Any process that results in a change in state or activity of the symbiont or its cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of detecting iron concentration in its host organism. The host is defined as the larger of the organisms involved in a symbiotic interaction.

The rigid or semi-rigid envelope lying outside the cell membrane of plant, fungal, most prokaryotic cells and some protozoan parasites, maintaining their shape and protecting them from osmotic lysis. In plants it is made of cellulose and, often, lignin; in fungi it is composed largely of polysaccharides; in bacteria it is composed of peptidoglycan; in protozoan parasites such as Giardia species, it's made of carbohydrates and proteins.