Prevalence and Early Detection of Hypodermosis in Goats using a Competitive ELISA System in Lorestan, Iran

Dot-ELISA based on recombinant Hypodermin C of Przhevalskiana silenus for field diagnosis of goat warble fly infestation

Goat warble fly infestation (GWFI) is an economically important myiasis caused by larvae of Przhevalskiana silenus (Diptera, Oestridae), prevalent in countries of the Mediterranean Basin and Indian subcontinent. GWFI is characterized by the presence of subcutaneous warbles at the lumbar and sacral region of dorsum in the infested animal. The early larval instars (L1 and L2) remain inaccessible to physical detection due to their small size and subcutaneous presence thus causing hindrance in the diagnosis. The objective of present study was to develop a field applicable early diagnostic intervention for GWFI monitoring and prophylactic management for effective control of the disease. Recombinant Hypodermin C (rHyC) antigen of P. silenus was expressed in Escherichia coli. The purified protein was used for optimizing dot-ELISA in a checkerboard titration using goat warble fly infested serum as known positive. The optimized assay was further tested for lower temperature (18°C) and incubation time (30 min). The optimized assay was assessed for inter-rater reliability and field samples. The optimized conditions require 188 ng of protein/dot, 1:800 dilution of serum sample, 1:4000 dilution of anti-goat IgG conjugate and 5% skim milk powder in phosphate buffer saline as blocking buffer. The assay was found to have a diagnostic sensitivity and specificity of 97.3% and 95.8%, respectively. The inter-rater reliability of dot ELISA with rHyC indirect ELISA was found to be almost perfect with a Cohen's kappa index of 0.973. Further testing at ambient temperature (18°C) and shorter incubation steps (30 min) supported suitability of the assay for field diagnosis of GWFI. The present study provides the first report of a sensitive and specific dot-ELISA for early diagnosis of GWFI which is rapid and cost effective. The test may provide an effective field applicable tool for sustainable control of GWFI.

First report of Przhevalskiana silenus derived recombinant hypodermin C based indirect ELISA for serodiagnosis of goat warble fly myiasis

Goat warble fly infestation (GWFI) is a subcutaneous myiasis caused by larvae of Przhevalskiana silenus, an insect belonging to the order Diptera. The diagnosis of GWFI is challenging in the early larval instars (L1 and L2) as they are occult under the skin and hair coat causing prolonged economic loss in form of meat and hide damage. This necessitates early diagnosis for disease control at herd level and its prophylactic management to prevent economic losses. Hypodermins, a class of serine proteases from Hypoderminae subfamily have been used as serodiagnostic antigens for the past four decades for diagnosis of warble fly myiasis. In this study,the immunodominant antigen Hypodermin C (HyC) from P. silenus has been recombinantly expressed in E. coli and immunogenic characterisation of expressed protein was done. The protein shows hallmark residues in conserved cysteine and catalytic triad typical of serine proteases along with similar profile of immunoreactivity towards Hypoderminae infestation. The present study reports an optimised indirect-ELISA based on recombinant HyC derived from P. silenus for early diagnosis of GWFI. The optimised indirect ELISA provides a sensitive and specific immunodiagnostic for mass surveillance of the GWFI with diagnostic specificity and sensitivity of 96% and 100%, respectively and not showing any cross reactivity against other important parasitic and bacterial diseases of goats. This study presents the first report of indirect ELISA based on recombinant Hypodermin C antigen derived from P. silenus for the serosurveillance of goat warble fly disease.