Anemia
Helminths may cause iron-deficiency anemia. This is most severe in heavy hookworm infections, as Necator americanus and Ancylostoma duodenale feed directly on the blood of their hosts. Although the daily consumption of an individual worm (0.02–0.07 ml and 0.14–0.26 ml respectively) is small, the collective consumption under heavy infection can be clinically significant. Intestinal whipworm may also cause anemia. Anemia has also been associated with reduced stamina for physical labor, a decline in the ability to learn new information, and apathy, irritability, and fatigue. A study of the effect of deworming and iron supplementation in 47 students from the Democratic Republic of the Congo found that the intervention improved cognitive function. Another study found that in 159 Jamaican schoolchildren, deworming led to better auditory short-term memory and scanning and retrieval of long-term memory over a period of nine-weeks. Cognitive changes
Malnutrition due to helminths may affect cognitive function leading to low educational performance, decreased concentration and difficulty with abstract cognitive tasks. Iron deficiency in infants and preschoolers is associated with "lower scores ... on tests of mental and motor development ... [as well as] increased fearfulness, inattentiveness, and decreased social responsiveness". Studies in the Philippines and Indonesia found a significant correlation between helminthiasis and decreased memory and fluency. Large parasite burdens, particularly severe hookworm infections, are also associated with absenteeism, under-enrollment, and attrition in school children.
A critique to this theory is that while mortuary cannibalism was banned in Papua New Guinea in the 1950s, that does not necessarily mean that the practice ended. Fifteen years later Jared Diamond was informed by Papuans that the practice continued.These researchers noticed a genetic variation in some people with kuru that has been known to promote long incubation periods. They have also proposed that individuals having contracted CJD in the early 1990s represent a distinct genetic subpopulation, with unusually short incubation periods for bovine spongiform encephalopathy (BSE). This means that there may be many more people with vCJD with longer incubation periods, which may surface many years later.Prion protein is detectable in lymphoid and appendix tissue up to two years before the onset of neurological symptoms in vCJD. Large scale studies in the UK have yielded an estimated prevalence of 493 per million, higher than the actual number of reported cases. This finding indicates a large number of asymptomatic cases and the need to monitor. Society and culture
In 1997, a number of people from Kentucky developed CJD. It was discovered that all had consumed squirrel brains. A coincidental relationship between the disease and this dietary practice may have been involved. In 2008, UK scientists expressed concern over the possibility of a second wave of human cases due to the wide exposure and long incubation of some cases of vCJD. In 2015, a man from New York developed vCJD after eating squirrel brains.