Merkel cell polyomavirus DNA found in spinal fluid of children with suspected brain infection

In a finding that is already rippling through pediatric neurology and infectious disease circles, researchers in Tehran have detected DNA from Merkel cell polyomavirus — a virus best known as the cause of a rare and aggressive skin cancer — in the cerebrospinal fluid of children suffering from suspected viral meningitis or encephalitis. Strikingly, every single child in whom the virus was found was also infected with HIV, raising urgent new questions about the role of opportunistic polyomaviruses in brain and spinal cord disease among immunocompromised children.

The study, published in Virology Journal, examined cerebrospinal fluid samples from 46 pediatric patients who arrived at hospital with clinical suspicions of viral central nervous system infection. Using a highly sensitive molecular technique known as TaqMan probe-based quantitative polymerase chain reaction, the team, led by Negar Hemmati and Bahman Abedi Kiasari of the University of Tehran together with Fatemeh Hoda Fallah of Valiasr and Imam Khomeini Hospitals at Tehran University of Medical Sciences, searched the samples for the genetic fingerprint of Merkel cell polyomavirus, commonly abbreviated MCPyV. The researchers targeted the viral large T-antigen gene, a regulatory region that is a standard bullseye for polyomavirus detection.

The results were unambiguous in one respect: MCPyV DNA turned up in six of the 46 children, a detection rate of 13 percent. What stunned the investigators was the pattern behind that number. All six MCPyV-positive patients were HIV-positive, an association so strong that the statistical probability of it arising by chance was just 0.001. When the team re-ran their analysis excluding children whose HIV status was unknown, the association held firm at a p-value of 0.002. In a cohort of children suspected of having viral brain infections, the presence of this particular virus appeared to travel exclusively with immune suppression.

Merkel cell polyomavirus is a relative newcomer to the catalogue of human viruses, first identified in 2008 in the tumors that give it its name — Merkel cell carcinoma, a rare but lethal neuroendocrine skin cancer. Like other polyomaviruses, it is a small, double-stranded DNA virus that is ubiquitous in the general population, spreading silently and usually causing no symptoms at all. In healthy individuals, the immune system keeps it in a dormant state. But in people whose immune defenses have collapsed, polyomaviruses can reactivate and, in some cases, invade tissues they would normally never touch. The most infamous example is JC virus, a close relative that causes progressive multifocal leukoencephalopathy, a devastating demyelinating brain disease, in AIDS patients and others with profound immunodeficiency.

The Tehran team did not stop at detection. To guard against the possibility of false positives — always a concern when hunting for viral DNA in clinical samples — they re-tested positive specimens by amplifying an entirely independent genetic target, the viral VP1 gene, which encodes the protein forming the virus’s outer shell. They then performed bidirectional Sanger sequencing on the re-amplified products, essentially reading the actual genetic letters of the virus to confirm that what they had detected was genuinely MCPyV and not a laboratory artifact or a closely related polyomavirus. This two-target confirmation strategy, combined with sequencing, puts the findings on solid molecular ground.

Genetic analysis of the recovered viruses revealed that four isolates belonged to genotype I and two to genotype IIc, showing that at least two distinct viral lineages were circulating in these patients rather than a single clone. This diversity hints that the children may have acquired or harbored separate viral strains, a pattern consistent with independent reactivation events in a suppressed immune environment.

Beyond the mere presence of viral DNA, the study uncovered a telling clinical picture. Compared with children in whom MCPyV was not detected, the six virus-positive patients showed measurable signs of inflammation and biochemical disturbance in their cerebrospinal fluid. Their CSF contained a higher percentage of lymphocytes — 89 percent versus 84 percent in the negative group, a statistically significant difference — indicating a cell-mediated immune response within the central nervous system. Their CSF protein concentrations were elevated, averaging 79 milligrams per deciliter compared with 68 in the negative group, reflecting leakage of proteins across an inflamed blood-brain barrier. At the same time, their glucose concentrations were lower, at 51 versus 55 milligrams per deciliter, a classic sign of metabolically active infectious or inflammatory processes within the fluid bathing the brain and spinal cord.

