What Is: Zoonotic Spillover

Scientific Frontline: Extended "At a Glance" Summary: Zoonotic Spillover

The Core Concept: Zoonotic spillover is the successful transmission of a pathogenic entity—such as a virus, bacterium, or parasite—from a non-human animal reservoir into a human population. This rare but consequential event occurs when a pathogen successfully crosses the strict biological boundary between species.

Key Distinction/Mechanism: Unlike regular endemic transmission, a zoonotic spillover is dictated by the "Spillover Barrier Model." A pathogen must overcome a hierarchical series of formidable biological and ecological obstacles. Spillover only succeeds when specific vulnerabilities across these barriers perfectly align in both space and time, allowing the pathogen to bind to human cellular receptors and evade immediate immune destruction.

Major Frameworks/Components:

• The Three Layers of Biological Barriers: The zoonotic reservoir layer (host density and distribution), the environmental and vector layer (pathogen persistence in abiotic conditions), and the recipient spillover host layer (human exposure, susceptibility, and cellular infection dynamics).
• Viral Shedding Dynamics: Pathogens are often excreted in discrete temporal and spatial "pulses" triggered by demographic shifts or environmental stress.
• Epidemiological Transmission Models:
• SIR (Susceptible-Infectious-Recovered): Seasonal epidemic cycles driven by natural host population fluctuations.
• SIRS (Susceptible-Infectious-Recovered-Susceptible): Cyclical circulation driven by waning immunity within a reservoir.
• SILI (Susceptible-Infectious-Latent-Infectious): Persistent infections triggered by stress-induced viral reactivation.

Bat-Borne Sarbecoviruses Spilled Over in Southeast Asia Pre-Pandemic

Elephant loggers bring in a timber harvest in Myanmar.
Photo Credit: Tierra Smiley Evans/UC Davis

Scientific Frontline: "At a Glance" Summary: Bat-Borne Sarbecoviruses Spilled Over in Southeast Asia Pre-Pandemic

• Main Discovery: A virus previously found exclusively in bats was detected in the antibodies of human populations in rural Myanmar, demonstrating that exposure to diverse sarbecoviruses, including strains closely related to SARS-CoV-2, occurred prior to the pandemic.
• Methodology: Researchers collaborated with local clinics to screen nearly 700 rural and urban residents for sarbecoviruses between July 2017 and February 2020. The surveillance relied entirely on human patient sampling, targeting individuals seeking medical treatment and healthy populations near elephant logging camps, without collecting direct wildlife samples.
• Key Data: Blood screenings revealed that 12 percent of the study participants possessed antibodies indicating past exposure to a sarbecovirus, though no active infections were found. Exposure was exclusively identified in rural residents, particularly those working in logging, hunting, or bat guano harvesting, which put them in direct proximity to bats.
• Significance: The results yield concrete epidemiologic and immunologic evidence that zoonotic spillover of bat-borne coronaviruses is actively occurring. The data strongly suggests that human intrusion into newly disturbed, biodiverse environments substantially elevates the risk of wildlife-to-human viral transmission.
• Future Application: The findings establish a baseline for developing targeted mitigation strategies and underscore the necessity of continuous viral surveillance at the human-wildlife interface in Southeast Asia. This reconnaissance approach will be utilized to predict and potentially intercept the future emergence of novel zoonotic diseases.
• Branch of Science: Virology, Epidemiology

Dog coronavirus jumps to humans, with a protein shift

N-terminus: The end of a peptide or protein primary structure in which the amino acid residue is not part of a peptide bond. The terminal group is often (but not always) an amine or ammonium cation.
Image Credit: Courtesy of Cornell University

Scientific Frontline: "At a Glance" Summary: Zoonotic Spillover of Canine Coronavirus

