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. 2022 Jul;8(4):1671-1682.
doi: 10.1002/vms3.818. Epub 2022 May 5.

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

Kalthoum Sana  1 , Sghaier Soufien  2 , Ben Hassine Thameur  3 , Teodori Liana  4 , Spedicato Massimo  4 , Guesmi Kaouther  1 , Gharbi Raja  1 , Hajlaoui Haikel  1 , Bel Haj Mohamed Bassem  1 , Khalfaoui Wiem  1 , Lachtar Monia  1 , Ben Salem Ameni  1 , Fatnassi Naouel  1 , Dhaouadi Anissa  1 , Ben Ali Mehdi  1 , Thabet Sarah  2 , Seghaier Chedia  1 , Savini Giovanni  4 , Hammami Salah  5
Affiliations

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

Kalthoum Sana et al. Vet Med Sci. 2022 Jul.

Abstract

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.

Keywords: Tunisia; bluetongue; risk factors; risk-based sampling; serotyping; sheep.

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Conflict of interest statement

The authors declare no conflic of interest. The funders had no role in the study (sampling, analyses, interpretation of results) or in the decision to publish the results.

Figures

FIGURE 1
FIGURE 1
Risk map of bluetongue (BT) exposure in Tunisia demonstrating sheep farms within specific governorates (red sections) and sectors (black sections) of four different risk categories (negligible, low, high and very high) in which samples were taken
FIGURE 2
FIGURE 2
Bluetongue virus (BTV) serotypes circulating across 67 sampled sectors (n = 200 sheep sera) in Tunisia between November 2019 and January 2020 as identified by serum neutralization test following a positive competitive enzyme‐linked immunosorbent assay (c‐ELISA) result
See this image and copyright information in PMC

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