CHAPTER 62 - Calicivirus Infections

Until the early 1970s, the cause of most gastroenteritis was unknown. Cases were attributed to the known infectious agents, mainly bacteria, and many other causes, including teething, weaning, diet, old age, drugs, and malnutrition. In 1972, immune electron microscopy of fecal specimens derived from an outbreak at a school in Norwalk, Ohio, USA, resulted in the identification of Norwalk virus, the first time a viral agent was shown to cause gastroenteritis. Subsequently, electron microscopy of stools of young children in the United Kingdom and Japan identified viruses morphologically similar to animal caliciviruses. Intensive investigation over the next three decades led to the identification of several viral agents of gastroenteritis and the development of new assays to identify the viral etiology of sporadic episodes and epidemics of gastroenteritis. In 1990, the Norwalk virus genome was cloned and, with the development of reverse transcription–polymerase chain reaction (RT-PCR), many genetically related but antigenically diverse viruses were identified and placed into groups called the “Norwalk-like viruses” and “Sapporo-like viruses.” In 2001, these groups were given the genus names of Norovirus and Sapovirus, respectively. With the identification of new viral agents of gastroenteritis, it has become clear that viruses cause a significant proportion of the enteric illnesses that did not earlier have a defined etiology. Improvements in sanitation and hygiene and better standards of living resulted in a decrease in the proportion of diarrheal disease attributed to bacteria, and an increase in the proportion of cases associated with viral infections. Human caliciviruses are now acknowledged as one of the most frequent causes of gastroenteritis in developed countries and are being increasingly recognized in developing countries and/or tropical regions.