microbio chapter 12 (viral diseases)

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human immunodeficiency virus (HIV) and acquired immunodeficiency syndrome (AIDS)

structure of HIV

• retrovirus

• two identical + stranded RNA genome molecules

• reverse transcriptase and integrase enzymes

• phospholipid envelope gp120 glycoprotein spikes

HIV modes of transmission

• sexual contact with infected individual

• blood transfusions

• needle sharing

• mother to fetus/infant

HIV avoids detection and destruction by immune system by:

• remaining as a latent provirus within host cell nucleus

• moving from cell to cell by cell-cell fusion

  • undergoing a high rate of mutation

no vaccine available

antiretroviral therapy (ART)

multiple drugs given simultaneously

• goal lower viral load and minimize the survival of resistant strains

measles (rubeola)

• cold or flu-like symptoms, macular rash

• koplik’s spots appear before the characteristic measles rash symptoms appear

• measles encephalitis in 1 in 1000 cases

• severe complication subacute sclerosing panencephalitis rare

measles transmission

• transmitted by the respiratory route

• highly contagious

measles treatment

prevented by MMR vaccine

MMR vaccine

measles, mumps, rubella vaccine

• not recommended for pregnant women

rubella (German measles)

rubella virus

• macular rash and light fever

  • milder than measles

• transmitted via the respiratory route

• prevented by the MMR (measles, mumps, rubella) vaccine

congenital rubella syndrome

• fetal damage, deafness, heart defects, mental retardation in 35% of cases

chickenpox (varicella)

varicella-zoster virus (VZV) (human herpesvirus 3/HHV-3)

• causes pus-filled vesicles

  • reye’s syndrome

• virus becomes latent in root ganglia

chickenpox transmission

transmitted via respiratory route

reye’s syndrome

severe complications of chickenpox; vomiting and brain dysfunction

chickenpox vaccine

prevented by a live attenuated vaccine

shingles (herpes zoster)

reactivation of latent VZV that moves from ganglia along peripheral nerves to the skin

• due to stress/lowered immunity

• highest incidence is in older adults

• painful pustular lesions over a dermatome; limited to one side fo the body

• an individual with shingles can shed the V-Z virus and infect nonimmune individuals with chicken pox

shingles vaccine

prevention: Shingrix vaccine

smallpox

a contagious, disgusting and often deadly disease that has affected humans for thousands of years

• transmitted via respiratory route → moves into bloodstream → infects many integral organs and the skin

• human is only host

• completely eradicated from the human population by vaccination

• potential bioterrorism agent

monkeypox (MPOX)

related to smallpox, but less severe

• zoonotic transmission

  • from animals (primates, rodents)

  • can be transmitted from human → human by prolonged close contact

  • 2022 outbreak in US: >30,000 cases, primarily affecting men who have sex with men

  • prevention by smallpox vaccination

herpes simplex virus type 1 (HSV-1)

belong to human herpesvirus (HHV)

• primarily spread by oral contact → causes cold sores/fever blisters

  • not the cause of canker sores

herpes simplex virus type 2 (HSV-2)

• spread primarily sexually → causes genital herpes

herpes simplex

recurrences from viruses that are latent in nerve ganglia

• outbreaks triggered by the sun, stress, hormonal changes, or weakened immune system

• virus can be shed even when no lesion present

• complications:

  • herpes encephalitis

  • neonatal herpes

herpes encephalitis

virus spreads to brain

• treated with acyclovir

neonatal herpes

usually results from transmission during childbirth

• can be devastating to an infant leading to permanent brain, eye damage, or even death

common/genital warts

caused by human papillomavirus (HPV)

• more than 200 types identified

  • most infect skin & cause common warts on skin

  • some infect mucous membranes and cause genital warts

    • low-risk mucosal types

    • high-risk mucosal types, e.g., HPV 16 & 18

      • cervical cancer and other cancers

common/genital warts transmission

transmitted via contact

common/genital warts vaccine

prevention with Gardasil 9, nine-valent HPV vaccines

epstein barr virus (EBV)

human herpesvirus 4

• mainly infects B cells and causes mono (infectious mononucleosis)

