sars epidemiolody and morphology of the virus

SARS - EPIDEMIOLOGY

• SARS : severe acute respiratory syndrome.• The agent appears to be a new virus distinct from

other corona viruses which had been classified into types1 & 2( mammalian viruses);type 3(avian viruses).

• New SARS virus becomes corona virus type 4 & confirmed by vero cell culture , animal

inoculation, cloning , sequencing and histology.• Corona viruses are a group of spherical or pleomorphic

; enveloped viruses.• Their genome is unsegmented single stranded positive

sense RNA.• Nucleo capsid is helical.

• Envelope contains large widely spaced club or petal shaped spikes.

• They replicate in cytoplasm.• It is difficult to grow them in

cell culture.• They belong to family

coronaviridae and genus betacoronovirus.• It may be a recombinant of some animal and human

corona viruses.

• The outbreak of sars erupted in southern china in late 2002 and by the time it waned in mid 2003 had resulted in 8000 cases in 29 countries with over 800 deaths.( case fatality is approximately 10%)

• In almost all cases, there was a history of close contact with a SARS patient or of recent travel to an area where SARS was reported. International air travel allowed SARS to spread around the world with unprecedented speed. The experience with SARS illustrated that in a globalized world, an infectious disease outbreak anywhere places every country at risk.

MODE OF TRANSMISSION:• The primary mode of transmission appears

to be through direct or indirect contact of mucous membranes of eyes, nose, or mouth with respiratory droplets or fomites.

• The use of aerosol-generating procedures (endotracheal intubation, bronchoscopy, nebulization treatment) in hospitals may amplify the transmission of SARS coronavirus

• The virus is shed in stools but the role of faecal-oral transmission is unknown

• The natural reservoir appears to be the horseshoe bat (which eats and drops fruits ingested by civets, the earlier presumed reservoir and a likely amplifying host)

• The SARS virus can survive for hours on common surfaces outside the human body and upto 4 days in human waste

• The virus can survive at least for 24 hours on a plastic surface at room temperature and can live for extended periods in the cold.

• Interestingly, a few persons with SARS were identified as “super spreaders”; each appeared to have infected more than 10 contacts.

• Incubation period ranges from 2 to 10 days.

SARS: Timeline of an Outbreak Nov. 16, 2002 -- The first case of an atypical pneumonia in the Guangdong province in China.

February 14, 03 : 305 cases & 5 deaths from an unknown acute respiratory syndrome

• Feb 28, 2003 -- World Health Organization officer Carlo Urbani, MD, examined an American businessman with an unknown form of pneumonia in a French hospital in Hanoi, Vietnam

March 03: New reports of outbreaks came in from Hong Kong, Singapore & Vietnam. New syndrome was

designated as severe acute respiratory syndrome or SARS

• March 10, 2003 -- Urbani reported an unusual outbreak of the illness, which he called sudden acute respiratory syndrome or SARS, to the main office of the WHO. He also noted that the disease has infected an usually high number of healthcare workers (22) at the hospital. March 11, 2003 -- Outbreak of a mysterious respiratory disease is reported among healthcare workers in Hong Kong

• March 12, 2003 -- WHO issued a global alert about a new infectious disease of unknown origin In both Vietnam and Hong Kong .

• March 24, 2003 -- CDC officials present the first evidence that a new strain of a virus most frequently associated with upper respiratory infections and the common cold in humans called The corona virus might be likely cause of SARS.

• March 29, 2003 -- Carlo Urbani, who identified the first cases of SARS, died as a result of the disease.

• April 9, 2003 -- WHO investigative team gave initial report on Guangdong outbreak. The team found evidence of "super spreaders“ who were capable of infecting as many of 100 persons.

• April 16, 2003 -- A new form of a corona virus never before seen in humans is confirmed as the cause of SARS according to Koch's postulates, which are four specific conditions that must be

met for a pathogen to be confirmed as a causal agent of disease.

• April 20-25, 03: Outbreaks in Hanoi, Hong Kong, China, Singapore &Toronto showed signs of peaking.

• April 25, 03: Nearly 3000 SARS cases have been identified in China.

• Internationally, more than 8,098 people became ill with severe acute respiratory syndrome. The World Health Organization (WHO) stated a total of 774 people died because of the SARS 2003 outbreak. According to the CDC, the illness spread to more than two dozen countries in North America, South America, Europe, and Asia before the SARS global outbreak of 2003 was contained

• Health care workers especially those

involved in generating aerosols accounted for 21% of all cases.

• Children are rarely affected by SARS .to date , there have been 2 reported cases of transmission from children to adults and no report of transmission from child to child .

• 3 separate epidemiological investigations have not found any evidence of SARS transmission in schools.

• No evidence of SARS has been found infants of mothers who were infected with pregnancy.

• International flights have been associated with the transmission of SARS from symptomatic probable cases to passengers or crew.

• WHO recommends exit screening and other measures to reduce opportunities for further international spread of the disease during epidemics.

INFECTIOUSNESS OF SARS• Factors affecting infectiousness are– Viral load of the secretion from index patient– Aerosol-generation procedures– Distance of the index patient

WHO case definitions of SARS• SUSPECTED CASE A person presenting after 1st nov 2002 with

High fever Cough or breathing difficulty H/o contact with a probable case of SARS 10

days prior.

• PROBABLE CASE • A suspect case of SARS having X-ray findings of pneumonia Autopsy findings consistent of RDS without

an identifiable cause Positive for SARS corona Virus by one or

more of the assays in a lab using appropriate quality control procedure

references

• Textbook of microbiology –ananthanarayan & panikar

• Lange medical microbiology• K park community medicine• Wikipedia SARS.