Dairy Cattle Density and Temporal Patterns of Human Campylobacteriosis and Cryptosporidiosis in New Zealand

Abstract

Public health risks associated with the intensification of dairy farming are an emerging concern. Dairy cattle are a reservoir for a number of pathogens that can cause human illness. This study examined the spatial distribution of dairy cattle density and explored temporal patterns of human campylobacteriosis and cryptosporidiosis notifications in New Zealand from 1997 to 2015. Maps of dairy cattle density were produced, and temporal patterns of disease rates were assessed for urban versus rural areas and for areas with different dairy cattle densities using descriptive temporal analyses. Campylobacteriosis and cryptosporidiosis rates displayed strong seasonal patterns, with highest rates in spring in rural areas and, for campylobacteriosis, summer in urban areas. Increases in rural cases often preceded increases in urban cases. Furthermore, disease rates in areas with higher dairy cattle densities tended to peak before areas with low densities or no dairy cattle. Infected dairy calves may be a direct or indirect source of campylobacteriosis or cryptosporidiosis infection in humans through environmental or occupational exposure routes, including contact with animals or feces, recreational contact with contaminated waterways, and consumption of untreated drinking water. These results have public health implications for populations living, working, or recreating in proximity to dairy farms.

Keywords: dairy cattle density; public health; zoonoses.

Figure 1

Total dairy cattle in New Zealand (including bobby calves). There was no Agricultural Survey carried out in 1997 or 1998 Adapted from Statistics New Zealand (2017).

Figure 2

Total number of dairy herds and average herd size in New Zealand Adapted from LIC & DairyNZ (2019).

Figure 3

Dairy cattle density in New Zealand in (a) 2000, (b) 2006, and (c) 2014 at the meshblock level. Adapted from Agribase™ database.

Figure 4

Change in dairy cattle density in New Zealand from 2000 to 2014 at the census area unit level. Adapted from Agribase™ database.

Figure 5

Seasonal decomposition of the weekly incidence of campylobacteriosis in New Zealand (1997–2015). MSE = mean squared error; Lambdas = smoothing parameters; Trend = the long-term temporal trend; Seasonality = a repeating seasonal pattern that changes slowly or remains constant over time; Random = the remainder of the data after the Trend and Seasonality components are removed; Fit/Forecast = Trend + Seasonality. The original data can be obtained by adding the Trend, Seasonality, and Random components.

Figure 6

Seasonal decomposition of the weekly incidence of cryptosporidiosis in New Zealand (1997–2015). MSE = mean squared error; Lambdas = smoothing parameters; Trend = the long-term temporal trend; Seasonality = a repeating seasonal pattern that changes slowly or remains constant over time; Random = the remainder of the data after the Trend and Seasonality components are removed; Fit/Forecast = Trend + Seasonality. The original data can be obtained by adding the Trend, Seasonality, and Random components.

Figure 7

Seasonal pattern of human campylobacteriosis rates stratified by (a) rural and (b) urban and status. Error bars represent 95% confidence intervals for the means.

Figure 8

Seasonal pattern of human cryptosporidiosis rates stratified by (a) rural and (b) urban status. Error bars represent 95% confidence intervals for the means.

Figure 9

Seasonal pattern of human campylobacteriosis rates stratified by average dairy cattle density: (a) no dairy, (b) low dairy density, (c) medium dairy density, and (d) high dairy density. Error bars represent 95% confidence intervals for the means.

Figure 10

Seasonal pattern of human cryptosporidiosis rates stratified by average dairy cattle density: (a) no dairy, (b) low dairy density, (c) medium dairy density, and (d) high dairy density. Error bars represent 95% confidence intervals for the means.