Can Alcoholic Beverages Provide Protection Against Trichinosis?*

The parenteral (muscle) larvae of Trichinella spiralis were found much more susceptible than previously reported to the deleterious effect of ethanol in vitro. Larvae were reversibly paralyzed when immersed for 6 hours in water containing 6% ethanol; at concentrations of 12-25%, the paralysis was irreversible. When trichinous meat was digested in artificial gastric juice containing 6-12% ethanol, there was only slight impairment of the release of larvae from capsules; but subsequent inoculation of the freed larvae into mice revealed very marked suppression of infectivity. Experiments in rats and pigs (using free larvae as well as infected flesh) indicated that the prophylactic effect of ethanol or commerical whiskey is dependent more on the concentration of ethanol administered than on the dosage of ethanol as a function of body weight. Rats were fully protected from infection by a single dose of 2.5 ml 30% ethanol; but they were only partially protected when the same total dosage was administered as single or multiple doses of 15% ethanol. Because of the critical importance of a high ethanol concentration, and the necessity of imbibing the ethanol at or about the time of ingestion of infective meat, alcoholic beverages are unlikely to play a practical role in the prevention of trichinosis. Where prevention is achieved experimentally, or under unusual practical circumstances, the effect can be attributed both to an impaired release of larvae from flesh and to a direct deleterious effect on the larvae. The alleged benefit of alcohol in providing protection against trichinosis is almost exactly as old as our knowledge of trichinosis as a clinical disease. One evening, just over a hundred years ago, a man drank large amounts of whiskey for several days after dining on pork. He had been dining with his wife and mother-in-law; and while this may or may not have had a bearing on his intake of whiskey, it is of significance in the light of subsequent events. The man got trichinosis and lived, while his abstemious companions got trichinosis and died. Soon there were other similar stories, and before long alcohol was being recommended by some as a safeguard against trichinosis (Gould, 1945). There were contrary opinions, of course, but it wasn't until the late 1930's that the possible prophylactic efficacy of ethanol was subjected to experimental study. On the basis of experiments in vitro and in rats, McNaught and Pierce, of Stanford University, concluded that "a concentration of 25% alcohol has little direct action on trichinella in vitro" and that protective action observed in rats "was due to alcoholic interference with the digestive liber* A talk given at a meeting of the New York Society of Tropical Medicine, November 1973. ation of encysted trichinella" (Pierce and McNaught, 1937; McNaught and Pierce, 1939). Their views have become entrenched in reviews and textbooks and have been so generally accepted that practically nobody now believes that ethanol has a specific prophylactic effect in trichinosis. The question was reopened by a past-President of this Society—Dr. Benjamin H. Kean. Several years ago Dr. Kean and Dr. D. W. Hoskins presented to the Society at least suggestive evidence of an inverse relationship between the number of cocktails consumed at a party and the severity of the trichinosis that resulted from the consumption of pork hors d'oeuvres at that party. In view of this report, we decided to try to confirm the work of McNaught and Pierce. We were astonished to find that we disagreed completely with the finding that Trichinella larvae were unaffected in vitro by the concentrations of ethanol that were used. Closer inspection of the Stanford date revealed that our observations were in agreement —but our conclusions were radically different. For example, Pierce and McNaught (loc. cit.) reported that there were "no changes" in larvae that were immersed for 6 hours in concentraCopyright © 2011, The Helminthological Society of Washington OF WASHINGTON, VOLUME 44, NUMBER 2, JULY 1977 121 Table 1. Effect of ethanol on number and condition of larvae recovered by digestion of infected muscle in 1% pepsin with 1% hydrochloric acid. In Part A the duration of digestion was 18 hr; in Parts B-D it was 2-2.5 hr. Ratio of fluid to tissue in parentheses. N.D. — not done. % % Ethanol Larvae/ Encapsuin digest g lated