Chap 25 -- RNA Viruses

Influenza infections

Virus attaches to and multiples in cells of respiratory tract

Segments of RNA genome enter nucleus

Finished viruses are assembled and bud off the cell

Influenza glycoproteins spikes (2) + both frequently undergo what

Hemagglutintin (H): 15 subtypes. Most important virulence factor, binds to host cells

Neuraminidase (N): 9 subtypes. Hydrolyzes mucus and assists viral budding and release

Both undergo genetic changes —> decreases effectiveness of host immune response

Antigenic drift (Influenza)

Constant mutation of influenza — gradually change their amino acid composition

Antigenic shift (Influenza)

One of genes/RNA strands is substituted with gene or strand from another influenza virus from a different animal host

• Genome of virus consists of 10 genes encoded on 8 separate RNA strands

Influenza strands

A: most virulent —> used to infect birds but underwent antigenic shift and began to infect humans

B: antigenic drift only

C: cause minor respiratory disease. no epidemics

Influenza A characteristics + symptoms

• Acute, highly contagious respiratory illness

• Seasonal. Top 10 causes of death, elderly + small children

  • Fever, headache, myalgia, shortness of breath, coughing

Influenza A binds to what + causes what + weakened host defenses predispose them to what

• Binds to ciliated cells of respiratory mucosa

• Causes rapid shedding of cells, stripping respiratory epithelium (severe inflammation)

• Predispose patients to secondary bacterial infections (pneumonia)

Rabies (nonsegmented ssRNA virus) progression + what causes it

Virus enters through bite —> grows at trauma site for a week + multiplies —> enters nerve endings and goes to ganglia, spinal cord, and brain

Infection cycle completed when virus replicates in salivary glands

Rhabdovirus, genus Lyssavirus

Common carriers of rabies

Wild mammals: canines, skunks, raccoons, cats, bats

Spreads to humans through bites, scratches, or inhalation of droplets

Clinical phases of rabies

Prodromal phase: fever, vomiting, tingling, headache

Furious phase: agitation, seizures, twitching, disorientation

Dumb phase: paralyzed, disoriented

Progresses to coma phase —> death

Coronaviruses (nonsegmented ssRNA virus) structure + common in what + agents of what

Large RNA viruses with spikes on envelopes

Common in domesticated animals — bats

5 types of human coronavirus —> agents of:

• Cold

• Viral pneumonia/myocarditis

• Enteric infection

• Severe Active Respiratory Syndrome (SARS)

SARS — transmission, symptoms, diagnosis

• Transmitted through droplet/direct contact

• Fever, body ache. Could have respiratory symptoms w/ breathing problems

• Diagnosis relies on exclusion of other likely agents, detection of antibodies against SARS-CoV. Loss of taste/smell

Development of SARS

Binds to angiotensin-converting enzyme 2 (ACE2) prior to fusion of viral envelope and cellular membrane

Hepatitis C (nonsegmented ssRNA virus) caused by what + acquired how

Caused by flavivirus (HCV — hepatitis C flavivirus)

Acquired through blood contact — blood transfusions, needle sharing

Characteristics of hepatitis C + treatment + vaccine

75-85% remain infected forever

Chronic liver disease

Possible cancer

Treatment: interferon/ribavirin to lessen liver damage

No cure no vaccine

Two types of hemorrhagic fevers

Yellow fever + dengue fever. Caused by flavivirus

Not in US

Yellow fever patterns of transmission (2) + symptoms

Urban cycle: Humans/mosquitoes. Aedes egypti

Sylvan cycle: Forest monkeys/mosquitoes. South America

Symptoms: headache, muscle pain, oral hemorrhage, nosebleed, vomiting. Liver/kidney damage

Dengue fever carried by what + symptoms

Flavivirus carried by Aedes mosquito

Dengue hemorrhagic shock syndrome, extreme muscle and joint pain

Retroviruses — what is it, example

RNA virus that converts RNA to DNA by using the enzyme reverse transcriptase in host cell

• HIV, genus Lentivirus

• Viral genes permanently integrated into host DNA

• Provirus (integrated DNA into host cell)

