Culicoides and Arbovirus Dynamics in Mauritius and the Southwest Indian Ocean

 

1. Taxonomic and Biological Overview of Culicoides

Culicoides are very small biting midges (1 to 3 mm) belonging to the family Ceratopogonidae. Their biological characteristics and classification are critical for identifying vector potential:

• Classification:
  • Phylum: Arthropoda.
  • Class: Insecta (Hexapoda).
  • Order: Diptera.
  • Family: Ceratopogonidae.
• Global Diversity: There are approximately 5,400 species within the family across 50 genres. However, only four genres are of medical or veterinary interest: Leptoconops, Austroconops, Forcipomyia, and Culicoides.
• Vector Specificity: Of the 1,400 Culicoides species identified worldwide, approximately 60 are confirmed vectors of pathogens. Identification is primarily achieved through wing coloration patterns.
• Life Cycle: The cycle involves four stages: Eggs, Larvae (4 stages), Pupae, and Adults.
  • Environmental Requirements: Larvae develop in humid zones rich in organic matter.
  • Trophogonic Cycle: Adult females require a blood meal for egg maturation and oviposition.

2. Arboviral Threats and Economic Impact

The emergence and spread of arboviruses transmitted by Culicoides have severe sanitary and economic consequences globally and regionally.

Veterinary Pathogens

• Bluetongue Virus (BTV) & Epizootic Hemorrhagic Disease Virus (EHDV): Between 2022 and 2025, Europe experienced a major economic crisis due to these viruses, resulting in high morbidity, loss of fertility, movement restrictions for animals, and high vaccination costs.
• African Horse Sickness (AHSV): A 2020 outbreak in Thailand demonstrated the extreme lethality of this virus, with 394 deaths out of 438 confirmed cases (a 90% lethality index).
• Orbiviruses in Mauritius: Historically, orbiviruses were detected in Rusa deer in Mauritius as early as 2007.

Human Pathogens: The Oropouche Virus (OROV)

OROV is a zoonotic arbovirus primarily transmitted by Culicoides paraensis and certain mosquitoes.

• Recent Emergence (2024-2025):
  • South/Central America: Over 11,600 confirmed cases across 12 countries in 2024, rising to 12,786 in 2025.
  • Clinical Severity: Recent outbreaks in Brazil have reported deaths in healthy individuals, cases of Guillain-Barré syndrome, and vertical transmission leading to fetal death and neonatal microcephaly.
  • Imported Risk: In July 2024, 19 cases were imported into Europe and 21 into the USA, primarily from Cuba.
• Regional Context for French Territories: Presence of C. paraensis has been confirmed in French Guiana and Martinique, and was detected in Guadeloupe in 2025, raising the risk level to "High" according to PAHO (2024).

3. Situation Analysis: Mauritius

Mauritius has a history of research partnership regarding animal health, though faunal inventories remain incomplete.

Species Inventory and Distribution

Recent work, including the thesis of Yannick Grimaud and research by Iyaloo et al. (2025), identifies four major species on the island:

1. Culicoides imicola (A primary vector of BTV and AHSV).
2. Culicoides bolitinos.
3. Culicoides enderleini.
4. Culicoides kibatiensis.

Historical Milestones

• 1992: Initial census identified C. imicola and other afrotropical species.
• 2007: Detection of orbiviruses in the local Rusa deer population.
• 2025-2026: Implementation of spatial-temporal monitoring and trans-island spatial transects.

Regional Connectivity

Research is investigating the phylogenetic links between Culicoides populations in Mauritius and La Réunion. There is a hypothesis of passive aerial transport (wind-borne) between the two islands, which may influence the spread of BTV and EHDV.

4. Strategic Research and Future Perspectives (2026)

The roadmap for Mauritius involves several high-priority research initiatives scheduled for 2026:

Objective	Description	Timeline
Anthropophile Assessment	Verify the presence of Culicoides outside of livestock areas to assess human risk (OROV).	2026
Rodrigues Inventory	Conduct an entomological census of Culicoides in livestock holdings on Rodrigues island.	April-May 2026
Multi-Vector Mission	Animal health mission involving dedicated researchers (Marlène & Brice).	Feb-March 2026
Modeling	Development of spatial-temporal models to track BTV and EHDV circulation.	Ongoing
Genetics	Study the genetic structure and gene flow of C. imicola across the SWIO region.	Ongoing

5. Methodology and Technological Innovation

Effective surveillance is currently hampered by the limitations of existing technology and taxonomic expertise.

Surveillance Tools and Challenges

• Trapping Limitations: The standard Onderstepoort Veterinary Institute (OVI) trap is no longer commercialized and is ineffective for anthropophilic species like C. paraensis.
• Innovation: There is a pressing need to develop and test home-made trap alternatives, such as those designed by David Wilkinson and Albin Fontaine (adapted for Culicoides).
• Sample Strategy: Emphasis is placed on taking representative samples of circulating viruses rather than sheer quantity, ensuring the system is not saturated.

Advanced Detection Technologies

1. MX Technology: A proof of concept has demonstrated that viruses transmitted by Culicoides can be detected using MX technology.
2. Early Detection: Implementation of early detection systems for BTV and EHDV in sheep and cattle holdings.
3. Metabarcoding: Utilization of metabarcoding for precise vector identification.
4. Genotypic Characterization: Used to trace the origin and propagation of viral strains.

Regional Expertise

The "One Health OI" partnership provides a published methodological corpus, including morphological identification keys for the Culicoides of the Mascarene Islands and regional mapping of C. imicola. However, taxonomic expertise remains limited in areas like the Comoros and Madagascar due to the high diversity of the afrotropical region.