By Lillian Parr and Michael R. Zarfos
Over the past three months, two African nations have experienced their first ever outbreaks of Marburg virus, a relative of Ebola, a hemorrhagic fever virus that according to the WHO has a case-mortality ratio of up to 88%. Equatorial Guinea and Tanzania have suffered 14 confirmed deaths combined, though the actual numbers are likely higher. The Marburg outbreak in Equatorial Guinea is the fourth largest ever recorded. While the source of the recent outbreaks is unknown, they are thought to have originated with the Egyptian fruit bat, a known reservoir of the virus. Scientists have emphasized that these outbreaks are part of a larger trend: the spillover of zoonotic diseases, which has been increasing in frequency at an alarming rate.
Because zoonotic diseases pose a significant threat to human health, a great deal of pandemic prevention research focuses on detecting and addressing emerging pathogens in regions at high risk for spillover.
Sampling and surveillance
Some of this research in regions at high risk of spillover focuses on sampling animals that often harbor zoonotic diseases (such as bats, pangolins, and raccoon dogs) to detect any anomalies or new viruses. Through these efforts, researchers hope to provide situational awareness and raise the alarm before a disease spills over into human populations. Researchers might then have a headstart in developing medical countermeasures and enhancing the safety of populations living close to the threat. There is, however, debate within the scientific and policy community about how much help advanced warning would provide, and whether it is possible to predict which viruses will pose a risk to humans through other means.
Another approach to pandemic prevention focuses on monitoring human populations living in high-risk regions. This work includes routine disease surveillance, such as wastewater sequencing, as well as sequencing of samples from patients presenting suspicious symptoms without a clear diagnosis. In this way, if a new virus emerges or re-emerges, it may be quickly detected and contained.
While surveillance in high-risk regions is a crucial component of pandemic prevention, it does not address the root causes of zoonotic disease outbreaks. Research suggests that habitat fragmentation, ecosystem degradation, land conversion, deforestation, and wildlife trade have all contributed to the steady increase in disease spillover over the past several decades. Climate change is also shifting some diseases into regions where they were previously absent.
The fragmentation or conversion of ecosystems for development, mineral extraction, and deforestation, all increase the chances of human interaction with wildlife that may carry zoonotic diseases. In the case of Marburg, some researchers have suggested that human-bat encounters within the mines and caves where this species likes to roost may have precipitated past outbreaks.
Wildlife harvesting and trafficking also create opportunities for contact among species that usually do not interact in the wild. Wildlife in unhealthy ecosystems—such as those stressed by overuse or pollution—may have weakened immune systems, leading to a higher rate of viral shedding. In these scenarios any interaction between a sick animal and another species is more likely to result in infection, giving the pathogen more opportunities to adapt to new hosts.
Conservation offers many benefits beyond reducing zoonotic spillover. First, it is a less invasive measure than some surveillance programs, which may require research teams to enter sensitive environments and interact with animals through sampling. Second, conservation of natural ecosystems preserves the services they provide to society. For example, intact forests help to manage water resources, reduce flooding or polluting runoff, and they sequester carbon.
It is, however, essential to consider the needs of communities engaged in ecosystem conversion and wildlife harvest before any conservation efforts are undertaken. Are people subsisting off wildlife? Are they making a living from activities that require deforestation? Are some of these practices a part of their culture and traditions? These and other questions of equity, food security, and economic opportunity need to be addressed in each community, with the community’s input, and while maintaining their agency.
These sociological and economic considerations are key to successful and respectful conservation interventions. For instance, a recent ProPublica article highlighted impactful work being done by a non-profit called Health in Harmony. This group encourages indigenous populations to halt deforestation and wildlife poaching. It seeks to understand why people rely on these activities, and helps them to fulfill their needs through alternative, more environmentally friendly means. It also employs locals to ensure community involvement throughout the intervention. This strategy has had quantifiable success in reducing deforestation and outbreaks of malaria and tuberculosis.
This is just one example of how conservation, disease spillover reduction, and other human health initiatives can work in concert. Unfortunately, programs like these often struggle to find funding, as many grantmakers focus exclusively on health or conservation. In reality, conservation and human health interventions work synergistically, and should not be siloed.
A holistic approach
Ultimately, pandemic prevention efforts would benefit from a more holistic approach that regards ecosystem health and human health as intrinsically linked. Protecting ecosystems and wildlife can reduce spillover frequency at the source, and also provide a host of other benefits to society. Conservation initiatives will be more successful where communities receive aid, investment, alternative sources of food, and opportunities for income. These ecological interventions should be coupled with monitoring of species known to harbor zoonotic diseases and surveillance of communities where spillover is likely to occur. These efforts will complement others to develop more robust therapeutics and vaccines, equitable distribution networks, powerful predictive models, and novel prevention technologies. It will take a cross-disciplinary, silo-busting global effort to prevent the next pandemic.
Post updated with edits: March 31, 2023, 10:15 ET