Specific IgA antibody has been shown to play an important role in resistance to gastrointestinal nematode (GIN) infections in sheep, particularly in Teladorsagia circumcincta parasitosis. In some breeds, negative associations have been shown between IgA levels and worm burden in experimentally infected sheep. In the present study, we have studied the relationship between IgA levels in naturally infected sheep (582 ewes in total; 193 younger than one year old and 389 older than one year old) and fecal egg count (FEC) in the Assaf, Castellana, and Churra breeds. ELISA assays were performed to measure IgA levels against the somatic antigen of T. circumcincta third larval stage (L₃) and a 203-amino-acid fragment of the protein disulfide isomerase from the same GIN species. A multilevel random intercept model was developed to predict the infection risk according to age or breed. Spearman’s correlation rank was used for statistical analysis. The prediction model showed that breed was not an influential factor in this study, although the Assaf breed could be considered slightly more susceptible than the others. In addition, age affected the infection risk, with the young ewes more susceptible to infection than the adult groups, except for the Castellana breed, whose risk of infection was similar at all ages. The most significant positive association was found between FEC and IgA measured in the nasal secretions of young ewes using both antigens (Rho = 0.5; p = 0.00); the correlation of FEC with IgA in serum was moderately significant (Rho = 0.306; p = 0.00). Comparing both antigens, the protein disulfide isomerase antigen was less reactive than the somatic antigen from L₃. In conclusion, under natural conditions, specific IgA against GIN was positively associated with FEC in sheep, with nasal secretions from young animals being the sample where this association is stronger, which, therefore, could be used as a marker of infection in further studies.

Gastrointestinal nematode infections (GINs) in ruminants are a major constraint to efficient livestock production worldwide. Currently, only a limited number of anthelmintic drugs are available for the control of these infections, but their widespread use in preventive deworming campaigns and the incorrect administration of the drugs are responsible for the emergence of resistance. Therefore, new anthelmintic drugs are urgently needed. However, drug discovery methods for new anthelmintics based on GINs isolated from ruminants often have low throughput. In this study, a screening of five commercial collections of chemical compounds, including one collection of anti-infective drugs, three plant-based natural product collections, and one collection from the FDA-approved Chinese Pharmacopoeia, with a total of 2228 molecules, have been carried out in a high-throughput format. In the single slot screen, 32 compounds (1.44% success rate) achieved a >70% motility inhibition rate. Of these, 10 are known anthelmintic drugs, while the remaining 22 were tested against Haemonchus contortus and a resistant strain of Teladorsagia circumcincta. Four compounds (two flavonoids, chalcone and trans-chalcone), and two anti-infectives (octenidine and tolfenpyrad), showed anthelmintic activity with EC₅₀ values below 20 µM, and were further tested for their safety against HepG2 spheroids and mouse intestinal organoids. Trans-chalcone and chalcone emerged as promising candidates for future development, showing selective indexes > 5, while tolfenpyrad and octenidine require careful evaluation due to their toxicity profiles.

Fasciola infection, which is widely distributed and has a major impact on livestock production, is emerging as a significant zoonotic parasitic disease affecting both human and animal health worldwide. The main control strategy currently relies on a limited number of anthelmintic drugs, especially benzimidazoles such as albendazole and triclabendazole. The aim of this study was to evaluate the efficacy of albendazole and triclabendazole in a sheep flock in northwestern Spain naturally infected with F. hepatica and to test fenbendazole and oxfendazole as alternative formulations. For this purpose, a faecal egg count reduction test (FECRT) was conducted applying various statistical methods based on the guidelines used for gastrointestinal nematodes. This study represents the first application of the new classification framework for F. hepatica, emphasizing the urgent need for standardized resistance detection protocols for this parasite and underlining the growing challenge of anthelmintic resistance in the treatment of fasciolosis.