Tag: post-infectious sequelae

Does Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) Represent a Poly-Herpesvirus Post-Virus Infectious Disease?

Abstract:

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating multisystem illness with unknown etiology. An estimated 17-24 million people representing approximately 1% of the population are afflicted worldwide. In over half of cases, ME/CFS onset is associated with acute “flu-like” symptoms, suggesting a role for viruses. However, no single virus has been identified as the only etiological agent.

This may reflect the approach employed or more strongly the central dogma associated with herpesviruses replication, which states that a herpesvirus exists in two states, either lytic or latent. The purpose of this review is to address the role that abortive lytic replication may have in the pathogenesis of ME/CFS and other post-acute viral infections and also to raise awareness that these syndromes might be poly-herpesviruses mediated diseases.

Source: Ariza ME, Mena Palomo I, Williams MV. Does Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) Represent a Poly-Herpesvirus Post-Virus Infectious Disease? Viruses. 2025 Dec 16;17(12):1624. doi: 10.3390/v17121624. PMID: 41472292. https://www.mdpi.com/1999-4915/17/12/1624 (Full text)

Proposed Mechanistic Axis of Infections and mTOR Hyperactivation: A Multidisciplinary Review of Immune, Rheumatologic, and Psychiatric Links

Abstract:

Early-life infections can produce durable changes in immune function and behavior. We propose a mechanistic hypothesis positioning the mechanistic target of rapamycin (mTOR) as the link between peripheral inflammation and central nervous system dysfunction in pediatric post-infectious syndromes. Based on clinical, translational, and experimental literature, we outline a stepwise pathway.

First, sustained mTOR activation skews T-cell and macrophage differentiation toward pro-inflammatory and autoimmune states. Second, endothelial mTOR signaling weakens tight junctions and increases vesicular transport, compromising blood-brain barrier integrity. Third, cytokines and sometimes autoreactive cells enter the brain and engage mTOR in microglia and neurons, driving neuroinflammation, impaired synaptic maintenance and plasticity, and neurotransmitter disruption.

This framework accounts for features observed in Long COVID, myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), and pediatric acute neuropsychiatry syndrome (PANS/PANDAS) and yields testable predictions on pathway activity and barrier permeability. It also motivates targeted interventions that modulate mTOR-related processes in immune and endothelial compartments and within neural circuits in children. So, this article aims to outline a mechanistic framework linking infection-driven mTOR activation to post-infectious neuropsychiatric syndromes.

Source: Fronticelli Baldelli G, Buonsenso D. Proposed Mechanistic Axis of Infections and mTOR Hyperactivation: A Multidisciplinary Review of Immune, Rheumatologic, and Psychiatric Links. Children (Basel). 2025 Nov 25;12(12):1603. doi: 10.3390/children12121603. PMID: 41462744. https://www.mdpi.com/2227-9067/12/12/1603 (Full text)

The lingering shadow of epidemics: post-acute sequelae across history

Significance:
Long COVID, a chronic multisystemic health condition, impacts hundreds of millions around the world. Long COVID has brought light to other related post-acute infection syndromes (PAIS) that are triggered by a wide array of pathogens. This opinion article highlights historical accounts of PAIS through the centuries and emphasizes the need for integrated approaches to understanding and treating PAIS.
Highlights:

