These are RNA viruses that predominately affect infants and young children, causing gastroenteritis and sometimes necrotizing enterocolitis. Diarrhea is usually present. Diagnosis is by electron microscopy of stool specimens. Some homemade EIA serologic tests have been described. This virus appears at present to be found in only a relatively small proportion of gastroenteritis patients.
Tag: Viral Infections
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Calciviruses (Non-Norwalk)
These RNA viruses cause gastroenteritis primarily in infants and young children, similar clinically to rotavirus infection; sometimes as severe as rotavirus but often somewhat milder. Cluster outbreaks in institutions and sporadic occurences have been reported. One report indicated that calciviruses cause 3% of gastroenteritis in U.S. day-care centers. Some cluster infections in adults from contaminated food or water have been reported. Diagnosis can be made through EM of stool. Some homemade EIA methods have been described. High antibody positivity rates (90%-100%) have been found by late childhood or early adulthood.
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Astroviruses
These RNA viruses are said to cause about 5% of infant gastroenteritis (range, 2%-9%). Symptoms are various combinations of vomiting and diarrhea, lasting 0.5-4.0 days. They originally were identified by EM of stool specimens. Culture is also possible using special procedures. EIA test methods using homemade reagents have been described.
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Norwalk Viruses
These are small round RNA viruses. There are some similarities to calciviruses. Infection predominately involves adults, adolescents, and older children. About 55%-75% of adults have antibodies against this virus. Third-world countries have a higher incidence of antibody. Epidemiologically, disease in the United States usually occurs in clusters (outbreaks); reviews found 34%-47% of such gastroenteritis outbreaks (cruise ships, schools, camps) were due to Norwalk viruses. Clinical disease is usually relatively mild and self-limited. Incubation appears to be about 24 hours (range, 10-50 hours). Nausea and vomiting are usually more prominent than diarrhea. The acute phase usually ends in 24-48 hours and most patients do not require hospitalization. The virus appears to affect the jejunum. Diagnosis has been difficult; until recently, stool EM was required. However, EM apparently has sensitivity of only 34%-48%. Even nucleic acid probes with PCR amplification appear to detect less than 85% of cases (using homemade reagents). Enzyme immunoassay methods using monoclonal antibody against Norwalk antigen in stool have also been reported using homemade reagents; these have generally detected less than 50% of cases. The organism has not been cultured to date.
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Enteric Fastidious Adenoviruses
These DNA viruses (unlike other adenoviruses) could not be cultured using standard virus culture systems. The most frequent are types 40 and 41. These enteric adenovirus species are the second most common cause of severe gastroenteritis in young children (after rotavirus), comprising about 10%-15% of cases (range, 5%-52%). It has also been the second or third most common overall cause of infant gastroenteritis. Diarrhea is the predominant symptom. Vomiting may be present but is less prominent than that seen in rotavirus infection. The gold standard for diagnosis has been EM of stool specimens. However, EM cannot differentiate between fastidious and other adenovirus species. Culture can be done in some cases using nonroutine tissue culture cells. Several EIA tests for virus antigen in stool have been described and one commercial kit for types 40 and 41 is now available. Nucleic acid probes have also been used experimentally.
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Rotavirus
These DNA viruses (unlike other adenoviruses) could not be cultured using standard virus culture systems. The most frequent are types 40 and 41. These enteric adenovirus species are the second most common cause of severe gastroenteritis in young children (after rotavirus), comprising about 10%-15% of cases (range, 5%-52%). It has also been the second or third most common overall cause of infant gastroenteritis. Diarrhea is the predominant symptom. Vomiting may be present but is less prominent than that seen in rotavirus infection. The gold standard for diagnosis has been EM of stool specimens. However, EM cannot differentiate between fastidious and other adenovirus species. Culture can be done in some cases using nonroutine tissue culture cells. Several EIA tests for virus antigen in stool have been described and one commercial kit for types 40 and 41 is now available. Nucleic acid probes have also been used experimentally.
