Acute encephalopathy and pandemic (H1N1) 2009

Acute Encephalitis Syndrome with an Unusual Diagnosis

Four-year old boy was admitted with acute onset of fever with seizures and altered sensorium. His mother had history of contact with influenza A H1N1 virus (H1N1) infection. Blood counts, electrolytes, blood sugar and ammonia were normal. Liver enzymes were mildly elevated. CSF study showed elevated protein, normal sugar and no pleocytosis. Cerebrospinal fluid (CSF) viral panel was negative. Magnetic resonance imaging brain was suggestive of acute necrotizing encephalopathy. His throat swab and sputum polymerase chain reaction was positive for H1N1. He was managed with ventilation, intravenous steroids and other supportive measures. At discharge his sensorium improved but had neurological sequelae. We are presenting this case as this is a very rare complication of H1N1 infection with high rate of mortality. Early supportive measures and steroids/intravenous immunoglobulin may save the patient.

Localization of pandemic 2009 H1N1 influenza A virus RNA in lung and lymph nodes of fatal influenza cases by in situ hybridization: new insights on virus replication and pathogenesis

BACKGROUND

Pandemic 2009 H1N1 influenza A (pH1N1) virus has caused substantial morbidity and mortality globally and continues to circulate. Although pH1N1 viral antigens have been demonstrated in various human tissues by immunohistochemistry (IHC), cellular localization of pH1N1 RNA in these tissues has largely remained uninvestigated.

OBJECTIVES

To examine the distribution of pH1N1 RNA in tissues of fatal cases in order to understand the virus tissue tropism, replication and disease pathogenesis.

STUDY DESIGN

Formalin-fixed, paraffin embedded autopsy tissues from 21 patients with confirmed pH1N1 infection were analyzed by influenza A IHC and by in situ hybridization (ISH) using DIG-labeled sense (detects viral RNA) and antisense probes (detects positive-stranded mRNA and cRNA) targeting the nucleoprotein gene of pH1N1 virus.

RESULTS

pH1N1 RNA was localized by ISH in 57% of cases while viral antigens were detected by IHC in 76%. However, in cases with a short duration of illness (1-3 days), more cases (69%) were positive by ISH than IHC (62%). Strong ISH staining was detected by antisense probes in the alveolar pneumocytes of the lungs, mucous glands and in lymph nodes. IHC staining of viral antigens was demonstrated in the lung pneumocytes and mucous glands, but no immunostaining was detected in any of the lymph nodes examined.

CONCLUSIONS

This study demonstrates cellular localization of positive-stranded pH1N1 RNA in the lungs, mucous glands and lymph nodes that suggests viral replication in these tissues. The novel ISH assay can be a useful adjunct for the detection of pH1N1 virus in tissues and for pathogenesis studies.

Influenza A 2009 H1N1 encephalitis in adults with viral RNA in cerebrospinal fluid

We present 3 cases of influenza A 2009 H1N1 encephalitis occurring in adults, corroborated by viral genome detection in cerebrospinal fluid (CSF) and evidence of meningeal inflammation on brain histopathology. This paper emphasizes the possibility of viral detection in CSF and stresses the lack of an effective treatment for neurological manifestations of influenza.

Pandemic (H1N1) 2009 encephalitis in woman, Taiwan

We report an unusual case of pandemic (H1N1) 2009–related encephalitis in an immunocompetent woman. Although rare cases of pandemic (H1N1) 2009 associated with encephalitis have been reported previously, in this patient, direct viral invasion of the central nervous system was shown by simultaneous detection of viral RNA and pleocytosis.

Histopathological and immunohistochemical findings of 20 autopsy cases with 2009 H1N1 virus infection

Twenty autopsy cases with 2009 pandemic influenza A (2009 H1N1) virus infection, performed between August 2009 and February 2010, were histopathologically analyzed. Hematoxylin-eosin staining, immunohistochemistry for type A influenza nucleoprotein antigen, and real-time reverse transcription-PCR assay for viral RNA were performed on formalin-fixed and paraffin-embedded specimens. In addition, the D222G amino acid substitution in influenza virus hemagglutinin, which binds to specific cell receptors, was analyzed in formalin-fixed and paraffin-embedded trachea and lung sections by direct sequencing of PCR-amplified products. There were several histopathological patterns in the lung according to the most remarkable findings in each case: acute diffuse alveolar damage (DAD) with a hyaline membrane (four cases), organized DAD (one case), acute massive intra-alveolar edema with variable degrees of hemorrhage (three cases), neutrophilic bronchopneumonia (five cases) and tracheobronchitis with limited histopathological changes in alveoli (four cases). In two cases, the main findings were due to preexisting disease. Influenza virus antigen was only detected in the respiratory tract in 10 cases by immunohistochemistry. The antigen was detected in type II pneumocytes (three cases) in the epithelial cells of the trachea, bronchi and glands (six cases), and in the epithelial cells in both of the above (one case). The four cases with acute DAD presented with antigen-positive type II pneumocytes. In one case, the D222G substitution was detected in the lung as a major sequence, although 222D was prominent in the trachea, suggesting that selection of the viral clones occurred in the respiratory tract. In five cases, the pathogenesis of 2009 H1N1 was confirmed to be viral infection in pneumocytes, which caused severe alveolar damage and fatal viral pneumonia. Further studies on both host and viral factors in autopsy or biopsy materials will be essential to elucidate the other pathogenic factors involved in influenza virus infection.