BACKGROUND: Digenetic trematodes, including blood flukes, intestinal flukes, liver flukes, lung flukes, and pancreatic flukes, are highly diverse and distributed widely. They affect at least 200 million people worldwide, so better understanding of their global distribution and prevalence are crucial for controlling and preventing human trematodiosis. Hence, this scoping review aims to conduct a comprehensive investigation on the spatio-temporal distribution and epidemiology of some important zoonotic digenetic trematodes.
METHODS: We conducted a scoping review by searching PubMed, Web of Science, Google Scholar, China National Knowledge Infrastructure, and Wanfang databases for articles, reviews, and case reports of zoonotic digenetic trematodes, without any restrictions on the year of publication. We followed the inclusion and exclusion criteria to identify relevant studies. And relevant information of the identified studies were collected and summarized.
RESULTS: We identified a total of 470 articles that met the inclusion criteria and were included in the review finally. Our analysis revealed the prevalence and global distribution of species in Schistosoma, Echinostoma, Isthmiophora, Echinochasmus, Paragonimus, Opisthorchiidae, Fasciolidae, Heterophyidae, and Eurytrema. Although some flukes are distributed worldwide, developing countries in Asia and Africa are still the most prevalent areas. Furthermore, there were some overlaps between the distribution of zoonotic digenetic trematodes from the same genus, and the prevalence of some zoonotic digenetic trematodes was not entirely consistent with their global distribution. The temporal disparities in zoonotic digenetic trematodes may attribute to the environmental changes. The gaps in our knowledge of the epidemiology and control of zoonotic digenetic trematodes indicate the need for large cohort studies in most countries.
CONCLUSIONS: This review provides important insights into the prevalence and global distribution of some zoonotic digenetic trematodes, firstly reveals spatio-temporal disparities in these digenetic trematodes. Countries with higher prevalence rate could be potential sources of transmitting diseases to other areas and are threat for possible outbreaks in the future. Therefore, continued global efforts to control and prevent human trematodiosis, and more international collaborations are necessary in the future.

Three new species of Gyrodactylus are described from three species of bitterling in Donghu Lake, China: Gyrodactylus ocellorhodei n. sp. from Rhodeus ocellatus; G. sinenorhodei n. sp. from Rhodeus sinensis; and G. acheilorhodei n. sp. from Acheilognathus macropterus. All the three new species showed similar opisthaptor morphology, especially the marginal hooks: all had a slender and perpendicular sickle shaft, and flat sickle base with distinct heel and inner arch which was different from the G. rhodei-group species parasitic on bitterling. Multivariate analyses based on hamulus and marginal hooks suggested that these three new species cannot be completely distinguished, despite some morphology divergence observed in certain less reliable morphometric features, such as hamulus root length, ventral bar total length and process shape. These three new species shared an identical 18S ribosomal RNA gene sequence, while the variation in the Internal Transcribed Spacers (ITS1-ITS2) sequence among them (8.4-11.2%, K2P) far exceeded the 1% ITS sequence difference that had been suggested as a threshold for species delimitation of Gyrodactylus. Phylogenetic analysis based on ITS1-ITS2 showed that all these sequenced Gyrodactylus spp. parasitic on the subfamily Acheilognathinae host formed a monophyletic group. However, a clear differentiation (18.9-20.9%, K2P of ITS1-ITS2) could be found between the subgroup from China (G. ocellorhodei n. sp., G. sinenorhodei n. sp. and G. acheilorhodei n. sp.) and that from Europe (G. rhodei).

Liver flukes (Fasciola spp.) and rumen flukes (Paramphistomum spp.) are significant parasites in livestock worldwide, and Fasciola spp. are considered an important zoonotic parasite. To our knowledge, there are no reports on fluke species identification and epidemiological prevalence in yak and Tibetan sheep around Qinghai Lake, China. Therefore, this study aimed to identify the major fluke species and determine the prevalence of fluke infections among yak and Tibetan sheep in this area. A total of 307 fecal samples were collected and fluke eggs identified using morphology and molecular methods. Our study is the first to display that the predominant fluke species were F. hepatica and P. leydeni in yak and Tibetan sheep around Qinghai Lake. The overall prevalence of fluke infections in yak and Tibetan sheep was 57.7% (177/307). Specifically, the prevalences of F. hepatica and P. leydeni were 15.0% (46/307) and 31.6% (97/307), respectively, and the co-infection of both species was 11.1% (34/307). No significant difference existed in the prevalence of overall fluke infection between yak and Tibetan sheep (p < 0.05). However, F. hepatica prevalence was significantly different in yak and Tibetan sheep (p < 0.05) but not P. leydeni. The findings of this study provide useful information about the current status of natural fluke invasion in yak and Tibetan sheep around Qinghai Lake, which could be important for monitoring and controlling these parasites in the region.

