 Your new post is loading...
|
Scooped by
Juan Lama
|
Significance The recent Covid-19 pandemic highlighted that understanding the channels of disease transmission is crucially important for public health policies. However, measuring transmissions occurring through casual contact in the public space is highly challenging as researchers generally do not observe when infected individuals intersect casually with noninfected individuals. We overcome this methodological challenge in the context of the Covid-19 pandemic by combining card payment data, indicating exactly where and when individuals visited stores, with test data indicating when they were infected. We document that exposure to an infected individual in a store is associated with a significantly higher infection rate in the following week. Our estimates imply that transmissions between retail shoppers made a substantial contribution to the Covid-19 pandemic. Abstract This paper presents quasiexperimental evidence of Covid-19 transmission through casual contact between customers in retail stores. For a large sample of individuals in Denmark, we match card payment data, indicating exactly where and when each individual made purchases, with Covid-19 test data, indicating when each individual was tested and whether the test was positive. The resulting dataset identifies more than 100,000 instances where an infected individual made a purchase in a store and, in each instance, allows us to track the infection dynamics of other individuals who made purchases in the same store around the same time. We estimate transmissions by comparing the infection rate of exposed customers, who made a purchase within 5 min of an infected individual, and nonexposed customers, who made a purchase in the same store 16 to 30 min before. We find that exposure to an infected individual in a store increases the infection rate by around 0.12 percentage points (P < 0.001) between day 3 and day 7 after exposure. The estimates imply that transmissions in stores contributed around 0.04 to the reproduction number for the average infected individual and significantly more in the period where Omicron was the dominant variant. Published in PNAS (April 17, 2024):
|
|
Scooped by
Juan Lama
|
Small animal models have been a challenge for the study of SARS-CoV-2 transmission, with most investigators using golden hamsters or ferrets. Mice have the advantages of low cost, wide availability, less regulatory and husbandry challenges, and the existence of a versatile reagent and genetic toolbox. However, adult mice do not robustly transmit SARS-CoV-2. Here we establish a model based on neonatal mice that allows for transmission of clinical SARS-CoV-2 isolates. We characterize tropism, respiratory tract replication and transmission of ancestral WA-1 compared to variants Alpha (B.1.1.7), Beta (B.1.351), Gamma (P.1), Delta (B.1.617.2), Omicron BA.1 and Omicron BQ.1.1. We identify inter-variant differences in timing and magnitude of infectious particle shedding from index mice, both of which shape transmission to contact mice. Furthermore, we characterize two recombinant SARS-CoV-2 lacking either the ORF6 or ORF8 host antagonists. The removal of ORF8 shifts viral replication towards the lower respiratory tract, resulting in significantly delayed and reduced transmission in our model. Our results demonstrate the potential of our neonatal mouse model to characterize viral and host determinants of SARS-CoV-2 transmission, while revealing a role for an accessory protein in this context. Here the authors develop a neonatal mouse model for SARS-CoV-2 transmission, characterize differences in viral replication and shedding of variants of concerns, and show that deletion of ORF8 shifts viral replication to the lower respiratory tract and delays transmission. Published in Nature Comm. (May 25, 2023): https://doi.org/10.1038/s41467-023-38783-0
|
|
Scooped by
Juan Lama
|
Even as cases rise, genetic analysis suggests that the virus has been silently circulating in people since 2018. When the first monkeypox cases were identified in early May, European health officials were stumped. The virus was not known to spread easily among people, let alone infect dozens — and soon hundreds — of young men. The origins of the outbreak are now becoming clearer. Genetic analysis suggests that although the monkeypox virus is rapidly spreading in the open, it has been silently circulating in people for years. Health officials have already identified two versions of monkeypox among American patients, suggesting at least two separate chains of transmission. Researchers in several countries have found cases with no known source of infection, indicating undetected community spread. And one research team argued last month that monkeypox had already crossed a threshold into sustainable person-to-person transmission. The genetic information available so far indicated that, at some point in the last few years, the virus became better at spreading between people, said Trevor Bedford, an evolutionary biologist at the Fred Hutchinson Cancer Research Center in Seattle. “Genomic patterns would suggest this occurred around 2018,” Dr. Bedford said. If the virus has adapted to include people as hosts, monkeypox outbreaks could become more frequent and more difficult to contain. That carries the risk that monkeypox could spill over from infected people into animals — most likely rodents — in countries outside Africa, which has struggled with that problem for decades. The virus may persist in infected animals, sporadically triggering new infections in people. “We can also transmit this back to animals that can spread the disease within wildlife and back to humans,” said Sagan Friant, an anthropologist at Pennsylvania State University who has studied human-animal interactions in Nigeria for about 15 years. The longer it