Investigation and study on the fauna and epidemiology of rodent endoparasites in the desert of northwest China

Zoonoses are severe and have attracted wide attention in society. Many animal parasitic diseases can cause human infection, so it is necessary to study the host of parasites and their transmission routes. The sampling investigation in the inland arid desert area of northwestern China - Xinjiang, a total of 963 rodents belonging to 21 species, 15 genera, four families, and two Lepus yarkandensis,17 Crocidura leucodon were captured in the arid desert region of Xinjiang. Among them, 33 species of endoparasite were detected, including 17 species of nematodes,15 species of tapeworm, and one acanthocephalan species. A total of 127 positive specimens were detected. The infection rate of endoparasite was 13.19%, Nematode infection rate was 6.63%, and the tapeworm infection rate was 7.98%. Epidemiological studies were carried out, and the conclusions are as follows: The infection rate of endoparasite in rodents in this area is not related to gender but is closely related to the host’s age, distribution area, host species, cluster lifestyle, and season. The infection intensity is not related to the number of infected endoparasite species and the infection rate but is mainly related to specic parasite species and rodent species. With the succession of rodent communities, the infection intensity increases from desert to articial forest, farmland, and residential area, indicating that the direction and route of parasite transmission from primitive desert to articial environment have formed.


Introduction
With the development of the economy, the relationship between humans and nature is getting closer and closer. Some zoonoses had been discovered successively, especially the outbreak and spread of SARS in 2003SARS in , avian u in 2004SARS in , swine u in 2009, and novel coronavirus in 2020, which did great harm. Therefore, it is essential to know the host, foci, transmission route, and transmission mode of zoonotic diseases to prevent and control parasitic diseases. Currently, the study of animal parasites is more focused on the external parasites, and the object of study mainly concentrated on domestic animals (Fanyao Kong,1997), pets (Ming Wang, 2004), and experimental animals (Ting-heng Wen et al., 1987 andXinru Chen et al., 1996). Research reports on wild animals, especially wild rodents' endoparasites, are commonly found in West Asia (Asghar et al. 2018 andNasser Hajipour et al., 2016) and Africa (Khalafalla R E et al., 2011 andFredrick O. et al., (2019). However, few research reports in this eld in China and data are relatively scarce (Zhengmei Huang et al., 1995 andZilin Zhou et al., 1993). There are only sporadic investigations on the ecological characteristics and epidemiology of rodents' endoparasite in inland arid desert areas. (Wei Jiang et al., 1999, Wei Jiang et al., 2000and Chinese Academy of Sciences, 1959. In this paper, the endoparasitic infections in different areas, different host, different genders, and ages in Xinjiang was investigated and analysed; the aim was to clarify the life history of endoparasites, the model, and way of transmission.
Moreover, put forward the corresponding prevention measures. Investigation and research results were as follows:

Specimens Source
According to the zoogeographic regionalization of Xinjiang (Rongzhu Zhang, 1999), we chose ve sampling points, which belong to three zoogeographic subregions respectively. The ve sample plots are as follows:(1) Tarim Basin in southern Xinjiang, which belongs to the western desert subregion;(2) Mosuowan (a place name in Xinjiang) reclamation area, extending 60 kilometres to the hinterland of Junggar Basin, belongs to the western desert subregion;(3) Fukang Farm, located in the southern edge of Junggar, belongs to the western desert subregion;(4) Mulei steppe belongs to the eastern steppe subregion;(5) Bole Mountain belongs to Tianshan Mountain subregion. A total of 963 rodents were examined in this necropsy, including 21 species of rodents. A total of 963 rodents belonging to 21 species, 15 genera, four families, and two Lepus yarkandensis 17 Crocidura leucodon were captured. These rodents' specimens were examined, and the conclusions were as follows:

Inspection method
We referred to "Domestic Animal Parasitology" (Fanyao Kong,1997), "Clinical Parasitology and Experimental Guide to Parasitology" (Qingren Zeng, 2003), and "Human and zoonotic nematology" (Zhongzhang Tang, Chongti Tang, 1987) Field inspection: The captured rodents were identi ed (Sibo Wang et al., 1983 andYingxiang Wang, 2003), registered with male and female numbers, and measured body weight, body length, tail length, carcass weight, reproductive and developmental conditions. The captured rodents' stomach and intestines were cut off on the spot and stored in 10% neutral formaldehyde or 70% alcoholic semen.
Laboratory examination: Gastrointestinal body specimens were removed from the immersion solution, numbered, cut into sections, and rinsed with normal saline. Furthermore, specimens were examined by sections of the stomach, small intestine, cecum, and large intestine. Besides, endoparasites were collected by picking needles. The tapeworm was washed, pressed, stained with hydrochloric acid magenta, and examined under a microscope. The nematodes were rinsed, transparent with milk phenol, and classi ed and identi ed under the microscope.

