Since the SARS outbreak invaded human society, human experts have been searching for coronaviruses, and bat species in nature have become a key research object.
A few days ago, a study on Burmese bats once again discovered three new α coronaviruses and three new β coronaviruses. α coronavirus and β coronavirus have a significant impact on human health, of which SARS-CoV, SARS-CoV-2 and MERS-CoV, the most serious infectious diseases in humans to date, belong to the latter. The researchers note that ongoing land-use change brings humans closer to wildlife, which remains an important driver of the emergence of zoonotic diseases, and justifies continued surveillance and vigilance on a large scale, the research paper was published in the journal PLOS ONE.
The project is designed by researchers from the Smithsonian National Institute of Zoological Park and Conservation Biology, the University of California, Davis Institute of Medicine, and has worked intensively with three Ministries of the Myanmar government, including: the Ministry of Livestock, Agriculture, and Irrigation; the Ministry of Health and Sports; and the Department of Natural Resources and Environmental Protection.
Between May 2016 and August 2018, the team conducted sample and data collection at three selected sites in Myanmar, covering the northern region of Yangon, pa'an city area of Kayin State, and the Town of Sripo in Sagae Province. As land-use change increases the distance between humans and wildlife and increases potential human exposure to wildlife through livelihoods, recreation, commerce and religious or cultural activities, these sites are identified as potentially high-risk areas, two of which feature cave tours, where people are regularly exposed to bats through guano collection, religious activities and ecotourism.
Figure | Map of Bat Capture Sites in Myanmar 2016-2018 (Source: PLOS ONE)
Bat sampling is collected by trained field personnel. All bats are captured with special webs, and each individual is manually identified, morphologically assessed, and sampled. Where possible, oral and rectal swabs were collected using a sterile polyester head applicator, and also a sample of bird droppings consisting of urine and feces was collected from the environment using a plastic tarp.
In terms of samples, the researchers captured and sampled a total of 464 bats from at least 11 species in 6 families and 8 genera, and collected and tested a total of 759 samples (464 oral swabs, 140 rectal swabs, 155 stool excreta samples). A total of 461 samples (244 oral swabs, 117 rectal swabs and 100 stool excreta samples) were sampled during the dry season and 298 samples (220 oral swabs, 23 rectal swabs and 55 fecal excreta samples) were sampled during the rainy season.
Photo| summary of positive and coronavirus detected in Burmese bats (Source: PLOS ONE)
The results showed that coronaviruses were detected in 48 samples: The researchers detected coronavirus fragments from an unidentified tomb bat (Taphozous sp.), three Hipposideros larvatus (also known as midshoe bats), and three Asian giant yellow bats (Scotophilus heathii). In addition, of the 40 positive specimens detected in bat feces, 36 were from the middle-hoofed bat, which belongs to the genus Chickopteridae, and the host of the remaining 4 positive specimens is Chaerephon pcatali.
A total of 54 sequences were recovered from the analysis, clustered within 7 different coronavirus genotypes. Using established cutoffs and methods, the researchers detected four α coronaviruses (predicted CoV-35, 47, 82, and 90) and three β coronaviruses (predicted CoV-92, 93, and 96). Among them, α coronavirus PREDICT_CoV-35 has been previously known and was found between 2013 and 2017 in the Cambodian and Vietnamese high-headed bat (Scotophilus kuhlii), the unknown myotis and unspecified host bats.
The remaining 6 coronaviruses are new viruses. PREDICT_CoV-92 is the most common, with 36 samples of mixed bat excrement belonging to the middle-hoofed bat. Interestingly, three coronaviruses were found to be co-infected: PREDICT_CoV-90 was detected by PREDICT_CoV-35, PREDICT_CoV-93 was detected by PREDICT_CoV-96, and PREDICT_CoV-96 was detected by PREDICT_CoV-92.
Figure | the final edited sequence and gene bank registration number (Source: PLOS ONE)
The researchers noted in their discussions that three new α coronaviruses, three new β coronaviruses, and one known α coronavirus found in Burmese bats are not one, but none of which is strongly associated with SARS-CoV, MERS-CoV, or SARS-CoV-2, with bat fecal excrement samples accounting for the majority of positive samples, suggesting an important transmission route for coronavirus virus leakage in bats. In addition, there are differences in coronavirus positivity rates between bat species, with samples taken from middle hoof bats accounting for 83% of the positive rate, and the researchers note that coronavirus populations may be significantly associated with bat host taxa at the family level, however, further evidence is needed to elucidate the relationships and ecology.
In addition, the study's limitations mention that the sampling volume of Myanmar bats is still relatively small, only several coronaviruses have been detected in insectivorous bats, suggesting that there may be more coronaviruses to be detected, it is estimated that bats carry more than 3200 coronaviruses, most of which have not yet been detected, given the possible public health consequences of the expansion of human activities, it is necessary to continue to monitor coronaviruses, especially in other species and human-wildlife aspects.
Figure | The middle-hoofed bat, scientific name Hipposideros larvatus grandis, is an animal of the genus Hoofed bats in the family Jupiterae (Source: Wikipedia)
The final foothold of the study on burmese bats once again emphasizes the balanced relationship between humans and species in nature. According to statistics, 60%-75% of emerging infectious diseases (EIDs) are made up of zoonotic diseases, of which more than 70% are said to originate from wildlife species, and viral spillover effects are largely attributable to changes in human activity after population index growth since the second half of the 20th century.
Large-scale land-use changes, such as deforestation and the conversion of agricultural land, can alter host-pathogen relationships, increase human exposure to wildlife and their pathogens, and make cross-species transmission events more likely. For established pathogens, human-mediated biodiversity loss tends to lead to a decrease in the number of suboptimal host species, and an increase in the number of hosts capable of evolving or amplifying viruses, which can lead to higher rates of human infection. In addition, the intensification of livestock and poultry production systems leads to anthropotentogenic density of livestock populations, leading to the amplification and spillover of pathogenic bacteria.
Historically, human activities have arguably played an important role in interspecies transmission events. After the SARS outbreak, the coronavirus was found in many bat species around the world, including Asia, Africa, Europe, the Americas and Australasia. The growing body of evidence supports the role of bats in the transmission of viruses, including SARS-CoV and MERS-CoV, poses a huge threat to public health, and the potential for unknown bat-borne coronaviruses to trigger zoonotic diseases warrants vigilance and continuous monitoring, necessitating the establishment of high-risk identification and identification mechanisms between humans, domestic animals and wild animals.
Despite these infectious threats, bats are an important part of ecosystems and provide key roles such as seed propagation, pollination, control of insect populations , including crop pests and vectors , and are a potential valuable asset to the agricultural industry and smallholder farming.
The researchers say public health efforts should promote preventive measures to protect people from the spread of disease, but also enable human communities and bat species to coexist in a harmonious environment.