Viruses can infect all types of life forms:animals, plants and microorganisms, including bacteria

Latin: virus = referring to POISON or NOXIOUS LIQUID

"organisms at the edge of life"Considered a life form because they:* carry genetic material* reproduce* evolve through natural selection

NOT considered a life form because they* do not have their own metabolism* cannot naturally reproduce outside a host cell* reproduce through self assembly (not cell division)

Virology (a sub-speciality of microbiology)studies viruses

When outside of a host cell viruses are independent

particles known as VIRIONS

Protein coat; protects the genetic material

lipid coat; protects the capsid when outside of a living cell

Viral infections in animals trigger an immune response that usually eliminates the infecting virus

Some antiviral drugs have been developed

Antibiotics have NO effect

Vaccines: confer an artificially acquired immunity to the specific viral infection

Means of spreadingVectors: disease bearing organisms

However, viruses including those that cause AIDS and VIRAL HEPATITIS avoid these immune

responses and cause chronic infections

They are "protected" from medicines,

which usually move through your bloodstream

Viral infections are hard to treat because

viruses live inside your body's cells

The Viral Life Cycle

Other Infectious Agents

VIROIDS: the smallest infectious pathogens know composed of a short strand of circular, single-stranded, RNA without protein coat. -Affect plants

PRION: an infections agent composed entirely of protein material, called PrP (short for prion protein), that can fold in multiple, structurally distinct ways, at least one of which is transmissible to other prion proteins, leading to disease-Affect animals/humans