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Social networks predict microbial transmission pathways in free-ranging giraffes in Kenya

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Sometimes research requires a bit of dirty work. Kim VanderWaal collected giraffe droppings to map disease transmission patterns in wildlife.

Aug. 2013

Tracking the spread of disease in giraffes is more challenging than guessing which sniffling kid from preschool passed along their cold to your child. But the role of social networks in wildlife disease transmission isn’t all that different from humans, as Kim VanderWaal discovered during her recent PhD research.

As a doctoral student in the interdisciplinary Animal Behavior Graduate Group, VanderWaal focused on a tower (as groups of giraffes are called) of about 200 individuals at Ol Pejeta Conservancy in Kenya to develop ways to map disease transmission patterns in wildlife. Basically, her goal was to determine how pathogens might spread from one individual to another in wild African herbivore populations. 

She answered this question by focusing her approach on commensal E. coli (a species of bacteria found in an animal’s gut) as a proxy for pathogen spread. Researchers inferred who was transmitting E. coli to whom based on which giraffe shared E. coli with the same DNA ‘fingerprint’; Animals sharing E. coli were interlinked in a “transmission network”.

By following giraffes in a Jeep and waiting for them to poop, VanderWaal was able to collect fresh fecal samples from approximately 200 giraffes. After months of observation, VanderWaal knew each individual by name and appearance (all giraffe have unique spots), where their home ranges were located (spatial network), and which other giraffe they tended to spend time with (social network). Using these behavioral data, she explored how social networks and patterns of space use predicted the transmission network. 

Results of this study in the Journal of Animal Ecology, showed that individuals who were social “hubs” (had a large number of connections to others in their social network) also were hubs in the transmission network, which means that they have great potential to be “superspreaders” of pathogens. In addition, individuals who served as social “bridges” between different cliques in the social network also tended to be bridges in the transmission network.

“This study is among the first to show, through the use of microbial genetics that the structure of transmission networks is closely correlated with social networks. Understanding the structure of transmission networks may allow us to selectively target individuals (or species in multi-species networks) for interventions in disease spread,” VanderWaal said.

Professor Brenda McCowan, a behavioral biologist with expertise in network science in the Department of Population Health and Reproduction who co-mentored VanderWaal, noted that this network approach for understanding disease transmission is crucial for pursuing the One Health perspective on how disease spreads among co-mingled human and animal populations either sharing the same environment or in close contact. Such an approach permits one to go beyond simple detection and begin to address critical questions about the processes that underlie disease transmission at multiple scales, allowing for the potential for intervention at key steps.

Additional UC Davis collaborators include Professor Lynne Isbell  from the Department of Anthropology who provided expertise in behavioral ecology; Professor Rob Atwill  from the Department of Population Health and Reproduction who provided expertise in medical ecology and epidemiology of infectious disease; and Professor Fushing Hsieh from the Department of Statistics who is an expert in computational mathematics.

The study was funded by grants from the National Science Foundation and several other foundations to Dr. Kim Vanderwaal, a list of which can be found in the upcoming publication in the Journal of Animal Ecology.

More images from the field. Photo credit: Kim VanderWaal

Kim VanderWaal had a little help in the field:

Brenda McCowan's lab is also part of the International Institute for Human-Animal Networks, which conducts research on the health, well-being and conservation of animals in managed environments. Visit their Facebook page here.

Trina Wood--Communications officer; 530-752-5257