What common source may contribute to the spread of Psittacosis?

Psittacosis is a disease caused by the bacterium Chlamydia psittaci, which is primarily associated with birds, particularly psittacine birds like parrots. However, it can also be spread by other birds, with pigeons being a notable source of transmission. The bacteria are often found in the droppings or respiratory secretions of infected birds, and humans can become infected through inhaling dust containing these pathogens or by direct contact with contaminated surfaces.

Pigeons, as common urban birds, can be carriers of Psittacosis, making them a significant public health concern in areas where people have frequent interactions with these birds. This highlights the importance of controlling pigeon populations in urban settings, especially near places where humans congregate.

The other choices, like dogs, shellfish, and cats, do not serve as significant reservoirs for the bacteria associated with Psittacosis. While they may have their own sets of diseases and health risks, they are not directly involved in the transmission of this particular infection. Understanding the correct sources of transmission is crucial in public health and sanitation practices to prevent outbreaks.