SARS-CoV-2 Cell-to-Cell Spread: Nanotubes, Syncytia and Vesicles

Most explanations of coronavirus infection describe one route: a virus floats up to a cell, its spike protein grabs a receptor called ACE2, it gets inside, and new viruses later float off to infect other cells. That route is real and important. This guide explains a 2022 microscopy study suggesting infected cells may also have inside routes to their neighbors, and what that might mean.

How does SARS-CoV-2 usually infect cells?

1. A virus particle reaches a cell.
2. Its spike protein binds the ACE2 "door" on the cell surface.
3. The virus gets inside and makes copies of itself.
4. New virus particles leave and travel to other cells.

The researchers behind this paper asked a different question: what if infected cells can pass the virus to nearby cells without sending it on that outside trip? Their images showed three structures that might make that possible: tiny bridges, fused cells and small bubble-like packages.

What was the study?

The paper is An intra-cytoplasmic route for SARS-CoV-2 transmission unveiled by Helium-ion microscopy by Merolli and colleagues. It was published in Scientific Reports, a Nature Portfolio journal, in March 2022.

The team grew Vero E6 cells, monkey kidney cells that scientists often use because SARS-CoV-2 infects them easily. They infected the cells with a version of the virus engineered to glow green (mNeonGreen), which made infected cells easy to find.

They then imaged the cells with several methods, including helium-ion microscopy. Imagine a camera so sharp it shows the tiny bumps, threads and bubbles on a cell's surface. It uses a beam of helium ions instead of light to reveal details an ordinary microscope can't see.

What did the researchers see?

1. Long bridges between cells

Infected cells grew long, thin connections called tunneling nanotubes, some linking two or more cells over submillimeter distances. That's far wider than a single cell.

Think of two houses with a covered bridge between their windows. People inside could pass things across without going down to the street. Cells use nanotubes to move material in the same way, and the idea is that SARS-CoV-2 could use them too.

2. Cells fused into giant shared cells

At 24 hours after infection, many infected cells had fused into large clusters. A group of fused cells is called a syncytium (plural: syncytia), and the researchers didn't see this fusion in uninfected cells. Syncytia aren't just a lab curiosity: an autopsy study found them in the lungs of people who died of severe COVID-19 (Bussani et al., 2020).

Imagine several apartments knocking down their shared walls to make one big room with many front doors. Once cell interiors join, material can move through the shared space without crossing each outer wall.

3. Lots of bubble-like packages

Infected cells were surrounded by many extracellular vesicles of various sizes. Cells use vesicles as tiny parcels, filling them with proteins, fats or genetic instructions and sending them out for other cells to pick up.

The researchers suggested infected cells might pack viral material into some of these parcels. The study didn't prove what the vesicles carried, but their sheer number makes them worth investigating.

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Why would these back roads matter?

Antibodies are very good at recognizing virus particles they can reach outside cells. A virus moving through a protected bridge or a shared cell interior might be harder for antibodies to catch. The authors suggest this could help explain how SARS-CoV-2 evades some immune surveillance.

That doesn't make the virus invisible. The body has other defenses, including immune cells that find and destroy infected cells. The simpler point is that SARS-CoV-2 may have more than one way to reach a new cell, so blocking the front door may not block every route.

Could this help explain lingering virus or spike protein?

It's one possible piece, not a proven one. If virus can move between cells without fully leaving them, it could in theory linger in tissues where antibodies don't reach it well. That's relevant to questions about persistent spike protein, which we cover in spike protein persistence testing.

Persisting spike matters because of what it can do. Spike fragments can form amyloid fibrils that interfere with clot breakdown, as explained in spike protein amyloid fibrils and fibrinolysis. A 2026 review also argues that stressed, infected cells may produce sticky spike fragments, which we assess in is spike protein a prion?

Dying infected cells may matter too. When cells break apart they release DNA, which the body clears with enzymes called DNases. Research on how COVID-19 affects that cleanup is covered in DNase and NET clearance in Long COVID. None of these links has been tested with the structures seen in this study.

What the study did not prove

The study didn't:

• film a complete, infectious virus traveling through a nanotube
• prove the vesicles carried infectious virus
• show how often these routes are used inside a human body
• test human lung, brain or blood-vessel tissue
• show that these routes cause Long COVID or any specific symptom
• test a treatment that blocks the proposed routes

So it gives a strong visual clue, not a finished answer.

A simpler way to picture it

Imagine a burglar who normally walks from house to house, trying each front door. The police learn to watch the street and guard the doors.

Then someone looks down from above with a super-powerful camera. Some houses have built secret hallways between their windows, others have knocked down walls and joined together, and small delivery bubbles are moving around outside.

The camera doesn't show exactly what the burglar carries through each hallway or package. It does show the neighborhood has more paths than anyone could see from the street. That's the paper's main idea: SARS-CoV-2 may not always need to leave one cell completely before reaching another.

What does this mean if you have Long COVID?

Not much that's practical yet. This is cell-culture research, and nothing in it changes testing or treatment today. Long COVID research has moved toward measurable problems such as fibrin amyloid microclots, explained in our pillar on amyloid microclots and Long COVID.

If you want to know what can be measured in blood now, our guide to the amyloid fibril test explains how Thioflavin T detects amyloid, and our at-home amyloid test applies that method to fibrin amyloid microclots in a dried blood sample. It doesn't detect virus or spike protein and isn't a diagnosis. For everyday steps, see the Long COVID survival guide.

The bottom line

Researchers found long cell bridges, giant fused cells and many tiny vesicles in a lab culture infected with SARS-CoV-2. Those structures could create inside routes from cell to cell, possibly helping the virus avoid some defenses aimed at particles outside cells.

It's an interesting and plausible idea. It isn't yet proof that any of these routes spreads infectious virus inside people.

This article is educational and doesn't diagnose illness or recommend treatment.