An epidemiological investigation of the African horsesickness outbreak in the Western Cape Province of South Africa in 2004 and its relevance to the current equine export protocol.

The research paper investigates the African Horsesickness (AHS) outbreak that took place in the Western Cape Province of South Africa in 2004, and compares it to a similar outbreak in 1999. It seeks to understand the factors contributing to the outbreak and the effectiveness of existing control measures in preventing the spread of the disease.

Study Outline

• This paper is a retrospective epidemiological study, which means it uses historical data and observations to understand disease patterns and causes. In this case, the data was collected during an outbreak of AHS in the control area of the Western Cape Province in 2004.
• A questionnaire survey was conducted within a 30 km radius surrounding the first recorded case (or the “index” case) of the outbreak. This was used to gather information about the spread and management of the disease.
• The study aims to describe the spatial, temporal, and population patterns of the AHS outbreak. These are key epidemiological factors that help to understand how, when and where the disease spread.

Key Findings

• The study found that the outbreak occurred before any significant rainfall, and the primary AHS vector, a particular species of midge called Culicoides imicola, was present in large numbers during the outbreak.
• It was observed that 63% of cases took place at temperatures less than or equal to 15 degrees Celsius, indicating that AHS might thrive in certain temperature conditions. Also, the Eerste River Valley was noted as a high-risk area for the disease.
• On the side of disease control, the study revealed that only 17% of horse owners used vector protection measures, while 70% vaccinated their horses at the start of the outbreak. Despite these precautions, the disease spread significantly.

Conclusions and Implications

• The researchers concluded that the current AHS control measures are not fully effective. The high percentage of vaccinations in the surveillance zone resulted in a lack of “sentinel” animals, which are unvaccinated individuals used to monitor the disease’s presence. This led to failure in the early warning system for detecting the spread of AHS.
• The study discusses alternative options for controlling AHS that could enable continued horse exports. This is crucial as an outbreak of AHS in a control area can result in a ban on horse exports for at least two years, impacting the country’s economy.