VPA 221: Veterinary Entomology and Acarology (1+1)

EFFECT ON THE HOST - OX WARBLE FLIES

Due to Adult fly

• The characteristic buzzing noise and the persistant ovipositing behaviour of the fly causes  panic in cattle
• The flies may cause gadding in animals which run madly about resulting in injury, spontaneous abortion, and even death of young animals
• The animal stops feeding, becomes restless.  Since the feed intake is affected the condition of the animals deteriorate
• There is retarded growth and reduced milk yield

Due to larval stage

• Due to first larval stage
  • Many larvae enter through the same opening in the skin which results in an exudate from the injured heel region
  • The opening made by the larvae is prone to bacterial infection and to myiasis
  • The entry holes are oedematous and inflamed
• Due to the second and third stage larvae
  • Migration of the larvae through the subcutaneous tissue results in the production of greenish yellow tracts with eosinophilic infiltrations
  • The affected beef is called ‘licked beef’  while the gelatinous tracks in the beef are temed ‘butchers jelly’
  • The beef is unaesthetic and hence extensive trimming of the affected areas are required before sale, this results in extensive loss to the farmer
  • The affected beef even following trimming has a short shelf life
  • The presence of the first and second stage larve in the oesophageal region can cause stenosis of the oesophagus
  • Causes rupture?
  • The presence of the second and the third stage larvae on the back of the animal results in formation of warbles
  • In addition to being painful to the animal these warbles due to the perforation in them downgrades the quality of hide to a great extent
  • Accidental rupture of the warbles can result in anaphylactic shock
  • It can also result in the production of abscess, due to bacterial infection
  • The perforation can also attract other myiasis producers
  • Affected animals are generally debilitated in appearance
  • Thus carcass and hide depreciation are the most important features of this infestation
• Abberant host
  • Man has been known to be affected – result in painful warbles in the chest region
  • Horses can also be affected