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