Have any heard of this?
http://jvi.asm.org/cgi/reprint/54/3/873.pdf http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2820273&dopt=Abstract http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=551090 http://iai.asm.org/cgi/reprint/29/1/165.pdf