Sentence:  Wound tumor virus is a leafhopper transmitted <WSD>virus</WSD> not easily transmissible by mechanical inoculation ( Black , 1944 ; Brakke et al. , 1954 ) . 
Meaning of the word marked with <WSD> tags:  (virology) ultramicroscopic infectious agent that replicates itself only within cells of living hosts; many are pathogenic; a piece of nucleic acid (DNA or RNA) wrapped in a thin coat of protein