Regarding your questions:
 
Coronaviruses are a specific family of RNA viruses that cause a wide
variety of disease in animal species.  Coronaviruses are best known for
causing enteric disease in domestic species, including transmissible
gastroenteritis in pigs, coronavirus diarrhea in dogs, and feline
infectious peritonitis.
 
Coronaviruses are best identified by electron microscopy of feces or
tissue, and are recognizable due to the presence of peplomers
(characteristic of coronaviruses) surrounding the viral particle (it
resembles a crown).
 
Coronaviruses are different in many ways from other viruses in the way
that they replicate, the diseases that they cause, the tissues that they
choose to infect, the receptors that are used to gain entry to cells, their
ability to be grown in culture, cell cultures that may be used to grow the
cells, and of course, their characteristic size and appearance.
 
There are few viruses that can be directly treatable with drugs, and
coronaviruses are not one against which there are any specific treatments.
The best that we can due with coronaviruses, and other viruses that affect
the intestine, is to empirically treat the symptoms and support the animal
until it can support itself.
 
The source of the coronavirus of ECE is simply another animal, which has
shed infectious virus.  The shedding period of ECE is considered
anecdotally to be approximately 6-8 months.
 
With kindest regards,
Bruce Williams, dVM
[Posted in FML issue 3397]