Development and application of a delayed-release anthelmintic intra-ruminal bolus system for experimental manipulation of nematode worm burdens

Abstract

SUMMARYIn order to quantify the impact of parasites on host population dynamics, experimental manipulations that perturb the parasite-host relationship are needed but, logistically, this is difficult for wild hosts. Here, we describe the use of a delayed-release anthelmintic delivery system that can be administered when the hosts can be captured and its activity delayed until a more appropriate period in the host-parasite cycle. Our model system is Svalbard reindeer infected with a nematode parasite, Marshallagia marshalli, which appears to accumulate during the Arctic winter. To determine the extent to which this occurs and the effect on host fitness, reindeer need to be treated with anthelmintics in late autumn but they can only be caught and handled in April. To solve this problem, we devised an intra-ruminal capsule that releases the anthelmintic from up to 6 months after being administered. The capsule was trialed in cannulated sheep and red deer to determine optimum capsule orifice size and release rates. Capsules were estimated to release placebo for 100–153 days followed by abamectin for 22–34 days. To test the efficacy of treatment in reindeer, capsules were administered in April and retrieved in October. All capsules had fully released the anthelmintic and treated reindeer had significantly lower worm burdens than controls. Thus, success of this system allows repeated treatment over several years to test the effect of winter parasitism on host fitness.

Little impact of over‐winter parasitism on a free‐ranging ungulate in the high Arctic

“…Each April from 2006 until 2011, all captured animals older than 12 months of age were randomly allocated to either the non‐treated control group or the anthelmintic treatment group. In the latter group, the anthelmintic was administered via a novel delayed‐release intra‐ruminal bolus (Carlsson, Wilson, & Irvine, ) which acted to remove nematodes at the start of winter (October) providing protection against re‐infection for around 4–5 weeks. After this period, animals became re‐infected with the nematode M. marshalli, but not O. gruehneri which is only transmitted in the summer months (Carlsson, Irvine, et al., ; Carlsson, Wilson, et al., ).…”

“…In the latter group, the anthelmintic was administered via a novel delayed‐release intra‐ruminal bolus (Carlsson, Wilson, & Irvine, ) which acted to remove nematodes at the start of winter (October) providing protection against re‐infection for around 4–5 weeks. After this period, animals became re‐infected with the nematode M. marshalli, but not O. gruehneri which is only transmitted in the summer months (Carlsson, Irvine, et al., ; Carlsson, Wilson, et al., ). Animals receiving the delayed‐release intra‐ruminal bolus (DB) also received a single dose of short acting 1% moxidectin (Cydectin, Pfizer, UK) at 0.2 mg per kg live mass.…”

“…The efficacy of the DB in reducing burdens of the different stages of M. marshalli and O. gruehneri , and the data and methods used to establish this are presented elsewhere (Carlsson, Irvine, et al., ; Carlsson, Wilson, et al., ). Here, we re‐analyse these data to demonstrate the effect of treatment on total nematode abundance, i.e.…”

Experimental removal of nematode parasites increases growth, sprint speed, and mating success in brown anole lizards

“…Over time, these factors can reduce any differences in parasite prevalence and intensity between treatment groups while increasing variance within treatment groups, thereby complicating inferences about treatment effects, especially when the study is conducted over a time span that exceeds the half‐life of the drug (Easterly et al, 1992 ; Ezenwa et al, 2010 ; Friant et al, 2016 ; Irvine et al, 2000 ; Knowles et al, 2013 ; Ranjan et al, 1997 ; Thomas & Morgan, 2013 ; Wahid et al, 1989 ). Therefore, extended‐release drug formulations have many advantages over traditional drug formulations that require frequent dosing to maintain their effectiveness against parasites (Carlsson et al, 2012 ; Ezenwa et al, 2010 ).…”