The prevalence of Babesia microti in rodents captured from different cities in Fujian province
A total of 1087 rodents were captured from 26 surveillance points in eight cities in Fujian Province (Figs. 1 and 2, Table 1, Additional file 1: Table S1). The captured rodents belonged to Rodentia, including two families, seven genera, and twelve species (Table 2). Sequencing analysis by blastn showed that 3.96% (43/1087) of rodents were infected by B. microti (Table 1).
Table 1
The prevalence of B. microti in rodents captured from eight cities in Fujian Province
Cities | No. of traps | No. of rodents tested | No. of positive for B. microti | Density (%) | Positive rate (%) | Odd ratio |
Sanming | 2307 | 171 | 17 | 7.41 | 9.94 | 5.96 |
Ningde | 2549 | 209 | 15 | 8.20 | 7.18 | 4.18 |
Nanping | 3922 | 330 | 8 | 8.41 | 2.42 | 1.34 |
Fuzhou | 1790 | 165 | 3 | 9.22 | 1.82 | 1.00 |
Putian | 355 | 30 | 0 | 8.45 | 0.00 | |
Quanzhou | 1549 | 110 | 0 | 7.10 | 0.00 | |
Zhangzhou | 439 | 41 | 0 | 9.34 | 0.00 | |
Longyan | 584 | 31 | 0 | 5.31 | 0.00 | |
Total | 13495 | 1087 | 43 | 8.05 | 3.96 | |
Table 2
The prevalence of Babesia in host animals of different species
Orders | Families | Genera | Species | No. of examined | No. of positive (%) |
Rodentia | Muridae | Rattus | R. norvegicus | 337 | 3(0.89) |
R. losea | 215 | 3(1.40) |
R. tanezumi | 163 | 1(0.61) |
R. edwardsi | 17 | 1(5.88) |
R. rattus | 4 | 0(0.00) |
Apodemus | A. agrarius | 32 | 1(3.13) |
Mus | M. musculus | 5 | 1(20.00) |
Niviventer | N. confucianus | 47 | 8(17.02) |
N. fulvescens | 152 | 7(4.61) |
Berylmys | B. bowersi | 50 | 1(2.00) |
Bandicota | B. indica | 56 | 17(30.36) |
Cricetidae | Microtus | M. fortis | 9 | 0(0.00) |
Artiodactyla | Bovidae | Capra | C. a. hircus | 316 | 4(1.27) |
Bos | B. bubalis | 85 | 0(0.00) |
Suidae | Sus | S. s. domesticus | 18 | 1(5.56) |
Carnivora | Canidae | Canis | C. l. familiaris | 56 | 1(1.79) |
Of the 12 species of trapped rodents, the brown rat (Rattus norvegicus) accounted for the most (30.00%, n = 337), followed by Rattus losea (19.78%, n = 215), whilst Rattus rattus accounted for the least (0.37%, n = 4). With the exception of Microtus fortis and R. rattus, 10 of 12 species tested positive for B. microti infection. The positive infection rates of B. microti ranged from 0.61% (1/163) in Rattus tanezumi to 30.36% (17/56) in Bandicota indica (Table 2). There was no significant difference in the prevalence of B. microti in the common domestic rats from residential areas (R. norvegicus and R. tanezumi (P = 0.739)). Within the wild rodents, (from irrigated cropland, shrub, and forest), the sum of B. microti infection rates in the rats B. indica and Niviventer confucianus was 24.27%, which was significantly higher than that of other species of rodents (χ2 = 66.003, P = 0.000).
Infected rodents were caught from four cities, including Sanming, Ningde, Nanping, and Fuzhou (Table 1). Rodents collected from Sanming had the highest B. microti infection rate of 9.94% (17/171). B. microti infection rates in hosts from Sanming and Ningde were both significantly higher than in hosts captured in Fuzhou (odds ratios: 5.96, 4.18, respectively; P < 0.05) (Table 1).
