Transcriptomic Analysis of Peripheral Blood Mononuclear Cells During Ostertagia ostertagi Infection in Cattle Highlights a Generalized Host Immune Reaction

One of the most concerning ruminant infections is the parasite <i>Ostertagia ostertagi</i>. Known commonly as the brown stomach worm, it is ingested by grazing cattle where it then progresses its life stages, occupying the host abomasum and then the intestine, causing illness. This results in lower commercial production and at worst, death of young calves. Over time, anthelmintic treatment has become less efficacious against cattle nematodes. As a result, alternative control strategies are needed. Our study looked to elucidate mechanisms underlying attenuation of the host immune response by examining global immune expression in cattle during infection. To this end, four steers were infected with the third stage larvae (L3) of <i>O. ostertagi</i>, then peripheral blood mononuclear cells (PBMCs) were collected weekly for 26 days post-infection (dpi). After sequencing, gene expression was compared between each timepoint. The analyses indicated that the immune responses to <i>Ostertagia</i> are targeted to the parasite's life stages and mimics anti-viral gene expression. Overall, the results showed that <i>O. ostertagi</i> led to host immune responses characterized by multiple gene ontology and pathway terms indicating that by 26 dpi the host immune system transitions from fighting the parasite to repairing the host intestine.