ORIGIN of SARS-CoV

The genome of SARS-CoV has been recorded and compared with other known coronaviruses.  There are three major antigenic groups of coronaviruses, and SARS-CoV nucleotide sequence indicates that it is not homologous with any of the three groups.

Coronaviruses are known for their messenger RNA’s ability to recombine with mRNA from other coronaviruses.  Holmes describes the process:

The unique RNA-dependent RNA polymerase of coronaviruses often switches template strands during replication, causing RNA recombination when a cell is infected with several coronaviruses.  This error-prone polymerase also generates point mutations and large deletions or insertions of foreign RNA into the viral genome.  (Holmes, 2003)

Recombination in coronaviruses.  Picture taken from the Johns Hopkins Public Health Magazine, Fall 2003 edition.  Photo from Photo Researchers.  http://www.jhsph.edu/Magazine/SARS/page3.html

The first reports of SARS were cases of atypical pneumonia in butchers and chefs of exotic animals in Guangdong restaurants.  Specimens were collected from such animals in the exotic animals markets of Guangdong Province.  Isolates of the SARS-CoV were obtained from specimens taken from raccoon dogs, Nyctereutes procyonoides, and Himalayan palm civets, Paguma larvata.

	A raccoon dog.  Picture taken from http://www.lioncrusher.com/animal.asp?animal=25
	A Himalayan Palm Civet.  Picture taken from: http://www.lioncrusher.com/animal.asp?animal=108

Civet cats are an expensive delicacy.  Restaurants will frequently have the animals in small cages on the premises.  Patrons will pick a live civet cat, which is then butchered and cooked.  One of the most famous dishes including civet cat is Dragon, Tiger, and Phoenix Soup.  It includes snake, civet cat, and chrysanthemum leaves and is very expensive. 

Another animal, a Chinese ferret badger, had antibodies against SARS-CoV, indicating that it had previously suffered infection. 

For more information on the animals associated with the outbreak, please consult the following links. 

Wildlife and SARS:

http://www.humanesociety.com/disparticle.asp?thisrel=SARSbackground#species

Raccoon Dogs:

http://www.canids.org/SPPACCTS/raccoond.htm

Masked Palm Civets:

http://www.wii.gov/envis/evisdec99/maskedpalmcivet.htm

Chinese Ferret Badgers:

http://www.wii.gov.in/envis/envisdec99/smalltoothchbadger.htm

As human sera obtained before the outbreak occurred had no antibodies to SARS-CoV, it appears that this virus is new, having never before appeared in the human population.  The likely hypothesis is that the civet cats and raccoon dogs found in the markets spread coronaviruses among each other.  When one animal became infected with multiple coronaviruses, the viruses recombined, forming what is now known as SARS-CoV.  The animal then spread the virus to its human handlers through its feces or respiratory secretions.