Human herpesviruses-6 and -7 each cause significant neurological morbidity in Britain and Ireland

Area of Science:

• Pediatric Infectious Diseases
• Virology
• Neurology

Background:

• Primary human herpesvirus-6 and -7 (HHV-6/-7) infections can lead to febrile illness, convulsions, and rarely, encephalopathy in children.
• Understanding the specific contribution of these viruses to severe pediatric illness is important for diagnosis and management.

Purpose of the Study:

• To determine the prevalence and clinical impact of primary HHV-6 and HHV-7 infections in hospitalized young children presenting with severe illness, fever, and convulsions.
• To identify age-related patterns and predisposing factors associated with HHV-6 and HHV-7 infections in this cohort.

Main Methods:

• A three-year prospective study involving 205 children (2-35 months) hospitalized with suspected encephalitis and/or severe febrile illness with convulsions.
• Blood samples were collected and tested for primary HHV-6 and HHV-7 infections through the British Paediatric Surveillance Unit network.

Main Results:

• 17% (26/156) of children aged 2-23 months had primary HHV-6 or HHV-7 infection coinciding with acute illness, significantly higher than expected by chance.
• These infections were associated with high rates of fever, convulsions (including status epilepticus), and need for ventilation, with a median hospital stay of 7.5 days.
• Age was a predisposing factor for HHV-6, while lack of prior HHV-6 infection was noted for HHV-7.

Conclusions:

• Primary HHV-6 and HHV-7 infections are significant contributors to severe febrile illness and convulsions in children under two years old, with equal contribution from both viruses.
• Clinical investigation for primary HHV-6/-7 infections should be considered in children with neurological disease, particularly to differentiate from vaccine reactions.
• Age and prior infection status are key factors influencing susceptibility to HHV-6 and HHV-7 induced illness.