Megaviru , MINIVIRUS AND parvovirus

Megavirus^[1] is a viral genus containing a single identified species named Megavirus chilensis (MGVC),

phylogenetically related to Acanthamoeba polyphaga Mimivirus (APMV).

•  In colloquial speech, MGVC is more commonly referred to as just “Megavirus”. It has the largest capsid diameter of all known viruses, as well as the largest and most complex genome among all known viruses.

Mimivirus is a viral genus containing a single identified species named Acanthamoeba polyphaga mimivirus (APMV), or is a group of phylogenetically related large viruses (designated usually MimiN).

• ^] In colloquial speech, APMV is more commonly referred to as just “mimivirus”. Until October 2011, when a larger virus Megavirus chilensis was described, it had the largest capsid diameter of all known viruses.^[2] Mimivirus has a large and complex genome compared with most other viruses. Mimivirus, short for "mimicking microbe", is so called to reflect its large size and apparent Gram-staining properties

Parvovirus, often truncated to "parvo",

• . Parvoviruses are typically linear, non-segmented single-stranded DNA viruses, with an average genome size of 5000 nucleotides. Parvoviruses are some of the smallest viruses (hence the name, from Latin parvus meaning small) and are 18–26 nm in diameter.

Gram staining (or Gram's method) is a method of differentiating bacterial species into two large groups (Gram-positive and Gram-negative).

• It is based on the chemical and physical properties of their cell walls. Primarily, it detects peptidoglycan, which is present in a thick layer in Gram positive bacteria.^[1]
•  A Gram positive results in a purple/blue color , Gram-positive cell walls typically lack the outer membrane found in Gram-negative bacteria
• while a Gram negative results in a pink/red color.

The Gram stain is almost always the first step in the identification of a bacterial organism, and is the default stain performed by laboratories over a sample when no specific culture is referred.
While Gram staining is a valuable diagnostic tool in both clinical and research settings, not all bacteria can be definitively classified by this technique, thus forming Gram-variable and Gram-indeterminate groups as well.


WHAT IS A VIRUS

• A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea.
• ^] Viruses are found in almost every ecosystem on Earth and are the most abundant type of biological entity.
•  The study of viruses is known as virology, a sub-speciality of microbiology.

Virus particles (known as virions) consist of two or three parts:

•  the genetic material made from either DNA or RNA,
•  long molecules that carry genetic information; a protein coat that protects these genes; and in some cases an envelope of lipids that surrounds the protein coat when they are outside a cell.
•  The shapes of viruses range from simple helical and icosahedral forms to more complex structures.
• The average virus is about one one-hundredth the size of the average bacterium. Most viruses are too small to be seen directly with a light microscope.

The origins of viruses in the evolutionary history of life are unclear: some may have evolved from plasmids – pieces of DNA that can move between cells – while others may have evolved from bacteria.

 In evolution, viruses are an important means of horizontal gene transfer, which increases genetic diversity.


Antibiotics have no effect on viruses, but several antiviral drugs have been developed.


Viruses spread in many ways; viruses in plants are often transmitted from plant to plant by insects that feed on the sap of plants, such as aphids; viruses in animals can be carried by blood-sucking insects.

• These disease-bearing organisms are known as vectors.
•  Influenza viruses are spread by coughing and sneezing. Norovirus and rotavirus, common causes of viral
•  gastroenteritis, are transmitted by the faecal-oral route and are passed from person to person by contact, entering the body in food or water.
•  HIV is one of several viruses transmitted through sexual contact and by exposure to infected blood.
•  The range of host cells that a virus can infect is called its "host range". This can be narrow or, as when a virus is capable of infecting many species, broad.^[8]

Viral infections in animals provoke an immune response that usually eliminates the infecting virus. Immune responses can also be produced by vaccines, which confer an artificially acquired immunity to the specific viral infection. However, some viruses including those that cause AIDS and viral hepatitis evade these immune responses and result in chronic infections.