• Main Discovery: Researchers discovered a molecular shift in the N-terminus of the canine coronavirus spike protein, specifically the loss of the O-domain, which transforms the virus from a gastrointestinal and respiratory pathogen in animals to an exclusively respiratory pathogen in humans.
• Methodology: Scientists utilized advanced molecular evolution tools to evaluate natural selection pressures on the virus, comparing the genetic sequence of the canine coronavirus to related strains to identify the specific loss of the sialic acid-binding O-domain.
• Key Data: The modified canine coronavirus was initially identified in two Malaysian human patients with pneumonia between 2017 and 2018, and a similar variant was detected in Haiti in 2021, potentially marking it as the eighth known human coronavirus.
• Significance: The findings reveal a repeating evolutionary pattern of relaxed selection where coronaviruses lose their gastrointestinal binding capabilities to successfully jump to alternative hosts and establish respiratory infections.
• Future Application: Recognizing this tropism shift provides a critical framework for researchers to monitor the N-terminus domain of spike proteins, including in SARS-CoV-2, to predict, track, and potentially neutralize future zoonotic spillovers.
• Branch of Science: Virology, Evolutionary Biology, Veterinary Medicine
• Additional Detail: While the primary receptor for the Alphacoronavirus genus to enter human cells is APN, it is the degradation of the sialic acid co-receptor function within the O-domain that facilitates this specific transition to a human respiratory pathogen.

Can Artificial Intelligence Predict Spatiotemporal Distribution of Dengue Fever Outbreaks with Remote Sensing Data?

Image Credit: Sophia University
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Researchers train machine learning model with climatic and epidemiology remote sensing data to predict the spatiotemporal distribution of disease outbreaks

Cases of dengue fever and other zoonotic diseases will keep increasing owing to climate change, and prevention via early warning is one of our best options against them. Recently, researchers combined a machine learning model with remote sensing climatic data and information on past dengue fever cases in Chinese Taiwan, with the aim of predicting likely outbreak locations. Their findings highlight the hurdles to this approach and could facilitate more accurate predictive models.

Outbreaks of zoonotic diseases, which are those transmitted from animals to humans, are globally on the rise owing to climate change. In particular, the spread of diseases transmitted by mosquitoes is very sensitive to climate change, and Chinese Taiwan has seen a worrisome increase in the number of cases of dengue fever in recent years.

Like for most known diseases, the popular saying “an ounce of prevention is worth a pound of cure” also rings true for dengue fever. Since there is still no safe and effective vaccine for all on a global scale, dengue fever prevention efforts rely on limiting places where mosquitoes can lay their eggs and giving people an early warning when an outbreak is likely to happen. However, thus far, there are no mathematical models that can accurately predict the location of dengue fever outbreaks ahead of time.

Veterinary Science: In-Depth Description

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Veterinary Science is the branch of medicine and science concerned with the prevention, control, diagnosis, and treatment of diseases, disorders, and injuries in animals. Beyond clinical care, the field encompasses animal rearing, husbandry, breeding, research on nutrition, and product development. Its primary goals are to safeguard animal health, relieve animal suffering, conserve animal resources, promote public health through the control of zoonotic diseases, and advance medical knowledge through comparative medicine.

Research suggests deer could be a possible source of human infection

Douglas Watts, Ph.D., right, professor of biological sciences at The University of Texas at El Paso, and Pedro Palermo, manager of the UTEP Border Biomedical Research Center’s Biosafety Level 3 Infectious Disease Research Program laboratory, are authors of a study that proves for the first time that COVID-19 is present in white-tailed deer in Texas, a finding published recently in Vector-Borne and Zoonotic Diseases.
Photo: J.R. Hernandez / UTEP Marketing and Communications

Scientific Frontline: "At a Glance" Summary: Research Suggests Deer Could Be a Possible Source of Human Infection

• Main Discovery: White-tailed deer in Texas have been found carrying SARS-CoV-2 neutralizing antibodies, providing the first reported evidence of COVID-19 infection among deer in the state and indicating that the virus is widespread in this abundant wildlife species.
• Methodology: Researchers analyzed blood samples collected from male and female white-tailed deer of varying ages in Travis County, Texas, during the first two months of 2021, amidst the ongoing pandemic.
• Key Data: Evidence of SARS-CoV-2 neutralizing antibodies was discovered in more than one-third (37%) of the sampled deer, a prevalence rate comparable to the 40% rate previously identified in deer populations across states like Illinois, Michigan, Pennsylvania, and New York.
• Significance: The presence of COVID-19 in white-tailed deer expands the known geographical range of the virus in UTEP animal populations and suggests that deer could serve as a potential reservoir for the transmission of SARS-CoV-2 to humans, wildlife, and domestic animals.
• Future Application: Subsequent investigations will aim to further explore the mechanisms of COVID-19 transmission between humans and animals, helping to develop strategies that mitigate the risks associated with deer acting as a source of human infection.
• Branch of Science: Biology, Epidemiology, Virology

