369 TRANSACTIONS OF THE ROYAL SOCIETY OF TROPICAL MEDICINE AND HYGIENE, VOL. 72, No. 4,1978 Serological survey of toxoplasmosis in the northern part of Iran, using indirect fluorescent antibody technique M. GHORBANI, GH. H. EDRISSIAN AND N. ASSAD Department of Medical Parasitology and Mycology, School of Public Health and Institute of Public Health Research, University of Teheran, P.O. Box 1310, Teheran, Iran Summary A total of 1,779 persons from the Caspian Sea area, Iran, were serologically examined by the indirect fluorescent antibody technique for Toxo- plasma antibodies. 55 -7 % were positive with titres of 1:20 or higher. No significant difference was demonstrated between the sexes, The highest antibody level as well as a high geometric mean of reciprocal titres were observed in the population between the ages of two and 19 years. Introduction Infection with Toxoplasma gondii occurs almost throughout the world, but its prevalence varies in different places. Human toxoplasmosis in Iran has been reported by ANSARI & MINOU (1948), GHORBANI & SAMII (1973) and GHORBANI et al. (1977). For an epidemiological survey of toxoplasmosis, serological tests are usually used. Of the serological methods available, the indirect fluorescent antibody (IFA) technique, which has good agreement in snecificitv and sensitivity with the Sabin-Feldman dye test,-is the most practical (FULTON & VOLLER, 1964: FLETCHER. 1965: WALTON et al.. 1966: STA&O & THIE&N, i973). ’ 2 The present paper reports the distribution of Toxoplasma antibodies in man, as measured by the IFA technique, in the Caspian Sea area, North Iran, in 1975. Materials and Methods Study Area This survey was carried out in two provinces of Iran, Mazandaran and Gilan, which are located on the south coast of the Casnian Sea. The temoerature in these provinces usually varies between* 20 and 35°C in summer and rarely drops to zero in winter, The annual rainfall is about 800 to 1200 mm and the relative humidity varies between 70 and 100% (MOTABAR, 1977). Four villages were selected for study: Ali-Abad (population 708) and Vozramahallah (nonulation &606j in Mazandaran province and‘- Miandeh (oonulation 597) and Doran (oooulation 517) in Gil& province.’ The villages &e-in a plaint area, almost covered with trees and other vegetation, located between the Alborz mountains and the Caspian Sea,and all have similar climatic conditions. The life style of the inhabitants of the villages is also similar, with rather poor sanitation. The source of their animal protein, which is inadequate, is beef, mutton, goat meat and occasionally chicken and fish. Drinking water is usually provided from wells and, rarely, streams. Cattle, sheep and domestic fowl are kept by most families. Domestic and stray cats are present in all villages. Most of the residents are farmers, especially occupied in rice fields. Almost all children play and live close to soil around the houses. Blood Sampling Blood samples were collected from finger pricks in heparinized micro-haematocrit capillary tubes from as many people as possible (about 75 % of the total population). Preparation and maintenance of the plasma samples were carried out in the Babol and Rasht Field Research Stations of the Institute of Public Health Research, according to the procedure used by EDRISSIAN 81 AFSHAR (1974). Altogether a total number of 1,779 plasma samples were collected and transferred to the central laboratory of the School of Public Health, Teheran, and stored at -70°C. Serological Examination The antigen was prepared according to the method of GOLDMAN (1957) from peritoneal exudate of mice infected three days previously with the RH strain of T. gondii; the antigen slides (12 uniform thick smears) were prepared-according to the method described bv VOLLER & O’NEILL (1971). The procedure yielded uniform smears with approximately 100 to 150 toxoplasms per high power field. The IFA test was also done following the technique of VOLLER & O’NEILL (1971). ‘Wellcome’ anti-human serum conjugate was used at a dilution of 1:20 in phosphate-buffered saline with 0.1% Evans Blue. Each olasma samole was first examined at dilutions of 1:20 and 1: 160; if the latter dilution gave a positive result, further two-fold dilutions were made in order to determine the end-point. The films were examined under a Leitz (Dialux) fluorescence microscope, equipped with a Phillips CS 200 W-4 mercury lamp, and a combination of exciter filters BG,, and BG, and 570 rnp barrier filter. Results The distribution of IFA antibodies to T. gondii in the 1,779 plasma samples collected from the inhabitants of the four villages in the Caspian Sea area are shown in Table I. Blood samples from children under four months could not be collected. The only positive case in the four to 11-month age group, with a low titre, could be due to acquired