Study on the aggregation patterns of fleas parasitizing the great gerbil (Rhombomys opimus) in the Junggar Basin plague natural focus.

Abstract

Background: The great gerbil (Rhombomys opimus), whose ectoparasitic fleas significantly influence the transmission and prevalence of plague, was the dominant rodent species in the Junggar Basin in Northwestern China. However, the distribution pattern of fleas parasitizing the great gerbils and whether that pattern affected the intensity of plague prevalence in different regions remains unclear.

Methods: A total of 17,780 fleas were collected from 2258 great gerbils throughout 90 investigations. This study focused on analyzing the rate of flea infestation and the flea indices of species that parasitized the great gerbils. The aggregation patterns of fleas parasitizing the great gerbils were measured using the parameter b of Taylor's power law, and the differences in the aggregation index of plague epidemic areas were compared.

Results: We observed an aggregated distribution of ectoparasitic fleas in the great gerbils. The aggregation degree of combined fleas was higher (P > 0.05) in the eastern area of the Junggar Basin than in the western area. The primary species of ectoparasitic fleas of the great gerbils were Xenopsylla skrjabini, Xenopsylla minax, Xenopsylla hirtipes, and Nosopsyllus laeviceps laiveceps. X. skrjabini exhibited the highest (P < 0.01) degree of aggregation in the eastern zone (III), with an aggregation index of 1.61. In addition, in the middle zone (II), the aggregation index of X. minax and X. hirtipes reached their peak, with values of 1.53 and 1.56, respectively. Conversely, the degree of aggregation of N. laeviceps was more pronounced in the eastern zone than in the western zone of the Junggar Basin. Notably, the aggregation degree of the combined fleas of the great gerbils during the low-intensity plague epidemic period, with an index of 1.93, was significantly higher (P < 0.001) than during the high-intensity epidemic period, with an index of 1.50.

Conclusions: Fleas exhibited an aggregated distribution within the great gerbil population. The levels of flea aggregation varied across zones characterized by differing intensities of plague epidemics. In addition, the degree of flea aggregation was significantly correlated with the intensity of plague prevalence.