Controlling enteric zoonoses in New Zealand - Vetscript February 2010

Collaboration and the "One World, One Health" approach

by Nigel French, Professor of Food Safety and Veterinary Public Health and Petra Mullner, Consultant, EpiCentre, Massey University

Recent efforts to control enteric zoonoses in New Zealand illustrate the "One World, One Health" interdisciplinary approach in action (see Vetscript, October 2009). The most important zoonoses in this country include the enteric diseases: campylobacteriosis, cryptosporidiosis and salmonellosis. Together, these three diseases make a substantial contribution to the domestic public health burden, resulting in considerable morbidity, time lost from work and school and, occasionally, serious sequelae and death.

The bacterium VTEC O157 is also a major concern for New Zealand. Although this enteric pathogen causes relatively fewer domestic human cases, it is of considerable importance for market access and international trade in meat products (Table 1).

Interdisciplinary approach required

The above described enteric zoonoses are all caused by multi-host pathogens that are amplified in food animals - often without evidence of clinical disease. This means that identifying the most important animal reservoirs contributing to human disease and tracing their transmission pathways presents a formidable challenge - one that requires interdisciplinary teamwork and a "one health" approach. After identifying the predominant sources and pathways of infection, the development and implementation of control strategies requires further collaboration between individuals with human and animal health expertise and a strong and productive partnership between the relevant industries and regulatory bodies such as the New Zealand Food Safety Authority (NZFSA). These activities need to be supported by good surveillance of human cases (and, where relevant, animal cases) and the monitoring of pathogens in the food chain.

Table 1: Important enteric zoonoses in New Zealand

* From http://www.surv.esr.cri.nz/PDF_surveillance/NZPHSR/2009/NZPHSR2009Sept.p....

** Although the primary concern relates to the costs associated with market access, the number of human cases within New Zealand has been rising in recent years, and the per-capita rate is high by international standards.

Reducing campylobacteriosis: "one health" in action

The recent successful campaign to reduce the burden of campylobacteriosis - New Zealand's most frequently notified infectious disease - provides a good illustration of how collaborative interdisciplinary teamwork can have a direct impact on public health.

In 2006, human campylobacteriosis notifications in New Zealand reached an all-time high. Around 16,000 cases were notified, which was one of the highest per-capita rates reported anywhere in the world (Baker et al, 2006). A concerted effort over the last two-to-three years has seen case rates fall dramatically to less than half the rates reported in 2006 (Figure 1). This was achieved by an interdisciplinary team - a collaboration between members of the medical and veterinary professions, who combined forces with health protection officers, micro- and molecular biologists, population geneticists, epidemiologists, mathematicians, industry specialists and the national regulator to achieve a common goal.

Figure 1: Number of campylobacteriosis notifications and hospitalisations by year, 1997-2008

Source: Dr Ann Sears, Wellington School of Medicine.

Source attribution, epidemiology and surveillance

One of the crucial steps towards implementing a successful intervention strategy was to quantify the contribution of different animal reservoirs and pathways to the burden of human infection. Classical epidemiological approaches, such as case-control studies (Ikram et al, 1994; Eberhart-Phillips et al, 1997), had helped to identify putative risk factors, but until recently there was still considerable controversy about the relative roles of different food, water and environmental sources. This was hampering efforts to implement effective control programmes.

In an attempt to overcome these problems, a sentinel surveillance site was established in the Manawatu in 2005 with funding from the NZFSA. Enhanced surveillance of human cases was provided by a collaborative partnership between the Institute of Environmental Science and Research Ltd (ESR) Public Health Surveillance team, MidCentral Public Health Services, the regional medical laboratory (Medlab Central) and Massey University. The newly established Molecular Epidemiology Laboratory (part of the EpiCentre), located in the Hopkirk Research Institute at Massey, provided the micro- and molecular biological resources for isolating and genotyping Campylobacter isolates from human clinical cases, food sources, environmental water and domestic and wild animal faeces.

