The Ever-changing Battle against Haemonchosis: Epidemiology, Diagnosis and Control Strategies: A Review

Haemonchosis, caused by the hematophagous nematode Haemonchus contortus, remains a major challenge to ruminant health and production worldwide. This review explores the epidemiology, diagnosis and control strategies for haemonchosis, emphasizing the growing threat of anthelmintic resistance. The parasite thrives in warm, humid climates, with transmission dynamics significantly influenced by regional environmental conditions. Epidemiological investigations, including tracer animal studies, fecal sample analyses and slaughterhouse surveys, provide crucial insights into parasite burden and infection trends. However, seasonal variations and host immunity complicate accurate assessments. Climate plays a pivotal role in the persistence and transmission of H. contortus. In tropical and subtropical regions, continuous parasite transmission occurs, whereas hypobiosis ensures survival in harsh climates. Understanding these regional infection patterns aids in designing effective parasite control programs. The increasing prevalence of anthelmintic resistance, characterized by genetic mutations in β-tubulin, nicotinic acetylcholine receptors and glutamate-gated chloride channels, necessitates alternative control measures. The failure of benzimidazoles, imidazothiazoles and macrocyclic lactones due to resistance highlights the urgency of sustainable strategies, including targeted selective treatment, pasture management and genetic selection for parasite-resistant breeds. Advancements in diagnostic methodologies, such as molecular techniques (PCR, LAMP) and immunodiagnostics, have enhanced the precision of haemonchosis detection. Traditional approaches, including fecal egg count, hematological parameters and post-mortem findings, remain valuable but require integration with modern diagnostics for improved accuracy. This review underscores the need for a multifaceted approach combining epidemiological surveillance, innovative diagnostics and integrated parasite management strategies to mitigate the economic and health impacts of haemonchosis in grazing ruminants.