While I like to study many different aspects of biology, at heart I am a virologist. So my first post will be about the viruses that cause FIP in cats (and is a post for the virus aficionados out there)
It has been well documented that there are two serotypes of feline coronavirus; serotypes I and II, with type I viruses being much more prevalent in the cat population and the leading cause of FIP. I like to be comparative, and so at first pass these two feline coronaviruses could be viewed like influenza virus H1(N1) and H3(N2) – antigenically distinct but basically the same virus. However, the more we study the two feline coronaviruses, the more they seem to be very different. A better analogy might be with paramyxoviruses in humans. Some years ago, parainfluenza virus type 3 (PI3) and respiratory syncytial virus (RSV) were classified together, simply as serologically distinct paramyxoviruses, but now we place them in completely different genera; respiroviruses and pneumoviruses. Not only are they antigenically distinct, they have different receptors, they are activated for cell entry and fusion in very different ways, and have quite different pathogenesis profiles and cell tropism. They are different viruses. Even more years ago, paramyxoviruses and influenza viruses were all considered as one – as myxoviruses.
What impacts our understanding of feline coronavirus biology is that type II viruses are readily isolatable in cell culture and type I viruses are not. Because of this, we know much more about the biology of type II viruses, and much of our current thinking about FIP as a disease is based this. On the flip side, none of the currently available diagnostic tests for feline coronaviruses are able to discriminate between the two viruses, so clinically FIP is considered to be caused by a single virus, albeit one with different biotypes (FECV and FIPV)
Current research in the Whittaker lab (and elsewhere) is coming to the conclusion that feline coronavirus types I and II are much more than serological variants. They have different receptors, different means of activation and, as shown in our recent paper, would be considered taxonomically as being in distinct clades with different biological properties. They are different viruses. What does this mean for FIP? We are not sure, but we hope to find out soon.
– Dr. Gary R. Whittaker