The prevalence of Angiostrongylus cantonensis in rodent hosts in China and several Asian countries: a systematic review and meta-analysis

Background Angiostrogylus cantonensis (A.cantonensis) is a zoonotic parasitic nematode, with a worldwide distribution, causing eosinophilic meningitis or meningoencephalitis in humans. Although the biology of A.cantonensis is relatively well known, little is understood about the transmission level in different zoogeographical regions, especially in Asia. Here, to evaluate the prevalence of A.cantonensis in rodent hosts in China and several Asian countries, we conducted a systematic review registered with PROSPERO (CRD42020161665). Methods Records were selected systematically from 7 databases (Medline via to Pubmed, Web of science, Scopus, Google Scholar, CNKI, Wangfang, CBM). Forest plots and random-effects model were used to display pooled estimates. The Freeman-Tukey double arcsine transformation of R software was used to conduct meta-analysis and statistical significance was set at 0.05. Results A total of 67 studies met the inclusion criteria and were included in the systematic review and meta-analysis. The pooled prevalence estimates of A.cantonensis infection in rodents was 0.1003 (95%CI: 0.0765, 0.1268). There was significant heterogeneity in reported outcomes (p<0.0001). So we considered that there was no publication bias in the included studies. Conclusion The A.cantonensis infection rate among rodent hosts was still high in Asia, particularly in China, especially in Rattus norvegicus, and thus comprehensive measures should be taken for rodent hosts control to avoid an angiostrongyliasis outbreak. Due to the wide distribution and movement of rodent hosts, people in all regions of China, even in other Asia area live at risk of an infection. Hence, the development of more reliable diagnostic tests will be key for an effective identification of cases as well as improved patient care. Consequently, further studies are required to updated strategies for controlling A.cantonensis infection among human population.


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Traditionally, with the wider domain of climate and health, the neglected tropical diseases (NTDs), are a collection of infectious diseases affected hundreds of millions of individuals living in tropical and subtropical countries. Recently, such dramatic habitat changes are linked to accelerated biodiversity loss, which has been linked to major changes in the epidemiology of human diseases: increased disease risks and the emergence of novel pathogens resulting from increased contacts among wildlife, domesticated animals, and humans [1][2][3]. In particular, angiostrongyliasis, as a kind of NTDs, was found in the Pacific Islands, Southeast Asia, parts of South and Central America and the Caribbean, even in European countries [4][5][6]. Recently, although researchers gradually pay more attention to investment towards reducing the burden of NTDs, they still collectively contribute to productively loss, illness and suffering in many countries [7,8]. Recent estimates of their overall burden suggest NTDs kill over 350,000 people per annum and cause the loss of between 27 and 56 million disability-adjusted life years [9]. To date, more than 2000 cases of eosinophilic meningitis have been recorded in China, even 100 cases in Taiwan and most human cases of angiostrongyliasis (~1300 cases) have been reported in Thailand [5,10], where between 0.3 and 2 people per 100,000 become infected annually [11,12]. These findings indicate that the extensive distribution of A.cantonensis in globally is high, thus putting humans as a higher risk of A.cantonensis infection.
In recent decades, more than 20 species of feral rodents have been categorized as pests in tropical and subtropical countries, and these species cause tremendous losses and damages to crops and food stocks [13]. Feral rodents are known to transmit 4 diseases and act as reservoir hosts to many zoonotic parasites that pose health risks to humans, including A.cantonensis, hantaviruses, Leptospira spp., Bartonella spp., Trypanosoma spp., and Babesia spp. [14][15][16] [17]. Importantly, the development of control methods against zoonotic parasites depends on knowledge of their life cycles and transmission patterns in different zoogeographical regions. Therefore, it is essential to survey the relationship between parasites and rodents in order to identify the sources of zoonotic infections [18].
Surprisingly, despite rodents being the dominant vertebrate species in many of these altered tropical systems and the key hosts for numerous zoonotic microparasites (viruses, bacteria, and protists), consistent patterns between habitat fragmentation and environment change with the epidemiology of multiple parasite diseases have yet to be determined, and studies that address the context of pathogen circulation are lacking.
Indeed, simultaneous to the technical and targeted approaches being, recommended by WHO are much wider attempts at sustainable development, most visible through 5 the lens of the sustainable development goals [19]. Meanwhile, there are little diagnostic methods and effective treatment methods. Furthermore, we need do more research to solve this challenge. Here, in this study, we aim to identify the prevalence of A.cantonensis in rodent hosts in China and several Asian countries, providing essential recommendations for the researchers and policy makers.

Methods
The protocol for this systematic review was defined in advance and registered with PROSPERO (CRD42020161665). This study was conducted in accordance with the PRISMA guidelines (Preferred Reporting Items for Systematic Reviews and Meta-analysis) for systematic review and meta-analysis. The PRISMA checklist (Table S1) was used to ensure inclusion of relevant information in the analysis.

Literature search
To evaluate the prevalence of A.cantonensis in rodent hosts in China and several Asian countries, we carried out a systematic review of the literature (full-text) published online in the English and Chinese between May 1946 and December 2019.
Records were selected systematically from 7 databases (Medline via to Pubmed, Web of science, Scopus, Google Scholar, CNKI, Wangfang, CBM). This range of years was important to study the prevalence since the first study was reported. The modified searches were performed by various combinations of the following terms using Boolean operator "AND" and "OR": (rat lungworm OR Angiostrongylus cantonensis OR Angiostrongyliasis OR Angiostrongylidae) AND (prevalence OR distribution OR epidemic OR incidence OR frequency OR occurrence OR detection OR identification 6 OR characterization OR investigation OR survey OR rate) AND Asia. The reference lists of selected articles also were screened manually and appropriate articles were included. Full text articles were downloaded or obtained through library resources.

