Toxoplasma infection at different ages, studied by the skin-test method

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Abstract
On the basis of previously published work, the skin test for toxoplasmosis has been judged to be a convenient and sufficiently reliable method for carrying out epidemiological group investigations intended to elucidate the spread of the disease. With it one can probably detect as many persons with serologically demonstrable antibodies against toxoplasma as when the same persons are examined by means of the routine dye test. An investigation employing skin testing has been carried out on 648 persons between the age of 0 and 45 years, all living in or adjacent to a town in Central Sweden. The reagent used (toxoplasmin) was prepared from toxoplasma cultures grown on embryonated hen's eggs by the State Bacteriological Laboratories, Stockholm. Amongst 379 children under the age of 15 years, only one gave a positive reaction, whereas in the higher age groups the frequency of positives rose rather rapidly to 40% in the age group 30–45 years. The results show fair agreement with those previously reported from similar investigations, with one very noticeable exception: in North Sweden skin reactions have proved positive in a bare 10% of adults studied. The significance of this observation is discussed in regard to the epidemiological characters of the disease. Having due regard to our incomplete knowledge of the subject, attention is drawn to the possibility that reservoirs of infection are extrahuman and that transfer of the disease to human beings occurs through the medium of biting insects or contaminated food.