Patterns of Flea Infestation in Rodents and Insectivores From Intensified Agro-ecosystems, Nw Spain

Background: Fleas frequently infest small mammals and play important vectoring roles in the epidemiology of (re)emerging zoonotic disease. Rodent outbreaks in intensified agroecosystems of NW Spain have been recently linked to periodic zoonotic disease spillover to local human populations. Obtaining qualitative and quantitative information about the composition and structure of the whole flea and small mammal host coexisting communities is paramount to understand disease transmission cycles and to dilucidate the disease-vectoring role of flea species. Methods: Here we report on a large spatial (6 locations) and temporal (6 years with 3 samplings/year) survey conducted in intensively farmed landscapes in NW Spain, aiming to: (i) characterise the flea community parasitizing the small mammal host guild (Microtus arvalis, Apodemus sylvaticus, Mus spretus, Crocidura russula) in terms of flea-host specificity, abundance, prevalence, intensity and aggregation; (ii) evaluate patterns of co-infection by different flea species in hosts; and (iii) study the variation of flea abundance according to season and host sex. Results: Three flea species dominated the system (99.4%): Ctenophthalmus apertus, Leptopsylla taschenbergi and Nosopsyllus fasciatus. Results showed a high aggregation pattern of fleas in all hosts. C. apertus and N. fasciatus were shared by all host species in the guild, but L. taschenbergi mainly parasitized mice (M. spretus, A. sylvaticus). We found significant male-bias infestation patterns in mice, and significant seasonal variations in flea abundances for all rodent hosts (M. arvalis, M. spretus, A, sylvaticus). Simultaneous infections by 2 or 3 flea species were found in 36.8% of all hosts, and N. fasciatus was the most common flea co-infecting hosts. Conclusions: Our study shows that flea infestation patterns differ among hosts and seasons, influencing their potential vectoring role of diseases. Further investigation should be carried out on abundant and polyphagous fleas (e.g. N. fasciatus), since they may have higher competence to circulate zoonoses in natural systems.