Parasite load seems to affect negatively cognitive abilities.
Decreased Parasite Load and Improved Cognitive Outcomes Caused by Deworming and Consumption of Multi-Micronutrient Fortified Biscuits in Rural Vietnamese Schoolchildren
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3144834/
Decreased Parasite Load and Improved Cognitive Outcomes Caused by Deworming and Consumption of Multi-Micronutrient Fortified Biscuits in Rural Vietnamese Schoolchildren https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3144834/
Parasite load explains 67% of the worldwide variation in intelligence: "Parasite prevalence and the worldwide distribution of cognitive ability" https://royalsocietypublishing.org/doi/abs/10.1098/rspb.2010...