Chapter 25: RNA viruses

Influenza

• 3 distinct types

  • A

  • B

  • C

• Have glycoprotein spikes that frequently undergo genetic changes, decreasing host immune response effectiveness

  • Hemagglutinin (H)

  • Neuraminidase (N)

Hemagglutinin (H)

• Glycoprotein of influenza

• 15 subtypes

• Most important virulence factor

• Binds to host cells

Neuraminidase (N)

• Glycoprotein of influenza

• 9 subtypes

• Hydrolyzes mucus and assists viral budding and release

Antigenic drift

• Constant mutation

• Influenza gradually change their amino acid composition

Antigenic shift

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

Influenza A

• Most virulent

• Acute, highly contagious respiratory illness

• Underwent antigenic shift to from infecting birds to humans

• Binds to ciliated cells of respiratory mucosa

• Causes rapid shedding of cells, stripping the respiratory epithelium and severe inflammation

Parainfluenza

• Infection by paramyxovirus

• Widespread influenza but more benign

• Respiratory transmission

• Causes cold, bronchitis, bronchopneumonia, croup

Mumps

• Caused by the mumps virus

• Causes epidemic parotitis

Epidemic parotitis

• Self-limited illness

• Associated with painfull swelling of the parotid salivary glands

• Humans are the only reservoir

• Incubates for 2-3 weeks causing fever, muscle pain, malaise, and swelling in one or both cheeks

• Live attenuated vaccine MMR

Measles

• Caused by morbillivirus

• AKA red measles or rubeola

• Very contagious via respiratory aerosols

• Invades the mucosal lining of the respiratory tract

• Causes sore throat, dry cough, headache, conjunctivitis, lyphadenitis, fever, koplik’s spots, and exanthem

Kopliks spots

• Oral lesions

• Caused by measles

Exanthem

• Characteristic red maculopapula

• Eruption on the head, progressing to the trunk and extremities to cover most of the body

• Seen in measles

Subacute sclerosing panencephalitis (SSPE)

• Most serious complication of measles

• A progressive neurological degeneration of the cerebral cortex, white matter, and brain stem

• Defective virus spreading through the brain by cell fusion and destroys cells

Respiratory syncytial virus (RSV)

• AKA pneumovirus

• Infects the upper respiratory tract and produces giant multinucleate cells

  • Epithelia of the nose and eyes

• Cause of respiratory infection of children

  • Fever, runny nose, pharyngitis, otitis, croup

• Treated with synagis and ribavirin

Rabies

• Rhabdovirus family; genus lyssavirus

• Evneloped, bullet shaped virons

• Slow and progressive zoonotic disease

• Wild animal reservoirs =

• Spread via wild animal and domestic animal bites, scratches, and inhalation of droplets

Phases of rabies

• Prodromal

• Furious

• Dumb

• Progress to comma

Prodromal rabies phase

• Fever, nausea, vomiting, headache, and fatigue

• Some experience pain, burning, tingling sensations at the site of wound

Furious rabies phase

agitation , disorientation, seizures, twitching, and hydrphobia

Dumb rabies phase

Paralyzed, disoriented, and stuporus

Progress to coma rabies phase

Coma resulting in death

Corona viruses

• Large RNA viruses with distinctly spaced spikes on their envelopes

• 5 types causing agents of

  • Common cold

  • Some forms of viral pneumonia and myocarditis

  • Some human enteric infections

  • Severe acute respiratory syndrome (SARS)

SARS

• Severe acute respiratory syndrome

• Transmitted through droplet or contacts

• Family of more than 100 viruses

• Enveloped, single stranded with crown shaped surface spikes

• Three highly pathogenic viruses

  • SARS-CoV

  • SARS-CoV-2

  • MERS-CoV

SARS-CoV-2

• COVID-19 caused by SARS-CoV-2

• Transmission via airborn droplets or contaminated fomites after 15 minutes

• Presents with flu-like respiratory symptoms (dry cough, fever, labored breathing)

Rubella

• Caused by rubivirus (rubella virus), a tongavirus

• ssRNA with a loos envelope

• AKA German “measles”

• An endemic disease of adolescents and yound adults

• Transmission via respiratory secretions

• Two forms

  • Post natal

  • Congenital

• Attenuated viral vaccine MMR

Postnatal rubella

• Malaise, fever, sore throat, lymphadenopathy, rashm generally mild, lasting 3 days

Congenital rubella

• Infection during the 1st trimester

• Most likely to induce miscarriage or multiple defects

  • Cardiac abnormalities

  • Ocular lesions

  • Deafness

  • Mental and physical retardation

Arboviruses

• Viruses spread by arthropod vectors

  • Mosquitoes, ticks, flies, and gnats

• Tongaviruses, flavaviruses, bunyaviruses, and reoviruses

• Mild fevers; sever encephalitis, life threatening hemorrhagic fever

West nile virus

• Arbovirusinfection of the USA

• Transferred to humans by mosquitoes infected by bird’s blood

• 80% of people infected show no symptoms

• Less than 1% develope neurological encephalitis or meningitis

Chikungunya virus

• Arbovirusinfection of the USA

• Infections in the caribbean in 2013

• Most patiens experienced fever, headache, muscle and joint pain, nausea, and vomiting

