Addressing knowledge gaps in the sources, epidemiology and genetic diversity of important foodborne pathogens

Challenges

There are significant gaps in our knowledge regarding the epidemiology and transmission of two foodborne pathogens: Campylobacter spp. and Toxoplasma gondii. These pathogens are some of the most important foodborne pathogens in Europe in terms of disease burden. Despite this, there remain gaps in our understanding, and have been identified as priorities for future research by food safety authorities:

• How certain animal reservoirs contribute to the overall burden of disease
• Information relating to the genetic diversity of strains circulating in livestock populations
• The role of the environment in their transmission

Campylobacter is a versatile foodborne pathogen with the ability to evolve rapidly. Foodborne Campylobacter spp., which includes Campylobacter jejuni and Campylobacter coli, colonise the gut of a wide range of animal species and while some genotypes are associated with specific hosts, others have evolved to become more generalistic. While the major source of campylobacteriosis in Scotland is raw or undercooked poultry, studies have also highlighted livestock as an important reservoir. Furthermore, Campylobacter spp. may also play a role as a vehicle for antimicrobial resistance genes (ARGs) through the food supply chain. However, the role of antimicrobial selective pressure in the emergence of Campylobacter resistance in livestock is not well understood.

Toxoplasma gondii is a zoonotic parasite of global importance and can infect all warm-blooded animals, including humans. One of the most important transmission routes for people is through the consumption of undercooked meat from infected animals. Indeed, foodborne transmission is thought to be attributable to up to 50% of cases of toxoplasmosis. Despite this, there are still significant knowledge gaps surrounding the sources and epidemiology of foodborne toxoplasmosis. In particular, the role of livestock in transmission as well as the genetic diversity of strains circulating in food animals and the environment. Both the European Food Safety Authority and the UK Food Standards Agency have highlighted the urgent requirement for further studies to address these knowledge gaps.

Questions

Solutions

The aim of this project is to investigate the role of Scottish livestock and their environments in transmission of important foodborne pathogens, Toxoplasma gondii and Campylobacter spp., to humans. 

Circulation of Campylobacter within farmed ecosystems

We adopt two approaches to improve our understanding of how Campylobacter spp. circulating within sheep farms may contribute to the burden of human disease in Scotland. Firstly, we are applying comparative genomics of Campylobacter isolates from sheep, wildlife, and environmental samples to assess on-farm transmission. We are carrying out an intensive sampling campaign from a lowland sheep farm, which will include samples from farm animals as well as the wider ecosystem, including wildlife faecal samples and the environment. Samples from sheep, wild birds and rodents are being used to investigate host restriction of Campylobacter genotypes and the presence of generalist strains which may result in increased Campylobacter burden and dissemination of Campylobacter–associated ARGs. Water and soil samples are being used to investigate the role of the environment in the transmission of Campylobacter on-farm.

Secondly, we are focusing on host factors which may influence carriage and shedding by sheep, potentially identifying risk factors for increased transmission. We are monitoring the carriage of Campylobacter by a cohort of sheep through a longitudinal study over a year and successive lambing seasons. The health status of the animals will be recorded, their genetic background will be defined, and the farming practices will be well-controlled. This cohort will allow us to explore carriage association with several factors including age, season, and reproductive status.

Carriage of Campylobacter spp. by farmed deer in Scotland represents a further significant knowledge gap, with potential implications for the safety of venison meat and we are also investigating the presence and diversity of Campylobacter strains circulating in farmed deer populations.

The metabolic versatility in host association and clinical outcome

Metabolic versatility may influence the ability of Campylobacter subtypes to colonise multiple hosts by utilising different substrates within the host intestine, potentially increasing Campylobacter incidence on farms as well as the dissemination of ARGs. An improved understanding of substrate utilisation within the gut of animal reservoirs could also inform dietary interventions which decrease the bacterial load. We are conducting a survey of metabolic traits within 6000 Campylobacter genomes to investigate the distribution of metabolic traits within sequence types that are associated with human clinical disease and animal reservoirs, including poultry, livestock, and wild birds.

Genetic diversity of Toxoplasma gondii in Scotland

We are furthering our understanding of the sources and epidemiology of T. gondii in Scotland and identifying interventions to reduce disease. We are doing this by:

• Investigating the genetic diversity of T. gondii in livestock, humans, and the environment (water)
• Determining the seroprevalence of T. gondii in food animals
• Exploring intervention strategies to reduce foodborne disease

Project Partners

Progress