CHAPTER 24/25: DNA/RNA Viruses

all DNA viruses are ds except for what virus

parvoviruses which have ssDNA

all RNA have ssRNA except for what viruses

dsRNA reoviruses

viruses are limited to what

specific host and cell type

where are DNA viruses usually released

budded off the nucleus

where do RNA viruses multiply and release from

the cytoplasm

what are common manifestations for viral infections

rashes, fever, muscle aches, respiratory involvement, swollen lymph nodes

what are the body’s defenses against viral infections

• combined action of interferon

• antibodies

• cytotoxic T cells (frequently results in lifelong immunity)

many viral infections have a rapid course called

lytic cycle

what are the 2 types of persistent infections

• chronic infections

• latent infections

what are chronic infections

virus is detectable in tissue samples, multiplying at a slow rate; symptoms mild or absent

what are latent infections

after a lytic cycle, virus enters a dormant phase; generally not detectable; can reactivate and result in recurrent infections

what are the kinds of DNA viruses causing human disease

• enveloped DNA

• nonenveloped DNA

• nonenveloped ssDNA

what are the eruptive skin pustules that leave scars

pocks or pox

characteristics of the largest and most complex animal viruses

• have the largest genome of all viruses

• dsDNA

• multiply in the cytoplasm in factory areas

• specificity for cytoplasm of epidermal cells and subcutaneous connective tissues

what was the first disease to be eliminated by vaccination

smallpox

how is one exposed to smallpox

inhalation or skin contact

what are the symptoms of smallpox

fever, malaise, prostration, rash

describe variola major

• highly virulent

• causes toxemia, shock, and intravascular coagulation

describe variola minor

less virulent

how does the smallpox vaccine work

a single drop of vaccinia virus punctured into the skin with a double pronged needle

is poxvirus enveloped or non enveloped

enveloped

are herpesviruses enveloped or non enveloped

enveloped

all members of the herpesvirus show what

latency and recurrent infections become more severe with advancing age, cancer chemotherapy, or other conditions the compromise the immune defenses

describe the herpesviruses structure

• large enveloped icosahedral dsDNA

• replicates within nucleus

humans are susceptible to what 2 varieties of the herpes simplex virus

HSV-1 and HSV-2

what does HSV-1 cause

lesions in the oropharynx, cold sores, fever blisters

when does HSV-1 typically occur

early childhood

what does HSV-2 cause

lesions in genitalia, possibly oral

when does HSV-2 typically occur

ages 14-29

*can be spread without visible lesions

where does HSV-1 stay latent

trigeminal ganglion

where does HSV-2 stay latent

primarily in sacral ganglia

what is the transmission or herpes simplex

direct exposure to secretions containing the virus; active lesions most significant source; genital herpes can be transmitted in the absence of lesions

where does HSV-1 enter after multiplying in sensory neurons

5th cranial nerve

where does HSV-2 enter after multiplying in sensory neurons

lumbosacral spinal nerve trunk ganglia

recurrent infection of herpes simplex is triggered by what various stimuli

fever, UV radiation, stress, mechanical injury

what is herpes labialis

• aka oral herpes

• fever blisters or cold sores

• most common recurrent HSV-1 infection

what is herpetic gingivostomatitis

• inflammation of oral mucosa (gums, tongue, soft palate, lips)

• especially in young children

what is herpetic keratitis

• ocular herpes

• inflammation of the eye

• gritty feeling in eyes, conjunctivitis, sharp pain, sensitivity to light

• latent virus travels into the ophthalmic rather than the mandibular branch or trigeminal nerve

what is genital herpes and what does it cause

• herpes genitalia

• starts with malaise, anorexia, fever, bilateral swelling and tenderness in groin; clusters of sensitive vesicles on the genitalia, perineum, and buttocks; urethritis, painful urination, cervicitis, itching; vesicles ulcerate

• recurrent bouts usually less severe, triggered by menstruation, stress, and concurrent bacterial infection

how is herpes transmitted rom mother to child

infant contaminated by mother before or during birth; hand transmission by mother to infant

what is infected when it comes to herpes in a newborn

infection of mouth, eyes, CNS

what does Varicella-Zoster Virus cause (VZV)

varicella aka chickenpox

what are the only natural hosts for VZV

humans

how is VZV infection transmitted

respiratory droplets or contact

what is the primary infection of VZV

varicella aka chickenpox

characteristics of varicella or chicken pox

• characteristic vesicles

• enters neurons and remains latent

what is the reactivation of VZV

herpes zoster aka shingles

characteristics of herpes zoster or shingles

• dermatomes

• most common in older patients

what are the viruses involved in hepatitis when it comes to DNA viruses

Hepadnaviruses (major group)

what is the DNA virus that is involved with hepatitis

Hepatitis B virus (HBV)

what are the RNA viruses that is involved with hepatitis

1. Hepatitis A virus (HAV)

2. Hepatitis C virus (HCV)

3. Hepatitis E virus (HEV)

4. Hepatitis D virus (HDV)

about HAV

• from contaminated food

• less virulent

about HCV

• from blood

• causes transfusion hepatitis

about HEV

• from fecaly contaminated food

• newly identified

• causes diseases similar to HAV

about HDV

• defective RNA virus

• only infects cells already infected with HBV

where is HBV exclusively in

the liver, where it continuously seeds blood with viruses (chronic)

how can HBV be transmitted

• minute amounts of blood, blood products can transmit infection; sexually transmitted

