Gaza - The health ministry in Gaza has declared the Palestinian territory a "polio epidemic area," accusing Israel's military campaign of destroying health infrastructure, which it says led to the recurrence of the virus.

The CPV2 strain of the virus has been detected in sewage samples collected from the southern Khan Yunis area and central governorates, the ministry said.

It did not say if any human cases had been detected but said the presence of the virus "constitutes a health threat to the residents of the Gaza Strip and neighboring countries and a setback to the global polio eradication program."

The wild version of the virus is now endemic only in Afghanistan and Pakistan, but a type of vaccine that contains small amounts of weakened but live polio still causes occasional outbreaks elsewhere.

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United Nations agencies said recently that such vaccine-derived type-2 poliovirus had been detected in samples collected from sewage.

"The brutal Israeli aggression that deprived the people of usable water, the destruction of the sanitation infrastructure, the accumulation of tonnes of garbage, and a lack of food security" had led to the recurrence of the virus, the ministry said.

On Tuesday, the World Health Organization said it was "looking at a very problematic situation."

"Having vaccine-derived poliovirus in the sewage very likely means that it's out there somewhere in people," WHO spokesman Christian Lindmeier told journalists. But again, about 75% of people infected by polio don't even show any symptoms.

"That means it most likely is in the population but it doesn't necessarily mean that we see an outbreak of cases."

He said a campaign to distribute vaccines across the Gaza Strip was needed.

"It's not enough just to get it [the vaccine] into Ben Gurion airport and then hopefully get it into Gaza. It needs to reach people," Lindmeier said.

Israel's bombardments and ground assaults have devastated swathes of Gaza, displacing the vast majority of its 2.4 million population and leaving over 39,000 dead.