A Qualitative Risk Assessment for the Incursion of Bluetongue Disease and African Horse Sickness into London Zoo

Masters Thesis Culicoides biting midges Bluetongue



Bluetongue disease (BTV) and African horse sickness (AHSV) are two closely related animal viruses vectored by Culicoides biting midges. They are considered exotic to the United Kingdom (UK), however the 2007 outbreak of BTV in the UK highlights their potential for introduction and onward transmission. Given the susceptibility of some animals kept in zoo collections to vector-borne diseases, the risk of BTV and AHSV to animals in London Zoo was assessed.


A qualitative risk assessment for the introduction of BTV and AHSV to London Zoo was performed using OIE’s Import Risk Assessment Framework, Gale et al. (2016)’s estimation of risk pathway probability, and the European Food Safety Authority’s qualitative probability definitions. The determination and likelihood of risk pathways were analysed using available literature and data on the transmission and epidemiology of the diseases.


Three BTV and two AHSV risk pathways were determined to have a non-negligible probability of resulting in the infection of an animal in the Zoo collection, and these were investigated in detail. The probability of BTV infection ranged from low to low to medium, with the greatest risk posed by the long-distance spread of infected-Culicoides being carried by wind across the English Channel. The probability of AHSV infection was very low and very low to low, with the probability of an infected equine imported to the UK posing a slightly higher risk than that of an infected zoo import.


The proximity of ongoing disease events in mainland Europe and proven capability of transmission to the UK places London Zoo at higher risk of BTV transmission than AHSV. However, given the recent long-range expansion of AHSV to Thailand and the ability of closed related viruses to replicate in temperate climates, AHSV continues to pose a non-negligible threat to animals in London Zoo collection.