• high incidence amongst homosexuals and drug abusers

HBV can increase what

risks of liver cancer: hepatocellular carcinoma

how does HBV enter the body

• break in skin or mucous membrane

• injection into blood stream

what does HBV do after it reaches the liver cells

multiplies and releases viruses into the blood; 7 week incubation

what are the symptoms that can come with HBV

malaise, fever, chills, anorexia, abdominal discomfort, diarrhea

what are the symptoms in HBV in more extreme cases

• fever, jaundice, rash, arthritis

• smaller number of patients develop chronic liver disease: cirrhosis and necrosis

what is the general structure of the adenovirus

• non-enveloped

• ds DNA

what does the adenovirus infect

lymphoid tissue, respiratory and intestinal epithelia, conjunctiva

how is the adenovirus spread

respiratory and ocular secretions

what symptoms can the adenovirus cause

colds, pharyngitis, conjunctivitis, keratoconjunctivitis, acute hemorrhagic cystitis

what is the general structure of parvoviruses

• non-enveloped

• ssDNA

• small diameter and genome size

what does parvovirus cause

• distemper in cats, enteric disease in dogs, fatal cardiac infections in puppies

• few cause infections in humans

Parvovirus B19 causes what

erythema infectiosum (fifth disease): rash of childhood

what are symptoms of erythema infectiosum

• children may have fever and rash on cheeks (slap face syndrome)

• severe fatal anemia can result in pregnant women, transmits virus to fetus

what is adeno-associated virus (AAV)

defective virus; cannot replicate in host cell without adenovirus

where do influenza viruses attach and multiple

cells of respiratory tract

segments of influenza RNA genome enters what

nucleus and finished viruses are assembled and budded off

what are the glycoprotein spikes

• Hemagglutinin (H) — 15 subtypes; most important virulence factor; binds to host cells

• Neuraminidase (N) — 9 subtypes; hydrolyzes mucus and assists viral budding and release

what is constant mutation called

antigenic drift — gradually changing their amino acid composition

what is antigenic shift

one of the genes or RNA strands is substituted with a gene or strand from another influenza virus from a different animal host (influenza A for example)

what are the influenza strains

• influenza A

• influenza B

• influenza C

about influenza A

• most virulent

• after 2003, strains of influenza A viruses that infected birds underwent an antigenic shift and began to infect humans

about influenza B

• only undergoes antigenic drift not shift

about influenza C

• known only to cause minor respiratory disease; probably not involved in epidemics

what is influenza A

acute, highly contagious respiratory illness

where does influenza A bind

ciliated cells of respiratory mucosa causing rapid shedding of cells, stripping the respiratory epithelium; severe inflammation

what symptoms do influenza A cause

fever, headache, myalgia, pharyngeal pain, shortness of breath, coughing

what are the enveloped non-segmented ssRNA viruses

• Rhabdoviruses

  • rabies virus, genus Lyssavirus

• Coronaviruses

  • Covid-19

• Flaviviruses

  • Hepatitis C

• Filoviruses

  • Ebola virus

how does the rabies virus enter into the body

through bite and grows at trauma site for a week then multiples, then enters nerve endings and advances towards the ganglia, spinal cord and brain

when is the rabies virus infection cycle completed

when virus replicates in the salivary glands

what are the clinical phases of rabies

1. prodromal phase

2. furious phase

3. dumb phase

4. progress to coma stage, resulting in death

what happens during the prodromal phase

fever, nausea, vomiting, headache, fatigue; some experience pain, burning, tingling sensations at site of the wound

what happens during the furious phase

agitation, disorientation, seizures, twitching, hydrophobia

what happens during the dumb phase

paralyzed, disoriented, stuporous

coronaviruses are most common in what

domesticated animals

what can coronavirus cause

• common cold

• some forms of viral pneumonia and myocarditis

• some human enteric infections

• severe acute respiratory syndrome (SARS)

  • airborne transmission

how is Severe Acute Respiratory Syndrome Associated Coronavirus SARS transmitted

droplets or direct contact

what are some symptoms that can come with SARS

fever, body aches, malaise

what is hepatitis C caused by

flavivirus (HCV)

how is HCV acquired

blood contact: blood transfusions, needle sharing

what are the 2 hemorrhagic fevers

• yellow fever

• dengue fever

what are the 2 patterns of transmission of yellow fever

• urban cycle — humans and mosquitoes, aedes aegypti

• sylvan cycle — forest monkeys and mosquitos; South America

what are some symptoms yellow fever can cause

acute fever, headache, muscle pain; may progress to oral hemorrhage, nose bleed, vomiting, jaundice, and liver and kidney damage; significant mortality rate

what is dengue fever caused by

flavivirus carried by aedes mosquito