Effects of Spigelia anthelmia decoction on sheep gastrointestinal nematodes

Abstract

The use of herbal medicines either in combination with or instead of synthetic anthelmintics is an approach to reducing the exposure of parasites to synthetic chemicals. The present study aimed to assess the in vitro and in vivo effects of Spigelia anthelmia decoction (SaDec) on sheep gastrointestinal nematodes. SaDec was obtained by extracting active constituents of the plant in boiling water. The condensed tannins present in SaDec were quantified and subjected to phytochemical analysis. The egg hatch test (EHT), the larval development test (LDT), and an adult worm motility (AWM) assay were performed. Ultrastructural changes in the cuticle of the adult Haemonchus contortus were evaluated by scanning electron microscopy (SEM). Acute toxicity tests in mice were performed to define the safe dose of SaDec to be administered in the fecal egg count reduction test (FECRT) In the FECRT, fecal samples were collected at days 0, 7 and 14 post-treatment to estimate the eggs per gram (epg) and to identify the most prevalent nematode genera. The results of the EHT and LDT were analyzed using analysis of variance (ANOVA) and compared using Tukey’s test (P<0.05). The effective concentration to inhibit 50% (EC50) of egg hatching or larval development was determined by the probit method. In the AWM assay, worm survival was analyzed with the non-parametric stratified Cox regression test. The efficacy in the FECRT was calculated using BootStreat 1.0 software. The phytochemical screening detected high concentrations of condensed tannins, flavonoids, flavones, saponins, alkaloids and xanthones. The weights of the total phenolics and the condensed tannins were 96.56 and 51.25mg gallic acid equivalents (GAE)/g dry weight (DW), respectively. The EC50±95% confidence interval values of SaDec for the EHT and LDT were 1.4 (1.2–1.6) and 1.2 (1–1.3)mg/ml, respectively. Treatment with SaDec at 1.6mg/ml produced 100% inhibition of worm motility after 12h of exposure. SEM revealed ultrastructural changes in the cephalic region and cuticle of H. contortus females. In the acute toxicity test, there was no mortality in mice. SaDec at 350mg/ml reduced the sheep epg by 47% at 14days post-treatment. Haemonchus was the most prevalent nematode genus. This study demonstrated that SaDec shows promising efficacy against gastrointestinal nematodes in small ruminants.