Sao Paulo: People infected with SARS-CoV-2 are more likely to have increased load of Torquetenovirus (TTV), an apparently inoffensive virus most frequently found in humans, which can be used as a marker of Covid-19 severity and recovery, according to researchers.
Besides humans, TTV is also common in monkeys and domestic animals. Its presence has not been associated with any known disease, but its excessive replication is a sign that something is wrong with the immune system.
The correlation between high TTV load and immunosuppression has been used in medicine in certain contexts, such as monitoring transplant patients who take medication to prevent rejection of the transplanted organ.
A study by researchers at the University of Sao Paulo (USP) in Brazil analysed samples from 91 patients diagnosed with SARS-CoV-2 by RT-PCR, and from 126 people with flu symptoms who tested negative. TTV and SARS-CoV-2 viral loads were measured in saliva samples.
The results, reported in the journal PLOS ONE, showed that TTV titer is higher in subjects infected by the novel coronavirus. The higher the titer, the longer they remained sick and the symptoms disappeared as viral load decreased.
None of the participants had diseases that cause immunosuppression, such as cancer or HIV/AIDS.
“Covid-19 appears to lead to a degree of immunodepression by causing an immune system imbalance, and this favours replication of TTV. In uninfected subjects, TTV titer remained stable throughout the symptomatic period,” said Maria Cassia Mendes-Correa, Professor at the Medical School (FM-USP).
While the discovery has no direct clinical applications, it may in future contribute to improved Covid-19 diagnosis and prognosis.
TTV has been analysed as a potential biomarker for certain clinical outcomes measured in different biological fluids. The researchers have investigated how elimination of SARS-CoV-2 varies over time in different body fluids, such as blood, urine and saliva.
“We then had the idea of analysing TTV load in these samples in order to find out whether it correlated with Covid-19 severity. The results showed that TTV can indeed serve as a marker of the progression and outcome of this disease. The more symptomatic the patient, the higher the TTV loads in the sample,” Mendes-Correa said.