Viral aggregation: effects of salts on the aggregation of poliovirus and reovirus at low pH.

As a first step toward the understanding of virus particle interactions in water, we have used the modified single particle analysis test to follow the aggregation of poliovirus and reovirus as induced by low pH in suspensions containing varying amounts of dissolved salts. Salts composed of mono-, di-, and trivalent cations and mono- and divalent anions were tested for their ability to reduce or increase the aggregation of these viruses in relation to that obtained by low pH alone. Mono- and divalent cations in concentrations covering those in natural waters were generally found to cause a decrease in aggregation, with the divalent cations having a much greater effectiveness than the monovalent cations. Trivalent ions (Al3+), in micromolar concentrations, were found to cause aggregation over that at low pH alone. Anions, whether monovalent or divalent, had little ability to produce inhibition of viral aggregation, and thus the overall effects were due almost exclusively to the cation. This was true regardless of whether the overall charge on the virus particle was positive or negative, as determined by the relation between the isoelectric point and the pH at which the tests were carried out. Thus, whereas virus particles conform to classical colloid theory in many respects, there are specific exceptions which must be taken into account in the design of any experiment in which viral aggregation is a factor.