Viruses and intestinal disease Flashcards
Why is diarrhoea more common in younger animals?
Under developed gut microbiota => more susceptible to viruses
No memory cells/immunological memory
Maternally derived antibodies from colostrum levels fall
Failure of sufficient colostrum transfer
How might an animal ingest viruses shed within faeces?
Aerosols from diarrhoea
Contaminated foodstuffs, drinking water and fomites
Describe the common features of enteric virus infections
Small infectious dose
Lytic life cycle => acute infection and cell damage
Large amounts shed in faeces
Can survive low pH of stomach
Secondary bacterial infection is common
Diarrhoea common
Can die from dehydration
Why do enteric viruses cause diarrhoea?
Increased secretion
Increased cell permeability
Altered gut motility
Decreased absorption (due to villus atrophy)
Label the viruses that target different sites of the villus?
What are the main viruses associated with the GIT?
Rotavirus
Parvovirus
Coronavirus
Paramycovirus
Pestivirus
What is important about viruses with a segmented genome?
if 2 viruses with segmented genomes infect the same cells
RNA molecules mix => new combinations of RNA sequences => new properties
Reassortment
Describe features of rotaviruses
Icosahedral
Non-enveloped
dsRNA segmented genome
3 capsids
Cytoplasmic replication
Very stable in environment (can persist in environment after outbreak)
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 virus after infection
Reinfection with other strains possible
Vaccine protection is limited to strains closely related to vaccine strain
How might a new strain of rotavirus arrive onto a farm?
Newly introduced animals from other farms
Fomites
Describe rotavirus infection
Infection of enterocytes at tips of villi in SI
Villi become shorter
=> Reduced lactase production and impaired Na transport
Why is lactase production in young animals?
Primarily fed on milk so lactose needs to be digested
What are the consequences of villus damage due to rotavirus?
Decreased digestion and absorption of milk in upper SI
=> undigested milk in lower SI and LI
Substrate from secondary bacterial overgrowth in lower intestinal tract
Osmotic diarrhoea due to reduced reabsorption of water in LI
=> Watery scour
Describe the basis of virus entry into cells
Virus binds to sialic acid, then integrins, then other proteins on cell surface
Describe the importance of rotavirus
Affects piglets, calves and foals
Pasty/watery diarrhoea
Secondary infection with E.coli, other viruses, or coccidia => more severe disease
Reluctance to suckle
Dehydration
