Impact of climatic factors on the propagation of Covid-19
.tif "Climate change effects on Covid-19 spread") |
| Climate change effects on Covid-19 spread |
Abstract
The survival of certain coronaviruses depends on meteorological and solar factors. Current studies aim to find out whether these conclusions would also apply to COVID-19. Some of these studies indicate that there is a correlation between the climate and the spread of this pandemic. Higher temperatures and higher humidity levels could reduce the spread of SARS-CoV-2. However, other more recent ones suggest that summer temperatures will not contain the transmission of COVID-19. With these contradictory conclusions, much uncertainty reigns on this subject. WHO has therefore declared that there is no information to predict that the coronavirus will disappear with the arrival of summer. Social distancing and barrier gestures will be essential. The objective of this review is to discuss all the studies and hypotheses concerning the correlation between the different climatic factors and the propagation of covid-19.
Keywords: COVID-19; SARS-CoV-2; Epidemic; Meteorological and solar factors; Temperature; Humidity.
1. Introduction
Like any epidemic, the appearance and spread of Covid-19 is multifactorial in origin. Two main factors can be distinguished; population density and displacement, and the climatic factor, which is relatively predictable and well-studied in the case of seasonal influenza. In a respiratory infection, a high and dry air temperature has an immediate effect on the projected liquids (saliva, droplets ...) which dry faster on a surface [1]. In addition, the vectors of an infection (virus, bacteria, etc.) have a variable survival time depending on the temperature and exposure to solar radiation. Like the flu and cold viruses, which are reduced every year during the summer season. Respiratory coronavirus viruses are also dependent on weather conditions. If the cold keeps these viruses, the heat, humidity and UV radiation from the sun could decrease their longevity. The lifespan of certain coronaviruses therefore depends, among other things, on weather and solar factors [2]. Based on these results, the current studies aim to find out whether these conclusions would also be valid for COVID-19. Very recent studies attempt to determine the role of the advance towards the summer season on the evolution of the pandemic. Preliminary results of the influence of the weather on the new coronavirus suggest that the epidemic could be slowed down by higher temperatures and humidity [3]. Scientists are looking at this, among other things, on the impact of weather conditions in order to understand the future evolution of the COVID-19 pandemic [4,5]. Coronaviruses are respiratory viruses of which COVID-19 is a part. In this regard, it is considered to be weather-sensitive, potentially suffering the effects of weather fluctuations. The climate has an effect on any respiratory epidemic. Even if its effect is not yet proven for the Covid-19, this hypothesis must be taken into account.
The objective of this review is to provide a bibliographic summary, on respiratory viral infections in general and on coronavirus in particular, as well as the impact of weather and climate conditions on the spread of the covid-19 pandemic.
2. Emerging viral respiratory infections
Viral respiratory infections are common conditions of varying severity. Viral infections commonly affect the upper or lower respiratory tract. Respiratory viruses include the epidemic influenza viruses (A and B), H5N1 and H7N9 avian influenza A viruses, parainfluenza viruses 1 through 4, adenoviruses, respiratory syncytial virus A and B and human metapneumovirus, and rhinoviruses [6].
Although respiratory infections can be classified by the causative virus (eg, influenza), they are generally classified clinically according to syndrome (eg, the common cold, bronchiolitis, croup, pneumonia). Although specific pathogens commonly cause characteristic clinical manifestations (eg, rhinovirus typically causes the common cold, respiratory syncytial virus [RSV] typically causes bronchiolitis), each can cause many of the viral respiratory syndromes [6].
