Comparison of methods for introducing and producing artificial infection of ixodid ticks (Acari: Ixodidae) with Ehrlichia chaffeensis

摘要

Only 29.5±8.91% of engorged Amblyomma americanum nymphs that were inoculated with E. chaffeensis moulted successfully to adults compared with 75.8±7.46% of engorged nymphs that were not inoculated. However, 65.4±6.02% of unfed nymphs of this specieswere exposed for 2 h to E. chaffeensis suspension introduced to them through glass capillaries gained weight. These nymphs were placed on rabbits, and～50% of them completed their feeding and moulted successfully to adults. Weight gained was higher (71.8±17.33% and 69.8±23.26%) for unfed A. americanum females that fed from capillaries for 2 and 24 h, respectively, than for nymphs. Similar values were recorded for Dermacentor variabilis (61.0±16.23%) and Rhipicephalus sanguineus (59.0±18.62%) females after 24 h of capillary feeding. The amount of E. chaffeensis suspension taken in by females of A. americanum, D. variabilis and R. sanguineus during 24 h of feeding was 11.2±3.56, 10.9±4.29 and 6.3±2.35μl, respectively. This volume is equivalent to～12 969, 12 622, and 7295 infected cells ingested by the species mentioned above. Positive correlation between the volume taken in by the ticks and the weight gained by the females was found, but the initial weight of the unfed females did not affect the weight they gained. The pathogen was found in the females of all 3 species by PCR procedures for at least 7 days, indicating that the capillary feeding method can be successfully used for infecting unfed ticks. The potential use of this method is discussed.