Circulation of a Meaban-like virus in yellow-legged gulls and seabird ticks in the western Mediterranean basin

Abstract

In recent years, a number of zoonotic flaviviruses have emerged worldwide, and wild birds serve as their major reservoirs. Epidemiological surveys of bird populations at various geographical scales can clarify key aspects of the eco-epidemiology of these viruses. In this study, we aimed at exploring the presence of flaviviruses in the western Mediterranean by sampling breeding populations of the yellow-legged gull (Larus michahellis), a widely distributed, anthropophilic, and abundant seabird species. For 3 years, we sampled eggs from 19 breeding colonies in Spain, France, Algeria, and Tunisia. First, ELISAs were used to determine if the eggs contained antibodies against flaviviruses. Second, neutralization assays were used to identify the specific flaviviruses present. Finally, for colonies in which ELISA-positive eggs had been found, chick serum samples and potential vectors, culicid mosquitoes and soft ticks (Ornithodoros maritimus), were collected and analyzed using serology and PCR, respectively. The prevalence of flavivirus-specific antibodies in eggs was highly spatially heterogeneous. In northeastern Spain, on the Medes Islands and in the nearby village of L'Escala, 56% of eggs had antibodies against the flavivirus envelope protein, but were negative for neutralizing antibodies against three common flaviviruses: West Nile, Usutu, and tick-borne encephalitis viruses. Furthermore, little evidence of past flavivirus exposure was obtained for the other colonies. A subset of the Ornithodoros ticks from Medes screened for flaviviral RNA tested positive for a virus whose NS5 gene was 95% similar to that of Meaban virus, a flavivirus previously isolated from ticks of Larus argentatus in western France. All ELISA-positive samples subsequently tested positive for Meaban virus neutralizing antibodies. This study shows that gulls in the western Mediterranean Basin are exposed to a tick-borne Meaban-like virus, which underscores the need of exploring the spatial and temporal distribution of this flavivirus as well as its potential pathogenicity for animals and humans.

Figure 1. Locations of the colonies sampled in the western Mediterranean (A) and of the nests sampled in the Medes colony (B).

(A) Colony numbers are those indicated in Table 1. Red stars indicate colonies that had at least one egg that was positive for antibodies against the flavivirus envelope protein, while turquoise circles indicate colonies that had no positive eggs. (B) The color of a nest indicates its flavivirus-specific antibody status (red: positive, turquoise: negative), and the symbol indicates the sampling year (triangle: 2010, square: 2011, circle: 2012; GPS data were not available for 2009). Doubtful samples were considered to be negative (see text). Pictures by J. González-Solis and taken from Wikimedia commons.

Figure 2. Unrooted maximum-likelihood tree constructed using NS5 partial gene sequences (143 bp) amplified from O. maritimus ticks (red) and a set of sequences from the flavivirus complex (see text).

Only bootstrap support values above 70% are indicated above the branches. Reference sequences obtained for viruses belonging to the seabird tick-borne flavivirus group are indicated; these include Meaban (red: this study, dark-red: reference), West Nile (blue), Usutu (orange), and tick-borne encephalitis (green).