A controlled study on gastrointestinal nematodes from two Swedish cattle farms showing field evidence of ivermectin resistance

Abstract

BackgroundAnthelmintic resistance (AR) is an increasing problem for the ruminant livestock sector worldwide. However, the extent of the problem is still relatively unknown, especially for parasitic nematodes of cattle. The effect of ivermectin (IVM) (Ivomec inj.®, Merial) was investigated in Swedish isolates of gastrointestinal nematode (GIN) populations showing signs of AR in the field to further characterise the AR status by a range of in vivo and in vitro methods.MethodsThree groups, each of 11 calves, were infected with an equal mixture of third stage larvae (L3) of Cooperia oncophora and Ostertagia ostertagi. Group A was inoculated with an IVM-susceptible laboratory isolate and groups B and C with isolates originating from ‘resistant’ cattle farms. Faecal egg counts (FEC) were monitored from 0 to 45 days post infection (d.p.i.), and L3 were harvested continuously for larval migration inhibition testing (LMIT) and species-specific PCR (ITS2). At 31 d.p.i., one calf from each group was necropsied and adult worms were recovered pre-treatment. At 35 d.p.i., calves from all groups were injected with IVM at the recommended dose (0.2 mg/kg bodyweight). At 45 d.p.i., another two animals from each group were sacrificed and established gastrointestinal worms were collected and counted.ResultsA few animals in all three groups were still excreting eggs (50-150 per g faeces) 10 days post IVM injection. However, there was no significant difference in the FEC reductions in groups A (95%; 95% CI 81-99), B (98%; 92-100) and C (99%; 97-100) between 35 and 44 d.p.i. Furthermore, LMIT showed no significant difference between the three groups. Approximately 100 adult O. ostertagi were found in the abomasum of one calf (group B), whereas low to moderate numbers (400-12 200) of C. oncophora remained in the small intestine of the calves in all three groups at 45 d.p.i. PCR on L3 harvested from faecal samples up to 10 days post treatment showed a ratio of 100% C. oncophora in the calves inoculated with isolates A and B, whereas C also had 8% O. ostertagi.ConclusionsOverall, this experiment showed that the animals were successfully treated according to the Faecal egg count reduction test (FECRT) standard (≥ 95% reduction). However, several adult worms of the dose-limiting species C. oncophora demonstrably survived the IVM treatment.

Gene expression of ABC transporters in Cooperia oncophora after field and laboratory selection with macrocyclic lactones

“…Furthermore, those authors found that L3 both susceptible and resistant to anthelmintics showed increased expression of Con-pgp11, Con-pgp12, Con-pgp16 and Con-mrp1 after in vitro exposure to ML [15]. Con-pgp9 was included because increased expression of this gene has been reported in C. oncophora surviving ML treatment [5]. In addition, increased expression of P-gp9 has been reported in ML resistant T. circumcincta and H. contortus [12,13].…”

“…After patency, adult worms were collected at necropsy from one animal 4 days before treatment and from another animal 10 days after subcutaneous injection of the calves with IVM (Ivomec ® vet, 0.2 mg per kg), as described by Areskog et al [5].…”

“…However, extensive overuse of these anthelmintics has led to worldwide emergence of anthelmintic resistance (AR) in cattle nematodes, as reviewed by Sutherland and Leathwick [3]. Swedish reports of AR in cattle GIN only involve resistance to ML in the intestinal species C. oncophora [4,5].…”

A real-time PCR approach to identify anthelmintic-resistant nematodes in sheep farms

“…Another case of IVM resistance in T. circumcincta populations was suspected in the present study in one farm with a fecal egg count reduction of 84%. However, in absence of an IVM-controlled efficacy test using animals experimentally infected with the Bputativer esistant strain, pharmacokinetic analyses, and post-mortem examinations after treatment, the results obtained in the present study should be taken carefully as some discrepancies have been reported between FECR tests obtained with naturally grazing animals in one hand and experimentally infected animals in the other (Areskog et al 2013). If demonstrated, the Bmultiple^resistance detected in farm B may either be due to the presence of sub-populations of parasites that are monoresistant, i.e., only resistant to a single class of anthelmintic or by the presence of parasites carrying resistance to multiple anthelmintic drugs.…”

Association between Epidemiology and Haematophagous Behaviour of <i>Haemonchus contortus</i> and <i>Ostertagia ostertagi</i> Infecting Sheep of Kashmir Valley, India

“…Parasites acquire their food from their hosts, causing poor health and stress in the host organism that leads to an increased vulnerability to other diseases. The widespread emergence of anthelminticresistant strains of the highly pathogenic parasitic nematode Haemonchus contortus and other economically important parasites has resulted in the need to develop unconventional control strategies 2 . H. contortus and Ostertagia ostertagi are mostly pathogenic to sheep and cause effects ranging from mild anaemia to mortality in young animals because of their blood-feeding behaviour.…”