Infectious diarrhea is a leading cause of disease and death worldwide. During a 1-year period in Asia, Africa, and Latin America, it was estimated that 3 to 5 billion episodes of infectious diarrhea accounted for 5 to 10 million deaths. Rotaviruses; adenoviruses; small, round viruses (eg, Norwalk agent); caliciviruses; coronaviruses; and astroviruses are responsible for acute viral gastroenteritis. Rotaviruses, adenoviruses, and small, round viruses account for the majority of viral gastroenteritis in childhood.
Epidemiology
Since their initial identification as a cause of human disease in 1973, rotaviruses have been found to be the most important cause of acute gastroenteritis in infants and young children in all countries. Studies in the United States, England, Australia, Japan, and Bangladesh found that 34 to 63% of children hospitalized with acute diarrhea were infected with rotaviruses. Rotavirus causes 3 to 4 million cases of diarrhea, 500,000 outpatient visits, 50,000 hospitalizations, and approximately 40 deaths per year in the United States. Rotavirus-induced gastroenteritis primarily affects children 6 to 24 months of age, and most initial infections are symptomatic. The peak prevalence of the disease occurs between November and April in temperate climates, and year-round in tropical climates; infections are usually sporadic and occasionally epidemic. Rotaviruses are transmitted from person-to-person by the fecal-oral route, with an incubation period of 1 to 3 days.
Epidemiology
Since their initial identification as a cause of human disease in 1973, rotaviruses have been found to be the most important cause of acute gastroenteritis in infants and young children in all countries. Studies in the United States, England, Australia, Japan, and Bangladesh found that 34 to 63% of children hospitalized with acute diarrhea were infected with rotaviruses. Rotavirus causes 3 to 4 million cases of diarrhea, 500,000 outpatient visits, 50,000 hospitalizations, and approximately 40 deaths per year in the United States. Rotavirus-induced gastroenteritis primarily affects children 6 to 24 months of age, and most initial infections are symptomatic. The peak prevalence of the disease occurs between November and April in temperate climates, and year-round in tropical climates; infections are usually sporadic and occasionally epidemic. Rotaviruses are transmitted from person-to-person by the fecal-oral route, with an incubation period of 1 to 3 days.
Adenoviruses are probably the second most important cause of acute gastroenteritis in childhood. Disease is associated primarily with adenovirus types 40 and 41. . Similar to rotaviruses, enteric adenoviruses primarily infect children younger than 2 years of age, but unlike rotaviruses, adenovirus infections occur year-round. Although outbreaks in hospital nurseries have occurred, these viruses appear to be endemic rather than epidemic. Enteric adenoviruses have an incubation period of 3 to 10 days, which is longer than that for infection with either rotaviruses or small, round viruses.
In 1968, an outbreak of illness characterized by vomiting and fever occurred in a group of elementary school children in Norwalk, Ohio. Virus particles, 27 nm in diameter, were subsequently isolated from this outbreak by electron microscopy. Norwalk agent was the forerunner of a group of morphologically similar noncultivable agents named for the geographic location where they were found to cause disease (eg, Montgomery County agent, Hawaii agent). The morphologic similarity of a number of smaller viruses associated with gastroenteritis (including parvoviruses) led to the description of these agents as small, round viruses. Unlike rotaviruses and adenoviruses, infections with small, round viruses are usually epidemic and responsible for family and community-wide outbreaks of gastroenteritis in school-aged children, family contacts, and adults. Small, round viruses are transmitted by the fecal-oral route, with an incubation period of 1 to 2 days.
Clinical Manifestations
Rotavirus infection is characterized by diarrhea, fever, and vomiting. Occasionally, congestion and coryza precede the onset of intestinal symptoms. Stools are watery and rarely contain blood, mucus, or white blood cells. Diarrhea is often associated with increased losses of sodium and chloride in the stools, isotonic dehydration, and a compensated metabolic acidosis. Vomiting often lasts 2 to 3 days and diarrhea 5 to 8 days. An encephalopathic picture occurs rarely. Subsequent rotavirus infections are progressively less likely to induce moderate-to-severe symptoms.
In 1968, an outbreak of illness characterized by vomiting and fever occurred in a group of elementary school children in Norwalk, Ohio. Virus particles, 27 nm in diameter, were subsequently isolated from this outbreak by electron microscopy. Norwalk agent was the forerunner of a group of morphologically similar noncultivable agents named for the geographic location where they were found to cause disease (eg, Montgomery County agent, Hawaii agent). The morphologic similarity of a number of smaller viruses associated with gastroenteritis (including parvoviruses) led to the description of these agents as small, round viruses. Unlike rotaviruses and adenoviruses, infections with small, round viruses are usually epidemic and responsible for family and community-wide outbreaks of gastroenteritis in school-aged children, family contacts, and adults. Small, round viruses are transmitted by the fecal-oral route, with an incubation period of 1 to 2 days.