  • New or persistent symptoms following COVID-19, known as ‘long COVID’, occur in an estimated 4–20% of pediatric and 10–20% of adult patients after acute infection with SARS-CoV-2. Long COVID is associated with dysregulation of both innate and adaptive immunity.
  • While long COVID is a relatively new clinical entity, post-acute infection syndromes (PAIS) have been well documented for over a century.
  • A wide variety of pathogens are associated with PAIS, including divergent classes of viruses, bacteria, and parasites. While each PAIS has a unique trigger and pathology, similarities in symptom profiles and immunological findings suggest these conditions may share features or involve overlapping biological mechanisms.
  • Despite being well described in the literature, PAIS remain understudied relative to their high disease burden. Patients often face stigma and psychologization from medical professionals when disease biomarkers are not readily apparent, exemplified by the historic dismissal of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS).
Abstract:
The SARS-CoV-2 pandemic has drawn global attention to post-acute infection syndromes (PAIS), with millions affected by post-acute sequelae of COVID-19 (PASC, or Long COVID). While Long COVID is newly defined, PAIS have been described for over a century following epidemic infections. Multiple pathogens – including influenza, Epstein-Barr virus, and Borrelia burgdorferi, among others – can precipitate persistent, poorly understood symptoms. Chronic illnesses such as myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) have long been linked to infectious triggers. This recurring association highlights critical knowledge gaps and underscores the need for systematic investigation. Unlike prior pandemics, the current era offers advanced technologies and analytic tools to address these gaps. Defining the biology of Long COVID may yield broader insights into host–pathogen interactions and mechanisms of chronic illness.
Source: Miller CM, Moen JK, Iwasaki A. The lingering shadow of epidemics: post-acute sequelae across history. Trends Immunol. 2025 Dec 4:S1471-4906(25)00267-4. doi: 10.1016/j.it.2025.10.010. Epub ahead of print. PMID: 41350176. https://www.cell.com/trends/immunology/fulltext/S1471-4906(25)00267-4 (Full text)

Causes of symptoms and symptom persistence in long COVID and myalgic encephalomyelitis/chronic fatigue syndrome

Abstract:

Debilitating symptoms for many years can follow acute COVID-19 (“long COVID”), myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), and various post-acute infection syndromes (PAISs). Together, long COVID and ME/CFS affect 60-400 million individuals, globally. Many similar underlying biological abnormalities have been identified in both conditions including autoantibodies against neural targets, endothelial dysfunction, acquired mitochondrial dysfunction, and a pro-inflammatory gut microbiome. Each of these abnormalities may directly cause some of the symptoms.

In addition, the symptoms also may be caused by ancient, evolutionarily conserved symptomatic and metabolic responses to vital threats-sickness behavior and torpor-responses mediated by specific, recently discovered neural circuits. These neural circuits constitute a symptom-generating pathway, activated by neuroinflammation, which may be targeted by therapeutics to quell neuroinflammation.

Many factors cause the symptoms to become chronic, including persistent infectious agents (and/or their nucleic acids and antigens) and the fact that many of the underlying biological abnormalities reinforce each other, creating ongoing physiological vicious cycles.

Source:Komaroff AL, Dantzer R. Causes of symptoms and symptom persistence in long COVID and myalgic encephalomyelitis/chronic fatigue syndrome. Cell Rep Med. 2025 Jul 25:102259. doi: 10.1016/j.xcrm.2025.102259. Epub ahead of print. PMID: 40744021. https://www.cell.com/cell-reports-medicine/fulltext/S2666-3791(25)00332-5 (Full text)

Inflammation, Autoimmunity, and Infection in Fibromyalgia: A Narrative Review

Abstract:

Fibromyalgia (FM) is a chronic disease characterized by widespread musculoskeletal pain of unknown etiology. The condition is commonly associated with other symptoms, including fatigue, sleep disturbances, cognitive impairment, and depression. For this reason, FM is also referred to as FM syndrome. The nature of the pain is defined as nociplastic according to the latest international classification and is characterized by altered nervous sensitization both centrally and peripherally. Psychosocial conditions have traditionally been considered critical in the genesis of FM. However, recent studies in animal models and humans have provided new evidence in favor of an inflammatory and/or autoimmune pathogenesis.

In support of this hypothesis are epidemiological data of an increased female prevalence, similar to that of autoimmune diseases, and the frequent association with immune-mediated inflammatory disorders. In addition, the observation of an increased incidence of this condition during long COVID revived the hypothesis of an infectious pathogenesis. This narrative review will, therefore, discuss the evidence supporting the immune-mediated pathogenesis of FM in light of the most current data available in the literature.

