A research paper has been published that identifies the cause fatal disease Inclusion Body Disease (IBD) in Boa Constrictors and Annulated Tree Boas. It appears this disease is a new virus belonging to the Arenavirus group. There is no evidence that this virus is transmissible to mammals (including humans)
Infected snakes often show odd behaviors such as star gazing and an inability to right themselves if laid on their back. Often they also have symptoms of respiratory distress and partial paralysis. Typically blood smears show inclusions bodies in their red and white blood cells.
It is suspected this virus is spread by snake mites (and possibly ticks) between snakes
Although there is currently no treatment for this disease the identification of the virus means that improved diagnostic tests can be developed to help exclude infected animals from collections.
Sources
Original paper (open access)
http://mbio.asm.org/content/3/4/e00180-12
Review paper (open access)
http://labs.vetmed.ufl.edu/files/201...JexoticPet.pdf
BBC news item
http://www.bbc.co.uk/news/science-environment-19261506