<prompt> Most common mode of transmission of polio virus-Droplet infectionFecal-oral routeBlood transfusionVertical transmission  <response>: Ans. is b i.e., Fecal-oral routeo Polio transmission is mostly restricted to developing countries where fecal-oral route is the most common mode of transmission.Polio Viruso Belongs to Picomaviruso A nonenveloped RNA virus ss RNA.o Has four viral proteins, VP1-VP4. VP 1 Carries the major antigenic site.o Three types - Type 1,2 and 3o Type 1 is most common and causes most epidemicso Type 2 usually causes endemic infectionso Type 3 also causes epidemics.Pathologyo Virus multiplies selectively in neurons and destroys them,o Earliest change - Chromatolysis Degeneration of nissel bodieso Lesions are mostly in the anterior horns of the spinal cord.Some important points about poliovirus strains Type I. II. IIIo Most common cause of epidemics- Type Io Most difficult to eradicate - Type I because vaccine response to it is not goodo Most common cause of vaccine induced paralytic poliomyelitis-Type III due to mutationo Most commonly associated with paralysis -Type Io Most effective antigen -Type IIModes of transmission1. Fecal-oral route-Most common in developing countries.2. Droplet infection-More important in developed countries through inhalation or through conjuctiva 