takes to contain the virus, the higher the odds that it will find a permanent new home in people or animals, Dr. Friant said. As of Wednesday, the United States had identified 156 cases in 23 states and the District of Columbia. The global toll has surpassed 3,400 confirmed cases, and another 3,500 cases are being evaluated, tripling the numbers from two weeks ago. In Africa, eight countries had reported more than 1,500 suspected cases and 72 deaths as of June 10, most of which were in the Democratic Republic of Congo. Monkeypox is a large double-stranded DNA virus, about seven times as large as the coronavirus. DNA-based viruses can correct their own errors when they replicate their genetic material. They may collect just one or two mutations per year compared with 20 to 30 mutations for an RNA virus like the coronavirus. But the monkeypox virus seems to have amassed an unexpectedly high number of mutations — nearly 50 compared to a version that circulated in 2018, according to preliminary analyses. Of the 47 mutations identified in one analysis, 42 carry the distinct signature of an enzyme called Apobec3. This enzyme, first discovered by researchers studying H.I.V., is a so-called host defense factor — an immune-system weapon that animals and people use to disarm viruses like monkeypox. The enzyme essentially forces viruses to make mistakes when they try to replicate, causing them to self-destruct. Mice carry just one version of this enzyme, while humans have seven. The rapid accumulation of mutations, characteristic of the enzyme since 2018, suggests that monkeypox may have switched to people as hosts around then, Dr. Bedford said. It is unclear how the mutations might change the virus. Of 48 mutations identified in Britain, 21 may affect how the disease spreads, its severity and how well it responds to a treatment called tecovirimat, according to the U.K. Health Security Agency. But because mutations introduced by the enzyme Apobec3 are meant to harm the virus, their quantity alone is not worrying, said Michael Malim, a virologist at King’s College London who discovered Apobec3 in 2002. The effect of the mutations is “more likely to be debilitating,” he said. Comparing the current version of the virus with samples from the past few years might help understand how it has evolved, but that information is scarce. Nigeria did not have the ability to sequence genetic material until 2017. Since then, scientists there have been analyzing the sequences from about 50 monkeypox cases, according to Dr. Ifedayo Adetifa, director of the Nigeria Center for Disease Control. But without the specialized equipment or expertise needed for rapid analysis, the scientists have not yet completed their work, he said. Although the researchers have fielded several requests for the data from outside Nigeria, Dr. Adetifa said they would wait to publish their work to prevent teams with more resources from outcompeting them and grabbing credit. “I’m all for open data sharing and all of that,” he said. “Question is, who benefits?” Some experts have cautioned for years that the eradication of smallpox in 1980 left the world vulnerable to the broader family of poxviruses and raised the odds of monkeypox evolving into a successful human pathogen. In West Africa, the incidence of monkeypox has increased at least twentyfold since 1986. In African countries generally, Dr. Adetifa said, “we suspect some underreporting because there’s been relatively low awareness and maybe low perceived risk of monkeypox.” Nigeria is stepping up its surveillance of monkeypox, and case numbers may rise as more people become aware of the virus, he added. Although monkeypox has a distinctive rash that appears on the palms of the hands and soles of the feet, it is frequently confused with chickenpox. Many men in the current outbreak have lesions on their genitalia, but those can be mistaken for sexually transmitted infections such as syphilis, gonorrhea and chlamydia. Researchers in Italy and Germany have reported finding monkeypox DNA in semen, but it is unclear if the virus spreads that way or is merely present in semen and vaginal secretions. The spread among young men with genital ulcers was observed at least once before. In 2017, Nigeria recorded 228 suspected cases of monkeypox and confirmed 60. The virus spread primarily among young men who had genital ulcers. Britain’s experience indicates how complicated it can be to trace contacts of a virus that may be sexually transmitted, especially in cases where infected people have had multiple anonymous partners. In an initial analysis of a subset of cases, officials said they were able to obtain names for fewer than one-third of the 78 reported sexual contacts. Many cases in Africa have been traced back to contact with wild animals or the use of animal products for medicinal or cultural practices. As deforestation and urbanization drive people and animals into closer quarters, more viruses may make the jump to human hosts. Monkeypox is most likely to leap to people from rodents. There are some 2,000 species of rodents worldwide, composing 40 percent of all mammalian species. The African rope squirrel is a leading candidate as the primary reservoir for monkeypox, but there are other contenders, including striped mice and dormice, giant pouched rats, rusty-nosed rats and brush-tailed porcupines. In a 2003 outbreak in the United States, a shipment of Gambian pouched rats imported from Africa transmitted monkeypox to prairie dogs, which then infected 71 Americans. But officials did not find signs of the virus in animals in the United States once the spate of cases had ended. There’s no guarantee that luck will hold this time. “These spillovers from other species, and what that means and what the trajectory is — it’s very unpredictable,” Dr. Malim said. “And it’s occurring more and more.”
