How does a flea transmit plague? - briefly
When a flea feeds on an infected rodent, it ingests Yersinia pestis, which multiplies in the insect’s foregut and creates a blockage. Subsequent bites cause the flea to regurgitate the bacteria into the bite wound of a new host, transmitting the infection.
How does a flea transmit plague? - in detail
Fleas act as vectors for Yersinia pestis, the bacterium that causes plague, through a series of physiological and behavioral processes that enable the pathogen to move from infected rodents to new hosts.
When a flea ingests a blood meal from a rodent carrying the bacterium, the bacteria enter the insect’s foregut. Within 24–48 hours, Y. pestis multiplies and forms a dense biofilm that adheres to the proventricular valve, partially obstructing the passage of blood. This blockage creates a feeding difficulty that triggers the flea to attempt repeated bites.
During subsequent feeding attempts, the flea regurgitates portions of the infected gut contents back into the bite site. The regurgitated material contains large numbers of viable bacteria, which are deposited directly into the dermal tissue of the new host.
Key steps in the transmission cycle:
- Acquisition: ingestion of infected blood from a reservoir host (typically rodents).
- Multiplication: bacterial replication and biofilm formation in the flea’s foregut.
- Obstruction: partial blockage of the proventriculus, inducing feeding frustration.
- Regurgitation: expulsion of bacteria-laden material during forced feeding attempts.
- Inoculation: deposition of Y. pestis into the skin of the next host, initiating infection.
The efficiency of this mechanism depends on flea species, temperature, and the bacterial load in the initial blood meal. Blocking fleas are more likely to transmit the pathogen because the mechanical difficulty forces multiple, aggressive bites, increasing bacterial transfer. Once introduced into a mammalian host, the bacteria multiply in lymph nodes, leading to the characteristic symptoms of plague.