Verocytotoxigenic Escherichia coli (VTEC) and cryptosporidiosis are emerging zoonotic infections. Intensive agricultural land use has been implicated in their emergence and sustained incidence. New Zealand has large numbers of dairy cattle, beef cattle, and sheep that may be reservoirs for VTEC and Cryptosporidium. The aim of this study was to assess the relationship between the density of the major farm animals in New Zealand (dairy cattle, beef cattle and sheep), and the rates of notified VTEC and cryptosporidiosis. To supplement this, the study also described the epidemiology of VTEC and cryptosporidiosis.
VTEC and cryptosporidiosis notifications, denominator and animal density data were obtained for the years 2004 to 2009. Notification rates of VTEC and cryptosporidiosis were described in relation to time, person, and rurality. The relationships between the density of each of the major farm animals in New Zealand and disease were evaluated using Poisson regression. Age, sex, ethnicity, deprivations and animal density were included as covariates. Notification data, animal density and denominator data were linked at the level of meshblocks.
Notification rates of VTEC and cryptosporidiosis increased over the study period and varied by season. For both diseases, rates were highest amongst individuals less than five years old, those in the least deprived areas, and those of European ethnicity. For each animal type, rates were higher in areas with animals relative to those with no animals. Within dairying areas, relative to the lowest dairy density areas (between 0 and 25 animals/km2 exclusive), adjusted rates of VTEC were significantly higher in some dairy areas but there was no linear gradient. In contrast, there was a linear gradient between dairy density and cryptosporidiosis (p for trend <0.001); a similar relationship was observed for cryptosporidiosis in sheep areas. There was a trend for decreasing VTEC and cryptosporidiosis rates as beef cattle density increased (p<0.075 for VTEC and p<0.001 for cryptosporidiosis).
The findings of this study, combined with those from other research, suggest a causal association between both dairy cattle density and sheep density, and cryptosporidiosis in New Zealand. While the association between dairy density and VTEC in this study was less clear, the higher rates of VTEC in some dairying areas warrant further attention. The findings of this study suggest that rural land use changes in New Zealand may have adverse effects on human health. In this context, this study recommends greater involvement of the public health sector in agricultural policy making, planning and research.||