Number and virulence of the parasites that a host organism harbours
Parasite load is a measure of the number and virulence of the parasites that a host organism harbours. Quantitative parasitology deals with measures to quantify parasite loads in samples of hosts and to make statistical comparisons of parasitism across host samples.
^Thornhill, Randy et al. Zoonotic and Non-zoonotic Diseases in Relation to Human Personality and Societal Values: Support for the Parasite-Stress Model. Evolutionary Psychology, 2010. 8(2): 151-169