The 1996 outbreak of African horse sickness in South Africa–the entomological perspective.
Abstract: During the 1996 summer season (January-April) in South Africa an estimated 500 horses died of African horse sickness (AHS); 80% of deaths were due to AHS virus serotypes 2 and 4. Nearly all cases occurred in the northern, north-eastern and central parts of South Africa. This study reports the first attempt to verify the involvement of the biting midge Culicoides imicola in a field outbreak of AHS in southern Africa. In light-trap collections made at 47 sites over 12 weeks, C. imicola comprised 94.2% of 4.78 million Culicoides. Culicoides imicola was the most prevalent of 34 species captured and was the only species whose distribution matched that of the disease. Record catches of C. imicola were made, and reveal that in years of above average rainfall its numbers can show a 200-fold increase over those in dry years. Soil type appeared to determine strongly the distribution of C. imicola. The largest populations of C. imicola were found in areas with clayey, moisture-retentive soils whereas the lowest numbers, or none, occurred in areas where the soils were sandy and quick-draining. The deaths of two horses (confirmed AHS) in a sandy area were perplexing as they occurred in a region known to be free of C. imicola. The probable origin of these infections was established.
Publication Date: 1998-10-24 PubMed ID: 9785497DOI: 10.1007/978-3-7091-6823-3_8Google Scholar: Lookup
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- Journal Article
Summary
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This research investigation looked at the 1996 outbreak of African horse sickness in South Africa, particularly the role of the biting midge Culicoides imicola in transmission. It found that the distribution of C. imicola, which thrives in wet areas with clayey soil, matched the spread of the disease. However, there were two cases that occurred outside this insect’s known range.
Aim of the Study
- The main objective of this research was to investigate the cause of the 1996 outbreak of African horse sickness (AHS) in South Africa.
- The study focused specifically on identifying whether the biting midge Culicoides imicola (C. imicola) was involved in transmitting the disease.
Research Methods
- The researchers conducted light-trap collections at 47 different sites over a period of 12 weeks.
- From these collections, they scrutinized the prevalence and species of Culicoides to identify any potential links between the insects and the outbreak of AHS.
Key Findings
- Out of 4.78 million Culicoides collected, about 94.2% were C. imicola.
- The distribution of C. imicola closely matched the outbreak areas of AHS, suggesting a strong correlation.
- The study revealed that C. imicola flourished dramatically during times of above-average rainfall, with populations increasing up to 200 times larger than in dry years.
- The research suggested that soil type also had a significant influence on the distribution of C. imicola, with the insect being more prevalent in clayey, moisture-retentive soils and much less prominent, or absent, in sandy, quick-draining soils.
Unusual Cases
- Although the distribution of C. imicola accounted for most cases of AHS, there were a couple of anomalies where AHS cases occurred in areas not known to be inhabited by the insect.
Conclusion
- The study confirmed the involvement of the biting midge Culicoides imicola in the transmission of African horse sickness during the 1996 outbreak.
- However, the two unusual cases suggest that other factors or carriers could also be involved in the spread of the disease.
Cite This Article
APA
Meiswinkel R.
(1998).
The 1996 outbreak of African horse sickness in South Africa–the entomological perspective.
Arch Virol Suppl, 14, 69-83.
https://doi.org/10.1007/978-3-7091-6823-3_8 Publication
Researcher Affiliations
- Onderstepoort Veterinary Institute, South Africa.
MeSH Terms
- African Horse Sickness / epidemiology
- African Horse Sickness / prevention & control
- African Horse Sickness / transmission
- Animals
- Ceratopogonidae / physiology
- Disease Outbreaks / veterinary
- Horses
- Housing, Animal
- Insect Vectors / physiology
- Rain
- Seasons
- South Africa / epidemiology
Citations
This article has been cited 11 times.- Neupane S, Davis T, Olds C, Nayduch D, McGregor BL. Unraveling the relationships between midge abundance and incidence, microbial communities, and soil and water properties in a protected natural tallgrass prairie. Parasit Vectors 2025 Apr 19;18(1):146.
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- Hassine TB, Sghaier S, Thabet S, Ammar HH, Hammami S. Role of eco-climatic factors in the distribution of bluetongue in endemic areas in Tunisia. Open Vet J 2022 Jan-Feb;12(1):114-123.
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- Leta S, Fetene E, Mulatu T, Amenu K, Jaleta MB, Beyene TJ, Negussie H, Kriticos D, Revie CW. Updating the global occurrence of Culicoides imicola, a vector for emerging viral diseases. Sci Data 2019 Sep 30;6(1):185.
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- Gordon SJ, Bolwell C, Rogers C, Musuka G, Kelly P, Labuschagne K, Guthrie AJ, Denison E, Mellor PS, Hamblin C. The occurrence of Culicoides species, the vectors of arboviruses, at selected trap sites in Zimbabwe. Onderstepoort J Vet Res 2015 May 29;82(1):e1-e8.
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- Acevedo P, Ruiz-Fons F, Estrada R, Márquez AL, Miranda MA, Gortázar C, Lucientes J. A broad assessment of factors determining Culicoides imicola abundance: modelling the present and forecasting its future in climate change scenarios. PLoS One 2010 Dec 6;5(12):e14236.
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