NIHR recently announced a funding opportunity for research into the treatment and management of post-acute infection syndromes (PAIS), including long COVID and ME/CFS – but what are PAIS?
In a commentary, published in the journal ‘Proceedings of the National Academy of Sciences’ (PNAS), Prof Anthony Komaroff explains that PAIS are illnesses – with very similar symptoms – which occur after acute infections caused by different pathogens – bacteria, viruses, fungi, and protozoa.
Notably, pathogen reactivation may explain the ongoing symptoms experienced by some people following an acute infection. Researcher Dr. Amy Proal – who is working on research funded by ME Research UK – explains what pathogen reactivation is:
Throughout our lives – and even as a baby in the womb, we acquire pathogens – viruses, bacteria, and fungi, which – while they are “kept in check” by our immune system, lie dormant in our cells. However, under conditions of immunosuppression or immune dysregulation – such as stress, pregnancy, exposure to toxins, or potentially when a person gets another infection that “throws off the immune response for a period of time”, these dormant pathogens can activate and change their activity to cause “chronic complex illnesses” – which research suggests includes ME/CFS.
Within his article, Prof Komaroff states that “long COVID surely is a PAIS (since the inciting infectious agent is known), and ME/CFS likely often is (even though inciting agents often have not been pursued by physicians)”
Interestingly, Prof Komaroff also explains that PAIS are only one of an even larger umbrella category known as ‘infection associated chronic illnesses’ (IACIs).
IACIs can be grouped into three categories:
- New organ injury: This is where the acute infection causes damage in the body which leads to chronic illness. Examples include the development of multiple sclerosis following primary Epstein-Barr virus infection, and duodenal ulcers caused by Helicobacter pylori.
- Accelerated incidence of disease processes: Here, the acute infection leads to acceleration of disease processes that had not yet become apparent before the time of infection. Examples include accelerated build-up of fats, cholesterol, and other substances known as ‘plaque’ in the artery walls (atherosclerosis) and neurodegeneration – the progressive loss of neurons in the brain – after a COVID-19 infection.
- Post-acute infection syndromes: Ongoing symptoms which develop following an infection.
The commentary by Prof Komaroff also highlights the need for more research in the area including studies investigating why some infections lead to PAIS while others do not. ME Research UK adds that it is also important to consider the mechanisms which lead some people to develop PAIS – such as ME/CFS or long COVID – after a specific infection while others do not.
