Plague has struck in Idaho, but doctors think he picked up the deadly disease elsewhere in the US.
The child, from Elmore County east of the state capital Boise, is recovering after receiving antibiotics, NBC reports.
It's believed he contracted the bubonic form of the disease after being bitten by a flea, perhaps after a recent trip the family took to Oregon.
The plague is caused by Yersinia pestis. In the 1300s its bubonic form killed around half of the entire population of Europe, and it took the world's population 200 years to recover.
It's the first case of the plague in Idaho since the 1990s, but it's more common in the US than you might think - there have been eight cases in Oregon since 1990, NBC reports, and 30 died in Los Angeles in 1924.
The US reports about nine cases a year, but it's rarely fatal nowadays. It's much less dangerous than the pneumonic plague, according to the World Health Organization.
There have been outbreaks in Zambia, Peru, China, Madagascar and Congo in recent years.
No cases have been detected in New Zealand since 1911 according to the Ministry of Health, but the fleas that carry it remain.