Joining the dots between climate change, livestock systems and zoonotic disease in Tanzania
The year 2020 underlined the importance of tracking emerging diseases. Funded research, led by the University of Glasgow, found new links between climate change and zoonoses, along with significant human health, social and economic impacts. This new understanding allows policymakers and researchers to recalculate disease risks and adjust health interventions for farming populations.
BBSRC, along with the Defence Science and Technology Laboratory (DSTL), Foreign, Commonwealth and Development Office (FCDO), Economic and Social Research Council (ESRC), Medical Research Council (MRC), and Natural Environment Research Council (NERC) funded the Zoonoses and Emerging Livestock Systems (ZELS) research initiative.
ZELS supports interdisciplinary research on zoonotic diseases in low to low-middle income countries, specifically focusing on the transmission of diseases between livestock species and humans.
- New data enables policymakers to detect and respond to changes in disease transmission.
- Identified that a shift from farming cattle to sheep or goats in pastoral communities was triggered by climate uncertainty and land-use policies.
- Highlighted the potential for health and economic issues, such as the emergence of new diseases, from the livestock change.
- Found that the disease ormilo caused 25% of sheep and goat losses.
- Implemented a successful public engagement campaign, raising awareness of simple behavioural measures to prevent the transmission of one disease, ormilo, and opening communication channels for other zoonotic and livestock diseases. Better disposal of contaminated materials increased over the next year, plus a decrease in reported cases of ormilo.
- Identified a Rift Valley fever (RVF) outbreak in an animal host in a new geographical area, which was linked with climate change, enabling health officials to plan interventions, and highlighting the area for future research. Increased extreme rainfall and mosquito adaptation to urban areas could increase the population that is affected by RVF.
- Earlier research (BACZOO) built pivotal infrastructure, research partnerships and relationships with policymakers, essential for developing effective health interventions.
- Over £500,000 of further funding for the ‘Operationalising One Health Interventions in Tanzania’ (OOHTZ) follow-on ZELS project, which aimed to co-develop suitable interventions for preventing human and livestock diseases.
Following the causes of fevers
The SEEDZ (Social, Economic and Environmental Drivers of Zoonoses) project was based in Tanzania and focused on three zoonotic diseases: brucellosis, Q fever, and Rift Valley fever (RVF). ‘Zoonotic disease’ (or ‘zoonoses’) are infectious diseases that occur when a pathogen, like a virus or a bacterium, ‘jump’ from an animal into humans. As well as threatening human and animal health, zoonoses affect livestock productions, causing economic and social harm to communities.
Building on over a decade of research within the sector, SEEDZ investigated the environmental, social, and economic drivers of change in Tanzanian livestock systems, such as the increasing frequency of droughts or the conversion of rangeland into cropland. By tracking these changes, SEEDZ aimed to understand whether and how these changes affected the risk of zoonotic livestock infections and, in turn, how those zoonotic infections related to human disease and wider social and economic impacts.
“In Africa 10 years ago, almost every fever was considered to be malaria. Even though malaria has been declining, fever is still a very common presenting syndrome,” explains Professor Sarah Cleaveland, the principle investigator who led the SEEDZ study. “Colleagues at the Kilimanjaro Christian Medical Centre set out to do a study on what is causing fever1,2. They found about 60% of people seriously ill with fever were clinically diagnosed with malaria, but less than 2% actually had malaria. A third of the illnesses were caused by zoonotic infections linked with livestock, including Q fever, brucellosis, and leptospirosis.”
As a precursor project to SEEDZ, Sarah and colleagues had set up an earlier zoonosis study – BACZOO (The impact and social ecology of bacterial zoonoses in northern Tanzania3). BACZOO was jointly funded by the BBSRC and National Institute of Health (NIH), through the Ecology and Evolution of Infectious Disease Programme. BACZOO investigated the transmission of Q fever, leptospirosis, and brucellosis and was fundamental in creating a platform for the later ZELS projects. It established pivotal internal and external partnerships, built physical infrastructure with the establishment of a zoonoses lab and was key for engaging policymakers from the ministries of Tanzania, allowing for the development of ideas and the translation of findings into change on the ground.
