Pcb. Turnbull et al., AIRBORNE MOVEMENT OF ANTHRAX SPORES FROM CARCASS SITES IN THE ETOSHA NATIONAL-PARK, NAMIBIA, Journal of applied microbiology, 84(4), 1998, pp. 667-676
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.