cross section of a smallpox pathogen with cell membrane, nucleocapsid, cell wall and glycoproteins

biological biology blood care cell contagion contagious cross disease dna epidemic eradicated germ glycoproteins health hygiene ill illustration immune immunization infected infection infectious infestation medicals medicine membrane microbiology microorganism microscopic monkey nucleocapsid organism outbreak pandemic particle pathogen pathogens pox quarantine research respiratory scientific section skin smallpox structure symptoms transmission vaccination vaccine viral virions virology virus wall