Every year, the world faces vector-borne diseases including arboviral (arthropod-borne viral) diseases caused by several, possibly fatal flaviviruses. The way they spread is related to a complex episystem involving several elements including vector abundance, animal carriers, and the flavivirus itself, which makes the disease difficult to manage. Here, we serologically screened 556 animals (358 dogs and 198 horses) using ELISA and a serum neutralisation test (SNT) for the anti-IgG antibodies directed against the West Nile (WNV) and Usutu (USUV) viruses. The animals investigated were split into two groups according to their exposure to the risk linked to the abundance of mosquitoes and migratory birds as well as the geographical distribution of arbovirus cases (458 animals from areas exposed to risk and 98 not exposed to risk). Overall, 25/310 dogs (8.1%) and 2/148 horses (1.3%) tested positive for SNT WNV and/or USUV in geographically exposed areas. Animals in unexposed areas were all negative. The geographical distribution of WNV seroprevalence in dogs was the same as the distribution of reported autochthonous human cases. Interestingly, a non-negligible seroprevalence caused by an as yet unidentified flavivirus other than WNV, USUV, or tick-borne encephalitis virus (TBEV) was detected in 18.6% (28/150) and 3.7% (4/106) of the investigated dogs and horses from the Hérault department, in the southeast of France, respectively. These data highlight the role of outdoor dogs as suitable sentinels for the evidence of WNV and USUV circulation in each area. In addition, the serological detection of an as yet unidentified flavivirus circulating in the Hérault department deserves greater attention, as this may constitute a serious threat to public and animal health.

Coxiella burnetii, also known as the causal agent of Q fever, is a zoonotic pathogen infecting humans and several animal species. Here, we investigated the epidemiological context of C. burnetii from an area in the Hérault department in southern France, using the One Health paradigm. In total, 13 human cases of Q fever were diagnosed over the last three years in an area comprising four villages. Serological and molecular investigations conducted on the representative animal population, as well as wind data, indicated that some of the recent cases are likely to have originated from a sheepfold, which revealed bacterial contamination and a seroprevalence of 47.6%. However, the clear-cut origin of human cases cannot be ruled out in the absence of molecular data from the patients. Multi-spacer typing based on dual barcoding nanopore sequencing highlighted the occurrence of a new genotype of C. burnetii. In addition, the environmental contamination appeared to be widespread across a perimeter of 6 km due to local wind activity, according to the seroprevalence detected in dogs (12.6%) and horses (8.49%) in the surrounding populations. These findings were helpful in describing the extent of the exposed area and thus supporting the use of dogs and horses as valuable sentinel indicators for monitoring Q fever. The present data clearly highlighted that the epidemiological surveillance of Q fever should be reinforced and improved.