Bats attract many unflattering myths, but one aspect is true: the diseases they carry are extremely virulent. Still, Cara Brook, a disease ecologist who spends two to three months a year in Madagascar, loves her fruit bat subjects. By studying bat viruses, she is able to protect both them and us.
Brook began work in UC Berkeley’s Department of Integrative Biology this past July. She spoke with writer Alexander Rony about the importance of her work.
I came to Berkeley in 2017 as a Miller Fellow. As soon as I found out that I'd been offered the fellowship, I had no doubts that I was going to take it and come to Berkeley. I'm from Sonoma County, and I was excited about the idea of coming home.
I was excited about the idea of coming home. Berkeley is a beautiful place, very integrated into the natural world, which is also attractive to me. There is so much potential when you walk on campus. You feel like there are opportunities to accomplish anything and everything. There are so many different brilliant people doing so many different things. If you know where to look and who to ask, you can find just about everything at UC Berkeley.
I'm what we call a disease ecologist. Ecology is the study of the interactions of organisms with each other and their environment. Disease ecology adds parasites and pathogens to the mix.
We study three species of fruit bat that act as reservoir hosts for viruses that can infect people. These bats are consumed as human food, so they pose risks for zoonotic exposure. By understanding these processes, we build knowledge about the mechanisms that underpin transmission, how these viruses are maintained in their wild hosts, and what predisposes them to spill over to the human population.
As a part of that, we end up having to do a fair amount of virus discovery. Before we can ask about transmission mechanisms, we need to understand what is actually out there. Zoonoses emerge frequently — often from viral families that are known — but the pathogen itself that spills over is unique. SARS-CoV-2 is a perfect example. We've known that there is risk of recombination within the SARS virus clade for many years — certainly since SARS-CoV-1 — and yet, we still lack a basic understanding of how those pathogens are maintained in their wild hosts. By studying novel viruses in wild systems, we prepare ourselves for future pandemic risks.
My group is focused on the establishment of a vaccine in wild bats to eradicate potentially zoonotic henipaviruses prior to human emergence. We vaccinate dogs to prevent rabies, thereby protecting humans. This is something we could undertake more broadly in other wildlife-borne pathogens. If we could remove viruses that have zoonotic potential from the wild bat reservoir, then we would mitigate the risk of spillover to the human population.
I always emphasize not to blame bats. Bats shed viruses at the highest rates when they're nutritionally compromised and environmentally stressed, so land conversion and hunting actually exacerbate our zoonotic risk. Some communities implemented culling efforts in response to COVID-19. Basically, when you cull part of the population, more pups survive the next year, and they have not yet seen infection, which actually can accelerate the transmission of some viruses.
One of the more exciting aspects of moving to Berkeley is that they built us a tissue culture space. So we are able to do virus experiments in bat cell lines. For example, we have an ongoing project to understand the features in bat immune systems that might select for the evolution of high replication rates and viruses that would be likely to cause pathology in humans.
I did lose two supplemental awards this spring that were funding students who came from diverse, low-income backgrounds. I lost about half a million dollars in direct costs. I'm continuing to support those researchers through other funding mechanisms, but it is an extremely challenging environment for any early career researcher.
I have a Ph.D. student who's studying HIV transmission in Madagascar. It's been reported as under one percent prevalence, but there hasn't been a national prevalence study in over a decade.
We were approached by USAID a couple of years ago. They were hoping that Madagascar would qualify for PEPFAR [President's Emergency Plan for AIDS Relief] status, and they wanted quantitative estimates of the burden of HIV in Madagascar. One way to accomplish that with limited surveillance is through genomic sequencing. When I brought in this student to work on this project, I remember thinking that there would always be funding for HIV in Africa, and that is so far from the truth in the current environment, which is quite tragic. Any kind of international work is threatened.
One other project has impacted a close collaborator. Brian Fisher is an entomologist at the California Academy of Sciences. We inaugurated a lab adjacent to the zoo where we're building this captive bat colony, and we'll do all of the associated molecular work in this space.
He became involved in farming crickets for insect protein powder and giving that protein powder to schools to prevent malnutrition. We were in the process of applying for a project that links his work with zoonosis. We were hoping to do an intervention experiment where we distributed this protein powder; the idea being that a protein supplement could limit human consumption of wildlife, thereby promoting wildlife conservation and minimizing zoonotic risks. Given that their efforts were USAID-funded, they are on pause right now. I think that project is dead in the water until things change.
We have a few things in our favor. Our tools for scientific collaboration are much stronger. Globally, the COVID pandemic stimulated a whole host of pathogen genomic sequencing efforts across low- and middle-income countries. My group was involved in building the first Illumina sequencing platform on Madagascar, and several other African countries have adopted pathogen genomic sequencing capacities that were nonexistent prior to the emergence of SARS-CoV-2.
Spillover pandemic preparedness is more a question of public health infrastructure and political will, and it requires international collaboration and policy-sharing at an administrative level. It's one of the reasons I'm interested in pre-pandemic preparedness efforts. Can we prevent spillover prior to human emergence that takes out the political question? Once a virus spills over into a human population and is already spreading, then that's left up to governments and public health agencies to control. But if we avoid that outcome from the beginning through some effort like wildlife vaccination, then that becomes a non-issue.
It's a challenging field to work in. One is never recognized or rewarded for the absence of something happening. There's no way to be certain that you prevented a future pandemic.
So I think we are better prepared for future pandemics. We have some infrastructure in place. We could respond quickly and effectively, but it's going to require political will and organization to implement. If that is not there, we are going to be in just as dire, if not worse, of a situation.
I'm excited to be back and to work with Mike Boots again. Why infections cause disease is a deep question in evolutionary theory. The focus of my work is on bats as reservoirs for zoonoses. They host viruses that cause the highest known case fatality rates of any mammalian zoonosis. Working with Mike was an opportunity to dig into the theoretical underpinnings of that. It was a natural fit.
In addition, there are a number of people with whom I collaborated with as a postdoc. Peter Sudmant is a faculty member in integrative biology. He studies the genomics of aging. Bats are some of the longest lived mammals for their body size, and we think that a number of their mechanisms to prevent aging-related disease correspond to tolerance of viral infection.
José Pablo Vázquez-Medina studies oxidative stress and metabolically active animals. Marine mammals are his specialty, but he's also interested in flying organisms and bats, so I'm excited to interact with him. There are a number of people from the disease ecology world. Britt Koskella, Charlie Whitaker, and Tierra Smiley Evans were recently hired.
It's going to be a great, collaborative environment.