Trematodes of the genus Ogmocotyle are intestinal flukes that can infect a variety of definitive hosts, resulting in significant economic losses worldwide. However, there are few studies on molecular data of these trematodes. In this study, the mitochondrial (mt) genome of Ogmocotyle ailuri isolated from red panda (Ailurus fulgens) was determined and compared with those from Pronocephalata to investigate the mt genome content, genetic distance, gene rearrangements and phylogeny. The complete mt genome of O. ailuri is a typical closed circular molecule of 14 642 base pairs, comprising 12 protein-coding genes (PCGs), 22 transfer RNA genes, 2 ribosomal RNA genes and 2 non-coding regions. All genes are transcribed in the same direction. In addition, 23 intergenic spacers and 2 locations with gene overlaps were determined. Sequence identities and sliding window analysis indicated that cox1 is the most conserved gene among 12 PCGs in O. ailuri mt genome. The sequenced mt genomes of the 48 Plagiorchiida trematodes showed 5 types of gene arrangement based on all mt genome genes, with the gene arrangement of O. ailuri being type I. Phylogenetic analysis using concatenated amino acid sequences of 12 PCGs revealed that O. ailuri was closer to Ogmocotyle sikae than to Notocotylus intestinalis. These data enhance the Ogmocotyle mt genome database and provide molecular resources for further studies of Pronocephalata taxonomy, population genetics and systematics.

OBJECTIVE: To analysize the temporal trends in the disease burden of major human parasitic diseases in China from 1990 to 2019, so as to provide the evidence for improving the parasitic disease control strategy in China.
METHODS: The disability-adjusted life years (DALYs) of malaria, intestinal nematode infections, schistosomiasis, food-borne trematodiases, cysticercosis and echinococcosis in China from 1990 to 2019 were captured from the Global Burden of Disease Study 2019 (GBD 2019), and age- and gender-specific DALYs of parasitic diseases were estimated. The temporal trends in DALYs of malaria, intestinal nematode infections, schistosomiasis, food-borne trematodiases, cysticercosis and echinococcosis were evaluated in China from 1990 to 2019 using average annual percent change (AAPC) with Joinpoint regression analysis.
RESULTS: The DALYs were 643 836.42 person-years due to food-borne trematodiases, 156 853.03 person-years due to cysticercosis, 79 764.62 person-years due to schistosomiasis, 70 989.73 person-years due to intestinal nematode infections, 4 258.61 person-years due to echinococcosis and 264.86 person-years due to malaria in China in 2019, respectively. The overall DALYs of six parasitic diseases were higher among men (546 441.93 person-years) than among women (409 525.33 person-years), and were greater among adults at ages of 14 to 65 years (684 780.84 person-years) than among children at 14 years and lower (35 437.38 person-years) and the elderly at ages of 65 years and older (235 749.04 person-years). During the period from 1990 to 2019, food-borne trematodiases were the leading cause of DALYs among the six parasitic diseases, and cysticercosis shifted from the fourth leading cause in 1990 to the second leading cause of DALYs in China in 2019, while intestinal nematode infections shifted from the second leading cause in 1990 to the fourth leading cause of DALYs in 2019. The DALYs of major human parasitic diseases appeared an overall tendency towards a decline in China from 1990 to 2019, with the fastest drop seen in DALYs due to malaria (AAPC = -19.6%, P = 0.003), followed by due to intestinal nematode infections (AAPC = -8.2%, P < 0.001) and schistosomiasis (AAPC = -3.1%, P < 0.001), and a slow decline was seen in the DALYs of food-borne trematodiases (AAPC = -1.0%, P < 0.001), while there were no significant decrease in the DALYs of echinococcosis (AAPC = -0.5%, P = 0.264) and the DALYs of cysticercosis appeared a tendency towards a rise (AAPC = 0.7%, P < 0.001).
CONCLUSIONS: The disease burden of major human parasitic diseases appeared an overall tendency towards a decline in China from 1990 to 2019, with a high disease burden seen due to food-borne parasitic diseases, no remarkable reduction seen in echinococcosis, and a tendency towards a rise seen in cysticercosis. It is recommended to focus on echinococcosis control, and continue to consolidate the control achievements of other major human parasitic diseases in China; meanwhile, the surveillance and prevention of food-borne parasitic diseases should be reinforced.
［摘要］ 目的 掌握1990—2019年我国主要人体寄生虫病疾病负担时间变化趋势, 为完善寄生虫病防治策略提供参 考。方法在2019全球疾病负担研究(global burden of disease study 2019, GBD 2019)数据中, 提取1990—2019年我丨玉丨疟 疾、肠道线虫感染、血吸虫病、食源性吸虫病、囊尾蝴病和棘球蝴病等寄生虫病伤残调整寿命年(disability-adjusted life years, DALYs), 对其DALYs从大到小进行排序, 并描述年龄和性别分布。使用Joinpoint回归模型分析各病种DALYs平 均年度变化百分比 (average annual percent change, AAPC)。结果2019年我国主要人体寄生虫病DALYs由大到小依次 为：食源性吸虫病 (643 836.42人•年) 、囊尾蝴病 (156 853.03人•年) 、血吸虫病 (79 764.62人•年) 、肠道线虫感染 (70 989.73人•年) 、棘球蝴病 (4 258.61人•年) 和疟疾 (264.86人•年), 男性DALYs (546 441.93人•年) 高于女性 (409 525.33 人•年), 青壮年(14∼65 岁, 684 780.84 人年) i高于儿童 (≤ 14 岁, 35 437.38 人•年) 和老年 (≥ 65 岁, 235 749.04 人•年) 。1990—2019年, 我国食源性吸虫病DALYs在6种寄生虫病中一直居首位, 囊尾蝴病由1990年的第4位上升至 2019年的第2位, 肠道线虫感染则由1990年的第2位下降至2019年的第4位。1990—2019年, 我国主要人体寄生虫病 DALYs总体呈下降趋势, 疟疾DALYs下降速度最快(AAPC = -19.6%, P=0.003), 其次是肠道线虫感染(AAPC = -8.2%, P < 0.001)和血吸虫病(AAPC = -3.1%, P < 0.001), 食源性吸虫病DALYs下降趋势较缓(AAPC = -1.0%, P < 0.001), 棘球蝴 病DALYs下降不明显(AAPC = -0.5%, P= 0.264), 囊尾蝴病DALYs呈增长趋势(AAPC = 0.7%, P <0.001)。结论 1990—2019年, 我国血吸虫病、肠道线虫感染与疟疾等重点寄生虫病疾病负担显著降低, 食源性寄生虫病疾病负担较高, 棘球 蝴病疾病负担下降不明显, 囊尾蝴病疾病负担有上升趋势。建议我国以棘球蝴病防控为重点, 在继续巩固其他重点寄生 虫病防治成果的同时, 加强食源性寄生虫病的监测和预防。.

