Human Infections with Spirometra decipiens Plerocercoids Identified by Morphologic and Genetic Analyses in Korea

Abstract

Tapeworms of the genus Spirometra are pseudophyllidean cestodes endemic in Korea. At present, it is unclear which Spirometra species are responsible for causing human infections, and little information is available on the epidemiological profiles of Spirometra species infecting humans in Korea. Between 1979 and 2009, a total of 50 spargana from human patients and 2 adult specimens obtained from experimentally infected carnivorous animals were analyzed according to genetic and taxonomic criteria and classified as Spirometra erinaceieuropaei or Spirometra decipiens depending on the morphology. Morphologically, S. erinaceieuropaei and S. decipiens are different in that the spirally coiled uterus in S. erinaceieuropaei has 5-7 complete coils, while in S. decipiens it has only 4.5 coils. In addition, there is a 9.3% (146/1,566) sequence different between S. erinaceieuropaei and S. decipiens in the cox1 gene. Partial cox1 sequences (390 bp) from 35 Korean isolates showed 99.4% (388/390) similarity with the reference sequence of S. erinaceieuropaei from Korea (G1724; GenBank KJ599680) and an additional 15 Korean isolates revealed 99.2% (387/390) similarity with the reference sequences of S. decipiens from Korea (G1657; GenBank KJ599679). Based on morphologic and molecular databases, the estimated population ratio of S. erinaceieuropaei to S. decipiens was 35: 15. Our results indicate that both S. erinaceieuropaei and S. decipiens found in Korea infect humans, with S. erinaceieuropaei being 2 times more prevalent than S. decipiens. This study is the first to report human sparganosis caused by S. decipiens in humans in Korea.

Keywords: Spirometra decipiens; Spirometra erinaceieuropaei; mitochondrial gene; molecular identification; morphology.

Fig. 1.

Gravid proglottids of Spirometra erinaceieuropaei and Spirometra decipiens. (A, B) Whole mounted specimens of proglottids showing the uterus and cirrus sac (×40), (C, D) Longitudinal section of a gravid proglottids showing the cirrus sac (CS), seminal vesicle (SV), and uterus (U) (H&E stain).

Fig. 2.

A phylogenetic tree of spirometrid tapeworms based on partial cox1 sequences inferred from neighbor-joining analysis. Numbers on branches indicate the bootstrap supporting values based on 1,000 replicates and bootstrap values by the maximum parsimony, maximum likelihood, and neighbor-joining methods are shown from left to right. The partial cox1 sequences of S. erinaceieuropaei and S. decipiens were divided into 2 clades, which differed by 29-32 nucleotides from each other. There were 390 bp corresponding to positions 732-1,122 bp of the cox1 gene.