intestinal viruses Flashcards
why is viral diarrhea more common in young animals
- antibodies arent developed against viruses yet
- suckling from teats exposes young animals to unclean environments
- gastric acid and mucosal integrity probably not fully developed yet
what is the most common route of infection for GI viruses
fecal oral route
outline the fecal-oral route cycle of viral transmission
- ingestion
- replication in intestine
- excretion of virus in feces
how might an animal ingest viruses that are shed within the feces
- can be she in high levels in diarrhea which can be explosive leading to aerosols
- contamination of food, water and fomites (clothes, material etc)
- poor disinfection of the environment may fail to stop the disease from spreading
list common features of enteric virus infections
- infection dose is often small
- normally have a short incubation and the life cycle is lytic causing an acute infection and damaging cells
- large amounts of virus shed in feces
- viruses are generally tough and capable of surviing the low ph of the stomach an the environment
- secondary bacterial infection is common
- may have multiple viral infections at once (esp if young or in herd)
- diarrhea common (+/- vomiting, but differs between species)
- deaths from dehydration mostly (+/- acid base imbalance
list mechanisms of viral diarrhea
- increased secretion (cl imbalance)
- increased cell permeability
- altered gut motility
- decreased absorption
list viruses that cause major clinical signs associated with the GIT
- rotaviruis
- parvovirus
- coronavirus
- paramycovirus
- pestivirus
what are the basic features of roatviruses
- icosahedral
- non enveloped
- outer, middle and inner capsid
- core contains a ddsRNA segmented genome (leads to reasortment)
- very stable in environment
if there are multiple virus strains and a segmented genome what might this mean about the effectiveness of an immune response
- lots of virus variation
- protection only against closely related cirus after infection means that reinfection with other strains is possible
- vaccine protection is limited to strains closely related to the vaccine strain of the virus
how might a new strain of rotavirus arrive on a farm
- bought anials is the most likely source
- could come from fomites
how are rotaviruses spread
fecal/oral transmission
explain what happens on a cellular level in a rotavirus infection
- infection of enterocytes at the tips of the villi in the small intestine
- villi become shorter
- reduced lactase production and impaired Na transport
rotavirus reduces lactase production in the GIT. why is that important in young animals especially
- primarily feed on milk so need lactase to digest lactose
- causes scours
what happens to villi in a rotavirus infection
enterocytes damaged due to virus infection causing lysis
how does rotavirus enter cells
- virus binds to sialic acid, then integrins, then other proteins on the cell surface
what is the clinical importance of rotavirus
- affects piglets, calves and foals
- leads to pasty/watery diarrhea
- secondary infection with E. coli, other viruses, coccidia, leads to more severe disease
- leads to reluctance to suckle and dehydration
- pigs infected with rotavirus take 5 day longer to reach 25 kg weight
how is rotavirus diagnosed
- collect samples from feces or gut contents (at PM)
- detection of viral antigen via ELISA or latex agglutination test
- detection of viral RNA via RT-PCR
- virus often present in healthy animals!
- post mortem exam detects pathological damage to tissue
- rapid fixation of intestinal tissue post-euth is very important to detect pathological changes
how is rotavirus controlled
- importance of getting young animals colostrum
- dont mix groups
- good hygiene (disinfection, removal of feces in farrowing units, prevent food/water contamination)
- vaccines availible for cows and horses (NOT PIGS)
- aim of vaccine is to increased colostral Ab
list basic features of parvoviruses
- icosahedral
- no envelope
- small linear ssDNA genome
- infect and kill ACTIVELY REPLICATING cells
- persists for long periods in the environment
why are young animals more susceptible to severe parvovirus infections
parvoviruses infect actively dividing cells. young animals have more of them, therefore more cells to infect
list variants of parvoviruses that are of veterinary important
- feline panleukopenia virus
- canin parvovirus
- porcine parvovirus
- mink enteritis virus
- aleutian disease
- goose parvovirus
where on the villi does parvovirus infect and what are the impacts
the dividing stem cells of the crypt
- villi tip cells turnover normally but are not replaced because the virus has killed the stemcells
- leads to stunted villi, malabsorption, maldigestion, crypt dilation and necrosis
discuss feline parvovirus
- fecal oral transmission
- persists in environment for up to a year
- high titre in feces
- infects lymph nodes of naso and oro pharynx then spreads to other tissues
- needs rapidy dividing cells to propagate
- mainly infects intestinal cells and bone marrow
- kittens most susceptible however unvaccinated older cats also infeted
- if queen is infected can lead to wobbly kittens (cerebellar hypoplasia)
list clinical signs of feline parvovirus
- pyrexia
- vomiting
- diarrhea
- dehydration
- shock and sepsis due to compromised intestinal mucosa
- mortality rate very high if not rapidly and aggresively treated
- can cause sudden death in kittens and cats in shelters
- treatment requires support of circulation/hydration and antibiotics to cover risk of sepsis from secondary bacterial infection
