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◆Never-before-seen microbes locked in glacier ice could spark a wave of new pandemics if released
【Live Science：Harry Baker 2022年7月1日】
Stunned scientists have uncovered more than 900 never-before-seen species of microbes living inside glaciers on the Tibetan Plateau. Analysis of the microbes’ genomes revealed that some have the potential to spawn new pandemics, if rapid melting caused by climate change releases them from their icy prisons.
In a new study, researchers from the Chinese Academy of Sciences took ice samples from 21 glaciers on the Tibetan Plateau — a high-altitude region in Asia wedged between the Himalayan mountain range to the south and the Taklamakan Desert to the north. The team then sequenced the DNA of the microscopic organisms locked inside the ice, creating a massive database of microbe genomes that they named the Tibetan Glacier Genome and Gene (TG2G) catalog. It is the first time that a microbial community hidden within a glacier has been genetically sequenced.
The team found 968 microbial species frozen within the ice — mostly bacteria but also algae, archaea and fungi, the researchers reported June 27 in the journal Nature Biotechnology (opens in new tab). But perhaps more surprisingly, around 98% of those species were completely new to science. This level of microbial diversity was unexpected because of the challenges associated with living inside glaciers, the researchers said. “Despite extreme environmental conditions, such as low temperatures, high levels of solar radiation, periodic freeze-thaw cycles and nutrient limitation, the surfaces of glaciers support a diverse array of life,” the study authors wrote.
The researchers aren’t sure exactly how old some of these microbes are; prior studies have shown that it is possible to revive microbes that have been trapped in ice for up to 10,000 years, according to the study.
This is not the first time that scientists have found a surprising abundance of microbes living in Tibetan glaciers. In January 2020, a team that analyzed ice cores from a single glacier uncovered 33 different groups of viruses living within the ice, 28 of which had never been seen before.
The surprising microbial diversity within glaciers, coupled with an increase in melting glacial ice due to climate change, boosts the chances that potentially dangerous microbes — most likely bacteria — will escape and wreak havoc, researchers said. “Ice-entrapped pathogenic microbes could lead to local epidemics and even pandemics” if they are released into the environment, the authors wrote.
Evidence suggests that some of the newfound bacteria could be very dangerous to humans and other organisms. The team identified 27,000 potential virulence factors — molecules that help bacteria invade and colonize potential hosts — within the TG2G catalog. The researchers warned that around 47% of these virulence factors have never been seen before, and so there is no way of knowing how harmful the bacteria could be.
Even if these potentially pathogenic bacteria do not survive for long after escaping their glaciers, they can still cause problems, the researchers said. Bacteria have the unique ability to exchange large sections of their DNA, known as mobile genetic elements (MGEs), with other bacteria. So even if the glacial bacteria die shortly after being thawed out, they can still pass on some of their virulence to other bacteria they encounter. This genetic interaction between glacier microbes and modern microorganisms “could be particularly dangerous,” the scientists wrote.
The Tibetan Plateau glaciers could be a hot spot for unleashing future pandemics because they feed fresh water into a number of waterways, including the Yangtze River, the Yellow River and the Ganges River, which supply two of the most populated countries in the world: China and India. Pandemics spread quickly through highly populated areas, as the world witnessed during the COVID-19 pandemic.
But this potential problem won’t just affect Asia. There are more than 20,000 glaciers on Earth covering around 10% of the planet’s land mass, and each glacier is likely to have its own unique microbial communities. In April 2021, a study using satellite images of glaciers found that nearly every glacier on Earth showed an accelerated rate of ice loss between 2000 and 2019, which increases the risk that pandemic-spawning microbes could escape anywhere on the planet. The researchers warned that the “potential health risks [of these microbes] need to be evaluated” before they are released from their icy prisons.
However, there is a silver lining to this new study. Genetic records of microbial communities, such as the TG2G catalog, could be used as “toolkits” for bioprospecting — exploring natural systems to find valuable new compounds that can be used in medicine, cosmetics and other beneficial technologies. That makes databases like TG2G very important, especially if the newly discovered species go extinct in the future; an outcome that is all too likely if they cannot adapt to the changes in their frozen habitat, the researchers wrote.
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An imported case of monkeypox was diagnosed in December 2019 in a traveller returning from Nigeria to the UK. Subsequently, environmental sampling was performed at two adjoining single room residences occupied by the patient and their sibling. Monkeypox virus DNA was identified in multiple locations throughout both properties, and monkeypox virus was isolated from several samples three days after the patient was last in these locations. Positive samples were identified following use of both vacuum and surface sampling techniques; these methodologies allowed for environmental analysis of potentially contaminated porous and non-porous surfaces via real-time quantitative PCR analysis in addition to viral isolation to confirm the presence of infection-competent virus.
