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What is SARS and explain in detail?
Severe acute respiratory syndrome (SARS) is a viral respiratory disease of zoonotic origin caused by severe acute respiratory syndrome coronavirus (SARS-CoV or SARS-CoV-1), the first identified strain of the SARS coronavirus species severe acute respiratory syndrome–related coronavirus (SARSr-CoV). The first known cases occurred in November 2002, and the syndrome caused the 2002–2004 SARS outbreak. In the 2010s, Chinese scientists traced the virus through the intermediary of Asian palm civets to cave-dwelling horseshoe bats in Xiyang Yi Ethnic Township, Yunnan.SARS was a relatively rare disease; at the end of the epidemic in June 2003, the incidence was 8,469 cases with a case fatality rate (CFR) of 11%. No cases of SARS-CoV-1 have been reported worldwide since 2004.In December 2019, another strain of SARS-CoV was identified as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This new strain causes coronavirus disease 2019 (COVID-19), a disease which brought about the  COVID-19 pandemic.

Signs and symptoms
SARS produces flu-like symptoms which may include fever, muscle pain, lethargy, cough, sore throat, and other nonspecific symptoms. The only symptom common to all patients appears to be a fever above 38 °C (100 °F). SARS often leads to shortness of breath and pneumonia, which may be direct viral pneumonia or secondary bacterial pneumonia.The average incubation period for SARS is 4–6 days, although it is rarely as short as 1 day or as long as 14 days.

Transmission
The primary route of transmission for SARS-CoV is contact of the mucous membranes with respiratory droplets or fomites. While diarrhea is common in people with SARS, the fecal–oral route does not appear to be a common mode of transmission. The basic reproduction number of SARS-CoV, R0, ranges from 2 to 4 depending on different analyses. Control measures introduced in April 2003 reduced the R to 0.4.

Diagnosis
SARS-CoV may be suspected in a patient who has:
Any of the symptoms, including a fever of 38 °C (100 °F) or higher, and
Either a history of:
Contact (sexual or casual) with someone with a diagnosis of SARS within the last 10 days or
Travel to any of the regions identified by the World Health Organization (WHO) as areas with recent local transmission of SARS.
Clinical criteria of Sars-CoV diagnosisEarly illness: equal to or more than 2 of the following: chills, rigors, myalgia, diarrhea, sore throat (self-reported or observed)
Mild-to-moderate illness: temperature of >38 °C (100 °F) plus indications of lower respiratory tract infection (cough, dyspnea)
Severe illness: ≥1 of radiographic evidence, presence of ARDS, autopsy findings in late patients.For a case to be considered probable, a chest X-ray must be indicative for atypical pneumonia or acute respiratory distress syndrome.
The WHO has added the category of "laboratory confirmed SARS" which means patients who would otherwise be considered "probable" and have tested positive for SARS based on one of the approved tests (ELISA, immunofluorescence or PCR) but whose chest X-ray findings do not show SARS-CoV infection (e.g. ground glass opacities, patchy consolidations unilateral).The appearance of SARS-CoV in chest X-rays is not always uniform but generally appears as an abnormality with patchy infiltrates.

Prevention
There is no vaccine for SARS, although immunologist Anthony Fauci mentioned that the CDC developed one and placed it in the US national stockpile.  That vaccine, however, is a prototype and not field-ready as of March 2020. Clinical isolation and quarantine remain the most effective means to prevent the spread of SARS. Other preventive measures include:

Hand-washing with soap and water, or use of alcohol-based hand sanitizer
Disinfection of surfaces of fomites to remove viruses
Avoiding contact with bodily fluids
Washing the personal items of someone with SARS in hot, soapy water (eating utensils, dishes, bedding, etc.)
Avoiding travel to affected areas
Wearing masks and gloves
Keeping people with symptoms home from school
Simple hygiene measures
Isolating oneself as much as possible to minimize the chances of transmission of the virusMany public health interventions were made to try to control the spread of the disease, which is mainly spread through respiratory droplets in the air, either inhaled or deposited on surfaces and subsequently transferred to a bodys mucous membranes. These interventions included earlier detection of the disease; isolation of people who are infected; droplet and contact precautions; and the use of personal protective equipment (PPE), including masks and isolation gowns. A 2017 meta-analysis found that for medical professionals wearing N-95 masks could reduce the chances of getting sick up to 80% compared to no mask. A screening process was also put in place at airports to monitor air travel to and from affected countries.SARS-CoV is most infectious in severely ill patients, which usually occurs during the second week of illness. This delayed infectious period meant that quarantine was highly effective; people who were isolated before day five of their illness rarely transmitted the disease to others.As of 2017, the CDC was still working to make federal and local rapid-response guidelines and recommendations in the event of a reappearance of the virus.It has been found that those with a Vitamin D deficiency were at a 19.61-fold higher risk of having a critical result from Covid-19 disease versus those with an adequate amount of vitamin D. Patients with low vitamin D levels had worse symptoms, were more likely to be hospitalized, and had a greater risk of death. It is believed the reason vitamin D supplementation helps with the prevention of Covid-19 is due to the fact that vitamin D combats cytokine storms that are brought on because of Covid-19. Vitamin D supplementation is only effective in preventing Covid-19 but has been shown to have no effect after Covid-19 is contracted.

