How SARS-CoV-2, Hantaviruses, Zika virus, and Other Pathogens Hijack Extracellular Vesicles to Invade the Brain and Drive Neuroinflammation

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Over recent years, research has revealed a more indirect and sophisticated way that viruses influence the nervous system. Rather than relying solely on direct infection, multiple viruses exploit extracellular vesicles (EVs)—small, membrane-bound particles naturally used for cell-to-cell communication—to spread viral material, evade immune defenses, and trigger inflammation. This EV-mediated mechanism provides a compelling explanation for neurological symptoms seen during acute infections and in post-viral syndromes such as long COVID.

Extracellular Vesicles: A Double-Edged Sword

Extracellular vesicles are essential for normal biological communication. Cells use them to transport proteins, lipids, and RNA between one another. However, many pathogens—including SARS-CoV-2 and Zika virus—co-opt this system.

Evidence shows that infected cells release EVs containing viral RNA, proteins, and sometimes intact viral particles. These vesicles function as stealth carriers:

  • They shield viral components from neutralizing antibodies
  • They enable infection of cells that might otherwise resist viral entry
  • They allow long-distance dissemination, including into the central nervous system

This mechanism bypasses traditional receptor-mediated entry pathways and expands the range of susceptible cells.

Viral Exploitation of Cellular Machinery

Viruses such as hantaviruses, respiratory syncytial virus, and influenza rely on host pathways like the Rab GTPase system to facilitate viral budding and release. Similarly, Zika virus manipulates host cell machinery to alter EV production, modifying their size and molecular cargo.

Instead of relying solely on complete viral particles, Zika can package its RNA and proteins into EVs, enabling transmission in a concealed and efficient manner. This strategy enhances viral replication, dissemination, and immune evasion.

Parallels in Bacterial Systems

This vesicle-based strategy is not unique to viruses. Bacteria also produce extracellular vesicles:

  • Gram-negative bacteria release outer membrane vesicles (OMVs)
  • Gram-positive bacteria produce cytoplasmic membrane vesicles (CMVs)

These vesicles, typically 20–400 nm in size, carry bioactive molecules that support communication, immune modulation, and survival under stress. This highlights a broader biological principle: pathogens across domains exploit vesicle-based transport systems.

Alternative Routes Into Neuronal Cells

One key discovery is that SARS-CoV-2 can affect neurons lacking the ACE2 receptor, previously thought essential for infection.

EVs enable this alternative pathway:

  • Infected cells package viral components into vesicles
  • Vesicles are released and taken up by neighboring or distant cells
  • Viral material is delivered intracellularly without receptor binding

Additionally, tunneling nanotubes—thin cytoplasmic connections between cells—may allow direct transfer of EVs, further shielding viral material from immune detection.

EV-Mediated Neuroinflammation

Beyond transport, EVs actively contribute to inflammation in the brain.

Cells expressing SARS-CoV-2 spike protein release EVs enriched with microRNAs such as:

  • miR-148a
  • miR-590

When these vesicles are taken up by microglia, the brain’s resident immune cells, they alter gene expression and activate inflammatory signaling pathways, particularly the USP33–IRF9 axis.

The USP33–IRF9 Pathway

Normal Function

The USP33–IRF9 pathway helps maintain controlled immune activity in the central nervous system:

  • USP33 stabilizes IRF9 by removing ubiquitin tags
  • IRF9 supports balanced interferon signaling
  • This prevents excessive inflammation while maintaining antiviral defense

Disruption by Viral EVs

SARS-CoV-2 disrupts this system through EV-mediated delivery of microRNAs:

  1. EVs deliver miR-148a into microglia
  2. miR-148a suppresses USP33 expression
  3. Reduced USP33 leads to degradation of IRF9
  4. IRF9 loss disrupts interferon signaling

This results in failure of the ISGF3 complex, a critical regulator of antiviral gene activation.

Cytokine Release and Neuroinflammation

The breakdown of interferon signaling contributes to uncontrolled immune activation, similar to Cytokine Release Syndrome.

Microglia become hyperactivated and release inflammatory mediators:

  • TNF-α
  • NF-κB
  • IFN-β

This leads to sustained neuroinflammation and downstream damage.

Consequences of Microglial Hyperactivation

Chronic activation of microglia has widespread effects:

  • A1 Astrocyte Induction: Neurotoxic astrocytes lose supportive roles and damage neurons
  • Synaptic Dysfunction: Impaired plasticity and cognitive decline
  • Neurodegeneration: Links to diseases such as Alzheimer’s disease, Parkinson’s disease, and multiple sclerosis

Immune Evasion via Vesicle Shielding

EV-mediated transport allows viruses to evade immune detection:

  • Encapsulated viral material is not easily recognized by antibodies
  • Vesicles circulate without triggering strong immune responses
  • Viral cargo is delivered directly into host cells

This “Trojan horse” strategy enhances persistence and may contribute to prolonged symptoms after infection.

Implications for Long-Term Neurological Effects

The involvement of EVs provides a framework for understanding persistent neurological symptoms, including:

  • Brain fog
  • Cognitive impairment
  • Headaches
  • Mood disturbances

EVs may sustain:

  • Chronic low-grade inflammation
  • Endothelial dysfunction
  • Coagulation abnormalities

Because EVs can remain in circulation, they may continue influencing cells even after active viral replication has declined.

Broader Significance

This mechanism reshapes understanding of how infections impact the nervous system:

  • Viruses exploit host communication systems rather than relying only on direct infection
  • EV pathways may become therapeutic targets
  • EV-associated biomarkers could aid diagnosis and prognosis
  • Insights may inform research into virus-induced neurodegeneration

Conclusion

SARS-CoV-2 and other pathogens utilize extracellular vesicles as a highly adaptive strategy to expand their influence within the body. By transporting viral components, disrupting immune regulation through the USP33–IRF9 pathway, and driving neuroinflammation, these viruses can affect the brain in subtle but persistent ways.

This EV-mediated model helps explain neurological symptoms in cases without clear direct brain infection and opens new directions for understanding, preventing, and treating long-term complications.

Pathway Summary

  • USP33: Stabilizes IRF9 → suppressed by EV-delivered miR-148a
  • IRF9: Regulates immune signaling → degraded
  • Microglia: Become hyperactivated → drive neuroinflammation

In essence, a protective immune regulatory system is repurposed by viral EVs to initiate and sustain inflammatory damage in the brain.

References: 

Extracellular vesicles in ZIKV infection: Carriers and facilitators of viral pathogenesis?
https://pmc.ncbi.nlm.nih.gov/articles/PMC11748155/ 

Extracellular vesicles: the double-edged sword in viral infections
https://www.sciencedirect.com/org/science/article/pii/S2150751125008081 

Extracellular Vesicles: The Invisible Heroes and Villains of COVID‐19 Central Neuropathology
https://pmc.ncbi.nlm.nih.gov/articles/PMC10933635/

Biogenesis and Biological Functions of Extracellular Vesicles in Cellular and Organismal Communication With Microbes  https://pmc.ncbi.nlm.nih.gov/articles/PMC8895202/ 

© 2000-2030 Sieglinde W. Alexander. All writings by Sieglinde W. Alexander have a five-year copyright. Library of Congress Card Number: LCN 00-192742 ISBN: 0-9703195-0-9   

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