Blood sera from 100 persons from a plantation near Escuintla, Guatemala (elevation about 1,000 feet above sea level) were tested for Toxoplasma antibodies by the Sabin-Feldman dye test. Males and females, ages 16 to 70, were included. All sera from persons above 25 years of age gave positive reactions. The overall prevalence was 94.0 per cent.
A group of 30 Guatemalan military recruits was likewise tested. These were males, ages 15 to 26 years, from various localities in Guatemala but chiefly from the central highlands (elevation 5,000 feet or higher). The overall prevalence of positive tests was 50.0 per cent.
Similar tests were done on 156 sera collected at Turrialba, Costa Rica (1,800 feet elevation). Donors were males and females, ages 20 to 70 years. The overall prevalence of positive sera was 88.5 per cent.
Comparison of males, 15 to 29 years of age, from the three test groups indicated a tendency for lower titers to be produced at higher altitudes. The possibility is discussed that transmission may be more frequent in warm climates than in cold. The present data seem to fit such an hypothesis, since sera from the Guatemalan and Costa Rican lowlands showed much higher prevalences of positive sera and higher titers than did the sera from the Guatemalan military recruits, who came chiefly from higher elevations. However, sufficient data are not yet available to test this relationship adequately.
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