Risk-based surveillance for bluetongue virus in cattle on the south coast of England in 2017 and 2018

Clinical disease in British sheep infected with an emerging strain of bluetongue virus serotype 3

BACKGROUND

Bluetongue virus serotype 3 (BTV-3) was detected for the first time in cattle and sheep in southern England in 2023, the first UK BTV incursion for more than 15 years. Clinical signs were not observed, yet severe clinical disease and mortality were reported during recent BTV-3 outbreaks in northern Europe.

METHODS

To investigate the clinical disease and infection kinetics associated with this UK BTV-3 strain, five British sheep were infected with a UK BTV-3 isolate using Culicoides biting midges. Clinical signs, pathology, infection dynamics, immune responses and Culicoides infection rates were assessed.

RESULTS

All sheep were infected with BTV-3 and developed mild to moderate clinical bluetongue disease, characterised by fever, haemorrhagic diarrhoea, lameness, depression and widespread petechial haemorrhage. Three sheep reached clinical humane endpoints and were euthanased. Clinical signs/severity, infection kinetics and immune responses were highly variable. Infectious BTV-3 was isolated from sheep blood up to 28 days postinfection.

LIMITATIONS

The impact of BTV-3 infection on British cattle and infection rate in UK Culicoides require investigation to fully determine the risk of this strain to UK livestock.

CONCLUSIONS

This study confirms the potential impact of a BTV-3 incursion/outbreak on the UK sheep population, highlighting the need for an effective vaccine.

A Qualitative Risk Assessment for Bluetongue Disease and African Horse Sickness: The Risk of Entry and Exposure at a UK Zoo

Bluetongue virus (BTV) and African horse sickness virus (AHSV) cause economically important diseases that are currently exotic to the United Kingdom (UK), but have significant potential for introduction and onward transmission. Given the susceptibility of animals kept in zoo collections to vector-borne diseases, a qualitative risk assessment for the introduction of BTV and AHSV to ZSL London Zoo was performed. Risk pathways for each virus were identified and assessed using published literature, animal import data and outputs from epidemiological models. Direct imports of infected animals, as well as wind-borne infected Culicoides, were considered as routes of incursion. The proximity of ongoing disease events in mainland Europe and proven capability of transmission to the UK places ZSL London Zoo at higher risk of BTV release and exposure (estimated as low to medium) than AHSV (estimated as very low to low). The recent long-range expansion of AHSV into Thailand from southern Africa highlights the need for vector competence studies of Palearctic Culicoides for AHSV to assess the risk of transmission in this region.