Treatment
As SARS is a viral disease, antibiotics do not have direct effect but may be used against bacterial secondary infection. Treatment of SARS is mainly supportive with antipyretics, supplemental oxygen and mechanical ventilation as needed. While ribavirin is commonly used to treat SARS, there seems to have little to no effect on SARS-CoV, and no impact on patients outcomes. There is currently no proven antiviral therapy. Tested substances, include ribavirin, lopinavir, ritonavir, type I interferon, that have thus far shown no conclusive contribution to the diseases course. Administration of corticosteroids, is recommended by the British Thoracic Society/British Infection Society/Health Protection Agency in patients with severe disease and O2 saturation of <90%.People with SARS-CoV must be isolated, preferably in negative-pressure rooms, with complete barrier nursing precautions taken for any necessary contact with these patients, to limit the chances of medical personnel becoming infected. In certain cases, natural ventilation by opening doors and windows is documented to help decreasing indoor concentration of virus particles.Some of the more serious damage caused by SARS may be due to the bodys own immune system reacting in what is known as cytokine storm.

Vaccine
Vaccines can help immune system to create enough antibodies and also it can help to decrease a risk of side effects like arm pain, fever, headache etc. According to research papers published in 2005 and 2006, the identification and development of novel vaccines and medicines to treat SARS was a priority for governments and public health agencies around the world. In early 2004, an early clinical trial on volunteers was planned. A major researchers 2016 request, however, demonstrated that no field-ready SARS vaccine had been completed because likely market-driven priorities had ended funding.

Prognosis
Several consequent reports from China on some recovered SARS patients showed severe long-time sequelae. The most typical diseases include, among other things, pulmonary fibrosis, osteoporosis, and femoral necrosis, which have led in some cases to the complete loss of working ability or even self-care ability of people who have recovered from SARS. As a result of quarantine procedures, some of the post-SARS patients have been diagnosed with post-traumatic stress disorder (PTSD) and major depressive disorder.

Epidemiology
SARS was a relatively rare disease; at the end of the epidemic in June 2003, the incidence was 8,422 cases with a case fatality rate (CFR) of 11%.The case fatality rate (CFR) ranges from 0% to 50% depending on the age group of the patient. Patients under 24 were least likely to die (less than 1%); those 65 and older were most likely to die (over 55%).As with MERS and COVID-19, SARS resulted in significantly more deaths of males than females.

Outbreak in South China
The SARS epidemic began in the Guangdong province of China in November 2002. The earliest case developed symptoms on 16 November 2002. The index patient, a farmer from Shunde, Foshan, Guangdong, was treated in the First Peoples Hospital of Foshan. The patient died soon after, and no definite diagnosis was made on his cause of death. Despite taking some action to control it, Chinese government officials did not inform the World Health Organization of the outbreak until February 2003. This lack of openness caused delays in efforts to control the epidemic, resulting in criticism of the Peoples Republic of China from the international community. China officially apologized for early slowness in dealing with the SARS epidemic.The viral outbreak was subsequently genetically traced to a colony of cave-dwelling horseshoe bats in Xiyang Yi Ethnic Township, Yunnan.The outbreak first came to the attention of the international medical community on 27 November 2002, when Canadas Global Public Health Intelligence Network (GPHIN), an electronic warning system that is part of the World Health Organizations Global Outbreak Alert and Response Network (GOARN), picked up reports of a "flu outbreak" in China through Internet media monitoring and analysis and sent them to the WHO. While GPHINs capability had recently been upgraded to enable Arabic, Chinese, English, French, Russian, and Spanish translation, the system was limited to English or French in presenting this information. Thus, while the first reports of an unusual outbreak were in Chinese, an English report was not generated until 21 January 2003. The first super-spreader was admitted to the Sun Yat-sen Memorial Hospital in Guangzhou on 31 January, which soon spread the disease to nearby hospitals.In early April 2003, after a prominent physician, Jiang Yanyong, pushed to report the danger to China, there appeared to be a change in official policy when SARS began to receive a much greater prominence in the official media. Some have directly attributed this to the death of an American teacher, James Earl Salisbury, in Hong Kong. It was around this same time that Jiang Yanyong made accusations regarding the undercounting of cases in Beijing military hospitals. After intense pressure, Chinese officials allowed international officials to investigate the situation there. This revealed problems plaguing the aging mainland Chinese healthcare system, including increasing decentralization, red tape, and inadequate communication.Many healthcare workers in the affected nations risked their lives and died by treating patients, and trying to contain the infection before ways to prevent infection were known.