This report confirms the potential for infection-competent monkeypox virus to be recovered in environmental settings associated with known positive cases and the necessity for rapid environmental assessment to reduce potential exposure to close contacts and the general public. The methods adopted in this investigation may be used for future confirmed cases of monkeypox in order to establish levels of contamination, confirm the presence of infection-competent material, and to identify locations requiring additional cleaning.
Originality-Significance Statement Several imported cases of human monkeypox infection, an emerging infectious disease with a case fatality rate of up to 10%, have been identified in recent years including importations into the United Kingdom, the United States, Israel, and Singapore. It is likely that this phenomenon relates to decreased immunity against monkeypox infection in endemic regions that was previously provided via the smallpox vaccination programme. It is therefore likely that further imported cases of monkeypox will be reported in future; such occurrences will require significant clinical oversight, including suitable infection control measures. Environmental sampling to identify contaminated sites that may pose a risk can inform infection control guidance. This report documents an environmental sampling response following an imported case detected in late 2019 in the UK. Monkeypox virus DNA was readily identified in numerous locations throughout two domestic residences associated with the infected patient and infectious virus was isolated from several environmental samples confirming that contaminated environmental settings may pose a risk for onward transmission. The methods utilised in this report may advise future environmental responses following cases of this high consequence emerging viral disease in order to prevent secondary cases in close contacts or members of the public.
Monkeypox is a re-emerging zoonotic disease resulting from infection by monkeypox virus (MPXV), a double-stranded DNA virus classified within the Orthopoxvirus genus in the family Poxviridae. The clinical disease resulting from infection with MPXV is similar to smallpox but with marked lymphadenopathy; however, the symptoms and severity are typically far milder. Following an incubation period of approximately 5-14 days, early symptoms include fever, fatigue, myalgia, swollen lymph nodes, and a rash. Monkeypox disease is typified by rash progression from characteristic macular through papular, vesicular, and pustular phases (Damon, 2011). The duration of illness is typically 2-4 weeks and human infection has a case fatality rate of approximately 3.6% for the West African clade of MPXV and 10.6% for the Central African clade of MPXV (Durski et al., 2018; Beer and Rao, 2019; Bunge et al., 2022).
The animal reservoir for MPXV is not fully understood; however, it is likely that both large mammals and small rodents play a role in the natural zoonotic cycle (Doty et al., 2017; Alakunle et al., 2020). Primary human cases of monkeypox likely occur due to a spillover event from contact with an infected mammal (Damon, 2011). MPXV can be transmitted between people through contact with infected bodily fluids or lesions, and possibly via large droplet, aerosol, and/or fomite transmission; however, person-to-person transmission is not frequent with an estimated R0 of <1.0 (Alakunle et al., 2020). The endemic regions for MPXV are Central and West Africa with the majority of human cases reported from the Democratic Republic of Congo since its first identification as a human pathogen in 1970 (Durski et al., 2018; Sklenovská and Van Ranst, 2018; Beer and Rao, 2019). In 2017, human cases of monkeypox were reported in Nigeria for the first time since the late 1970s (Yinka-Ogunleye et al., 2018); more than 400 cases were reported in the following three years implying a sustained focus of endemicity and a notable threat to human health in the region (Alakunle et al., 2020). During this period, imported cases of monkeypox were identified following travel to Nigeria on four occasions: two separate importations into the United Kingdom 2018 (Vaughan et al., 2018), one importation into Israel in 2018 (Cohen-Gihon et al., 2020), and one importation into Singapore in 2019 (Mauldin et al., 2020; Yong et al., 2020). Onward transmission was recorded in only one of these importations – during the second 2018 importation into the UK where a health worker treating the patient contracted monkeypox after changing the patient’s bedding and clothing without respiratory protection prior to initial diagnosis (Vaughan et al., 2020). In early December 2019, a traveller in their 40’s sought medical assistance shortly after return to the UK following a 4-week trip to Nigeria. Symptoms began approximately two weeks before their return with a 4-day febrile illness followed by a persistent widespread pustular rash. Upon examination, the patient was apyrexial and felt well but had overt lesions covering many parts of the body including their genitals, the palms of the hands, and soles of the feet. They reported no known contact with animals, vermin or raw foods, and no travel to rural areas whilst in Nigeria. Blood EDTA, urine, throat swab, and swabs from three lesions were for tested at the Rare and Imported Pathogens Laboratory at UK Health Security Agency, Porton; all samples were positive when analysed by both pan-orthopox and MPXV-specific real-time quantitative PCR (RT-qPCR) assays confirming the diagnosis of monkeypox. Following diagnosis, the patient was transferred to a specialist infectious disease hospital for observation and treatment; this report focusses on the parallel work to establish risk of onward transmission for environments in which the patient spent prolonged periods of time since return to the UK and prior to diagnosis. The locations identified included adjoining residences occupied by the patient and their sibling in addition to a long-distance commercial bus used by the patient to travel approximately 200 miles from the airport to their residence.