The impact and social ecology of bacterial zoonoses in northern Tanzania

It is well recognized that zoonotic pathogens - agents which can lead to diseases that are transmitted from animal to human populations - predominate as the cause of emerging human diseases, but in the shadow of the high-profile emerging zoonoses, such as Influenza A H5N1 and SARS corona virus, zoonoses that are prevalent in localised areas have often been overlooked. However, awareness is growing that many of these localised zoonoses are responsible for a substantial burden of disease both in terms of public health and livestock health, and that these dual impacts contribute to perpetuating cycles of poverty in the marginalized communities that are most affected. In northern Tanzania, the location of this research, human diseases caused by three zoonotic diseases (leptospirosis, Q-fever and brucellosis) result in 11 times as many hospital admissions as malaria. However, almost nothing is known about transmission patterns among animal hosts, which host species are responsible for human disease, or the key behavioural determinants of human disease risk in different settings.

The aim of this research is to quantify the impacts of these three zoonoses in different communities (located at the edge of town, in agricultural landscapes and in pastoral areas) and to develop a predictive understanding of the impact of environmental and social relationships on disease risk. Specifically, they address infection and transmission patterns between animals and from animals to humans, ecological and social determinants of transmission, and the cultural, social, behavioural and economic and environmental dimensions of disease communication. The results of this work are directly applicable to policy and practice that is relevant to both public health and economic development related to livestock production.

With growing recognition of the widespread over-diagnosis of malaria in many parts of Africa, increasing attention is being given to other causes of human febrile illness. Preliminary studies in northern Tanzania indicate that febrile disease caused by the zoonotic diseases, leptospirosis, Q-fever and brucellosis, result in 11 times as many cases of febrile admissions as malaria. These pathogens can infect and be transmitted among a wide range of host species. However, almost nothing is known about transmission patterns among animal hosts, which host species are responsible for human disease, or the key social, economic and behavioural determinants of human disease risk in different agro-ecological settings. This study aims to address the overarching question: what are the origins and determinants of human disease risk for bacterial zoonoses? In addition, the research will determine how risk factors vary among different livestock-owning communities and explore the effectiveness of different control and prevention strategies in these communities. The project will integrate several different disciplinary approaches, including social behavioral studies, human febrile illness surveillance, and linked human-animal epidemiological studies (cross-sectional and case-control studies), to generate data for incorporation into models of human disease risk. These models, together with an understanding of community risk perception and knowledges, will allow us to identify appropriate strategies for disease control and prevention. The project brings together medical, social science, veterinary and ecology research groups working together to conduct the first integrated research into this group of bacterial zoonoses in Africa.

Leptospirosis, brucellosis and Q-fever comprise a group of bacterial zoonoses that occur throughout Africa, but have been neglected as a cause of human disease and livestock production losses. This interdisciplinary research will draw on medical, veterinary, social science and ecological expertise to generate valuable data on the impact and social ecology of these diseases in northern Tanzania, and will provide outputs that will inform the design of effective and appropriate disease control strategies for different communities. As such, the research will have wide-ranging impacts:

(a) The study will generate the first quantitative data on disease incidence and burden (DALYs) for human leptospirosis and Q-fever, and the most detailed data on the burden of human brucellosis in Africa, proving a valuable evidence-base for engaging with public health policy makers at national and international level about the importance of these diseases in Africa, which hitherto have been virtually ignored;
(b) Quantitative data on livestock infection prevalence in different communities will generate awareness about the relative importance of these diseases in different livestock-owning communities and thus allow livestock control measures (e.g. vaccination) to be targeted most appropriately;
(c) Data on the relative importance of different animal origins of human infection and different ecological and behavioral risk factors (through case-control studies and cross-sectional studies) will provide critical information for the design of control and prevention strategies in human populations, which will be evaluated through modeling;
(d) Qualitative data from social science approaches will provide critical insight for understanding how knowledges and perceptions in different communities affect disease risk, and how these may also affect the uptake of potential control strategies;
(e) These quantitative and qualitative outputs will directly assist in developing control measures that can be designed to suit the specific social and ecological context of different rural and peri-urban communities in Tanzania, increasing the likelihood that control strategies will be adopted by communities and that they will significantly improve public health and livestock production (where interventions in the animal population are implemented).
(f) Enhanced capacity for effective diagnosis of these diseases in human and livestock populations in Tanzania, and improved diagnostic awareness among clinicians will result in more rapid and effective treatment and management of these conditions and hence mitigation of disease burden.

Given the findings of preliminary studies, which suggest that the incidence of these bacterial zoonoses in northern Tanzania is likely to be high (exceeding malaria), the potential public health impacts of this research are likely to be substantial. Febrile illness is the most common reason for presentation to health facilities in much of Africa, therefore small improvements in diagnosis and management of febrile illness have the potential to lead to major health gains.

Conceptual knowledge and understanding will be enhanced by developing a genuinely inter-disciplinary approach, whereby social scientists and veterinary/medical scientists engage together on the same research objectives, rather than simply conducting a series of discipline-specific studies in parallel. An on-going, iterative process of knowledge exchange will further support this approach.

In addition to enhancing diagnostic capacity for zoonoses, the project will also support research capacity-building within Tanzania by providing scientific and technical training and mentorship for Tanzanian post-doctoral fellows, graduate students and laboratory technicians. Furthermore, the study will provide opportunities for developing new partnerships between regional research consortia to build an effective network for bacterial zoonoses research in East Africa.