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Biomedical subjects

P B McKenna

Publications and source records attributed to P B McKenna.

At least 19 recordsLinked to original sources
PubMed2006

Resistance to a triple combination of broad-spectrum anthelmintics in naturally-acquired Ostertagia circumcincta infections in sheep.

AIM: To measure the efficacy of two macrocyclic lactone-levamisole-benzimidazole combination drenches against naturally-acquired abomasal nematode infections on a sheep farm in the North Island, New Zealand. METHODS: Eighteen lambs carrying naturally-acquired worm burdens were removed from pasture and randomly allocated to one of three equal-sized groups, consisting of an untreated control group and two treatment groups. One treatment group was given a single oral dose of a triple-combination anthelmintic administered at the manufacturer's recommended dose rate of 0.2 mg/kg ivermectin, 7.5 mg/kg levamisole and 5.0 mg/kg albendazole. The other treatment group received a similar dose of another triple-combination drench consisting of 0.2 mg/kg abamectin, 8.0 mg/kg levamisole and 4.5 mg/kg oxfendazole. Worm counts were carried out post mortem on the abomasa of all animals in all groups, 10 days after treatment. RESULTS: While the abamectin-levamisole-oxfendazole combination was highly effective against all three abomasal nematode species present, the ivermectin-levamisole-albendazole combination was not. In the latter instance, a reduction of only 78% was achieved against infections of Ostertagia (=Teladorsagia) circumcincta. CONCLUSIONS: These results provide evidence of resistance to an ivermectin-levamisole-albendazole combination drench by O. circumcincta. CLINICAL RELEVANCE: Besides representing the first confirmed report of resistance to a combination drench consisting of three broad-spectrum anthelmintics, the present results provide further evidence of the continuing escalation of multiple anthelmintic resistance in sheep nematodes in New Zealand.

Albendazole↗
PubMed2006

Further comparison of faecal egg count reduction test procedures: sensitivity and specificity.

In a recent communication (McKenna 2006), a comparison was made between four different methods for calculating results from faecal egg count reduction (FECR) tests (FECRTs). The first and most complex of these, referred to as FECRT1, involved the use of the formula: FECR = 100 x (1-[T2/T1][C1/C2]), where T1 and T2 represented the mean pre- and post-treatment faecal nematode egg counts (FECs) of a treated group, and C1 and C2 represented the mean pre- and post-treatment FECs of an untreated control group, respectively. The other three formulae consisted of more simplified versions of this procedure. In one of them (FECRT2), only post-treatment samples were considered, whereas the other two were based on comparisons between the FECs of groups of animals sampled at the time of anthelmintic treatment (pre-treatment) with those sampled several days later (post-treatment). Thus, FECRT2 was determined according to the formula: FECR = 100 x (1-[T2/C2]), while FECRT3 was calculated from FECR = 100 x (1-[T2/T1]). The fourth procedure (FECRT4) was based on a further simplification of FECRT3, where pre-treatment FECs from only one treatment group were used for comparison with all post-treatment results. This base-line pre-treatment group thus effectively functioned as an untreated control group and hence the formula for FECRT4 was FECR = 100 x (1-[T2/C1]). The study was based on an analysis of 210 previously published FECRTs performed in sheep or goats. In each case, FECRs were calculated using all four of these FECRT formulae, and their results compared. The results of these comparisons indicated that the use of any one of them was likely to result in similar estimates of anthelmintic efficacy and the detection of comparable numbers of cases of anthelmintic resistance continued.

Animals↗
PubMed2005

A survey of the prevalence of emerging macrocyclic lactone resistance and of benzimidazole resistance in sheep nematodes in the lower North Island of New Zealand.

AIM: To investigate the occurrence of emerging macrocyclic lactone (ML) resistance and of resistance to benzimidazole anthelmintics on a number of sheep farms in the North Island of New Zealand. METHODS: On commercial sheep farms (n=30) in the Taihape district in the North Island of New Zealand, 30 animals were randomly allocated to one of two equal-sized groups and treated with either half of the recommended dose rate of ivermectin (half of 0.2 mg/kg), or with the full recommended dose rate of oxfendazole (4.5 mg/kg). The ivermectin treatment only was used on a further six properties. Faecal egg counts, accompanied by pooled larval cultures, were conducted on all samples at the time of treatment and 7-10 days later. RESULTS: Resistance, as indicated by a <95% faecal egg count reduction (FECR) in both instances, was found to oxfendazole on 13/30 (43%) farms and to a half dose of ivermectin on 12/36 (33%) properties. For oxfendazole, such resistance was found to involve all six nematode genera whereas for ivermectin it was almost entirely restricted to Ostertagia and Cooperia infections. CONCLUSIONS: These results indicate that emerging ML resistance may be more common on sheep farms in New Zealand than is generally realised. They also suggest that the half-dose ivermectin faecal egg count reduction test (FECRT) may offer some very practical benefits for parasite control by providing early warning of developing resistance to ML drenches and by signalling the possible imminent failure of these at their therapeutic dose rates. The sensitivity and reliability of this procedure may be further enhanced by the inclusion of larval cultures.

