VirusesThe deadly microscopic world.

Viruses• Nucleic acid within a protein coat• Jenner – smallpox vaccine• Non-living• No metabolism• Cannot replicate without a host• No scientific name, instead family names

Influenza virus

Structure of a Virus

• Viruses that infect bacteria – bacteriophage

• General Characteristics:• Nucleic acid – either

RNA or DNA• Outer protein capsid• Optional features

for protection

• Envelope, spikes, slime layers

Capsid protein

DNA or RNATail

Tail fibers

Attaching to Cells • Prior to replication, virus must enter cell

• Protein on virus interlock with surface markers on cells

• Each virus has specific cell to “dock” with

• EX: polio virus attaches to nerve cells

Viral Replication Cycles

• Lytic 1A. Virus

attaches to cell

2A. Inserts DNA3A. Replication

of viral parts

4A. Assembly of new viruses

5A. Cell lyses

• Lysogenic1B. Virus attaches to

cell2B. Inserts DNA3B. DNA integrates into

host DNA - prophage4B. Cell replicates

normally with viral DNA altering protein synthesis

5B. Viral DNA comes out of the host DNA

6B. Begin Lytic Cycle

How Viruses Damage Cells• Inhibit protein synthesis of host• Open lysosomes• Bind membranes together• Create a toxic level of proteins

The human body protects itself from viruses using antibodies and fever. Viruses prefer body temperature.

Which of these diseases is likely to be caused by a lytic virus?

Characteristics of some Viral Diseases

Disease Symptoms Incubation

Measles Rash, Fever 9-11 days

Shingles Pain, itching on skin Years

Warts Bumpy area on skin Months

Influenza Body aches, fever, runny nose 1-4 days

HIV fatigue, weight loss, fever 2-5 years

Viral Diseases

Smallpox•Last seen in 1977•Eradicated by WHO due to obvious symptoms and short life cycle•CDC and Moscow•Self-replicating

Chicken Pox•Fluid filled blisters•Itching and burning•Common in kids•Vaccine to prevent

Herpes zoster – shingles•Reactivated chicken pox•Highly contagious•Viral DNA remains in neurons, dormant•Pain, fever, skin lesions, pus filled spots•Can be due to sun, stress, fever, trauma, but main cause unknown

Untreated shingles

Herpes simplex 2•Genital herpes•Virus lives in bottom of the spine•Same reactivation•Congenital herpes in newborns•Tingling, pain during urination, thick discharge, fluid filled vesicles•Found in 25 mil Americans

Genital Herpes

Cold Sores •Herpes simplex•Virus lives in a nerve in face•Reactivated similar to shingles•Fever, sore throat, mouth pain, edema

Untreated cold sores

HIV•Retrovirus RNA DNA•Reverse transcriptase•Fluid transmission•Enters immune system by endocytosis into WBC•Prevents WBC from making a receptor (CD4) that normally detects pathogens•Symptoms treated with drug cocktail

HIV•Exposure symptoms – headache, sore throat, occasional rash•Upon reactivation – rapid weight loss, dry cough, night sweats, unexplained fatigue, white spots in mouth, memory loss

Kaposi’s Sarcoma – HIV side affect

Burkitt’s Lymphom

a – HIV Side

Affect

Rabies•Virus lives in salivary glands of animal•Virus destroys the nerves•Produces Negri bodies in brain• Initial symptoms – tingling and cold around bite, nervous•Phase II – anxiety, photophobia, arrhythmia, pupil dilation, difficulty swallowing•Gamma globulin treatment

Mononucleosis•Fluid transmission•“kissing disease”• Infects WBC’s •Enlarged lymph nodes, swollen spleen, sore throat,nausea, weakness, fatigue•Can last up to 6 wks•Remains latent in nerves

Measles•Highly contagious•Respiratory droplet spread•Nasal discharge, dry cough, fever, headache, pink eye, pink lesions, ear infection•Targeted for eradication•MMR vaccine

Viral Hepatitis B• Initially asymptomatic•1-3 month incubation•Fever, loss of appetite, pain, nausea, fatigue, jaundice, swollen liver•3 step vaccine

Hanta Virus•Deermice and ticks•No human to human•2-3 day incubation•Cough, pulmonary edema, hemorrhaging, renal failure, achy muscles•60% death rate

Ebola•93% death rate•Hemorrhagic fever• High temperature• Blood from orifices

Scott lives on a farm in the country. He started feeling sick with flu-like

symptoms. After a couple of days, his pupils became dilated and he had difficulty swallowing. His parents

rushed him to the emergency room. X-rays revealed that Scott has small

lesions forming on his brain. He also had an animal bite on his lower leg.

rabies

Mary is a 23 year old college student who went to the doctor after several

weeks of general sickness. She complained of fatigue, chills, sweating

at night, a continuous cough, and slight diarrhea. It was noted during the exam that her glands under her arms and in her neck were swollen. The doctors

performed a blood test.

HIV

A child, age 7, came home from school complaining of a sore throat. Her mom took her fever, which was 1020F. The child was taken to the doctor after a couple of days with no improvement.

The doctor noticed that she was developing a pink rash and seemed to

have an ear infection. She had not been vaccinated with the MMR. What

illness does this child likely have?

measles

Viral Diseases• Steroids given if severe – boost immune function• Usually cause fever• Some vaccinations are weakened forms of actual virus• Many viruses stay in your system even after recovery

A

B

J