An evaluation of the influence of livestock movements on the transmission, spread and persistence of infectious diseases in northern Tanzania

Chaters, Gemma (2021) An evaluation of the influence of livestock movements on the transmission, spread and persistence of infectious diseases in northern Tanzania. PhD thesis, University of Glasgow.

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Abstract

In northern Tanzania livestock are heavily relied upon as a main source of income, social status and nutritional security, especially by those living in the most impoverished communities (Covarrubias et al., 2012; Government of Tanzania, 2017). The high dependence on livestock is accompanied by a high burden of infectious production-limiting and zoonotic pathogens circulating within the livestock population but poor access to veterinary services. Zoonotic pathogens can spill over to cause disease in people, which are often misdiagnosed and erroneously treated leading to worse patient outcomes (Crump et al., 2013; Zhang et al., 2016). For pathogens that cause disease in livestock alone, the economic returns from investing in disease control can far outweigh the costs (Jones et al., 2016). Improved livestock health and productivity is widely recognised as a route out of and away from poverty for people living in the most marginalised communities (Randolph et al., 2007). Funding and resources to invest in the livestock sector and livestock disease control are often lacking as the broad benefits to individuals, societies and economies are poorly documented and often overlooked (Rich and Perry, 2011; World Organisation for Animal Health (OIE), 2013). Policy makers need clear guidelines to develop efficient livestock disease control programmes that reduce livestock and zoonotic pathogen burden through minimal use of resources for maximal societal gains (FAO, 2009; Dutilly et al., 2020).

Livestock movements are widely recognised as providing a route to move pathogens between populations (Fevre et al., 2006). These movements can drive large epidemic outbreaks of disease and also provide opportunities for pathogens with relatively low R0 to persist in populations (Green, Kiss and Kao, 2006a; Prentice et al., 2017). Where dense comprehensive data on livestock movements is available, this can be used by policy makers to guide effective disease control programmes (Kao et al., 2006). However, information on livestock movements is not routinely collected and centrally recorded in Tanzania and is therefore not available to guide livestock disease control programmes.

Through this PhD, I gather and analyse data on three major types of permanent livestock movements in cattle and small ruminants across and beyond the Arusha, Manyara and Kilimanjaro regions in northern Tanzania. Permanent movements are those into or out of household herds and flocks with no plan to return the animal(s) to their origin. Using household survey data in conjunction with livestock serological data, market survey data and government movement permit data, I evaluate how livestock movements contribute to epidemiological connectivity and disease risk. Movements to and from households, including market movements go largely unreported in the study area but can cover long distances up to 300 km in a single movement. I use the data to construct networks of livestock movements and use concepts from network analysis to identify sub-village and ward locations that can be targeted with efficient disease control and surveillance interventions.

My analysis shows that high risk locations for disease introduction are also those at high risk of onward transmission, and that locations at high risk for small ruminant pathogen transmission are also high risk for cattle pathogen transmission. Additionally, I show that locations at risk of introduction and onward transmission of less transmissible pathogens (e.g. Brucella spp.) are also high risk for epidemic-prone pathogens (e.g. Foot and Mouth disease virus) that are rapidly transmitted. The positive correlations identified between locations’ risk ranks show that multi-species interventions which aim to prevent introduction and onward transmission of multiple pathogens could be an efficient use of disease control resources in northern Tanzania. Specifically, I show that household cattle introductions and sub-village betweenness are positively associated with cattle’s risk of bovine viral diarrhoea virus (BVDV) exposure and this risk is ubiquitous across the study area. For other pathogens investigated, the associations between introductions and exposure are complex and vary depending on pathogen and the agro-ecological (A-E) class of the livestock keeping system. This complexity is likely driven by the varying transmission routes and shedding cycles of different pathogens, in combination with the different livestock mixing and contact rates between infectious and susceptible individuals in the different A-E systems. Nevertheless, risk factors relating to household and sub-village livestock introductions are identified and can be used to guide disease control interventions in different settings.

I also identify that livestock market movements are most often made on foot with increased risk of these livestock contacting local non-moving livestock and creating opportunities for pathogen dissemination across the landscape. Frequently travelled routes to and from market are therefore also identified as areas where an increase in active surveillance would benefit both local livestock and animals moving into the market system. Findings from this work will be useful for policy makers in northern Tanzania who have minimal resources available to reduce livestock and zoonotic pathogen burden. High risk locations identified in this analysis can be made targets for knowledge exchange and information dissemination, active surveillance and multi-pathogen vaccination programmes. Additionally, the results from this study can be used to guide future research questions which address how temporary contacts between livestock from different herds and flocks might affect pathogen transmission in the area.

Item Type: Thesis (PhD)
Colleges/Schools: College of Medical Veterinary and Life Sciences > Institute of Biodiversity Animal Health and Comparative Medicine
Funder's Name: Biotechnology and Biological Sciences Research Council (BBSRC)
Supervisor's Name: Johnson, Dr. Paul and Kao, Professor Rowland and Matthews, Professor Louise and de Glanville, Dr. Will and Allan, Dr. Kathryn
Date of Award: 2021
Depositing User: Theses Team
Unique ID: glathesis:2021-82428
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 10 Sep 2021 15:12
Last Modified: 10 Sep 2021 15:12
Thesis DOI: 10.5525/gla.thesis.82428
URI: http://theses.gla.ac.uk/id/eprint/82428
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