MALARIA INFECTION-RATE OF AMAZONIAN PRIMATES INCREASES WITH BODY-WEIGHT AND GROUP-SIZE

The quantitative relationship between the emission rate of host attractants (whether olfactory or visual) and the host-seeking rate of insect vectors of disease will determine the relationship between host group size and the prevalence of vector-borne diseases within each group. A comparative study was carried out to test whether interspecific differences in social behaviour significantly influence the malaria infection rates of different Amazonian primate species. The aetiological agent of monkey malaria in Amazonia is Plasmodium brasilianum Gonder & Berenberg-Gossler, 1908, and blood smear examinations of 3599 Amazonian primates over three decades have demonstrated an average infection rate with P. brasilianum of 10.4%. P. brasilianum has been detected in only 17/33 species examined, and the infection rate of those 17 species ranged from 2.1 to 50.0%. Logistic and standard linear regressions, at three different taxonomic levels, demonstrate that a significant proportion of the interspecific variation in infection rate can be explained by variation in average body weight (W) and average sleeping group size (G). Infection rate could increase with W and G due to enhanced odour production attracting a greater number of anopheline mosquito vectors of monkey malaria per host. Given that parasites reduce host fitness, the results suggest that, contrary to conventional wisdom, mosquito-borne diseases are a significant cost associated with larger group size.