Which insect is known as an ectoparasite and is associated with the transmission of plague and murine typhus?

The Oriental rat flea is identified as an ectoparasite that plays a significant role in the transmission of serious diseases such as plague and murine typhus. Ectoparasites are organisms that live on the outside of a host, feeding on their blood, which is exactly what fleas do. The Oriental rat flea specifically has been closely associated with rodents, particularly rats, which are often the primary reservoirs for the pathogens responsible for these diseases.

Fleas can carry the bacterium Yersinia pestis, the causative agent of plague, and Rickettsia typhi, which is responsible for murine typhus. When fleas feed on infected rodents and then bite humans, they can transmit these pathogens, hence their considerable public health importance.

Other options, such as the cat flea, common bed bug, and American dog tick, do not significantly contribute to the transmission of these specific diseases. The cat flea mainly infests cats and dogs and does not play a major role in plague transmission. The common bed bug feeds on human blood but is not linked to plague or murine typhus. The American dog tick can transmit diseases like Lyme disease but is not associated with the transmission of plague or murine typhus.