In recent years, advances in molecular biology techniques have made it possible to identify respiratory viruses which have been present in humans for a long time, but which until then have been unknown. These include the human metapneumovirus (HMPV), the new human coronaviruses HCoV-NL63 HCoV-NH and HCoV-HK, the human Boca virus (HBoV) and the new human polyomaviruses KI and WU. In addition to these newly identified viruses, we have observed in recent years the emergence in humans of new viruses responsible for respiratory infections. These viruses recently introduced into the human species come from an animal reservoir. They generally have a major pathogenic power with a high mortality rate. Respiratory viruses are a major global cause of mortality worldwide. These viruses are henipaviruses (Hendra and Nipah viruses), new world hantaviruses responsible for hantavirus pulmonary syndrome, severe acute respiratory syndrome coronavirus (SARS-CoV) and avian influenza virus H5N1. The latter virus poses the threat of a deadly pandemic raising the specter of the Spanish flu of 1918-1919, responsible for 20 to 50 million deaths [7]. Severity of viral respiratory illness varies widely; severe disease is more likely in older patients and infants. Morbidity may result directly from viral infection or may be indirect, due to exacerbation of underlying cardiopulmonary conditions or bacterial superinfection of the lung, paranasal sinuses, or middle ear [8].
3- Coronavirus infections
Coronaviruses are enveloped RNA viruses, characterized by surface protein spikes, which, under electron microscopy, resemble the sun’s corona. Numerous coronaviruses, first discovered in domestic poultry in the 1930’s, cause respiratory, gastrointestinal, liver, and neurologic diseases in animals. Only 7 coronaviruses cause disease in humans (HCoV). Four of the 7 HCoV (HCoV-NL63, -229E, -OC43, and -HKU1) cause mild and self-limiting upper respiratory tract infections, such as the common cold, but can cause severe lower respiratory tract infections, including pneumonia, in infants, the elderly, and the immunocompromised. These HCoV infections show a seasonal pattern with most cases occurring in the winter months in temperate climates. Three of the 7 HCoV (SARS-CoV, MERS-CoV, and SARS-CoV2) have caused major outbreaks of deadly pneumonia in the 21st century [9].
In 2002 and 2003, an outbreak of severe acute respiratory syndrome (SARS) caused a number of deaths mostly in China and Hong Kong. There have been no cases of SARS reported since 2004. The source of SARS was palm civets (cat-like mammals) that had been sold as food at local live animal markets in Guangdong. Once introduced into humans, SARS-CoV readily spread person-to-person by large respiratory droplets, aerosols, and by fecal-oral transmission (diarrhea is a common manifestation of the infection).
In 2012, a novel coronavirus Middle East respiratory syndrome coronavirus (MERS-CoV) appeared in Saudi Arabia; it can cause severe acute respiratory illness and is sometimes fatal. MERS-CoV, like SARS-CoV, is a zoonosis, spread by direct or indirect contact with dromedary camels. MERS-CoV also spreads human to human by direct contact, fomites, and respiratory droplets. 42% of all cases in 2018-2019 were linked to clusters of human-to-human transmission in households or healthcare facilities. The source was unknown for 60%. MERS-CoV virus is detected respiratory tract secretions, feces, serum, and urine, and virus has been detected in survivors for a month or more after onset.
In 2019, another coronavirus (SARS-CoV2) that can cause an acute, sometimes fatal respiratory illness (COVID-19) emerged in Wuhan, China and is currently spreading worldwide. Respiratory viruses are typically spread from person to person by contact with infected respiratory droplets [6]. Coronaviruses, like other respiratory viruses, are pathogens whose impact must be taken into account in public health. Their surveillance is particularly necessary among the most susceptible populations such as the elderly, children and immunocompromised people because the consequences of an HCoV infection are greater, even fatal. In addition, coronaviruses are characterized by a high evolutionary potential and by a risk of emergence in the human population from a not insignificant reservoir. At least two of the "circulating" coronaviruses, HCoV-OC43 and HCoV-NL63, appear to have a zoonotic origin [10, 11]. This is also the case for SARS-CoV and MERS-CoV, the successive emergences of which in the human population from animal reservoirs over the past 15 years tend to confirm the permanent risk posed by Coronaviruses [12, 13].
