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

Only 29.5 +/- 8.91% of engorged Amblyomma americanum (L.) nymphs that we in oculated with Ehrlichia chaffeensis molted successfully to adults compared with 75.8 +/- 7.46% of engorged nymphs that were not inoculated. However, 6 5.4 +/- 6.02% of unfed nymphs of this species were exposed for 2 h to E. ch affeensis suspension introduced to them through glass capillaries gained we ight. These nymphs were placed on rabbits, and approximate to 50% of them c ompleted their feeding and molted successfully to adults. Weight gained was higher (71.8 +/- 17.33% and 69.8 +/- 23.26%) for unfed A. americanum femal es that fed from capillaries for 2 and 24, h respectively, than for nymphs. Similar values were recorded for Dermacentor variabilis (Say) (61.0 +/- 16 .23%) and Rhipicephalus sanguineus (Latreille) (59.0 +/- 18.62%) females af ter 24 h of capillary feeding. The amount of E. chaffeensis suspension take n in by females of A. americanum, D. variabilis, and R. sanguineus during 2 4 h of feeding was 11.2 +/- 3.56, 10.9 +/- 4.29 and 6.3 +/- 2.35 mu l, resp ectively. This volume is equivalent to approximate to 12,969, 12,622, and 7 ,295 infected cells ingested by the species mentioned above. Positive corre lation between the volume taken in by the ticks and the weight gained by th e females was found, but the initial weight of the unfed females did not ef fect the weight they gained. The pathogen was found in the females of all 3 species by polymerase chain reaction procedures for at least 7 d, indicati ng that the capillary feeding method can be successfully used for infecting unfed ticks. The potential use of this method is discussed.