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SOUTH AFRICAN EQUINE VETERINARY ASSOCIATION (SAEVA) WORKSHOP ON VETERINARY SUPPORTIVE TREATMENT OF AFRICAN HORSE SICKNESS

Posted: 25/3/2012, 12:19

African horse sickness (AHS) is a non-contagious, infectious, insect-borne viral disease of equids characterised by fever, oedema of the lungs and subcutaneous tissues, transudation into body cavities and serosal haemorrhages. The mortality rate in immunologically naive horses may be as high as 90%, with donkeys and mules being less susceptible. African horse sickness virus (AHSV) replicates in and injures microvascular endothelial cells.  Endothelial injury and activation of monocyte/ macrophages results in capillary leakage, haemorrhage, inflammation and disseminated intravascular coagulation. Four clinical forms of AHS have been described; a peracute ‘dunkop’ or pulmonary form, a subacute ‘dikkop’ or cardiac form, a ‘mixed’ cardiopulmonary form and a mild fever form. The clinical signs of AHS may be confused with those of equine encephalosis. Recently polymerase chain reaction (PCR) has become available as a rapid diagnostic technique to confirm infection with AHSV. There is no specific curative therapy for AHS and supportive therapy is usually administered.

A workshop for veterinarians attending the annual SAEVA Congress was held on Sunday 12 February 2012. The goal of the workshop was to discuss and document supportive treatment options used by veterinarians treating AHS cases, with focus on the scientific rationale for treatment, scientific evidence supporting efficacy and safety of the treatment, AHS-specific data available, and reach agreement on whether the treatment was considered justified as veterinary supportive treatment for AHS or not. The workshop was attended by a total of 34 veterinarians from Southern Africa, various international delegates and representation by the AHS Trust.

  • It was emphasised and agreed that there is no generic veterinary supportive treatment guideline for every AHS case and that veterinary supportive treatment must be customised on a patient by patient basis.
  • The workshop participants agreed that treatment with nonsteroidal anti-inflammatories, short to medium acting corticosteroids and antimicrobials is justified as veterinary supportive treatment of AHS cases.
  • The rationale for treatment with nonsteroidal anti-inflammatories is anti-inflammatory, analgesic, and antipyretic effects, based on cycloxygenase (COX) inhibition. There is strong scientific evidence supporting the rationale, efficacy and safety of NSAIDs such as flunixin and phenylbutazone in horses. 
  • The rationale for corticosteroid treatment includes potent anti-inflammatory effects (lipoxygenase and cycloxygenase), stabilization of cell membranes and preservation of vascular membrane integrity.  There is strong scientific evidence supporting the rationale, efficacy and safety of corticosteroids in horses. 
  • The rationale for antimicrobial treatment is as prophylactic for secondary bacterial infection, particularly bacterial pneumonia as AHS cases with pulmonary oedema, leukopaenia and neutropaenia are considered at risk. There is strong scientific evidence supporting the rationale, efficacy and safety of specific antimicrobials in horses.
  • Other supportive treatments agreed on were crystalloid and colloid intravenous fluids and DMSO. There is scientific evidence supporting a rationale, efficacy and safety of these treatments in horses.
  • Whilst not a veterinary treatment per se participants agreed unanimously that strict rest was mandatory for horses suffering from AHS. 
  • It was emphasised that the treatments agreed with are supportive in basis and not curative. Many other factors, such as vaccination status and immunocompetence, are important in individual horse response to AHSV infection.
  • It was noted that treatment with homeopathic remedies is utilized by some practitioners and owners as a supportive treatment in the field. Workshop participants did not agree on treatment with homeopathic remedies as a veterinary supportive treatment for horses suffering from AHS, as whilst they may do no harm there is no strong scientific evidence supporting a rationale and efficacy in AHS cases. Horse owners are advised to consult their veterinarian regarding use.
  • Whilst the freedom and rights of horse owners to select the health care of their choice is recognised, the irrational use of ‘medications’ without scientific evidence is not in the best interests of horse welfare.
  • Participants agreed that the use of unregistered products such as sodium hypochlorite/ bleach, colloidal silver, hydrogen peroxide, and ozone for treatment of horses is not supported. As there is no recognized scientific efficacy or safety data for these products in horses, horse owners and trainers are cautioned against use of these remedies and are advised to consult their veterinarian.
  • There was overall consensus by veterinarians attending the workshop on the majority of points raised, which was supported by the results of the written survey circulated.
  • The report on the workshop has been circulated to SAEVA members. Horse owners and trainers are advised to consult their veterinarians for further information.

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