Seasonality in Human Zoonotic Enteric Diseases: A Systematic Review

BACKGROUND: Although seasonality is a defining characteristic of many infectious diseases, few studies have described and compared seasonal patterns across diseases globally, impeding our understanding of putative mechanisms. Here, we review seasonal patterns across five enteric zoonotic diseases: campylobacteriosis, salmonellosis, vero-cytotoxigenic Escherichia coli (VTEC), cryptosporidiosis and giardiasis in the context of two primary drivers of seasonality: (i) environmental effects on pathogen occurrence and pathogen-host associations and (ii) population characteristics/behaviour. METHODOLOGY/PRINCIPAL FINDINGS: We systematically reviewed published literature from 1960-2010, resulting in the review of 86 studies across the five diseases. The Gini coefficient compared temporal variations in incidence across diseases and the monthly seasonality index characterised timing of seasonal peaks. Consistent seasonal patterns across transnational boundaries, albeit with regional variations was observed. The bacterial diseases all had a distinct summer peak, with identical Gini values for campylobacteriosis and salmonellosis (0.22) and a higher index for VTEC (Gini  0.36). Cryptosporidiosis displayed a bi-modal peak with spring and summer highs and the most marked temporal variation (Gini = 0.39). Giardiasis showed a relatively small summer increase and was the least variable (Gini = 0.18). CONCLUSIONS/SIGNIFICANCE: Seasonal variation in enteric zoonotic diseases is ubiquitous, with regional variations highlighting complex environment-pathogen-host interactions. Results suggest that proximal environmental influences and host population dynamics, together with distal, longer-term climatic variability could have important direct and indirect consequences for future enteric disease risk. Additional understanding of the concerted influence of these factors on disease patterns may improve assessment and prediction of enteric disease burden in temperate, developed countries

Skill mastery inhibits adoption of observed alternative solutions among chimpanzees (Pan troglodytes)

Geographic variation in socially transmitted skills and signals, similar to human culture, has been well documented for great apes. The rules governing the adoption of novel behaviours, however, are still largely unknown. We conducted an innovation-and-transmission experiment with two groups of chimpanzees living at hopE Primate Sanctuary Gänserndorf, Austria, presenting a board on which food had to be manoeuvred around obstacles to be acquired. Most chimpanzees used sticks to acquire the food, but five adults independently invented a novel technique, rattling, which was subsequently tested by almost all group members. However, individuals who had become proficient with sticks were reluctant to switch to rattling, despite it being more efficient. Similarly, after rattling was prevented, rattle specialists kept trying to rattle and made no attempt to use the stick technique, despite their knowledge about its existence. We conclude that innovators stimulate others to experiment with the solutions they display, but that chimpanzees are nevertheless conservative; mastery of a skill inhibits further exploration, and hence adoption of alternative techniques even if these are more efficient. Consequently, conformity among group members should not be expected in great apes when individuals develop proficiency at different techniques. Conservatism thus joins conformity as a mechanism to bring about cultural uniformity and stability