• Causes AIDS

Human immunodeficiency virus characteristics + caused by what + symptoms

• Severe pneumonia caused by pneumocystis jirovecii

• Rare vascular cancer called kaposi sarcoma

• Sudden weight loss and swollen lymph nodes. General loss of immune function

HIV structure

Glucoprotein spikes on surface that allow virus to attach to and enter host cells, stick out from envelope:

• GP-120: binds to CD4 receptor and co-receptor. this is first

• GP-41: helps viral envelope fuse with host cell membrane

# refers to molecular weight

Types of HIV

HIV1 — most common, more transmissible, more severe

HIV2 — progress slowly, less common

HIV can only infect what

Host cells that have the required CD4 marker plus a co-receptor, must bind to specific receptors on cell surface

How does HIV develop

1. HIV enters through mucous membrane/skin and travels to dendritic phagocytes beneath epithelium, multiples, and is shed

2. Virus is taken up and amplified by macrophages in skin, lymph organs, bone marrow, and blood

3. HIV attaches to CD4 and co-receptor, fuses with cell membrane

4. Reverse transcriptase enzyme makes DNA copy of RNA

5. Viral DNA integrated into host chromosome

6. Can produce lytic infection or remain latent

Diagnosis of HIV

Level of viruses

Level of T cells in blood

Primary effects of HIV infection

Extreme leukopenia (lymphocytes)

Formation of giant T cells and other syncytia, virus spreads

Infected macrophages release virus in CNS with toxic effect

Secondary effects of HIV

CD4 lymphocytes destruction — opportunistic infections and malignancies during full-blown AIDS

Treatment of HIV

Protease inhibitors: Prevents activation of assembled viruses

Integrase inhibitors: Prevents integration of HIV DNA into host cell DNA

Hepatitis A Virus structure + symptoms + how is it devloped

Cubical picronavirus resistant to heat and acid

Does not cause chronic infection, does not remain in body long-term

Infection occurs but minimal/absent symptoms

Fecal-oral transmission: virus from feces enters another person’s mouth (contaminated food/water) —> multiplies in small intestine and enters blood and carried to liver

Hepatitis A treatment and vaccination

No treatment

Vaccination:

• Inactivated (contains killed virus —> cannot replicate and stimulates immunity). Body make antigen

• Attenuated vaccine (weakened live virus). Body make antigen

• Injection of antibodies from donors —> immediate short-term protection. Temporary

Measles

• Caused by morbillivirus

• Transmitted by respiratory aerosols

• Humans only

• Invades mucosal lining of respiratory tract

• Sore throat, dry cough, headache, conjunctivities

Koplik’s spots and exanthem (Measles)

Koplik spots: Red blisters with white specks on mucosal lining of cheeks

Exanthem: Eruption/rash of skin on head, progresses to trunk/extremities until whole body is covered

Rubella

German measles, caused by togavirus

Mild but dangerous in pregnancy because it can cause congenital rubella syndrome, leading to deafness, heart defects, cataracts in newborns

Skin rash, no koplik spots

West Nile virus cause of what + spread how

Prevalent cause of arboviral disease

Mosquitoes become infected when they feed on birds infected with virus, bite and transmit virus to humans

Zika Virus

Aedes mosquito bites, spread through sex/pregnancy.

Can cause brain defects, otherwise asymptomatic

Fever, rash, joint pain, red eyes

Mumps

Painful swelling at angle of jaw, targets parotid salivary glands

Salivary/respiratory secretions

Caused by paramyxovirus

MMR Vaccine

Measles, mumps, rubella. Live attenuated vaccine (weakened forms of viruses) — are alive but do not cause disease and stimulates strong immunity

Ebola

• Filovirus

• Headache, fever, chills —> rash, nausea, pain in throat/chest —> uncontrolled bleeding, shock, multiorgan failure

• Treatment: two monoclonal antibody based drugs

Hantavirus

• Transmitted by rodent droppings/animal wastes

• Caused by bunyavirus

• Causes Korean hemorrhagic fever