Zika virus

• Arbovirusinfection of the USA

• Symptoms very similar to infection with chikungunya or dengue virueses

• Birth defects if mother is infected during pregnancy

Yellow fever

• Hemorrhagic fever

• Acute fever, headache, muscle pain

• May progress to oral hemorrhage, nosebleed, vomiting, jaundice, and liver and kidney damage

• Significant moratlity rate

• Two patterns of transmission

Urban yellow fever cycle

• Humans mosquitoes

• Aedes aegypti

Sylan yellow fever cycle

• Forest monkeys and mosquitoes

• South america

Dengue fever

• Hemorrhagic fever

• Flavivirus carried by aedes mosquito

• Not in the US

• Usually mild infection

Dengue hemorrhagic shock syndrome

• Breakbone fever

• Extreme muscle and joint pain

• Can be fatal

Human immunodeficiency virus

• Aquired immunodeficiency syndrome

• Causes

  • Severe pneumonia caused by pneumocystit jirovecii

  • Rare cancer called Kaposi sarcoma

  • Sudden weight loss and general loss of immune function

Characteristics of HIV

• Retrovirus, in genus lentivirus

• Encodes the reverse transcriptase enzyme

  • Makes a double stranded DNA from the single stranded RNA

• Viral genes are permanently integrated into its host’s DNA

• Causes acquired immunodeficiency syndrome (AIDS)

Transmission of HIV

• Direct and specific routes

• Mainly through sexual intercourse and transfer of blood or blood products

• Babies can be infected before or during birth and from breast feeding

• Does not survive outside of the body

Pathogenesis and virulence factors of HIV

• Enters through mucous membranes or skin

• Travels to dendritic phagocytes beneth the epithelium, multiplies, and is shed

• Virus is taken up adn amplified by macrophages in the skin, lymph organs, bone marrow, and blood

• Fuses with the cell membrane, uses reverse transcriptase, and lytic or latent infection occurs

Stages of HIV and AIDS

• Primary effects of infection

  • Extreme leukopenia (lymphocytes)

  • Formation of giant T cells and other syncytia; virus spreads

  • Infected macrophages release the virus into the CNS; inflammation

• Secondary effects of infection

  • CD4 lymphocytes destruction

  • Opportunistic infections and malignancies during full blown AIDS

AIDS

• Immune system destruction

• When T4 cell level falls beliw 200/ml

• Symptoms appear

  • Fever, swollen lymph nodes, diarrhea, weight loss, neurological symptoms, opportunistic infections, and cancers

Poliomyelitis

• Polio

• Acute enteroviral infection of the spinal cord that can cause neuromuscular paralysis

• Transmitted via fecal-oral route; can spread to the spinal cord and brain

Poliovirus

• Naked capsid

• Resistant to acid, bile, and detergents

• Can durvive stomach acids when ingested

• Adheres to receptors of mucosal cells in the orpharynx and intestine, multiply, and shed in the throat and feces

Post polio syndrome

• Decades later

• Progressive muscle deterioration

• Occurs in 25-50% of patients infected with poliovirus in childhood

Bulbar poliomyelitis

• Paralytic disease of the legs, abdomen, back, intercostals, diaphragm, pectoral girdle, and bladder

• Rare cases, requires mechanical respirators

• Brainstem, medulla, or cranial nerves are affected

• Muscle atrophy

Hepatitis A

• Cubical piconavirus relatively resistant to heat and acid

• Not carried chronically, reservoirs are asymptomatic

• Transmission via fecal oral route

  • Multiplies in the small intestine and eneters the blood and carried to the liver

• Jaundice is rarely present

Human T cell lymphotropic viruses

• Leukemia is a malignant disease of the while blood cell forming elements in bone marrow

• Aquired, not inherited

Human T-cell lymphotropic virus I (HTLV-I)

• associated with a form of leukemia called adult T-cell leukemia

• Some cases first present with cutaneous T-cell lymphoma

Rhinoviruses

• More than 110 serotypes associated with the common cold

• Unique molecular surface makes vaccine development hard

• Many strains circulating at a time

• Sensitive to acidic environments

Noroviruses

• Norwalk agent

• Believed to cause ⅓ of all viral gastroenteritis cases

• Transmitted via fecal oral route

• Acute onset of nausea, vomiting, cramps, diarrhea, and chills

Reoviruses

• Unusual double stranded RNA genome

• Two best known viruses

  • Reovirus

  • Rotavirus

Reovirus

• Cold-like upper respiratory infection

• Enteritis

Rotavirus

• Oral fecal transmission

• Primary viral cause of mortality and morbidity resulting from diarrhea infants and children

Prions

• Proteinaceous infectious particles

• Highly resistant to chemicals, radiation, and heat

• Cause transmissible spongiform encephalopathies (TSEs) in humans

• No nucleic acid

spongiform encephalopathies examples

• Creutzfeldt-jakob disease

• Animals (cow disease)

Creutzfeldt-jakob disease (CJD)

• Alteration in the structure of normal PrP protein found in the brain

  • Abnormal form converts normal into abnormal

• Abnormal PrP results in nerve cell death, spongiform damage, and sever loss of brain function

• Transmission via direct or indiract contact with infected brain tissue

Hepatitis C

• Faused by flavivirus

• Aquired through blood contact

  • Transfusions, needle sharing

• Characteristics vary

  • 75-85% will remain infected indefinitely

  • Chronic liver disease

  • Cancer