The clinical differences were just as striking. More than eight in ten MCPyV-positive children — 83.3 percent — presented with altered consciousness, compared with only 37.5 percent of those without detectable virus. Altered consciousness, ranging from confusion to unresponsiveness, is one of the most worrying signs in suspected encephalitis, suggesting that the infection or the immune reaction against it is affecting brain function directly. The association reached statistical significance at a p-value of 0.039. In one of the six positive patients, the researchers also co-detected Epstein-Barr virus DNA, another herpesvirus known to flourish under conditions of immune impairment, adding a further layer of complexity to the viral landscape in these young patients.

The authors are careful to frame their conclusions with appropriate scientific caution. Detecting viral DNA in cerebrospinal fluid does not, by itself, prove that the virus is causing the disease. Viral DNA fragments can persist after infection, low-level latent infection of immune cells trafficking through the central nervous system cannot be excluded, and contamination, however carefully controlled, can never be ruled out entirely in molecular work. What the study establishes is a possible association — MCPyV detection in children with suspected viral CNS infection occurred exclusively in those with HIV and was accompanied by inflammatory CSF abnormalities and more severe neurological presentations. The team explicitly states that these findings suggest a link between MCPyV detection, immunosuppression, and CNS inflammation, but do not establish causality.

Nevertheless, the implications are significant. If MCPyV is confirmed as a genuine neuropathogen, pediatric diagnostic protocols for suspected meningitis and encephalitis — which already routinely screen for herpesviruses, enteroviruses, and in some settings JC virus — may eventually need to add MCPyV to the panel, particularly for children with known or suspected immune compromise. Missed diagnoses of viral CNS infection carry heavy costs: untreated encephalitis can leave children with lasting seizures, cognitive impairment, and developmental delays. A targeted antiviral approach, should one prove effective against MCPyV, would depend first on knowing to look for the virus.

The findings also slot into a growing body of evidence connecting polyomaviruses with neurological disease in the immunosuppressed. Related work has detected JC virus DNA in the CSF of pediatric patients with neurological disorders that do not meet the criteria for progressive multifocal leukoencephalopathy, and earlier research has linked elevated antibody levels against MCPyV with progression to AIDS in HIV-infected adults. The Tehran study is among the first to examine MCPyV specifically in the CSF of children, and its exclusive detection in HIV-positive patients fits neatly into the established paradigm of polyomaviruses as opportunistic agents that emerge when immune surveillance fails.

Why the virus would be present in the central nervous system at all remains an open question. MCPyV normally resides on the skin, where it infects Merkel cells and other cutaneous residents. Routes to the CSF could include hematogenous spread of reactivated virus, carriage within infected immune cells crossing the blood-brain barrier, or reactivation from as-yet unidentified reservoirs in deeper tissues. Answering these questions will require larger, multicenter studies with matched control groups, longitudinal sampling, and perhaps tissue-based analyses capable of demonstrating active viral replication in the nervous system rather than mere molecular presence.

The study’s scale is admittedly modest — 46 patients and six positives — and the authors themselves call for larger multicenter investigations to confirm and extend their results. Yet even at this scale, the statistical signals are hard to dismiss. In a field where the causes of a substantial fraction of pediatric encephalitis cases remain unexplained even after exhaustive testing — a phenomenon clinicians call encephalitis of unknown etiology — any new candidate pathogen deserves attention. Viral screenings that come back negative for the usual suspects leave families without answers and physicians without therapeutic direction. If even a small subset of those mystery cases involves reactivated polyomaviruses in immunocompromised hosts, the Tehran findings could eventually change how those children are evaluated and treated.

The research, which received no specific external funding, was approved by the institutional ethics committee, with written informed consent obtained from the parents or legal guardians of all participants. The team has acknowledged the technical staff of the Clinical Virology Laboratory for their support. The article is published open access under a Creative Commons license, allowing clinicians and researchers worldwide to examine the data in full.

For now, the message for the medical community is one of heightened vigilance rather than alarm. Children with HIV who develop signs of meningitis or encephalitis — fever, headache, neck stiffness, seizures, or altered consciousness — represent a population in whom unusual opportunistic infections must be considered. The discovery that Merkel cell polyomavirus, until now a virus of the skin and the cancer ward, can appear in the spinal fluid of such patients adds one more name to the list of pathogens that physicians caring for immunocompromised children cannot afford to ignore. Whether this virus is a true invader of the nervous system or a molecular bystander, the answer will shape the future of pediatric neurovirology — and the six children in this study have already ensured that the question will not be ignored.