SPP- or GTP-positive (46) and -negative (216) serum samples were tested, using conditions for SPP/GTP iELISA. Based on the S/P% values, the cut-off for the SPP/GTP iELISA was 19.22%, using all three statistical approaches (Supplementary Figure S6). The ROC analysis estimated the area under the curve (AUC) to be 99.18% (Supplementary Figure S7). the LRRC15 antibody implementation of capripox control programs through serosurveillance and the screening of animals for trade. Keywords:capripoxvirus, iELISA, A34, A36, LSDV, SPPV, GTPV == 1. Introduction == Sheeppox virus (SPPV), goatpox virus (GTPV), and lumpy skin disease virus (LSDV) are large, double-stranded DNA viruses of the genusCapripoxvirusof thePoxviridaefamily [1]. Although these three viruses share high sequence similarity (96 to 97% nucleotide identity) [2,3], they display specific host preferences [4,5]. SPPV and GTPV can infect sheep and goats, causing sheeppox (SPP) and goatpox (GTP), respectively. Though most strains cause disease in sheep and goats, some strains show preferences for either one or the other species [3,6]. Additionally, GTPV infection in wildlife has recently been reported [7,8]. Likewise, LSDV causes lumpy skin disease (LSD) in cattle Cilostazol and buffaloes, while clinical signs have been reported in Springbok antelope, oryx, and gazelle [9]. LSD, SPP, and GTP are categorized by the World Organization for Animal Health (WOAH) as notifiable diseases [10], and are included on the list of potential bioterrorist agents by the United Kingdom and the United States Department of Agriculture [11,12]. SPP and GTP remain endemic in Asia, Africa (except for southern Africa), the Middle East, and Turkey [13,14], with sporadic outbreaks of SPP in Greece and parts of Eastern Europe [13]. LSD was endemic only in the Middle East and sub-Saharan Africa, including Egypt [15]. However, in 2015, the first outbreaks of LSD occurred in Greece, the Russian Federation, Central Asia, and most Cilostazol of the Balkans [13,16]. LSD was detected in the remaining part of Asia in 2019, where it is likely to become endemic [17]. Several highly efficient tests for the molecular identification and differentiation of capripoxviruses have been developed and are currently used [4,5,18,19,20,21,22,23,24,25,26]. In contrast, only a few serological assays have been described. All of them Cilostazol present several drawbacks. For example, the WOAH-recommended virus neutralization test (VNT) for anti-CaPV antibody detection [6,27] requires large amounts of sera, is not easy to implement, and its results can be difficult to read [9,28]. In addition, VNT also requires the use of live viruses, which limits its use to BSL-3 facilities in capripox non-endemic countries or in well-equipped virological laboratories in endemic countries. The indirect fluorescent antibody test (IFAT), also on the WOAH list of available serological tests, cross-reacts with orf (contagious pustular dermatitis) in sheep and other poxviruses [6,27]. Western blot and agar gel immunodiffusion tests can also be used in serological capripoxvirus antibody detection, but while the former is expensive to perform and not convenient in high-throughput testing [6,27], the latter cross-reacts with antibodies against parapoxviruses [6,27]. Several ELISAs have also been developed, using either purified viral preparations [29] or recombinant capripoxvirus proteins [30,31,32]. However, these ELISAs have encountered practical problems, hampering their use. For example, recombinant proteins have shown a loss of activity due to protein instability of the recombinant antigens [29] or poor protein expression levels [30]. Meanwhile, ELISAs based on inactivated viruses bear the Cilostazol high cost of producing large amounts of the antigen [31]. Other tests have reported problems detecting a particular category of antibodies: Tian et al. (2010) based their iELISA on two synthetic peptides of CaPV P32, but this assay performed well only on sera from immunized sheep [32]. In addition, the test by Bowden et al. (2009), targeting anti-SPPV and anti-GTPV antibodies by using CaPV core virion proteins for an indirect ELISA, performed well with experimentally infected, but not with vaccinated, sheep and goat sera samples or LSDV-infected cattle serum [33]. The present study builds on previous work performed in our laboratory [34], where several antigenic targets were analyzed in order to develop a capripoxvirus iELISA. We considered two target antigens, the capripoxvirus homologs of the vaccinia virus C-type lectin-like protein A34 and the EEV glycoprotein A36, from a panel of five surface and immunomodulatory proteins. We also compared several blocking buffers and secondary antibodies to improve binding Cilostazol and detection. Finally, based on those results, we established two test conditions, using the recombinant.