Nearly 1,450 hospitals across region are also in low-lying coastal areas vulnerable to extreme weather, UN report finds.
Essequibo residents express anxiety as Venezuela advances its claims over the region, largely seen as part of Guyana.
A British warship arrives for defence exercises with Guyana as Venezuela launches war games near contested region.
Leaders hold talks after Venezuela organised referendum to claim oil-rich territory that makes up two-thirds of Guyana.