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Humans infecting animals infecting humans − from COVID-19 to bird flu, preventing pandemics requires protecting all species

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theconversation.com – Anna Fagre, Veterinary Microbiologist and Wildlife Epidemiologist, Colorado State University – 2024-09-04 07:28:49

Human, animal and environmental health are interconnected.
Tambako the Jaguar/Moment via Getty Images

Anna Fagre, Colorado State University and Sadie Jane Ryan, University of Florida

When the World Health Organization declared COVID-19 a pandemic on March 11, 2020, humans had been the only species with reported cases of the disease. While early genetic analyses pointed to horseshoe bats as the evolutionary hosts of SARS-CoV-2, the virus that causes COVID-19, no reports had yet surfaced indicating it could be transmitted from humans to other animal species.

Less than two weeks later, a report from Belgium marked the first infection in a domestic cat – presumably by its owner. Summer 2020 saw news of COVID-19 outbreaks and subsequent cullings in mink farms across Europe and fears of similar calls for culling in North America. Humans and other animals on and around mink farms tested positive, raising questions about the potential for a secondary wildlife reservoir of COVID-19. That is, the virus could infect and establish a transmission cycle in a different species than the one in which it originated.

Researchers have documented this phenomenon of human-to-animal transmission, colloquially referred to as spillback or reverse zoonotic transmission, in both domestic and wild animals. Wildlife may be infected either directly from humans or indirectly from domestic animals infected by humans. This stepping-stone effect provides new opportunities for pathogens to evolve and can radically change how they spread, as seen with influenza and tuberculosis.

Diagram showing pathways of disease transmission between humans, an original reservoir, a new maintenance reservoir and a new dead-end host
Pathogen transmission is bidirectional between animals and humans.
Fagre et al. 2022/Ecology Letters, CC BY-NC-ND

For example, spillback has been a long-standing threat to endangered great apes, even among populations with infrequent human contact. The chimpanzees of Gombe National Park, made famous by Jane Goodall’s work, have suffered outbreaks of measles and other respiratory diseases likely resulting from environmental persistence of pathogens spread by people living nearby or by ecotourists.

We are researchers who study the mechanisms driving cross-species disease transmission and how disease affects both wildlife conservation and people. Emerging outbreaks have underscored the importance of understanding how threats to wildlife health shape the emergence and spread of zoonotic pathogens. Our research suggests that looking at historical outbreaks can help predict and prevent the next pandemic.

Spillback has happened before

Our research group wanted to assess how often spillback had been reported in the years leading up to the COVID-19 pandemic. A retrospective analysis not only allows us to identify specific trends or barriers in reporting spillback events but also helps us understand where new emergent threats are most likely.

We examined historical spillback events involving different groups of pathogens across the animal kingdom, accounting for variations in geography, methods and sample sizes. We synthesized scientific reports of spillback across nearly a century prior to the COVID-19 pandemic – from the 1920s to 2019 – which included diseases ranging from salmonella and intestinal parasites to human tuberculosis, influenza and polio.

We were also interested in determining whether detection and reporting bias might influence what’s known about human-to-animal pathogen transmission. Charismatic megafauna – often defined as larger mammals such as pandas, gorillas, elephants and whales that evoke emotion in people – tend to be overrepresented in wildlife epidemiology and conservation efforts. They receive more public attention and funding than smaller and less visible species.

Complicating this further are difficulties in monitoring wild populations of small animals, as they decompose quickly and are frequently scavenged by larger animals. This drastically reduces the time window during which researchers can investigate outbreaks and collect samples.

Mouse with clipped ear leaning over the edge of a gloved hand
Small animals such as deer mice are harder to surveil.
Christopher Kimmel/Moment via Getty Images

The results of our historical analysis support our suspicions that most reports described outbreaks in large charismatic megafauna. Many were captive, such as in zoos or rehabilitation centers, or semi-captive, such as well-studied great apes.

Despite the litany of papers published on new pathogens discovered in bats and rodents, the number of studies examining pathogens transmitted from humans to these animals was scant. However, small mammals occupying diverse ecological niches, including animals that live near human dwellings – such as deer mice, rats and skunks – may be more likely to not only share their pathogens with people but also to be infected by human pathogens.