Source: Paroli M, Gioia C, Accapezzato D, Caccavale R. Inflammation, Autoimmunity, and Infection in Fibromyalgia: A Narrative Review. Int J Mol Sci. 2024 May 29;25(11):5922. doi: 10.3390/ijms25115922. PMID: 38892110; PMCID: PMC11172859. https://pmc.ncbi.nlm.nih.gov/articles/PMC11172859/ (Full text)

Long COVID as an Infection-Associated Chronic Condition: Implications

In-Brief:

A link between infection and chronic illness has been recognized, along with the complexities of interactions between pathogen, environment, host genetics, route of exposure, and timing of outcomes. The COVID-19 pandemic has brought this issue to the forefront and Long COVID is recognized to be an infection associated chronic condition. However, given the wide range of Long COVID presentations, the singular expression gives a false sense of simplicity. Long COVID is best considered as a group of infection associated conditions requiring developing research studies and treatment trials that address the inherent heterogeneity.
Source: Unger ER. Long COVID as an Infection-Associated Chronic Condition: Implications. Am J Health Promot. 2025 Jul;39(6):960-965. doi: 10.1177/08901171241308066b. Epub 2025 Jun 8. PMID: 40485158. https://journals.sagepub.com/doi/10.1177/08901171241308066b (Full text)

Incidence and Prevalence of Post-COVID-19 Myalgic Encephalomyelitis: A Report from the Observational RECOVER-Adult Study

Abstract:

Background: Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) may occur after infection. How often people develop ME/CFS after SARS-CoV-2 infection is unknown.

Objective: To determine the incidence and prevalence of post-COVID-19 ME/CFS among adults enrolled in the Researching COVID to Enhance Recovery (RECOVER-Adult) study.

Design, setting, and participants: RECOVER-Adult is a longitudinal observational cohort study conducted across the U.S. We included participants who had a study visit at least 6 months after infection and had no pre-existing ME/CFS, grouped as (1) acute infected, enrolled within 30 days of infection or enrolled as uninfected who became infected (n=4515); (2) post-acute infected, enrolled greater than 30 days after infection (n=7270); and (3) uninfected (1439).

Measurements: Incidence rate and prevalence of post-COVID-19 ME/CFS based on the 2015 Institute of Medicine ME/CFS clinical diagnostic criteria.

Results: The incidence rate of ME/CFS in participants followed from time of SARS-CoV-2 infection was 2.66 (95% CI 2.63-2.70) per 100 person-years while the rate in matched uninfected participants was 0.93 (95% CI 0.91-10.95) per 100 person-years: a hazard ratio of 4.93 (95% CI 3.62-6.71). The proportion of all RECOVER-Adult participants that met criteria for ME/CFS following SARS-CoV-2 infection was 4.5% (531 of 11,785) compared to 0.6% (9 of 1439) in uninfected participants. Post-exertional malaise was the most common ME/CFS symptom in infected participants (24.0%, 2830 of 11,785). Most participants with post-COVID-19 ME/CFS also met RECOVER criteria for long COVID (88.7%, 471 of 531).

Limitations: The ME/CFS clinical diagnostic criteria uses self-reported symptoms. Symptoms can wax and wane.

Conclusion: ME/CFS is a diagnosable sequela that develops at an increased rate following SARS-CoV-2 infection. RECOVER provides an unprecedented opportunity to study post-COVID-19 ME/CFS.

Source: Vernon SD, Zheng T, Do H, Marconi VC, Jason LA, Singer NG, Natelson BH, Sherif ZA, Bonilla HF, Taylor E, Mullington JM, Ashktorab H, Laiyemo AO, Brim H, Patterson TF, Akintonwa TT, Sekar A, Peluso MJ, Maniar N, Bateman L, Horwitz LI, Hess R; NIH Researching COVID to Enhance Recovery (RECOVER) Consortium. Incidence and Prevalence of Post-COVID-19 Myalgic Encephalomyelitis: A Report from the Observational RECOVER-Adult Study. J Gen Intern Med. 2025 Jan 13. doi: 10.1007/s11606-024-09290-9. Epub ahead of print. PMID: 39804551. https://link.springer.com/article/10.1007/s11606-024-09290-9 (Full text)

Infection-associated chronic conditions: Why Long Covid is our best chance to untangle Osler’s web

Abstract:

The recognition of Long Covid has renewed efforts to understand other infection-associated chronic conditions (IACCs). Here, we describe how studies of Long Covid and other IACCs might inform one another. We argue for the importance of a coordinated research agenda addressing these debilitating illnesses.

