Sgt. Frog Episode 139: 556 Central Tokyo is a Man`s Battlefield
Episode 139 of 358 of Sgt. Frog, aired December 8, 2006, 25 minutes. Available with English subtitles and dub where released.
Episode summary
556 has caught a space cold, and he`s spreading it to everyone he meets. Horrifyingly, it makes everyone act exactly like him! Just like a Caries War, the Keroro Platoon shrinks down to go into his body and destroy the invaders there. Source: crunchyroll