No abstract

A B S T R A C T Through a series of controlled experiments in volunteers, quantitative aspects of infection, illness, and immunity to ECHO-11 virus were studied. ECHO-11 is a transmissable viral infection in man and equally infectious to the upper respiratory and the intestinal tracts. The rate of infection was directly related to the dose of virus exposure, but any infectious dose of virus produced illness in only about one-third of the infected subjects. The infectious dose for man varied over a billionfold range. Larger challenge doses caused no difference in the local symptoms at the portal of entry or in the peak severity of illness, but symptoms were more diverse and prolonged after a higher dose. Persons with asymptomatic infections became just as heavily infected as ill persons.In respiratory secretions from natural infection, the titer of infectious virus was found to be about 102 median infective doses in tissue culture (TCID50)/ml. At this level, up to 40% of exposed contacts could be infected per milliliter of secretion.The observed rate of spread was 24%. This lowdose inoculum caused illness in 12%o' of volunteers