RESUMEN
Bluetongue virus (BTV) hitherto consisted of 26 recognized serotypes, of which all except BTV-26 are primarily transmitted by certain species of Culicoides biting midges. Three variants of an additional 27th bluetongue virus serotype (BTV-27v01-v03) were recently detected in asymptomatic goats in Corsica, France, 2014-2015. Molecular characterization revealed genetic differences between the three variants. Therefore, in vivo characteristics were investigated by experimental infection of a total of 15 goats, 11 sheep and 4 cattle with any one of the three variants in separated animal trials. In goat trials, BTV-naïve animals of the same species were kept in a facility where direct contact was unhindered. Of the 15 inoculated goats, 13 and 14 animals were found positive for BTV-RNA and antibodies (Ab), respectively, until the end of the experiments. Surprisingly, BTV-Ab levels as measured with ELISA and neutralization test (SNT) were remarkably low in all seropositive goats. Virus isolation from whole-blood was possible at the peak of viremia until 49 dpi. Moreover, detection of BTV-27v02-RNA and Ab in one contact goat indicated that-similar to BTV-26-at least one of three BTV-27 variants may be transmitted by contact between goats. In the field, BTV-27 RNA can be detected up to 6 months in the whole-blood of BTV-27-infected Corsican goats. In contrast, BTV RNA was not detected in the blood of cattle or sheep. In addition, BTV-27 Abs were not detected in cattle and only a transient increase in Ab levels was observed in some sheep. None of the 30 animals showed obvious BT-like clinical signs. In summary, the phenotypes observed for BTV-27v01-v03 phenotypes correspond to a mixture of characteristics known for BTV-25 and 26.
Asunto(s)
Anticuerpos Antivirales/sangre , Virus de la Lengua Azul/fisiología , Lengua Azul/transmisión , Enfermedades de los Bovinos/virología , Ceratopogonidae/virología , Enfermedades de las Cabras/virología , Animales , Enfermedades Asintomáticas , Lengua Azul/virología , Virus de la Lengua Azul/inmunología , Virus de la Lengua Azul/aislamiento & purificación , Virus de la Lengua Azul/patogenicidad , Bovinos , Enfermedades de los Bovinos/transmisión , Ensayo de Inmunoadsorción Enzimática/veterinaria , Francia , Enfermedades de las Cabras/transmisión , Cabras , Masculino , Pruebas de Neutralización/veterinaria , Fenotipo , Serogrupo , OvinosRESUMEN
Bluetongue virus serotype 8 (BTV-8) re-emerged in Central France in August 2015. The viral strain identified is nearly identical to the one that circulated during the 2006/2009 massive outbreak throughout Europe. To address the question of an undetected BTV-8 circulation on the French territory, a serological study was conducted on young cattle along a transect of seven departments, three of them located in areas where the virus presence had been confirmed by RT-PCR by winter 2015/2016. Sera from 2,565 animals were collected during the winters preceding and following the re-emergence, with 414 animals being sampled in each of the two consecutive years. All samples were tested by competitive ELISA (IDVet) and, when enough serum was available, ELISA-positive samples were confirmed by seroneutralization tests. In areas with infected holdings, seropositive animals were found before the re-emergence (N = 14 of 511), significantly more on the following year (N = 17 of 257), and eight animals (N = 158) seroconverted over 2015. Seropositive animals were also detected as early as winter 2014/2015 in one department without known infected holdings (N = 12 of 150), and in winter 2015/2016 in three of them (N = 21 of 555), where seven animals (N = 154) seroconverted over 2015. These results suggest that BTV-8 may have spread at low levels before the re-emergence, even in areas considered virus-free. Unfortunately, whole blood from the seropositive animals was not available to definitely confirm the virus presence by RT-PCR.
Asunto(s)
Virus de la Lengua Azul/aislamiento & purificación , Lengua Azul/virología , Enfermedades de los Bovinos/virología , Enfermedades Transmisibles Emergentes/veterinaria , Brotes de Enfermedades/veterinaria , Animales , Lengua Azul/epidemiología , Virus de la Lengua Azul/genética , Virus de la Lengua Azul/inmunología , Bovinos , Enfermedades de los Bovinos/epidemiología , Enfermedades Transmisibles Emergentes/epidemiología , Ensayo de Inmunoadsorción Enzimática/veterinaria , Francia/epidemiología , Reacción en Cadena en Tiempo Real de la Polimerasa/veterinaria , Estaciones del Año , SerogrupoRESUMEN
In November 2016, sheep located in the south of Corsica island exhibited clinical signs suggestive of bluetongue virus (BTV) infection. Laboratory analyses allowed to isolate and identify a BTV strain of serotype 4. The analysis of the full viral genome showed that all the 10 genomic segments were closely related to those of the BTV-4 present in Hungary in 2014 and involved in a large BT outbreak in the Balkan Peninsula. These results together with epidemiological data suggest that BTV-4 has been introduced to Corsica from Italy (Sardinia) where BTV-4 outbreaks have been reported in autumn 2016. This is the first report of the introduction in Corsica of a BTV strain previously spreading in eastern Europe.
Asunto(s)
Virus de la Lengua Azul/genética , Lengua Azul/virología , Enfermedades de los Bovinos/virología , Genoma Viral/genética , Secuenciación Completa del Genoma , Animales , Lengua Azul/epidemiología , Virus de la Lengua Azul/aislamiento & purificación , Bovinos , Enfermedades de los Bovinos/epidemiología , Brotes de Enfermedades/veterinaria , Europa Oriental , Francia/epidemiología , Islas , Italia , Filogenia , Serogrupo , OvinosRESUMEN
Undetected in Europe since 2010, bluetongue virus serotype 8 (BTV-8) re-emerged in August 2015 in Central France. To gain insight into the re-emergence on the French territory, we estimated the seroprevalence in cattle before the detection of BTV-8 in 2015, in areas differentially affected by the current outbreak. A retrospective survey based on the analysis of stored sera was thus conducted in the winter preceding the re-emergence in seven French departments including the one where the virus was first detected. A total of 10,066 sera were retrieved from animals sampled in 444 different herds in winter 2014/15. Between-herd seroprevalence revealed the presence of seropositive animals in almost all herds sampled (97.4%). The animal-level seroprevalence averaged at 44%, with a strong age pattern reflecting the cumulative exposure to both natural infection and to vaccination. A multivariable analysis allowed separating the respective effects of both exposures. A higher proportion of seropositivity risk was attributed to vaccination (67.4%) than to exposure to natural infection (24.2%). The evolution of seroprevalence induced by the two main risk factors in 74 mainland departments was reconstructed between the vaccination ban (2013) and the re-emergence (2015). We showed a striking decrease in seroprevalence with time after the vaccination ban, due to population renewal, which could have facilitated virus transmission leading to the current outbreak situation.