Multi-omic Profiling, Structural Characterization and Potent Inhibitor Screening of Evasion Related Proteins of a Parasitic Nematode, Haemonchus contortus, Surviving Vaccine Treatment

Abstract

The emergence of drug-resistant parasitic nematodes of both humans and livestock calls for development of alternative and cost-effective control strategies. For the economically important ruminant strongylid Haemonchus contortus, Barbervax® remains the only registered vaccine available. Here we compared the microbiome, genome-wide diversity and transcriptome of H. contortus adult male populations that survived vaccination with an experimental vaccine after inoculation in sheep. Our genome-wide SNP analysis revealed 16 putative candidate vaccine evasion genes. However, we did not identify any evidence for changes in microbial community profiling based of 16S rRNA gene sequencing results of vaccine surviving parasite populations. A total of 58 genes were identified as significantly differentially expressed with six being long non-coding (lnc) RNAs and no putative candidate SNP associated genes. The genes highly upregulated in surviving parasites from vaccinated animals were associated with GO terms belonging to predominantly molecular function and a few biological processes that may have facilitated evasion or potentially lessened the effect of the vaccine. These included five targets: astacin (ASTL), carbonate dehydratase (CA2), phospholipase A2 (PLA2), glutamine synthetase (GLUL) and fatty acid-binding protein (FABP3). We searched all five DEG targets against the proteomes of selected Nematoda (Clades III, V, IV, C, I) and Platyhelminthes (Clades Monogenea, Trematoda, Cestoda, Rhabditophora) to determine homologs within the H. contortus NZ_HCO_NP v1.0 genome and identified single-copy orthologous groups (OGs) in selected proteomes. All but one (FABP3) demonstrated high levels of duplication and wide-spread occurrence in closely related Caenorhabditis elegans and Pristionchus pacificus, with complete absence of all five gene targets among other Clade III (Toxocara canis) and V (Ascaris suum, Ascaris lumbricoides and Parascaris univalens) nematodes, further supporting their vital biological functions in nematodes. Phylogenetic analyses inferred the presence of only ASTL and CA2 in almost all Nematoda, platyhelminthes and metazoans examined, with loss of GLULs observed among all outgroup vertebrate species and the presence of FABP3 in only three other species (Schmidtea mediterranea, Fasciola gigantica and F. hepatica). Our tertiary structure predictions and modelling analyses were used to perform in silico searches of all published and commercially available inhibitor molecules or substrate analogues with potential broad-spectrum efficacy against nematodes of human and veterinary importance.