COVID-19 and pandemic flu

In our historical analysis of spillback prior to the COVID-19 pandemic, the only evidence we found supporting the establishment of a human pathogen in a wildlife population were two 2019 reports describing H1N1 infection in striped skunks. Like coronaviruses, influenza A viruses such as H1N1 are adept at switching hosts and can infect a broad range of species.

Unlike coronaviruses, however, their widespread transmission is facilitated by migratory waterfowl such as ducks and geese. Exactly how these skunks became infected with H1N1 and for how long remains unclear.

Shortly after we completed the analysis for our study, reports describing widespread COVID-19 infection of white-tailed deer throughout North America began surfacing in November 2021. In some areas, the prevalence of infection was as high as 80% despite little evidence of sickness in the deer.

This ubiquitous mammal has effectively become a secondary reservoir of COVID-19 in North America. Further, genetic evidence suggests that SARS-CoV-2 evolves three times faster in white-tailed deer than in humans, potentially increasing the risk of seeding new variants into humans and other animals. There is already evidence of deer-to-human transmission of a previously unseen variant of COVID-19.

There are over 30 million white-tailed deer in North America, many in agricultural and suburban areas. Surveillance efforts to monitor viral evolution in white-tailed deer can help identify emerging variants and further transmission from deer populations into people or domestic animals.

Investigations into related species revealed that the risk of spillback varies. For instance, white-tailed deer and mule deer are highly susceptible to COVID-19 in the lab, while elk are not.

H5N1 and the US dairy herd

Since 2022, the spread of H5N1 has affected a broad range of avian and mammalian species around the globe – foxes, skunks, raccoons, opossums, polar bears, coyotes and seals, to name a few. Some of these populations are threatened or endangered, and aggressive surveillance efforts to monitor viral spread are ongoing.

Earlier this year, the U.S. Department of Agriculture reported the presence of H5N1 in the milk of dairy cows. Genetic analyses point to an introduction of the virus into cows as early as December 2023, probably in the Texas Panhandle. Since then, it has affected 178 livestock herds in 13 states as of August 2024.

How the virus got into dairy cow populations remains undetermined, but it was likely by migratory waterfowl infected with the virus. Efforts to delineate exactly how the virus moves among and between herds are underway, though it appears contaminated milking equipment rather than aerosol transmission, may be the culprit.

One cow, among a herd of cows on a pasture, sniffing a person's hand
Researchers are investigating outbreaks of H5N1 in cows.
Jacob Wackerhausen/iStock via Getty Images Plus

Given the ability of influenza A viruses such as avian flu to infect a broad range of species, it is critical that surveillance efforts target not only dairy cows but also animals living on or around affected farms. Monitoring high-risk areas for cross-species transmission, such as where livestock, wildlife and people interact, provides information not only about how widespread a disease is in a given population – in this case, dairy cows – but also allows researchers to identify susceptible species that come into contact with them.

To date, H5N1 has been detected in several animals found dead on affected dairy farms, including cats, birds and a raccoon. As of August 2024, four people in close contact with infected dairy cows have tested positive, one of whom developed respiratory symptoms. Other wildlife and domestic animal species are still at risk. Similar surveillance efforts are underway to monitor H5N1 transmission from poultry to humans.

Humans are only 1 part of the network

The language often used to describe cross-species transmission fails to encapsulate its complexity and nuances. Given the number of species that have been infected with COVID-19 throughout the pandemic, many scientists have called for limiting the use of the terms spillover and spillback because they describe the transmission of pathogens to and from humans. This suggests that disease and its implications begin and end with humans.

