Epizootic Haemorrhagic Disease Virus Serotype 8 in Tunisia, 2021

Abstract

Epizootic haemorrhagic disease (EHD) is a Culicoides-borne viral disease caused by the epizootic haemorrhagic disease virus (EHDV) associated with clinical manifestations in domestic and wild ruminants, primarily white-tailed deer (Odocoileus virginianus) and cattle (Bos taurus). In late September 2021, EHDV was reported in cattle farms in central/western Tunisia. It rapidly spread throughout the country with more than 200 confirmed outbreaks. We applied a combination of classical and molecular techniques to characterize the causative virus as a member of the serotype EHDV-8. This is the first evidence of EHDV- 8 circulation since 1982 when the prototype EHDV-8 strain was isolated in Australia. This work highlights the urgent need for vaccines for a range of EHDV serotypes.

Keywords: EHDV; EHDV serotype 8; Tunisia; circulation; virus characterization.

Figure 1

Clinical signs in cattle. (A) Teat erosions; (B) oral congestion and erosions; (C) submandibular oedema, conjunctivitis, and lacrimation; (D) nasal discharge and mucosal erosion. Reprinted/adapted with permission from the Tunisian Veterinary Services. Copyright 2021, copyright Dr Bel Hadj Mohamed Bassem (A,C); Dr Nadia Hemriti (B); Dr Meriem Ben Abdallah (D).

Figure 2

Virus neutralisation assays. (A) Serum neutralisation test results using EHDV serotype 6 (cyan) and serotype 8 (purple) reference isolates. (B) Values represent the log reduction in cytopathic effects (neutralisation).

Figure 3

Phylogenetic trees for EHDV segments (amino acid sequences for segment 2, nucleotide sequences for all other segments). Maximum likelihood trees were estimated using IQ-TREE employing the best-fit model of substitution. The trees shown are a representative selection of the different serotypes to simplify visualisation. The different serotypes are indicated. Trees are annotated according to serotype (segment 2) and sequences from the study here are shown in bold and yellow box (Tunisia 2021). Blastn outputs are shown in black. Branch length indicates the number of nucleotide substitutions per site for segments 1, 3–10 and amino acid substitutions per site for segment 2. Note, a putative new serotype has only recently been reported in viruses from China (white) [10]. Number of sequences used in the displayed trees; segment 2 n = 34, segment 1 n = 24, segment 3 n = 25, segment 4 n = 23, segment 5 n = 23, segment 6 n = 30, segment 7 n = 19, segment 8 n = 22, segment 9 n = 22, and segment 10 n = 21 sequences.