Novel Coronaviruses Are Riskiest for Spillover

A wildlife surveillance team member samples a bumblee bat for viruses in Myanmar.
Credit: Smithsonian Conservation Biology Institute

In the past decade, scientists have described hundreds of novel viruses with the potential to pass between wildlife and humans. But how can they know which are riskiest for spillover and therefore which to prioritize for further surveillance in people?

Scientists from the University of California, Davis created network-based models to prioritize novel and known viruses for their risk of zoonotic transmission, which is when infectious diseases pass between animals and humans.

Their study, published in the journal Communications Biology, provides further evidence that coronaviruses are riskiest for spillover and should continue to be prioritized for enhanced surveillance and research.

The machine learning models were designed by the EpiCenter for Disease Dynamics at the UC Davis One Health Institute in the School of Veterinary Medicine.

Prioritizing novel viruses

The models found that novel viruses from the coronavirus family are expected to have a larger number of species as hosts. This is consistent with known viruses, indicating this family of viruses should be most highly prioritized for surveillance.

To Prevent Future Pandemics, Leave Bats Alone

Photo Credit: Clement Kolopp

A new paper in the journal The Lancet Planetary Health makes the case that pandemic prevention requires a global taboo whereby humanity agrees to leave bats alone—to let them have the habitats they need, undisturbed.

Like the SARS coronavirus outbreak of 2003, the COVID-19 pandemic can be traced back to a bat virus. Whether someone handled or ate an infected bat or was exposed to a bat’s bodily fluids in a cave or some other way, or was exposed to another animal that had been infected by a bat, we will quite likely never know. Even a virus released via a lab accident would still have originally come from a bat. But we don’t need to know all of the details in order to act.

Bats are known to be reservoirs for a wide range of viruses that can infect other species, including people. They are a source of rabies, Marburg filoviruses, Hendra and Nipah paramyxoviruses, coronaviruses such as Middle East Respiratory Syndrome (MERS) Coronavirus, and fruit bats are strongly believed to be a source of Ebolaviruses. A new analysis points to the value of a global taboo whereby humanity agrees to leave bats alone—not fear them or try to chase them away or cull them (activities that only serve to disperse them and increase the odds of zoonotic spillover)—but to let them have the habitats they need and live undisturbed.

Farmed carnivores may become disease reservoirs posing human health risk

 Farming large numbers of carnivores, like mink, could allow the formation of undetected ‘disease reservoirs’, in which a pathogen could spread to many animals and mutate to become a risk to human health.

Research led by the University of Cambridge has discovered that carnivores have a defective immune system, which makes them likely to be asymptomatic carriers of disease-causing pathogens.

Three key genes in carnivores that are critical for gut health were found to have lost their function. If these genes were working, they would produce protein complexes called inflammasomes to activate inflammatory responses and fight off pathogens. The study is published today in the journal Cell Reports.

The researchers say that the carnivorous diet, which is high in protein, is thought to have antimicrobial properties that could compensate for the loss of these immune pathways in carnivores – any gut infection is expelled by the production of diarrhoea. But the immune deficiency means that other pathogens can reside undetected elsewhere in these animals.

“We’ve found that a whole cohort of inflammatory genes is missing in carnivores - we didn’t expect this at all,” said Professor Clare Bryant in the University of Cambridge’s Department of Veterinary Medicine, senior author of the paper. 

She added: “We think that the lack of these functioning genes contributes to the ability of pathogens to hide undetected in carnivores, to potentially mutate and be transmitted becoming a human health risk.”

Zoonotic pathogens are those that live in animal hosts before jumping to infect humans. The COVID-19 pandemic, thought to originate in a wild animal, has shown the enormous damage that can be wrought by a novel human disease. Carnivores include mink, dogs, and cats, and are the biggest carriers of zoonotic pathogens. 

