Inactivation of Ascaris Suum Eggs by Exposure to Ultraviolet (UV) Irradiation

The ultraviolet (UV) irradiation dose required to prevent full development (embryonation) of unembryonated Ascaris suum eggs in buffered water was studied. UV irradiation has been used in the past on larvated (embryonated) Ascaris suum eggs in an attempt to produce an attenuated vaccine for use in pigs. Such studies used doses of irradiation aimed at decreasing the infectivity of the eggs given as inocula. However, to our knowledge, there have been no studies that have examined the dose of UV irradiation required for full inactivation of unembryonated and embryonated eggs, nor have there been any studies which have described the effects of UV light on different types of eggs (e.g. eggs from feces versus eggs from the uteri of female worms versus eggs with the cortical layer removed).In our studies, non-infectious (unembryonated) eggs were exposed to UV doses ranging from 0 mJ/cm2 to as much as 1053.63 mJ/cm2 using a collimated beam apparatus containing two low-pressure mercury vapor lamps. A comparison between “tanned” eggs (collected from the feces of naturally infected pigs), and “untanned” or “ex utero” eggs (obtained from the uteri of female worms), was conducted. A subset of each of these two groups of eggs was treated with Clorox® solutions at different concentrations (0.56% to 2.5% sodium hypochlorite), for varying times, in order to erode the cortical (albuminous), vitelline, and lipid layers of the eggshells.Decorticated (tanned and untanned) eggs treated with a 9-10% Clorox® solution for 25 or 10 min respectively, were found to be the most vulnerable to inactivation by UV irradiation. Corticated, tanned eggs, not treated with Clorox®, were the most resistant; this is the type of egg most likely to be encountered in the environment, and thus the type whose response to UV light perhaps has the most relevance to real-world situations. It should be noted that although an attempt was also made to use untanned, corticated eggs in the study, these proved to be extremely “sticky”, and we were unable to recover them from the surfaces of the Petri dishes and the culture flasks used.All Clorox®-decorticated groups (whether tanned or untanned) reached 100% inactivation, (which we defined as 0% embryonation after a period of 2 weeks at 28 °C in the presence of oxygen), after exposure to doses ≥25.1 mJ/cm2. Tanned, corticated eggs required much higher doses, ≥333.62 mJ/cm2, to reach complete inactivation. Thus, it appears that treatment of eggs with Clorox®, and perhaps the length of such treatment, leads to a reduction in the dose of UV required for full inactivation of unembryonated egg populations.Future studies are planned to determine the ability of infectious (embryonated eggs) to retain their infectivity in a mouse-model after exposure to this range (0-1096.63 mJ/cm2) of irradiation.