Select Committee on Science and Technology Written Evidence

Memorandum by Professor Tony Hart and Professor Nigel French, University of Liverpool

  Thank you for giving us the opportunity to contribute to the session on "Food and the risk to public health" at the recent meeting in Birmingham. In our brief discussions after the session you suggested we should forward any further thoughts to you. We would like to take this opportunity to raise some broad issues, which, we feel, are relevant to the debate, but were not discussed in detail during the meeting.

  The first issue concerns "food-borne" pathogens and addresses the relative contribution of both food and non-food pathways to the burden of human infection by bacteria such as E coli O157, Salmonella spp and Campylobacter jejuni. Although food is an important vehicle for these enteric pathogens, we are exposed to these bacteria via many other pathways: water (mains, private supplies and recreational), occupational (farmers, vets and abattoir workers), environmental (picnicking, "open" farm visits, camping), domestic pets and person to person spread. Although particular food routes are often strongly implicated in outbreaks of infectious enteric disease, we have little understanding of the relative contribution of different foodstuffs, and other non-food exposures, to apparently sporadic infections. This lack of quantified information on the relative importance of different food and non-food pathways hinders progress towards devising targeted interventions and control measures that are likely to have the greatest impact on human health. As an example, the isolation of Campylobacter jejuni in poultry has, arguably, lead to an overemphasis on measures aimed at blocking this route of transmission and a focus on interventions towards the consumer-end of the food chain. Recent developments in molecular typing have indicated that non-poultry and non-food pathways may be of increasing importance (this is also likely to be true for E coli O157). This obviously has major implications for the control and prevention of these infections.

  Developments in Quantitative Microbial Risk Assessment (eg Codex Alimentarius Commission and World Health Organization guidelines) have led to a plethora of complex simulation-based studies that are usually focused on specific food pathways and pathogens. We feel this will lead to a very disjointed approach to the management of such risks. Given that humans are exposed to a range of zoonotic infections via multiple exposure-pathways, we favour a more holistic approach to risk reduction that considers interventions in terms of their specificity for pathogen and pathway and their relative costs and benefits. For example, farm-level interventions aimed at reducing the prevalence and loads of zoonotic pathogens may be generic for both pathogen and pathway (eg improving hygiene barriers could reduce carriage of both campylobacter and VTEC and affect both food and non-food routes). Likewise, pathogen-specific interventions (eg vaccination) applied at farm-level may also reduce human exposure through both food and non-food routes. We recommend that the relative value of farm-level interventions be considered alongside control measures introduced further along the food chain—taking into account their effects on both food and non-food pathways, and their impact on the multiple pathogens of major public health importance. We also recommend that recent developments in molecular typing and modelling be applied to the quantification of human health risks from food and non-food pathways in the UK.

  The second issue concerns the impact of changes in agricultural and food-production practices on the risk to human health from emerging pathogens (via food and non-food pathways). An obvious UK example is the emergence of new variant CJD, but similar devastating problems have emerged in other countries—for example the clearing of forests in Malaysia resulted in an outbreak of Nipah virus that caused 265 cases of human encephalitis, including 105 deaths, in persons in close contact with pigs. This outbreak underlined the importance of wildlife, domestic animal and human interaction and the effects of perturbing an ecosystem. The recently emerged sudden acute respiratory syndrome (SARS) is also likely to be caused by another member of the Paramyxoviridae family and this family has been responsible for other emerging zoonoses (two outbreaks associated with Hendra virus in horses).

  The problem of antimicrobial resistance and the emergence of E coli O157 and rising problem of campylobacteriosis may also be attributed, in part, to evolution and dissemination enhanced by current practices. At the moment we appear to have limited capacity to anticipate and prevent the emergence of zoonotic pathogens. We would recommend efforts be directed towards improving our understanding of the relationship between changes in agricultural and other related practices, and pathogen evolution and transmission. This will require a thorough understanding of the evolutionary dynamics of pathogens and their transmission through complex livestock systems and human exposure pathways.

28 March 2003

previous page contents next page

House of Lords home page Parliament home page House of Commons home page search page enquiries index

© Parliamentary copyright 2003