Persistence of dead Ostertagia ostertagi in the abomasal mucosa following anthelmintic treatment

Abstract

Anthelmintic trails, conducted with albendazole, fenbendazole and ivermectin for efficacy against gastrointestinal nematodes, principally inhibited early fourth larval stages of Ostertagia ostertagi in naturally infected cattle. Cattle wee slaughtered seven to 20 days after treatment. O ostertagi was the predominant abomasal nematode recovered with occasional small numbers of Haemonchus species and Trichostrongylus axei. Control calves uniformly had very large O ostertagi infections, primarily early fourth stage larvae. Viable surviving worms and variable numbers of dead and degenerate worms were recovered in abomasal contents and washings. These O ostertagi larvae and adults were characterised by adherent debris or proteinaceous material, degenerated cuticles and distortion of internal structures. This study demonstrated the necessity for proper timing of slaughter for anthelmintic trial evaluation to allow clearance of dead nematodes, specifically O ostertagi larvae which are sequestered in the abomasal glandular tissue. Nematode collection within seven to 12 days after treatment will include dead and degenerate larval nematodes. The peripheral coating of larvae was suggestive of the Splendore-Hoeppli effect which has been associated with immunological responsiveness. The antigenic stimulus for this material and the lymphocyte and eosinophil infiltration was suspected to be early fourth stage O ostertagi larvae within the mucosa but was not identified definitively.

Mucocutaneous Splendore‐Hoeppli phenomenon

“…Clinically, the lesions may present as purpuric eruptions or linear streaks associated with cutaneous invasion by the larvae. The histological diagnosis is based on the identification of the cross and oblique sections of S. stercoralis in the dermis associated with RBCs extravasation and occasional Splendore‐Hoeppli reaction 58,59 …”

Unexpected Decrease in Milk Production after Fenbendazole Treatment of Dairy Cows during Early Grazing Season

“…(i) In yearling beef cattle naturally infected with O . ostertagi , treated with fenbendazole while a large number of early fourth stage inhibited larvae had been established, and then slaughtered 7 to 12 days after treatment, Snider III et al (1985) [ 62 ] observed an aggravation of the abomasal inflammatory lesions compared to those found in untreated calves. This aggravation was related to the persistence of dead and degenerate O .…”

“…Indeed, these degenerate larvae were not observed in the tissues of untreated calves nor in calves treated with ivermectin, and were thus attributed to the fenbendazole treatment. Histologically, the presence of a marked eosinophil and lymphocyte infiltration and of an unidentified material coating the degenerate larvae suggested an inflammatory and/or immunological response initiated or exacerbated by the presence of such larvae [ 62 ]. (ii) Similar results were found in horses naturally infected with cyathostomins and treated either with fenbendazole or moxidectin [ 63 ]: in contrast to moxidectin effects, the killing of larvae due to fenbendazole treatment was associated with severe tissue damage.…”

“…However, considering the persistence of the negative effect of treatment on MP, one may wonder what the duration of the pro-inflammatory effect of dead larvae is. Snider III et al (1985) [ 62 ] indicated that these degenerate Ostertagia larvae were found up to 20 days after treatment, but in smaller proportion than between 7 to 12 days after treatment, and that the time needed for dead nematode clearance is unknown for O . ostertagi and other GIN.…”