I was really excited when, a few years ago now, an opportunity arose for me to work on an interdisciplinary project looking at bats and zoonotic disease(diseases that go from animal to humans).  The truth was that I was more excited about the bats than the zoonotic disease stuff.

I’ve always loved bats for their soft, velvet touch, tiny faces full of expression and translucent wings. I also love their mystique and their anthropological symbolism.

Anthropologically, bats are anomalous and liminal animals. They are not easy to categorise: they look like mice but fly like birds; they are social but occupy the night. I had one of the best times in my anthropological career when I was invited to spend a night catching and tagging bats in Ghana.

Working with an interdisciplinary team, I came to learn much more of the many diseases harboured by bats (perhaps I will never again have the opportunity to go bat catching and to handle bats with the same naked enthusiasm). In the social science research on bats and zoonotic diseases (as I did actually have to do some anthropology and wasn’t able to convert to a full-time bat catcher), we focused on bat-human interactions and the policy implications thereof.

Disease spillover

The interactions between humans, domestic animals and wildlife are, in my view, the critical nexus where the scope for disease spillover occurs and, potentially, where a solution might lie. In my conceptualisation of animal-human interactions I focused on immediate, physical interactions – moments when humans and bats came together (men hunting bushmeat; kids playing with bats; families living in close proximity with bats), and in times and spaces where humans came into contact with bats’ bodily fluids or faeces (cleaning bat droppings off the car, eating fruit previously bitten by a bat).

Cast forward a few years, and I’m lucky enough to be involved in another interdisciplinary zoonotic disease project. This time it’s in Tanzania and I am focusing on cattle and pastoralists.

Now cows aren’t bats. And I can’t say that I have always loved cows. But, they are beautiful and regal (and, in Tanzania, a little bit scary).

And like bats, cows have important anthropological significance: in Southern Africa, where I grew up, cows are used for bridewealth, for establishing and solidifying social relationships, for determining lineages and for livelihoods. Similarly in Tanzania, where Maasai cattle are critical for establishing marriage relations, they bring children into lineages and have religious significance.

Working in Tanzania, and thinking about zoonotic disease, has made me realise just how complex animal-human interactions can be. I have come to realise that my focus – my own inbuilt bias – emphasised live human beings interacting with either live or dead animals, or with the bodily products of those animals, in a kind of one-to-one relationship. In my head, all these people were villagers or ordinary people going about their normal lives (my anthropological bias coming to the fore). For me, for a zoonotic disease to occur, a human had to interact with an animal that was sick or with the bodily fluids of that animal.

Rethinking animal-human interactions

But attending a workshop in Tanzania, in which vets, geographers, epidemiologists, modellers and more came together to discuss zoonotic diseases forced me to reconceptualise human-animal interaction in relation to zoonoses. It led me to start thinking about the many different ways in which animals can get sick and how human behaviours – often unseen and apparently unconnected – can affect animals’ states of health and the potential for human infection.

I came to realise that I hadn’t really considered how chains of interactions could occur between humans and animals, and nor had I considered the ways in which human-animal interactions could involve a microbial dimension or, if you will, microbial-animal–human interactions.

My work with others on fruit bats had already alerted me to the ways in which in Bangladesh, Australia and elsewhere bats roosting or eating fruit above domestic animals (horses in Australia, pigs in Bangladesh) can cause illness in these animals which can, in turn, infect humans. In some instances, perhaps exemplified in peri-urban environments (i.e. those at the interface between town and country) where wild and domestic animals are often in close proximity, people may not always be aware of the animal-to-animal-to-human interactions that are occurring.

Exactly which animals are interacting with other animals also affects the disease dynamics and which pathogens are involved. For example, fruit bats carry Henipaviruses which can be transmitted to pigs, horses (and humans) but other bats do not; similarly, foot and mouth disease affects ruminant wildlife and livestock, but not carnivores. Brucellosis affects many different animals – buffalo, cattle, pigs, sheep – and there are many different species of Brucella, with goats being associated with the most pathogenic of these species.

Movement and social networks

Movement and transportation offer further scope for understanding interactions and affect the possibility of infection. Transporting animals (sick and healthy) is significant as it can allow diseases to ‘jump’ across time and space, and markets play a key role. Here the length of time the animals are together is significant: for bovine tuberculosis short contacts at markets are not important, but foot and mouth is highly contagious even over brief contact periods.

The effect of movement is also influenced by the social networks of the livestock owners, both in terms of who these owners come into contact with and in terms of who they exchange animals with. And some livestock owners may act as ‘super spreaders’ by having a large number of networks and frequent interactions with many different people.

Thus, indirect human-to-human interactions completely removed from the animals themselves can shape how human-animal interactions take place.

The microbial dimension

Another dimension, although surely not the last, occurs at the level of microbial-animal-human ‘interactions’ and food-borne zoonotic diseases such as non-typhodial Salmonella and Campylobacter. Here, abattoirs, slaughter practices and cooking habits are particularly relevant as these diarrhoea-causing bacteria live on the skin and in the guts of animals.

Factors such as how an animal is slaughtered come into play: does, for example, raw meat come into direct contact with skin or faeces when a knife penetrates the intestines? But these bacteria could equally well live independently of animals – on knives, cutting surfaces, in the vehicles used to transport meat, on human hands – and can in this way infect both humans and animals. So microbial-human ‘interactions’ have a role to play too in considering zoonotic disease infection.

Now microscopic bugs are not cute, aren’t regal and don’t have an important symbolic role in anthropological literature. But isn’t it fascinating how many different kinds of interactions shape whether or not zoonotic disease infection occurs?

Having to think well beyond immediate face-to-face, physical interactions between humans and animals opens new horizons on how we conceptualise Livestock, Livelihoods and Health and in terms of how we respond to zoonotic diseases. Which reminds me: my role in this interdisciplinary project is to focus on policy understandings of zoonotic disease. I wonder what conceptualisations of animal-human interaction underlie current zoonoses-relevant policies in Tanzania?

Dr Linda Waldman is a Research Fellow at the STEPS Centre (Institute of Development Studies/University of Sussex).

Article originally appeared on the Livestock, livelihood and Health website on 30th March, 2016 authored by Dr Linda Waldman. Available at: http://livestocklivelihoodsandhealth.org/blog/musings/