Study selection
All selected articles had to meet the following inclusion criteria: (i) a cross-sectional study; (ii) the study published between May 1946 and December 2019; (iii) the language was limited to Chinese or English; (iv) full-text article; (v) infection cases in Asia, provided geographical location; (vi) reported as animal level prevalence data, not laboratory infected animals; (vii) exact total numbers and positive cases numbers; (viii) rodent hosts numbers higher than fifty, clearly rodents species; (ix) no relevant outcomes reported.
Investigations without these criteria were excluded. Also, if the same study data were published in both English and Chinese sources, the articles with less detailed information would be excluded from this study. When any authors found articles difficult to judge, the first author was consulted and eventual differences discussed to reach a consensus decision on whether to include or exclude the article.

Quality assessment
The included articles were evaluated using a 10-item quality appraisal checklist ( Text S1). An item would be scored '0' if it was answered 'no data available' or 'unclear'; if it was answered 'yes', then the item scored '1'. Article quality was assessed as follows: low quality = 0-3; moderate quality = 4-7; high quality = 8-10. 7 For the data extraction, the two independent assessors applied the inclusion criteria selected the articles and extracted the data. Discrepancies were resolved by consensus.

Data extraction
The detailed characteristics of each study were extracted using a pre-designed data-collection excel form. Information was collected as followings: first author, year of publication, location, geographical region, sample size, number of positive cases, diagnostic methods, types of rodent hosts, quality score of each study.

Statistical analysis
The statistical software used in the analysis was R software version (3.6.3). Estimated pooled prevalence and 95% confidence intervals (CI) were calculated with the Freeman-Tukey double arcsine transformation. Heterogeneity testing was performed using the I 2 and Cochran' Q statistic methods. A significant value (p<0.05) in the analysis suggested a real effect difference. The I 2 values of 25%, 50% and 75% were considered as low, moderate and high heterogeneity, respectively. The risk of study publication bias was assessed using the funnel plots, and the Egger's regression test.
Also a significant value (p<0.05) in the analysis suggested a real effect difference.
Furthermore, subgroup analysis were done if the heterogeneity were overlapping moderate I 2 . Four potential sources of heterogeneity were examined: country, animal species, publication year, quality score. The Q and I 2 statistics values were calculated for each subgroup to determine the effective factors on the prevalence A.cantonensis and heterogeneity about all the included studies.  Table 1.

Pooling and heterogeneity analysis
The pooled prevalence estimates of A.cantonensis infection in rodent hosts with individual studies are shown in a forest plot (Fig 3). A substantial heterogeneity is observed among studies (χ 2 =4979.77, P<0.05; I 2 =99.0%). When calculated using a random-effects model, the overall infection rate is 0.1003 (95%CI: 0.0765,0.1268).
The estimates of infection rates for different subgroups and heterogeneities are presented in Table 2

Publication bias
Despite the significant heterogeneity, the funnel plot displayed a symmetric spread of studies in terms of relative weight and effect size, thereby we could not directly judge whether there was publication bias in the included studies (Fig. 5). The results of Egger's test showed P=0.9147 (P>0.05). Therefore, we considered that there was no publication bias in the included studies. Notably, the total number of studies was reasonable, and the individual studies were of variable sample size. Moreover, Duval and Tweedie's trim and fill procedure for the detection of publication bias did not support the possibility of missing studies from the analysis.

Discussion
In previous study, rodents may play an important role in the transmission of certain (i) are considered as dominant species in several Asian countries [20,21]; (ii) live close to human dwellings [22]; (iii) they were also known to prey on snails not plants [23].
This result is consistent with Chen D's report [24].
Before 2008, there were outbreaks in Beijing, Wenzhou, Guangzhou and other areas in China, particularly, 160 cases infected in Beijing [25].  [26], larvae of Tsetse flies [27] and burrows of mammals fed on by triatominae insects [28]. With the land surface temperatures increasing, the chemical elements and physical properties of the soil have changed. All these soil changes can lead the definitive host survival rate up or down. Also, water is important to the natural history of many parasites or their vectors equally. Thermal tolerance may be a critical issue for many water-based, or semiaquatic organisms involved in

Conclusion
In conclusion, our systematic review and meta-analysis estimated a pool national prevalence of A.cantonensis in rodent hosts in Asian areas, particularly in south China, which provided a scientific basis for prevention a control of the spread of 1 6 angiostrongyliasis. The A.cantonensis infection rate among rodent hosts was still high in China, especially in Rattus norvegicus, and thus comprehensive measures should be taken for rodent host control to avoid a potential angiostrongyliasis outbreak.
Moreover, public health officials, epidemiologists, researchers, clinical technicians, medical practitioners, parasitologists, and veterinarians, as well as the general public, should be aware of such risks, and integrated strategies should be taken to reduce or eliminate such risks [32]. Consequently, further studies are required to updated strategies for controlling A.cantonensis infection risk among human population.
Text S2. References of the selected articles included in the systematic review.

Availability of data and materials
All data are included in this article.

Ethical approval and consent to participate
Not applicable.

Consent for publication
Not applicable.