India's Nipah patient is from an area that has reported multiple outbreaks since 2018.
The ratings aren't intended as a detailed threat assessment and don't indicate which pathogen is most likely to trigger the next pandemic, but instead are a guide for research investment.
Tests are under way on samples from five contacts who reported symptoms.
Nipah virus, which has a high fatality rate, is a top target for countermeasure development.
State officials said the boy had eaten plum fruit from the neighborhood before his symptoms began.
Two more locally acquired dengue cases have been reported in the Florida Keys.
Researchers have raised concerns about the possibility of larger outbreaks if the virus takes hold in urban areas or if the virus becomes more transmissible to humans.
The patients had both consumed potentially contaminated raw date palm sap, a known risk factor for contracting the virus.
Having tools to identify outbreaks early is crucial for containing outbreaks for both dangerous pathogens.
The patients are from the same district, and both had consumed raw date juice, a known risk factor.
