The wound site becomes very infected and in some cases bloodstream infection occurs. These birds also carry a host of parasites such as ticks, fleas, mites and other ectopatasites. Over forty types of parasites live either on the birds, in their nests or in the places they roost. They are responsible for the transmission of several hundred viral and bacterial agents. Pigeons roosting on roof-top air ducts of restaurants are a serious health concern and require immediate attention.
Pigeons sometimes nest in chimneys and ventilation systems spreading diseases through the system.
These birds can actually block airflow, which can cause carbon monoxide poisoning.