Mikel Delgado, Purdue University and Judith Stella, Purdue University

Many people have seen dogs fetch, but cats like to get into the game too. Despite their very different hunting and play styles, fetching appears to combine elements of predatory and social behavior for both species.

Although their domestication histories and natural behaviors are very different, cats and dogs share many similarities. Both species are predators, live closely with humans and are capable of enjoying rich social experiences with us.

In our newly published study, we found that more than 40% of cats described in our survey data played fetch, compared with almost 80% of dogs. We also outlined several possible reasons for fetching, including play, selection during domestication, and learning effects.

Scant research

Our research group sat up and took note when British researchers published a study in 2023 that explored some key characteristics of fetching in cats. The scientists surveyed 924 owners of cats that fetched, and they found that the cats would retrieve a wide variety of objects, from pet toys and balls of paper to pens, bottle caps and even shoes.

Perhaps most intriguing was the fact that the cats generally were not trained to fetch – they offered the behavior spontaneously. Cats also preferred to be the one to start the fetch game and were more likely to play when they brought a toy to their human, rather than the human tossing a toy.

Prior to this study, fetching behavior in cats hadn’t received much scientific attention. But because this review surveyed only owners of cats that fetched, there was no way to compare those animals with cats that didn’t. We wondered whether there was something about the cats themselves that made some more likely to fetch than others.

And what about dogs? Fetching is one of the most common forms of play between dogs and humans. Many dogs have been bred and selected specifically for assisting human hunts by retrieving prey. We expected to find abundant research about fetching behavior in dogs, but we learned that it was rarely addressed in dog behavior studies.

Fluffy, get the ball!

To help fill this gap, our group teamed with University of Pennsylvania researcher James Serpell, who developed two survey-based tools to assess dog and cat behavior. The surveys include basic questions about each animal’s breed, age and living environment, followed by dozens of questions about their behavior, including traits such as predatory behavior, sociability with humans, activity level and fearfulness. Both surveys also included questions about fetching.

Using these survey results, we analyzed data from thousands of cat and dog owners to explore just how common fetching is and what characteristics of a cat or dog and their environment are likely to predict fetching.

We found that fetching was much more common in cats than we anticipated. Over 40% of cat owners had a cat that “sometimes, usually, or always” fetched. For comparison, we also provided the first estimate of the prevalence of fetching behavior in dogs. Almost 78% of dogs represented in the data were reported to fetch.

Interestingly, being male was associated with increased fetching in both species. Being older and having health problems decreased the likelihood that either cats or dogs would be fetchers. And for both species, sharing a home with a dog also made the animal represented in the survey less likely to fetch.

There were breed differences too, especially among dogs. Breeds known for being responsive to human instructions and taking interest in toys, such as German shepherd dogs, golden retrievers and Labrador retrievers, were among the most likely breeds to fetch. In contrast, hounds and livestock guard dogs were among those least likely to fetch.

Fetching was correlated with trainability in dogs, regardless of breed, pointing to the potential importance of early selection of dogs to be human helpers, long before we started developing dog breeds.

There are far fewer breeds of cats than dogs, and fewer purebred cats were represented in our study compared with dogs. Still, we also found breed differences among cats. Siamese, Tonkinese, Burmese and Bengals were the most likely cats to fetch.

Fetching was correlated with activity level: Cats that were more likely to run, jump, engage with new items in the home and initiate play with their owners were also more likely to fetch.

From hunting to playing catch

The roots of fetching behavior lie in both species’ hunting practices. Cats are known as stalk-and-rush hunters, meaning that they sneak up on their prey and pounce at an opportune moment. Dogs are believed to be pursuit predators that chase prey over longer distances.

Development of breeds has altered dogs’ typical predatory behavior sequence, which goes like this: orient, eye, stalk, chase, grab-bite, kill-bite. Dog breeds that have been bred for exaggerated or increased “chase and/or grab-bite” behavior – such as pointers and retrievers – are more likely to fetch and less likely to complete the predatory sequence and “kill-bite.”

But both cats and dogs will carry prey items away from the kill site, which may also partially explain how a behavior such as fetch could arise.

