VIRUSES

Lytic vs. Lysogenic

Vaccines• First made was in 1700’s- fight smallpox• Help prevent viral infections, but they cannot cure most

viral infection • Some recently-developed drugs do combat some viruses,

mostly by interfering with viral nucleic acid synthesis.• AZT interferes with reverse transcriptase of HIV.• Acyclovir inhibits herpes virus DNA synthesis.

WHAT IS HIV??

• “Human Immunodeficiency Virus”• A unique type of virus (a retrovirus)

• Invades the helper T cells in the body of the host

• Preventable, managable but not curable

WHAT IS AIDS ???• “Acquired Immunodeficiency Syndrome”

• HIV is the virus that causes AIDS

• Disease limits the body’s ability to fight infection due to reduced helper T cells.

• Patients predisposed to multiple opportunistic infections leading to death.

Stage 1 - Primary• Short, flu-like illness - occurs one to six weeks after infection

• Mild symptoms

• Infected person can infect other people

Stage 2 - Asymptomatic

• Lasts for an average of ten years

• This stage is free from symptoms

• There may be swollen glands

• The level of HIV in the blood drops to low levels

• HIV antibodies are detectable in the blood

Stage 3 - Symptomatic

• The immune system deteriorates

• Opportunistic infections and cancers start to appear.

Stage 4 - HIV AIDS

• The immune system weakens too much as CD4 cells decrease in number.

Opportunistic Infections associated with AIDS• Bacterial infections

• Tuberculosis (TB)• Herpes Simplex• Herpes Zoster• Vaginal candidiasis• Hairy leukoplakia• Kaposi’s sarcoma

Opportunistic Infections associated with AIDS

• Pneumocystic carinii• Toxoplasmosis• Cryptococcosis• Coccidiodomycosis• Cryptosporiosis• Non hodgkin’s lymphoma

HAART = highly active anti-retroviral treatment

Transduction

• Definition: Gene transfer from a donor to a recipient by way of a bacteriophage

Transduction

• Types of transduction– Generalized - Transduction in which

potentially any donor bacterial gene can be transferred

Generalized Transduction

• Release of phage

• Phage replication and degradation of host DNA• Assembly of phages particles

• Infection of recipient• Legitimate recombination

• Infection of Donor

Transduction

• Types of transduction• Generalized - Transduction in which potentially any dornor

bacterial gene can be transferred.

– Specialized - Transduction in which only certain donor genes can be transferred

Specialized TransductionLysogenic Phage

• Excision of the prophage

gal

bio

gal bio

gal bio

gal

bio

bio

gal

• Replication and release of phage

• Infection of the recipient

• Lysogenization of the recipient– Legitimate

recombination also possible

Transposable Genetic Elements

• Definition: Segments of DNA that are able to move from one location to another

• Properties• “Random” movement• Not capable of self replication• Transposition mediated by site-specific recombination

• Transposase

• Transposition may be accompanied by duplication