ABSTRACT
Environmental parameters are often important determinants of health, particularly with respect to infectious diseases. For example, temperature can be crucial in some instances: the minimum survival temperature for anopheline mosquitoes, the vectors of malaria, is between 8 and 10 degrees Celsius, while the actual plasmodium malaria pathogens have minimum temperature threshold limits for development of around 18 degrees Celsius in the case of P. falciparum and 15 degrees Celsius for P. vivax. Humidity is also an important factor, as mosquitoes generally cannot survive long enough for malaria transmission to occur if average monthly relative humidity falls below 60 per cent. Dengue fever, the other leading mosquitovectored scourge, in turn has minimum temperature thresholds of 6-10 degrees Celsius for the Aedes carriers and approximately 12 degrees Celsius for the pathogen, and hence a wider geographic range. Non-arthropod vector-borne infectious diseases likewise have thresholds. The Cercariae larval parasites involved in schistosomiasis, for instance, on being released by the disease’s freshwater snail vector, have a minimum temperature threshold of approximately 14 degrees Celsius for disease transmission (McMichael et al., 2001).