Dr Jo Halliday was a postdoctoral researcher on the BACZOO project, later leading a ZELS-funded sister project to SEEDZ that focused on the transmission of brucellosis. “These diseases are a big concern for both human health and livestock productivity,” Jo says. “In choosing to work on these specific zoonoses, we wanted to focus our efforts on those diseases where interventions are available.”
Too hot to survive
The increasing frequency and duration of droughts and extreme weather in East Africa is widely documented4,5.
“There's a very large livestock population [in Tanzania], and a large proportion of people in the country are heavily dependent on livestock,” Sarah says, as she explains how extreme weather plays a role in Tanzanian livestock systems.
“When droughts occur, they now persist for longer and have huge impacts on livestock, particularly on cattle which are less able to survive droughts than sheep or goats. There’s also been a large-scale shift from rangelands to croplands. Pastoral people are becoming increasingly constrained in their access to grazing land, and this has been exacerbated by land-use policies. As a result, people who would preferentially keep cattle are now shifting to a reliance on sheep and goats. Today cattle have much less access to high-quality grazing land than in the past and struggle to survive the long periods of drought – it is a stark reality in these communities that when livestock die, people go hungry and die.”
“Our research shows why an interdisciplinary approach is so valuable,” Sarah adds, “because you can draw on different perspectives. Key insights have come from social science and community-based research, which reinforced our understanding of the links between climate change in East Africa and changes in livestock management systems.”
For the Maasai in Tanzania, cattle hold a fundamental cultural significance. Cattle are the centre of Maasai life, with “birth, daily chores, division of labour, and rituals of maturation and marriage [revolving] around livestock”6.
“You now see changes in Maasai communities because the livestock production base is insufficient to meet food needs,” highlights Sarah. “Land management and ecosystem health is a very complex problem, particularly in areas close to wildlife protected areas. It’s one reason why we need an interdisciplinary outlook and systems thinking. You can't tackle the issue by focusing on a single idea from a single sector – for example, improving livestock production, supporting human health, supporting agricultural development or wildlife conservation. In terms of what’s prioritised for policy, there will be a few win-wins but not many. Mostly there will be trade-offs.”
Changing livestock, changing diseases
“When you see changes in host species, such as going from cattle to sheep, and changes in the way they’re moved and managed, you are very likely to see changes in the risk of disease transmission,” says Sarah, “we need to be prepared to detect and respond to those changes.”
During the study, the SEEDZ team flagged a disease, locally named ‘ormilo’, which causes brain cysts. “It’s a well-known small ruminant disease to vets, but nobody had any idea of the scale and its importance,” Sarah explains. “We confirmed that the vast majority of these cases are caused by the parasite Taenia multiceps, causing massive losses - 25% of sheep and goats on average. We don’t know yet if it is an important human health problem, but it is a really important livestock disease and food security issue.”
The team developed a public engagement campaign for ormilo, advising livestock owners not to feed sheep brains to their dogs, preventing the spread back to sheep via dog faeces. Sarah describes its success: “The communities were already concerned, so it was fairly straightforward to engage with them and introduce behavioural interventions, such as the safe disposal of infected materials. We could show them the cysts, what’s causing the sheep to run around in circles – it makes sense because it’s visible. Word spread throughout the communities quickly.”
After the engagement campaign, the SEEDZ team found an increase in brains being burned instead of fed to dogs, plus a decrease in reported cases of ormilo, over the course of a year.
“With this information, people can make sense of the disease and be empowered to think about ways they can more safely dispose of infected materials. Then we can start communicating about other diseases (including those that are zoonotic) associated with small ruminants and cattle that might be transmitted through handling placental or foetal material.”
Heavy rain and dangerous impacts
“Rift Valley fever is very clearly linked with high exceptional rainfall, and Q fever is associated with temperature, rainfall, wind patterns, and tree cover,” says Sarah.
Heavy rain and flooding cause a massive increase in mosquitoes, which carry RVF and spread the virus to livestock. Humans become infected by either interacting with livestock, such as handling foetal material, or by mosquito bites. RVF epidemics are characterised by high rates of cattle abortion and nearly 100% mortality in new-born cattle. In humans, RVF can cause an influenza-like illness, a haemorrhagic fever with liver issues, encephalitis, and vision damage7.
