For most people, dangerous viruses seem to appear suddenly, as if out of nowhere. COVID-19 taught the world that diseases jumping from animals to humans can change daily life very quickly.
Now, scientists are warning that two lesser-known animal viruses may be quietly moving in a similar direction.
These viruses are influenza D virus and canine coronavirus. So far, they have stayed mostly under the radar, but experts say the conditions are right for them to spread more widely among humans if we are not careful.
This warning comes from a group of infectious disease researchers who reviewed years of scientific studies. Their work was published in the journal Emerging Infectious Diseases.
According to the researchers, these viruses already show signs that they can infect humans, but surveillance and testing have not kept up. This means infections may be happening without being noticed.
Influenza D virus was first identified in 2011. At the time, it was mainly linked to cattle and pigs. Since then, scientists have found it in many other animals, including chickens, deer, giraffes, and even kangaroos.
In cows, influenza D virus is believed to play a role in a serious lung illness called bovine respiratory disease. This disease costs the U.S. cattle industry about one billion dollars every year, showing how damaging the virus can be in animals.
What worries scientists is that people who work closely with animals are already being exposed. Studies carried out by the research team in Colorado and Florida showed that up to 97 percent of cattle workers had antibodies against influenza D virus. Antibodies mean the immune system has seen the virus before.
Most of these people did not report feeling sick, which suggests the infections were mild or silent. However, silent infections can still be dangerous because they allow viruses to spread and adapt without being detected.
Viruses are known to change over time. Influenza viruses, in particular, are good at mutating and adapting to new hosts. One recent strain of influenza D virus found in China has already shown the ability to spread from person to person.
While it has not yet caused serious illness in humans, this change is a warning sign. If the virus continues to evolve, it could become much easier to transmit and more harmful.
Canine coronavirus is another virus raising concern. This virus normally causes stomach illness in dogs and is not the same as the coronavirus that caused COVID-19. For many years, it was thought to only affect animals.
However, several cases have now shown that it can infect humans as well. Some of these infections have been linked to pneumonia and hospital stays, especially in Southeast Asia.
In 2021, researchers from the University of Florida isolated a canine coronavirus from a medical worker who had traveled to Haiti. The person experienced mild symptoms such as fever and feeling unwell.
The virus strain was later named HuCCoV_Z19Haiti. Around the same time, another research group discovered a nearly identical strain in a child hospitalized in Malaysia. That strain was named CCoV-HuPn-2018.
Since then, this canine coronavirus strain has been found in people with breathing problems in Thailand, Vietnam, and even in Arkansas in the United States. This shows that the virus is already spreading across different countries and continents.
Despite this, routine testing for canine coronavirus in humans is rarely done. As a result, the true number of infections is unknown.
The researchers stress that this situation is familiar. In past pandemics, viruses circulated quietly for years before suddenly gaining the ability to spread easily between people. Once that happens, outbreaks can grow very fast, especially if most people have no immunity.
The scientists argue that better monitoring of animal and human viruses is urgently needed. More reliable tests would help doctors identify infections early. Research into treatments and vaccines could also reduce the risk of large outbreaks. Right now, knowledge about how these viruses spread, who they affect, and how severe the illnesses can be is very limited.
When reviewing the study’s findings, one clear message stands out. These viruses are not causing widespread illness yet, but they show warning signs that should not be ignored. Influenza D virus is already common in animals and frequently reaches humans who work with livestock.
Canine coronavirus has crossed into humans multiple times and is already circulating internationally. The lack of routine testing means public health systems are likely missing early signals.
The study does not claim that a new pandemic is certain. Instead, it highlights missed opportunities to act early.
With stronger surveillance, better diagnostics, and early research into prevention, the risks could be reduced before these viruses gain a stronger foothold in humans. The findings serve as a reminder that waiting for clear danger is often waiting too long.
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