In two communities of similar size and age structure (a and b) there were outbreaks of viral illness (virus a in community a and virus b in community b), both of which were traced back to a single source. exposure to these viruses in each community confers permanent immunity. in community a, 200 susceptible people were exposed to an index case, 150 people were infected (not including the index case), 75 people became ill, and 40 people died. in community b, pathogenicity was 40%, infectivity was 90% and virulence was 60%.a. which virus had the greatest infectivity? b. which virus was most pathogenic? c. which virus was most virulent?