SARS (Severe acute respiratory syndrome)

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Description:
SARS, or Severe acute respiratory syndrome, is the disease caused by SARS coronavirus. It causes an often severe illness marked initially by systemic symptoms of muscle pain, headache, and fever, followed in 2–10 days by the onset of respiratory symptoms,[3] mainly cough, dyspnea, and pneumonia. Another common finding in SARS patients is a decrease in the number of lymphocytes circulating in the blood.

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Virus classification:-

Group: Group IV ((+)ssRNA)

Order: Nidovirales

Family: Coronaviridae

Genus: Coronavirus

Species: SARS coronavirus

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. The SARS virus has 13 known genes and 14 known proteins. There are 265bp in the 5’UTR and 342bp in the 3’UTR. 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 functions of several of these proteins are known:  ORFs 1a and 1b encode the replicase and there are four major structural proteins: nucleocapsid, spike, membrane and envelope. It also encodes for eight unique proteins, known as the accessory proteins, with no known homologues. The function of these accessory proteins remains unknown.
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.

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 genus.

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.

Causes:
SARS is caused by a strain of coronavirus, the same family of viruses that causes the common cold. Until now, these viruses have never been particularly dangerous in humans, although they can cause severe disease in animals. For that reason, scientists originally thought that the SARS virus might have crossed from animals to humans. It now seems likely that it evolved from one or more animal viruses into a completely new strain.
 
How do SARS spread:
Most respiratory illnesses, including SARS, spread through droplets that enter the air when someone with the disease coughs, sneezes or talks. Most experts think SARS spreads mainly through face-to-face contact, but the virus also may be spread on contaminated objects — such as doorknobs, telephones and elevator buttons.

Symptoms:
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.

SARS typically begins with flu-like signs and symptoms — signs and symptoms include:

*Fever of 100.4 F (38 C) or higher
* Dry cough
*Shortness of breath

Complications:
The main complication of SERS  is that most people develop pneumonia. Breathing problems can become so severe that a mechanical respirator is required. SARS is fatal in some cases, often due to respiratory failure. Other possible complications include heart and liver failure.

People older than the age of 60 — especially those with underlying conditions such as diabetes or hepatitis — are at highest risk of serious complications.

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Risk Factors:
In general, people at greatest risk of SARS have had direct, close contact with someone who’s infected, such as family members and health care workers.

Diagnosis:
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 lymphocyte white blood cells).

The incubation period for SARS-CoV is from 2–10 days, sometimes lasting up to 13 days, with a mean of 5 days.  So symptoms usually develop between 2–10 days following infection by the virus. As part of the immune response, IgM antibody to the SARS-CoV is produced. This peaks during the acute or early convalescent phase (week 3) and declines by week 12. IgG antibody is produced later and peaks at week 12.

Tests:
When SARS first surfaced, no specific tests were available to help doctors diagnose the disease. Now several laboratory tests can help detect the virus. But no known transmission of SARS has occurred anywhere in the world since 2004.

Treatment:
Although global efforts are still on, scientists have not yet found out any effective treatment for SARS. Antibiotic drugs don’t work against viruses and antiviral drugs haven’t shown much benefit.

Prevention:
Researchers are working on several types of vaccines for SARS, but none has been tested in humans.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.

Novel subunit vaccine constructs for an S protein SARS vaccine based on the receptor binding domain (RBD) are being developed by the New York Blood Center. The re-emergence of SARS is possible, and the need remains for commercial vaccine and therapeutic development. However, the cost and length of time for product development, and the uncertain future demand, result in unfavorable economic conditions to accomplish this task. In the development of therapeutics and next-generation vaccines, more work is required to determine the structure/ function relationships of critical enzymes and structural proteins.

If SARS infections resume, follow these safety guidelines if you’re caring for an infected person:

 *Wash your hands. Clean your hands frequently with soap and hot water or use an alcohol-based hand rub containing at least 60 percent alcohol.

* Wear disposable gloves. If you have contact with the person’s body fluids or feces, wear disposable gloves. Throw the gloves away immediately after use and wash your hands thoroughly.

* Wear a surgical mask. When you’re in the same room as a person with SARS, cover your mouth and nose with a surgical mask. Wearing eye glasses also may offer some protection.

* Wash personal items. Use soap and hot water to wash the utensils, towels, bedding and clothing of someone with SARS.

* Disinfect surfaces. Use a household disinfectant to clean any surfaces that may have been contaminated with sweat, saliva, mucus, vomit, stool or urine. Wear disposable gloves while you clean and throw the gloves away when you’re done.

Follow all precautions for at least 10 days after the person’s signs and symptoms have disappeared. Keep children home from school if they develop a fever or respiratory symptoms within 10 days of being exposed to someone with SARS. Children can return to school if signs and symptoms go away after three days.

Disclaimer: This information is not meant to be a substitute for professional medical advise or help. It is always best to consult with a Physician about serious health concerns. This information is in no way intended to diagnose or prescribe remedies.This is purely for educational purpose.

Resources:
http://en.wikipedia.org/wiki/SARS_coronavirus
http://www.mayoclinic.com/health/sars/DS00501/DSECTION=prevention

 

 

 

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