Source and transmission of infection Flashcards
Infection
Presence of micro-org in or on host tissues
Disease
Pathological and clinical conseq of infection
Opportunistic pathogens
Some commensal or enviro micro-orgs
True pathogens
Initiate disease as a conseq of their presence on tissues
Fx of commensals
Metabolism
Dev of imm syst
Colonisation resis
Virulence or pathogenicity
Capacity of a particular org to cause dis assessed by Koch’s postulates
Koch’s postulates
Org must be recovered from all cases of the disease
Must be cultures in vitro
Reinoc must reproduce dis
Same org must be reisolated from lesions of induced dis
Issues with kochs postulates
Ignores host factors
Some are non-culturable
Poly microbial infections not accounted for
Strain difference not accounted for
Pathogenesis
Mech by which an agent induces symptoms or pathology
What can understanding of the pathogenic process lead to
Dev of appropriate methods for diagnosis, prevention, control and or therapy
Sources of infection and disease
Endogenous
Animals within group
Other species of animals
Enviro
Endogenous sources of disease
Commensal can become opportunistic with right conditions eg antibio misuse, stress, imm compromised
Animals within grp as source of disease
Most important source
Can produce epizootic/epidemic - outbreak
Or enzootic/endemic - continuous
Most pathogens multiply best in natural host
Other species as source of disease
Some microorgs can infect a variety of hosts but charcteristics of infection may differ
Zoonoses (vet has spec responsibility to control risk and report)
Enviro as source of infection
Some pathogens or oppotunists can survive in enviro or grow on plant or organic material. Usually ltd direct animal-animal transmission
Direct transmission
Animal-animal
Oral, resp,cutaneous, urogenital, bidy fluid trasmission
Indirect transmission
Food and water supply (could be contam by faeces) Fomites Arthropod vectors Iatrogenic Nosocomial infections
Fomites
Inanimate object that can transfer infection
Iatrogenic infection
Result of himan interference eg introduced by vet in surgery
Nosocomial infection
Acquired during hospitalisation
Congregation of diseased animals and vet interference
Anti-infective agent use can cause drug res prevalence
Horizontal transmission
Between animals within a group
Vertical transmission
Parent to offspring via germ line, in utero or milk or colostrum
Vector borne bact pathogen examples
Borrelia, coxiella and tularemia
How does Borrelia (burgdorferi) move
A spirochete, motile via endoflagella cont within periplasmic space between semirigid peptidoglycan layer and multi-layer flexible outer mem sheath
Filaments rotate in this space and cause corkscrew fashion bact movement (may be adaptation to viscous enviro eg aquatic sediments, mucosal tissue)
Outer surf pro of Borrelia burgdorferi
Various unique Osps (Osp A - F) presumed to play role in virulence
A & B most abundant
Small, Linear chromosome
Borellia transfer and reservoir hosts
Ixodes Ticks transfer from natural reservoir of white footed mouse to other warm blooded animals. Bact invades blood and tissues. In humans dogs and others it can cause lyme disease
(On pacific coast western black legged tick)
Borrelia can persist by
Immune suppression and or evasion
How does borrelia control its own virulence
Bu regulating virulence gene expression in resp to enviro (diff hosts)
Lyme disease distrib
Wide distrib in N temperate regions
(US: NE and NC states)
UK incr prevelence or better awareness and diagnostics
Canine lyme disease manifestation
Doesnt manifest for weeks or months, arthritis sign noticed and neurological issues rare
Most serious long term potential is glomerular dis
Glomerular dis
Kidney dam where imm syst stim for long time lead to circulating imm complexes get stuck in filtration mem of glomerulus causing inflam and eventually a small hole
Can be Caused by canine lyme dis
Canine lyme dis treatment
Respond rapidly to inexpensive antibio course
Goal to bring patient into premunitive state (state of dogs infected that never get ill) so organism in bodies latently but not cause infection
Coxiella transmission, manifest in diff species, spore or nonspore?
Produce spores C. Burnetti cause Q fever in man
Ruminant often asymptomatic
Cattle excrete in milk and there is placental colonisation
Ovine similar but can cause the odd abortion
Not just tick transmission
Tularemia
Bact septicaemia affecting domestic mammals birds reptiles fish people
Tularemia cause
F tularensis
highly virulent facultative IC pathogen
Inoc/inhal 10 organism can cause severe dis so is a category A agent (likely bio weapon)
