Researchers found the association of habitat loss and the global emergence of infectious diseases

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Auburn University researchers have published a new hypothesis that could provide the foundation for new scientific studies looking into the association of habitat loss and the global emergence of infectious diseases.

They present their research in the paper, “The Coevolution Effect as a Driver of Spillover,” in the latest issue of the scientific journal, Trends in Parasitology.

“We provide a new perspective about how habitat loss can facilitate the emergence of infectious diseases in humans,” said Sarah Zohdy, assistant professor in the School of Forestry and Wildlife Sciences and the College of Veterinary Medicine, who coauthored the study with Tonia Schwartz and Jamie Oaks, assistant professors in the Department of Biological Sciences in the College of Sciences and Mathematics.

Globally, scientists believe habitat loss is associated with emerging infectious diseases, or EIDs, spreading from wildlife to humans, such as Ebola, West Nile virus, SARS, Marburg virus and others.

The Auburn team developed a new hypothesis, the coevolution effect, which is rooted in ecology and evolutionary biology, to explain the underlying mechanisms that drive this association.

Schwartz said the team integrated ideas from multiple aspects of biology, including disease ecology, evolutionary biology and landscape genetics, to develop the new hypothesis on why diseases are more likely to spill over from wildlife to humans in deforested habitats.

“We provide a testable hypothesis that we hope other researchers will try to test with their data, as we will be doing,” Schwartz said. “Whether or not these studies fully support this new hypothesis, we anticipate it will provide a new perspective that other researchers in this field can use and build on, to ultimately push this field forward to understand disease spillover and prevent it.”

New hypothesis links habitat loss and the global emergence of infectious diseases
Auburn researchers have published a new hypothesis, the coevolution effect, that could provide the foundation for new scientific studies looking into the association of habitat loss and the global emergence of infectious diseases. Pictured, forest fragments, as shown within Mangevo, Madagascar, act as separate coevolutionary engines to cause divergence in pathogens among fragments. This loss of habitat connectivity increases the probability that new variants will have zoonotic potential in other species, such as humans. Credit: Sarah Zohdy

The field of disease ecology is heavily based on a hypothesis known as the dilution effect, which was released at the turn of this century. 

It is essentially the idea that biodiversity conservation can protect humans from emerging infectious diseases.

Zohdy said the dilution effect highlights the critical role that wildlife conservation can play in protecting human health and has transformed the understanding of zoonotic infectious diseases.

However, until now, even after a wealth of research in the past few decades has explored that hypothesis and found associations between the loss of biodiversity and EIDs, there has been no explanation for where the microbes that cause EIDs come from and how they get to humans.

“Through our hypothesis, we propose that as humans alter the landscape through habitat loss, forest fragments act as islands, and the wildlife hosts and disease-causing microbes that live within them undergo rapid diversification,” Zohdy said

“Across a fragmented landscape we would then see an increase in diversity of disease-causing microbes, increasing the probability that any one of these microbes may spill over into human populations, leading to outbreaks.”

Oaks said he is encouraged that the research will impact the way these problems are perceived.

“Our paper introduces an evolutionary mechanism to explain the association between habitat fragmentation and disease spillover into human populations, which we hope will complement the ecological perspectives on this global health challenge,” he said.

School of Forestry and Wildlife Sciences Dean Janaki Alavalapati said the paper’s findings are compelling.

“Dr. Zohdy and her fellow researchers provide noteworthy insights in the field of emerging infectious diseases and the driving forces behind them,” Alavalapati said. “Their findings could result in a significant shift in the way the origins of these diseases are perceived.”


Detecting, reporting, and responding to significant public health events occurring in areas where the public health system is unable or unwilling to report the event to appropriate public health authorities is a constant challenge for those monitoring global disease activity.

To better track public health events in these situations, agencies can conduct event-based surveillance, which is defined as the organized collection, monitoring, assessment, and interpretation of unstructured information regarding public health events that may represent an acute risk to human health.1 

When conducting event-based surveillance, information can be collected through formal channels, such as already-established public health surveillance systems; in such instances, event-based surveillance can be complementary to indicator- or case-based surveillance systems that collect information on individual cases rather than events. Event-based surveillance can also be conducted through informal channels, such as through monitoring media reports, blogs, or even social media.

Because events reported through informal channels commonly involve unconfirmed media reports, they must be verified before any action is taken.

In 2004, the US Congress authorized an appropriation of funding to establish a global disease detection program based at the Centers for Disease Control and Prevention (CDC), and in 2007, the Global Disease Detection Operations Center (GDDOC) was created to serve as CDC’s platform dedicated to conducting worldwide event-based surveillance.

Surveillance, including event-based surveillance, is now being highlighted as part of the “detect” element of the Global Health Security Agenda (GHSA), launched in 2014, which works toward making the world more safe and secure from disease threats through building capacity to better “Prevent, Detect, and Respond” to those threats.

