Neonatal encephalitis in Wuhan confirms Japanese encephalitis virus genotype V in mainland China
A fatal encephalitis case in a 21-day-old neonate from Wuhan has confirmed Japanese encephalitis virus genotype V in mainland China, ending years of uncertainty about whether this lineage was still circulating outside of South Korea and the original 1952 reference strains. The diagnosis was established through cerebrospinal fluid testing, serology, and next-generation sequencing, which together pointed to a single, devastating viral cause of coma, convulsions, and death. In practical terms, the case shows that JEV GV is not an archival lineage confined to old phylogenetic trees; it can still reach human hosts in central China and cause fulminant neurologic disease.
The infant was delivered vaginally on October 6, 2025, and both mother and neonate were discharged in good health. There was no recent travel or residence history suggesting exposure outside Wuhan, and maternal laboratory testing found no evidence of recent or past JEV infection. The mother was IgM-negative, IgG-negative, and qRT-PCR–negative 3 days after illness onset in the infant, and she had not been vaccinated against Japanese encephalitis. On day 21 after birth, the neonate developed a high fever of 39.3°C and was admitted to Wuhan Children’s Hospital. During hospitalization from October 27 through November 6, the illness evolved rapidly into persistent high fever, coma, and convulsions. The child died on November 7.
This clinical pattern is consistent with the biology of Japanese encephalitis: a mosquito-borne flavivirus with a marked neurotropic tendency once it breaches host defenses. In neonates, the central nervous system may be particularly vulnerable because encephalitic injury can progress quickly before a diagnosis is secured. The abrupt transition from fever to coma leaves little margin for recovery, especially when no specific antiviral therapy exists and treatment remains supportive.
CSF PCR and serology established the diagnosis before sequencing clarified the lineage
Five specimens were tested in total: two cerebrospinal fluid samples and three serum samples. The initial CSF sample, obtained at admission on October 27, was positive for JEV nucleic acid by qRT-PCR. Serum collected on day 10 of illness contained JEV-specific IgM. All other specimens were negative for JEV RNA and IgM.
Those results matter because they fit the timing of acute flaviviral infection in a way that routine clinical assessment alone could not. Detection of viral RNA in CSF provided direct evidence of central nervous system infection, while IgM in serum supported a recent immune response. Together, they narrowed the differential from broad viral encephalitis to a specific arboviral diagnosis. In a neonate with coma and convulsions, that distinction is not academic; it determines whether the case should trigger genotype-specific surveillance, mosquito investigation, and retrospective review of local transmission risk.
Next-generation sequencing on the admission CSF sample yielded the complete genome of the virus, designated the neonate strain and submitted under GenBank accession number PZ393248. Phylogenetic analysis based on open reading frame sequences showed that JEV genotypes I through V separate into distinct lineages, with genotype V splitting into two major clades. One clade contained the prototype strains from 1952, Muar from Malaysia and Tengah from Singapore. The other included contemporary isolates, among them the neonate strain, the XZ0934 strain from Tibet in 2009, and viruses recovered from human cases and mosquitoes in South Korea since 2015.
The sequencing result confirmed that the encephalitis in this infant was caused by JEV genotype V, not by the more commonly detected genotype I that has dominated mainland Chinese surveillance in recent years. A second phylogenetic analysis of envelope gene sequences placed all genotype V strains into three evolutionary clades: clade A with the 1952 prototype strains, clade B with the neonate and XZ0934 strains, and clade C with all South Korea isolates. The pattern points to independent evolution after genotype V reemerged in 2009, rather than a single homogeneous viral population spreading unchanged across East Asia.
Surveillance in China now has to account for a genotype thought to be absent
Genotype V has already been well documented in South Korea, where it has become the dominant genotype in mosquitoes and has produced human cases since 2015. Mainland China looked different for years. After genotype V was first isolated from mosquitoes in Tibet in 2009, surveillance from mainland China largely detected genotype I in mosquito pools and human clinical samples, creating the impression that genotype V had vanished from the region. This neonatal case breaks that assumption.
The geographic implications are broader than one infant in Wuhan. A retrospective serologic analysis of laboratory-confirmed Japanese encephalitis cases from 2018 to 2020 had already suggested possible genotype V infection in eastern China, specifically in Shandong and Zhejiang provinces. Previous surveillance in Wuhan had shown genotype I in mosquitoes in 2009 to 2010, while genotype III had been detected in earlier mosquito collections. The identification of the neonate strain in central China, together with the earlier Tibet isolate, now supports the presence of genotype V in southwestern, central, and eastern China.
That distribution raises a straightforward public health concern: surveillance systems that rely on genotype assumptions can miss circulating viruses until they present as human disease. Mosquito-borne flaviviruses do not respect administrative boundaries, and shifts in genotype prevalence can alter the epidemiology of outbreaks even when the clinical syndrome appears unchanged. The report also notes that cases caused by genotypes IV and V have been increasing, with geographic expansion into Australia and South Korea. Against that backdrop, a single fatal pediatric case in Wuhan becomes evidence of a wider evolutionary and epidemiologic pattern.
For prevention and control, the message is concrete. Genotype-based detection should be strengthened, not treated as optional enhancement, because a region may appear to be seeing only one lineage while another is already circulating at low levels or in ecological niches not captured by routine sampling. In a disease as severe as Japanese encephalitis, missing that shift means missing the chance to map transmission before more children present with irreversible neurologic injury. The immediate clinical cost is measured in rapidly progressive encephalitis; the broader cost is a surveillance system that lags behind viral evolution.
The case also leaves unresolved questions about how genotype V reached this neonate and whether local mosquito vectors are already sustaining silent circulation in central China. The article does not establish the route of transmission, and it does not provide vector data from the child’s immediate environment. Those gaps are exactly where follow-up field investigation will matter most, because the next case may arrive before a genotype is recognized in routine surveillance.