Introduction: DWV is not just a virus, but a pathogenic complex

From a clinical perspective, Deformed Wing Virus (DWV) is a pathogenic RNA virus from the family Iflaviridae that has naturally existed at low levels in honeybee populations. However, with the emergence of the Varroa destructor mite as a biological vector, the ecological balance of this virus has been disrupted, turning it into a primary cause of Colony Collapse Disorder (CCD).

The key takeaway is this: DWV without Varroa is low-risk. Varroa without DWV is manageable. But their combination is a disaster.

Main DWV Strains and Recent Genetic Developments

Three main strains of DWV have been identified:

• DWV-A: The original strain, less virulent, prevalent in the 1980s.
• DWV-B: A new, highly pathogenic strain that has spread since the early 2000s.
• VDV-1: A related virus, often found in combination with DWV.

Recent genomic analyses (2023) show that DWV-B has higher environmental stability, a faster replication rate within the mite's body, and a greater ability to evade the bee's innate immune response compared to DWV-A. This virus can even suppress the bee's RNA silencing system (RNAi).

Transmission Mechanism: How Varroa Acts as a "Viral Syringe"

The Varroa destructor mite is not just a parasite; it is an active biological vector that plays a central role in the virus's evolution.

Clinical and Pathological Effects on Bees

While the most obvious symptom is small, crumpled, and abnormal wings, the virus's damage starts from within:

• Nervous System Damage: The virus attacks the bee's brain and central nervous system, causing disorientation, impaired learning, and an inability to return to the hive.
• Reduced Lifespan: Infected bees survive for a maximum of 48 hours after symptoms appear.
• Physical Weakness: A small, rounded abdomen, paralyzed legs, and an inability to fly.
• Reproductive Issues: Infected queens produce infertile eggs, and the health of drones is also affected.
• Weakened Immune System: Infected bees are far more susceptible to other pathogens (such as bacteria and fungi).

Global Spread and Epidemiological Developments (2020–2024)

Analyses conducted by an international team from MLU University and the Global Bee Health Initiative, based on a review of over 5000 genetic datasets from honeybee and Varroa mite samples in the NCBI and Bumblebee Conservation Trust databases, indicate:

• Europe: Since 2015, DWV-B has become the dominant strain (over 85%).
• North America: The prevalence of DWV-B has increased from 30% in 2018 to over 70% in 2023.
• Asia: Identified in 2015 and rapidly spreading in China, India, and Iran. Hybrid DWV-A/B strains have been reported in some areas.
• Australia: Still without an official report of DWV-B — likely due to strict controls on Varroa mite entry and strong biosecurity policies.
• Wild Bees: DWV-B has been identified in samples from bumblebees (Bombus spp.) and mason bees (Osmia spp.), indicating inter-species transmission and a broader threat to biodiversity.

Modern Colony Management Strategies: From RNA Vaccines to Resistant Bees

Based on recommendations from the MLU research team, the World Organisation for Animal Health (WOAH), and the International Apicultural Association (IAB), the following strategies are essential for controlling and preventing the virus's spread:

1. Hive Hygiene and Winter Management: Regular cleaning of hives, replacing old combs, and reducing colony density during the winter season.
2. Biological and Genetic Control: Using mite-resistant bees (such as Varroa Sensitive Hygiene - VSH or Suppressed Mite Reproduction - SMR strains).
3. Smart Chemical Control: Using approved treatments like oxalic acid, flumethrin, or thymol at appropriate times and with rotation to prevent resistance.
4. Future-Forward Vaccination: Research is ongoing to develop vaccines based on RNA interference (RNAi) that would allow bees to detect the virus and prevent its replication.
5. Maintaining Plant Diversity: Planting a variety of pollen and nectar-producing plants to strengthen the bees' immune systems.
6. Regular Monitoring and Genetic Testing: Using quantitative PCR to track the viral load in hives and make timely decisions for treatment.

A Specialist's Final Word: Bees Need Us

As a bee disease specialist, we emphasize that the DWV crisis is not just a beekeeping problem; it's an ecosystem disease. We are witnessing an evolutionary shift where a virus, aided by a parasite, is gaining dominance over a key species in our ecosystem.

As Professor Robert Paxton noted: “Nobody else is looking out for them.” It is our responsibility as beekeepers, consumers, and global citizens to protect these vital creatures with smart actions. This is only possible through education, monitoring, and financial support for local beekeepers.