|dc.description.abstract||Global, national, and local pressures have shaped the New Zealand dairy industry and have led to the intensification of dairy farming. There are a number of potential health impacts, both positive and negative, associated with dairy farming. This thesis aims to identify and describe causal pathways linking dairy farming and public health, and to quantify selected impacts associated with the intensification of dairy farming in New Zealand.
Review of the literature identified zoonotic diseases; occupational hazards; direct and indirect environmental health impacts; antimicrobial resistance; foodborne hazards; diet-related health harms and benefits; and indirect economic, social, and cultural effects as potential health impacts associated with dairy production and consumption. However, there are considerable difficulties involved in quantifying the effects of the intensification of dairy farming on human health, particularly with regard to complex and indirect causal pathways, such as climate change and diet. Health impact assessment, the environmental burden of disease approach, and integrated assessment modeling were identified as appropriate methodologies for a comprehensive and transdisciplinary assessment of the potential health impacts associated with the intensification of the dairy sector. While these approaches were deemed too resource-intensive to complete as a part of this thesis, components of this thesis could provide useful input into such an assessment in the future.
Dairy cattle numbers have increased substantially in New Zealand in recent decades. High dairy cattle density represents a significant potential exposure to zoonotic pathogens. This thesis primarily focused on bovine enteric zoonoses, due to the historically high enteric infection rates in humans in New Zealand. Specifically, the influence of dairy density on campylobacteriosis, cryptosporidiosis, giardiasis, salmonellosis, and Shiga toxin-producing Escherichia coli (STEC) infection was investigated.
Environmental exposure to bovine zoonotic pathogens is of particular concern in rural and peri-urban areas. Descriptive analyses indicated that there may be higher risk of infection in areas where dairy cattle were newly introduced than in longstanding dairy farming regions. In particular, campylobacteriosis and cryptosporidiosis notification rates in New Zealand display strong seasonality and distinct patterns between urban and rural areas. For both diseases, increases in rural cases often preceded increases in urban cases, suggesting that rural exposures drive some of the burden of disease in urban areas. Detection of space-time clusters also demonstrated differences in disease risk between urban and rural areas.
Classification and regression tree analysis indicated that estimated river E. coli concentration was an important predictor for campylobacteriosis and cryptosporidiosis clusters. Therefore, waterborne transmission may play an important role in the development of some disease clusters. Livestock densities were important predictors for both clusters and seasonal notification rates of both diseases. Additionally, Poisson generalized linear models indicated that cattle are an important source of disease for young children in rural areas.
There may be human health benefits to limiting dairy cattle numbers in areas where environmental factors facilitate pathogen transport to waterways. However, the relationship between dairy cattle density and enteric disease rates is complex and pathogen specific. Importantly, local and larger scale environmental characteristics and social factors appear to strongly modulate disease risk.||