People entering the U.S. first need to get a visa. A visa allows the visa holder to travel to a port of entry in the United States and request the immigration officials permission to enter the country. The visa could be a non-immigrant visa if the person intends to stay in the U.S. temporarily.
Tobacco mosaic virus (TMV) is a positive-sense single stranded RNA virus that infects a wide range of plants, especially tobacco and other members of the family Solanaceae.The infection causes characteristic patterns, such as  mosaic -like mottling and discoloration on the leaves (hence the name).TMV was the first virus ever to be discovered.Although it was known from the late 19th century that an infectious disease was damaging tobacco crops, it was not until 1930 that the infectious agent was determined to be a virus.lthough it was known from the late 19th century that an infectious disease was damaging tobacco crops, it was not until 1930 that the infectious agent was determined to be a virus.
An RNA virus is a virus that has RNA (ribonucleic acid) as its genetic material. This nucleic acid is usually single-stranded RNA (ssRNA) but may be double-stranded RNA (dsRNA).Notable human diseases caused by RNA viruses include Ebola hemorrhoragic fever, SARS, influenza, hepatitis C, West Nile fever, polio, and measles.his nucleic acid is usually single-stranded RNA (ssRNA) but may be double-stranded RNA (dsRNA). Notable human diseases caused by RNA viruses include Ebola hemorrhoragic fever, SARS, influenza, hepatitis C, West Nile fever, polio, and measles.