Further potential limitations of the undifferentiated faecal egg count reduction test for the detection of anthelmintic resistance in sheep

Fifteen (36%) of 42 mixed gastro-intestinal nematode infections in sheep, identified as drench-susceptible by the undifferentiated faecal egg count reduction test, were found to harbour anthelmintic-resistant worms when analysed on the basis of changes in the egg counts of individual nematode genera. Most of these cases involved resistance in a single nematode genus, with Ostertagia and Trichostrongylus being implicated most frequently. The possible contributory role of larval culture results in helping to reduce the chances of the faecal egg count reduction test producing these and similar types of errors is discussed.     

Topically applied ivermectin and Cooperia infections in cattle

Extract

I have read with some interest a recent report in this journal⁽¹⁾ that topically applied ivermectin (Ivomec Pour-On, MSD Agvet NZ Ltd) was found to be largely ineffective against Cooperiu infection in cattle.     

Has the optimum time for faecal nematode egg count reduction testing in sheep in New Zealand changed?

Abstract

AIM: To determine what, if any, changes have taken place in the optimum time, for undertaking faecal egg count reduction tests (FECRT) in sheep in New Zealand.

METHODS: A comparison was made between the numbers and types of nematode genera adequately represented for testing purposes (faecal nematode egg count (FEC) of >50 epg) in initial FECRT case submissions to a veterinary laboratory in New Zealand, during two 4-year periods, in 1992–1995 and 2006–2009.

RESULTS: Although there were some minor differences between them, the seasonal patterns of occurrence remained basically the same for all parasite genera in both datasets, with their individual peak periods of representation occurring during February to May in all instances. Not surprisingly, this period of maximum seasonal occurrence for each parasite genus also coincided with those months of the year when the greatest numbers of worm genera were adequately represented for faecal nematode egg count reduction (FECR) testing.

CONCLUSIONS: The results of this study indicate that the optimum time for conducting FECRT in sheep in New Zealand continues to be during the late summer-autumn months of February to May. However, they also reaffirmed that even during this optimal period there are still likely to be many occasions when relatively few nematode genera may be sufficiently well represented for satisfactory FECR testing. Accordingly, veterinary practitioners ought to be aware that, in order to obtain a complete picture of the resistance status of all worm genera on a particular property, such testing may need to be carried out on more than one occasion.     

Oxfendazole resistance in Nematodirus spathiger

The occurrence of anthelmintic resistance in a field strain of Nematodirus spathiger is reported for the first time. In a controlled anthelmintic trial with naturally-acquired infections, oxfendazole at 5 mg/ kg and levamisole at 8 mg/kg were 0 and 86% effective respectively, against this strain.     

Persistent anthelmintic activity of topically administered ivermectin in cattle

The persistent anthelmintic effect of ivermectin as a topical treatment at 500 microg/kg was evaluated against induced infections of Ostertagia ostertagi, Trichostrongylus axei and Dictyocaulus vivparus in calves. The results showed a highly significant (P<0.001) anthelmintic activity for at least 14 days against O. ostertagi and T.axei (>99 per cent efficacies) and for at least 28 days (98 per cent efficacy) against D. viviparus.     

Evaluation of von Willebrand Factor During Pregnancy,Lactation and Oestrous Cycle in Bitches Affected and Unaffected by von Willebrand Disease

Plasmatic concentrations of von Willebrand Factor (vWF) increase during pregnancy in humans and dogs; however the mechanism of such increase is still not well defined. The aims of this study were: (i) to evaluate changes in vWF concentration during pregnancy and during the subsequent oestrous cycle in bitches affected and unaffected by von Willebrand Disease (vWD); (ii) to correlate the vWF levels and cortisol levels in both groups. Seven vWD affected (GI) and nine unaffected (GII) bitches were used. The animals were assessed during pregnancy, parturition, lactation and non‐gestational oestrous cycle in 11 moments (Pregnancy 1, Pregnancy 2, Parturition, Lactation 1, Lactation 2, Lactation 3, Anestrus, Proestrus, Oestrus, Diestrus 1, and Diestrus 2). The following tests were performed; measurement of von Willebrand factor antigen (vWF:Ag), albumin and cortisol. In both groups, vWF concentration remained stable during the non‐gestational oestrous cycle, but increased during pregnancy, with the highest value observed at parturition. Increases of 70% and 124% in vWF were seen in GI and GII, respectively, compared to anestrus. No correlation was found between vWF and cortisol. Values of vWF:Ag changed during pregnancy, with a peak at parturition, both in vWD affected and unaffected animals. Values of vWF were not altered in the different phases of the oestrous cycle following pregnancy in both groups. Evaluation of vWF during pregnancy can cause false negative results for vWD, but assessment can be performed at any point in the oestrous cycle of non‐pregnant bitches.