Desert creature (5)
(Other definitions for camel that I've seen before include "It is called the ship of the desert" , "Desert ruminant" , "Dromedary, perhaps" , "One travelling in caravan" , "Pale brown - animal" .)
I believe this is a double definition.
'desert' is the first definition.
(abandon treacherously)
'creature' is the second definition.
(rat is a kind of animal)
(Other definitions for rat that I've seen before include "Scumbag" , "Treacherous person" , "Rodent; informer (colloq.)" , "Contemptible person" , "Grass" .)