
Rotavirus occurs year-round, but may have seasonal peaks. In temperate climates, incidence of rotavirus typically peaks during the winter season. In tropical settings, rotavirus occurs year round and seasonality may be masked by high background levels (1).
As a result, an infant born in a temperate country after the winter season will not be exposed to the virus until the following year, but those born in a tropical country will be exposed to the virus year round. Thus, the average age of onset of infection is younger in tropical countries, where children get sick in the first year of life, compared to the average for those dwelling in temperate countries, where two to three year olds tend to first experience infection.
Rotavirus surveillance in the Americas shows peaks in rotavirus during the cool winter months.
An initial infection induces a local and systemic immune response to the serotype responsible for the infection as well as to a high percentage of other serotypes. Thus, after an initial infection, 88% of children are protected against severe infection. After a second infection, 100% have developed immunity against severe infection, and the majority against any rotavirus disease.
In developing countries, 65%-80% of children have rotavirus antibodies by the age of 12 months, and 95% by the age of 24 months. Thus, the incidence of symptomatic illness declines rapidly after 24 months of age, and repeated infections may be asymptomatic or accompanied by mild symptoms.
In general, infants less than 3 months of age with rotavirus infections are asymptomatic, while those infected for the first time after that age generally show symptoms. The explanation for this finding is not entirely clear, but appears to be linked to the presence of maternal antibodies.
Prevention and Control
Two rotavirus vaccines are available on the market and prequalified by WHO. Since 2006, 14 countries and one territory have introduced this vaccine in their national vaccination schedule: in 2006, Brazil, El Salvador, Mexico, Panama, Nicaragua, the United States, and Venezuela; in 2007, Ecuador; in 2008, Bolivia; in 2009, Colombia, Guyana, Honduras, Peru, and the British territory of Cayman Islands. The countries of the Region of the Americas were the first to introduce this vaccine into their vaccination programs, and for the first time ever, a new vaccine is being introduced in developing and developed countries at the same time.
Regional Office for the Americas of the World Health Organization