The family Cyathocotylidae trematode is a world-widely distributed parasite whose adults are mainly found in fish, reptiles, birds, and mammals in both freshwater and marine environments. However, little is known of the prevalence of these trematode in China. For the first time, we found Cyathocotylidae trematode in the Wuhu area. Therefore, we investigated the prevalence of metacercariae in Carassius auratus from Zhang Lake, Kui Lake, Qingyi River, and Yangtze River (Wuhu Section) in Wuhu area. A total of 392 one-year-old C. auratus were tested in January, April, July, and October 2019, respectively. After the fish were euthanized, the back, chest, and tail muscles were used for preliminary screening for the presence of metacercariae by direct compression method. Metacercariae were isolated by the artificial digestion method and then morphologically and molecularly identified by cox1 (642 bp) and ITS2 (418 bp) sequences amplification by PCR. Based on morphological features and sequence analysis, they were identified as cyathocotylid metacercariae. The four water sources have different degrees of prevalence throughout the year, the prevalence ranges from 28.45% (29/102) in Yangtze River to 50.55% (46/91) in Zhang Lake, with an average prevalence of 40.56% (159/392). There were also differences in the prevalence in different months: The highest occurred in July, which was 81.63% (80/98), while the lowest occurred in January, which was 8.89% (8/90). This study can provide basic data for the prevention and control of cyathocotylid trematode in this area.

Host density is a key regulatory factor in parasite transmission. The goldfish (Carassius auratus)-Gyrodactylus kobayashii model was used to investigate effects of host density on population growth of gyrodactylids. A donor fish infected by five gravid gyrodactylids was mixed with 11 parasite-free goldfish at five host densities. There was a significant positive correlation between host density and mean abundance of G. kobayashii throughout the 58-day experiment. During early infection (days 15–24), mean abundance in medium high (0.5 fish L−1) and high host density groups (1 and 2 fish L−1) was significantly higher than that in the low host density groups (0.125 and 0.25 fish L−1). At high host density, prevalence increased more rapidly, and the peak prevalence was higher. Fitting of an exponential growth model showed that the population growth rate of the parasite increased with host density. A hypothesis was proposed that higher host density contributed to increased reinfection of detached gyrodactylids. A reinfection experiment was designed to test this hypothesis. Both mean abundance and prevalence at a host density of 1 fish L−1 were significantly higher than those at 0.25 fish L−1 on days 1 and 3, which suggested that more reinfections of G. kobyashii occurred at the higher host density. Density-dependent transmission during the early infection was an important contributor of population growth of G. kobayashii, as well as density-dependent reinfection of the detached gyrodactylids.

