Hoek, A., van

Nodelijk, G.

Vos-de Jong, C.J., de

English

Name not available

Risk of introducing African horse Sickness into the Netherlands by importation of equids

Wageningen Yield 

4th Annual Meeting of EPIZONE, 7-10 June 2010, St. Malo, France 
 
Risk of introducing African horse sickness into the Netherlands by importation 
of equids 
 
Clazien de Vos, Alies Hoek, Gonnie Nodelijk 
 
Quantitative Veterinary Epidemiology and Risk Analysis, Central Veterinary Institute of Wageningen 
UR, PO Box 65, 8200 AB Lelystad, the Netherlands. E-mail: clazien.devos@wur.nl 
 
African horse sickness (AHS) is a vector-borne viral disease of equids that is transmitted by 
Culicoides spp. (C. imicola and C. bolitinos). Mortality in horses can reach 95%. AHS virus 
(AHSV) is an orbivirus belonging to the family Reoviridae, which also comprises bluetongue 
virus (BTV). The emergence of BTV serotype 8 in North-western Europe in 2006 has 
demonstrated that also Palaearctic species of Culicoides can be competent vectors for these 
orbiviruses. This has resulted in increased awareness of the risk of AHS in the Netherlands. 
However, not much information and data are available to evaluate this risk. 
Risk modelling is a useful tool to provide insight into the major variables influencing 
the risk of disease introduction and can help in optimizing prevention and control strategies. 
To analyze the probability of release and establishment of AHSV in the Netherlands by 
importation of equids, an import risk analysis was conducted. Countries worldwide were 
grouped into three risk categories: (a) high risk, i.e., those countries in which the virus is 
circulating, (b) low risk, i.e., those countries that have experienced outbreaks of AHS in the 
past or where C. imicola is present, and (c) very low risk, i.e., all other countries. Imports of 
equids were grouped according to species: (a) horses, (b) donkeys, mules, and hinnies, and 
(c) zebras. A scenario tree was constructed to outline all steps required for successful 
release of AHSV in the Netherlands and subsequent establishment. This scenario tree was 
the basis for a risk model in Excel and @Risk to quantify the contribution of risk regions and 
groups of equids to the overall risk of AHSV introduction into the Netherlands. More insight 
into the relative risk of these risk regions and groups of equids will help decision-makers in 
prioritizing preventive measures. The model contained information on importations of equids 
into the Netherlands, occurrence of AHS in the risk regions, disease parameters in host 
species, vector biology, and import regulations. The probabilities of release and 
establishment were calculated taking into account seasonal effects. 
First model calculations indicated that establishment of AHS in the Netherlands is 
only possible when average daily (24h) temperatures are greater than 10°C, i.e., in the 
months May up till October. The risk of introduction of AHSV is highest in July. Despite low 
numbers of equids imported from high risk regions and implementation of preventive 
measures including quarantine and testing, these regions constitute a higher average risk for 
AHSV introduction than low and very low risk regions. Zebras contribute most to the risk of 
AHSV introduction, although numbers imported are very low. The estimated risk per 
imported animal is, however, highest for zebras due to the virtual absence of clinical 
symptoms and a longer viraemic period. 
Although the model returned an estimate of the probability of AHSV release and 
establishment in the Netherlands, absolute values are an underestimate of the real risk since 
only importations of equids as given by import statistics were taken into account. 
Furthermore, model calculations did not include the risk of introduction of AHSV by other 
pathways, such as vectors, live animal products and vaccines (modified live). Besides, the 
model contained many uncertain input parameters. Sensitivity analysis will be performed to 
indicate those parameters that are major sources of uncertainty in model output and those 
with the best options for prevention. 
 
Key-words: African horse sickness, establishment, import risk analysis, release assessment, 
scenario tree 


Risk of introducing African horse Sickness into the Netherlands by importation of equids

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