Three genes appear to be in the process of being lost entirely in carnivores: the DNA is still present but it is not expressed, meaning they have become ‘pseudogenes’ and are not functioning. A third gene important for gut health has developed a unique mutation, causing two proteins called caspases to be fused together to change their function so they can no longer respond to some pathogens in the animal’s body.

“When you have a large population of farmed carnivorous animals, like mink, they can harbour a pathogen - like SARS-CoV-2 and others - and it can mutate because the immune system of the mink isn’t being activated. This could potentially spread into humans,” said Bryant.

The researchers say that the results are not a reason to be concerned about COVID-19 being spread by dogs and cats. There is no evidence that these domestic pets carry or transmit COVID-19. It is when large numbers of carnivores are kept together in close proximity that a large reservoir of the pathogen can build up amongst them, and potentially mutate.

This research was funded by Wellcome.

Source / Credit: University of Cambridge

Research explores origins of blood feeding in mosquitoes

An interdisciplinary team of Virginia Tech researchers is seeking to understand the physiological and biomechanical characteristics of blood feeding in mosquitoes and their evolutionary transition from sugar to blood feeding — knowledge that may help future work to stop disease transmission.

“Mosquitoes are the deadliest animals on the planet due to the pathogens they transmit to humans and other animals,” said Chloé Lahondère, an assistant professor of biochemistry in the College of Agriculture and Life Sciences and an affiliate faculty member of the Center for Emerging, Zoonotic, and Arthropod-borne Pathogens in the Fralin Life Sciences Institute.

“Female mosquitoes transmit pathogens while biting a host,” she continued. "Females can also feed on plants, so food sources include blood, nectar, and plant fluids, which differ widely in viscosity and temperature. One of the key objectives of our project is to understand the specific adaptations that allow certain species of female mosquitoes to feed on such a wide range of fluids.”

Lahondère and Clément Vinauger, also an assistant professor in biochemistry in the College of Agriculture and Life Sciences and an affiliate faculty of the Center for Emerging, Zoonotic, and Arthropod-borne Pathogens, will work with Jake Socha, the Samuel Herrick Professor in biomedical engineering and mechanics, and Mark Stremler, professor in biomedical engineering and mechanics in the College of Engineering, to analyze the biomechanical constraints and trade-offs between sugar and blood feeding in mosquitoes, thanks to a $1 million grant from the National Science Foundation.

Escherichia albertii: The still unfolding journey of a misdiagnosed pathogen

Animal to human bacteria pathways
Escherichia albertii is primarily found in mammals and birds, suggesting it is a novel zoonotic pathogen.
Image Credit: Osaka Metropolitan University

Escherichia albertii, initially identified as Hafnia alvei, by the commercial identification biochemical strip, API 20E, was isolated from an infant with diarrhea in Bangladesh in 1989. However, this bacterium was later renamed as a novel species, E. albertii because of its similarities in biochemical and genetic properties to the genus Escherichia, but different from those of any known species in the genus. E. albertii possesses many pathogenic attributes including a key one, which is the ability to produce attaching and effacing (A/E) lesions in the intestinal mucosa mediated by genes on a 35-kb pathogenicity island called the locus of enterocyte effacement. Therefore, it is a member of the family of A/E pathogens.

Rates of infectious disease linked to authoritarian attitudes and governance

 

According to psychologists, in addition to our physiological immune system we also have a behavioral one: an unconscious code of conduct that helps us stay disease-free, including a fear and avoidance of unfamiliar – and so possibly infected – people.

When infection risk is high, this “parasite stress” behavior increases, potentially manifesting as attitudes and even voting patterns that champion conformity and reject “foreign outgroups” – core traits of authoritarian politics.

A new study, the largest yet to investigate links between pathogen prevalence and ideology, reveals a strong connection between infection rates and strains of authoritarianism in public attitudes, political leadership and lawmaking.

While data used for the study predates COVID-19, University of Cambridge psychologists say that greater public desire for “conformity and obedience” as a result of the pandemic could ultimately see liberal politics suffer at the ballot box. The findings are published in the Journal of Social and Political Psychology.

Researchers used infectious disease data from the United States in the 1990s and 2000s and responses to a psychological survey taken by over 206,000 people in the US during 2017 and 2018. They found that the more infectious US cities and states went on to have more authoritarian-leaning citizens.

