IMMUNOLOGY

Detailed explanation-1: -Viroids: the smallest and simplest agents of infectious disease.

Detailed explanation-2: -But few will know about the smallest infectious pathogens discovered to date: viroids. These biological oddities are to blame for a host of different crop diseases, causing huge losses across many different agricultural industries.

Detailed explanation-3: -Viruses are the smallest of all the microbes. They are said to be so small that 500 million rhinoviruses (which cause the common cold) could fit on to the head of a pin. They are unique because they are only alive and able to multiply inside the cells of other living things.

Detailed explanation-4: -Finally, you have been introduced to the two smallest types of pathogen – viruses and prions – which are not formed from cells so are not considered to be alive.

Detailed explanation-5: -Viroids. Not to be confused with virusoids or viruses, viroids are the smallest known infectious pathogens. Viroids are small single-stranded, circular RNA that are only known to cause plant diseases, such as the potato spindle tuber viroid that affects various agricultural crops.