“For the first time, we detected an outbreak of RVF in a peri-urban area of Tanzania – where rural country meets the urban city outskirts,” Sarah highlights. “It's normally associated with pastoral cattle or small ruminants, but this one was in dairy cattle. We also found the infection in milk, which is significant because public health guidelines do not often highlight milk consumption as an important risk factor for human infection. Human outbreaks are being missed because it’s a non-specific fever – we picked up on it because we were investigating livestock abortions. Climate change is likely to be an important factor. As we get more extreme periods of rainfall, we can expect more outbreaks to occur, and as the mosquito vectors adapt to urban habitats, the populations at risk are also likely to expand.”
Following through with interventions
The SEEDZ team was awarded over £500,000 for the Operationalising One Health Interventions in Tanzania (OOHTZ) ZELS project, led by Jo and Sarah, which aimed to build on SEEDZ findings.
In terms of next steps, both Jo and Sarah emphasise the need for longitudinal data studies for disease surveillance: “The bottom line is we have way too little rigorous information on disease burden. Once we start doing decent diagnostics, we’ll find more unexpected disease problems. We need more initiatives to generate that data.”
|37 days||average decrease in the ‘long rain’ period in Tanzania, between 1960 and 20108.|
|25%||of sheep and goats killed due to ormilo.|
|Up to 100%||mortality rate for ruminant new-borns due to Rift Valley fever.|
|Up to 79%||of rural household income lost due to cattle, sheep, and goat deaths9.|
“Prevention of emerging zoonoses is a tough sell because it’s hard to show that investments have been effective. If we do invest in preventive measures that focus on endemic diseases, the worst that can happen is we save human lives, reduce disease burden, and increase livestock production. At best, you’ll build the capacities and relationships needed to detect and prevent the onward spread of a significant new disease problem so that it can be contained more quickly.”
- Crump JA, Morrissey AB, Nicholson WL, Massung RF, Stoddard RA, et al. (2013) Etiology of Severe Non-malaria Febrile Illness in Northern Tanzania: A Prospective Cohort Study. PLOS Neglected Tropical Diseases 7(7): e2324.
- Hertz, J.T., Munishi, O.M., Sharp, J.P., Reddy, E.A. and Crump, J.A. (2013), Comparing actual and perceived causes of fever among community members in a low malaria transmission setting in northern Tanzania. Trop Med Int Health, 18, 1406-1415.
- Gathering the puzzle pieces: the impact and social ecology of bacterial zoonoses in northern Tanzania (BACZOO)
- Kihupi, N., Tarimo, A., Masika, R., Boman, B. and Dick, W., 2015. Trend of Growing Season Characteristics of Semi-Arid Arusha District in Tanzania. Journal of Agricultural Science, 7(9).
- Pathways to Resilience in Semi-arid Economies (PRISE), Centre for Climate Change Studies (CCCS), University of Dar es Salaam, Tanzania., 2015. Tanzania: Country situation assessment, working paper [online].
- Quinlan, R. J., Rumas, I., Naiskye, G., Quinlan, M., & Yoder, J. (2016). Searching for Symbolic Value of Cattle: Tropical Livestock Units, Market Price, and Cultural Value of Maasai Livestock. Ethnobiology Letters, 7(1), 76–86.
- GERDES, G., 2004. Rift Valley Fever. Revue Scientifique et Technique de l'OIE, 23(2), pp.613-623.
- de Glanville WA, Davis A, Allan KJ, Buza J, Claxton JR, et al. (2020) Classification and characterisation of livestock production systems in northern Tanzania. PLOS ONE 15(12): e0229478.
- Ahmed, Haseeb & Yoder, Jonathan & De Glanville, Will & Alicia, Davis & Kibona, Tito & Mmbaga, Blandina & Lankester, Felix & Swai, Emmanuel & Sarah, Cleaveland. (2019). Economic burden of livestock disease and drought in Northern Tanzania. Journal of Development and Agricultural Economics. 11. 140-151. 10.5897/JDAE2018.1028.