Introduction
Goat warble fly infestation (GWFI) is a myiasis caused by larvae ofPrzhevalskiana silenus (P. silenus) which belongs to subfamilyHypoderminae of Oestridae family1. This disease
is associated with huge economic losses by reduction in milk yield, meat
and hide quality2, 3, and it is characterized by the
presence of subcutaneous warbles on dorso-lumbar region of affected
goats and wild ruminants.4 All three larval stages
(L1, L2 and L3) cause subcutaneous infestation for 7-9 months and no
internal migration is observed in contrast to other hypoderminae members
such as Hypoderma bovis (H. bovis ) and Hypoderma
lineatum (H. lineatum ).5
GWFI is widespread and commonly present in the Mediterranean Basin and
Indian subcontinent that includes northern India, Pakistan, Iran, Turkey
and southern Italy.2,6-10 In India, the disease is
most common in northwestern Himalayan area (Union Territory of Jammu and
Kashmir), particularly in goats of the Bakerwali breed characterized by
long hairy coat with a prevalence rate ranging between 13 to 56.5 % in
Jammu region.2
Physicoclinical observation by palpation of warbles on infested animals
is routinely used for diagnosis at L2 and L3 stages which occurs about 3
months after infestation. Serological tests have advantages over
physicoclinical observation in terms of early detection and high sample
throughput along with wide diagnostic time window, as antibodies in the
infested host may persist for about 16 weeks.11,12 The
serodiagnostic assays for hypoderminae insects have been explored with
the key serine proteases namely Hypodermin A (HyA), Hypodermin B (HyB)
and Hypodermin C (HyC). Among the three serine proteases, HyC is
primarily produced in early stage of L1 that helps in the penetration of
the skin due to its collagenolytic activity. HyC is characterized as a
major immunodominant antigen. The conserved nature of HyC shows cross
reactivity among Hypoderminae subfamily due to shared
epitopes.11, 13-18
Several enzyme immunoassays have been developed based on native and
recombinant HyC derived from H. bovis and H. lineatumbased indirect ELISAs have been developed for diagnosis of cattle
hypodermosis.19-23 Presently, recombinant protein
based microtitre plate-ELISAs are widely used in routine diagnosis and
seroepidemiological studies of hypodermosis.6,18,23However, the assay is expensive, time-consuming and requires equipment
like ELISA reader and expertise to analyse the data. Diagnostic labs
performing spectrophotometric ELISA are scarce in developing countries,
especially at remote veterinary diagnostic centres. In contrast to such
challenges, a simple, rapid and easy to perform test is required.
Dot-ELISA is an inexpensive, sensitive and specific assay that provides
utility to be performed at less equipped regional labs and provide
visual readouts without spectrophotometry.24
Several dot-ELISA have been developed for various zoonotic and
veterinary parasitic diseases such as Toxocariosis based onToxocara canis Excretory –Secretory Antigens (TES), Taenia
solium cysticercosis (neurocysticercosis) with partially purified
antigen fraction (Cathepsin L like activity); Toxoplasmosis based on
recombinant surface antigen (rSAG) and dense granule antigens (rGRA7),
recombinant cathepsin L-cysteine proteinase for Fasciola
gigantica , truncated recombinant merozoite antigen (rBgSA1) forBabesia gibsoni among others.24-28
The present study aimed to develop a dot-ELISA based on recombinant HyC
derived from P. silenus for the serodiagnosis of GWFI in order to
develop an economical, rapid and field applicable tool for
serosurveillance of this myiasis during disease control programs.