Acute ill-health following treatment of sheep for ectoparasites

Posted on February 12, 2012

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Last friday one of my PhD students, Hanaa Bayomy, originally from Egypt, has succesfully defended here thesis. So a new Doctor of Philosophy has been made.

She did some very interesting work on “Acute ill-health following treatment of sheep for ectoparasites“. Hereby the abstract of her thesis. If you are, however, interested in more details I have no doubt that we will see the papers appear in peer-reviewed literature over the next months.

So without further ado, her Hanaa’s work:

In the last two decades attention has been directed towards flu-like symptoms (“dipper’s flu”; DF) in sheep farmers following the treatment of sheep against ectoparasites using organophosphate (OP) based dips. However the nature and cause of DF remain unclear. The overall aims of this project were to identify the clinical pattern of acute ill-health arising after sheep treatment and to evaluate whether this ill-health may be caused by pesticide exposure through statistical analysis of the data collected by the UK Health and Sheep Dipping Survey. This prospective study collected detailed information on (i) health and exposures, (ii) urine samples pre- and post-treatment, and (iii) symptoms reported in a diary during the week following treatment

This analysis included: (i) identifying the determinants of exposure to pesticides (OPs and synthetic pyrethroids) by measurement of urinary metabolites before and after treatment, (ii) management of missing data in Health Questionnaires (HQs) completed before and after treatment using a multiple imputation approach, (iii) assessing the association between pesticide exposure and DF using previously published definitions of DF derived from the HQs using least square regression, (iv) identifying patterns of self-reported acute symptoms using Exploratory Factor Analysis (EFA) of HQ responses, (v) determining the association between pesticide exposure and any newly identified symptom patterns and (vi) assessing of the risk of daily ill-health in relation to pesticide exposure using biologically distributed lag models.

Sheep treatment was associated with increased exposure to OPs (diazinon), but not pyrethroids as levels of total diazinon urinary metabolites were higher post-treatment (P=0.01). Increased urinary levels of diazinon metabolites were associated with product splashing (P=0.02), the number of sheep treated (P=0.005) and the number of hours treating (P<0.001), but not with concentrate handling. DF scores based on previous definitions provided weak evidence of ill-health following sheep treatment as scores derived from the HQs were not increased after treatment. EFA of self-reported symptoms identified six clinically definable factors (musculoskeletal, gastrointestinal, upper respiratory tract, thermostasis, rhinitis and cognitive symptoms). Musculoskeletal symptoms were consistently reported irrespective of sheep treatment. The sum of the six extracted factors was then used as a new case definition of DF. Reported pre-treatment health and past history of DF were the main determinants of DF. However, in addition to these determinants DF remained associated with self-reported OP-use and handling concentrate. There was no association between DF and the levels of diazinon urinary metabolites. Daily symptom reporting was higher among both OP and non-OP users on days 1 and 2 of the treatment week. There was little evidence that this symptom reporting was associated with numbers of sheep treated (as a proxy of exposure) except on days 4 and 6, although this was not related to specific lag of exposure, since the lags differed (lags 0-3).

Overall this study provides a new case definition of acute ill-health following sheep treatment based on a systematic approach to define the common themes of reported symptoms. Increased symptom reporting after the use of pesticides with diverse modes of action plus the lack of any associations between ill-health and (i) urinary diazinon metabolites and (ii) plausible lags of exposure suggest that other factors related to sheep treatment may be as well important. If taken further, identification of these factors and susceptible subjects could lead to a reduction in the problem of DF.

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