Clinical Manifestations
Rotavirus infection is characterized by diarrhea, fever, and vomiting. Occasionally, congestion and coryza precede the onset of intestinal symptoms. Stools are watery and rarely contain blood, mucus, or white blood cells. Diarrhea is often associated with increased losses of sodium and chloride in the stools, isotonic dehydration, and a compensated metabolic acidosis. Vomiting often lasts 2 to 3 days and diarrhea 5 to 8 days. An encephalopathic picture occurs rarely. Subsequent rotavirus infections are progressively less likely to induce moderate-to-severe symptoms.
Infection with enteric adenoviruses is characterized by fever, diarrhea, and occasionally vomiting. Although initial symptoms of adenovirus infection in young children are generally milder than rotavirus infections, diarrhea may be prolonged, with an average duration of approximately 9 days. Similar to rotaviruses, adenoviruses may present with upper respiratory tract symptoms.
Symptoms associated with small, round virus infection are usually explosive in onset and, unlike rotaviruses and adenoviruses, last only 24 to 48 hours. Signs and symptoms include vomiting, diarrhea, abdominal cramps, nausea, headache, low-grade fever, myalgia, anorexia, and malaise.
Diagnosis and Treatment
Although rotaviruses, enteric adenoviruses, and small, round viruses may be detected directly in stools by electron microscopy or polyacrylamide gel electrophoresis, these procedures are not readily available in most hospitals. Fortunately, rapid diagnosis of rotaviruses and adenoviruses by solid-phase immunoassays of stool are commercially available, relatively inexpensive, and quite sensitive and specific when compared with electron microscopy. Commercial assays for the rapid detection of small, round viruses are not currently available.
Prevention
A rotavirus vaccine was licensed by the Food and Drug Administration on August 31, 1998, and recommended for use in all infants as a series of three doses given by mouth at 2, 4, and 6 months of age. On October 22, 1999, the Centers for Disease Control and Prevention provided evidence that the rotavirus vaccine was associated with intussusception. Infants inoculated with rotavirus vaccine were about 60% more likely to develop intussusception than infants not inoculated with rotavirus vaccine. For this reason, the rotavirus vaccine was withdrawn for use. Because intussusception in not clearly a consequence of natural rotavirus infection, the pathogenesis of intussusception following immunization remains unclear.
Alternative vaccine strategies include bovine × human reassortant rotaviruses and live, attenuated human rotaviruses. Both of these strategies are effective in preventing moderate-to-severe rotavirus infections in infants. However, large safety trials are required to demonstrate that these vaccine candidates are not also associated with intussusception.
Symptoms associated with small, round virus infection are usually explosive in onset and, unlike rotaviruses and adenoviruses, last only 24 to 48 hours. Signs and symptoms include vomiting, diarrhea, abdominal cramps, nausea, headache, low-grade fever, myalgia, anorexia, and malaise.
Diagnosis and Treatment
Although rotaviruses, enteric adenoviruses, and small, round viruses may be detected directly in stools by electron microscopy or polyacrylamide gel electrophoresis, these procedures are not readily available in most hospitals. Fortunately, rapid diagnosis of rotaviruses and adenoviruses by solid-phase immunoassays of stool are commercially available, relatively inexpensive, and quite sensitive and specific when compared with electron microscopy. Commercial assays for the rapid detection of small, round viruses are not currently available.
Prevention
A rotavirus vaccine was licensed by the Food and Drug Administration on August 31, 1998, and recommended for use in all infants as a series of three doses given by mouth at 2, 4, and 6 months of age. On October 22, 1999, the Centers for Disease Control and Prevention provided evidence that the rotavirus vaccine was associated with intussusception. Infants inoculated with rotavirus vaccine were about 60% more likely to develop intussusception than infants not inoculated with rotavirus vaccine. For this reason, the rotavirus vaccine was withdrawn for use. Because intussusception in not clearly a consequence of natural rotavirus infection, the pathogenesis of intussusception following immunization remains unclear.
Alternative vaccine strategies include bovine × human reassortant rotaviruses and live, attenuated human rotaviruses. Both of these strategies are effective in preventing moderate-to-severe rotavirus infections in infants. However, large safety trials are required to demonstrate that these vaccine candidates are not also associated with intussusception.
No comments:
Post a Comment