The electron microscopical and physical characteristics of small round human fecal viruses: An interim scheme for classification

Abstract

Many of the small round human fecal viruses implicated in outbreaks of nonbacterial gastroenteritis have been collected together and examined under the electron microscope. Negatively stained preparations without the addition of antibody were used so that the surface morphology of the virus particles remained clearly visible. It was apparent that several viruses, previously thought to be simply antigenic variants within the Norwalk group of viruses, show distinct morphological differences and quite clearly belong to other virus groups. By comparing the features of all the viruses examined in this study, both with each other and with standard cell culture strains of enterovirus, parvovirus, and calicivirus, it has been possible to propose an interim classification scheme, based primarily on the morphological appearance of the particles and supported by estimations of size and buoyant density.

An outbreak of food-borne gastroenteritis in two hospitals associated with a Norwalk-like virus

“…This virus was not shown to cause gastroenteritis in the original studies and no evidence was obtained in the present study to support an aetiological role. Dual infections with agents morphologically similar to SRFV and SRSV have been reported previously (Murphy et al 1979;Grohmann et al 1980;Caul & Appleton, 1982). It was notable that in the present study SRFV's were seen in a control specimen but Norwalk-like particles were never seen in controls.…”

“…Oysters (Murphy et al 1979), contaminated drinking water supply (Kaplan et al 1982) and swimming in sewage-contaminated water (Baron et al 1982) have been incriminated in the transmission of small round structured viruses (Norwalklike or SRSV) which have been shown to constitute a separate group of viruses (Caul & Appleton, 1982) from the small round featureless viruses (parvovirus-like or SRFV) recently incriminated in an outbreak associated with the consumption of cockles (Appleton & Periera, 1977). It is unusual and usually impossible to identify a specific item of food in the spread of enteric viruses (Gunn et al 1980).…”

“…This paper describes an outbreak in an orthopaedic ward that was unfortunately transferred to a geriatric ward. The agent most probably responsible was a small round structured virus (SRSV) (Caul & Appleton, 1982) morphologically resembling the Norwalk agent (Kapikian et al 1972).…”

Evidence for airborne transmission of Norwalk-like virus (NLV) in a hotel restaurant

“…They are 32 nm viruses with an amorphous surface and ragged outline and a buoyant density of 1-36-1-41 g/cm3 [2]. NLVs have the ability to cause outbreaks of gastrointestinal infection characterized by vomiting which is often sudden and projectile [3], as well as diarrhoea.…”

An epidemiological investigation of Norwalk virus infection in South Africa

“…SRSVs, including the prototype Norwalk virus (NV), are well-established causes of food and waterborne outbreaks of gastroenteritis in people of all age groups, but particularly adults and the elderly [2,3]. However, the true incidence of NV and SRSV-associated infections is unknown as many cases of viral gastroenteritis go unreported or no definitive diagnosis is made because the detection of these viruses has, until recently, been dependent on EM [3][4][5] and immune electron microscopy (IEM) [6][7][8]. The diagnosis of these infections has been further hampered by the inability to grow SRSVs in vitro [9].…”