Considering humans as one node in a large network of transmission possibilities can help researchers more effectively monitor COVID-19, H5N1 and other emerging zoonoses. This includes systems-thinking approaches such as One Health or Planetary Health that capture human interdependence with the health of the total environment.The Conversation

Anna Fagre, Veterinary Microbiologist and Wildlife Epidemiologist, Colorado State University and Sadie Jane Ryan, Professor of Medical Geography, University of Florida

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How nonprofits abroad can fill gaps when the US government cuts off foreign aid

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theconversation.com – Susan Appe, Associate Professor of Public Administration and Policy, University at Albany, State University of New York – 2025-01-30 07:50:00

How nonprofits abroad can fill gaps when the US government cuts off foreign aid

The U.S. Agency for International Development distributes a lot of foreign aid through local partners in other countries.

J. David Ake/Getty Images

Susan Appe, University at Albany, State University of New York

The U.S. government gives other nations US$68 billion of foreign assistance annually – more than any other country. Over half of this sum is managed by the U.S. Agency for International Development, including funds for programs aimed at fighting hunger and disease outbreaks, providing humanitarian relief in war zones, and supporting other lifesaving programs such as the President’s Emergency Plan for AIDS Relief.

President Donald Trump suspended most U.S. foreign aid on Jan. 20, 2025, the day he took office for the second time. The next day, Secretary of State Marco Rubio issued a stop-work order that for 90 days halted foreign aid funding disbursements by agencies like USAID.

A week later, dozens of senior USAID officials were put on leave after the Trump administration reportedly accused them of trying to “circumvent” the aid freeze. The Office of Management and Budget is now pausing and evaluating all foreign aid to see whether it adheres to the Trump administration’s policies and priorities.

I’m a scholar of foreign aid who researches what happens to the U.S. government’s local partners in the countries receiving this assistance when funding flows are interrupted. Most of these partners are local nonprofits that build schools, vaccinate children, respond to emergencies and provide other key goods and services. These organizations often rely on foreign funding.

A ‘reckless’ move

Aid to Egypt and Israel was spared, along with some emergency food aid. The U.S. later waived the stop-work order for the distribution of lifesaving medicines.

Nearly all of the other aid programs remained on hold as of Jan. 29, 2025.

Many development professionals criticized the freeze, highlighting the disruption it will cause in many countries. A senior USAID official issued an anonymous statement calling it “reckless.”

InterAction, the largest coalition of international nongovernmental organizations in the U.S., called the halt contrary to U.S. global leadership and values.

Of the $35 billion to $40 billion in aid that USAID distributes annually, $22 billion is delivered through grants and contracts with international organizations to implement programs. These can be further subcontracted to local partners in recipient countries.

When this aid is frozen, scaled back or cut off altogether, these local partners scramble to fill in the gaps.

The State Department manages the rest of the $68 billion in annual U.S. foreign aid, along with other agencies, such as the Peace Corps.

Marco Rubio, standing in a hallway, holding something in his hand.

The start of Marco Rubio’s tenure as U.S. secretary of state was marked by chaos and confusion regarding foreign aid flows.

Kevin Dietsch/Getty Images

How local nonprofits respond and adapt

While sudden disruptions to foreign aid are always destabilizing, research shows that aid flows have fluctuated since 1960, growing more volatile over the years. My research partners and I have found that these disruptions harm local service providers, although many of them manage to carry on their work.

Over the years, I have conducted hundreds of interviews with international nongovernmental organizations and these nonprofits’ local partners across Latin America, Africa and Asia about their services and funding sources. I study the strategies those development and humanitarian assistance groups follow when aid gets halted. These four are the most common.

1. Shift to national or local government funding

In many cases, national and local governments end up supporting groups that previously relied on foreign aid, filling the void.

An educational program spearheaded by a local Ecuadorian nonprofit, Desarrollo y Autogestión, called Accelerated Basic Cycle is one example. This program targets young people who have been out of school for more than three years. It allows them to finish elementary school – known as the “basic cycle” in Ecuador – in one year to then enter high school. First supported in part by funding from foreign governments, it transitioned to being fully funded by Ecuador’s government and then became an official government program run by the country’s ministry of education.

2. Earn income

Local nonprofits can also earn income by charging fees for their services or selling goods, which allows them to fulfill their missions while generating some much-needed cash.

