Pathological characteristics of Linguatula serrata (aberrant arthropod) infestation in sheep and factors associated with prevalence in Iran.

Linguatula serrata is a cosmopolitan zoonotic parasite in which carnivores and herbivores serve as final and intermediate hosts, respectively. The aim of this study was to compare the L. serrata nymphal infection rate and intensity of infection (mean number of nymphs ± standard error) to the appearance and pathological changes of mesenteric lymph nodes (MLNs) infected with L. serrata using sheep slaughtered in Tabriz, Iran. In addition, the effect of age, sex, and season on the prevalence of L. serrata infection was evaluated. For this purpose, over a four-year period, 31,078 MLNs from 3199 sheep were examined, with 4972 (15.99%) MLNs infected representing 518 (16.20%) sheep. Collected MLNs were categorized by color as normal, red or black and by consistency as normal, soft or hard. L. serrata were found in 8.88% of normal-colored MLNs, 14.45% of red (hemorrhagic) MLNs and 44.57% of black-colored MLNs, with the difference being significant for infection and infection intensity (P < 0.0001). In regards to MLN consistency, 7.98% of normal, 31.52% of soft and 5.42% of hard lymph nodes were found to be infected with the infection rate and intensity in soft nodes being significantly different (P < 0.0001). Pathological changes in MLNs infected with L. serrata nymph with normal color and consistency had calcification of the L. serrata nymph, granulomatous inflammation around the nymph and some neutrophils. Granulomatous inflammation around the L. serrata nymph, haemosiderophage, macrophage and lymph node depletion from lymphocytes were observed in MLNs infected with L. serrata nymph with soft consistency. In addition, MLNs infected with L. serrata nymph with hard consistency and black color contained neutrophils in the capsule's wall, caseous necrotic mass and L. serrata surrounded by a thick capsule. In regards to prevalence, age, sex and season (autumn) were significant (P < 0.0001, P < 0.01, respectively). These study results suggest that targeted meat inspection and targeted animal interventions could be used to decrease human exposure to L. serrata and animal infection.