Development of Acanthocheilonema reconditum (Spirurida, Onchocercidae) in the cat flea Ctenocephalides felis (Siphonaptera, Pulicidae)

Acanthocheilonema reconditum has a global distribution and in many geographical areas is the sole or the most prevalent filarioid infesting dogs (Brianti et al., 2012, Parasitology, 139:530-536). Despite its large frequency and distribution information on its biology and life history is meagre. Our research aimed at studying the development of Acanthocheilonema reconditum (Spirurida, Onchocercidae) inside the cat flea, Ctenocephalides felis instrumentally to elucidate: i) the correlation between the concentration of microfilariae in the blood and the rate of flea infection; ii) the development time span from microfilariae to infective third stage larvae; iii) the anatomical localization of the developing larvae inside the flea’s body. Ctenocephalides felis fleas were fed through an artificial feeding system, named “artificial dog” (Wade and Georgi, 1988, J Med Entomol, 25:186-190), with A. reconditum infected blood at different concentrations of microfilariae (i.e., low, group L = 250; medium, group M = 500; high number, group H = 1,500 microfilariae/ml) or with uninfected dog blood (group C). Fleas were sampled in 12 different time-points throughout the study period (i.e., D1-D28) and A. reconditum was detected by dissection, PCR and histology. Of 2,105 fleas fed with infected dog blood, 891 (38.7%) died during the study before being sampled and the remaining (n = 1,214) were examined for A. reconditum. No statistically significant differences in the mortality rate were detected among infected groups and between these and the control group at any time-point. At the dissection first-stage larvae (L1) were identified after 2 days post infection (D2), the second stage (L2) at D13, and infective third-stage larvae (L3) were found at D15 (Figure 1). Eighteen (30%) flea pools of the 60 molecularly examined tested positive. Although not statistically significant, positive pools were higher in group M (8/19; 42.1%) and H (7/20; 35.0%) than in group L (3/21; 14.3%). At the histology, L2 were detected at D13 in the sub-cuticle region of one female flea embedded in the back muscle (Figure 2). This study demonstrates that the “artificial dog” may be successfully used to infect the cat flea with A. reconditum larvae, reducing the use of live animals in the experimentation. Although arthropod-transmitted pathogens may cause alterations in the vector’s fitness, playing an important role in the dynamics of transmission (Hurd, 2003, An. Rev. Entomol., 48:141–161), findings herein presented suggest that the development of A. reconditum larvae do not impair the survival of C. felis. In artificially infected fleas, the development of A. reconditum to L3 infective stage takes 15 days being one of the shorter times among filarioids of dogs. Although further confirmatory studies are needed, results of the present study confirm that fleas act as an intermediate host of A. reconditum and suggest that the transmission to dogs may occur via the ingestion of infected fleas.