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What causes long Covid? US study finds 4 factors, including viral load & Type-2 diabetes

Preliminary findings of study — conducted by Institute for Systems Biology and University of Washington, in association with Swedish Medical Center, US — published in 'Cell'. 

People wear masks as a precaution against coronavirus | Representational image | PTI
People wear masks as a precaution against coronavirus | Representational image | PTI

Bengaluru: Many people who recover from Covid experience what is known as “long Covid”, where cognitive and neurological symptoms from the disease persist for weeks or months after infection. In medical terms, it is called Post-Acute Sequelae of Covid-19 (PASC) or Post-Acute Covid Syndrome (PACS), and is not well studied or understood yet. 

Now, in a first study of its kind, American researchers from the Institute for Systems Biology, Washington, and the University of Washington, in association with the Swedish Medical Center in Seattle, have quantified risk factors that they say increase the likelihood of long Covid and narrowed it down to a combination of four factors.

From an initial study of a group of Covid patients, they corroborated their findings with dozens of other people affected by the disease. 

The four factors they zeroed in on are the development of auto antibodies, Type 2 diabetes, a higher viral load of the disease, and the reactivation of the common herpes virus. The researchers hope that the disease can be managed better in patients who are identified with the biological factors.

The preliminary findings were published in the journal Cell this week. 


Also read: What is ‘Long Covid’ and why some patients who have recovered continue to feel ill for months


‘Patients with more symptoms had one contributing factor’

In the first phase of their study, the researchers examined 209 patients through their diagnosis and followed up with them for three months. The study was done in multiple centres across the US. 

The group of Covid patients had been infected in 2020 or early 2021. They were monitored for 20 symptoms associated with long Covid, including shortness of breath, fatigue and brain fog.

Of these patients, 37 per cent reported three or more symptoms persisting for two-three months after infection. An additional 24 per cent reported one or two symptoms, while 39 per cent reported no symptoms. Of those reporting three or more symptoms, 95 per cent had at least one of the four contributing factors identified. 

The most prominent of the factors that the researchers found were the development of auto antibodies, which start attacking the body’s internal systems. The development of these antibodies correlated with the concentration levels of other antibodies that targeted very specific parts of the coronavirus and its spike protein. 

The level of viral RNA or the Covid-19 viral load in the body upon infection also played a role in the development of long Covid, with those with a higher viral load having an increased probability of severe disease as well. 

The third factor was the reactivation of the common herpes virus, the Epstein-Barr virus (EBV). This virus infects most people when they are young, lying dormant in the body until the immune system is compromised enough for it to surface. 

The final factor was having Type-2 diabetes, but the authors clarify that it could potentially be only one of the conditions that could contribute to the risk. Many of those who had developed severe forms of Covid were hospitalised due to comorbidities. 

‘Covid can be managed better’

The researchers corroborated their findings in the second phase of the study with 100 additional patients, many of whom had only had mild infections, as well as with data from a further 457 patients who did not develop long Covid after infection. 

The identification of the four biological factors, the researchers said, means that Covid patients can be managed better, for example, by being offered antiviral treatments soon after diagnosis to keep viral loads in check and against EBV. 

The researchers also noted that those with higher auto antibodies had lower protective antibodies, making them susceptible to reinfection.

Additionally, they observed that those who had more severe forms of Covid were more prone to developing long Covid. Independent of the severity of disease, those who had a history of lung ailments, including asthma and bronchitis, were at a higher risk of developing prolonged symptoms as well. 

(Edited by Saikat Niyogi) 


Also read: Long Covid patients face fatigue, muscle pain, lack of sleep even after 1 year, UK study says


 

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