Analysis on the investigation results of plague natural foci in Yulong County of Yunnan Province in 2017 / 中华地方病学杂志

ABSTRACT

Objective:To investigate and determine the epidemic scope of plague natural foci in Yulong County of Yunnan Province, and to assess its epidemic risk, so as to providing basis for monitoring, prevention and control of plague.Methods:In 2017, 2 - 3 natural villages were selected from 8 villages and towns in Yulong County according to geographical landscape, altitude, population and area. During October and November, small mammal hosts and their parasitic fleas were captured by the night trap (cage) method, Yersinia pestis was isolated from host animal organs, and plague F1 antigen and antibody were detected by colloidal gold test. Plague specific antigen was detected by reverse indirect hemagglutination test (RIHA) in self-dead small mammals. Animal serum from dogs, cats and mice were collected for detection of plague F1 antibody by indirect hemagglutination test (IHA). Results:A total of 1 019 host animals including self-dead small mammals were collected, belonging to 22 species, 12 genera, 6 families, 4 orders. Among them, 1 016 small mammals were captured by tools and 996 were outdoors, with the capture rate of 25.28% (996/3 940). The dominant species of small mammals outdoors were Apodemus chevrieri, Rattus (R.) rattus, Eothenomys miletus and Crocidura attenuate, which accounted for 30.32% (302/996), 22.09% (220/996), 17.37% (173/996) and 12.35% (123/996). The common species were Niviventer confucianus, R.nitidus and R.norvegicus, which accounted for 8.13% (81/996), 4.02% (40/996) and 1.81% (18/996). A total of 20 small mammals of 9 species were captured indoors in the residential area, and the capture rate was 1.11% (20/ 1 800). The dominant species were R.norvegicus, R.nitidus and Mus musculus, which accounted for 30.00% (6/20), 25.00% (5/20) and 10.00% (2/20). Eighteen small mammals of 8 species were infected with 67 parasitic fleas, belonging to 5 species, 5 genera, 3 families. The total flea infection rate was 1.77% (18/1 019) and the total flea index was 0.070. Among them, 49 parasitic fleas from 4 small mammals of 3 species were collected indoors. The flea infection rate was 19.05% (4/21) and the flea index was 2.333. Leptopsylla segnis had the highest flea infection rate of 9.52% (2/21) and flea index of 0.571. Ctenocephalides felis had the highest flea index of 1.571 and flea infection rate of 4.76% (1/21). They were the main flea species on the body surface of small mammals in residential areas. There were 14 small mammals infected with parasitic fleas outdoors, and 18 fleas in 5 species were collected with flea infection rate of 1.40% (14/998) and flea index of 0.018. Among them, Leptopsylla segnis had the highest flea infection rate was 0.50% (5/998) and the flea index was 0.005. The flea infection rate of Neopsylla specialis specialis was 0.40% (4/998), and the flea index was 0.004. Ctenophthalmus quadratus had the highest flea index of 0.007, and the flea infection rate ranked the third with 0.30% (3/998). The flea infection rate and flea index of Frontopsylla spadix spadix were the lowest, which were 0.20% (2/998) and 0.002, respectively. Ctenophthalmus quadratus, Leptopsylla segnis and Neopsylla specialis specialis were the dominant parasitic fleas on the surface of outdoor small mammals. A total of 419 indicator animal sera were collected, including 402 dog sera. One of them was positive by IHA, with a positive rate of 0.25% (1/402). Seventeen serum samples were collected from cats and mice, and IHA test results were negative. Yersinia pestis was isolated and cultured from the organs of small mammals and the detection of Yersinia pestis by colloidal gold test was negative. RIHA test of self-dead small mammals was negative. Conclusion:A plague indicator animal positive spot is newly found in the plague natural foci in Yulong County, and the plague epidemic monitoring, prevention and control in this region should be strengthened.