Administration, Oral↗
PubMed2005

Libyostrongylus infections in ostriches--a brief review with particular reference to their detection in New Zealand.

Following the recent discovery of Libyostrongylus douglassii in ostriches in New Zealand, information relating to this nematode is reviewed. Amongst some of the topics considered are the parasite's distribution and prevalence, its life cycle and survival, and its diagnosis and control. Of particular interest from a New Zealand perspective is the potential for the parasite to infect other ratites, especially the kiwi. While the current evidence suggests that this may be unlikely to occur, the possibility that it might be able to do so cannot be ruled out entirely.

Animals↗
PubMed2005

Confirmation of resistance to ivermectin by Cooperia curticei in sheep.

AIM: To investigate the occurrence of resistance to a full dose of oral ivermectin by Cooperia curticei in sheep. METHODS: Twelve lambs on a sheep and cattle property in the North Island of New Zealand were randomly allocated to one of two equal-sized groups. One group was treated orally with a single dose of ivermectin at the manufacturer's recommended dose rate of 0.2 mg/kg, while the other remained as an untreated control. Worm counts were carried out post mortem on the abomasa and small intestines of all animals in both groups 7 days after treatment. RESULTS: While treatment with ivermectin reduced the numbers of all other worm genera to almost zero, those of Ostertagia(= Telodorsagia) circumcincta and C. curticei were reduced by only 37% and 19%, respectively. CONCLUSIONS: These results provide clear evidence of resistance to ivermectin by O. circumcincta and C. curticei. They also appear to represent the first record of macrocylic lactone (ML) resistance in C. curticei in sheep in New Zealand or elsewhere.

Abomasum↗
PubMed2004

Resistance to moxidectin and abamectin in naturally acquired Ostertagia circumcincta infections in sheep.

AIM: To investigate the occurrence of resistance to macrocyclic lactone (ML) anthelmintics by Ostertagia circumcincta in lambs on a sheep and cattle property in the North Island of New Zealand. METHODS: Thirty lambs were randomly allocated to one of five equal-sized groups, consisting of an untreated control and four treatment groups. The treatments, which were administered at the manufacturer's recommended dose rates, included oral moxidectin, oral abamectin (both at 0.2 mg/kg), an albendazole-levamisole combination, and an albendazole-levamisole-ivermectin combination. Post mortem worm counts were undertaken 7 days after treatment to determine the efficacy of each anthelmintic. RESULTS: The albendazole-levamisole and albendazole-levamisole-ivermectin combinations both reduced O. circumcincta burdens to zero whereas for moxidectin and abamectin efficacies of only 72% and 29%, respectively, were recorded. CONCLUSIONS: These results clearly demonstrated the occurrence of resistance to MLs by O. circumcincta. Although this is not the first occasion where resistance to this anthelmintic family has been detected in this parasite in sheep in New Zealand, it is the first instance that resistance to either moxidectin or abamectin has been reported.

Journal Article↗
PubMed2003

Probable multigeneric resistance to macrocyclic lactone anthelmintics in cattle in New Zealand.

AIM: To establish the efficacy of topical formulations of eprinomectin and abamectin against naturally acquired abomasal and small intestinal nematode infections in cattle purchased from a North Island bull-beef property. METHODS: A controlled slaughter trial, involving eighteen 6-8-month-old mixed breed calves, was conducted in May 2002.The animals were randomly allocated on the basis of faecal egg count to one of three equal-sized groups (n=6), consisting of an untreated control group and two treatment groups. One of the treatment groups was treated with a topical formulation of eprinomectin, the other with abamectin. Both anthelmintics were administered as a single topical treatment on an individual liveweight basis, at the manufacturer's recommended dose rates of 0.5 mg/kg. All calves were housed in separate groups with no access to pasture throughout the entire trial and were slaughtered 7-10 days after treatment. RESULTS: Both anthelmintic treatments were highly effective(worm count reduction >98%) against Ostertagia ostertagi, Trichostrongylus axei and Cooperia punctata, but were not effective at reducing worm counts significantly of either Cooperia oncophora or Trichostrongylus longispicularis. Against these latter two parasites, worm count reductions of only 72% and 79%, and 81% and 76%, respectively, were recorded following treatment with eprinomectin or abamectin, respectively (all p>0.05). CONCLUSIONS: These results demonstrate evidence of resistance to macrocyclic lactone anthelmintics by C. oncophora and probably T. longispicularis also. CLINICAL RELEVANCE: As well as perhaps providing the first record of resistance to any anthelmintic by T. longispicularis, the present findings may also represent the first case of resistance to macrocyclic lactone anthelmintics exhibited by more than one parasite species at a time in cattle in New Zealand.

