Molecular Evidence of a Broad Range of Pathogenic Bacteria in Ctenocephalides spp.: Should We Re-Examine the Role of Fleas in the Transmission of Pathogens?

The internal microbiome of common cat and dog fleas was studied for DNA evidence of pathogenic bacteria. Fleas were grouped in pools by parasitized animal. DNA was extracted and investigated with 16S metagenomics for medically relevant (MR) bacteria, based on the definitions of the International Statistical Classification of Diseases and Related Health Problems (WHO). The MR bacterial species totaled 40, were found in 60% of flea-pools (N = 100), and included Acinetobacter baumannii, Bacteroides fragilis, Clostridium perfringens, Enterococcus faecalis, E. mundtii, Fusobacterium nucleatum, Haemophilus aegyptius, Kingella kingae, Klebsiella pneumoniae, Leptotrichia buccalis, L. hofstadii, Moraxella lacunata, Pasteurella multocida, Propionibacterium acnes, P. propionicum, Proteus mirabilis, Pseudomonas aeruginosa, Rickettsia australis, R. hoogstraalii, Salmonella enterica, and various Bartonella, Staphylococcus, and Streptococcus species. B. henselae (p = 0.004) and B. clarridgeiae (p = 0.006) occurred more frequently in fleas from cats, whereas Rickettsia hoogstraalii (p = 0.031) and Propionibacterium acnes (p = 0.029) had a preference in fleas from stray animals. Most of the discovered MR species can form biofilm, and human exposure may theoretically occur through the flea-host interface. The fitness of these pathogenic bacteria to cause infection and the potential role of fleas in the transmission of a broad range of diseases should be further investigated.