Document Type

Thesis - University Access Only

Award Date

2012

Degree Name

Master of Science (MS)

Department / School

Biology and Microbiology

First Advisor

Michael. B. Hildreth

Abstract

Haemonchus contortus is a ruminate parasite, commonly found in sheep and goat. This parasite is distributed worldwide and is very detrimental to the sheep industry through its ability to cause anemia that can be fatal to the host in severe cases. Broad spectrum anthelminitcs have been used intensely to control this parasite problem. However, due to increased anthelmintic resistance (AR) of H contortus the parasite is becoming harder to control. Furthermore, Haemonchus contortus infections are becoming increasingly more common in the northern latitudes despite their cold weather susceptibility. This thesis focuses on the AR, overwintering strategies, and allele frequency of H contortus in the Northern Great Plains region of the United States. An AR suspected closed farm flock from Brookings County, SD was the focus for this study. Detection of resistance was performed by fecal egg count reduction tests performed over a 4 year span involving three different anthelmintics: Dectomax®, Valbazen® and Cydectin®. Overwintering strategies focused on both free-living third stage juveniles (J3s) and tissue-dwelling fourth stage juveniles (J4s). J3s were assessed trough fecal egg counts (FEC) of narve tracer lambs exposed to a previous year's contaminated pasture of H contortus, whereas J4s were assessed through spring FEC succeeding fall anthelmintic treatment the previous year. Lastly, allele frequency was assessed through gel based allele specific PCR at the ~-tubulin isotype 1 condon 200. The results of these studies showed AR was found in Dectomax® (68.5 % efficacy arithmetic mean [AM] and 80.45% efficacy geometric mean [GM]), marginal resistance was found in Valbazen® (90.65% efficacy AM and 94.68% efficacy GM) and no resistance was found in Cydectin® ( 100% efficacy AM and GM). However, juvenile allele frequency analysis suggests resistance is more severe than initially calculated in benzimidazole (Valbazen®), with resistance around 77.78%. Spring fecals obtained from Valbazen® and Cydectin® trials showed high post-lambing FEC. Valbazen pre-lambing fecals averaged only 4.0 eggs per gram ( epg) AM where post-lambing fecals increased to 454.21 epg AM. Cydectin® treated sheep showed low number of epg 5.96 AM, egg counts only in 2 sheep, compared to the Cydectin® controls epg of 1422 AM. Overwinter pasture exposed narve tracer lambs only averaged 6.57 epg AM whereas drylot control lambs averaged 1. 72 epg AM. These results suggest that drug resistance is evident in Dectomax® and Valbazen®, and yearly transmission of H contortus is predominately through drug-resistant J4s, in this Brookings County flock.

Library of Congress Subject Headings

Haemonchus contortus
Ruminants -- Parasites -- Control -- Great Plains
Anthelmintics

Publisher

South Dakota State University

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Rights Statement

In Copyright