of an adult patient who was admitted to our hospital with a rapidly progressive encephalopathy and behavioural changes.

Case presentation {#cesec20}
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The patient was born at a military hospital in rural southern India in 1985 and migrated to Canada in 2009. Her past medical history was unremarkable, and she received routine childhood vaccinations, including measles vaccination at age 1 year. As an adult she had mild environmental asthma and suffered miscarriages at 18 gestational weeks in 2012 and at 12 gestational weeks in 2013. Her prenatal serology was typical: positive measles IgG (30·5 IU/mL); positive rubella IgG (87·2 IU/mL); positive varicella IgG; negative hepatitis B surface antigen; negative syphilis antibody screen; cervical swabs negative for *Chlamydia trachomatis, Neisseria gonorrhoeae*, bacterial vaginosis, and trichomonas; and negative HIV serology.

She became pregnant forthe third time and at 21 weeks\' gestation she and her husband travelled to the state of Tamil Nadu in India, where they stayed in a small village and visited the port city of Tuticorin. During her stay she was exposed to chickens and wild pigeons on her parents\' property and had several mosquito bites. She drank only bottled water and avoided raw fruits and vegetables as much as possible. She did not take malaria prophylaxis. Her 4 week stay was noteworthy only for a mild upper respiratory illness with coryza, cough, rhinorrhoea, and malaise for several days, which had resolved by the time she returned to Canada.

7 days after her return to Canada she developed mild confusion and intermittently unbalanced gait. Over the next few days she