Harshi Peiris, Ph.D. Profile picture
Jun 26 β€’ 10 tweets β€’ 5 min read β€’ Read on X
BREAKING 🧡

A gut bacterium is showing up β€” or rather disappearing β€” across all three phases of COVID-19.

Severely ill patients have less of it.
Recovered patients get it back.
Long COVID patients don't.

Its name is Faecalibacterium prausnitzii. And what it does explains a lot. πŸ‘‡
F. prausnitzii is one of the most abundant bacteria in a healthy human gut.

It produces butyrate β€” a molecule that:

β€’ Fuels your colon lining
β€’ Seals your gut barrier
β€’ Suppresses inflammatory signals
β€’ Regulates your immune system

When it disappears, all of that fails at once.Image
Severe COVID-19

A 2025 meta-analysis pooling data across 10 independent studies confirmed:

F. prausnitzii depletion: logFC = -1.24 (95% CI -1.68 to -0.80)

Translation: It was significantly lower in every severe COVID cohort analyzed.

The more depleted. The sicker the patient.
Recovery

Patients who fully recovered from COVID-19 showed normalization of their gut microbiome β€” including return of F. prausnitzii β€” within approximately 6 months.

Butyrate-producing bacteria were among the first to come back.

The gut was healing. The bacteria were the signal.Image
Long COVID

Liu et al. 2022 (Gut journal) tracked 106 Long COVID patients over 6 months.

F. prausnitzii and Bifidobacterium pseudocatenulatum showed the STRONGEST inverse correlation with Long COVID development of any bacteria studied.

Less of them at baseline = more likely to have persistent symptoms.Image
Why does this matter beyond the gut?

↓ F. prausnitzii β†’ ↓ butyrate β†’ gut barrier breaks down
β†’ inflammatory signals enter bloodstream
β†’ cross into the brain
β†’ microglial activation
β†’ brain fog, memory problems, fatigue

This is the same gut-brain pathway seen in Parkinson's and Alzheimer's disease.

Long COVID may be hijacking the same route.Image
A randomized controlled trial just tested this.

463 Long COVID patients. Synbiotic targeting gut bacteria (SIM01) vs placebo. 6 months.

Results (Lancet Infectious Diseases 2024):

Difficulty concentrating: 62% vs 39% alleviated βœ“
Memory loss: 42% vs 27% βœ“
Fatigue: 63% vs 43% βœ“

Pulmonary symptoms: no significant difference.

The gut fixed the brain symptoms. Not the lungs. That tells us something.Image
What we do NOT yet know:

β€’ Whether F. prausnitzii depletion causes Long COVID β€” or is caused by it β€” or both
β€’ The SIM01 trial used vitamin C as placebo, not inert starch
β€’ Results need independent replication
β€’ Direct F. prausnitzii supplement does not exist yet

Association is strong. Causation is unproven. That's where the science actually is.Image
No F. prausnitzii supplement exists yet. But you can feed it.

It thrives on fermentable fibre:

βœ“ Jerusalem artichoke
βœ“ Chicory root
βœ“ Leeks, asparagus, onion
βœ“ Resistant starch (underripe banana, cooled rice)
βœ“ Mediterranean diet pattern overall

NOTE: Probiotics carry real risks for immunocompromised individuals and the elderly. Always consult your doctor.Image
This is part of a disease series on Faecalibacterium prausnitzii β€” one gut bacterium found depleted across Parkinson's, Alzheimer's, MS, IBD, diabetes, cancer, and now Long COVID.
Parkinson’s
x.com/Neuroscope_mp/…
Alzheimer’s x.com/Neuroscope_mp/…
Aging x.com/Neuroscope_mp/…
Full referenced deep-dive on coming soon

Follow @Neuroscope_mp so you don't miss the next thread.

#LongCOVID #Microbiome #GutBrainAxis #NeuroscienceImage

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More from @Neuroscope_mp

Jul 20
BREAKING: A new Alzheimer's drug just did something no tau therapy has ever done in a randomized trial β€” cut tau in the brain by up to 65% AND slowed cognitive decline.

The trial is CELIA, run for 76 weeks.

But there's a twist that has Wall Street nervous. 🧡
Most Alzheimer's drugs (like Leqembi) target amyloid plaques.

This one β€” diranersen (BIIB080) β€” targets tau, the OTHER hallmark protein that tangles up inside brain cells and tracks more closely with memory loss. Image
Image
Instead of cleaning up tau after it builds up, Diranersen turns down production at the source.

