Novel applications of feather tip extracts from MDV‐infected chickens; diagnosis of commercial broilers, whole genome separation by PFGE and synchronic mucosal infection

Marek's disease virus (MDV) productive replication occurs in the feather follicle epithelium and the feather tips are valuable both for research and disease diagnosis. Three novel applications of feather tip extracts are described now: (A) As a source of DNA for amplifying either MDV and/or ALV‐J. In two clinical situations a marked advantage was obtained compared to blood and organs; in broiler breeder flocks with a mixed MDV and ALV‐J infection, and in young broilers with neurological Marek's disease (MD). (B) Separation of the large (∼200 kbp) MDV genome directly from the infected chickens. Using pulsed field gel electrophoresis, the DNA extracted from tumors or feather tips was separated and hybridized to a 132 bp tandem repeat MDV probe. Compared to 2/55 polymerase chain reaction (PCR) positive tumor samples, 15/61 feather tip extracts contained whole MDV genomes. (C) Experimental MDV infection was induced by the mucosal route by dripping feather tip extract to the eye and mouth of the bird. That attempted to reproduce the native infection process, however the use of extracts, instead of dry feather dust was a compromise, aimed to synchronize the infection. In one trial, tumors were induced 6 weeks after dripping day‐old broilers, while in another, feather tips were PCR positive 16 days after dripping of 2‐month‐old layers.