A RISK ASSESSMENT COMPILED BY A RENOWNED EPIDEMIOLOGIST FROM AUSVET CONFIRMS THAT THE RISK OF AFRICAN HORSE SICKNESS CAN BE MANAGED WHEN EXPORTING FROM SA
The Equine Health Fund enlisted the help of internationally acclaimed Epidemiologist, Dr Evan Sergeant, of AusVet, to conduct an assessment on the risk of exporting horses from South Africa, particularly with regard to African horse sickness. Dr Sergeant worked in collaboration with the Horse Import Export Task Team (HIETT), in particular Prof Alan Guthrie (Equine Research Centre), Dr John Grewar (Western Cape Department of Agriculture – Veterinary Services) and Dr Camilla Weyer (ERC Epidemiology Unit). Dr Sergeant presented his paper at the International Symposium for Veterinary Epidemiology and Economics (ISVEE Congress) in Mexico in November 2015, and it was very well received. This project was generously funded by Rainbow Beach Trading and Drakenstein Stud.
African horse sickness risk assessment – Summary Report
The aims of the project were to:
· Model the probability of undetected AHS infection in horses exported from an infected zone/country;
· The model assumed:
Ø OIE recommended vector-protected pre-export quarantine (PEQ)
Ø 16 day pre-export quarantine and AHS RT- PCR test prior to and during the PEQ period
Ø Quarantine facility located in either low-risk (current free zone) or endemic area (rest of SA)
Ø Included the addition or not of post-arrival vector-protected quarantine (PAQ) and PCR in the importing country
· Five pathways identified possible times where an undetected, infected horse could be exported, depending on when infection might occur in relation to quarantine period and PCR testing.
· Pathways modelled in a quantitative probability model.
· Probabilities entered as probability distributions to reflect uncertainty about true values.
· Results presented as median estimate and 95% probability interval.
· The median annual probability of exporting one or more undetected infected horses from the low-risk area, assuming 300 horses exported annually, was 1.6 x 10-3 (95% interval: 1.5 x 10-4 – 1.2 x 10-2), with no post-arrival quarantine.
· Addition of post-arrival quarantine and PCR further reduced the risk by about 12-fold.
· Exporting from the endemic area increased the risk by about 16-fold.
· Assuming a higher (and more realistic) value for PCR sensitivity reduced the risk by 7 and 77-fold, without or with post arrival quarantine and PCR respectively.
· The most important risk period was the 12 days immediately prior to entering quarantine.
· AHS risk can be managed
· Exports from the low-risk area and/or with post-arrival quarantine and PCR testing
· Higher risk for endemic area can be managed by post-arrival vector-protected quarantine and PCR
· The model assumes that exports can occur year-round and regardless of the occurrence of AHS outbreaks. Risk could be further reduced by :
Ø Limiting exports to low-risk time of the year or
Ø Suspending exports during outbreaks
Ø Extending the proposed quarantine period (currently 16 days in the model)
Ø Final choice of risk management measures depends on the level of risk acceptable to the importing country.
The median probability of an export horses being infected and not detected was equivalent to one undetected infected horse in every 187 000 horses exported from the low-risk area with no post-arrival quarantine. An additional PCR test while in vector-protected post-arrival quarantine reduced this probability by 12-fold.
Probabilities for horses exported from an area where AHS is endemic were approximately 15 to 17 times higher than for horses exported from the low-risk area under comparable scenarios.
Import and export conditions are negotiated between veterinary administrations of the two countries. One of the important factors importing countries take into account is the level of risk an import poses. A sound risk assessment allows the importing country to make decisions based on science. South Africa will use the information in the risk assessment to negotiate with potential importing countries.