Spread to other regions
The epidemic reached the public spotlight in February 2003, when an American businessman traveling from China, Johnny Chen, became affected by pneumonia-like symptoms while on a flight to Singapore. The plane stopped in Hanoi, Vietnam, where the patient died in Hanoi French Hospital. Several of the medical staff who treated him soon developed the same disease despite basic hospital procedures. Italian doctor Carlo Urbani identified the threat and communicated it to WHO and the Vietnamese government; he later died from the disease.The severity of the symptoms and the infection among hospital staff alarmed global health authorities, who were fearful of another emergent pneumonia epidemic. On 12 March 2003, the WHO issued a global alert, followed by a health alert by the United States Centers for Disease Control and Prevention (CDC). Local transmission of SARS took place in Toronto, Ottawa, San Francisco, Ulaanbaatar, Manila, Singapore, Taiwan, Hanoi and Hong Kong whereas within China it spread to Guangdong, Jilin, Hebei, Hubei, Shaanxi, Jiangsu, Shanxi, Tianjin, and Inner Mongolia.

Hong Kong
The disease spread in Hong Kong from Liu Jianlun, a Guangdong doctor who was treating patients at Sun Yat-Sen Memorial Hospital. He arrived in February and stayed on the ninth floor of the Metropole Hotel in Kowloon, infecting 16 of the hotel visitors. Those visitors traveled to Canada, Singapore, Taiwan, and Vietnam, spreading SARS to those locations.Another larger cluster of cases in Hong Kong centred on the Amoy Gardens housing estate. Its spread is suspected to have been facilitated by defects in its bathroom drainage system that allowed sewer gases including virus particles to vent into the room. Bathroom fans exhausted the gases and wind carried the contagion to adjacent downwind complexes. Concerned citizens in Hong Kong worried that information was not reaching people quickly enough and created a website called sosick.org, which eventually forced the Hong Kong government to provide information related to SARS in a timely manner. The first cohort of affected people were discharged from hospital on 29 March 2003.

Canada
The first case of SARS in Toronto was identified on 23 February 2003. Beginning with an elderly woman, Kwan Sui-Chu, who had returned from a trip to Hong Kong and died on 5 March, the virus eventually infected 257 individuals in the province of Ontario. The trajectory of this outbreak is typically divided into two phases, the first centring around her son Tse Chi Kwai, who infected other patients at the Scarborough Grace Hospital and died on 13 March. The second major wave of cases was clustered around accidental exposure among patients, visitors, and staff within the North York General Hospital. The WHO officially removed Toronto from its list of infected areas by the end of June 2003.The official response by the Ontario provincial government and Canadian federal government has been widely criticized in the years following the outbreak. Brian Schwartz, vice-chair of Ontarios SARS Scientific Advisory Committee, described public health officials preparedness and emergency response at the time of the outbreak as "very, very basic and minimal at best". Critics of the response often cite poorly outlined and enforced protocol for protecting healthcare workers and identifying infected patients as a major contributing factor to the continued spread of the virus. The atmosphere of fear and uncertainty surrounding the outbreak resulted in staffing issues in area hospitals when healthcare workers elected to resign rather than risk exposure to SARS.

Identification of virus
In late February 2003, Italian doctor Carlo Urbani was called into The French Hospital of Hanoi to look at Johnny Chen, an American businessman who had fallen ill with what doctors thought was a bad case of influenza. Urbani realized that Chens ailment was probably a new and highly contagious disease. He immediately notified the WHO. He also persuaded the Vietnamese Health Ministry to begin isolating patients and screening travelers, thus slowing the early pace of the epidemic. He subsequently contracted the disease himself, and died in March 2003.The CDC and Canadas National Microbiology Laboratory identified the SARS genome in April 2003. Scientists at Erasmus University in Rotterdam, the Netherlands demonstrated that the SARS coronavirus fulfilled Kochs postulates thereby suggesting it as the causative agent. In the experiments, macaques infected with the virus developed the same symptoms as human SARS patients.

Origin and animal vectors
In late May 2003, a study was conducted using samples of wild animals sold as food in the local market in Guangdong, China. The study found that "SARS-like" coronaviruses could be isolated from masked palm civets (Paguma sp.). Genomic sequencing determined that these animal viruses were very similar to human SARS viruses, however they were phylogenetically distinct, and so the study concluded that it was unclear whether they were the natural reservoir in the wild. Still, more than 10,000 masked palm civets were killed in Guangdong Province since they were a "potential infectious source." The virus was also later found in raccoon dogs (Nyctereuteus sp.), ferret badgers (Melogale spp.), and domestic cats.In 2005, two studies identified a number of SARS-like coronaviruses in Chinese bats. Phylogenetic analysis of these viruses indicated a high probability that SARS coronavirus originated in bats and spread to humans either directly or through animals held in Chinese markets. The bats did not show any visible signs of disease, but are the likely natural reservoirs of SARS-like coronaviruses. In late 2006, scientists from the Chinese Centre for Disease Control and Prevention of Hong Kong University and the Guangzhou Centre for Disease Control and Prevention established a genetic link between the SARS coronavirus appearing in civets and in the second, 2004 human outbreak, bearing out claims that the disease had jumped across species.It took 14 years to find the original bat population likely responsible for the SARS pandemic. In December 2017, "after years of searching across China, where the disease first emerged, researchers reported ... that they had found a remote cave in Xiyang Yi Ethnic Township, Yunnan province, which is home to horseshoe bats that carry a strain of a particular virus known as a coronavirus