This case report, authored by paediatric specialists from the University of Toronto and Toronto's Hospital for Sick Children (SickKids), documents a case of Lyme disease in a 21-day-old infant who presented with symptoms of disseminated Lyme disease after being bitten on the arm by a blacklegged tick (Ixodes scapularis) that subsequently tested positive for Borrelia burgdorferi, the bacterium that causes Lyme disease.
The child was bitten at the family's farm in rural Ontario and was taken to the SickKids emergency room by her parents after the distinctive expanding red rash long associated with Lyme disease -- erythema migrans (EM) -- started spreading out from the site of the tick bite. The child had also become lethargic and had a limited appetite. She was clinically diagnosed with Lyme disease based on her symptoms -- the rash, in particular -- and her history of exposure. Doctors did not have her tested for Lyme disease due to the poor sensitivity of Lyme tests in the first few weeks following a tick bite. The presence of the rash, the tick bite, and the added bonus of the tick testing positive for Lyme disease were sufficient for a clinical diagnosis.
Following the start of what would ultimately be successful intravenous antibiotic treatment, the infant developed a worsening of symptoms associated with a Jarisch-Herxheimer reaction. Those symptoms included a fever and a rapid heartbeat. The reaction abated and within days the rash resolved. Treatment continued for two weeks and a follow-up appointment a couple of weeks following treatment determined that the infant's symptoms had fully resolved.