A study of the kinetics and mechanism of inactivation of a DNA- containing enteric virus by chlorine

TR Number



Journal Title

Journal ISSN

Volume Title


Virginia Polytechnic Institute and State University


A newly discovered enteric virus has recently been associated with large outbreaks of waterborne gastroenteritis. Most commonly referred to as the Norwalk agent, this virus appears to be morphologically and biophysically similar ·to the parvoviruses. Presently there is very little known about the fate of parvoviruses in environmental systems.

In this study the parvovirus H-1, a putative human virus containing single-stranded DNA (ssDNA), was used as a model virus for chlorine inactivation experiments. The purpose of this research was two-fold: first, to investigate the kinetics of inactivation of parvovirus H-1 by low levels of free chlorine (0.05 - 0.20 mg L⁻¹) at pH 7 and at 5, 10, 20, and 30°C; and secondly, to determine the mechanism by which chlorine inactivates this virus.

Inactivation occurred in the usual dose-response relationship, that is, increasing the chlorine dose caused an increase in the rate of inactivation. The results indicated that perhaps more than one reaction mechanism was responsible for inactivation, and the reaction mechanism was a function of temperature. The energy required for the inactivation reaction using 0.05 mg L⁻¹ free chlorine from 5 to 30°C was graphically determined to be 2.4 Kcal mole⁻¹. The change in entropy was calculated to be -52.34 entropy units.

From the mechanism study it was concluded that the initial action of chlorine on parvovirus H-1 was on the capsid. Alterations in the two major capsid proteins caused the virion to rupture, and, as evidenced by electron microscopy the ssDNA was exposed. Also, the adsorption ability of the chlorine-treated virions to host cells was significantly inhibited. This was presumably due to the effect on the spatial arrangement of the capsid proteins in their entirety rather than a loss of, or change, in only one polypeptide. The sedimentation rate of the chlorine-treated whole virus decreased from 116S to 43S. The chlorine caused certain sites on the capsid proteins to become highly reactive which facilitated the formation of higher molecular weight aggregates as detected by fluorographs of electrophoretic protein patterns in polyacrylamide gels. Most significant was the discovery that the ssDNA remained undamaged and was still capable of in vitro replication even after 60 minutes of exposure to 5 mg L⁻¹ of sodium hypochlorite at pH 7.