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SARS coronavirus

SARS coronavirus

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The SARS coronavirus, sometimes shortened to SARS-CoV, is the virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...

 that causes severe acute respiratory syndrome
Severe acute respiratory syndrome
Severe Acute Respiratory Syndrome is a respiratory disease in humans which is caused by the SARS coronavirus . Between November 2002 and July 2003 an outbreak of SARS in Hong Kong nearly became a pandemic, with 8,422 cases and 916 deaths worldwide according to the WHO...

 (SARS). On April 16, 2003, following the outbreak of SARS in Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...

 and secondary cases elsewhere in the world, the World Health Organization
World Health Organization
The World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...

 (WHO) issued a press release stating that the coronavirus
Coronavirus
Coronaviruses are species in the genera of virus belonging to the subfamily Coronavirinae in the family Coronaviridae. Coronaviruses are enveloped viruses with a positive-sense single-stranded RNA genome and a helical symmetry. The genomic size of coronaviruses ranges from approximately 16 to 31...

 identified by a number of laboratories was the official cause of SARS. Samples of the virus are being held in laboratories in New York
New York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...

, San Francisco, Manila
Manila
Manila is the capital of the Philippines. It is one of the sixteen cities forming Metro Manila.Manila is located on the eastern shores of Manila Bay and is bordered by Navotas and Caloocan to the north, Quezon City to the northeast, San Juan and Mandaluyong to the east, Makati on the southeast,...

, Hong Kong
Hong Kong
Hong Kong is one of two Special Administrative Regions of the People's Republic of China , the other being Macau. A city-state situated on China's south coast and enclosed by the Pearl River Delta and South China Sea, it is renowned for its expansive skyline and deep natural harbour...

, and Toronto
Toronto
Toronto is the provincial capital of Ontario and the largest city in Canada. It is located in Southern Ontario on the northwestern shore of Lake Ontario. A relatively modern city, Toronto's history dates back to the late-18th century, when its land was first purchased by the British monarchy from...

.

On April 12, 2003, scientists working at the Michael Smith Genome Sciences Centre in Vancouver, British Columbia finished mapping the genetic sequence of a coronavirus believed to be linked to SARS. The team was led by Dr. Marco Marra
Marco Marra
Marco Marra, OBC, Ph.D. is the director of Canada's Michael Smith Genome Sciences Center located at the BC Cancer Agency since 2000 and a leading expert in the field of genomics....

 and worked in collaboration with the British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...

 Centre for Disease Control and the National Microbiology Laboratory in Winnipeg, Manitoba, using samples from infected patients in Toronto
Toronto
Toronto is the provincial capital of Ontario and the largest city in Canada. It is located in Southern Ontario on the northwestern shore of Lake Ontario. A relatively modern city, Toronto's history dates back to the late-18th century, when its land was first purchased by the British monarchy from...

. The map, hailed by the WHO as an important step forward in fighting SARS, is shared with scientists worldwide via the GSC website (see below).

Dr. Donald Low of Mount Sinai Hospital
Mount Sinai Hospital (Toronto)
Mount Sinai Hospital is a hospital in Toronto, Ontario, Canada. Although it is physically linked by bridges and tunnels to two University Health Network hospitals , Mount Sinai is an independently operated facility...

 in Toronto described the discovery as having been made with "unprecedented speed."

The sequence of the SARS coronavirus has since been confirmed by other independent groups.

SARS



SARS, or Severe Acute Respiratory Syndrome
Severe acute respiratory syndrome
Severe Acute Respiratory Syndrome is a respiratory disease in humans which is caused by the SARS coronavirus . Between November 2002 and July 2003 an outbreak of SARS in Hong Kong nearly became a pandemic, with 8,422 cases and 916 deaths worldwide according to the WHO...

, is the disease caused by SARS coronavirus. It causes an often severe illness marked initially by systemic symptoms of muscle pain, headache
Headache
A headache or cephalalgia is pain anywhere in the region of the head or neck. It can be a symptom of a number of different conditions of the head and neck. The brain tissue itself is not sensitive to pain because it lacks pain receptors. Rather, the pain is caused by disturbance of the...

, and fever
Fever
Fever is a common medical sign characterized by an elevation of temperature above the normal range of due to an increase in the body temperature regulatory set-point. This increase in set-point triggers increased muscle tone and shivering.As a person's temperature increases, there is, in...

, followed in 2–10 days by the onset of respiratory symptoms, mainly cough, dyspnea, and pneumonia. Another common finding in SARS patients is a decrease in the number of lymphocytes circulating in the blood. In the SARS outbreak of 2003, about 9% of patients with confirmed SARS infection died. The mortality rate was much higher for those over 50 years old, with mortality rates approaching 50% for this subset of patients.

