commensals of the respiratory tract Flashcards
what is a commensal
nonpathogenic bacteria that co-evolved and co-exists hamoniously with the host
they have a potential to be opportunistic pathogens
why are commensals beneficial to animals
important to health:
- can stimulate an immune response and support development of immunity
- can compete against pathogens. space colonized by commensals is not available to pathogens
- play a role in nutrition
describe how commensals colonize the upper respiratory tract
commensal organisms colonise epithelia surfaces
cilia and secretions prevent excessive accumulation of organisms
how are distal airways kept sterile from bacteria
- physical barriers (hairs and structure of nasal turbinates)
- movement of cilia and mucous in the trachea
- immune cells (macrophages
- non specific soluble factors (defensins, lysozymes, lactoferrin, complement)
bacteria should not be found (or at least not able to colonize in culture) in the healthy lower respiratory tract
what factors determine if a bacterium is a commensal or pathogen
- location on host (bite wound forces commensal bacteria from skin into bloodstream)
- acquisition of virulence genes
- change in gene expression (changes in surface capsule changes ability of macrophages to phagocyte bacteria and control bacterial growth
- host specific (some bacteria are commensals in some species but pathogens to others)
- host controls become impaired
- changes within the host (pregnancy, stress, reduces maternal antibodies in neonates)
- environment related (dehydration or cold)
- co-infection with another pathogen (infection with virus could damage mucosal function and allow overgrowth of commensal bacteria, etc.)
what are some risk factors that predispose the development of pneumonia in calves
- close confinement
- transportation or other stress
- poorly ventilated or overcrowded housing
- decline in maternal antibody
- intercurrent infections
name some common bacteria that are found in the healthy upper respiratory tract
- streptococcus sp.
- Actinobacillus
- pasteurella multocida
- Bordetella bronchiseptica
- escherichia coli
outline the diagnostic approach of determining upper respiratory infection
starting point:
- history
- clinical signs (discharge, couging, etc.)
- clinical exam
visual/imaging:
- endoscopy/rhinoscopy
- radiography
- ultrasonography?
sampling:
- haematology (indicators of general inflammation)
- bronchoalveolar lavage
- tracheal aspiration
- sawbs
cytology and microbiology on samples:
- demonstration of immune cells - look out for intracellular bacteria
- culture or visual - bacterial/fungal
- demonstration of viral antigens (detection method)
what is the role of the vet in infection control beyond treatment
husbandry
- reducing stress
- modify conditions where disease may spread more easily
- imporve health and therefore resistance to disease
- breeding
- biosecurity => how are animals housed to reduce chance of infection/access procedures
medical prevention
- vaccines
- pre/probiotics
- prophylactic treatment => problems with inducing antibiotic resistance and not recommended
discuss how you would approach treatment of a coughing dog at a rescue kennel
for kennel cough => generally not sampled. self limiting => use clinical judgement
if patient is well (Ii.e. no fever, cough is not too substantial, not other clinical signs) send home and advise to keep away from other dogs
if cough is substantial/patient is pyrexic (fever) treat with non steroidals to reduce inflammation and temp
if snotty as well as cough treat with antimicrobials as assuming secondary infection + NSAIDs
if very young/old might consider antibiotics as immune system may be weak and secondary infection could be severe
discuss how you would approach treatment of a coughing dog with a known Hx of chronic bronchitis and cough has not responded to first line of treatment
- Bronchoalveolar lavage under GA + thoracic radiographs
- sample => culture and antibiotic sensitivity +/- respiratory PCR panel to also cover viral diseases
as lungs are damaged already due to chronic bronchitis, infection is likely due to overgrowth of commensal bacteria or a specific pathogen => antibacterial treatment required even if only high levels of commensal isolated
discuss how you would approach treatment of a snotty horse (suspecting strangles)
sample: aspirate from absscess and long swab capable of reaching the back of the equine pharynx (swallowing reflex indiuced)
