Harbingers of Health: The Positive Effects of Helminth Infection and Environment in Determining Host Health

Abstract

Strachan’s Hygiene and Rook’s Old Friends Hypotheses both sought to explain the sharp rise in autoimmune disease incidence in post-industrial nations as the result of increased personal sanitation standards (Rook 2009; Strachan 1989). Rook specifically attributed the rise in immune-mediated disease to the eradication of helminths, which had co-evolved with humans throughout our evolutionary history (Rook 2009). Removing helminths from our environment caused our immune responses to mount excessive responses that lead to pathogenic inflammation and tissue damage (Gause 2013; Hubner 2013; Viney 2013). This study analyzed T. muris specimens from 55 mice to study how host health immune responses vary in three environmental conditions: Quarantine/hygienic, Mixed, and Stony Ford/natural. I imaged the helminths and measured the lengths and widths in order to calculate total helminth biomass per host. Hosts in natural conditions had elevated TH1 immune responses, reflecting a helminth survival strategy. Hosts in hygienic conditions had elevated TH2 and TREG immune responses, driving host susceptibility for atopic disease development. Host weight gain per day was used as a surrogate for relative host health (Foltz 1999). Helminths had the greatest biomass and total count in Stony Ford conditions, where infected hosts had the greatest weight gain per day and, thus, relative health. These results support the beneficial role of helminths as predicted by both the Hygiene and Old Friends Hypotheses, in addition to providing helminth biomass as a more accurate indicator of parasite burden than helminth count alone, especially for low-count infections. Biomass was also shown to be a more significant response variable than count for TH1 immune responses. The importance of helminth biomass has very important implications for interpreting past studies, which focus solely on helminth count, and for guiding future studies.