For example, SEND Ghana is a development organization that has promoted good governance and equality in Ghana since its founding in 1998. In 2009, SEND Ghana created a for-profit subsidiary called SENDFiNGO that administers microfinance programs and credit unions. That subsidiary now helps fund SEND Ghana’s work.

Bangladesh Rural Advancement Committee and the Grameen Bank, which is also in Bangladesh, use this approach too.

3. Tap local philanthropy

Networks such as Worldwide Initiatives for Grantmaker Support and Global Fund for Community Foundations have emerged to promote local philanthropy around the world. They press governments to adopt policies that encourage local philanthropy. This kind of giving has become easier to do thanks to the emergence of crowdfunding platforms.

Still, complex tax systems and the lack of incentives for giving in many countries that receive foreign aid are persistent challenges. Some governments have stepped in. India’s corporate social responsibility law, enacted in 2014, boosted charitable incentives. For example, it requires 2% of corporate profits to go to social initiatives in India.

4. Obtain support from diaspora communities

Diasporas are people who live outside of their countries of origin, or where their families came from, but maintain strong ties to places they consider to be their homeland.

Local nonprofits around the globe are leveraging diaspora communities’ desire to contribute to economic development in their countries of origin. In Colombia, for example, Fundación Carla Cristina, a nongovernmental organization, runs nursery schools and provides meals to low-income children.

It gets some of its funding from diaspora-led nonprofits in the U.S., such as the New England Association for Colombian Children, which is based outside of Boston, and Give To Colombia in Miami.

A push for the locals to do more

Trump’s stop-work order coincided with a resurgence of a localization push that’s currently influencing foreign aid from many countries.

With localization, nations providing foreign aid seek to increase the role of local authorities and organizations in development and humanitarian assistance. USAID has been a leading proponent of localization.

I believe that the abruptness of the stop-work order is likely to disrupt many development projects. These projects include support to Ukrainian aid groups that provide emergency humanitarian assistance and projects serving meals to children who don’t get enough to eat.

To be sure, sometimes there are good reasons for aid to be halted. But when that happens, sound and responsible donor exit strategies are essential to avoid the loss of important local services.The Conversation

Susan Appe, Associate Professor of Public Administration and Policy, University at Albany, State University of New York

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How satellites and AI help fight wildfires today

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theconversation.com – John W. Daily, Research Professor in Thermo Fluid Sciences, University of Colorado Boulder – 2025-01-30 07:48:00

How satellites and AI help fight wildfires today

The wind and terrain can quickly change how a fire, like this one near Los Angeles in January 2025, behaves.

AP Photo/Marcio Jose Sanchez

John W. Daily, University of Colorado Boulder

As wind-driven wildfires spread through the Los Angeles area in January 2025, fire-spotting technology and computer models were helping firefighters understand the rapidly changing environment they were facing.

That technology has evolved over the years, yet some techniques are very similar to those used over 100 years ago.

I have spent several decades studying combustion, including wildfire behavior and the technology used to track fires and predict where wildfires might turn. Here’s a quick tour of the key technologies used today.

Spotting fires faster

First, the fire must be discovered.

Often wildfires are reported by people seeing smoke. That hasn’t changed, but other ways fires are spotted have evolved.

In the early part of the 20th century, the newly established U.S. Forest Service built fire lookout towers around the country. The towers were topped by cabins with windows on all four walls and provided living space for the fire lookouts. The system was motivated by the Great Fire of 1910 that burned 3 million acres in Washington, Idaho and Montana and killed 87 people.

Two people stand on a fire tower with windows on all sides, looking out over the forest.

Before satellites, fire crews watched for smoke from fire towers across the national forests.

K. D. Swan, U.S. Forest Service

Today, cameras watch over many high-risk areas. California has more than 1,100 cameras watching for signs of smoke. Artificial intelligence systems continuously analyze the images to provide data for firefighters to quickly respond. AI is a way to train a computer program to recognize repetitive patterns: smoke plumes in the case of fire.

NOAA satellites paired with AI data analysis also generate alerts but over a wider area. They can detect heat signatures, map fire perimeters and burned areas, and track smoke and pollutants to assess air quality and health risks.

