Respiratory disease in adult farmed animals

Question 1

What is IBR (Infectious bovine rhinotracheitis) caused by?

Answer 1

Bovine Herpes Virus 1

Question 2

How is IBR spread?

Answer 2

• Respiratory infection spread by aerosol
• Direct contact or shared air space for sustained period
• Once infected (or vaccinated with a live vaccine), the animal remains infected for life
• Re-activation and shedding follows periods of stress

Question 3

What are the clinical signs of respiratory IBR?

Answer 3

• Mild disease: Conjunctivitis, epiphora, mild strain or immunity
• Subacute disease: Adult cattle – milk drop, pyrexia (40C), nasal discharge and hyperpnoea
• Acute disease: Growing cattle (e.g. heifers) with marked pyrexia and secondary infection, purulent nasal discharge and conjunctivitis

Question 4

What are the complications of IBR?

Answer 4

• Peracute disease: Very high fever and death in 24 hours
• Secondary bronchopneumonia
• Mortality can be 10% in younger animals
• Reproductive signs: abortion, genital lesions

Question 5

How would you diagnose IBR?

Answer 5

• Clues from history, e.g. new animals or groups into the herd
• Individual animal testing
  
  • Nasal and conjunctival swabs (presence of virus on FAT – rapid identification)
  • Paired blood samples from acute cases (rising titres on ELISA antibody test)
• Dairy herds
  
  • Bulk milk antibody test to monitor exposure of the herd

Question 6

What options are there to control/eradicate IBR?

Answer 6

• Do nothing!
• Vaccinate in the face of an outbreak
• Vaccinate to control clinical signs (i.e. routine herd vaccination)

Question 7

What are the conventional vaccination options for IBR (BHV-1)?

Answer 7

• Live intranasal strains
  
  • Tracherine (Pfizer)
  • Bovilis (Intervet)
• Combined with other pathogens
  
  • Rispoval 4 (Pfizer)
  • Immuresp RP (Pfizer)

Question 8

What biosecurity should be implemented to control IBR?

Answer 8

• Double fencing at boundaries
• Quarantine procedures (!)
  
  • Animals bought from herds
  • Re-introduction of cattle
  • Test on arrival and 28 days later

Question 9

Which two respiratory diseases in cattle are notifiable?

Answer 9

• Bovine Tuberculosis (bTB)
• Contagious Bovine Pleuropneumonia (CBPP) (eradicated in UK)

Question 10

What causes bovine TB?

Answer 10

• Mycobacterium bovis
• Gram-positive, acid-fast rods

Question 11

How does bovine TB spread?

Answer 11

• Routes of infection ingestion (outside or when wildlife reservoir involved) or inhalation (when housed)
• Excreted in urine, sputum, faeces, milk (baby calves!), exhaled air, vaginal and uterine discharge
• New infections from infected cattle or infected badgers
• Also from other wildlife and contaminated slurry

Question 12

What are the clinical signs of bovine TB?

Answer 12

• Soft, productive cough
• Worse if exercised or pharynx palpated
• Weight loss, LN enlargement?
• Can also have mastitis with udder induration
• Alimentary and generalised forms unusual

Question 13

How is TB diagnosed?

Answer 13

• Visible Lesions (VL) at PM in lymph nodes
• Culture of M. bovis
  
  • Neither are very sensitive (later in disease progression) but both are highly specific!
• Ante-mortem diagnosis involves the animal’s immune system:
  
  • Single Intradermal Comparative Cervical Tuberculin Test (SICCT)
  • g-interferon blood test (Bovigam)
• SICCT test

Question 14

How is the SICCT test carried out?

Answer 14

• Inject purified avian and bovine mycobacterial protein at separate sites on the neck
• Compare differences at 72 hours
• Increase in skin thickness of >2mm or oedema is a positive reaction (hypersensitivity)

Question 15

How sensitive/specific is the SICCT test?

Answer 15

• Sensitivity (median) ~80% (miss 1 in 5!)
• Very specific (99.9%)

Question 16

What is the y-interferon test and why is it used?

Answer 16

• y-interferon is a cytokine released by immune cells in response to mycobacterial antigens
• Detects infection 2-3 weeks earlier than SICCT
• Higher sensitivity (less false negatives) ~88%
• Lower specificity (more false positives) ~96%

Question 17

How can you reduce the risk of cattle to cattle spread of bovine TB?

Answer 17

• Closed herd
• Pre-movement testing of purchased cattle is imperfect
• Maintain fences and boundaries more than 3m apart
• Avoid shared grazing

Question 18

How can you reduce the risk of spread of bovine TB from contaminated feed and water (from badgers)?

Answer 18

• Feed stores must be vermin-proof
• Raise water troughs
• Fence cattle away from badger haunts

Question 19

What is Contagious Bovine Pleuropneumonia (CBPP) caused by?

Answer 19

• CBPP is notifiable in cattle (eradicated from the UK)
• Caused by Mycoplasma mycoides

Question 20

What are the clinical signs of CBPP?

Answer 20

• Pyrexia
• Lethargy
• Pneumonia and cough
• Elbows abducted, neck stretched, mouth open
• Pleurisy causes severe pain
  
  • Animal may be reluctant to stand
  • Nasal discharge and drool saliva

Question 21

What are the post-mortem findings of CBPP?

Answer 21

• Pleurisy
  
  • Large quantities of straw-coloured fluid is seen in pleural cavity
• Lesions often restricted to one lung
  
  • ‘Marbling’ appearance of lung tissue
  • Interlobular oedema and fibrin deposits
  • Thrombus formation can result in a portion of lung tissue dying

Question 22

How is CBPP controlled?

Answer 22

• Essentially, CBPP is a disease of movement so stop movement of cattle and slaughter infected animals and herds
• Vaccination
  
  • Live T1/44 vaccine
  • Side effects can be fatal and extensive coverage (and therefore increased costs!) is required
• Some success with the fluoroquinolone antibiotic danofloxacin (Advocin, Pfizer)