关键词: 棘球蚴病, 终末宿主, 粪便污染, PCR, 色达县

Abstract:

Objective To understand the feces contamination and characteristics of definitive hosts of Echinococcus in the field in Seda County, Sichuan Province, to provide a basis for a prevention and control strategy of the source of infection in the field. Methods In October 2020, survey spots were selected every 1-2 km apart along the main traffic routes and field grazing routes in Seda County using mechanical sampling method to record their geographic location, number of feces found, pasture type, topographic type, vegetation type, vegetation coverage, mean height of grass, small mammal densities, and feces type of definitive hosts. Canine fecal samples were collected from survey spots, and the DNA was extracted from fthe samples for detecting the infection of Echinococcus by PCR. PCR-positive products were sent for sequencing, and the sequences were compared against the NCBI database to determine the species of Echinococcus. SPSS 18.0 software was used to statistically analyze the field contamination of definitive hosts’ feces and its characteristics. Results In total, 40 survey spots were selected, among them 34 (85.00%) were found having canine feces, while Echinococcus-positive feces were detected in 17 survey spots (42.50%). A total of 227 canine fecal samples were collected and examined by PCR, revealing the positive rates of Echinococcus spp., E. shiquicus(Es) and E. multilocularis (Em) were 18.06% (41/227), 14.10% (32/227), and 4.85% (11/227), respectively. Among these samples, two were of mixed infection of Es and Em, while no Eg-positive feces was found. The fecal-positive rate of Echinococcus in winter and summer pastures was 19.90% (40/201) and 3.85% (1/26), respectively (P > 0.05). The fecal-positive rate of Es in winter pasture was 15.92% (32/201) higher than that in summer pasture (0, 0/26) (P < 0.05). There was no significant differences in fecal-positive rates of Echinococcus, Es, and Em on plain, hillside, and benchland sites(P > 0.05). Among the different vegetation types, there were no significant differences in the positive rates of Echinococcus, Es, and Em in fecal samples between altitude cold meadow and altitude cold bush-meadow. The feces density in altitude cold meadow (7.17/10 000 m ²) was higher than that of altitude cold bush-meadow (3.44/10 000 m²) (Z = -2.376, P < 0.05). There was no significant difference in the fecal-positive rates of Echinococcus, Es, and Em in areas with sparse, relatively sparse, medium, relatively dense, and dense vegetation coverage (P > 0.05). Among different mean grass heights, theere was no significant difference in the fecal-positive rates of Echinococcus, Es, and Em at mean grass heights ≤ 5 cm, 6-10 cm, 11-15 cm and ≥ 16 cm(P > 0.05). The small mammals density 401-600 heads/10 000 m² rendered the feces density 12.25/10 000 m², which was higher than that at the mammal density ≤ 200 heads/10 000 m ² (3.32/10 000 m²) (Z = -2.738, P < 0.008). The fecal-positive rates of Es at the mammal density≥ 601 heads/10 000 m² was 29.73% (11/37), which was higher than the positive rate 5.48% (4/73) at the density ≤ 200 heads/10 000 m ² (χ² = 12.261, P < 0.008). The fox fecal-positive rates of Echinococcus and Es were 25.95% (34/131) and 22.14% (29/131), respectively, which were both higher than that of canine feces (7.45%, 7/94; 3.19%, 3/94) (χ ² = 12.580, 16.103, P < 0.05). There was no significant difference in the positive rate of Em between dog feces (5.32%, 5/94) and fox feces (4.58%, 6/131) (P > 0.05). Conclusion The field surveyed in Seda County, Sichuan Province is highly contaminated by Echinococcus of definitive hosts’ feces, showing foxes as the main source of infection, high Em positive rate in dog feces, in Seda County, Sichuan Province. It was demonstrated that winter pasture, altitude cold meadow, and areas with high densities of small mammals may the key areas for control of sources of infection in the wild.

Key words: Echinococcosis, Definitive host, Fecal contamination, PCR, Seda county