• establishes latency in B lymphocytes

• almost universally present in human adults worldwide

• complications may include

  • burkitt’s lymphoma

  • nasopharyngeal carcinoma

epstein barr virus (EBV) transmission

transmitted via saliva

burkitt’s lymphoma

• most common childhood cancer in africa → malaria suppresses immune system response to virus

• in US, primarily seen in individuals with AIDS

cytomegalovirus (CMV)

human herpesvirus 5/HHV-5

• mainly infects leukocytes

• establishes latency in leukocytes

• may be asymptomatic or mild in adults

  • 80% of U.S. adults carry CMV

• causes cytomegalic inclusion disease (CID) in newborns

  • intellectual disabilities or hearing loss

• poses a threat to immunocompromised patients

  • life-threatening pneumonia

  • cytomegalovirus retinitis

cytomegalovirus retinitis

eye infection that can cause loss of vision in patients with AIDS

cytomegalovirus (CMV) transmission

• transmitted sexually

  • via blood, saliva, by transplanted tissue, & transmitted across the placenta

common cold

over 200 different viruses

• rhinoviruses (30-50%)

• coronaviruses (10-15%)

• sneezing, nasal secretion, congestion, mild cough, body aches

• antibiotics are of no use

rhinoviruses

thrive in temperatures lower than body temperature

influenza (flu)

influenza virus

• contains eight RNA segments enclosed in a protein capsid and an envelope (outer lipid bilayer) embedded with two types of spikes

• chills, fever, headache, and muscle aches

• avian, swine, and mammailian strains

  • swine serve as “mixing vessels” for new strains

influenza (flu) vaccine

• multivalent vaccine for the most important strains

  • composition of the vaccine determined annually by the identification of circulating viruses

    • does not provide long-term immunity

  • labor-intensive to produce in embryonated eggs in the past

  • new vaccines using cell culture techniques

hemagglutinin (HA) spikes (influenza)

recognize and attach to host cells

neuraminidase (NA) spikes (influenza)

help the virus separate from the infected cell

antigenic drift

minor antigenic changes in HA and NA

• allow the virus to elude some host immunity

antigenic shifts

changes great enough to evade most immunity

• leads to pandemics

• when 2 different viruses infect a host cell simultaneously; involve the reassortment of the eight RNA segments

coronavirus disease 2019 (COVID-19)

• declared a pandemic by the World Health Organization in March 2020

• caused by coronavirus SARS-CoV-2

  • nucleocapsid: sense (+) strand RNA genome bound to capsid proteins (nucleoprotein)

  • envelope surrounds nucleoprotein

    • embedded in the envelope:

      • S: spike protein (involved in attachment to host cells)

      • M: membrane protein

      • E: envelope protein

  • high mutation rate (characteristic of RNA viruses) → results in production of variants

coronavirus (COVID-19) transmission

• primarily spreads through respiratory droplets and aerosols (airborne particles); highly contagious

• range form minor to life-threatening

  • cytokine storm is a major contributor to the severity and mortality

coronavirus (COVID-19) diagnosis

• home ELISA test kits for rapid antigen detection

• PCR to amplify and detect viral RNA

“long COVID”

• 7.5% of adults develop it

  • difficulty breathing, fatigue, difficulty thinking (brain “fog”)

coronavirus prevention

vaccination is the most effective way to prevent severe illness

respiratory syncytial virus (RSV)

• most common viral respiratory disease in infants

  • almost all children are infected by age 2

  • can be mild cold-like symptoms or

    • life-threatening pneumonia in infants and older adults

• causes cell fusion (syncytium) in cell culture

• vaccines available

mumps

targets the parotid glands

• multiplies in respiratory tract and reaches the salivary glands via bloodstream

• potential severe complications in adults, male orchitis leading to infertility, meningitis, ovary inflammation, pancreaitis

mumps transmission

transmitted in saliva and respiratory secretions

mumps vaccine

prevented with MMR vaccine

rotavirus

viral gastroenteritis

primarily infants and young children (<5 yrs)

• low-grade fever, profuse watery diarrhea, vomiting

• symptoms may persist for a week; can be severe in infants

rotavirus transmission

fecal-oral transmission

rotavirus vaccine

prevented with a live attenuated oral vaccine (has decreased incidence by 98%)

norovirus

viral gastroenteritis

all ages — common in adults

• most common foodborne illness

• very contagious; low infectious dose (as few as 10 viruses)

