New York, Oct 27 (IANS): Suicidal thoughts, "paranoia-like fears", delusions and "foggy brain" have been identified in three adolescents who had mild or asymptomatic Covid-19, according to a new study which found rogue antibodies responsible for the condition.

The study, led by researchers at the University of California San Francisco, looked at anti-neural antibodies -- "turncoat" antibodies that may attack brain tissue -- in paediatric patients who had been infected with SARS-CoV-2.

In the study, published in JAMA Neurology, the researchers examined the three patients' cerebrospinal fluid, obtained via lumbar puncture, and found that two of the patients, both of whom had histories of unspecified depression and/or anxiety, had antibodies indicating that SARS-CoV-2 may have invaded the central nervous system.

The same patients, who had mild/asymptomatic Covid, also had anti-neural antibodies in their cerebrospinal fluid, which were identified by immunostaining brain tissue. This suggests an immune system running amok, mistakenly targeting the brain instead of infectious microbes, the team explained.

Unlike most psychiatric presentations, the three patients had symptoms with sudden onset and rapid progression, representing a marked change from their baselines, said Claire Johns, MD of the UCSF Department of Paediatrics.

"The patients had significant neuropsychiatric manifestations despite mild respiratory symptoms, suggesting potential short and long-term effects of Covid," Johns said.

However, "it is way too soon to know whether Covid is a common trigger for neuropsychiatric illnesses, but it does seem to be a potent trigger for the development of autoantibodies", said Samuel Pleasure, of the UCSF Department of Neurology and of the UCSF Weill Institute.

"It is currently totally unknown whether patients predisposed to neuropsychiatric illnesses are more likely to develop worsened symptoms after Covid, or whether Covid infection can act as an independent trigger," he added.

After weeks long hospitalisations and ongoing psychiatric medications, the two of three patients, whose cerebrospinal fluid tested positive for SARS-CoV-2 antibodies and anti-neural antibodies, were treated with intravenous immunoglobulin, an immunomodulatory therapy that curbs inflammation in autoimmune disorders.

Five days later, the first patient had "more organised thoughts, decreased paranoia and improved insight", the researchers said.

The second patient appeared to have a modest response to immunotherapy with improved cognition and working memory, but continued to have "impaired mood and cognitive symptoms" six months later.

The third patient, who had no psychiatric history and had neither SARS-CoV-2 antibodies nor anti-neural antibodies in their cerebrospinal fluid, made a complete recovery with psychiatric medications. His symptoms were ultimately attributed to recreational drug use.

A recent study conducted with Yale University also found a high level of autoantibodies in the cerebrospinal fluid of adult patients with acute Covid, who had neurological symptoms, including intractable headaches, seizures and loss of smell.

While the autoantibodies may be most clinically meaningful as markers of immune dysregulation, researchers haven't so far found evidence that they are actually causing the patients' symptoms.