Explain what a virus is and how it causes disease

-A virus is a small infectious agent that replicates only inside the living cells of other organisms. Viruses can infect all types of life forms, from animals and plants to bacteria and archaea.

-Viruses spread in many ways; viruses in plants are often transmitted from plant to plant by insects that feed on plant sap, 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.

-In biological taxonomy, a domain is the highest taxonomic rank of organisms in the three-domain system of taxonomy designed by Carl Woese, an American microbiologist and biophysicist. The domain is important in classifying any type of organism before classifying them further into sub categories.

Differences between bacteriophages and animal viruses.

bacteriophage only attack bacteria. their capsids have elongated 20 sided heads that enclose their DNA. attached to the head is a protein tail piece with tail fibers that the phages use to attach to a bacterium. bacteriophage, or simply called as phages, are the best understood of all viruses, although some of them are also among the most complex. research on phages led to the discovery that some double-stranded DNA viruses can produce by 2 alternative mechanisms: the lytic cycle and the lysogenic cycle (search it on google)

animal viruses attack animal cells. they have a very complex reproductive cycle. the virus entering the cell will have its genome released. then it will replicate and direct the viral protein synthesis. then it will replicate into a new virus. RNA viruses have reverse transcriptase which provides an RNA DNA information flow.

Similarities between bacteriophages and animal viruses.

-Single type of nucleic acid
-Require a host cell for replication
-Can be lytic or can integrate into the host genome and be transmitted vertically (analogous to lysogeny)

Why there is a new flu vaccine released each year?

Influenza viruses are highly variable and change from year to year. Therefore, it is possible to get influenza several times during a lifetime and become infected with the same virus (sub)type. The immunity provided by natural infection or vaccination with a given influenza virus strain does not necessarily provide protection against a newer virus strain. That is why the influenza vaccine composition is updated every year to include currently circulating virus strains.