How does the extrinsic incubation period (EIP) relate to the duration of mosquito infectiousness?

How does the extrinsic incubation period (EIP) relate to the duration of mosquito infectiousness?

• A. EIP is the time until mosquito dies after infection.
• B. EIP is time mosquitoes remain in the larval stage.
• C. EIP is the time from pathogen acquisition to when the mosquito becomes capable of transmitting the pathogen; after EIP, the mosquito can transmit for remaining life.
• D. EIP is time to first blood meal after emergence.

Answer: (C)

The key idea is that transmission becomes possible only after the pathogen has completed its development inside the mosquito. This waiting period is the extrinsic incubation period: the time from when the mosquito takes an infectious blood meal to when the pathogen has reached a stage that allows it to be transmitted to another host. Once this incubation is finished, the mosquito can transmit the pathogen during its subsequent bites for the rest of its life, as long as it remains alive and capable of biting and the pathogen remains viable. So, the EIP marks when infectiousness starts, not how long it lasts. If a mosquito dies before finishing the EIP, it will never be infectious. If it lives well beyond the EIP, it can continue to transmit with each bite until death. The other ideas—that EIP equals time to death, or that it corresponds to larval development, or to time to first blood meal—don’t describe the process of becoming capable of transmission.

The key idea is that transmission becomes possible only after the pathogen has completed its development inside the mosquito. This waiting period is the extrinsic incubation period: the time from when the mosquito takes an infectious blood meal to when the pathogen has reached a stage that allows it to be transmitted to another host. Once this incubation is finished, the mosquito can transmit the pathogen during its subsequent bites for the rest of its life, as long as it remains alive and capable of biting and the pathogen remains viable.

So, the EIP marks when infectiousness starts, not how long it lasts. If a mosquito dies before finishing the EIP, it will never be infectious. If it lives well beyond the EIP, it can continue to transmit with each bite until death. The other ideas—that EIP equals time to death, or that it corresponds to larval development, or to time to first blood meal—don’t describe the process of becoming capable of transmission.