Evaluating African horse sickness virus in horses and field-caught Culicoides biting midges on the East Rand, Gauteng Province, South Africa.

The study investigates the prevalence of African Horse Sickness Virus (AHSV) in Culicoides midges and its impact on horses in Gauteng Province, South Africa. Despite vaccinations, several horses contracted the virus, albeit in a subclinical form, while the virus was also found in field-collected midges, necessitating further research on the role of subclinical infection in disease transmission.

Methodology and Data Collection

• This study took place during 2013 to 2014, systematically collecting data on the presence of AHSV in two equine locations at East Rand, Gauteng Province, South Africa.
• The researchers studied a group of 28 resident horses and sampled Culicoides midges caught from the field.
• Biweekly collection of midges and horse blood samples allowed systematic tracking of AHSV presence and movements.

Techniques used for Detection of AHSV

• The detection of AHSV in Culicoides midges and blood samples from horses was achieved through the real-time quantitative reverse transcription polymerase chain reaction, a highly sensitive and reliable method for detecting viral RNA.

Findings and Observations

• Throughout the study period, nine out of the 28 horses, which had been immunised, nonetheless developed subclinical infections by AHSV. “Subclinical” means the disease did not show noticeable symptoms, despite the presence of the virus.
• AHSV was also identified in a pool of field-collected Culicoides midges. Culicoides midges are vectors known for transmitting the AHSV, reinforcing their role in the disease spread.

Significance and Further Research

• This research confirms previous findings on the presence of the AHSV in both Culicoides midges and horses, even those that had been immunised.
• The study importantly highlights the occurrence of subclinical infections, which might lead to a more covert and inadvertent spread of the disease. The role of these silent carriers in the overall disease epidemiology warrants further investigation.