INTRODUCTION

For nearly a century, individuals with medically unexplained chronic conditions, particularly those thought to be attributable to presumably transient infectious pathogens, have faced bewilderment, skepticism, or outright dismissal from the medical establishment. Debilitating symptoms lasting for years have been reported after acute infections with viruses [enterovirus, Epstein-Barr virus (EBV), influenza virus, Ebola virus, dengue virus, chikungunya virus, West Nile virus, and severe acute respiratory syndrome coronavirus 1 (SARS-CoV)], bacteria (Borrelia and Anaplasma), and protozoa (Giardia) (1). Myalgic encephalomyelitis (ME), sometimes referred to as chronic fatigue syndrome (CFS), is perhaps the best example of a disabling syndrome that many experts believe follows an acute, often undiagnosed viral infection. Several names have been applied to these syndromes, including post-acute infection syndromes (PAIS), infection-associated chronic illnesses, and infection-associated chronic conditions (IACCs). Here, we will use IACCs.
Despite consistent reports regarding these conditions dating back nearly 100 years (2–4), the biomedical establishment has made limited progress in defining the epidemiology, natural history, and pathogenesis of most IACCs. No diagnostic tests are available, no widely accepted treatments exist, and industry engagement on finding a cure has been limited. In her 1996 book Osler’s Web, investigative journalist Hillary Johnson catalogued the challenges facing ME/CFS research (5), which can be applied to many IACCs. Barriers to progress included the inability to fit ME/CFS into existing disease paradigms, variability and inconsistency in case ascertainment, skepticism on the part of many clinicians and scientists, and intense stigma that kept many of those affected from seeking medical care. William Osler, the “father of modern medicine,” emphasized the importance of listening to patients to discern important features of their condition. However, contemporary medical practice relies heavily on diagnostic tests, which are currently inadequate to confirm the presence of an IACC. This results in people being neglected or misdiagnosed and prevents them from receiving appropriate care and support.
The year 2020 has the potential to be a turning point in this story. Shortly after the COVID-19 pandemic began, reports of individuals with prolonged COVID-attributed symptoms emerged, a condition now often referred to as Long Covid. The synchronicity of the inciting infection, universality of the exposure, and visibility, aided by social, popular, and scientific media (6), resulted in the ideal environment for a coordinated effort to understand this new IACC. Substantial investment in scientific effort is starting to pay off, with real progress in defining the epidemiology, natural history, and biology of Long Covid now emerging. After a Congressional appropriation, the US National Institutes of Health rapidly launched the Researching COVID to Enhance Recovery (RECOVER) initiative, which is the first large-scale program aimed at tackling an IACC. The progress to date has been hard-won, however, in part because there is no widely accepted clinical definition, biomarker, or diagnostic test for Long Covid. However, clinical trials, slow to start, are now being pursued in earnest. Although there is no guarantee that this momentum will be sustained without dedicated scientific and financial commitments (7), there is reason to believe that efforts to understand Long Covid have the potential to draw attention to, reframe, and revitalize the efforts to study other IACCs.
High-quality academic reviews of Long Covid are multiplying rapidly (8–12). Our goal in this Viewpoint is not to provide a comprehensive overview of the field but rather to place efforts to study Long Covid in the context of other IACCs. In doing so, we hope to outline several areas that we believe will require consideration as the field attempts to make progress in navigating what has been described as a “labyrinth” (5).
Read the rest of this article HERE.
Source: Michael J. Peluso et al. Infection-associated chronic conditions: Why Long Covid is our best chance to untangle Osler’s web. Sci. Transl. Med.16,eado2101(2024). DOI:10.1126/scitranslmed.ado2101

Increased risk of chronic fatigue syndrome following pneumonia: A population-based Cohort study

Abstract:

Background: Chronic fatigue syndrome (CFS) has been linked to several conditions, including infections, immune system changes, or emotional stress. Our study aimed to assess the risk of CFS after a pneumonia diagnosis using data from National Health Insurance Research Database of Taiwan.

