In 1898 Friedrich Loeffler and Paul Frosch found evidence that the cause of the highly contagious hool-and-mouth disease in
livestock was a microscopic infectious particle. It was discovered that this particle requires a host cell to reproduce,
Which pathogen is most likely responsible for causing hoof-and-mouth disease in livestock?
A bacterium, because it is contagious
A fungus, because it infects livestock
A protist, because it is microscopic
A virus, because it requires a host cell to reproduce