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Strange structures have been found lurking in the blood of people suffering from long Covid. Medical researchers have observed something unusual under their microscopes that could be contributing to symptoms such as brain fog and fatigue.

Long Covid has been a mystery since the pandemic struck, but unique biomarkers have now been detected that could support two likely theories, both of which could prove to be correct.

The first is that the malaise is caused by tiny blood clots that hinder blood flow, while another part of the puzzle is the possibility of sticky webs of DNA that have a similar effect.

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It’s still early days, but docs are hopeful that if they figure out how these blood components affect long Covid, it will be a step towards treatment and even a cure.

In a study published in the Journal of Medical Virology, an international team led by Professor Alain Thierry of Montpellier University, working with South African physiologist Professor Resia Pretorius, analysed blood from 50 people with long Covid and 38 healthy volunteers.

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What they found lit up their microscopes: a dramatic surge in the clots - nearly 20 times more compared to healthy blood - and they were bigger too.

The clots are riddled with 'NETs' - neutrophil extracellular traps - which are sticky webs of DNA and enzymes released by white blood cells to ensnare invading viruses.

Normally, NETs do their job and disintegrate. But in these samples, the webs appeared physically embedded within the microclots, forming stubborn, gummy structures that could slow blood flow through capillaries and resist the body’s usual clean-up process.

.The team used imaging flow cytometry and fluorescence microscopy to spot these tangled clots, finding the NETs–microclot mash-up in all samples but far more pronounced in people with long Covid.

The difference was so striking that when the samples were anonymised, an AI system could identify the long Covid patients with approximately 91% accuracy. That raises the prospect of a potential biomarker to help doctors diagnose a condition that’s often waved away because standard tests come back 'normal'.

Back in 2021, Pretorius’s team first flagged microclots in long Covid; in 2022, Thierry’s group reported elevated NETs. Now, bringing those threads together, the new study suggests the two may be teaming up in the blood - and when that partnership goes rogue, trouble follows.