On May 15, Beijing time, according to foreign media reports, although it is understandable to pay attention to diseases affecting humans, it is also crucial to study and analyze how human diseases affect animals** Some scientists speculate that the new coronavirus variant may not originate from human patients, but from rats in the urban environment. They infect novel coronavirus by contacting sewage with novel coronavirus. The virus may mutate in rats, and then rats spread the virus to humans in the human living environment
The spread of pathogens is not a "one-way street". It seems that humans have introduced novel coronavirus into other species such as wild deer, minks, captive gorillas, pet dogs and cats. This transfer of disease transmission from humans to animals is popularly known as "spillover phenomenon". This infection may have a significant impact on wild species and humans.
When scientists consider the transfer of microorganisms between animal species, we usually focus on the "spillover phenomenon" - the transfer of pathogens from animals to humans. However, the spread of pathogens is not a "one-way street". It seems that humans have introduced novel coronavirus into other species such as wild deer, minks, captive gorillas, pet dogs and cats. This transfer of disease transmission from humans to animals is popularly known as "backflow phenomenon". This infection may have a significant impact on wild species and humans.
What diseases do humans transmit to animals
The virus may be the best research example of "spillback phenomenon". For example, in the swine flu incident caused by H1N1 virus in 2009, different species such as pigs and ferrets were infected by humans. At that time, H1N1 virus spread to pigs early in rural fairs (a common place for influenza to spread among species), and ferret breeders found ferrets infected with the virus. Urban wildlife has also been affected. Skunks carrying the H1N1 virus have been found in urban parks in Vancouver, Canada. It is reported that during the 1918 influenza pandemic, humans may spread the influenza virus to pigs. That influenza outbreak was also caused by the spread of H1N1 virus. Since then, the virus has been evolving and developing in the global pig population.
Is there a backflow of bacteria?
For various reasons, bacterial backflow may be more common than viral backflow. Bacteria can replicate in a wider range of species, because they usually do not need species-specific receptors on host cells like viruses. At the same time, bacteria may be better at replicating on various animal mucous membranes, skin or intestines, which will promote backflow between species.
However, since bacteria may be more likely to implant into the host than viruses, this means that they can replicate better on the host, but it does not necessarily lead to disease - bacterial transmission events are also more likely to be ignored.
Previous studies have confirmed that Mycobacterium tuberculosis (the bacterium that causes tuberculosis) has spilled back to animal populations. In ancient times, there were cases of elephants suffering from pulmonary tuberculosis. This bacterium may spread repeatedly between elephants and humans.
In addition, there are secondary spillback cases. Leprosy may have been first transmitted from humans to armadillos, and then humans re infected leprosy by hunting and eating armadillos.
How does backflow affect human health
When infectious microorganisms replicate in different populations, their evolutionary trajectories may be different due to species differences, resulting in new variants. If reintroduced into the human body, the human immune system may not be able to defend against these microbial variants.
Take Staphylococcus aureus as an example. This bacterium can cause a variety of diseases, such as mild skin infection, pneumonia, drug-resistant staphylococcus infection, etc. the host range of Staphylococcus aureus is wide, including mammals such as dolphins and North American wild goats, as well as some birds and fish. Like armadillo, many studies use genome sequencing to reconstruct the jump of species from human to animal and then to human, but for Staphylococcus aureus, There is an unfortunate turning point - the microorganism has been evolving and acquiring antibiotic resistance in animals. When the disease spreads to humans again through secondary spillback, the disease is more difficult to treat.
Similarly, human E. coli may follow a similar secondary spillback cycle, two-way transmission between pets and owners. In a study of European pet families, researchers analyzed pets with urethral infection, wound infection and diarrhea and found that there was a drug-resistant strain called "o25: h4-st131" in their bodies, which was also found in human patients.
In addition, we may have found the secondary spillback of novel coronavirus. Although many scientists believe that the Omicron virus variant appearing at the end of 2021 may come from a patient with chronic infection and low immunity, several Omicron virus variants have been found in the coronavirus lineage adapted to rodents, which may be derived from rodents, such as rats in urban environment, Human novel coronavirus is infected by sewage with virus, which makes novel coronavirus evolve into Omicron variant and spread to human in human living environment.
