Viruses Chapter 18

VIRUS: Latin word for poison Virus: Non-living, parasitic, biological particle. All viruses cause some sort of disease. Some even cause cancer.

VIRUSES do not “live” because: They can not reproduce outside a “host” cell They do not carry out cellular respiration They do not grow or develop

Virus structure DNA or RNA Core Capsid Holds the genetic material that will affect the host Capsid Outer protein coat that enables the virus to enter certain cells.

Virus structure Glycoproteins Projections that help the virus attach to host Not all viruses have glycoproteins.

Virus Size Viruses are smaller than the smallest cell

Virus Vocab Host: a cell in which a virus replicates Host Specific: most viruses or bacteria will only affect a single host or a small group of host species Examples: West Nile Virus – affects birds, horses, and people Influenza type B – affects only people not others Parvo – affects only dogs, not other organisms

Types of Viruses

Bacteriophages

Phages Viruses that attack bacteria are called bacteriophage or just phage T-phages are a specific class of bacteriophages with icosahedral heads, double-stranded DNA, and tails

T-phages The most commonly studied T-phages are T4 and T7 They infect E. coli , an intestinal bacteria Six small spikes at the base of a contractile tail are used to attach to the host cell Inject viral DNA into cell

Viruses Blow Up the Cell the Affect!!! Once the viral genes get inside a cell, the genes are expressed. This genetic program causes the host cell to make copies of the virus. In the process, the host cell is destroyed.

Viruses Blow Up the Cell they Affect!!! There are two ways this can occur The Lytic Cycle The Lysogenic Cycle

The Lytic Cycle Lysis – to break or rupture cells or cell membranes STEPS Attach Virus “docks” with host cell Injection Virus inject it’s DNA/RNA into host cell Replicate replication of virus parts Lysis cell ruptures and new virus’ invade tissues of the host Lysis – to break or rupture cells or cell membranes

The Lysogenic Cycle STEPS Attach Virus “docks” with host cell Injection Virus inject it’s DNA/RNA into host cell Incorporate DNA attaches to the cells own DNA Time Goes By Stress Replicate replication of virus parts Lysis cell ruptures and new virus’ invade tissues of the host

Examples of Lytic Viral Infections 1. Common Cold How do we catch it? Contact with contaminated objects; droplet inhalation What are the symptoms? Sneezing, Sore Throat, Fever, Headache, Muscle Aches

Examples of Lytic Viral Infections 2. Influenza How do we catch it? Contact with contaminated objects, droplet inhalation. What are the symptoms? Body Aches, Fever, Sore Throat, Nasal Congestion, Headache, Dry Cough, Fatigue.

Examples of Lytic Viral Infections 3. Ebola How do we catch it? exposure to blood or bodily secretions of an infected person, or through direct contact with the person. What are the symptoms? Sore Throat, Fever, Dry hacking cough, Weakness, Severe Headache, Joint and muscle aches, Diarrhea, Dehydration, Stomach pain, vomiting, Internal and external bleeding.

Examples of Lysogenic Viral Infections 1. Herpes Viruses Once a person is infected with a herpes virus they are infected for life. Examples: Chicken Pox can reappear later in life as Shingles HSV-1 (oral herpes) and HSV-2 ( genital herpes)

Example of a Retrovirus 2. HIV How do we catch it? Contact with contaminated blood or bodily fluids What are the symptoms? T cells (needed for normal immune function) are destroyed

Retroviruses Retroviruses are viruses that contain RNA as their genetic information Retroviruses get their name from the fact that their genetic information is copied backward, from RNA to DNA. HIV is the most infamous retrovirus

How Do Our Bodies Fight Viral Infections? Antibiotics do nothing for viral infections!!! After enough cell debris (from blown up cells) is detected your Immune system gets involved Macrophages are large white blood cells that get rid of debris by eating it. When they eat too much, they die. These dead cells and the cell debris are “puss”

How Do Our Bodies Fight Viral Infections? T- cells (thyroid cells) are called upon and go to the site of the infection to kill specific infected cells B-cells (bursal cells) make antibodies that go to the site and kill free viruses Other white blood cells pick up viral particles from the battle and carry it to Lymph nodes. In the lymph nodes, they look for cells to fight this type of virus.

How Do Our Bodies Fight Viral Infections? The best way to protect against most viral diseases lies in prevention, often by the use of vaccines. Most vaccines provide protection only if they are used before an infection begins.