A new species of Gyrodactylus was described on the body surface of zebrafish (Danio rerio) in China. Basing on morphological characteristics and ITS sequence, we identified the parasite as a new member of the Gyrodactylus-wageneri group. Morphologically, Gyrodactylus sp. nov. is greatly similar to \"G. zebrae\", another species parasitic on zebrafish: both have moderately stout hamulus, marginal hook sickle with a prominent heel and toe, as well as a curved blade. However, distinct haptoral shape differences were detected between these two species. The dorsal bar is straight in Gyrodactylus sp. nov. but strongly curved in \"G. zebrae\", and the sickle shaft in Gyrodactylus sp. nov. is approximately perpendicular to the base, but in \"G. zebrae\" it is slanted downwards. The ITS1-5.8S-ITS2 sequence also indicate that Gyrodactylus sp. nov. exhibits the highest similarity to \"G. zebrae\": 95.7% sequence identity suggests interspecific differentiation. Phylogenetic analysis of the ITS1-ITS2 sequence showed that Gyrodactylus sp. nov. formed a sister clade with \"G. zebrae\", and exhibited a relatively close phylogenetic relationship with G. kobayashii, G. gurleyi, and G. longoacuminatus, all of which parasitise on goldfish, Carassius auratus. To test the susceptibility of zebrafish and goldfish to the Gyrodactylus sp. nov., ten gyrodactylids were inoculated to the caudal fin of zebrafish and goldfish. The gyrodactylids exhibited the ability to attach themselves to the goldfish, and some gyrodactylids reproduced a few days after the inoculation. On day 9, however, the mean abundance sharply decreased to zero on goldfish and increased to more than 30 on zebrafish. The result suggested that golfish is an unsuitable host for Gyrodactylus sp. nov. Therefore, on the basis of morphology, molecular sequence similarity, and host susceptibility, we conclude that the gyrodactylid found on the zebrafish is a new species, which we named Gyrodactylus banmae.

Paradiplozoon opsariichthydis (Jiang, Wu et Wang, 1984) Jiang, Wu et Wang, 1989 (Platyhelminthes, Monogenea, Diplozoidae) is blood-feeding parasite from the gills of Asian cyprinid fish Opsariichthys bidens Günther, 1873. In this study, we present a morphological redescription of P. opsariichthydis neotype main morphological features e.g. size of body and clamps due to the fact that the type material is missing. We decided to supplement morphological descriptions by the relevant molecular data (internal transcribed spacer - ITS2) related to P. opsariichthydis adult worm isolates and other representatives of genus Paradiplozoon to cross verify our findings. In addition to that, this study also brings an attention to the host identification. Thus, parasite data were complemented by the determinant cytochrome oxidase b (cytb) sequences of its hosts. All novel sequences are deposited in GenBank. This combination of the morphological and molecular data related to both the parasite and its host seems to be the optimal approach to the general process of (re)description of highly host-specific parasitic organisms, which can then lead to a meaningful phylogenetic analysis.

Gyrodactylus spp. are common monogenean ectoparasites that may lead to significant fish mortality. To find effective anthelmintic agents with lower toxicity, a series of natural saponins were obtained and evaluated for their anthelmintic activity against Gyrodactylus kobayashii and acute toxicity to goldfish (Carassius auratus). Among all tested compounds, six compounds (1, 2, 3, 8, 10, and 13) shown higher anthelmintic activity and safety than widely used formaldehyde-based parasiticides, especially compound 1 having 100% anthelmintic efficacy against G. kobayashii at 0.3 mg/L and a therapeutic index of 16.6. Also, the three-dimensional quantitative structure-activity relationship (3D-QSAR) studies of these saponins have been performed to explore the structural features reasonable for the anthelmintic activity against G. kobayashii. These models demonstrated that the hydroxyl group at C-17 position and the sugar moieties at C-3 position, especially the hydroxyl groups of the sugar moieties, were critical to the anthelmintic activity. The QSAR studies could provide useful information for further rational design and optimization of novel saponins for the control of gyrodactylosis.