How can communicable diseases be transmitted?

Communicable diseases can be transmitted in several ways, and the correct choice highlights the versatility of these transmissions. Direct contact involves the physical transfer of pathogens from an infected person to a healthy one, such as through skin-to-skin contact or bodily fluids. Indirectly, transmission can occur through vectors, which are organisms like mosquitoes or ticks that carry pathogens between hosts. This means that a person may contract a disease not only through direct interaction but also by being bitten by a vector that has previously fed on an infected host.

The other options are limited in their scope. The idea that communicable diseases are only transmitted through blood transfusions is inaccurate, as many diseases can spread through various means, not just blood. Similarly, the notion that transmission occurs only through sexual contact is too narrow; while sexual contact is a route for certain diseases, it is far from the only one. Finally, transmission solely through the air overlooks the significant role that direct contact and vectors play in spreading various infectious diseases. Therefore, the selected choice appropriately encompasses the various methods through which communicable diseases can be transmitted.