The draft genome of the canine parasitic roundworm Spirocerca lupi

Abstract

Spirocerca lupi is a parasitic nematode of dogs and wild canids. It causes spirocercosis which is associated with aortic lesions that occasionally rupture and cause death, as well as oesophageal nodular masses that can undergo neoplasia and malignancy if left untreated. Spirocercosis can be difficult to detect early in the course of the infection and treatment may be ineffectual in later stages of infection. It is endemic to South Africa and is found in most countries but is more prevalent in tropical and subtropical regions where dung beetles serve as intermediate hosts. Identifying new anthelmintic and vaccine targets can lead to new treatments against this parasite. DNA was isolated from two adult S. lupi nematodes. The first was used to sequence the genomic DNA, and the second to sequence the transcriptome. The draft genome of S. lupi consists of 13,627 predicted protein coding genes and is approximately 150 Mb in length. The transcriptome was used to identify potential anthelmintic and vaccine targets. Seven priority anthelmintic targets were identified as well as seven potential vaccine targets along with several known vaccine and immune modulators. In addition to the nuclear genome, the mitochondrial genome was sequenced and compared to the mitochondrial genome of S. lupi sequenced in China. These two genomes were found to be mostly similar. We did identify that the mitochondrial genome is potentially heteroplasmic with cloned sequences of the nad2 gene region from a single adult nematode yielding different gene sequences. The genome of S. lupi was analysed to inform a vaccine that was designed following a reverse vaccinology and immunoinformatics approach. Gene targets were selected using a set of strict criteria. Through this approach eight genes were identified and eight multi-epitope vaccines against S. lupi were designed. Vaccine 6 model 4 was the vaccine that showed the most potential due to its antigenicity, non-toxicity, solubility, non-allergenicity and the more stable 3D structure and binding to both the TLR4/MD2 of the mouse and the domestic dog. This study demonstrates that genome in silico approaches can be used in vaccine target discovery and basic vaccine design although further in vitro and in vivo validation studies are still required to test the full efficacy and effects of any vaccine. This vaccine forms the basis for further study towards a vaccine for S. lupi. With the genome of S. lupi now available there is a vast array of potential future research avenues that can be explored. This includes but is not limited to: improved diagnostic tests, drug and vaccine design, investigation of the biology of the parasite such as the molecular machinery involved in its life cycle, migration through the host, reproduction, immunity, disease and identification of cancer-causing agents.