Diagnosing calf respiratory disease Flashcards
Definition of BRD
Bovine Respiratory Disease
- Definition involves interaction between respiratory tract infections with
environmental and animal factors.
Different scoring systems, do not discriminate between:
- Upper / lower respiratory tract disease
- Viral/bacterial disease
- Conditions that require/do not require antimicrobial treatment.
- Broad BRD definition only in productive animals (infectious + non-infectious).
- We treat BRD (also metaphylactically) mostly with antimicrobials. But we need to reduce this!
- You should make the assumption that viral infection complicates bacterial infection.
- Using BRD definition like this is oversimplified, dangerous and does not help in making reasonable treatment decisions.
Which definition of BRD would meet practical needs and objectives limiting the
use of AB?
Discriminate between:
* Upper respiratory tract disease (rhinitis, pharyngitis) = do not require antimicrobial treatment
- Lower respiratory tract disease (pneumonia, bronchitis) = usually requires antimicrobial treatment
And discriminate Viral vs bacterial.
How to discriminate between upper and lower resp. disease and whether a case needs antimicrobials? (2)
- Thoracic auscultation – dependent on the person, does not identify lung lesions, not
discriminate between viral / bacterial disease. - Thoracic ultrasonography – it can distinguish upper respiratory tract infections from lower respiratory tract infections; it does not differentiate active lesions from chronic damage.
- Treatment decisions are time-critical – there is an absence of animal-side tests discriminating bacterial contamination, colonization and infection of the lower respiratory tract.
- Limited possibilities today
Causes of calf respiratory disease.
Is very much multifactorial.
Animal related causes
Activity related causes
Pathogen related causes
Environment related causes
Important pathogens behind calf respiratory disease. (10)
Mycoplasma spp.
Pasteurella multocida
Histophilus somni
Mannheimia hemolytica
Salmonella dublin
Bovine respiratory syncytial virus
Bovine coronavirus
Bovine herpesvirus 1
Parainfluenza-3 virus
Bovine viral diarrhea virus
- Determine the pathogen indirectly e.g. by using..?
e.g. paired serology
- Maternal Ab-s in blood
- Vaccine Ab-s interfere
- Time-consuming (ca 1 month)
- Price
+/- In case of good luck / disease outbreak we detect seroconversion.
- Determine the pathogen directly by using..?
Bacteriology
+ Speed - 3 days
+ Antibiogram!
+/- Live/viable bacteria are detected
+ Price
- >5 days for mycoplasma
- Low Se
- Fast overgrowth for H. somni
- Requires special (transport)media
Pros and cons to PCR
+/- (Too?) high Se - also identifies
opportunists, contaminants, dead
bacteria - a link to the disease?
+ qPCR evaluates the amount of
pathogen
+ contamination does not affect
+ deComposed samples could be done
+ Fast
- Live vaccines 14 days
- The viral genome changes, the primers
may expire
- Price?
Sample taking options for resp. disease in cattle. (4)
nasal swab (fastest and easiest)
Deep nasopharyngeal swab (also fast and easy)
BAL/TAL (fast, easy and sample from lower resp. system)
transtracheal wash TTW
Describe Nasal swabs
The fastest and easiest
Sample from the cutaneous part of the nose
Very far from the lung tissue, does not represent the lower respiratory tract
Contamination by commensals
Possible complications:
Nosebleeds, stick fracture
Describe Deep nasopharyngeal swab
Fast and easy
Sample from respiratory and lymphoid
epithelium
Sampling area ≤0,5cm2
Opportunistic pathogens?!?
Far from lung tissue - how well it
represents the lower respiratory tract?
Possible complications:
Nosebleeds, stick fracture
Describe BAL/TBL
Fast and easy
Sample of unknown lung lobe (>10cm2) – pathogens may not be in this lobe
Ultrasound can be used in clinical settings to detect infected lung lobe + TBL under endoscope check.
Moderate risk of contamination (ca 20%)
It is not always technically easy
The best practical method for detecting viruses and bacteria?!
Possible complications:
Nosebleeds, pulmonary hemorrhage, respiratory distress (unabsorbed fluid)
Describe TTW
transtracheal wash
End of trachea, bronchial bifurcation (5-10cm2) – the mucociliary system brings the lung infection there?
In bacterial infections, the distal lung parts of the lung lobes are affected.
There is no risk of contamination of the sample.
Calming, local anesthesia, surgical preparation. The issue of well-being.
Possible complications:
Subcutaneous emphysema, wound infection, local bleeding, catheter rupture, respiratory distress (unabsorbed fluid)
Respiratory disease pathogens.
What is my list of diff-diagnoses? (3)
- Depends on signs of illness (whether diarrhea / sudden death / abortion etc.)
- Depends on endemic infections in the herd (whether the herd is negative for any disease).
- Depends on the prevalence of diseases in the population - do we have an overview of the incidence of all important diseases in
Estonia?
How to discern whether a pathogen is primary or secondary, or even apathogenic and just a secondary finding?
How many samples to take from the herd?
- Analyses are expensive, the number of samples is limited.
- The predominant aim is to identify the pathogen at the herd level.
- The best patient - in the acute stage of the disease, the first days of illness, untreated.
- The number of samples depends on the expected prevalence of the disease. (see image)
e.g. if you expect that 70% of the disease is caused by a specific pathogen then sampling from 5 ill animals will allow you to “catch” the pathogen the majority of the time with only 3% chance of missing it (dotted line on graph in image).
Diagnosing BRD - summary
Treatment of BRD depends on if it is
- Is it upper / lower respiratory tract disease?
- Is the disease bacterial? – how to define this in field?
- Is Mycoplasma spp involved? (if it is then it’ll affect your AB choice and the duration of treatment)
- Decisions based on the pathogen and antibiogram (at herd level)!
- Always include NSAID.
- Supportive therapy (fluids for respiratory acidosis) when needed.
Ideally, when would calves be vaccinated
before the point when maternal antibodies have decayed past protective levels and at the point when the calf would mount an effective immune response in time to provide continual protection against disease challenge, eliminating any window of susceptibility.
Intranasal Vaccination IFOMA in Clinical Practice
- Intranasal vaccination may circumvent interference by maternal antibodies; however, clinical protection is inconsistent and relatively short lived.
- Viral shedding can be decreased, and immunologic priming may be induced by IN vaccination IFOMA in seronegative and seropositive calves.
When to suspect M. bovis infections in the herd? (3)
- Calf respiratory disease, otitis and arthritis.
- Chronic disease, wasting and with poor recovery rate.
- Nodules with caseous necrosis in the lungs.
Describe mycoplasma bovis as a pathogen.
- Without a cell wall (immune system can’t recognize and kill this pathogen as easily without wall-antigens)
- Many antimicrobials have no effect
- Persist longer in cold, humid environment, susceptible to heat.
- Challenge for immune system, no long-term immunity.
- Reaction of immune system against the organism and not the pathogen.
Control of Bovine herpesvirus-1. (3)
Test and slaughter
* Serological investigation and culling of seropositive animals
* Herd replacement free of infection, Isolated keeping of heifers
Test, separate and replace
* Keep infected animals in separate buildings
* Gradual replacement of infected animals
(Prevalence among cows is <30% and heifers <20%)
Vaccinate with marker vaccine + test and slaughter.
* All animals from 3 months of age once/twice a year (depends on the vaccine).
* Vaccination program lasts 4-7 years depending on the within-herd prevalence.
- After that, serological investigation and the remaining 10% seropositive animals should be culled (vaccination does not eliminate virus circulation completely but reduces it considerably).