4. The relationship between respiratory disease viruses and the climate
Certain climatic conditions can be considered as the top predictors of respiratory diseases such as SARS. Climate variables can also be a direct cause of biological interactions between SARS-CoV and humans. Optimal temperature, humidity, and wind speed are variables that can determine the survival and transmission of the SARS virus. Humidity is a predominant factor, combined with heat. The possibly contaminated droplets (viral load) evaporate more quickly when it is hot, and are therefore contaminated for less time. Indeed, in air saturated with humidity, the droplets agglomerate, become heavier and fall quickly, reducing the range of the viral load. On the other hand, in dry air (which is often the case in winter when it is cold), the contaminated droplets remain longer in suspension and have a more extensive capacity for contamination. According to Sagripanti et al. [14], it is the absolute humidity rate (expressed in grams per cubic meter of air) which is used as a reference, but we can use the conversion into relative humidity, easier to interpret, which must be between 40% and 60% with a temperature of at least 20 ° C. This combination would then slow the spread of coronaviruses. Recently, a series of studies had shown that climatic factors are important factors in the transmission and survival of coronaviruses and other respiratory disease viruses (Table 1).
Temperature could increase or decrease the transmission risk by affecting the survival time of coronaviruses on surfaces. SARS transmission appeared to be dependent on seasonal temperature changes and the multiplicative effect of hospital infection [23]. It has also been documented that several factors, including climatic conditions (temperature and humidity), and population density might have affected the patterns of influenza spread and diversification [24]. including climatic conditions (temperature and humidity), and population density might have affected the patterns of influenza spread and diversification [24].
UV (ultraviolet) solar radiation destroys viruses and is the main germicide in the environment. Studies have shown that 90% of viruses in the Filoviridae family die after 20 to 100 minutes in the sun [14]. UV radiation is much more effective at inactivating the virus than high temperatures. The virucidal effect of natural sunlight can be mimicked ade-quately by an artificial light source with proven similar spectral characteristics in the UVB. Viral sensitivity to UVB or solar radiation can be correlated from experimental data obtained with UVC. The correlation factor between radiation measured at 300 ± 5 and 254 nm is between 33 and 60. The sensitivity of viruses either dry on surfaces or in liquid suspension is similar when in the presence of similar amounts of protein debris or growth media. More transparent media result in increased photocidal activity. The results of this study should assist in predicting the time whereby viruses remain a viable threat after natural broadcast from infected patients during epidemics or after an accidental or intentional release [14]. Also to the credit of the sun, it promotes the synthesis of vitamin D which seems to be sorely lacking in patients suffering from COVID-19. According to an Italian study by the University of Turin which analyzes the possible causes of the contagion of Covid-19, vitamin D could be proposed not as a remedy, but as a tool to reduce risk factors [25] La vitamine D est synthétisée par l'organisme humain en s'exposant à la lumière du soleil ne serait-ce que 20 minutes par jour. Toujours selon cette étude, un effet de la vitamine D serait de réduire le risque d'infections respiratoires d'origine virale, y compris celles causées par les coronavirus et de contrer les lésions pulmonaires causées par l'hyperinflammation [25].
5. Impact of weather conditions on the propagation of Covid-19
COVID-19 is the infectious disease caused by the last coronavirus that was discovered SARS-CoV2. This new virus and this disease were unknown before the outbreak appeared in Wuhan a city of over 11 million, in Hubei Province, Central China, in December 2019 [26]. COVID-19 presents as influenza-like illness. Fever, fatigue, cough ... the disease causes several common symptoms with the flu. This suggests that COVID-19 may eventually follow the same seasonality and disappear with the arrival of summer. From the start of the COVID-19 epidemic, researchers attempted to link weather conditions to the spread of the SARS-CoV2 virus, starting with the situation in China and, in general, South East Asia [27]. They deduced in particular that the propagation was faster by cold temperatures, than by warmer temperatures. An analysis was made by "the weather chain" on two Chinese studies looking for the link between temperature, humidity and the COVID-19 coronavirus [28].
In the first of these studies [3], the researchers studied 100 Chinese cities in which at least forty cases of COVID-19 were detected from January 21 to 23 (before confinement against the coronavirus). The results showed that the contagiousness of the virus is higher in the cities of northern China during this period, with a lower humidity and lower temperatures than the south-eastern coasts of the territory, subject to conditions warmer and more humid. According to their results, the epidemic was greater in countries where temperatures and humidity were lower, such as in Japan and Korea, unlike the warmer and wetter countries during this period, such as Malaysia and Thailand. These findings suggest that COVID-19 coronavirus is more easily transmitted in cooler, drier areas.
