Transmission and dynamics of VTEC O157:H7 : a story about the complex associations between pathogen, host and environment

• Verotoxin-producing Escherichia coli serotype O157:H7 (VTEC O157:H7), is a zoonotic pathogen often transmitted from cattle to humans. In Sweden, domestic transmission of a highly virulent subtype of VTEC O157:H7, originating in regional clusters of infected cattle farms, is increasing. To reduce the risk of transmission to humans a comprehensive picture of infection dynamics between and within farms are urgently needed.The aim of this thesis was to provide a holistic view of drivers of transmission and susceptibility from a regional, farm and animal perspective by combining epidemiology, microbiology, bioinformatics and animal welfare.The risk of introduction of VTEC O157:H7 on cattle farms was studied by collecting environmental samples in spring and fall from 80 farms. Information about farm characteristics, biosecurity and between farm contacts were collected by a questionnaire. On 4 farms, a more thorough environmental sampling with detailed analysis of strains was carried out during summer (between the spring and fall sampling). The results showed frequent transmission of VTEC O157:H7 between farms and that transmission occurs through human and animals contacts.To investigate drivers of colonisation and transmission on farm level, individual samples from calves on 12 dairy farms with VTEC O157:H7 (established through environmental sampling) were collected. In addition to collecting information about pen and calf environment, a novel approach, using indicators of animal welfare and behaviour to study individual differences, was used to explore differences between colonised and non-colonised calves. The results suggest that social and active individuals are more likely to be colonised by the pathogen while animals showing signs of poor health and welfare were less likely to be colonised. Colonised animals shedding high levels of the bacteria were important for transmission but environmental exposure also increased risk of transmission within pens.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Hälsovetenskap -- Folkhälsovetenskap, global hälsa, socialmedicin och epidemiologi (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Health Sciences -- Public Health, Global Health, Social Medicine and Epidemiology (hsv//eng)

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