Nov 26, 2010

Family Oestridae..Genus Oestrus (Nasal Bot Flies)

  • Larvae of these flies spend most of their time in the nasal passage of sheep & Goat. So called nasal bots
  • Adult flies are having short life span (1 week) whereas larvae having 1 year or more of life span.
  • Adult flies are 1cm in size and of grey color.
  • Small dark spots are present on the abdomen with a covering of short brown hair.
  • Size of Larvae is 3cm and color is yellowish white. Larva is tapering anteriorly with prominent step posteriorly.
  • Body is segmented having dark transverse bands dorsally (each segment).
Nasal Bot fly injecting larvae
Life Cycle
  • Adult female is viviparous and produce larvae.
  • Sheep become infected by squirting of jet of liquid containing larvae.
  • During the flight, fly deliver 25 larvae.
  • Newly emerged larva is 1mm in length.
  • Larva migrates from nasal passage to frontal sinuses.
  • Larva feed on mucous secreted by movement of larva.
  • In the nasal passage, larva mould to L2.
  • In the frontal sinuses, larva completes their development and then migrates to nostrils where they are active throughout the year.
  • Become dormant in winter season if temperature is below 18.
  • From the nostrils, L3 larvae fall on the ground and from larva, pupa develops.
  • From the pupa, adult emerges. Adult having very short life span
  • Survive for only 1 week and during this period, produce about 500 larvae.
Pathogenic effects
  • Itching and Irritation
  • Rubbing the nostrils against hard objects
  • Nasal discharge which later on becomes mucopurulent
  • In coordination, convulsions
  • Also called false gid (signs resembling coenurus cerebralis)
  • Cause swelling of eyes in human called as keratoconjunctivitis and inflammation of lips called stomatitis
  • Loss of weight
  • Refoxanide, Ranide…. 1ml/25kg BW subcutaneously
  • Nitroxynil, Trodex….1ml/20kg BW subcutaneously
  • Ivermectin………….1ml/50kg BW subcutaneously
Regular use of insecticidal drugs should be followed.


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