Viral Respiratory Infections Flashcards
mechanisms used by respiratory tract pathogens to initiate disease
sufficient number of virus inhaled or acquired by direct contact
infectious particles are often airborne
infectious virus must remain alive and viable during transmission
virus must be deposited on susceptible tissue in the host
general approaches to prevention/treatment of respiratoory infections
genetically engineered or selected vaccines
passive antibodies - humanized, pooled, or human monoclonals
drugs against virus specific proteins or enzymes
hand washing - avoiding close contact
supportive care
orthomyxovirus
influenza A, B, and C
A infects both humans and animals
B and C only infect humans
influenza A most important - associated with epidemics and pandemics
particles are highly pleiomorphic - mostly pspherical or ovoid
components of the influenza A virion
host derived lipid bilayer that includes hemagglutinin (HA) and neuraminidase (NA)
inner shell is composed of matrix protein (M1)
nucleocapsid contains viral genome with eight unique segments, all are required to be infectious
H antigen
hemagglutinin
required for binding the influenza virus to the host cell
N antigen
neuraminidase
helps the mature virus escape from the cell
Describe the replication cycle of influenza.
Influenza binds to surface, endocytosed
Channel protein allows acidification of the vurlent particle
Release of genome into cell
Genome made in nucleus, transport into cytoplasm
Virus assembled and released
Two key steps - acidification step and the neuraminidase release step
classification of influenza
three types of H antigen
two types of N antigen
different combinations make different viruses
antigenic drift
changes in the discrete highly variable domains of the viral proteins through random mutations
antigenic shift
dramatic changes in virus by reassortment with another influenza virus
animals serve as a pool and where reassortment occurs due too infection with both animal and human viruses
epidemic flue
cyclic and usually caused by type B or type A
type A occur every 2 to 3 years, and type B occurs every 4 to 6 years
overall mortality rate is 1%
route and spread of influenza infection
entry via respiratory tract through inhalation
viral infection and spread is normally lmited to the epithelial cells of the respiratory tract
influenza pathogenesis
infects primarily upper and lower respiratory tract
influx of macrophages and lymphocytes
spectrum of disease ranges from asymptomatic infection to primary viral pneumonia
release of IL1 triggers fiver
release of interferon triggers aches and pains
humoral response is important for the control of these infections
replication of the virus causes desquamationof the ciliated epithelium, hyperplasia of transitoral cells, and increased secretions
inbucation time is 1 to 3 days
prevention/treatment of influenza
vaccinate those who are at risk
vaccines made from reassortment of egg-adapted strains that are then formalin inactivated
M2 protein
influenza protein channel that allows acidification for uncoating of the virus
permits flow of ions from the endosome into the virion center to disrupt interactions and release the viral genome
amantadine and rimantadine
drugs active against influenza A viruses
target is the M2 protein
prevents uncoating of the virus
Relenza and Tamiflu (oseltamivir phosphate)
neuraminidase inhibitor
block the cleavage of sialic acid and prevent virus from budding out of the host cell and infecting other cells
relenza must be inhaled
syndromes potentially caused by influenza virus
uncomplicated rhinotracheitis
respiratory viral infection followed by bacterial pneumonia
viral pneumonia
usually rapid onset pneumonia
coronaviruses
~13 species in the family
infect not only humans but also cattle, pigs, rodents, cats, dogs, and birds
an example would be SARS
coronavirus morphology
particles are irregulalry-shaped
~60-220nm in diameter
outer envelope bearing distinctive “club-shaped” proteins
pathogenesis of coronaviruses
can cause respiratory infections, enteric infections, and neurologic syndromes
transmitted by aerosols of respiratory secretions
growth appears to be localize din the epithelium of URT
most infections cause a mild, self-limited disease
greatest incidence in children, less common in adults
reinfections appear to occur
immunization may be difficult
