An epidemic that has already infected more than 253 million people and killed more than 5 million Its origin is still debated: How did SARS-CoV-2 appear in humans in China? On the other hand, there is a hypothesis about the escape of the virus from a scientific laboratory operating in China. A letter published in the magazine Science On May 14, 18 eminent scientists, although only one of them an expert on coronavirus, asked not to be excluded. In the meantime, results are known about studies in bats that could have been the host species for the coronavirus and passed on to humans.
currently, A new study published in the journal Nature Communications reported the identification of MERS-CoV-related viruses in two horseshoe bats, which were sampled in Cambodia in 2010. This country is located south of the Indochina Peninsula, in Southeast Asia. It is bordered by Thailand to the northwest, Laos to the north, Vietnam to the east, and the Gulf of Thailand to the southwest. It has a population of more than 16 million.
Regarding the coronavirus that caused the epidemic, the origin, reservoir, diversity and range of circulation of its ancestors are still unknown. However, horseshoe bats are believed to be the main natural reservoir for SARS-related coronaviruses. Horseshoe bats from different provinces in China have been found to carry different types of coronavirus.
Southeast Asia is home to more than 25% of the world’s bat species and is a hot spot for emerging zoonotic diseases. In June 2020, a close relative of SARS-CoV-2 was identified in bats captured from a cave in Thailand.
currently, Cambodian bat study results have been added. UNESCO and the National Authority of Preah Vihear commissioned the National Museum of Natural History, in Paris, France, to conduct a study on the mammals of northern Cambodia in 2010.. During this study, bats were captured by fog nets and harp traps in two provinces, Preah Vihear and Ratanakiri. The diversity of bats on both banks of the Mekong River was compared. Fog net, also known as Japanese net or fog net, is a system for catching flying animals, especially birds and bats. Harp traps are used in ecology and bat studies.
In addition, PREDICT, an epidemiological research program funded by the United States Agency for International Development (USAID), was implemented. Launched in 2009 as a pandemic early warning system, bats are sampled in order to detect and detect viruses that can lead to epidemics and zoonoses. Oral and rectal swabs were collected from bats from 2012 to 2018.
The samples were tested for viruses associated with SARS-CoV-2. During the researchers’ mission at the Musée de France, two bats infected with the virus closely related to SARS-CoV-2 were collected. The researchers analyzed 430 archived samples, including 162 oral swabs and 268 rectal swabs. Sixteen rectal swabs (3.72%) were positive for MERS: 11 alpha coronaviruses and five beta coronaviruses.
Two of the beta-coronavirus samples were additionally positive by quantitative reverse transcriptase polymerase chain reaction assay. These two samples came from rectal swabs from horseshoe chameleon bats sampled in December 2010 in Stung Treng Province, Cambodia. Oral swabs from these bats were negative for betacoronviruses.
RNA from the two coronaviruses was processed for next generation metagenomic sequencing. The sequenced genome was compared to the genome of SARS-CoV-2. The genomic sequence was closely associated with SARS-CoV-2, with 92.6% identity throughout the genome. They also had an identical genomic organization. Therefore, these two coronaviruses are a subspecies of viruses associated with SARS-CoV-2, although they are geographically distant.
The fragment corresponding to the N-terminal domain of the spike protein was different from SARS-CoV-2. This region was similar to that of the outermost beta coronaviruses. These data indicate that the ancestors of these viral subspecies co-circulate across a wider geographic area and in more distinct bat species.
In silico structural analysis suggested that the structure of the outer subdomain of the receptor-binding domain (RBD) of the spike protein is very similar to that of SARS-CoV-2. Six amino acid residues determine the active binding of SARS-CoV-2 to the angiotensin-converting enzyme 2 (hACE2) receptor. According to the researchers, five out of six amino acid residues have been conserved.
Subsequently, the researchers performed pseudovirus entry assays using HEK293T cells that express either the bat ACE2 receptor or the human ACE2 receptor. Viral pseudo-particles mobilized the SARS-CoV-2 coronavirus, or bat coronavirus, Spike. Viral pseudoparticles expressing bat coronavirus spike were not able to infect human ACE2-expressing HEK293T cells, but were able to infect bat ACE2-expressing HEK293T cells. Furthermore, pseudoviral particles expressing high SARS-CoV-2 were able to infect bat HEK293T cells expressing ACE2.
“This study has detected viruses associated with SARS-CoV-2 in a type of bat that is not found in China,” said the team led by scientist Viasna Diong, who works at the Pasteur Institute in Cambodia and was one of the researchers. Leaders published in Nature Communications. This means that these viruses have a much wider geographical distribution than previously reported. They also cautioned that this study also suggests that Southeast Asia should be considered in order to monitor the coronavirus in the future.
In September, Dr. Dong stated that “humans have been responsible for the devastation caused by COVID-19, due to the interference and destruction of natural habitats. If we try to be close to wildlife, the chances of transmission of the virus by wildlife are higher than normal. The chances of the virus becoming infected with humans are also high.”
Southeast Asia has a great diversity of wildlife. There is also extensive trade in wild animals. In addition, there is a drastic change in land use from infrastructure development, urban development, agricultural expansion and human encroachment on wildlife. Because of these factors, human contact with wild SARS-like coronavirus hosts has increased. Therefore, Southeast Asia may represent a region to be considered for the ongoing investigation of the origins of SARS-CoV-2. It also highlighted the importance of continuous and extensive monitoring of bats and other wildlife in Southeast Asia as a key measure to prepare for and prevent future epidemics.
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