Risk-based serological survey of bluetongue and the first evidence of bluetongue virus serotype 26 circulation in Tunisia.

BACKGROUND: Bluetongue (BT), a vector-borne disease of wild and domestic ruminants, is responsible for severe economic losses in flocks. To reduce this impact, a surveillance and control plan was implemented in Tunisia. However, the epidemiological situation of BT remains incompletely understood, especially for the circulating serotypes. OBJECTIVE: The aim of this survey was to determine the seroprevalence, to identify the circulating serotypes and to identify the associated risk factors for bluetongue virus (BTV) circulation in Tunisia using risk-based sampling (RBS). METHODS: A total of 3314 blood samples were randomly collected from 67 sectors using risk-based sampling and screened by competitive enzyme-linked immunosorbent assays (c-ELISAs). Out of the 1330 positive samples, 200 samples were analysed by serum neutralization test (SNT) to identify circulating BTV serotypes. RESULTS: Of 3314 sera, 1330 were c-ELISA-positive (40.1%) for antibodies against the BTV structural protein VP7. The result of SNT showed the presence of BTV-1, BTV-2, BTV-3, BTV-4 and, for the first time in Tunisia, BTV-26. The logistic regression model revealed that older animals had nearly two times the odds of being infected with BTV compared to younger animals. Flocks with a history of BT were almost 1.5 times more likely to be at risk for contracting BTV infection. The flock size, housing indoors and intensive production system were significant protective factors. CONCLUSIONS: High seroprevalence of BTV among sheep was highlighted in Tunisia. The neutralization test showed the presence of the following BTV serotypes: BTV-1, BTV-2, BTV-3, BTV-4 and, for the first time in Tunisia, BTV-26. Age, production system and flock size were important variables associated with BTV infection in sheep. This finding is crucial, as it will allow the adjustment of the BT control programme in Tunisia.

Serological survey and associated risk factors' analysis of Trypanosomiasis in camels from Southern Tunisia.

Surra (Trypanosoma evansi infection) is one of the main causes of dromedary (Camelus dromedarius) abortion, besides generating severe economic losses in herds. A sero-epidemiological survey was carried out between December 2018 and December 2019 in Southern Tunisia to estimate the seroprevalence of Trypanosoma evansi infection in camels and to determine its possible associated risk factors. Two-stage sampling was conducted to select breeders and camels targeted in our study. A total of 1205 blood samples were collected from 277 randomly selected farms belonging to six governorates of southern Tunisia. Sera were tested with the card agglutination test for Trypanosoma evansi (CATT/T. evansi) to detect the presence of anti-Trypanosoma. evansi antibodies. The overall individual and herd seroprevalence were 30.8% (95%CI 27.9-33.1%), 64.9% (95%CI 61.7-73), respectively. The seroprevalence of T. evansi infection both at the animal (26.2% (95%CI 21.4-30.9%) and herd level (84.4 (95%CI 76.3-92.5)) was higher in Kebili than in other governorates (P = 0.003). At the animal level, the infection rate with T. evansi was significantly associated to the age group among camels (P = 0.0008), production system (P = 0.006), bioclimatic stage (P = 0.02), and herd size (P = 0.04) in the univariable analysis. Multivariable logistic regression indicated that only age group and herd size were potential risk factors associated with Trypanosoma evansi infection. However, no significant variation of the seroprevalence of T. evansi with the sex of camels, farm type, and previous trypanocidal treatment were detected (P > 0.05). The findings of this study are crucial for this disease surveillance and control. Further investigations on the efficacy of the treatment against surra are needed to explain the persistence of the disease in the south of Tunisia.