The World Health Organization warns of a high risk of the polio virus spreading across the war-wracked Gaza Strip due to the poor sanitary conditions.
A senior WHO official said on Tuesday that circulating vaccine-derived poliovirus has been identified in samples of Gaza sewage assessed by researchers.
Ayadil Saparbekov, the WHO's head of health emergencies in the occupied Palestinian territories, stressed that "we have not yet collected human samples" so it remains unclear if anyone has actually been infected with the virus.
But he acknowledged to reporters in Geneva via video link, "I am very much worried".
He added if the outbreak happens in the strip, it may spill over internationally at a very high point.
Earlier Palestinian health officials also warned that thousands of Gazans are at risk of contracting the virus.
Saparbekov said he was deeply concerned at the prospect of any diseases spreading in Gaza.
"I'm extremely worried about outbreaks happening in Gaza," he said, pointing to the confirmation late last year that hepatitis A was spreading, "and now we may have polio".
"With the crippled health system, lack of water and sanitation, as well as lack of access of the population to health services... this is going to be a very bad situation," he warned.
"We may have more people dying of different communicable diseases than from the injury-related diseases."
UN agencies have frequently warned of the outbreaks of cholera and other communicable diseases in the blockaded Palestinian territory.
The regime has killed over 39,000 Palestinians, most of them women, children, and adolescents, in Gaza since October.
It has been enforcing a near-total siege on the coastal territory, which has reduced into a trickle the flow of foodstuffs, medicine, electricity, and water into the Palestinian territory.