Coach Luboslav Penev called up the promising 20-year-old Litex Lovech midfielder following his outstanding performances in the domestic league. Slavchev has scored five goals in 10 matches this season.
Brazilian-born midfielder Marquinhos, who has netted seven times for Lokomotiv Sofia this season, has been recalled to the squad for the first time since November.
Playoff hopefuls Bulgaria, who have not reached the World Cup finals since 1998, are second in Group B with 13 points from eight matches, seven behind Italy who have already qualified for the next year's tournament in Brazil.
Denmark are third on 12 points, followed by Czech Republic and Armenia on nine.
Defenders: Ivan Ivanov (Basel), Pavel Vidanov (Zaglebie Lubin), Petar Zanev (Akmar Perm), Yordan Minev (Ludogorets), Veselin Minev (Botev Plovdiv), Nikolay Bodurov (Litex Lovech), Yordan Hristov (Botev Plovdiv), Iliya Milanov (Litex Lovech), Alexander Alexandrov (Cherno More Varna), Radoslav Dimitrov (Slavia Sofia)
Midfielders: Stanislav Manolev (PSV Eindhoven), Georgi Milanov (CSKA Moscow), Aleksandar Tonev (Aston Villa), Vladimir Gadzhev (Levski Sofia), Svetoslav Dyakov (Ludogorets), Hristo Zlatinski (Ludogorets), Simeon Slavchev (Litex Lovech), Marquinhos (Lokomotiv Sofia)
Forwards: Ivelin Popov (Kuban Krasnodar), Spas Delev (Las Palmas), Dimitar Rangelov (Luzern), Emil Gargorov (CSKA Sofia), Ventsislav Hristov (Beroe Stara Zagora)