Infection at the wildlife-livestock-human interface : three systems

• Main Author: Sandoval Barron, Elsa
• Published: University of Liverpool 2017
• Subjects: 614.5
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.722109

Zoonoses involve interactions between at least three species: the pathogen and two hosts, one of which is human and the other a non-human (vertebrate) animal. More than 60% of human infectious diseases are zoonotic, and many have a wildlife host. Urbanisation and human population growth have increased the demand for food and land resources, which have increased interaction between humans, domestic animals and wildlife and thus the potential for cross-species transmission of infections. Most studies of such systems take place in tropical and developing countries where population change and biodiversity makes the emergence of high profile infections (eg Ebola and SARS) more likely. This study, however, focuses on four well known infections within the UK: bovine tuberculosis, water-borne cryptosporidiosis and giardiasis, and campylobacteriosis. The aim of this study was to investigate, using four infectious diseases of economic and public health importance in the UK as study systems, the role of wildlife in the epidemiology of multihost, zoonotic infections. Bovine tuberculosis (bTB) is an important zoonosis in many parts of the world, but human infection is rare in the UK owing to a policy of 'test and cull' in cattle and pasteurisation of milk. However, there has been an epidemic of bTB in British cattle in recent decades, the control of which is complicated by infection in badgers (Meles meles) and controversy over the control of wildlife infection. I investigated TB in badgers in the Cheshire area, located on the edge of the epidemic in England, in collaboration with various stakeholders. Using a road-kill survey, I found M. bovis in 20 of 94 badgers: the estimated prevalence of 21.3% (95% CI 14.2-30.6) is comparable to the county-level prevalence found at the core of the epidemic. That all isolates were spoligotype SP25, suggests this is an expansion of infection from neighbouring counties. The directionality of any cross-species transmission of bTB between wildlife and livestock cannot be ascertained from this project. However, it showed that using road-killed badgers is a valuable approach to sampling, especially if combined with the engagement of stakeholders. Cryptosporidium spp and Giardia duodenalis are protozoa that can cause diarrhoea in many mammals including humans. Llyn Cowlyd, a major water reservoir in North Wales, had seen annual summer peaks of uncharacterised Cryptosporidium spp cysts, without human disease. My study aimed to determine the source(s) of the contamination and to investigate G. duodenalis in the same system. Water samples were collected from the reservoir and feeder streams, and faecal samples from livestock and wild rodents. In total, 97 rodents were sampled: 35 (35.7% CI 95% 26.9-45.6%) were positive for Cryptosporidium spp. and 11 (11.2% CI 95% 6.4-19%) for Giardia spp. Of cryptosporidia detected, 55% were novel genotypes and only 5% C. parvum (zoonotic). Of 11 livestock samples, only two samples were positive for C. parvum and G. duodenalis. All the rodent Giardia belonged to an apparently novel assemblage while livestock Giardia belonged to non-zoonotic assemblage E. The water samples contained C. ubiquitum, C. parvum, and G. duodenalis assemblages E, A (zoonotic), and the novel rodent assemblage. Campylobacter jejuni and C. coli, are common causes of diarrhoeal disease in humans. Infection is common in a wide range of livestock and wildlife species, usually, however, without disease. The aim of this study was to investigate the potential role of wild birds in the epidemiology of campylobacteriosis on dairy and poultry units already studied in depth as part of a larger research programme. In total, 299 birds were sampled and 14 (4.7% CI 95% 2.8-7.7%) were positive for C. jejuni. Multi-locus sequence typing showed each isolate to be different, and many of these sequence types found in wild birds have not been associated with human disease. Overall, these results show that while at first sight wildlife might be assumed to be potential sources of zoonotic infections, further characterisation of the agents involved often revealed separate cycles of infection in wildlife, livestock and humans.