Epidemiology and public health indicators
(1) Infection rate (2) Infection intensity

Results
Endoparasite fauna and species see Table 1 Through three zoogeographic fauna and ve sampling sites investigation in northwestern China's inland arid desert area -Xinjiang, 963 rodents belonging to 21 species, 15 genera, four families, and two Lepus yarkandensis 17 Crocidura leucodon were captured in the arid desert region of Xinjiang. Among them, 33 species of endoparasite were detected, including 17 species of nematodes,15 species of tapeworm, and one acanthocephalan species. One hundred twenty-seven positive specimens were detected. The infection rate of endoparasite was 13.19%, Nematode infection rate was 6.63%, and the tapeworm infection rate was 7.98%. Due to the limited identi cation conditions and levels, only four nematodes of the 18 species were identi ed to genera and species, while the other 14 nematodes could only be identi ed to orders and families. Among the 15 species of tapeworm, only four tapeworm species were identi ed to genus and species, while the other 11 species could only be identi ed to order and family. Endoparasite infection of rodent in different regions (see Table 2)  Table 3)  Table 4 Table 4  As shown in Table 3, according to the data of rodents in the Mosuowan area, 45 of 352 adult rodents were infected, the infection rate was 12.78%, and six of 118 juvenile rodents were infected; the infection rate was 5.08%. There was a signi cant difference between the two (P <0.05); adult rodents' infection rate was signi cantly higher than that of juvenile rodents. In terms of sex, the infection rate was 11.65% (29/249) in females and 9.95% (22/221) in males, and there was no signi cant difference between the two (p>0.05).

Parasite infection in rodents of different ages and sexes. (See
Endoparasite infection in different seasons see Table 5 Due to investigation time constraints, three consecutive seasons were not sampled from the same site. To eliminate the in uence of climate and region, we analysed the results of several sample sites located in Junggar Basin in northern Xinjiang. As shown in Table 4, the endoparasite infection rate was 3.78% in spring in the Fukang area, 10.85% in summer in the Mosuowan area, and 15.58% in autumn in the Mulei area. According to the seasonal analysis of parasitic infection rates of the three groups, the seasonal parasite infection rates in spring were lower than those in summer and lower than those in autumn, with an increasing trend from 3.78% to 10.85% to 15.58%, which existed to signi cant differences (P <0.05).   Table 5 in comparison with the infection rate of endoparasite among different rodent communities, it showed that there were signi cant differences among community (P<0.05), , , and community were signi cantly higher than the , , community. (P<0.05). The gerbil community and domestic rodent community's infection rate was higher than others, which might be related to the stable community and the camp cluster life. However, as for the intensity of infection, was the lowest, and was higher than the others. The number of parasites infected, the desert rodents were infected with nine species at most, and the other communities were three to four species.

Conclusion
Studies showed that: 1 The infection rate of endoparasite in rodents in this region is not related to gender but is closely related to the host's age, distribution area, host species, and season.
2 The rodents living in cluster life had a higher infection rate of endoparasites, especially infected with the same species, which indicated that their living habits facilitate the transmission of parasites within the population, thus having a more signi cant impact on the population quantity. In comparison, the rodents living in disperses had a lower infection rate and a smaller impact.
3 The infection intensity was not closely related to the species of infected endoparasites and the infection rate. It was mainly related to speci c endoparasite species and rodent species.
Infection situation in different rodent communities indicated that: First, the species of endoparasite in the source host is the most comprehensive. During migration and community succession to the human settlement area, some of the parasites did not adapt to the host change and remained in the original host and native environment. However, some parasites with strong adaptability completed the migration from the desert native environment to the human settlement environment. Second, although primitive desert rodent communities had high infection rates and parasite species, the infection intensity was low. In contrast, the infection intensity and infection rate from the transition zone to the residential area was more signi cant, and the harm was more serious than others. Third, some parasite species were found in almost every rodent community and indicated that some parasite species with low speci city spread in the rodent population and spread among different rodent populations. With the migration and succession of rodents, there was a tendency to spread from the desert to the residential area, threatening to humanity. Fourth, the infection rate of the dominant rodent species in each community was high, which indicated that the parasites had the characteristics of seeking bene ts and avoiding harm by selecting the dominant host. It is conducive to the parasite's reproduction.
In general, with the succession of rodent communities, the infection rate decreased from desert to arti cial forest, farmland, and residential area. In contrast, the infection intensity increased, indicating that the direction and route of parasite transmission from primitive desert to arti cial environment had been formed.
Due to the limited identi cation conditions and levels, only four nematodes of the 18 species were identi ed to genera and species, while the other 14 nematodes could only be identi ed to orders and families. Among the 15 species of tapeworm, only four species of tapeworm were identi ed to genus and species, while the other 11 species could only be identi ed to order and family.