Getting around the roundworms: Identifying knowledge gaps and research priorities for the ascarids

Abstract

The ascarids are a large group of parasitic nematodes that infect a wide range of animal species. In humans, they cause neglected diseases of poverty; many animal parasites also cause zoonotic infections in people. Control measures include hygiene and anthelmintic treatments, but they are not always appropriate or effective and this creates a continuing need to search for better ways to reduce the human, welfare and economic costs of these infections. To this end, Le Studium Institute of Advanced Studies organized a two-day conference to identify major gaps in our understanding of ascarid parasites with a view to setting research priorities that would allow for improved control. The participants identified several key areas for future focus, comprising of advances in genomic analysis and the use of model organisms, especially Caenorhabditis elegans, a more thorough appreciation of the complexity of host-parasite (and parasite-parasite) communications, a search for novel anthelmintic drugs and the development of effective vaccines. The participants agreed to try and maintain informal links in the future that could form the basis for collaborative projects, and to co-operate to organize future meetings and workshops to promote ascarid research.

Keywords: Disease prevention; Genomics; Host-parasite interactions; Nematode; Zoonosis.

Fig. 1

Live Ascaris suum collected from the packing plant.

Fig. 2

(A) Transverse section of female Ascaris suum in the anterior region of the worm. I: intestine of the worm. Cn: Canaliculi – canals for perienteric fluid. B: Bag region of the muscle cell. A: arm region of the muscle cells. S: spindle region of the muscle cells. L: lateral line. DN: Dorsal nerve cord. VN: Ventral region of the nerve cord. C: Cuticle. H: Hypodermis. (B) Whole mount preparation of the Ascaris intestine stained with the calcium dye, Fluo-3 for detection of calcium responses to anthelmintics. Notice that some of the cells (enterocytes) of the intestine are raised into folds that form towers or columns. Both panels modified from McHugh, M., Williams, P., Verma, S., Powell-Coffman, J.A., Robertson, A.P., Martin R.J., 2020. Cholinergic receptors on intestine cells of Ascaris suum and activation of nAChRs by levamisole. Int. J. Parasitol. Drugs Drug. Resist. 13, 38–50, under Creative Commons CC-BY-NC-ND.

Fig. 3

Overview of host environmental interactions of Ascaris. Ascaris shows a complex life cycle in which they encounter different environmental challenges. These multilateral interactions include the interwork with the bacterial gut microbiota, the confrontation with host immune and non-immune cells, direct and indirect exploitation of host nutrients and interspecies communication. Reactive elements mediating these interactions are excretory/secretory products of the worms as well as extracellular vesicles and worm metabolites.

Fig. 4

Genetic material lost during PDE. A linear presentation of Ascaris germline chromosomes. All chromosome ends and 12 internal regions are eliminated (shown in red). Many larger chromosomes have internally eliminated sequences which split them into smaller chromosomes in the soma. Eliminated regions containing 121-bp repeats are marked with a red asterisk. Modified from Estrem, B., Wang, J., 2023. Programmed DNA elimination in the parasitic nematode Ascaris. PLoS Pathog. 19, e1011087 under Creative Commons CC-BY.