Does it affect animal health
Backflow can also harm vulnerable wildlife populations. A recently published research report pointed out a hypothesis - the animal suffering from virus backflow is not a better disseminator, but a "dead corner host" that may cause a large number of deaths. For these affected species, virus backflow can be catastrophic for these populations and may even put them at risk of extinction.
Since scientists have long begun to monitor the critically endangered mountain gorillas in Central Africa, they found the human metapneumovirus (hMPV) backflow phenomenon in 2009. HMPV is a respiratory pathogen that can lead to influenza like infection in humans. Researchers found hMPV infection symptoms on a group of mountain gorillas in Rwanda wildlife conservation park, Finally, hMPV virus was detected in the tissue sample of a dead mountain gorilla. Although it is not clear how these mountain gorillas were infected, the hMPV strain in the body matches the tissue samples of infected patients in South Africa, and the deaths of mountain gorillas infected with the virus are common in parks. In addition, human metapneumovirus (hMPV) and human respiratory syncytial virus (HRSV) were also found in chimpanzees who died of respiratory infection in the Republic of C ô te d'Ivoire in 2008.
After that, the researchers conducted a detailed investigation on the virus backflow phenomenon of African ape populations. They found that foreign virus infection could have a devastating impact on ape populations. Scientists advise nearby tourists to keep a certain distance from apes, wear masks and get vaccinated to ensure immunity to some diseases. However, we don't know whether even doing so can protect the ape population.
Can other pathogens also cause backflow
Parasites and fungi can also spread from humans to animals, but because these pathogens are usually less deadly than bacteria and viruses, their impact on humans is usually ignored, so there are few recorded microbial spillback phenomena.
Parasite backflow is particularly difficult to track. Parasites have a complex life cycle, which reduces the possibility of cross species transmission. Moreover, many parasites are relatively stable in the living environment, so it is not clear whether humans are the source of infection. However, based on indirect evidence, some spillback phenomena suggest that humans are likely to transmit duodenal flagellates, a gastrointestinal parasite that causes diarrhea and spasm, to red colobus monkeys in western Uganda. Researchers found duodenal flagellates similar to those in human patients in red colobus monkeys near residential villages.
Fungi such as Candida albicans can cause a variety of human symptoms, such as vaginal, urethral, skin and oral infections. A study shows that although human pathogens are very rare in wild animals, they do exist in wild animals. The mode of transmission between people and wild animals can pollute the environment through "human survival by-products", such as diapers and leftovers. In addition, Researchers also found fungal strains picked up by humans in pets.
How do we identify backflow
The discovery of backflow is a matter of money and luck. Usually, it is found only in routine monitoring, for example, when scientists closely observe new pathogens or introduce pathogens that lead to the accumulation of HIV, SARS virus, novel coronavirus, Ebola virus and other viruses, the virus will be observed to overflow to the population. We rarely look for human pathogens in animal populations, so it's easy to ignore spillback.
When we find the backflow phenomenon, it usually occurs on the animals we closely monitor, such as pets, livestock, captive animals, etc. occasionally, we will closely observe endangered species. Generally, researchers will choose the animals with the most frequent contact with humans, which are most likely to be infected by microorganisms carried by humans.
In addition, it is difficult to find specific evidence of a large number of spillback phenomena. People often find that an animal carries a human pathogen, so it is inferred that the pathogen is transmitted from human to animals. However, since many pathogens remain stable in the environment, the two species may never be in close contact before transmission. Moreover, even if the molecular types of pathogens match, the direction of pathogen transmission may not be determined - from humans to animals or from animals to humans. The two species may even be infected by an unknown third source.
If we want to minimize the spread of human diseases, we need to better understand the organisms that share the natural environment with humans. Although it is understandable that we need to pay more in-depth attention to humans, this attention may eventually prove to be equally important for humans and those organisms that share the earth.