Biotic and abiotic factors influencing the prevalence, intensity and distribution of Eucoleus aerophilus and Crenosoma vulpis in red foxes, Vulpes vulpes from Romania.To understand the importance of host' habitat choice in determining parasite burden, we studied the distribution of two helminth parasites of the red fox (Vulpes vulpes) in south-eastern Europe (Romania): Crenosoma vulpis and Eucoleus aerophilus, both widely distributed respiratory nematodes parasitic in various carnivores.  Even though the life cycle and biology of the two nematodes follow a different pattern, both parasites appear to be co-distributed and often co-infect foxes with variable prevalences across their range.  Between July 2016 and August 2018, 550 red foxes, V. vulpes were collected by hunters in different localities from 22 counties of Romania and examined by necropsy.  All parasites found in the trachea and bronchial system were collected and preserved in 70% ethanol.  We characterised red fox/parasite habitats using seven predictors (fragmentation, altitude, presence/absence of water surface, per cent cover of arable land/grassland/urbanized areas/forest cover/wetlands).  Prevalence, abundance, intensity, and sex ratio were calculated and statistically analysed using the R software.  Out of the 550 examined foxes, 76.2% were infected with lungworms.  The overall prevalence was 32.0% for C. vulpis and 72.5% for E. aerophilus.  The mean intensity of infection was 13.70 for C. vulpis 6.15 for E. aerophilus.  For both nematodes, the prevalence was significantly higher in males than in females, and there was no influence of hosts' age.  No statistical differences were found for intensity and mean intensity in the case of infection with C. vulpis and E. aerophilus between age and sex categories.  The abundance of C. vulpis showed a strong positive relationship with the presence of wetlands and habitat fragmentation.  We found a significant correlation between the abundance of E. aerophilus and altitude, with foxes from higher elevations showing higher prevalences.
R