Of the identified or hypothetical viruses that occur in the feces, the agent or group of agents that induce so-called afebrile infectious nonbacterial gastroenteritis are the only ones known to cause watery diarrhea as a cardinal sign of illness. The rest of the clinical picture of this nonamebic nonbacillary diarrheal disease consists of anorexia, nausea, vomiting, and abdominal cramps, with little or no fever. It is a common syndrome of wide geographic distribution and is highly communicable, appearing in large epidemics as well as sporadically. While the disease is ordinarily self-limited, it can be incapacitating and is of importance because of its frequency.
Some epidemics of anorexia, nausea, and vomiting without diarrhea otherwise resemble outbreaks of afebrile nonbacterial gastroenteritis. Whether the respective causative agents are related is unknown. No recognized pathogen has been isolated from patients exhibiting either syndrome. Afebrile nonbacterial gastroenteritis with diarrhea can be transferred serially from one group of volunteers to another by feeding fecal ultrafiltrates. This is the chief evidence that one or more viruses may be the incitants.
Reinoculation experiments in volunteers indicate that following an attack of afebrile nonbacterial gastroenteritis specific active immunity develops, and that it may last for a year or longer. Since cases recur at yearly intervals in families and communities, it is necessary to postulate that there may be more than one antigenic type. The afebrile disease can be differentiated from a febrile, non-diarrheal entity by their different incubation periods, different clinical manifestations, and lack of cross-immunity.
The results of the first human volunteer experiments, reported by Reimann and his colleagues, indicated that a filterable agent could induce diarrheal disease when it was administered via the respiratory route. Some epidemiologic observations are consistent with these findings but several subsequent attempts to confirm experimental respiratory transmission in volunteers have failed. Respiratory symptoms and signs are conspicuously absent in experimentally induced attacks of afebrile nonbacterial gastroenteritis. At present the possibility that their occurrence in epidemic cases is adventitious must be strongly considered.
Further characterization of the nonamebic, nonbacillary diarrheal diseases awaits comparative studies of the agents now known and the detection of new ones. This will be difficult until practicable methods of laboratory propagation and immunologic identification are discovered.
Some of the experiments carried out by the author and his colleagues were conducted under the sponsorship of the Commission on Liver Disease, Armed Forces Epidemiological Board, and were supported in part by the Office of The Surgeon General, Department of the Army.