Reliably estimating proportion of vaccinated populations in wildlife

Japanese Wild Boar
Credit: KENPEI, CC BY-SA 3.0/Wikimedia Commons

Scientific Frontline: "At a Glance" Summary: Reliably Estimating Proportion of Vaccinated Populations in Wildlife

• Main Discovery: Researchers developed a mathematical model to accurately estimate the effectiveness of bait vaccinations in wild animals based on the proportion of immunized individuals and the number of vaccine applications.
• Methodology: Scientists constructed a model linking the changes over time in the proportion of immunized animals, the frequency of vaccine applications, and the overall effects of the vaccines, testing this framework using real-world data from a classical swine fever bait vaccination campaign targeting wild boars in Japan.
• Key Data: The model analyzed data stemming from a 2018 classical swine fever outbreak—the first in Japan in 26 years—and successfully tracked the cumulative increase of immunized wild boars over a 60-week period following four bait vaccination campaigns initiated in 2019.
• Significance: This study is the first to unequivocally quantify the increase in immunized wildlife due to bait vaccination without requiring extensive data on total animal population numbers, local movement tracking, or individual bait intake histories.
• Future Application: The computational model can be utilized to accurately measure the impact of oral vaccines for multiple diseases, compare distribution methods, and optimize vaccination strategies for wild animal populations where migration is negligible.
• Branch of Science: Biology, Conservation Biology, Veterinary Science

Zoology: In-Depth Description

Image Credit: Scientific Frontline / AI generated (Gemini)

Zoology is the branch of biology dedicated to the scientific study of the animal kingdom, encompassing the structure, embryology, evolution, classification, habits, and distribution of all living and extinct animals. As a discipline, it seeks to understand how animals interact with their ecosystems, how they function physiologically, and how they have adapted to diverse environments over millions of years.

Tick-borne pathogens increasingly widespread in Central Canada

Image Credit: 13smok

Tick-borne pathogens, known for causing illnesses such as Lyme disease, are on the rise in Central Canada – presenting new risks in areas where they were never previously detected.

The findings from researchers at McGill University and the University of Ottawa demonstrate the need for more comprehensive testing and tracking to detect the spread and potential risk of tick-borne pathogens to human and wildlife populations throughout Canada.

“Most people know that diseases can be transmitted to humans through the bite of infected ticks. Ticks can carry and spread several disease agents, called pathogens, that can make people and animals sick,” explains Kirsten Crandall, a PhD candidate under the joint supervision of McGill University Professor Virginie Millien and University of Ottawa Professor Jeremy Kerr.

“While the bacteria that causes Lyme disease is the most common tick-borne pathogen in Canada, other tick-borne pathogens are moving in,” she adds.

To investigate the presence and prevalence of several emerging tick-borne pathogens, Crandall and her team analyzed small mammals and ticks collected in Ontario and Quebec. The researchers found that five emerging pathogens were present across their study sites in Central Canada, including the pathogens causing Lyme disease and babesiosis, a malaria-like parasitic disease.

What Is: The Biosphere

A conceptual visualization of Earth's life-supporting envelope, illustrating the dynamic flow of energy and the intricate integration of living organisms with the planet's abiotic systems.
Image Credit: Scientific Frontline

Scientific Frontline: Extended "At a Glance" Summary: The Biosphere

The Core Concept: The biosphere is the comprehensive global ecological system integrating all living organisms and their complex relationships, including their continuous physical interactions with the planet's non-living elements. It serves as the biological connective tissue uniting Earth's major physical systems.

Key Distinction/Mechanism: Unlike the Earth's abiotic spheres (lithosphere, hydrosphere, atmosphere, and cryosphere), the biosphere is uniquely biotic. Mechanistically, it operates as a thermodynamically open system regarding energy (reliant on continuous solar input) but a largely closed system regarding matter, functioning through the relentless recycling of biogeochemical nutrients.

