Scott Hamilton

Random forest-based source attribution models were developed from a ‘One Health’ resource comprising 4,230 high-quality whole-genome assemblies from Escherichia coli . These were isolated from a wide range of sources, predominantly originating in Scotland, including wastewater, livestock, food and clinical infections of humans and dogs. Using these models, we derived a probabilistic assignment of E. coli isolates from food, shellfish and water samples to potential livestock and human sources of contamination. The incorporation of E. coli sequences from wastewater alongside those from human clinical infections enabled us to capture a wide diversity of human strains in our analyses. The sequence types (STs) of isolates from human bacteraemia and urinary tract infection (UTI) were compared with livestock and food isolates. While only 2.3% of the E. coli isolated from food samples in the study were from STs primarily associated with human bacteraemia and UTI, the models found a livestock signal associated with 15% of the human clinical isolates. In the food and private water samples, livestock-human co-attribution of E. coli isolates was common and consistent with routine human exposure to specific subsets of livestock E. coli , potentially a result of selection during food and water processing. Overall, this research demonstrates the potential value of including source attribution models in national surveillance programmes to understand the transmission of E. coli through the agri-food chain and support risk management to protect public health.

The salmon louse, Lepeophtheirus salmonis, is an ectoparasitic copepod which feeds on the mucus, skin and blood of salmonid fish species. The parasite can persist on the surface of the fish without any effective control being exerted by the host immune system. Other ectoparasitic invertebrates produce compounds in their saliva, excretions and/or secretions which modulate the host immune responses allowing them to remain on or in the host during development. Similarly, compounds are produced in secretions of L. salmonis which are thought to be responsible for immunomodulation of the host responses as well as other aspects of crucial host-parasite interactions. In this study we have identified and characterised the proteins in the excretory/secretory (E/S) products of L. salmonis using LC-ESI-MS/MS. In total 187 individual proteins were identified in the E/S collected from adult lice and pre-adult sea lice. Fifty-three proteins, including 13 serine-type endopeptidases, 1 peroxidase and 5 vitellogenin-like proteins were common to both adult and pre-adult E/S products. One hundred and seven proteins were identified in the adult E/S but not in the pre-adult E/S and these included serine and cysteine-type endopeptidases, vitellogenins, sphingomyelinase and calreticulin. A total of 27 proteins were identified in pre-adult E/S products but not in adult E/S. The assigned functions of these E/S products and the potential roles they play in host-parasite interaction is discussed.

It has long been established that the sheep Prnp genotype influences the susceptibility to scrapie, and some studies suggest that it can also determine several aspects of the disease phenotype. Other studies, however, indicate that the source of infection may also play a role in such phenotype. To address this question an experiment was set up in which either of two different natural scrapie sources, AAS from AA₁₃₆ Suffolk and VVC from VV₁₃₆ Cheviot sheep, were inoculated into AA₁₃₆, VA₁₃₆ and VV₁₃₆ sheep recipients (n = 52). The immunohistochemical (IHC) profile of disease-associated PrP (PrP^d) accumulation in the brain of recipient sheep was highly consistent upon codon 136 homologous and semi-homologous transmission, but could be either similar to or different from those of the inoculum donors. In contrast, the IHC profiles were highly variable upon heterologous transmission (VVC to AA₁₃₆ and AAS to VV₁₃₆). Furthermore, sheep of the same Prnp genotype could exhibit different survival times and PrP^d profiles depending on the source of infection, and a correlation was observed between IHC and Western blot profiles. It was found that additional polymorphisms at codons 112 or 141 of AA₁₃₆ recipients resulted in a delayed appearance of clinical disease or even in protection from infection. The results of this study strongly suggest that the scrapie phenotype in sheep results from a complex interaction between source, donor and recipient factors, and that the Prnp genotype of the recipient sheep does not explain the variability observed upon codon 136 heterologous transmissions, arguing for other genetic factors to be involved.

Prion diseases exhibit different disease phenotypes in their natural hosts and when transmitted to rodents, and this variability is regarded as indicative of prion strain diversity. Phenotypic characterization of scrapie strains in sheep can be attempted by histological, immunohistochemical and biochemical approaches, but it is widely considered that strain confirmation and characterization requires rodent bioassay. Examples of scrapie strains obtained from original sheep isolates by serial passage in mice include ME7, 79A, 22A and 87V. In order to address aspects of prion strain stability across the species barrier, we transmitted the above murine strains to sheep of different breeds and susceptible Prnp genotypes. The experiment included 40 sheep dosed by the oral route alone and 36 sheep challenged by combined subcutaneous and intracerebral routes. Overall, the combined route produced higher attack rates (~100%) than the oral route (~50%) and 2–4 times shorter incubation periods. Uniquely, 87V given orally was unable to infect any sheep. Overall, scrapie strains adapted and cloned in mice produce distinct but variable disease phenotypes in sheep depending on breed or Prnp genotype. Further re-isolation experiments in mice are in progress in order to determine whether the original cloned murine disease phenotype will reemerge.

Bovine spongiform encephalopathy (BSE), a member of the transmissible spongiform encephalopathies (TSE), primarily affects cattle. Transmission is via concentrate feed rations contaminated with infected meat and bone meal (MBM). In addition to cattle, other food animal species are susceptible to BSE and also pose a potential threat to human health as consumption of infected meat products is the cause of variant Creutzfeldt-Jakob disease in humans, which is invariably fatal. In the UK, farmed and free ranging deer were almost certainly exposed to BSE infected MBM in proprietary feeds prior to legislation banning its inclusion. Therefore, although BSE has never been diagnosed in any deer species, a possible risk to human health remains via ingestion of cervine products. Chronic wasting disease (CWD), also a TSE, naturally infects several cervid species in North America and is spreading rapidly in both captive and free-ranging populations.