Short Communications: Assessing morphological preservation of gastrointestinal helminths in ethanol versus formalin

Abstract

Abstract The accurate identification of gastrointestinal parasites from animal feces is vital for understanding many aspects of host-parasite interactions. Copromicroscopic parasite identification is a longstanding, frequently used, and cost-effective method, but its efficacy depends on the storage medium of the samples. In this study we compare the preservation of parasite larvae and eggs in ethanol versus formalin-preserved fecal samples collected from a wild population of Costa Rican capuchin monkeys (Cebus imitator). Samples were collected, halved, and stored in either 10% formalin or 96% ethanol at ambient temperature, then screened for the presence of parasites using a modified Wisconsin sedimentation technique and microscopy. Parasites were morphologically identified and graded on their preservation using a rubric we developed. We identified more parasitic morphotypes in samples preserved in formalin but found no difference in counts of parasites per fecal gram between mediums. The two most prevalent genera of parasites, Filariopsis and Strongyloides, were found in similar numbers in the different mediums and while Filariopsis larvae were better preserved in formalin, strongyle eggs showed no difference in preservation between mediums. Parasites preserved in ethanol and formalin were morphologically identifiable in samples stored up to 2 years, highlighting the suitability of both mediums in morphological parasite identification. While formalin-preserved samples may not be suitable for subsequent genetic analyses, ethanol-preserved samples can be studied further using molecular methods. Future studies may build on our current understanding of parasite ecology by pairing morphological and molecular methods to explore taxonomic diversity and deepen our understanding of host-parasite relationships.