Introduction to Viruses of Food Animals Flashcards
how do foreign avian viruses enter the US?
primarily migration of wild infected birds, importation, and carried in feed
why are backyard flocks a problem for commercial poultry farms?
there is not as much regulation for backyard flocks which could introduce disease to commercial poultry populations that have good biosecurity programs
virus defintion
a small micro-organism comprising nucleic acid and a protein coat that only replicates in living intact cells of other organisms
viruses have a ______ relationship with their hosts
parasitic
virus nucleic acid
DNA or RNA
virus structure
nucleic acid with protein capsid and sometimes a lipid envelope
virus size
much smaller than bacteria, 1000 x smaller, 20 nanometers to 0.3 microns
viruses cause many important diseases of food animals including
bovine viral diarrhea, herpesvirus, rabies, avain influenza
viruses also cause zoonotic diseases including
rabies and orf
rabies zoonoses
rarely contracted from food animals, most commonly contracted from bat bites
orf
infection in newborn goats and lambs from parapox
avian influenza zoonoses
caused by virus and could lead to potential human pandemic
many viral diseases are reportable and/or foreign animal diseases
regulated federally or at the state level
reportable viral diseases include
rabies and vesicular stomatitis
foreign animal viral diseases include
foot and mouth disease, virulent avian influenza, virulent newcastle disease, hog cholera
most viruses have a _____ host range than bacteria
narrower
PRRS virus host range
only pigs, host restricted
rabies host range
all mammals, large host range
ovine herpes virus 2 (OHV2) host range
sheep carry silent infection but can cause severe disease in cattle and bison
virion structure: naked
non-enveloped viruses are generally hardier and persist longer in the environment
virion structure: enveloped
enveloped viruses are generally more susceptible to disinfectants that melt membranes
viral classification factors
RNA or DNA, shape, enveloped or non-enveloped, single or double stranded, positive or negative sense
why is virus classification and structure important?
for controlling and preventing disease
virus transmission types
horizontal and vertical
horizontal transmission
animal to animal
horizontal transmission routes
respiratory aerosols, feco-oral route, and direct contact
vertical transmission
mother to fetus
vertical transmission routes
mother to fetus or mother to newborne via milk
why is it important to know viral transmission routes?
for prevention and control of viral disease
what does the lytic replication cycle cause?
acute disease
lytic cycle pathway
virus enters into cell, hijacks host machinery to replicate, causes cell damage and virion release to infect other cells, causes tissue damage and disease
the lytic cycle is important in acute viral infections including
BRSV, rotavirus, coronavirus, rabies, acute BVD
if the animal survives virus is usually cleared from the body
true
latent infections are formed from
herpesvirus
acute infection
sudden onset and short duration
latent infection
persistant and sub-clinical
what does the lysogenic replication cause?
chronic and latent infections
lysogenic replication cycle pathway
virus attatches to cell and penetrates to release nucleic acid, the nucleic acid gets integrated into host genome and the host cell divides to multiply the viral genome
what disease is the lysogenic replication cycle important for?
chronic viral infections, diseases with long incubation periods, and latent infections like small ruminant lentivirus
incubation period
time from infection to disease onset
viruses have preference for replication in specific organs and cell types
true
bovine respiratory syncytial virus replicates in which cells
lung airway cells to cause viral pneumonia
bovine popular stomatitis virus replicates in what tissue
nose, oral cavity, and esophagus
why is it important to know what organs and tissues viruses target?
important for understanding what tissues are damaged, what clinical signs may show, treatment and diagnosis
why is it important to know how and how long viruses survive in the environment?
for biosecurity measures, control of the disease, and how to clear the environment
robust viruses include
circovirus and parvovirus
robust virus transmission
direct or distant contact transmission
fragile viruses include
lentiviruses, influenza, porcine reproductive and respiratory syndrome
fragile virus favorable environment
cold and moist conditions
fragile virus transmission
direct or close contact transmission
how are viral diseases diagnosed?
manifestation in specific organs and diagnostic testing
clinical exam for diagnosis of viruses
organ system involved and consider bacterial or viral causes
diagnostic confidence
some viruses can be identified with confidence, like orf causing inflammation of the lips, but most require laboratory testing to confirm a diagnosis
samples needed for diagnosis of viral diseases
blood, secretions, excretions, and necropsy
diagnostic sample: blood
direct virus detection or serology for antibodies
diagnostic sample: secretions
used in live animals, nasal, oral, or ocular samples
diagnostic sample: excretions
feces for suspect viral enteritis
diagnostic sample: necropsy
tissues are often preferred over secretions and feces when the animal has died
direct detection of virus
electron microscopy, PCR, fluorescent antibody test, virus isolation in cultured cells, viral metagenomics, serology for detection of antibodies
electron microscope advantages
identify new viruses not specifically tested for, good for disease where large amounts of virus is produced
virus where large amounts of virus is produced example
viral enteritis
electron microscope disadvantages
low sensitivity and expensive
most common cause of viral diarrhea in calves in the first few weeks of life
bovine rotavirus and bovine corona virus
enveloped virus shape
flexible and variable in shape
capsid virus shape
regular and geometric shape
virus isolation in cell culture for disease diagnosis
clinical specimen is cleaned up to remove bacteria and dead cells, cytopathic effect is observed in cell culture
cell culture advantages
grow intact virus and can use for future research and sequencing genomes
cell culture disadvantages
takes 2-4 weeks, not all viruses cause cell death, low sensitivity, expensive, may grow zoonotic viruses
fluorescent antibody testing for rabies virus
transfer brain sample to slide, add fluorescently labeled antibodies and observe under fluorescent light
fluorescent antibody testing advantage
rapid turnaround, approx. 2 hours
detection of viral DNA or RNA through polymerase chain reaction
dependent on DNA primers binding directly to nucleic acids, amplification of target DNA is specific to the microbes being tested
PCR advantages
very sensitive, specific, quick, and cheap
PCR disadvantages
false negative results due to viral mutagenesis, variation in viruses can bind to primers, RNA viruses are highly variable, some PCR cannot detect all strains, and prone to false positives due to contamination
how is PCR used for diagnosis of viral diseases?
clinical specimen, nucleic acid extraction, if RNA it is reverse transcribed into cDNA, if DNA it is directly amplified by PCR and amplified DNA is detected
why is viral metagenomics important?
searching for novel viruses when a novel virus is suspected, tracking viral strains during outbreaks, and sequencing genomes of isolates to see which vaccines to use
co-infections are very common in food animals including
calf diarrhea: rota or corona virus and E. coli
bovine pneumonia: BRSV and pasteurella multocida/mannheimia hemolytica
bovine pneumonia: BVD and pasteurella multocida/mannheimia hemolytica
procine circovirus disease: mainests with co-infection
why is synergism important for co-infection?
results in more severe disease and increased mortality rates, important for management and control
what should be used in cases of concurrent bacterial infection?
antibiotics
