Possible over-wintering of bluetongue virus in Culicoides populations in the Onderstepoort area, Gauteng, South Africa

Authors

  • Jumari Steyn University of Pretoria
  • Gert J Venter University of Pretoria
  • Karien Labuschagne Agricultural Research CouncilOnderstepoort Veterinary Institute
  • Daphney Majatladi Agricultural Research CouncilOnderstepoort Veterinary Institute
  • Solomon N.B Boikanyo Agricultural Research CouncilOnderstepoort Veterinary Institute
  • Carina Lourens University of Pretoria
  • Karen Ebersohn University of Pretoria
  • Estelle H Venter University of Pretoria

Abstract

Several studies have demonstrated the ability of certain viruses to overwinter in arthropod vectors. The over-wintering mechanism of bluetongue virus (BTV) is unknown. One hypothesis is over-wintering within adult Culicoides midges (Diptera; Ceratopogonidae) that survive mild winters where temperatures seldom drop below 10 °C. The reduced activity of midges and the absence of outbreaks during winter may create the impression that the virus has disappeared from an area. Light traps were used in close association with horses to collect Culicoides midges from July 2010 to September 2011 in the Onderstepoort area, in Gauteng Province, South Africa. More than 500 000 Culicoides midges were collected from 88 collections and sorted to species level, revealing 26 different Culicoides species. Culicoides midges were present throughout the 15 month study. Nine Culicoides species potentially capable of transmitting BTV were present during the winter months. Midges were screened for the presence of BTV ribonucleic acid (RNA) with the aid of a real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) assay. In total 91.2% of midge pools tested positive for BTV RNA. PCR results were compared with previous virus isolation results (VI) that demonstrated the presence of viruses in summer and autumn months. The results indicate that BTV-infected Culicoides vectors are present throughout the year in the study area. Viral RNA-positive midges were also found throughout the year with VI positive midge pools only in summer and early autumn. Midges that survive mild winter temperatures could therefore harbour BTV but with a decreased vector capacity. When the population size, biting rate and viral replication decrease, it could stop BTV transmission. Over-wintering of BTV in the Onderstepoort region could therefore result in re-emergence because of increased
vector activity rather than reintroduction from outside the region.

Author Biographies

  • Jumari Steyn, University of Pretoria

    Department of Veterinary Tropical Diseases, University of Pretoria, South Africa

  • Gert J Venter, University of Pretoria

    Department of Veterinary Tropical Diseases, University of Pretoria, South Africa and Parasites, Vectors and Vector-Borne Diseases, Agricultural Research Council-Onderstepoort Veterinary Institute, South Africa

  • Karien Labuschagne, Agricultural Research CouncilOnderstepoort Veterinary Institute

    Parasites, Vectors and Vector-Borne Diseases, Agricultural Research Council-Onderstepoort Veterinary Institute, South Africa and Department of Zoology and Entomology, University of Pretoria, South Africa

  • Daphney Majatladi, Agricultural Research CouncilOnderstepoort Veterinary Institute

    Parasites, Vectors and Vector-Borne Diseases, Agricultural Research Council-Onderstepoort Veterinary Institute, South Africa

  • Solomon N.B Boikanyo, Agricultural Research CouncilOnderstepoort Veterinary Institute

    Parasites, Vectors and Vector-Borne Diseases, Agricultural Research Council-Onderstepoort Veterinary Institute, South Africa

  • Carina Lourens, University of Pretoria

    Equine Research Centre, University of Pretoria, South Africa

  • Karen Ebersohn, University of Pretoria

    Department of Veterinary Tropical Diseases, University of Pretoria, South Africa

  • Estelle H Venter, University of Pretoria

    Department of Veterinary Tropical Diseases, University of Pretoria, South Africa

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Published

2021-12-09

Issue

Vol. 87 No. 1 (2016)

Section

Original Research