• diarrhea and vomiting

norovirus transmission

fecal-oral transmission; vomitus droplets (aerosolized particles)

norovirus prevention and treatment

• prevention:

  • wash hands with soap and water

  • disinfect surfaces with bleach

• treatment: oral rehydration

• no vaccine yet

hepatitis A (HAV)

single-stranded RNA; lacks an envelope

• entry via oral route (contaminated food/water)

• acute infection without carrier state

• inactivated vaccine for prevention

hepatitis B (HBV)

double-stranded DNA; enveloped

• infection can be acquired at birth (perinatal) from infected mother due to exposure to the mother’s blood

• if healthy immune system, disease is readily cleared

• 10% of infected patients become chronic carriers

  • may lead to liver cirrhosis or liver cancer

hepatitis B (HBV) vaccine

inactivated vaccine for prevention

hepatitis B (HBV) transmission

transmitted via blood, bodily fluids, sex contact

hepatitis C (HCV)

single stranded RNA; enveloped

damages liver; may progress for 20 years before symptoms are noticed

• “silent epidemic”

• 85% of cases become chronic; 25% of chronic cases develop liver cirrhosis or cancer

• destruction of liver by HCV is a major reason for liver transplants

hepatitis C (HCV) transmission

often transfusion-transmitted via blood products

hepatitis C (HCV) vaccine

no vaccine

poliomyelitis (polio)

caused by the poliovirus

• vast majority of cases are very mild or asymptomatic

• initial symptoms: sore throat and nausea

• viremia may occur; enters the CNS

  • <1% of infected individuals develop paralysis

    • destruction of motor nerve cells

    • death from respiratory failure

• three serotypes of poliovirus: types 1, 2, and 3

• persistent reservoirs of polio remain in nigeria, pakistan, and afghanistan

poliomyelitis (polio) transmission

transmitted by the ingestion of water containing feces containing the virus

poliomyelitis (polio) vaccine

• vaccine for all three serotypes

  • salk vaccine: inactivated vaccine; injectable (IPV)

  • sabin vaccine: attenuated vaccine; oral; lifelong immunity (OPV)

    • risk of reversion of vaccine strain to virulence

    • today in the U.S: IPV is used

rabies

caused by the rabies virus

• single-stranded RNA; easily develops mutants

• in the U.S., silver-haired bats are most common cause

virus multiplies in skeletal muscles → travels through PNS → to brain cells → causes encephalitis → 

→ leads to muscle spasms of mouth & pharynx, hydrophobia, coma → death ensue unless patient has immunity

rabies transmission

usually transmitted by the saliva of an animal bite

• can also cross mucous membranes or enter through abraded skin

mosquito-borne viruses

belong to several families of viruses

primarily infect the central nervous system leading to encephalitis

• vector: mosquito

• reservoirs: birds (most), horses (some)

symptoms range from subclinical to severe

• prevention: controlling mosquitos and personal protection

west nile virus (WNV)

• maintained in bird-mosquito-bird cycle

• most human cases are subclinical and mild → but can cause poliolike paralysis and fatal encephalitis

eastern equine encephalitis (EEE) and western equine encephalitis (WEE)

example of encephalitis caused by mosquito-borne viruses

st. louis encephalitis (SLE)

distributed mostly in central and eastern united states

example of encephalitis caused by mosquito-borne viruses

zika virus disease

transmitted primarily through the bite of infected aedes spp. mosquitos

• other routes of transmission include sexual, mother to fetus, and blood transfusions

about 20% of infected show symptoms that are usually mild; fever, headache, muscle & joint pain, malaise, skin rash, conjunctivitis

infection during pregnancy greatly increases risk of microcephaly in infants → causes mild to severe developmental delays

nervous system diseases caused by prions

transmissible spongiform encephalopathies (TSE)

scrapie

caused by prions

TSE in sheep

chronic wasting disease

caused by prions

TSE in deer and elk

creutzfeldt-jakob disease (CJD)

caused by prions

TSE in humans

variant of CJD (vCJD)

caused by prions

occurs in younger individuals

kuru

caused by prions

TSE in humans that is caused by cannibalism

bovine spongiform encephalopathy

caused by prions

mad cow disease