SARS Coronavirus biology


SARS coronavirus is a positive and single stranded RNA virus belonging to a family of enveloped coronaviruses. Its genome is about 29.7kb, which is one of the largest among RNA viruses. SARS is similar to other coronaviruses in that its genome expression starts with translation of two large ORFs 1a and 1b, which are two polyproteins. The SARS virus has 13 known genes and 14 known proteins. There are 265bp in the 5'UTR and 342bp in the 3'UTR. Coronaviruses usually express pp1a (the ORF1a polyprotein) and the PP1ab polyprotein with joins ORF1a and ORF1b. The polyproteins are then processed by enzymes that are encoded by ORF1a. Product proteins from the processing includes various replicative enzymes such as RNA dependent polymerase, RNA helicase, and proteinase. The replication complex in coronavirus is also responsible for the synthesis of various mRNAs downstream of ORF 1b, which are structural and accessory proteins. Two different proteins, 3CLpro and PL2pro, cleave the large polyproteins into 16 smaller subunits.

SARS-Coronavirus follows the replication strategy typical of the Coronavirus
Coronavirus
Coronaviruses are species in the genera of virus belonging to the subfamily Coronavirinae in the family Coronaviridae. Coronaviruses are enveloped viruses with a positive-sense single-stranded RNA genome and a helical symmetry. The genomic size of coronaviruses ranges from approximately 16 to 31...

 genus.

SARS Coronavirus morphology


The morphology of the SARS coronavirus is characteristic of the coronavirus family as a whole. These viruses have large pleomorphic spherical particles with bulbous surface projections that form a corona around particles. The envelop of the virus contains lipid and appears to consist of a distinct pair of electron dense shells. The internal component of the shell is a single-stranded helical ribonucleoprotein. There are also long surface projections that protrude from the lipid envelop. The size of these particles are about 80–90 nm.

SARS Coronavirus evolution


SARS is most closely related to group 2 coronaviruses, but it does not segregate into any of the other three groups of coronaviruses. The closest outgroup to the coronaviruses are the toroviruses, with which it has homology in the ORF 1b replicase and the two viron proteins of S and M. SARS was determined to be an early split off from the group 2 coronaviruses based on a set of conserved domains that it shares with group 2.
A main difference between group 2 coronovirus and SARS is the nsp3 replicase subunit encoded by ORF1a. SARS does not have a papain-like proteinase 1.

Symptoms and Treatment


Once a person has contracted SARS, the first symptom that they present with is a fever of at least 38°C (100.4°F) or higher. The early symptoms last about 2–7 days and include non-specific flu-like symptoms, including chills/rigor, muscle aches, headaches, diarrhea, sore throat, runny nose, malaise, and myalgia (muscle pain). Next they develop a dry cough, shortness of breath, and an upper respiratory tract infection. At that time, a chest x-ray is ordered to confirm pneumonia. If the chest appears clear and SARS is still suspected, a HRCT scan will be ordered, because it is visible earlier on this scan. In severe cases, it develops into respiratory failure and acute respiratory distress syndrome (ARDS), and in 70-90% of the cases, they develop lymphopenia (low count of white blood cells).
The incubation period for SARS-CoV is from 2–10 days, sometimes lasting up to 13 days, with the mean being 5 days. This means that it can take between 2–10 days for the disease to manifest itself, once you have been exposed to the Coronavirus. The disease progresses in the following way. First you are exposed to the virus, and somewhere between 2–10 days you contract it. Next, the IgM antibody titrates to the SARS-CoV, then peaks during the acute or early convalescent phase (week 3) and declines by week 12. IgG peaks at week 12.

Engineering the SARS Coronavirus


Engineering of SARS virus has been done. In a paper published in 2006, a new transcription circuit was engineered to make recombinant SARS viruses. The recombination allowed for efficient expression of viral transcripts and proteins. The engineering of this transcription circuit reduces the RNA recombinant progeny viruses. The TRS (transcription regulatory sequences) circuit regulates efficient expression of SARS-CoV subgenomic mRNAs. The wild type TRS is ACGAAC. A double mutation results in TRS-1 (ACGGAT) and a triple mutation results in TRS-2 (CCGGAT). When the remodeled TRS circuit containing viruses are genetically recombined with wild type TRS circuits, the result is a circuit reduced in production of subgenomic mRNA. The goal of modifying the SARS virus with this approach is to produce chimeric progeny that have reduced viability due to the incompatibility of the WT and engineered TRS circuits.

See also

  • Carlo Urbani
    Carlo Urbani
    Carlo Urbani was an Italian physician and the first to identify severe acute respiratory syndrome as a new and dangerously contagious disease...

  • Progress of the SARS outbreak
    Progress of the SARS outbreak
    -November 2002:On November 16, 2002, an outbreak of what is believed to be severe acute respiratory syndrome , began in the Guangdong province of China, which borders on Hong Kong. The first case of infection was speculated to be a farmer in Foshan County...

  • Severe acute respiratory syndrome
    Severe acute respiratory syndrome
    Severe Acute Respiratory Syndrome is a respiratory disease in humans which is caused by the SARS coronavirus . Between November 2002 and July 2003 an outbreak of SARS in Hong Kong nearly became a pandemic, with 8,422 cases and 916 deaths worldwide according to the WHO...


External links