Our work on Joseon period samples has great academic significance. Therefore, this kind of research needs to be pursued, especially because only 24 cases have been investigated so far. In this regard, we should thoroughly examine more coprolite samples from newly discovered Korean mummies. By updating the data with new Joseon period cases, we can more accurately estimate the parasite infection rate in premodern Korean society.

Recently, we examined parasites in the coprolites from 4 Joseon period individuals recovered during archaeological excavations in the cities of Euijeongbu (Gyeonggi-do), Gumi (Gyeongsangbuk-do), and Wonju (Gangwon-do) (Fig. 1). The archaeological information related to each case is summarized in Table 1.

Microscopic analyses were performed on coprolites or pelvic bone sediments collected from fully or half-mummified Joseon period human remains. Specimens (0.5–4 g) were rehydrated in trisodium phosphate solution (0.5%) [3,4]. They were filtered through a mesh, precipitated, and dissolved in a trisodium phosphate solution (0.5%, 20 ml). The solution was dropped on slides for observations under a BH-2 light microscope (Olympus, Tokyo, Japan). A total of 200 μl was examined for each sample. The size of parasite eggs was measured for each species. The newly obtained data were then compared with those reported previously in the national survey from 1972 to 2019 [5,6].

Microscopic analyses revealed that mummy coprolites comprised the following variety of ancient parasite eggs: T. trichiura in Euijengbu-1 and -2; T. trichiura, A. lumbricoides, and C. sinensis in Gumi-2; and T. trichiura, A. lumbricoides, C. sinensis, and P. westermani in Wonju6-1 (Fig. 2). Average egg sizes are presented in Table 1. Table 2 shows the present and previous data of parasitological examinations (total case number=30). The overall positive infection rates of soil-transmitted helminths during the Joseon period were 86.7% (26/30) for T. trichiura and 56.7% (17/30) for A. lumbricoides. Regarding trematodes, C. sinensis and P. westermani infection rates were estimated to be 30.0% (9/30) and 30.0% (9/30), respectively. Compared with the Joseon period results (n=24) reported by Seo et al. [1], the estimated overall infection rate obtained in the present study is slightly different, albeit the difference is not significant.

Since limited information is available on parasite infection patterns in the Joseon period society, studies on Korean mummies are invaluable to parasitologists. Over the last few years, parasitological data on Joseon period mummy coprolites have been reported [2]. The results of the present study provide additional information to re-estimate the parasite infection rate in the Joseon society. Moreover, only a slight difference was observed between the present data and the last estimate of the Joseon period infection rate reported by Seo et al. [1]. Thus, we confirmed the changing pattern of parasite infection prevalence throughout the Joseon period to 21st century in Korea reported by Seo et al. [1]. Briefly, the infection prevalence of the trematodes C. sinensis and P. westermani was lower than that of the nematodes A. lumbricoides and T. trichiura. The trematode infection rates obtained from the data of the 1971 study and those obtained from the Joseon period are very different (26.7 and 4.6% for C. sinensis, respectively, and 33.3% and 0.09% for P. westermani, respectively). In contrast, the nematode infection rates in the Joseon period (83.3% for T. trichiura and 60.0% for A. lumbricoides) remained almost the same until 1971 (65.4% for T. trichiura and 54.9% for A. lumbricoides) but were greatly decreased (0.2% for T. trichiura and 0.3% for A. lumbricoides) in 1992. Various hypotheses have been proposed to explain these historical changes in the rate of parasitic infection [7]; however, none explains it completely so far. Further research and discussion are needed to accurately comprehend this subject.

Analyzing parasite infection during the Joseon period and comparing it with the 20th century national survey data provide remarkable insights into historical parasitism in premodern Korean society that could not be obtained using conventional research. In this regard, periodical updates with newly discovered cases provide supplementary information that further reinforces the reliability of our data on Joseon parasite infection. The present study analyzed newly discovered mummy coprolites and confirmed the human parasite infection rates in the Joseon society estimated previously by examining mummy coprolites.