Capacity to “detect” disease threats is built by establishing and strengthening global networks for real-time biosurveillance; strengthening rapid, transparent reporting and laboratory sample sharing; strengthening laboratory systems; and deploying an effective biosurveillance workforce.2 

Facilitating detection is the Biosurveillance Indications and Warning Analytic Community (BIWAC), which is a self-organized, informal biosurveillance information-sharing group with participants from multiple US government agencies.

The BIWAC shares data via unsophisticated web interfaces (eg, password-protected internet interface) and has focused on interagency collaboration and partnership.3 

A key member of the BIWAC is the Armed Forces Health Surveillance Branch (AFHSB), which also houses the Global Emerging Infections Surveillance and Response System (GEIS).4 

Pre-dating the GDDOC, GEIS was created in 1997 to provide a mechanism in the Department of Defense (DoD) to centralize coordination of surveillance efforts conducted by the DoD, including outbreak response, epidemiologic training and capacity building, and the support of research and innovation in the US military and partner organizations.4 

The GDDOC has a team of 6 staff and a director with professionally diverse backgrounds, including epidemiology, microbiology, and human, veterinary, and tropical medicine; it is situated in dedicated space located in CDC’s Emergency Operations Center (EOC), with which the GDDOC liaises both during GDDOC-supported international deployments of CDC teams and also when the EOC is activated to respond to an international disease event.

The GDDOC monitors approximately 30 to 40 public health events each day and most closely watches those events that could develop into public health emergencies of international concern to which CDC may be asked to respond bilaterally by the country experiencing the outbreak, through the Global Outbreak Alert and Response Network (GOARN), or via both routes. Coordinated by the World Health Organization (WHO), GOARN is an independent collaboration of institutions and networks ready to respond to all-hazard threats of international importance.5

Typically, the GDDOC monitors outbreaks of infectious disease and, to a lesser extent, events involving other disease threats, including disasters, intoxications, and chemical, radiological, or nuclear events.

The GDDOC also monitors outbreaks of unknown etiology, many of which are later determined to have an infectious cause; outbreaks among animals are also monitored for known zoonotic diseases and are continually assessed to determine whether human cases are associated with a particular outbreak.6 

The GDDOC was created to alert CDC programs as soon as possible for the purpose of responding rapidly to mitigate the effects of an event, and, by conducting event-based surveillance, the GDDOC is able to better position CDC to respond earlier.

Through rapid information gathering, prompt verification, and timely dissemination of information, the GDDOC ensures that CDC is always prepared to respond. CDC response teams can deploy internationally within 24 hours of learning about an outbreak.

During large-scale, international outbreaks or other public health events, the GDDOC may monitor up to 70 public health events, in different countries, attributable to a single etiology.

For example, in November 2016 the GDDOC actively monitored 65 events, of which 29 were events describing autochthonously circulating Zika virus transmission in the Americas.7 When CDC’s EOC is activated for such an event, the GDDOC also becomes part of the incident management system (IMS), a temporary, formal organization structure that supports a response, is flexible to meet rapidly changing demands of the response, and then disbands once the response is over.8

The GDDOC’s specific role in the incident management system is to serve as part of an international task force (ITF), to facilitate the rapid sharing of outbreak-related information collected during event-based surveillance, which, when verified, assists in informing evidence-based decisions, including those directing how to best position CDC staff, funding, and other resources.

This report serves as an update to a previously published article, “What We Are Watching: Five Top Global Infectious Disease Threats, 2012:

A Perspective from CDC’s Global Disease Detection Operations Center,” published in 2013.6 

The 5 top potential threats of 2012 were based on subjective judgment, with input from CDC subject matter experts, regarding high transmissibility, disease burden, and severity; established or pandemic potential; disease eradication; and lack of available preventive or treatment interventions.

The 5 potential top threats were not selected on the basis of an analytical algorithm or quantitative method.

They were: avian influenza A (H5N1), cholera, poliomyelitis, enterovirus-71, and extensively drug-resistant tuberculosis, with addenda of MERS-Coronavirus and avian influenza A (H7N9), both of which were newly emerging. The same judgment was used to arrive at the top potential threats during 2013 to 2016, and the rationale for the selection of each is provided here. These threats have been attributed to recent or current outbreaks around the world, and future potential international outbreaks are not limited to those described in this article. Further, the GDDOC is continuously monitoring threats that could evolve into international outbreaks in the near future that would warrant placement in future updates to this report.


More information: Sarah Zohdy et al, The Coevolution Effect as a Driver of Spillover, Trends in Parasitology (2019). DOI: 10.1016/j.pt.2019.03.010

Journal information: Trends in Parasitology
Provided by Auburn University

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