Recently developed molecular genotyping tools were deployed and new epidemiological and population genetic models were used to calculate the relative contribution of each source to the burden of human infection (Mullner et al, 2009a; Mullner et al, 2009b). The results from these different models (Figure 2) consistently showed that poultry was the most important source of human infection and interventions aimed at reducing the risk from fresh poultry were therefore likely to be the most successful.

In addition, the human surveillance data provided by ESR at a fine spatial scale was merged with the molecular genotyping data for each human case. This provided new insight into differences in exposure to poultry and ruminant genotypes between urban and rural populations and between different age groups. This information was valuable for identifying likely transmission pathways (eg, food versus environmental) and assessing the likely effectiveness of interventions in different sectors of the human population.

Figure 2: Proportion of 502 human campylobacteriosis cases attributable to each source: comparing, from left to right, the Dutch (I), modified Hald (II) and asymmetric island model (III)

Note: Error bars represent 95 percent confidence/credible intervals.

Intervention, post-intervention and conclusions

The findings of the epidemiological and source attribution studies were used to inform the NZFSA Campylobacter Risk Management Strategy (2007), which has subsequently included mandatory targets for limiting contamination with Campylobacter spp. of chilled poultry carcasses. The full cooperation of the poultry industry and the subsequent decline in contamination levels in fresh poultry has coincided with the striking reduction in human cases evident in Figure 1. This persisted through into 2009. Further "dynamic" source attribution modelling has shown that the decline in human cases is primarily due to a decline in poultry-associated cases.

In conclusion, the veterinary profession continues to play a pivotal role in protecting human health by engaging in an effective partnership with human health professionals and undertaking interdisciplinary teamwork. The successful control of enteric zoonoses, as demonstrated for campylobacteriosis, shows the effectiveness of the "one health" paradigm when applied to a preventable disease of major public health importance.

Acknowledgements

This work was funded by NZFSA and was done in collaboration with ESR Ltd and MidCentral Public Health Services. The following individuals and organisations contributed to the work and represent the wide range of disciplines and expertise: Dr Daniel Wilson, Dr Simon Spencer, Dr Anne Midwinter, Dr Julie Collins-Emerson, Tui Shadbolt, Dr Jill McKenzie, Dr Phil Carter, Ruth Pirie and Dr Tecklok Wong, Dr Grant Hotter, Dr Donald Campbell, Dr Peter van der Logt, Professor Steve Hathaway, Rebecca Pattison, Rukhshana Akhter, Errol Kwan, Lynn Rogers, Isabel Li, Jim Learmonth, Anthony Pita, Sarah Moore, Graham McBride, the New Zealand Poultry Industry Association, Professor Mike Hedley, Dr Geoff Jones, Dr Alasdair Nobel, Professor Martin Hazelton, Dr Michael Baker, Dr Ann Sears, Diane Richardson, Horizons Regional Council, and the participating farmers in the Manawatu.

References

Baker M, N Wilson, R Ikram, S Chambers, P Shoemack, G Cook G (2006) Regulation of chicken contamination is urgently needed to control New Zealand's serious campylobacteriosis epidemic, NZ Med J 119, U2264.

Eberhart-Phillips J, N Walker, N Garrett, D Bell, D Sinclair, W Rainger, M Bates M (1997) Campylobacteriosis in New Zealand: Results of a case-control study, J Epidemiol Community Health 51, 686-691.

Ikram, R, S Chambers, P Mitchell, MA Brieseman, OH Ikam (1994) A case control study to determine risk factors for campylobacter infection in Christchurch in the summer of 1992-93, NZ Med J 107, 430-432.

Mullner P, G Jones, A Noble, SE Spencer, S Hathaway, NP French (2009a) Source attribution of food-borne zoonoses in New Zealand: A modified Hald model, Risk Anal 29, 970-984.

Mullner P, S Spencer, D Wilson, G Jones, A Noble, A Midwinter, J Collins-Emerson, P Carter, S Hathaway, NP French (2009b) Assigning the source of human campylobacteriosis in New Zealand: A comparative genetic and epidemiological approach, Infect Genet Evol in press.