The prevalence of Babesia in domestic animals in Fujian
Blood samples from 316 domestic goats, 85 water buffalo, 56 domestic dogs, and 18 domestic pigs were also collected for the detection of Babesia infection. Surprisingly, no water buffaloes were infected with Babesia (Table 2). There was no significant difference in the prevalence of Babesia between male and female domestic goats (P = 0.129) (not shown in the table).
The risk factors associated with B. microti infection
Risk factors related to B. microti infection in rodents were analyzed with respect to sex, age, and ecological habitat (Table 3). There was no significant difference in the prevalence of B. microti between male and female rodents (χ2 = 0.466, P = 0.495). However, the prevalence of B. microti in adult rodents (4.53%) was significantly higher (χ2 = 4.645, P = 0.031) than in pubertal rodents (1.10%). It is worth noting that the prevalence of B. microti in mammals from irrigated cropland, shrub, and forest, which were 4.70%, 11.18%, and 4.55%, respectively, were all significantly higher than those in rodents from residential areas (P < 0.05, Tables 3 and 4). Furthermore, the multivariate logistic regression analysis suggested that irrigated cropland, shrub, and forest were risk factors for B. microti infection (Table 4).
Table 3
Risk factors related to Babesia microti based on univariate analyses
Variable | Simple size | Babesia microti infection |
cases | constituent ratio (%) | positive rate (%) | χ2 | P-value |
gender | | | | | |
male | 561 | 51.61 | 3.57 | 0.466 | 0.495 |
female | 526 | 48.39 | 4.37 | | |
age | | | | | |
pubertal | 181 | 16.65 | 1.10 | 4.645 | 0.031 |
adult | 906 | 83.35 | 4.53 | | |
habitat | | | | | |
residential areas | 504 | 46.36 | 0.99 | 35.438 | 0.000 |
irrigated cropland | 149 | 13.71 | 4.70 | | |
shrub | 170 | 15.64 | 11.18 | | |
forest | 264 | 24.29 | 4.55 | | |
Table 4
Risk factors related to Babesia microti infection based on multivariate logistic regression
Variable | OR(95% CI) | P-value |
gender | | |
male | 1 | |
female | 0.728 (0.390–1.360) | 0.319 |
age | | |
pubertal | 1 | |
adult | 0.307(0.072–1.304) | 0.110 |
habitat | | |
residential areas | 1 | |
irrigated cropland | 0.198 (0.061–0.635) | 0.006 |
shrub | 0.084(0.031–0.231) | 0.000 |
forest | 0.200(0.070–0.576) | 0.003 |
Genetic and phylogenetic analysis of Babesia species
Gene sequencing of the 18S rRNA gene from the positive samples found 43 samples containing B. microti, five containing Babesia sp., and one containing Babesia canis vogeli. In order to construct the phylogenetic tree, the 18S rRNA gene sequences of another 18 isolates of B. microti from other regions were included for comparison. Babesia sp. venatorum from Heilongjiang, Babesia sp. XXB/Hangzhou from Zhejiang and B. divergens from Ireland were used as the outgroup. All B. microti sequences from infected rodents shared 100% homology with sequences from Japan (AB032434.1). The sequence was deposited in GenBank with accession number MZ619064. Phylogenetic analyzes revealed that MZ619064 belonged to Kobe-type (Fig. 3).
The sequences of 18S rRNA genes with different Babesia species were used to reveal the phylogenetic relationship of Babesia identified in this study. Toxoplasma gondii (L24381.1) from Australia was used as an outgroup. Babesia canis vogeli detected in the domestic dog was identical to the sequences from Cote d’ Ivoire (MK495837.1) and Brazil (KU662365.1). Both domestic pigs and domestic goats in Fujian were infected with Babesia sp., and their homology was 98.17%. The sequences of B. canis vogeli from Canis lupus familiaris, Babesia sp. from Sus scrofa domesticus, and Babesia sp. from Capra aegagrus hircus in this survey were deposited in GenBank with accession numbers MZ618690, MZ619045, and MZ619046, respectively. Phylogenetic analyzes suggested that MZ618690, MZ619045, and MZ619046 belonged to Babesia (sensu stricto), while MZ619064 belonged to Babesia (sensu lato) (Fig. 4).