Opposite effects of anthelmintic treatment on microbial infection at individual versus population scales

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Science  09 Jan 2015:
Vol. 347, Issue 6218, pp. 175-177
DOI: 10.1126/science.1261714

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  1. Fig. 1 Effects of anthelmintic treatment on buffalo immunity.

    (A) Treatment increased IFN-γ responses to pokeweed mitogen stimulation. Accounting for season, herd, age, and capture interval, treated individuals had significantly higher IFN-γ levels than those of controls [linear mixed model (LMM), n = 212 individuals, 1020 observations, β estimate ± SE (control) = –0.0378 ± 0.0162, P = 0.02 (table S3)]. (B) Treatment had no effect on circulating neutrophil concentrations. Accounting for the same covariates as in (A), there was no difference between treated and control individuals in neutrophils [LMM, n = 211 individuals, 941 observations, β estimate ± SE (control) = –0.0011 ± 0.0023, P = 0.63 (table S3)]. Both IFN-γ and neutrophil concentrations were power-transformed for analysis.

  2. Fig. 2 Anthelmintic treatment had no effect on BTB incidence but increased survival of BTB-infected individuals with drastic consequences for microbe fitness.

    (A) Female buffalo were monitored for 4 years to evaluate the effects of treatment on the probability of BTB infection and post-infection mortality. (B) Survival curves showing the proportion of treated and control buffalo converting to BTB-positive as a function of time measured in days. Control and treated individuals had approximately equal probabilities of acquiring BTB (log-rank test: P = 0.976) (15). (C) Survival curves showing the proportion of BTB-infected buffalo that survived as a function of time in days. The probability of death given infection was significantly higher for control as compared with treated individuals (log-rank test, P = 0.0054). For both curves, vertical lines indicate individuals that were right-censored from the data set. (D) The estimated R0 of BTB for control and treated subsets of the buffalo population. R0 is approximately eight times higher for treated individuals (2 versus 15.5), with upper and lower estimates of 3.4 and 69.8, respectively (CIs were not calculated for controls). (E) Estimated R0 of BTB across the range of mortality rates observed for treated buffalo and control buffalo (~0.03 to 0.24), accounting for possible reductions in bacteria shedding due to treatment (range, 0 to 90%). The area shaded in gray shows the baseline R0 for control buffalo (R0 = 2). At a mortality rate of ~0.03, as observed for treated buffalo, a reduction in shedding of at least 90% is needed to decrease R0 to baseline levels.

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