Methods: In this nested case-control study, we identified 2,000,000 adult patients from a nationwide population-based health insurance claims database spanning from January 1, 2000, to December 31, 2017. Each case diagnosed with a pathogenic infection was matched with a corresponding control using propensity scores. We excluded individuals under 20 years of age, those with a history of pathogenic infections before the index date, or those with more than one potential pathogen. To estimate hazard ratios (HR) and the adjusted hazard ratio (aHR) with their respective 95 % confidence intervals (CI), we applied univariable and multivariable Cox proportional hazard models. The multivariable analysis incorporated adjustments for age, sex, and comorbidity-related confounders.

Results: The relationship between infection and the subsequent risk of CFS was assessed using Cox proportional hazards regression analysis. The incidence density rates were 6.13 and 8.70 per 1000 person-years among the non-pulmonary infection and pulmonary infection populations, respectively (adjusted hazard ratio [HR] = 1.4, 95 % confidence interval [CI] 1.32-1.5). Patients infected with Pseudomonas, Klebsiella pneumoniae, Haemophilus influenzae, Streptococcus pneumoniae, and influenza virus exhibited a significantly higher risk of CFS than those without these pathogens (p < 0.05). Additionally, patients with pneumonia had a significantly increased risk of thromboembolism compare with control group (p < 0.05).

Source: Hsu HJ, Chang H, Lin CL, Yao WC, Hung CL, Pang SP, Kuo CF, Tsai SY. Increased risk of chronic fatigue syndrome following pneumonia: A population-based Cohort study. J Infect Public Health. 2024 Jul 14;17(8):102495. doi: 10.1016/j.jiph.2024.102495. Epub ahead of print. PMID: 39018725. https://www.sciencedirect.com/science/article/pii/S1876034124002296 (Full text)

How Patient Input Helped Create Culturally Sensitive Multinational Instruments Assessing Post Viral Symptoms

Our study involves collaboration/participation in order to develop culturally sensitive multinational tools for assessing post viral symptoms.

We discuss the creation of questionnaires using patient participation, and the translation of these questionnaires using international collaboration.

Patient engagement in collaboration on the creation and use of these types of instruments is of particular importance for patients who historically have not been true partners in collaborative efforts to understand diseases.

This has occurred for those with the post-viral illness called Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), which has generated considerable resentment and estrangement among the patient community.

Our article reviews:

1) why participation of diverse groups/patients is important in the development of instruments to measure key symptoms of ME/CFS,

2) why the ME/CFS group of patients needs to be included specifically (as an example),

and

3) why structured health questionnaires are important/useful.

Our article also has an overall aim of demonstrating collaborative efforts with patients and others on creating multinational scales.

We provide examples of participatory processes used in developing and translating patient-driven instruments so that they can be used in non-English speaking countries.

Our article illustrates how patients and international researchers can be involved in efforts to develop and translate international assessment instruments to validly capture domains of unexplained illness like ME/CFS.

With the onset of another post-viral illness, Long COVID, there is a world-wide need to create valid and culturally sensitive assessment instruments to measure critical symptoms, many of which are similar to ME/CFS.

Source: Leonard A. Jason and Joseph A. Dorri. How Patient Input Helped Create Culturally Sensitive Multinational Instruments Assessing Post Viral Symptoms. The Australian Community Psychologist., Volume 32 No 1  https://psychology.org.au/getmedia/c300a432-c7fd-4f97-9322-ce16429067e4/ac-vol-32(1)-2023-final-draft.pdf#page=63 (Full text)