The significance of parasitic gastrointestinal nematodes (GIN) contribute large production and economic losses in livestock industries. Teladorsagia spp. and Trichostrongylus spp. are of great veterinary and medical significance in ruminant animals, particularly sheep. These species pose large threats to the wool and meat industry, and have demonstrated to be prevalent year round in Australian sheep species. Sheep become infected via ingestion of larvae in their infective stage (L3) from infected faecal matter when grazing. After infection, Teladorsagia spp. cause anorexia, diarrhoea, intermandibular oedema (bottle jaw), and weight loss; Trichostrongylus causes generalised enteritis including watery diarrhoea, which stains the rear fleece of the sheep (black scours), subsequent anaemia and weight loss. Sudden death of infected animals, particularly younger and older, is not uncommon. Means of parasitic management largely entail reducing the quantity of larvae residing within the pasture and soil of grazing animals through the use of anthelmintics such as benzimidazoles (BZ) and Levamisole (LEV). Drug- resistance to these methods is frequent and in vivo/in vitro monitoring techniques are innefficient and poorly utilised. Due to the high costs associated with the use of these control measures, resistance to these chemicals are greatly impacting the financial productivity of the sheep and wool industry. A report released by Meat and Livestock Australia (MLA) has estimated that the cost of internal parasites in the Australian sheep industry is $369m per annum, indicative of the great impact that GINs have on the industry.
Recent revelations in identifying resistance markers in nematode species, in particular, Haemonchus contortus (H. contortus) and adopting the use of PCR assays in order to identify whether sampled larvae carry the resistance to BZ and LEV have been effective. Hence, this project aims to expand upon previous research to enable this detection in other nematode species, such as Teladorsagia spp. and Trichonstrongylus spp. If this is successful, this will enable NSW-wide screening for the frequency of BZ and LEV resistance in an additional two species of parasitic GINs – generating an inclusive test for the top three most prevalent and troublesome parasites in the sheep and wool industry. This will better enable guidance for the appropriate use of these anthelmintic drugs and which will remain most effective to use.
Overall, this project will provide valuable insights into the resistance of Trichostrongylus spp. and Teladorsagia spp. resistance to specific anthelmintic drugs. In turn, targeted treatment approaches will impair the effects of these parasites on the Australian sheep industry.
This project is laboratory-based at the University of Sydney. Larval samples will be provided by the NSW department of Primary Industries (DPI), who have obtained larval samples from across NSW, providing a large GIN sample collection and allowing analysis of different affected populations. There is currently an MTA in place between the University of Sydney and NSW DPI. An initial set of 100 samples from across NSW will be used in my Honours project as a proof of principal study that gives sufficient power in our detection of resistance/susceptible frequencies.
We will use previous research studies (1) as a basis and conduct assay alteration in order to better suit Trichostrongylus spp. and Teladorsagia spp. in order to expand the capabilities of this newfounded assay. Development of primers to amplify the region displaying the marker for resistance in these species is required, however, deep-sequencing this region using metabarcoding as seen in (1) for LEV and BZ resistant SNPs is promising.
All resources are available in the parasitology lab at the University of Sydney.
1) Francis, E.K. et al. (2023) ‘A mixed amplicon metabarcoding and sequencing approach for surveillance of drug resistance to levamisole and benzimidazole in Haemonchus spp..’, International Journal for Parasitology [Preprint]. doi:10.1016/j.ijpara.2023.07.002.
The Australian sheep and wool industry is a great contributor to Australia’s national economy, through textile and live-trade exports. With Australian sheep farmers acquainted with the many diseases that these parasites cause, and the effect this has on the productivity, welfare, and quality of products from the industry. A deeper understanding of the survival mechanisms, resistance factors and management strategies will allow for an adaptive future in the sheep and wool industry. With an increase in anthelmintic drug resistance in GINs, alternate methods of control and management must be developed in order to protect the industry standards being upheld in Australia, which opens pathways to future research into GIN control mechanisms. Future opportunities will inevitably arise through continued research into these parasites, opening doors for alternate methods of control to be investigated.