Visualization of Malaria Parasites in the Skin Using the Luciferase Transgenic Parasite,<i> Plasmodium berghei</i>

We produced a transgenic rodent malaria parasite (<i>Plasmodium berghei</i>) that contained the luciferase gene under a promoter region of elongation factor-1α. These transgenic (TG) parasites expressed luciferase in all stages of their life cycle, as previously reported. However, we were the first to succeed in observing sporozoites as a mass in mouse skin following their deposition by the probing of infective mosquitoes. Our transgenic parasites may have emitted stronger bioluminescence than previous TG parasites. The estimated number of injected sporozoites by mosquitoes was between 34 and 775 (median 80). Since luciferase activity diminished immediately after the death of the parasites, luciferase activity could be an indicator of the existence of live parasites. Our results indicated that sporozoites survived at the probed site for more than 42 hours. We also detected sporozoites in the liver within 15 min of the intravenous injection. Bioluminescence was not observed in the lung, kidney or spleen. We confirmed the observation that the liver was the first organ in which malaria parasites entered and increased in number.

Visualization of malaria parasites in the skin using the luciferase transgenic parasite, <i>Plasmodium berghei</i>

Weproduced a transgenic rodent malaria parasite (<i>Plasmodium berghei</i>) that contained the luciferase gene under apromoter region of elongation factor-1α. These transgenic (TG) parasites expressed luciferase inall stages of their life cycle, as previously reported. However, we were the firstto succeed in observing sporozoites as a mass in mouse skin following theirdeposition by the probing of infective mosquitoes. Our transgenic parasites mayhave emitted stronger bioluminescence than previous TG parasites. The estimatednumbers of injected sporozoites by mosquitoes were between 34 and 775 (median 80). Since luciferase activity diminished immediately after the death of theparasites, luciferase activity could be an indicator of the existence of liveparasites. Our results indicated that sporozoites survived at the probed sitefor more than 42 hours. We also detected sporozoites in the liver within 15 minof the intravenous injection. Apart from the liver, bioluminescence was notobserved in the lung, kidney, or spleen. We reconfirmed that the liver was thefirst organ for malaria parasites to enter and increase in number.

One Injection of DsRed Followed by Bites from Transgenic Mosquitoes Producing DsRed in the Saliva Elicits a High Titer of Antibody in Mice

It has been proposed that transgenic mosquitoes can be used as a “flying syringe” for infectious disease control. We succeeded in generating a transgenic (TG) mosquito, <i>Anopheles stephensi</i>, excreting and discharging DsRed in saliva. DsRed was deposited on the membrane where the TG mosquito probed with its proboscis. Repeated feeding by the TG mosquitoes induced anti-DeRed as well as anti-SG antibodies in mice. This indicates that the TG mosquitoes can immunize the animal. Moreover, in this report, we employed a pre-immunization method before exposing mice to the TG mosquitoes. We injected DsRed to mice to prepare memory B cells and exposed the mice to bites by the TG mosquitoes excreting DsRed. The mice produced a higher titer of antibody to DsRed, suggesting that the bites from TG mosquitoes act as a booster and that primary immunization with a vaccine protein and exposure to TG mosquitoes excreting the vaccine protein in the saliva produces a synergistic effect.