Japanese encephalitis vaccine: is it being sufficiently used in travellers?

A 32-year-old woman presented to the Royal Brisbane Hospital immediately on disembarking from a flight from Bangkok. She had a 5-day history of gastrointestinal symptoms, fever and altered mental state. She was a university graduate and had travelled for 2 months across south-east Asia before becoming unwell in Phnom Penh, Cambodia. Her illness began with mood elevation, hallucinations, muscle spasms and paraesthesiae, shortly after ingestion of a “herbal pizza”. Within 24 hours, nausea, vomiting and profuse watery diarrhoea ensued. Despite empirical treatment for bacterial gastroenteritis, symptoms progressed to lethargy with altered mental state. The patient had been taking doxycycline for malaria prophylaxis, and had been vaccinated against viral hepatitis, tetanus, poliomyelitis and typhoid. She was aware of the availability of a Japanese encephalitis vaccine, but had been advised that it was not essential. On presentation, the patient was drowsy and dehydrated, with a temperature of 38°C and tachycardia. There was peripheral leukocytosis (white cell count, 17.9 x 109 cells/L; reference range [RR], 4.0–11.0 x 109 cells/L) with dominant neutrophilia, as well as hyponatraemia, but renal function was preserved. Fever and lethargy persisted over 48 hours despite rehydration and regular paracetamol. Increasing obtundation and a fine tremor were observed. The patient complained of persistent headache, mild photophobia and neck discomfort. Her partner commented on her slow mentation, reduced concentration and personality change. Investigations for malaria, typhoid, rickettsial disease and infectious diarrhoea were all negative. Magnetic resonance imaging of the brain detected no abnormalities. Cerebrospinal fluid (CSF) showed mononuclear pleocytosis (white cell count, 12 x 106 cells/L; 92% mononuclear cells [RR, < 5 x 106 mononuclears/L]), with mild elevation of protein level (0.62 g/L [RR, <0.45 g/L]), but was negative for herpes simplex virus by polymerase chain reaction. Flavivirus-specific IgM was detected in CSF and subsequently blood. The diagnosis of Japanese encephalitis was confirmed by a rise in titre of specific IgG in blood, from 80 (8 days after onset of illness) to 1280 (4 weeks after onset). The fever resolved spontaneously by Day 4 after presentation, and the patient was discharged after 10 days. At the time of discharge, her level of alertness had improved, but global impairment of higher cognitive functioning and tremor persisted. After a period of convalescence of approximately 5 months, during which she was cared for by her partner, the patient was able to return to work.