AIRBORNE MOVEMENT OF ANTHRAX SPORES FROM CARCASS SITES IN THE ETOSHA NATIONAL-PARK, NAMIBIA

Tests for airborne movement of anthrax spores downwind from three heav ily contaminated carcass sites were carried out under a range of wind conditions. Anthrax spores were detected in just three of 43 cyclone o r gelatin filter air samples taken at distances of 6, 12 and 18 m from the sites. In addition, nine positives resulted during sampling sessi ons in which the site was mechanically disturbed, with a further five positives being found in sessions subsequent to those in which the sit e had been disturbed. The three positive samples not related to man-ma de disturbance were associated with the highest winds experienced duri ng the study. Despite colony counts exceeding 100 on the culture plate s in three instances, calculations showed that these represented very low worst case probable spore inhalation rates for animals or humans e xposed to such levels. The low number of positives, the clear pattern of rapidly declining numbers of anthrax spores with distance downwind from the centres of the sites apparent on settle plates, and the persi sting levels of contamination despite wind and rain, collectively sugg est that the anthrax spores were associated with fairly heavy particle s, although this was not seen by electron microscopy on soil samples f rom the sites. Overall, the findings are interpreted as indicating tha t it is very unlikely that Etosha animals contract anthrax by the inha lation route while simply in transit near or across a carcass site. Th e significance of the observations in relation to weather conditions i n the Etosha, other studies on particulate aerosols in the region, and reports of long-distance airborne movement of microbes, is discussed.