In the second study [29], unlike the previous study, the authors seek to determine the meteorological influence on the mortality of the COVID-19 coronavirus. The authors determined, by their method, that the mortality rate per day is higher per day of high thermal amplitude, that is to say on a day during which there is a large difference between the temperature in the morning and in the afternoon. According to some studies, the thermal amplitude increases the risk of respiratory and cardiovascular diseases. However, the COVID-19 coronavirus leads precisely, in its most serious form, to respiratory diseases, the outcome of which is sometimes fatal. The cold air would make our lungs more vulnerable, by weakening the immune function. Dry air in turn makes our body more vulnerable to respiratory infections like pneumonia and Severe Acute Respiratory Syndrome (SARS) [28]. Temperature and humidity variations may be important factors that influence covid-19 mortality [29]. After the publication of Chinese studies on the spread and mortality of the COVID-19 coronavirus, another study looked at the link between temperature, humidity and spread of the virus over a period from January 20 to March 19, 2020 [30]. The researchers intend to answer the question "will summer slow the epidemic?". According to this study, the evolution of the epidemic could be slowed down by high temperatures and high humidity. This assumption is based on epidemiological data from several countries and temperature and absolute humidity readings for the period from January 20 to March 9, 2020. For tropical, hot and humid countries, such as Malaysia, Singapore and Thailand (temperature above 17 ° C and absolute air humidity above 10 g / m3), researchers note a slower spread of the virus than in colder countries (with a temperature between 3 and 17 ° C) and drier (absolute humidity between 3g / m3 and 9g / m3), such as Italy, New York and Washington in the United States [30]. For North America, researchers indicate a slower spread of the virus in the southern states (warmer and wetter than the northern states), with a few exceptions, such as Louisiana (south) which has more than 1,000 of cases, while Oregon (northwest) has only 200. Despite the good correlation observed between the spread of COVID-19 and meteorological factors, this hypothesis remains to be confirmed. Researchers do not believe that a rise in temperature alone could reduce the epidemic of the new coronavirus. Effective public health interventions should be implemented worldwide to slow the transmission of COVID-19. Indeed, other studies have shown that temperature and humidity are not correlated with the transmission of COVID-19 [31-33]. In a study carried out in 122 cities from china, investigated the nonlinear relationship between ambient temperature and daily COVID- 19 confirmed cases. The results indicate that mean temperature has a positive linear relationship with the number of COVID-19 cases when the temperature is below 3 °C [33]. According to the authors of this study, there is no evidence that the number of COVID-19 cases could decrease when the weather warms, which has useful implications for policy makers and the public. In Jakarta, the capital city of Indonesia, it has been shown that only temperature average was correlated with COVID-19, with the lowest average temperature of 26.1 0C and the highest temperature of 28.6 0C [34]. This correlation is in line with previous research that shows the relationship between weather transmission and Syncytial Virus Respiration (RSV) [35]. Jakarta is the main economic destination for job seekers who come from various regions in Indonesia. Jakarta's population density is also very high and this allows covid-19 transmission to be very fast. To understand the transmission mechanism of this highly contagious virus, a machine learning approach was presented to study the effect of temperature, humidity and wind speed on the number of infected people in the three most populous autonomous communities in Spain [36]. It was found that there is a moderate inverse correlation between temperature and the daily number of infections. This correlation manifests for temperatures recorded up to 6 days before the onset, which corresponds well to the known mean incubation period of COVID-19. The correlation for humidity and wind speed is not significant [36].
Despite the significant finding of the weather on covid-19, other studies have shown that meteorological factors, such as humidity, temperature, and wind speed are not correlated with the transmission of COVID-19. This contradiction suggests a need for further investigation on this topic and other factors must be considered such as virus resistance, population mobility, and population endurance.
6. Conclusion
Scientists suggest that, although respiratory viruses like the flu virus circulate more in winter, there is still nothing to say with certainty that the new coronavirus follows the same seasonality. The only certainty advanced by the authors of the studies carried out; Without sufficient social distancing, screening and health policies, meteorological assistance linked to the return of summer will not be sufficient to counter the COVID-19 pandemic.
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