VIRUS

Virus

•      -smaller than bacteria

•      -seen only in electron microscope

•      -1940’s first photograph of viruses were only obtained.

Characteristics

•      Obligate intracellular organism.

•      Filterable

•      Size -10 nm. To 250 nm.

•      Contain one type of nucleic acid.

•      No ATP generating system.

•      With ribosome but uses host cell’s ribosome.

•      Composition

Inside core:

            DNA or RNA- gives the virus the genetic and infective capacity.

                     Outside Coat ( CAPSID ) :

-made up of CAPSOMERES

-protect the inside

-gives shape

-antigenic specificity.

•      * To infect the viral protein must be absorbed and must react with the proper receptor sites of the host.

Classification according to genetic material:

•      RNA

•      DNA

Communicable Disease

Taxonomy

DNA viruses- HHAPPPy

        HERPES

        HEPADNA

        ADENO

        PAPOVA

        PARVO

        POX

Communicable Disease
Taxonomy

RNA viruses

        Toga

        Corona

       Retro

       Picorna

       Calici

       Reo

       Orthomyxo

       Paramyxo

       Rhabdo

       Arena

       Filo

Classification According to Shape of Capsids:

•      Polyhedral

•      Helical

•      Bullet shaped

•      Spherical

•      Complex combination

Classification According to the size of capsid

•      Size is determined by the size of facets and the number of capsomere in each.

Classification according to the kind of Host

•      Bacterio phage

•      Cyanophage

•      Mycophage

•      Phytophage

•      Zymophage

•      Zoophore

Classification according to the type of Nucleic Acid

•      Single- stranded DNA phages

•      Double- stranded DNA phages

•      Single-Stranded RNA phages

•      Double- Stranded RNA phages.

Steps in the multiplication of bacteriophage

•      Attachment- phages attach to the receptor on the surface of the bacterial cell.

•      Penetration- inject its DNA into the bacterial cell. Capsid remains the outer surface of the cell.

•      Biosynthesis- phage genes are expressed, resulting in the production of phage pieces or parts.

•      Assembly- phages pieces are assembled to create complete phages.

•      Release- complete phages escape from the bacterial cell.

Categories of bacteriophages by the events that occur following invation of bacterial cell.

•      Virulent phages-

•      Ends with the destruction (lysis) of bacterial cell from most phages.

•      Temperate phages-

•      Do not immediately initiate the lytic cycle, but rather their DNA remain integrated into the bacterial cell chromosome, generation after generation.

Steps in the multiplication of animal viruses

•      Attachment

•      Penetration

•      Uncoating

•      Biosynthesis

•      Assembly

•      Release

Virions

•      Complete virus particles that are very small and simple in structure one that has its parts including nucleic acid and capsid.

Viroids

•      Short, naked fragments of single stranded RNA.

•      Interfere with the metabolism of plant cell and even kill it.

•      Inclusion Bodies

•      Are remnants or collection of viruses that are often seen in infected cells and are used as a diagnostic tool to identify certain viral diseases. Found in cytoplasm and nucleus.

Prions

•      Small infectious proteins that apparently cause fatal neurologic disease in animals.

•      Selected Virus Types

           1. Poxviruses

                                   a. Variola- Small Pox

                                   b. Vaccinia- Cow Pox

                        2.  Polyoma- papilloma

                                    a.  Papillomavirus – warts

                                    b.  Polyomavirus- some tumor and cancer

            3. Herpes Virus

                                   a.  Herpes Simplex I – Cold Sores

                                   b.  Herpes Simplex II- Genital Herpes

                                   c.  Herpes Zoster- Shingles

                                   d.  Varicella- Chickenpox

                        4.  Adenovirus

                                   a.  Respiratory infection

                                   b.  Pneumonia, Conjunctivities, some tumor

           5.  Reoviruses

                                   a.  Enterovirus-  intestinal infection

                        6.  Picornaviruses

                                   a.  Rhinoviruses- colds

                                   b.  Poliovirus-  Polio myelitis

                                   c.  Herpes Type A &B-  Hepatitis

                                   d.  Coxsackie virus- respiratory infection,  meningitis.

          7.  Myxoviruses

                                   a.  Orthomyxoviruses- influenza

                                   b.  Myxovirus- Mumps

                                   c.  Paramyxovirus-  measles  (Rubeola)

                                  d.  Rhabdovirus-  Rabies

                          8.  Arbovirus

                                  a.  Mosquiito- borne type B – Yellow Fever

                                  b.  Mosquito –borne type A & B- Encephalitis

                                  c.  Tick- borne, Corona Virus-Colorado tick fever

            9.  Retrovirus

                                  a.  RNA tumor virus- tumor

                                  b.  HTLV virus- Leukemia

                                  c.  HIV- AIDS