Journal Article↗
PubMed2002

Nematodes and liver fluke in New Zealand.

A general review of the epidemiology, significance and control of nematode parasitism of sheep, goats, cattle and deer in New Zealand, the emergence of anthelmintic resistance and its effects, and the search for parasite control strategies that reduce reliance on anthelmintic use, is provided. The research that has formed the basis for present levels of understanding of this complex and important topic is summarised and sources of further information are indicated. Aspects of nematode infections of horses, pigs, dogs and cats, and the history of the liver fluke, Fasciola hepatica, in New Zealand are also reviewed briefly.

Journal Article↗
PubMed2001

Resistance to macrocyclic lactone anthelmintics by Haemonchus contortus and Ostertagia circumcincta in sheep in New Zealand.

AIM: To establish the efficacy of oral formulations of ivermectin and moxidectin against naturally acquired abomasal nematode infections on a North Island sheep farm. METHODS: Two controlled slaughter trials were undertaken. In the first, 30 sheep on pasture were randomly allocated on the basis of faecal egg count to 1 of 3 groups, comprising an untreated control group and 2 treatment groups. One treatment group was given a single oral dose of ivermectin and the other a single oral dose of moxidectin, both at the manufacturer's recommended dose rates of 0.2 mg/kg liveweight. Six days after treatment, all animals were slaughtered and their abomasa recovered for worm counting. The second trial, which involved 47 animals, was essentially the same as the first except that, as well as involving the slaughter of 30 sheep from all 3 groups, 6 days after treatment, it also included a further 8 untreated control animals and 9 moxidectin treated animals which were slaughtered 27 days after treatment. RESULTS: At 6 days after treatment, moxidectin was highly effective against all 3 of the abomasal nematodes present. While ivermectin was similarly effective against Trichostrongylus axei 6 days after treatment, it was not effective against either Ostertagia circumcinta or Haemonchus contortus, against which average efficacies of only 63.6% and 61.6%, respectively, were recorded. At 27 days after treatment, moxidectin, was also highly effective against T. axei (97.3% reduction) but not against either H. contortus (71.4% reduction) or O. circumcinta (61.0% reduction). CONCLUSIONS: These results provide the first record of macrocyclic lactone resistance in H. contortus in sheep or in any other host in New Zealand, and the first case where such resistance has been exhibited in more than one parasite species at a time. Although the therapeutic efficacy of moxidectin was high against these resistant H. contortus and O. circumcincta strains, resistance to moxidectin was indicated by its diminished prophylactic activity against them. It is suggested that this reduction in the prophylactic activity of moxidectin is also likely to reduce its apparent current high therapeutic efficacy. CLINICAL RELEVANCE: As well as providing further evidence that it can no longer be automatically assumed that macrocylic lactone anthelmintics will be effective on sheep farms in this country, these findings also present a warning that increasingly complex parasite control options may have to be faced in the future.

Journal Article↗
PubMed1999

Comparative evaluation of two emigration/sedimentation techniques for the recovery of dictyocaulid and protostrongylid larvae from faeces.

A comparison between the performance of a flask and a funnel method in recovering dictyocaulid and protostrongylid larvae from faeces revealed the clear superiority of the former. On an average, 137% (p<0.01) more Dictyocaulus viviparus, 175% (p<0.05) more Muellerius capillaris and 1709% (p < 0.01) more Elaphostrongylus cervi larvae were recovered from samples processed by flask rather than funnel. Attempts to further improve the flask method by substituting cloth stockinette for paper tissue, tended to result in the recovery of more faecal debris but no more larvae. In addition to its greater sensitivity, it is suggested that the flask method offers advantages over the funnel system both in terms of time-saving and in lessening the likelihood of cross-contamination.

Animals↗
PubMed1998

The effect of previous cold storage on the subsequent recovery of infective third stage nematode larvae from sheep faeces.

An investigation undertaken to determine the effect of previous cold storage on the recovery of third stage larvae of gastrointestinal nematodes of sheep, showed that increasing periods of exposure of faeces to 4 degrees C resulted in decreasing numbers of larvae subsequently recovered from them. Differences in the abilities of the eggs of the various genera, to survive such treatment, were found to lead to significant changes in the percentage generic compositions of their third stage larvae--in some cases following the prior refrigeration of faecal samples for as little as 24 h. These results suggest that where larval cultures are intended to provide estimates of the proportions of the various worm eggs in the faeces of sheep harboring mixed gastrointestinal nematode burdens, they should be performed only on freshly collected samples.

Animals↗