A Report on the Zoonotic Potential of Rotaviruses

Rotaviruses are the major cause of viral gastroenteritis in young children, and contribute significantly to morbidity and mortality worldwide. In the UK they seldom cause fatalities, but there are several thousand cases of infection reported each year. <P>
Rotaviruses are also common animal pathogens. There is increasing evidence that strains of animal rotaviruses can infect humans. However, the potential for zoonotic transmission of rotaviruses has not been fully defined. The work comprised a comprehensive review of current information on the extent and significance of zoonotic transmission of rotaviruses. The information was compiled from the body of scientific literature, supplemented with details of relevant gene and protein sequences held on databases, and complemented by expert opinion from leading UK and international rotavirologists, sources of veterinary experience, and sources within the farming industry. The Report is intended to provide an accessible overview of the areas pertinent to the issue of zoonotic rotaviruses, highlighting areas of significance and identifying knowledge gaps. A summary of the report follows:
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Rotaviruses have a triple-layered protein coat enclosing 11 segments of double stranded RNA. They are classified into groups, of which group A are most common in humans and are also found in animals. A dual typing classification system has been established for group A rotaviruses, defining at least 14 G and 20 P types, which are defined by variations in two coat protein genes.
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The diversity of rotavirus strains, along with the segmented genome, suggests that like other viruses such as influenza virus, rotaviruses can undergo recombination by a mechanism of reassortment. This can occur when two rotaviruses of different strains infect the same cell, and during replication and packaging they exchange genome segments. One of the underlying causes of rotavirus diversity may be reassortment between human and animal strains upon coinfection.
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In humans, the most common group A rotaviruses are of genotype G1P[8], G2P4], G3P8],and G4P[8]. There are several other genotypes which are less common. Rotavirus G9 strains are emerging globally. Group B and C rotaviruses also infect humans. Rotaviruses also infect a variety of animals, including domestic ones such as cats, dogs, cattle, horses, pigs, and sheep.
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Epidemiological studies have shown that there are several rotavirus types which are shared in common by humans and animals. Generally, rotaviruses are species-specific, but cross species transmission is possible. It has been demonstrated experimentally that rotaviruses which have been isolated from one species of animal, or humans, can infect another animal species. Several case studies have indicated infection of humans by animal rotaviruses. Comparison of genetic sequences of human and animal rotaviruses often reveals close identity.
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Surveillance of circulating rotaviruses in the human population of the UK has revealed the presence of several uncommon genotypes, such as G1P[9], G8P[8], and G9P[8]. Many of these virus types can be found in domestic animals. It is possible that they arose in the human population through zoonotic transmission or gene transfer by reassortment. The low incidence of uncommon strains in the UK however would suggest that such transmission, or at least the establishment of an animal rotavirus or a human / animal reassortant virus in the human population does not happen with any great frequency.
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However, in the UK population, many thousands of people are exposed year on year to animal rotaviruses. This happens within the farming community, and potentially to visitors to the countryside. There may be some measure of environmental contamination, through livestock excrement. Also there is a high level of pet ownership in the UK. This exposure may not result in high levels of infection, but some infection could occur. There may be a continual, albeit very low level, of input of rotavirus strains or sequences into the human population from the animal population.
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There are several areas in which information is lacking, which would allow a more precise recognition of any risk posed by zoonotic transmission of rotaviruses. The most significant is that there is currently no knowledge of the strains which are circulating in animals with close contact with humans, e.g. livestock and pets. Among other recommendations, it is proposed that a complementary surveillance system, with genotyping of all isolates, be established to determine the distribution of rotavirus types in humans and animals in the UK.

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