|
|
|
Scooped by
Juan Lama
|
A new analysis published in The Lancet Microbe shows how the SARS-CoV-2 virus spreads from the nose to the air and surfaces in the immediate surroundings. The findings are the second batch of results to come from the COVID-19 Human Challenge Program, led by Imperial College London and partners, and provide granular insights into how people infected with SARS-CoV-2 spread the virus to their immediate surroundings. In February 2021, 36 healthy, young participants with no previous immunity to the virus were infected with SARS-CoV-2 under controlled clinical conditions in a residential facility at the Royal Free Hospital in London, where they could be carefully monitored. They remained at the facility until they were no longer infectious. The facility enabled researchers to track the course of infection in great detail, with the clinical team taking daily swabs from participants' noses and mouths, as well as environmental samples of the air and swabs of surfaces in their rooms. Viral emissions Out of 36 initial participants, a total of 18 became infected. Analysis showed that two individuals emitted substantially more virus into the air than the other infected participants, but displayed no significantly worse symptoms. The researchers suggest this may represent the small proportion of individuals who have potential to be highly infectious, sometimes described as "superspreading." Analysis found large amounts of viral RNA in air samples, in exhaled breath, as well as swabs of participants hands and on surrounding surfaces, including frequently touched surfaces such as door handles and TV remote controls, showing how an infected person contaminates their surrounding environment and can spread the virus. Viral emissions correlated strongly with the level of virus detected in people's noses, more than in their throat, highlighting the nose as a significant route for infected people shedding virus into the air and environment. According to the researchers, the latest analysis further highlights the routes by which the virus is transmitted from person to person—directly into the air, depositing onto nearby surfaces, and transferred from contaminated hands to frequently touched surfaces, such as door handles and remote controls. Reliable indicators They also show that positive lateral flow tests and visible symptoms were reliable indicators of when people were infectious and emitting virus into the air and environment. The vast majority of virus was emitted after people noticed their first symptoms, with very little virus released into the environment before that (pre-symptomatically). They found no significant link between the severity of participants' symptoms and the amount of virus they shed into the environment. According to the researchers, the findings highlight the need to reinforce public health messaging around proper face mask use, hand washing and surface cleaning, as well as how human challenge studies continue to add to our knowledge of COVID-19 infection and transmission. Dr. Anika Singanayagam, NIHR Academic Clinical Lecturer in the Department of Infectious Disease at Imperial College London, and joint first author of the study, said, "Our latest findings add to the existing body of knowledge on COVID-19 transmission. By studying infection in a controlled environment, we can collect unique, detailed measurements of virus emitted that allow us to understand how and when people with COVID-19 are contagious to others. These types of measurements are challenging to collect in real-world studies. "Our data indicate that much of the virus people shed comes from the nose, further highlighting the importance of face masks covering the nose as well as the mouth when they're used. But it also shows how virus can be transferred from hands to contaminate surfaces, like door handles or remote controls, which become a source of infection." Dr. Jay, Jie Zhou, research associate in the Department of Infectious Disease at Imperial College London, and joint first author of the study, said, "Understanding when infected people are contagious and how to detect when they are contagious is important—it can help us to use interventions like face masks or social distancing more effectively. The data in our study highlights that being aware of, and acting on, the first minor symptoms that signal an infection, coupled with frequent self-testing with lateral flow tests, can effectively reduce onward spread." Professor Wendy Barclay, head of the Department of Infectious Disease at Imperial College London, said, "One of the most important things we need to know for controlling the spread of respiratory viruses, such as SARS-CoV-2, is when are people who are actively infected with the virus most likely to infect others? That information can help to tell us how the virus will spread, and how best to use interventions to stop the outbreak. "Human challenge studies enable us to gain granular insights into the infection which we might not otherwise be able to. They play an important role in our understanding of infectious diseases, and should be considered a part of future pandemic preparedness." Previous findings The latest findings add to several key clinical insights already gained from the COVID-19 Human Challenge Program, published in February 2022. These include that symptoms start to develop on average two days after contact with the virus, that infection first appears in the throat, infectious virus peaks about five days into infection and, at that stage, is significantly more abundant in the nose than the throat. The first analysis also found that lateral flow tests (LFTs) are a reassuringly reliable indicator of whether infectious virus is present in the nose and throat (i.e., whether they are a likely to be infectious to other people). Original research published (June 9, 2023) at The Lancet Microbe: https://doi.org/10.1016/S2666-5247(23)00101-5
|
|
Scooped by
Juan Lama
|
We describe animal-to-human transmission of SARS-CoV-2 in a zoo setting in Indiana, USA. A vaccinated African lion with physical limitations requiring hand feeding tested positive for SARS-CoV-2 after onset of respiratory signs. Zoo employees were screened, monitored prospectively for onset of symptoms, then rescreened as indicated; results were confirmed by using reverse transcription PCR and whole-genome virus sequencing when possible. Traceback investigation narrowed the source of infection to 1 of 5 persons. Three exposed employees subsequently had onset of symptoms, 2 with viral genomes identical to the lion’s. Forward contact tracing investigation confirmed probable lion-to-human transmission. Close contact with large cats is a risk factor for bidirectional zoonotic SARS-CoV-2 transmission that should be considered when occupational health and biosecurity practices at zoos are designed and implemented. SARS-CoV-2 rapid testing and detection methods for big cats and other susceptible animals should be developed and validated to enable timely implementation of One Health investigations. Published (April 17, 2023): https://doi.org/10.3201/eid2906.230150
|
|
Scooped by
Juan Lama
|
For the past couple of years, COVID has affected the way we live, shop, and work. It spreads easily, so we have had to take measures to stop it in its tracks. Have you ever wondered about other fast spreading viruses humanity has had to deal with in the past? This This infographic from NYRequirements takes a look:
|
