Findings

Background

Cryptosporidiosis is caused by species of Cryptosporidium, important zoonotic protozoan parasites [1–3]. Cryptosporidium spp. not only have a cosmopolitan distribution but can also infect a wide range of animals including foxes [1, 4]. Humans and animals are often infected through faecal-oral route and infection can result in acute or chronic diarrhea and even death [3, 5]. So far, more than 17 Cryptosporidium species/genotypes, such as C. andersoni, C. parvum, C. hominis, C. meleagridis, C. felis, C. canis, C. muris, C. suis and Cryptosporidium sp. deer genotype, have been identified in humans [6–10], but only C. parvum, Cryptosporidium sp. muskrat genotype II and C. canis have been found in foxes [6, 11, 12].

The Arctic fox (Vulpes lagopus) is common in the Arctic regions [4], and has been imported to China from the former Soviet Union in the 1950s [13]. In China, with the improvement of living standards, Arctic foxes were commonly raised by farmers to provide furs for humans. More importantly, because of the close  relationship between farmed foxes and humans, foxes can transfer indirectly or directly many pathogens to humans, such as T. gondii [14]. Some studies concerning Cryptosporidium spp. infections in foxes have been reported [4, 6, 12, 15], but no such information about Cryptosporidium spp. prevalence in foxes is available in China. The objective of the present study was to estimate the prevalence of Cryptosporidium infection in farmed foxes in China, for the first time.

Methods

Ethics statement

This study was approved by the Animal Ethics Committee of Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences (Approval No. LVRIAEC2013010). The Arctic foxes from which the faeces were collected, were handled in accordance with good animal practices required by the Animal Ethics Procedures and Guidelines of the People’s Republic of China.

Specimen collection

A total of 302 faecal samples from 91 foxes in Jilin Province, from 70 foxes in Heilongjiang Province, and from 141 foxes from Hebei Province, were collected in 2014. All foxes were in good health during the sampling time. Fresh faecal samples were collected from each animal using sterile gloves immediately after the defecation onto the ground and transported to the laboratory. Information regarding geographical origin, gender and age of the foxes were acquired by a questionnaire.

DNA extraction and PCR amplification

Genomic DNA was extracted from faeces using an EZNAR Stool DNA kit (OMEGA, USA) following the manufacturer’s instructions and stored at -20 °C until PCR analysis. Cryptosporidium species/genotypes were identified by nested PCR amplification of the small subunit ribosomal RNA (SSU rRNA) gene [3]. Every amplification included positive and negative controls. Amplification products were visualised on  1.5 % agarose gels containing GoldView™ (Solarbio, China).

Sequencing and phylogenetic analyses

Positive secondary PCR products from foxes were sequenced by the Genscript Company (Nanjing, China). Cryptosporidium species/genotypes were identified by comparison with reference sequences using BLAST (http://www.ncbi.nlm.nih.gov/BLAST/) and computer program Clustal X 1.83. Phylogenetic relationships of Cryptosporidium spp. were reconstructed using Neighbour-Joining (NJ) method implemented in  Mega 5.0 (Kimura 2-parameter model, 1,000 replicates). All representative nucleotide sequences obtained were deposited in the GenBank under accession numbers KU215430-KU215436.

Statistical analysis

The variation in Cryptosporidium spp. prevalence (у) in foxes in relation to geographical location (x1), gender (x2) and age (x3) were analysed by χ2 test using SAS version 9.1 (SAS Institute Inc., USA). Using multivariable regression analysis each of these variables was included in the binary Logit model as an independent variable. The best model was identified  by Fisher’s scoring algorithm. All tests were two-sided. Results were considered statistically significant at P < 0.05. Odds ratios (ORs) with 95 % confidence intervals (95 % CI) were also calculated.

Results and discussion

A total of 48 out of 302 Arctic foxes (15.9 %) were tested Cryptosporidium-positive by nested PCR amplification of the SSU rRNA gene (Table 1). The prevalence in different farms varied from 0 to 31.4 % (data not shown). Cryptosporidium spp. prevalence was 14.1 % (9/64) in pre-weaned foxes, 15.6 % (28/180) in young foxes, and 19.0 % (11/58) in adult foxes (Table 1). The prevalence in different regions varied between 7.8–23.1 % (Table 1). Moreover, female foxes (18.4 %, 30/163) had a higher Cryptosporidium prevalence than males (12.9 %, 18/139), although the differences were not significant (Table 1). Sequence analysis of the SSU rRNA gene indicated that all of the 48 isolates represented C. canis (Fig. 1).

Table 1 Prevalence of Cryptosporidium canis in farmed foxes in Jilin, Heilongjiang and Hebei Provinces, northern China
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Fig. 1
figure 1

Phylogenetic analysis of Cryptosporidium canis using Neighbour-Joining (NJ) method based on sequences of the small subunit ribosomal RNA (SSU rRNA) gene. Bootstrap values >50 % are shown. Isolates of C. canis identified in the present study are indicated by a solid circle

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In the present study, the overall Cryptosporidium spp. prevalence was 15.9 % (95 % CI 11.8-20.0) (Table 1), which was higher than that in wild Arctic foxes in the central Canadian Arctic (9 %) [4], wild foxes in wetlands adjacent to the Chesapeake Bay, USA (8 %) [6], wild red foxes in Ireland (1.6 %) and Warwickshire, UK  (8.7 %) [12],  and Norway (2.2 %) [16], but lower than that in red foxes in the Slovak Republic (38.7 %) [11]. These differences might be related to the detection methods, age distribution of the samples, the timing of sample collection, sample sizes and geo-ecological conditions in the investigation regions.

The effects of geographical location, gender and age were analysed using univariate analysis. The impacts of multiple variables on the prevalence of C.  canis were evaluated by forward stepwise logistic regression analysis using Fisher’s scoring technique. In the final model, only one variable had a significant effect, described by the equation y = 0.5964x1 + 0.4646. Region of origin has a positive effect on the risk of C. canis ( OR =1.8, 95 % CI 1.3–2.6). Foxes collected from the Jilin Province (23.1 %. OR = 3.6, 95 % CI 1.6–7.8) and Heilongjiang Province (22.9 %, OR = 3.5, 95 % CI 1.5–8.0) were found to be more susceptible than those collected from the Hebei Province (7.8 %, 95 % CI 3.4-12.2, P = 0.0015) (Table 1).

Three Cryptosporidium species/genotypes (C. parvum, C. canis and Cryptosporidium sp. muskrat genotype II) have been found in foxes [4, 6, 12, 15]. Of these, C. parvum and C. canis have also been reported in humans [17, 18] suggesting that foxes could be a potential resource for humans acquiring cryptosporidiosis. In the present study, all of the 48 Cryptosporidium-positive samples represented C. canis (Fig. 1), which was similar to previous studies showing that C. canis is more prevalent in foxes [4, 6, 11, 16]. However, probably due to the smaller sample sizes, C. parvum and Cryptosporidium sp. muskrat genotype II were not found in the present study.

Conclusions

The results of the present study indicated the existence (15.9 %, 48/302) of C. canis infections in farmed Arctic foxes in northern China. Logistic regression analysis indicated that region was the significant risk factor shown by this study for Cryptosporidium spp. infection in the foxes examined. The data could provide a foundation for the prevention and control of Cryptosporidium spp. infections in foxes, other animals and humans.