Old world camels in Germany: parasitic nematode communities characterized by nemabiome analysis showed reduced anthelmintic efficacy according to the fecal egg count reduction test

Abstract

Background

Gastrointestinal nematodes pose a significant health risk to grazing livestock and cause economic losses, which are further increased by anthelmintic resistance. This study examined the gastrointestinal parasite fauna of Old World Camels (OWCs) in Germany and evaluated the efficacy of anthelmintic treatment.

Methods

In total, nine German OWC-keeping farms that dewormed their stock in spring 2023 were examined. The farms with their veterinarians independently selected the drug for treatment. The number of strongyle eggs per gram (EPG) feces was determined in 107 OWCs, Camelus bactrianus (86.0%), Camelus dromedarius (6.5%), and hybrids (7.5%), using the FLOTAC method (multiplication factor = 1) before and 14 days after treatment (paired sample size: 100 OWCs). The fecal egg count reduction (FECR) was calculated using bayescount and eggCounts software. For the identification and relative quantification of strongyle species, deep amplicon sequencing (nemabiome analysis) was used.

Results

Farms differed widely regarding egg shedding intensities and prevalence. On most farms, the weight of the animals was only estimated. Evaluation of the anthelmintic efficacy revealed FECRs of 26.6–90.8% after treatment with albendazole, fenbendazole, ivermectin, moxidectin, or doramectin, while only on one farm treatment with monepantel resulted in > 99% FECR. The strongyle species diversity, as determined using the nemabiome approach, was low. With Trichostrongylus colubriformis, Haemonchus contortus, Trichostrongylus axei, and Cooperia oncophora abundant strongyles of German domestic ruminants dominated, while Camelostrongylus mentulatus also occurred. After deworming, strongyle communities almost completely consisted of T. colubriformis and H. contortus. In contrast, C. mentulatus and C. oncophora were consistently eliminated by treatments.

Conclusions

This study shows the insufficient efficacy of standard treatments chosen by farmers/veterinarians for OWCs in Germany. Since treatment eliminated some species but did not eliminate others, not underdosing but resistant nematode species presumably led to treatment failure. However, owing to the small sample size, assessment of animal weight only by visual estimation, and no drugs licensed for OWCs in Europe, the term resistance should be used with care. The species T. colubriformis and H. contortus that survived after anthelmintic treatment are also frequently resistant in ruminants in Germany.