Efficacy of anthelmintic treatment in captive-reared black stilts (Himantopus novaezelandiae) released to the wild.

AIMS: To assess the efficacy of praziquantel (PZQ) administered to control helminths in captive-reared critically endangered black stilts (Himantopus novaezelandiae) before their release into the wild and determine the effect on their survival shortly after release.

METHODS

Of 77 captive black stilts, 37 were treated with PZQ prior to release into the wild in South Canterbury, New Zealand, in August and September 2007. Faecal helminth egg counts (FEC) were measured before and after anthelmintic treatment, and before and after release to the wild using modified faecal flotation and sedimentation methods. In addition, total helminth counts were determined in 11 of the birds that died following release, as well as four captive and 11 other wild stilts.

RESULTS

The efficacy of PZQ against trematodes was 92% and against Capillaria spp. was 34%. No trematode or Capillaria spp. eggs were detected in treated birds 1 day after treatment, but FEC increased 3-5 days after treatment. There were no differences in the total helminth counts for trematodes, cestodes or Capillaria spp. in control or treated birds (p>0.2). Survival did not differ between treatment groups in the August or September releases (p>0.4). Of control and treated birds, 11/17 (65%) and 8/14 (57%) survived to 31 days, respectively, in the August release, and 16/20 (80%) and 10/15 (67%) survived to 84 days, respectively, in the September release.

CONCLUSION

Overall, the results suggest that PZQ treatment may be an unnecessary cost and the risks of producing anthelmintic resistance, injuring the birds during processing or producing an unnecessary stress response at the time of release could exceed any likely benefits.

CLINICAL RELEVANCE: It is recommended that pre-release anthelmintic treatment of black stilts should be used only if indicated by health screening. Any treatment should incorporate annual efficacy testing to monitor the emergence of anthelmintic resistance.