the person to whom the infectious agent is passed is contagious.
the person to whom the infectious agent is passed is contagious.
the person to whom the infectious agent is passed is?
contagious
his results were in accordance with the similar observation made by dmitri ivanovsky in 1892. like ivanovsky before him and adolf mayer, predecessor at wageningen, beijerinck could not culture the filterable infectious agent, however he concluded that the agent can replicate and multiply in living plants. he named the new pathogen "virus" to indicate its non-bacterial nature. beijerinck asserted that the virus was somewhat liquid in nature, calling it ""contagium vivum fluidum"" (contagious living fluid). it was not until the first crystals of the tobacco mosaic virus (tmv) obtained by wendell stanley in 1935, the first electron micrographs of tmv produced in 1939 and the first x-ray crystallographic analysis of tmv performed in 1941 proved that the virus was particulate.
martinus beijerinck
in the 1950's, carleton gajdusek began research which eventually showed that kuru could be transmitted to chimpanzees by what was possibly a new infectious agent, work for which he eventually won the 1976 nobel prize. during the 1960s, two london-based researchers, radiation biologist tikvah alper and biophysicist john stanley griffith, developed the hypothesis that the transmissible spongiform encephalopathies are caused by an infectious agent consisting solely of proteins. earlier investigations by e.j. field into scrapie and kuru had found evidence for the transfer of pathologically inert polysaccharides that only become infectious post-transfer, in the new host. alper and griffith wanted to account for the discovery that the mysterious infectious agent causing the diseases scrapie and creutzfeldt–jakob disease resisted ionizing radiation. (a single ionizing "hit" normally destroys an entire infectious particle, and the dose needed to hit half the particles depends on the size of the particles. empirical results of ionizing doses applied to the unknown infectious substance evidenced an infectious particle size too small to be a viral mechanism.) in his paper, entitled "self-replication and scrapie", griffith proposed three ways in which a protein could be a pathogen. in the first hypothesis, he suggested that if the protein is the product of a normally suppressed gene, and introducing the protein could induce the gene's expression, that is, wake the dormant gene up, then the result would be a process indistinguishable from replication, as the gene's expression would produce the protein, which would then go wake the gene up in other cells. his second hypothesis forms the basis of the modern prion theory, and proposed that an abnormal form of a cellular protein can convert normal proteins of the same type into its abnormal form, thus leading to replication. his third hypothesis proposed that the agent could be an antibody if the antibody was its own target antigen, as such an antibody would result in more and more antibody being produced against itself. however, griffith acknowledged that this third hypothesis was unlikely to be true due to the lack of a detectable immune response.
prion