Major Frameworks/Components: 

• The Noosphere: Vernadsky’s framework identifying the current evolutionary epoch in which human cognition, scientific thought, and anthropogenic activity act as dominant drivers of Earth's environmental change.
• Interacting Physical Systems: The continuous integration between the biosphere and the abiotic environment, driving processes such as nutrient extraction from the pedosphere and gas exchange with the atmosphere.
• Ecosystems and Biomes: The structural hierarchies organizing biotic communities and abiotic factors based on geographic scale, climatic drivers, and energy distribution.
• Thermodynamics and Energy Flow: The unidirectional transfer of solar energy through trophic levels, strictly limited by metabolic heat loss and defined by ecological constraints such as Lindeman's 10% Rule.
• Biogeochemical Cycles: The perpetual conservation and migration of essential matter (e.g., carbon, water, nitrogen) across biological and geological states.
• The Deep Subterranean Biosphere: Vast, high-pressure microbial ecosystems existing kilometers beneath the Earth's crust, functioning via chemolithoautotrophy entirely independent of solar energy.

Bird Flu: How It’s Spreading and What to Know About This Outbreak

A feeding frenzy of western sandpipers during the mass migration via Cordova, Alaska, a key study site in the paper.
Credit: Wendy Puryear

Scientific Frontline: "At a Glance" Summary: Bird Flu: How It’s Spreading and What to Know About This Outbreak

• Main Discovery: Wild geese and gulls are the primary drivers in the amplification and long-distance transmission of avian influenza viruses, expanding upon the previous assumption that dabbling ducks were the sole super-spreaders.
• Methodology: Researchers analyzed long-term, historical data on influenza viruses at a fine taxonomic scale to identify specific transmission patterns, comparing wild ducks, gulls, land birds, and geese against domestic poultry to determine spillover effects.
• Key Data: The current outbreak has infected approximately 40 different bird species across North America, whereas a previous major incursion in 2014 led to the necessary culling of about 40 million domestic turkeys and chickens.
• Significance: Identifying the distinct ecological roles of specific bird species, such as geese thriving in human-altered agricultural settings and gulls utilizing ocean tailwinds for rapid travel, explains how and why avian influenza spills over into new geographic regions and poultry populations.
• Future Application: The collected data will be integrated into epidemiological models to accurately forecast future virus emergence, predict regional entry timelines, and target high-risk wild bird populations for early detection and surveillance.
• Branch of Science: Virology, Epidemiology, Veterinary Medicine, and Ornithology.
• Additional Detail: While avian influenza is zoonotic, the current transmission threat to the general public remains exceptionally low, with strict precautionary measures primarily recommended for wildlife rehabilitators and poultry workers directly handling potentially infected animals.

Discovery of antibody structure could lead to treatment for Crimean Congo Hemorrhagic Fever virus

Scott D. Pegan, a professor of biomedical sciences
Photo Source: University of California, Riverside

A research team led by the University of California, Riverside, has discovered important details about how therapeutically relevant human monoclonal antibodies can protect against Crimean Congo Hemorrhagic Fever virus, or CCHFV. Their work, which appears online in the journal Nature Communications, could lead to the development of targeted therapeutics for infected patients.

An emerging zoonotic disease with a propensity to spread, CCHF is considered a priority pathogen by the World Health Organization, or WHO. CCHF outbreaks have a mortality rate of up to 40%. Originally described in Crimea in 1944–1945, and decades later in the Congo, the virus has recently spread to Western Europe through ticks carried by migratory birds. The disease is already endemic in Africa, the Balkans, the Middle East, and some Asian countries. CCHFV is designated as a biosafety level 4 pathogen (the highest level of biocontainment) and is a Category A bioterrorism/biological warfare agent. There is no vaccine to help prevent infection and therapeutics are lacking.

Scott D. Pegan, a professor of biomedical sciences in the UCR School of Medicine, collaborated on this study with the United States Army Medical Research Institute of Infectious Diseases, or USAMRIID, which studies CCHFV because of the threat it poses to military personnel around the world. They examined monoclonal antibodies, or mAbs, which are proteins that bind to antigens — foreign substances that enter the body and cause the immune system to mount a protective response.

In a previous publication, USAMRIID scientists Joseph W. Golden and Aura R. Garrison reported that an antibody called 13G8 protected mice from lethal CCHFV when administered post-infection. They provided Pegan with the sequence information for that antibody, clearing the way for UCR to “humanize” it and conduct further research.