Severe Acute Respiratory Syndrome (SARS)
a respiratory illness caused by a coronavirus
civets and ferrets harbor this virus
symptoms include cough, shortness of breath, difficult breathing
severe virus capable of causing death
MERS virus
coronavirus that went from bats to humans through camels
paramyxovirus
family divided into three genera - paramyxovirus, pneumovirus, and morbillivirus
parainfluenzavirus 1-4
a type of paramyxovirus that causes an acute respiratory disease
can cause mild influenza-like illness as well as bronchitis, croup, and pneumonia
common infection of children
transmitted by aerosols, usually limited to URT
infections of LRT lead to more serious symptoms
little serological variation, rare in adults
pneumovirus
a genera of paramyxovirus that includes respiratory syncytial virus (RSV)
morbillivirus
a genera of paramyxovirus that includes measles and canine distemper virus
mumps
humans are the only natural reservoir
transmission through saliva and respiratory secretions
typically causes painful swelling of parotid glands 16-18 days after infection
preceded by primary replication of the virus in epithelial cells of the URT and local lymph nodes
self-limited in children, but in adults a proportion of cases have other symptoms such as orchitis, meningitis, encephalitis, pancreatitis, myocarditis, nephritis
mumps prevention
one invariant serotype
vaccines are available
both formalin-inactivated and live attenuated exist
latter is widely used
measles
one of the most infectious diseases known
after a 10-12 day incubation period, dry cough, sore throat, conjunctivitis
rad rash and Koplik spots a few days later
complications include bronchopneumonia and otitis media and encephalitis
subacute schlerosing pan encephalitis results form a rare strain
prevention of measles
both live and killed vaccines exist
trivalent live attenuated vaccine (MMR) usually given
virus best avoided during pregnancy
RSV
major cause of LRT disease in infants and young children
highly infectious, transmission by respiratory secretions
primary multiplication occurs in epithelial cells of URT, producing a mild illness
in ~50% of children less than 8 months old, virus subsequently spreads into the LRT, causing bronchitis, pneumonia, and croup
currently no vaccine
infection does not result in lasting protection, so there can be repeated infections throghout life
treatment of RSV
ribavirin is used
effectiveness is not ensured
Respigram or Palivizumab are new drugs for prevention
picornaviruses
among the most diverse
genomic RNA is infectious
translates a large polyprotein
Coxackievirus
a subgroup of picornavirus
classified as an enterovirus
seasonal, epidemic pattern of infection
mostly sub-clinical
can be associated with meningitis, paralysis, and myocarditis
rhinovirus
a subgroup of the picornaviruses
~105 serotypes, repeated infections
optimum growth temperature of 33 degrees C, good for URT infection
symptoms due to damage to ciliated epithelium in URT
can predispose to secondary bacterial infections
no effective prophylaxis or treatment
little or no cross-protection between serotypes
adenovirus
frequent cause of acute URT infections
infections are common, most people have been infected by at least 1 type by age 15
commonly associated with a variety of clinical syndromes - little morbidity associated with infection
diseases associated with adenoviruses
acute respiratory illness
pharyngitis
gastro-enteritis
conjunctivitis
pneumonia
keratoconjunctivitis
acute hemorrhagic cystitis
hepatitis
adenovirus morphology
non-enveloped, 60-90nm in diameter
icosahedral symmetry
easily visible in the electron microscope by negative staining
thin glycoprotein fiber (IV) protrudes from the center of each penton
adenovirus prevention
no treatment options available
inactivated or attentuated vaccines have been developed
recent interest in gene therapy using adenoviruses for therapeutic purposes because the genome is easily manipulated in vitro
reovirus
produce minor upper respiratory tract infectiosn and gastrointestinal disease
hantavirus
infections caused by inhaling the virus contained in dried derr mouse (rodents) saliva, urine, or feces
may evolve into a fatal disease characterized by respiratory insufficiency
hantavirus pulmonary syndrome (HPS) characterized by an initial fever followed by the abrupt onset of acute pulmonary edema and shock
