Field evaluation of anticoccidial efficacy: A novel approach demonstrates reduced efficacy of toltrazuril against ovine Eimeria spp. in Norway

Odden, Ane; Denwood, Matthew; Stuen, Snorre; Robertson, Lucy J.; Ruiz, Antonio; Hamnes, Inger Sofie; Hektoen, L.; Enemark, Heidi L.

doi:10.1016/j.ijpddr.2018.05.002

Cited by 27 publications

(31 citation statements)

References 62 publications

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“…The field isolate of Eimeria spp. was obtained from one of the flocks (ID 35) participating in the recent FOCRT study [6]. According to the FOCRT results, toltrazuril had reduced efficacy against Eimeria in two flocks.…”

Section: Field Isolate Of Eimeriamentioning

confidence: 99%

“…However, neither of these flocks were available for the CET, due to geographical and practical reasons. Thus, treatment with toltrazuril in the selected flock had been found to have an efficacy of 56.0%, but the results were classified as inconclusive, due to the wide 95% confidence interval (CI) of -433.9 and 96.6% [6].…”

Section: Field Isolate Of Eimeriamentioning

confidence: 99%

“…Anticoccidial resistance (ACR), which develops mainly as a result of intensive long-term use of anticoccidial drugs, occurs widely in poultry production and has also been identified in Cystoisospora suis in piglets [1][2][3][4][5]. In addition, a field method for the evaluation of reduced anticoccidial efficacy (ACE) in ovine Eimeria spp., the faecal oocyst count reduction test (FOCRT), has recently been developed and indicated that the efficacy of toltrazuril is reduced in some Norwegian sheep flocks [6].…”

Section: Introductionmentioning

confidence: 99%

“…The World Association for the Advancement of Veterinary Parasitology guidelines for evaluation of ACE in mammals [25], states that there is a need for verified methods for evaluation of ACE. Field methods for assessment of drug efficacy, such as the FOCRT [6] and the faecal egg count reduction test used to evaluate anthelmintic efficacy [26], give only an indication of reduced efficacy, and need verification through controlled efficacy trials (CET) [27,28]. In addition, due to the variation in pathogenicity between ovine Eimeria spp., the differentiation of species should be considered separately [25].…”

Section: Introductionmentioning

confidence: 99%

“…The aim of the present study was to perform a CET in order to determine whether different species in a field isolate of ovine Eimeria spp. with suspected ACR, based on the FOCRT [6], actually demonstrated resistance to toltrazuril.…”

Section: Introductionmentioning

confidence: 99%

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Controlled efficacy trial confirming toltrazuril resistance in a field isolate of ovine Eimeria spp.

et al. 2018

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BackgroundCoccidiosis due to Eimeria spp. infections in lambs causes increased mortality and substantial production losses, and anticoccidials are important for control of the infection. Anticoccidial resistance has been reported in poultry and swine, and we recently described reduced toltrazuril efficacy in ovine Eimeria spp. in some Norwegian sheep farms using a newly developed faecal oocyst count reduction test (FOCRT). The aim of the present study was to use a controlled efficacy trial to assess the efficacy of toltrazuril against a field isolate suspected of being resistant.MethodsTwenty lambs, 17–22 days old and raised protected against exposure to coccidia, were infected with a field isolate of 100,000 Eimeria spp. oocysts. This isolate was obtained from a farm with a previously calculated drug efficacy of 56% (95% confidence interval: -433.9 to 96.6%). At day 7 post-infection, 10 of the lambs were orally treated with 20 mg/kg toltrazuril (Baycox Sheep vet., Bayer Animal Health), while the other 10 lambs (controls) were given physiological saline. Clinical examinations were conducted, and weight gains recorded. Daily faecal samples were scored for diarrhoea on a scale from 1 to 5, and oocyst excretion was determined using a modified McMaster technique. Oocysts were morphologically identified to species level. At 17–24 days post-infection, the lambs were euthanized and necropsied.ResultsThe tested Eimeria isolate was resistant against toltrazuril, and resistance was seen in both pathogenic and non-pathogenic species. In addition, no significant differences in faecal score, growth, gross pathology or histological changes were identified between the two groups. The pathogenic E. ovinoidalis was the dominant species, and no significant difference in the individual prevalence of E. ovinoidalis post-treatment was found between treated (66.9%) and control lambs (61.9%). Other species identified included E. crandallis/weybridgensis, E. parva, E. marsica, E. faurei, E. pallida, E. ahsata and E. bakuensis.ConclusionsThis study confirms toltrazuril resistance in ovine Eimeria spp.; in addition, the data support the use of FOCRT as an appropriate tool for field evaluation of anticoccidial efficacy. Due to limited anticoccidial treatment alternatives, these findings may have important implications for the sheep industry, particularly in northern Europe.Electronic supplementary materialThe online version of this article (10.1186/s13071-018-2976-4) contains supplementary material, which is available to authorized users.

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Section: Field Isolate Of Eimeriamentioning

confidence: 99%

Section: Field Isolate Of Eimeriamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Controlled efficacy trial confirming toltrazuril resistance in a field isolate of ovine Eimeria spp.

et al. 2018

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A review of Eimeria antigen identification for the development of novel anticoccidial vaccines

Venkatas

Adeleke

2019

Parasitol Res

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Coccidiosis is a major poultry disease which compromises animal welfare and costs the global chicken industry a huge economic loss. As a result, research entailing coccidial control measures is crucial. Coccidiosis is caused by Eimeria parasites that are highly immunogenic. Consequently, a low dosage of the Eimeria parasite supplied by a vaccine will enable the host organism to develop an innate immune response towards the pathogen. The production of traditional live anticoccidial vaccines is limited by their low reproductive index and high production costs, among other factors. Recombinant vaccines overcome these limitations by eliciting undesired contaminants and prevent the reversal of toxoids back to their original toxigenic form. Recombinant vaccines are produced using defined Eimeria antigens and harmless adjuvants. Thus, studies regarding the identification of potent novel Eimeria antigens which stimulate both cell-mediated and humoral immune responses in chickens are essential. Although the prevalence and risk posed by Eimeria have been well established, there is a dearth of information on genetic and antigenic diversity within the field. Therefore, this paper discusses the potential and efficiency of recombinant vaccines as an anticoccidial control measure. Novel protective Eimeria antigens and their antigenic diversity for the production of cheap, easily accessible recombinant vaccines are also reviewed.

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Eimeria infections in domestic and wild ruminants with reference to control options in domestic ruminants

Bangoura

Bhuiya²,

Kilpatrick³

2022

Parasitol Res

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Field evaluation of anticoccidial efficacy: A novel approach demonstrates reduced efficacy of toltrazuril against ovine Eimeria spp. in Norway

Cited by 27 publications

References 62 publications

Controlled efficacy trial confirming toltrazuril resistance in a field isolate of ovine Eimeria spp.

Controlled efficacy trial confirming toltrazuril resistance in a field isolate of ovine Eimeria spp.

A review of Eimeria antigen identification for the development of novel anticoccidial vaccines

Eimeria infections in domestic and wild ruminants with reference to control options in domestic ruminants

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