Histopathological abomasal lesions in different ruminant species induced by Haemonchus contortus

Haemonchus contortus is a highly pathogenic gastrointestinal nematode of ruminants, yet data on abomasal histopathology particularly for large ruminants remain limited. This study investigated abomasal histopathological lesions associated with natural H. contortus infection in sheep, goats, cattle and water buffaloes in Greece. A total of 2,134 abomasa were examined post-mortem and 200 H. contortus -infected abomasa (50 per species), along with non-infected controls, were selected for detailed histopathological evaluation. Total adult H. contortus counts were quantified. Inflammatory cell infiltration of the lamina propria was the most prevalent lesion across all species and showed a strong association with presence of H. contortus and parasite counts. Buffaloes and cattle exhibited significantly higher H. contortus infection than sheep and goats and developed more pronounced inflammatory infiltration, mucus cell hyperplasia and parietal cell decrease. In contrast, small ruminants displayed marked inflammatory responses despite lower parasite counts. Epithelial erosion was frequently observed but was not consistently associated with infection, indicating limited diagnostic specificity. Across all species, H. contortus infection was associated with a significant reduction in abomasal content volume, reflecting functional impairment of the abomasum. These findings demonstrate that while the qualitative pattern of abomasal lesions induced by H. contortus is broadly conserved among ruminants, lesion severity and diagnostic relevance vary according to host species and parasite load.