Forecasting fire behavior

Once a fire is spotted, one immediate task for firefighting teams is to estimate how the fire is going to behave so they can deploy their limited firefighting resources most effectively.

Fire managers have seen many fires and have a sense of the risks their regions face. Today, they also have computer simulations that combine data about the terrain, the materials burning and the weather to help predict how a fire is likely to spread.

Fuel models

Fuel models are based on the ecosystem involved, using fire history and laboratory testing. In Southern California, for example, much of the wildland fuel is chaparral, a type of shrubland with dense, rocky soil and highly flammable plants in a Mediterranean climate. Chaparral is one of the fastest-burning fuel types, and fires can spread quickly in that terrain.

For human-made structures, things are a bit more complex. The materials a house is made of – if it has wood siding, for example – and the environment around it, such as how close it is to trees or wooden fences, play an important role in how likely it is to burn and how it burns.

How scientists study fire behavior in a lab.

Weather and terrain

Terrain is also important because it influences local winds and because fire tends to run faster uphill than down. Terrain data is well known thanks to satellite imagery and can easily be incorporated into computer codes.

Weather plays another critical role in fire behavior. Fires need oxygen to burn, and the windier it is, the more oxygen is available to the fire. High winds also tend to generate embers from burning vegetation that can be blown up to 5 miles in the highest winds, starting spot fires that can quickly spread.

Today, large computer simulations can forecast the weather. There are global models that cover the entire Earth and local models that cover smaller areas but with better resolution that provides greater detail.

Both provide real-time data on the weather for creating fire behavior simulations.

Modeling how flames spread

Flame-spread models can then estimate the likely movement of a fire.

Scientists build these models by studying past fires and conducting laboratory experiments, combined with mathematical models that incorporate the physics of fire. With local terrain, fuel and real-time weather information, these simulations can help fire managers predict a fire’s likely behavior.

Examples of how computer modeling can forecast a fire’s spread. American Physical Society.

Advanced modeling can account for fuel details such as ground-level plant growth and tree canopies, including amount of cover, tree height and tree density. These models can estimate when a fire will reach the tree canopy and how that will affect the fire’s spread.

Forecasting helps, but wind can change fast

All these tools are made available to firefighters in computer applications and can help fire crews as they respond to wildfires.

However, wind can rapidly change speed or direction, and new fires can start in unexpected places, meaning fire managers know they have to be prepared for many possible outcomes – not just the likely outcomes they see on their computer screens.

Ultimately, during a fire, firefighting strategy is based on human judgment informed by experience, as well as science and technology.The Conversation

John W. Daily, Research Professor in Thermo Fluid Sciences, University of Colorado Boulder

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Gen Z seeks safety above all else as the generation grows up amid constant crisis and existential threat

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theconversation.com – Yalda T. Uhls, Founder and Executive Director of the Center for Scholars & Storytellers and Assistant Adjunct Professor in Psychology, University of California, Los Angeles – 2025-01-30 07:47:00

Gen Z seeks safety above all else as the generation grows up amid constant crisis and existential threat

Asked to rate the importance of 14 personal goals, Gen Z reported ‘to be safe’ as the top goal.

Darya Komarova/Getty Images

Yalda T. Uhls, University of California, Los Angeles

After many years of partisan politics, increasingly divisive language, finger-pointing and inflammatory speech have contributed to an environment of fear and uncertainty, affecting not just political dynamics but also the priorities and perceptions of young people.

As a developmental psychologist who studies the intersection of media and adolescent mental health, and as a mother of two Gen Z kids, I have seen firsthand how external societal factors can profoundly shape young people’s emotional well-being.

This was brought into sharp relief through the results of a recent survey my colleagues and I conducted with 1,644 young people across the U.S., ages 10 to 24. The study was not designed as a political poll but rather as a window into what truly matters to adolescents. We asked participants to rate the importance of 14 personal goals. These included classic teenage desires such as “being popular,” “having fun” and “being kind.”

None of these ranked as the top priority. Instead, the No. 1 answer was “to be safe.”

