Caudal Swellings in L1 Larvae of Elaphostrongylus (Nematoda: Protostrongylidae) from Cervid Feces in Belarus and China

Brain nematodes of the genus Elaphostrongylus parasitize cervids. Their presence can either remain unnoticed or cause severe neurological disorders and death of the host. Despite the localization of adult worms in the central nervous system, the diagnosis is easily made via life-time detection of the characteristic first-stage dorsal-spined larvae in the feces (coprolarvascopy). We report two cases of unusual caudal swellings in L1 of Elaphostrongylus and discuss their alternative explanations. In August 2023, freshly excreted feces of reindeer (Rangifer tarandus) were collected in China (51.35080 N; 121.50146 E).In February 2026, freshly excreted feces of moose (Alces alces) were collected in Belarus (53.94170 N; 26.38300 E). Protostrongylid larvae were found via standard fecal tests in both sets of samples: in reindeer — species E. rangiferi (GeneBank: PX720411), in moose — species E. alces. In both cases, a single larva with an unusual swelling was found. In L1 of E. rangiferi, the swelling occupied the region where caudal spike must be situated, dorsal spine remained. In L1 of E. alces, the swelling replaced both caudal spike and dorsal spine. These swellings could be due to: 1) developmental abnormality; 2) bacterial/viral/fungal/protozoan/other infection; 3) degenerative post-shedding change. These observations expand our current knowledge of morphological variation in Elaphostrongylus L1 larvae and may reflect previously unrecognized developmental pathology or biotic infection. Such findings are relevant to parasite diversity, wildlife health, and the study of host—parasite—microbe interactions in cervid systems.