Viruses Ch 19 – Lecture Monday 12/2/13

Tuesday: Lab Quiz: Protists and FungiWednesday: Lecture Quiz on Fungi

Thursday: LAB Exam* Bring book and notes

Importance of Viruses

1. Agent of diseases2. Vector of gene in biotechnology– 30% of human DNA is viral

3. Agent of evolution or mutation

Smallpox viral disease

• Infectious variola virus cause maculopapular rash• Transmission via respiratory droplets• Cause macropuplar rash (not itchy) with permanent scarring• Transmission via respiratory droplets• Humans are the only known host• Eradicated 1979• Russia and US have smallpox samples• Can be used as a bioweapon• Death occurs in 30% of cases due to respiratory

complications

Chicken pox and shingles

• Varicella zoster virus• Virus dwell in sensory nerves• Symptoms include rashes, fever, and general

malaise• Adult form: shingles

Rabies (hydrophia)

• Viral need treatment in 3 days• Zoonotic disease (spread by animals) that

cause encephalitis resulting in violence, madness, and hydrophobia

• Virus causes nervous damage• Delirium, coma, death• Bats are likely rabies vectors

Herpes I

• Herpes I cause sores and blisters

Herpes II

• Cause genital blisters• Mild and asymptomic in healthy adults• Can be transmitted to newborn

AIDS

• HIV targets specific cells. HIV kills white blood cells with CD4 antigen, primarily T helper cells

• T-helper cells are crucial in the activation of other white blood cells

• T helper cells are generals. They organize immune strategy.

• Death from AIDS is due to opportunistic infections– TB, PDP, Kaposi Sarcoma, toxoplasmosis

AIDS v HIV

• HIV positive:• AIDS: T cell count is below 200 micro-liter

Common cold, influenza, SARS, Hanta virus

• Cause respiratory problems

Hepatitis A

• Liver inflammation• Transmitted primarily contaminated water or

food• Infection occurs during childhood• Cause liver damage• Vaccine available

Hepatitis B

• Blood transfusion/exchange• Vaccine vacation • Can lead to liver cirrhosis (hardening) and

caner

Hepatitis C

• Transmitted via blood exchange• Most cases are asymptomatic• Can progress to liver cirrhosis and cancer req

requiring liver transplant• No effective vaccine available

Warts and cervical cancer

• Caused HPV• Can lead to cervical, ovarian, genital, and anal

cancers• We all have had it• Can transmit by casual contact • Vaccine available for 70% of cases called

Gardasil. You have to get it before you get sexually active.

Ebola & Marbug

• Mortality is as high as 90%• Cause shock due to loss of vascular integrity

and loss of coagulation• Endemic and sporadic

Structure of Viruses

• Viruses are NOT cells. • Viruses are obligate intracellular parasites. They are

active or reproduce only when inside host cells• Viruses consist of nucleic acid enclosed in capsid

(protein coat) and membranous envelope. • Each virus has a host range, a limit number of host

cells that it can inflect. – Herpes will attack only nerve cells, not muscle cells– H1N1 can go from one species to another

• Viruses are smaller and simpler than bacteria,.

All viruses

• 1. Have RNA or DNA• All viruses have protein shells or capsids.

Viral genomes

• All viruses have double or single RNA or DNA. It can’t be both DNA and RNA. It is one or the other.

capsid

• Protein shell that encloses the viral genome• Functions: attachment to host cell protection

of genome• Capsid of some virus is used as a vaccine to

induce immunity– BHV, HPV, and polio vaccines

Membranes (some viruses)

• Some viruses have membranous envelopes that surround the capsid which helped them infect host cells

• Viruses acquire membranes from host cells. • Host cell membranes allow viruses to escape

detection by host white blood cells.• exocytosis

spikes

• Some viruses have spikes protruding from their envelope (glycoprotein)

• Spikes help viruses attach to host cells• H (hemagluttin) N (neuranidase) H1N1: spikes

are made of proteins H and N.

Bacteriophages: viruses that infect bacteria

• Two types: lytic and lysogenic

Lytic (virulent phage)

• Upon entrance, virus directs host cell to synthesize more virus copies.

• Capsid stays out. Only DNA or RNA goes inside the host.

• Lytic cycle terminates in death of host cell. • Virulent phage: a phase that reproduces only

by lytic cycle• Virus only injects the genome into host cells,

not capsid

Lysogenic

• Viral DNA is incorporated into the host DNA• Virus knows when host cell will die• Prophage: integrated viral DNA• Every time host divides, virus genome also gets

copied and viral genome is passed on to daughter cells.

• Temperate phage: uses both lytic and lysogenic cycles. HIV is temperate

• Does NOT kill host cell immediately