A house burning down with huge flames.

It lurks everywhere: Gen Z’s perception of danger is further shaped by events like the recent fires devastating Los Angeles.

Agustin Paullier/AFP via Getty Images

What was once taken for granted

The findings are both illuminating and heartbreaking. As a teenager, I did countless unsafe things. My peers and I didn’t dwell on harm; we chased fun and freedom.

Whereas previous generations may have taken safety for granted, today’s youth are growing up in an era of compounded crises — school shootings, a worsening climate crisis, financial uncertainty and the lingering trauma of a global pandemic. Even though our research did not pinpoint the specific causes of adolescent fears, the constant exposure to crises, amplified by social media, likely plays a significant role in fostering a pervasive sense of worry.

Despite data showing that many aspects of life are safer now than in previous generations, young people just don’t feel it. Their perception of danger is further shaped by events like the recent fires that devastated Los Angeles, reinforcing a belief that danger, possibly caused by global crises like climate change, lurks everywhere.

This shift in perspective has profound implications for the future of this generation and those to come.

Especially vulnerable time

Adolescence, like early childhood, is a pivotal period for brain development. Young people are particularly sensitive to their surroundings as their brains evaluate the environment to prepare them for independence.

This developmental stage – when the capacity to regulate emotions and critically assess information is still maturing – makes them especially vulnerable to enduring impacts.

Studies show that adolescents struggle to put threats into context. This makes them particularly vulnerable to fear-driven messaging prevalent in both traditional and social media, which is further amplified by political rhetoric and blame-shifting. This vulnerability has implications for their mental health, as prolonged exposure to fear and uncertainty has been linked to increased rates of anxiety, depression and even physical health issues.

So when the media that Gen Z consumes are dominated by fear – be it through headlines, social media posts, political rhetoric or even storylines in movies and TV – it could shape their worldview in ways that may reverberate for generations to come.

Enduring generational impact

Historical events have long been shown to shape the worldview of entire generations.

For instance, the Great Depression primarily impacted the daily lives of the Silent Generation, those born between 1928 and 1945. Moreover, its long-term effects on financial attitudes and security concerns echoed into the Baby Boomer generation, influencing how those born between 1946 and 1964 approached money, stability and risk throughout their lives.

Similarly, today’s adolescents, growing up amid a series of compounded global crises, will likely carry the imprint of this period of heightened fear and uncertainty well into adulthood. This formative experience could shape their mental health, decision-making and even their collective identity and values for decades to come.

In addition, feelings of insecurity and instability can make people more responsive to fear-based messaging, which could potentially influence their political and social choices. In an era marked by the rise of authoritarian governments, this susceptibility could have far-reaching implications because fear often drives individuals to prioritize immediate safety over moral or ideological ideals.

As such, these dynamics may profoundly shape how this generation engages with the world, the causes they champion and the leaders they choose to follow.

Room for optimism?

Interestingly, “being kind” was rated No. 2 in our survey, irrespective of other demographics. While safety dominates their priorities, adolescents still value qualities that foster connection and community.

This finding indicates a duality in their aspirations: While they feel a pervasive sense of danger, they also recognize the importance of interpersonal relationships and emotional well-being.

Our findings are a call to look at the broader societal context shaping adolescent development. For instance, the rise in school-based safety drills, while intended to provide a sense of preparedness, may unintentionally reinforce feelings of insecurity. Similarly, the apocalyptic narrative around climate change may create a sense of powerlessness that could further compound their fears and leave them wanting to bury their heads in the sand.

Understanding how these perceptions are formed and their implications for mental health, decision-making and behavior is essential for parents, storytellers, policymakers and researchers.

I believe we must also consider how societal systems contribute to the pervasive sense of uncertainty and fear among youth. Further research can help untangle the complex relationship between external stressors, media consumption and youth well-being, shedding light on how to best support adolescents during this formative stage of life.The Conversation

Yalda T. Uhls, Founder and Executive Director of the Center for Scholars & Storytellers and Assistant Adjunct Professor in Psychology, University of California, Los Angeles

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