It's an β€œantisense oligonucleotide” (ASO) β€” think of it as software that tells the cell β€œmake less tau” before the mess even forms. Image
Read 10 tweets
Jul 16
🚨 BREAKING
A common diabetes pill β€” already in millions of medicine cabinets β€” may be the most targeted drug yet tested for the most common genetic form of ALS.

We're talking about Metformin + C9orf72 ALS.

Here's what the science actually says. πŸ§΅πŸ‘‡
First β€” what makes C9orf72 ALS different?

It's caused by a genetic mutation (a "repeat expansion") that produces toxic proteins called DPRs β€” dipeptide repeat proteins.

These proteins poison motor neurons. There's no approved drug that targets them.

Until now, maybe. 🧬 Image
Image
Here's the mechanism β€” stay with me, this is important:

C9orf72 mutation β†’ toxic RNA β†’ activates a stress enzyme called PKR β†’ PKR cranks up production of toxic DPR proteins β†’ motor neurons die.

Metformin BLOCKS PKR.

That's the target. That's the theory. 🎯 Image
Read 16 tweets
Jul 13
Your Alzheimer's or Parkinson's diagnosis might not be wrong β€” just incomplete.

Autopsy studies show most patients are carrying 2 to 4 overlapping brain diseases at once.

Doctors usually test for one. Every approved drug treats one.
Here's what that's costing patients and what you must knowπŸ§΅πŸ‘‡
An autopsy study of Alzheimer's clinical trial participants found only ~10% actually had "pure" Alzheimer's pathology.

About 2 in 3 had additional diseases layered in β€” Lewy bodies, vascular damage, TDP-43. 17% had FOUR overlapping pathologies at once. Image
Image
This is why levodopa β€” the gold-standard Parkinson's drug β€” barely works in Dementia with Lewy Bodies.

Acute response rate: 90% in pure PD vs just 55% in DLB.

And DLB patients who do respond LOSE the benefit faster over the following year. Image
Read 12 tweets
Jul 10
BREAKING:
A 27-million-patient study found new Parkinson's diagnoses spike after COVID-19 infection β€” peaking around 6 months later.

But the real story isn't what you'd expect. πŸ§΅πŸ‘‡
The study: 27,614,510 patients, propensity-matched for age/sex/smoking.

COVID+ patients had significantly higher odds of a new Parkinson's diagnosis at 3, 6, 9 & 12 months post-infection (peak odds ratio ~1.25 at 6 months). Image
Image
The twist: that elevated risk disappeared after 12–24 months.

That pattern doesn't scream "COVID causes Parkinson's from scratch." It looks more like that was already quietly developing. Image
Read 14 tweets
Jul 6
BREAKING: The shingles vaccine is linked to a 51% lower risk of dementia in the largest study yet β€” 329,000 people, published this year.

This is now the 6th major peer-reviewed study to find the same thing. (Paper published February 2026 in Nature Medicine)

Thread πŸ§΅πŸ‘‡
The headline number:
Kaiser Permanente followed 65,800 people who got 2 doses of Shingrix vs. 263,200 who didn't.

The vaccinated group had 51% lower dementia risk (HR 0.49).

Effect held even compared to a different vaccine (Tdap) β€” so it's not just "healthy people get vaccines."Image
Image
Image
This isn't a fluke. 2nd story ...

In Wales, a vaccine program had a strict birth-date cutoff β€” people born just DAYS apart ended up vaccinated or not, basically at random.

Result: 20% lower dementia risk over 7 years in ~280,000 people.
Published in Nature.
Read 10 tweets
Jul 3
This one bacterium keeps disappearing in Long COVID β€” and it might explain the brain fog and crushing fatigue.

Severe COVID patients lose it.
People who fully recover get it back.
Long COVID patients? It stays gone.
The lower your levels, the worse your symptoms.

Thread still worth reading πŸ‘‡
The same bacterium is missing in Parkinson's disease.

In Parkinson’s (especially gut-first type):
F. prausnitzii is consistently depleted.

Lower levels = worse motor symptoms, balance, and walking.
A recent study even showed restoring it in mice improved motor deficits and reduced alpha-synuclein aggregates in the brain.

Full thread here:
x.com/Neuroscope_mp/…
In Alzheimer’s:
Same depletion pattern.

It hits a different pathway β€” loss of butyrate β†’ weaker blood-brain barrier + ramped-up neuroinflammation β†’ faster amyloid and tau problems.

Lower levels correlate with worse cognitive scores (MMSE).
Full thread:
Read 5 tweets

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