Viruses

Are Viruses Living Things? Characteristics of Living things are… Made of cells Can reproduce Based on a universal genetic code Grow and develop Obtain and use materials and energy Respond to the environment Maintain homeostasis As a group, change over time * *

Viral Characteristics NON-LIVING REPRODUCE ONLY WITHIN A HOST CELL by hijacking the cells’ machinery NAMED FOR DISEASE THEY CAUSE OR PLACE THEY INFECT

Which type of cell will be infected by the virus shown below?

Name tells you this virus infects bacteria

Name tells you this virus causes influenza

Viral Size Viruses are very small. If an average virus were the size of an average person, a bacterial cell would be the size of a dinosaur over ten stories tall. Click on the picture for virus size activity

Whiteboard Activity Cell, Virus or Both

Activity: Cell, Virus, or Both? Contains nucleic acid as genetic material Both

Activity: Cell, Virus, or Both? Can grow and develop Cell

Activity: Cell, Virus, or Both? Can only replicate in a host Virus

Activity: Cell,Virus, or Both? Can reproduce on its own Cell

Activity: Cell, Virus, or Both? Obtain and use materials and energy Cell

Activity: Cell, Virus, or Both? Respond to the environment Cell

Activity: Cell,Virus, or Both? Maintain homeostasis Cell

Activity: Cell, Virus, or Both? Can contain DNA Both

Activity: Cell, Virus? Which is smallest? Virus

Activity: Cell, Virus, or Both?

Activity: Cell, Virus, or Both?

Ask students to note similarities and differences that they see in these pictures. Point out that the viruses all contain the same “major parts (i.e. genetic material and capsid), but are specific for specific types of cells. Viruses are typically classified according to the type of organism they infect.

Viral Structure All viruses have: genetic material (DNA or RNA) Capsid: protein coat that enables a virus to enter a living cell

How do viruses infect cells? Once a virus enters a host cell, two different processes can occur: Lysogenic cycle Lytic cycle

Lytic Cycle Virus enters the cell, makes a copy of itself, and causes the cell to burst.

Lytic Cycle viral DNA is injected into the host cell host cell begins to make mRNA from the viral DNA viral proteins shut down the host cell’s regular functions cell is used to make thousands of viruses (DNA and protein coats) host cell bursts (lyses) and releases viruses to infect other cells

Lysogenic Cycle Host cell makes copies of the virus indefinitely. Virus integrates its DNA into the DNA of the host cell, and the viral genetic information replicates along with the host cell’s DNA. Lysogenic viruses remain inactive for a period of time and do not lyse the cell immediately.

Lysogenic Cycle viral DNA is injected into the host cell DNA is integrated into the host DNA host cell divides with the viral DNA as a part of it eventually the viral DNA can be triggered to separate from the host cell DNA and pick up with the lytic cycle at step 2.

Turn to the person next to you and discuss the difference between the lytic and lysogenic cycles.

How do RNA viruses work? RNA viruses do not have built in proofreading, so they mutate and evolve quickly (like the flu). A special kind of RNA virus, called a retrovirus, can cause DNA to be made from their RNA. Certain cancers, and AIDS are caused by retroviruses.

Symptoms, causes and treatments Viral Diseases Symptoms, causes and treatments

Common Cold Symptoms Causes: Runny nose, sore throat, headache, cough 200+ viruses can cause it, including rhinoviruses There is no evidence for weather causing a cold

Influenza “the flu” Symptoms: Cause: influenza Status: Fever, headache, fatigue, body aches, congestion, Cause: influenza Status: Vaccines present, BUT it changes every year (RNA virus) Threat of flu pandemics worldwide

Smallpox Symptoms: Cause: Variola Status High fever, body aches, small raised bumps all over body Cause: Variola Status Vaccine present Can be fatal Eradicated worldwide

Herpes Simplex I (above the belt) Symptoms: Transmission Status: Cold sores around mouth Transmission Kissing, eating/drinking after one another Status: no vaccine, medication to reduce outbreaks Simplex II (below the belt) Symptoms: Pain, itching, burning during urination, blisters on genitals and thighs Transmission: Sexually transmitted, do not have to be showing signs, oral or vaginal sex Status: No vaccination, no cure, medication to reduce symptoms and reduce number of outbreaks

Herpes Virus ↑ Simplex I 

Genital Warts Symptoms: Cause: Human Papillomavirus (HPV) Raised or flat, single or multiple swellings on any genital surface, male or female, can appear cauliflower-like Can cause cervical cancer in women Cause: Human Papillomavirus (HPV) Transmission: sexual contact with infected partner, do not have to be showing signs Status: 6.2 million new cases a year in U.S. No cure, but removal is common. VACCINE AVAILABLE

Hepatitis B Symptoms: Cause: hepatitis B virus Transmission: Status: Cirrhosis (scarring of the liver), liver cancer, liver failure, death Do not have to look sick Cause: hepatitis B virus Transmission: Sexually blood contact (needles, razors, etc.) Status: Vaccine is available 1.25 million American live with chronic hepatitis B

Rabies Symptoms: Transmission: Status: Fever, headache, paralysis, hydrophobia, hallucinations, foaming at the mouth, ultimately death Transmission: bite from an infected mammal (carnivores and bats) Status: Cases have reduced in domestic animals greatly Vaccine is available, given to people at high risk of infection

HIV (Human Immunodeficiency Virus) Symptoms: Fever, headache, tiredness, enlarged lymph nodes AIDS (Acquired Immunodeficiency Syndrome) weight loss, fatigue, memory loss, Destroys CD4+ cells (part of immune system) so body cannot fight off illnesses caused by bacteria, other viruses, fungi, or parasites. Ultimate death

HIV (continued) Transmission: Status: Prevention: sexually (orally, vaginally) Blood (needles, or through mucus memranes) Breast milk mother to child NOT from kissing, touching, insects bites Status: No vaccine, several medicines prevent spread in body Worldwide, there are about 40 million people living with HIV/AIDS (2004), about 5 million newly infected in 2004, and 3.1 million deaths in 2004 Prevention: Abstinence, Safe sex, avoidance or risky behaviors associated with sex and drug use

Ebola Hemorrhagic Fever Symptoms: Fever, headache, muscle/joint pain, red eyes, skin rash Diarrhea, vomiting, rash, internal and external bleeding Cause: One of 4 Ebola viruses (a retrovirus) Transmission: Blood to blood or secretions to mucus membranes Air transmission in monkey Ebola only Status: Only identified in 1976 with few devastating outbreaks

Other viral diseases Polio Shingles/ chicken pox Hanta SARS Stomach virus (viral gastroenteritis) Viral meningitis Rubella, Measles, mumps For more information on these viruses, please go to websites sponsored by medical facilities, the CDC, WHO, NIH, or other credible sources