Although cats often are viewed as independent and aloof, recent studies have found that cats can show attachment to humans, pick up social cues from humans and even recognize their owner’s voice. We hope that our study further encourages people to understand that cats are capable of loving relationships with humans, especially when these popular pets are well socialized and provided with an enriched and safe environment. Including fetching, if your cat is so inclined.

For all of the differences between dogs and cats, we think it’s charming that they have converged on a similar behavior – fetching. Fetching also highlights the effect of the human-animal relationship. Humans clearly play an important role in fetching behavior, even if dogs and cats simply perceive us as the thing that makes the toy move so they can chase it.

Mikel Delgado, Senior Research Scientist, College of Veterinary Medicine, Purdue University and Judith Stella, Senior Research Scientist, College of Veterinary Medicine, Purdue University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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.

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.

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.

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.

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

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Harish Narasimhan, University of Virginia

The long-term effects of respiratory viral infections such as COVID-19 are a major public health burden. Some estimates suggest over 65 million people around the world suffer from long COVID-19.

Efforts to better understand this condition, however, have been hampered by its ability to affect multiple organ systems, such as those involving the lungs, brain and heart. This is further complicated by the lack of animal models that can sufficiently mimic the disease.

Animal models, such as mice and rats, are a crucial tool that researchers use to study human diseases and develop treatment strategies. Although there are major differences between humans and animal models, the vast majority of our immune and organs systems function similarly. Such similarities in physiology have made significant health care discoveries, including those related to COVID-19, possible.

I am an immunology researcher in the Sun Lab at the University of Virginia. We study the role the immune system plays in respiratory viral infections such as influenza and COVID-19. In our newly published research, we developed a new mouse model to study long COVID-19 and found that blocking certain overactive immune cells can restore lung function.

New models, new targets

Out team wanted to better understand the long-term effects of COVID-19 on the respiratory system. To do this, we worked to identify key features associated with lung scarring following COVID-19.

First, we examined lung samples from patients with long COVID-19. Although these patients were infected several months to years before the samples were taken, we found evidence of an overactive immune system in their lungs, particularly within areas that failed to fully repair themselves after infection.

Next, we aimed to create a mouse model for long COVID-19 by comparing the pathology of mice infected with four different types of respiratory viral infections. Surprisingly, we found that mice infected with influenza virus, rather than the COVID-19 mouse models scientists currently use, best replicated the physical features of severe chronic lung disease. The reasons why infections from different respiratory viruses affect the lungs in different ways are unclear. But preliminary evidence suggests it may be because each virus targets different types of cells “in humans and mice.”

Additionally, since long COVID-19 is about the damage left behind after infection, it seems less important what virus causes the problem in our animal model than that the damage is similar to what we want to address in human patients.

Using our new mouse model, we were able to identify the presence of an abnormal cluster of cells in mice lungs – made up of the same dysfunctional immune and epithelial, or structural, cells seen in the lungs of long-COVID-19 patients. Additionally, we found that the uncontrolled activity of these immune cells in the lungs impeded structural cells from repairing themselves. It also hindered them from restoring gas exchange, the process of taking in oxygen and releasing carbon dioxide.

Importantly, when we blocked the activity of proteins associated with this overactive immune response, it reduced lung scarring and restored optimal lung function in mice.

Treating respiratory viral infections

Most approaches to addressing long COVID-19 rely on starting treatment early after infection. To the best of our knowledge, our study is the first to identify strategies to treat the respiratory symptoms of long COVID-19 after this chronic disease develops.

The drugs we tested in our study have already been approved by the Food and Drug Administration to treat severe COVID-19 and other inflammatory conditions. We hope our findings can spur further research on using these drugs to treat long COVID-19.

Our work may have applications beyond long COVID-19. Growing evidence suggests that many respiratory viral infections, such as influenza, COVID-19 and respiratory syncytial virus, may result in chronic lung disease. Considering the four pandemics and even more respiratory viral epidemics that have occurred in the past 100 years, studying the cellular and molecular similarities between respiratory viral infections may be critical to how medical practitioners respond to future viral outbreaks.

Harish Narasimhan, Ph.D. Candidate in Immunology, University of Virginia

This article is republished from The Conversation under a Creative Commons license. Read the original article.