Virus in water. I. A preliminary study on a flow-through gauze sampler for recovering virus from waters.

A preliminary study was carried out on evaluating a flow-through gauze sampler for its efficiency in recovering virus from both fresh and seawater. An attenuated type 1 poliovirus was used as the working model. When tap water was sampled, the amounts of virus adsorbed by the gauze pads were very small, about 2% of the total number of virus particles flowing through the device. The virus adsorption and recovery increased to 15 to 19% when seawater was sampled. Addition of NaCl to tap water produced a much better effect on virus adsorption and recovery by this device, i.e., 47% of the total virus particles in each sample. The best viral elution from the pads was obtained by using buffer solution of pH 8.0 to 9.0 containing a small amount of animal serum. Repeated elutions from the pads were necessary to recover the most virus although the first eluate contained approximately 50% of the adsorbed virus. Further development of this device appears warranted, because of (i) the simplicity of the procedure, (ii) its capability of sampling large volume of water, (iii) the low cost of collecting samples, and (iv) the feasibility of obtaining a rough quantitative assessment of viral pollutants in water examined.

Viral depuration by assaying individual shellfish.

A study was carried out to further evaluate the practicability of viral depuration by assaying individual shellfish. The Northern quahaug and a strain of the type 1 attenuated poliovirus were used as the working model. Two types of depuration systems were employed: the small experimental tanks and a pilot-size tank with a capacity of approximately 24 bushels (836 liters) of shellfish. Volumes of the individual shellfish samples were found uniform throughout the experiments when a prior selection for the weight of the shellfish was made. There was also no significant difference in volumes of the individual samples during the course of depuration (24 to 96 hr). Under controlled hydrographic conditions, however, the uptake of virus in individual shellfish varied considerably. In general, the individual variability reached 10- to 100-fold. This wide variation would explain the variability of viral contents obtained in pooled samples during depuration as reported previously. During a later phase of depuration, although a great majority of shellfish were free of the virus, a few still harbored minimal amounts of contaminants. The presence of virus in some of the shellfish after various periods of depuration would, theoretically, be obscured by the pooling of the sampled shellfish. Further examination of the negative samples by assaying larger quantities than those routinely used revealed that a few still contained virus. To simulate naturally polluted shellfish as closely as technically possible, shellfish were polluted with minimal amounts of virus. The shellfish were cleansed more rapidly by the depuration process than were those polluted with more virus. Since the naturally polluted shellfish were shown to contain less virus than those studied in the laboratory, it is anticipated that the former type of shellfish may be cleansed more readily by this process within a reasonable period of time. Justification for a field trial of depuration in this country is presented.

Viral depuration of the Northern quahaug.

A study was conducted to evaluate critically the feasibility of using the self-cleansing mechanism as a practical means to obtain virus-free shellfish. Two systems supplied with fresh running seawater, three strains of human enterovirus and the Northern quahaug, were used as working models. Preliminary experiments in the experimental system under arbitrarily selected conditions showed that depuration of poliovirus-polluted quahaugs could be achieved by the method used for the Eastern oyster. The factors affecting viral depuration studied so far included: (i) initial concentration of shellfish pollution; (ii) temperature of seawater; and (iii) salinity of seawater. It was shown that purification of the lightly polluted shellfish was achieved sooner than of the heavily polluted ones. The efficiency of viral depuration was roughly a function of the water temperature within the range tested (5 to 20 C). Reduction of salinity to 50 to 60% of the original level stopped this process completely, but 25% reduction in salinity did not affect significantly the rate of depuration. Preliminary study in the pilot system showed that viral depuration in the large tank appeared to be equally as efficient as that in the small experimental tanks under the particular conditions.

Potency of adenovirus vaccines: comparison of unconcentrated, concentrated, and soluble antigen preparations.

Five adenoviruses were effectively concentrated and partially purified by methanol precipitation. The soluble antigens from one adenovirus concentrate were obtained by adsorption to and elution from calcium phosphate. Formaldehyde-inactivated vaccines prepared from the virus concentrates were more antigenic in guinea pigs than a National Institutes of Health reference vaccine or one prepared from unconcentrated adenovirus. The soluble antigens also proved to be antigenic. The data indicate that adenovirus vaccines of superior potency can be prepared from concentrated virus preparations and that the extracted soluble antigens are immunogenic.