What disease is transmitted by the bite of an infective flea (X. cheopis)?

The disease transmitted by the bite of an infective flea, specifically Xenopsylla cheopis, is Bubonic plague. This disease is caused by the bacterium Yersinia pestis, which is primarily associated with rodents but can be transmitted to humans through flea bites.

When an infected flea bites a human, the bacteria can enter the bloodstream, leading to the symptoms associated with the bubonic plague. This disease is characterized by swollen and painful lymph nodes, known as buboes, fever, chills, and malaise. Historically, bubonic plague is renowned for its role in pandemics, such as the Black Death in the 14th century.

The other diseases listed—Leptospirosis, Rocky Mountain spotted fever, and Typhus—are transmitted by other vectors or mechanisms, such as direct contact with contaminated water or other infected animals for Leptospirosis, ticks for Rocky Mountain spotted fever, and lice or fleas (specifically of a different type) for Typhus. Therefore, recognizing the specific vector and host relationship is crucial for understanding the transmission of these diseases.