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Viruses Predominately Associated with Gastroenteritis
Rotavirus is an RNA virus in the Reoviridae family. It infects many types of mammals and birds as well as humans. Rotavirus is the most frequent cause of infectious diarrhea of infants and young children. Symptoms include diarrhea (65%-100% of cases), fever, and vomiting (48%-92% of cases). Vomiting may precede diarrhea (usually by less than 24 hours) in 34%-55% of patients. Peak infection rates in the United States are in winter months but are equally distributed in tropical areas. Rotavirus has been reported to cause 36%-50% of gastroenteritis severe enough to need hospitalization in nontropical countries. Rotavirus can be identified in the stool of considerable numbers of hospitalized children without diarrhea and some clinically healthy young children, especially in day-care centers or nurseries (about 10%-20%; literature range, 2%-71%). Adults may also become infected (especially those in contact with infected infants or children, 20%-36% in several studies); the majority are asymptomatic, but some develop diarrhea. Diarrhea tends to be more common and severe in the elderly. Some patients with symptomatic rotavirus infection also have respiratory symptoms, either before or concurrent with diarrhea (although this was not present in some studies).
Rotavirus has not yet been cultured. The gold standard for diagnosis is electron microscopy (EM) of stool specimens. Same-day diagnosis can be obtained from stool specimens using ELISA or LA antigen-detection methods. Sensitivity of the various kits available is about 90% (range, 61%-100%), compared to EM. There is a significant difference in sensitivity between some of the kits.
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Arthropod-Borne Viruses (Arboviruses)
As the name suggests, these are viruses transmitted to humans by arthropods (mostly by mosquitos, but some by ticks). There are three groups of diseases: CNS infections (e.g., encephalitis and aseptic meningitis); hemorrhagic fever (e.g., yellow fever and dengue); and nonspecific fever (e.g., dengue and Colorado tick fever). Of encephalitis cases, the most common agent is St. Louis encephalitis, a flavivirus spread by Culex mosquitos. Only about 1% of humans infected develop clinical symptoms. Of these, about 75% have encephalitis. The next most common viral infection is the California bunyavirus group, most often the LaCrosse virus. This is transmitted by an Aedes mosquito. Less common are Western and Eastern equine encephalitis virus disease. Diagnosis can be made by CSF culture or by acute and convalescent serum antibody titers.
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Creutzfeldt-Jacob (C-J) Disease
This disease is also known as spongiform encephalopathy (describing the typical microscopic changes in affected brain tissue). It is transmitted by a protein agent known as a prion (proteinaceous infectious agent) that resembles one of the genes in structure. About 90% of cases are sporadic and 5%-15% are hereditary with autosomal dominant transmission. In the hereditary form a gene with point mutation appears to be the cause. The sporadic cases do not show a detectable gene mutation and the mechanism of disease is not known. A similar disease in sheep is called scrapie. Another similar disease in New Guinea tribesmen was known as kuru. In C-J disease, most patients develop symptoms at age 40-60 years (so-called presenile dementia). Symptoms resemble those of Alzheimer’s disease to some degree, but the disease progresses much more rapidly and 90%-95% of patients die within one year. Besides mental changes there is ataxia and myoclonal muscle contractions. The major brain area affected is the cerebral cortex frontal lobe; occasionally patients have occipital lobe or cerebellar involvement. There is neuron death with vacuolization of their cytoplasm accompanied by proliferation of astrocytes and fibrosis but no inflammatory cell response. CSF usually does not show any abnormalities. Diagnosis is made by brain biopsy.
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Jc Virus Infection
The JC virus belongs to the polyoma virus group of the papovavirus family, which are double-stranded DNA viruses without an envelope. BK virus is also in the polyoma virus group. It appears that infection by both viruses occurs during childhood or adolescence, with about 50% of the population demonstrating antibody before adulthood, rising later to 80%-90%. The JC virus localizes to and remains latent in the kidney, from whence it occasionally may reactivate. If a patient becomes immunosuppressed, especially during AIDS, reactivated JC virus can infect lymphocytes, be carried to the brain, infect oligodendroglia glial cells, and produce a demyelinating disease called progressive multifocal leukoencephalopathy. This occurs in about 4% of patients with AIDS. Diagnosis is made through biopsy using immunologic stains containing antibody against polyomavirus. One report applied a homemade nucleic acid probe with PCR amplification to urine of JC virus patients and obtained an excellent detection rate.