Warble fly (locally called as “Mehroo”) is a widespread pest of cattle and goats in hilly and semi-hilly areas of Pakistan. The larvae of the fly cause perforations in the skin of the affected animals resulting in huge economic losses to leather industry. Furthermore, reduced milk yield and lowered weight gain are other ill-effects of this menace. The adult fly lays eggs on the skin of the animal. After hatching, the larvae penetrate into the skin through hair follicle and start migrating towards back of the animal. During this travel, the larvae molt from first to second stage and finally to third stage. These larvae assemble underneath the skin of the animal and forms small nodule called warble. The larvae make perforations in the skin for respiration and fall on to the ground. The fly has rudimentary mouth parts and life span is up to 7 to 10 days only.
Studies have shown that species of warble fly in goats in Pakistan is Przhevalskiana silenus Brauer while Hypoderma lineatum infest cattle and buffaloes in Pakistan. Based upon prevalence, Pakistan can be divided into disease free regions as well as areas with low (1 to 10%), medium (11 to 35%) and high prevalence (> 35%). Based upon the studies on the biology of the fly, a control protocol involving a single injection of
ivermectin was devised. Extensive studies carried out in different regions with various prevalence rates have confirmed the effectiveness of this control strategy (Zero prevalence in treated vs 35 to 85% in untreated controls). For proper control, the ivermectin at the recommended dosage should be given in the months of October in goats and first week of September in cattle. The technology is economical as the drug is also effective against ecto and most of the endo- parasites of animals. Wide spread use of this control strategy can even result in eradication of warble fly from the country.
Key References
Khan, M. Q., Akhtar, S. and Cheema, A. H. (1994). Efficacy of ivermectin against goat warbles (Przhevalskiana silenus Brauer) in Pakistan. Veterinary Record, 135: 361.
Khan, M. Q., Afzal, M. and Khan, M. I. (1997). Efficacy of ivermectin against cattle warbles in Pakistan. Acta Parasitologica, 42: 173-175.
