A substance for use in treating or preventing infection by a virus in a mammal, wherein the substance is an inhibitor of a JMJD2 protein and is selected from (a) a compound of the formula: wherein R 1 and R 2 are each independently H or C 1 -C 6 alkyl, or together form =CH 2, =CH-(C 1 -C 6 alkyl) or =C(C 1 -C 6 alkyl)(C 1 -C 6 alkyl) where the C 1 -C 6 alkyl groups are the same or different; R 3 is H or a group of the formula: -Y-L-W wherein Y is linked to N and is CH 2, C=O, or NH, L is C 1 -C 8 alkylenyl, (CH 2) m -(C 6 -C 20 aryl)-(CH 2) n, or [(CH 2) r O] q CH 2, wherein m and n are each independently 0 to 6, q is 1 to 6, and r is 1 to 3, and W is R 6, COR 6, SO 2 R 6, CH=NR 7, or NHOR 7, wherein R 6 is NR 7 R 7, guanidinyl, a ureido moiety, a carbamate moiety, or OR 7, and each R 7 is independently H or CH 3; R 4 and R 5 are each independently H, C 1 -C 6 alkyl, C 6 -C 20 aryl, or C 6 -C 20 aryl C 1 -C 6 alkyl; and X is O, S, or NH; (b) a compound of the formula (c) a compound of the formula wherein R 10 is methyl, or CH 2 CH 2 Ph; (d) a compound of the formula (e) a compound of the formula wherein R 20 is OCH 3 or H and X' is S or CH 2; and (f) a compound of the formula wherein R 30 is or wherein R 40 is H, 2-methyl, 4-phenyl, 3-fluoro, 2,4-difluoro, 2-chloro, 3-methoxy, or 4-cyano, wherein R 50 is H, 2-methyl, 4-methyl, 2,4,6-trimethyl, 2-fluoro, 3,4-difluoro, 2-fluoro-3-trifluoromethyl, 4-chloro, 3-methoxy, 3-chloro, 2-nitro, 2-methoxy-5-nitro, 4-methoxycarbonyl, 3-cyano, or 4-(2,3,4-thiadiazolyl), wherein R 60 is wherein R 70 is wherein R 80 is or wherein R 90 is or or a pharmaceutically acceptable salt thereof. (a) a compound of the formula: wherein R 1 and R 2 are each independently H or C 1 -C 6 alkyl, or together form =CH 2, =CH-(C 1 -C 6 alkyl) or =C(C 1 -C 6 alkyl)(C 1 -C 6 alkyl) where the C 1 -C 6 alkyl groups are the same or different; R 3 is H or a group of the formula: -Y-L-W wherein Y is linked to N and is CH 2, C=O, or NH, L is C 1 -C 8 alkylenyl, (CH 2) m -(C 6 -C 20 aryl)-(CH 2) n, or [(CH 2) r O] q CH 2, wherein m and n are each independently 0 to 6, q is 1 to 6, and r is 1 to 3, and W is R 6, COR 6, SO 2 R 6, CH=NR 7, or NHOR 7, wherein R 6 is NR 7 R 7, guanidinyl, a ureido moiety, a carbamate moiety, or OR 7, and each R 7 is independently H or CH 3; R 4 and R 5 are each independently H, C 1 -C 6 alkyl, C 6 -C 20 aryl, or C 6 -C 20 aryl C 1 -C 6 alkyl; and X is O, S, or NH; R 1 and R 2 are each independently H or C 1 -C 6 alkyl, or together form =CH 2, =CH-(C 1 -C 6 alkyl) or =C(C 1 -C 6 alkyl)(C 1 -C 6 alkyl) where the C 1 -C 6 alkyl groups are the same or different; R 3 is H or a group of the formula: -Y-L-W wherein Y is linked to N and is CH 2, C=O, or NH, L is C 1 -C 8 alkylenyl, (CH 2) m -(C 6 -C 20 aryl)-(CH 2) n, or [(CH 2) r O] q CH 2, wherein m and n are each independently 0 to 6, q is 1 to 6, and r is 1 to 3, and W is R 6, COR 6, SO 2 R 6, CH=NR 7, or NHOR 7, wherein R 6 is NR 7 R 7, guanidinyl, a ureido moiety, a carbamate moiety, or OR 7, and each R 7 is independently H or CH 3; L is C 1 -C 8 alkylenyl, (CH 2) m -(C 6 -C 20 aryl)-(CH 2) n, or [(CH 2) r O] q CH 2, wherein m and n are each independently 0 to 6, q is 1 to 6, and r is 1 to 3, and W is R 6, COR 6, SO 2 R 6, CH=NR 7, or NHOR 7, wherein R 6 is NR 7 R 7, guanidinyl, a ureido moiety, a carbamate moiety, or OR 7, and each R 7 is independently H or CH 3; R 4 and R 5 are each independently H, C 1 -C 6 alkyl, C 6 -C 20 aryl, or C 6 -C 20 aryl C 1 -C 6 alkyl; and X is O, S, or NH; (b) a compound of the formula (c) a compound of the formula wherein R 10 is methyl, or CH 2 CH 2 Ph; (d) a compound of the formula (e) a compound of the formula wherein R 20 is OCH 3 or H and X' is S or CH 2; and (f) a compound of the formula wherein R 30 is or wherein R 40 is H, 2-methyl, 4-phenyl, 3-fluoro, 2,4-difluoro, 2-chloro, 3-methoxy, or 4-cyano, wherein R 50 is H, 2-methyl, 4-methyl, 2,4,6-trimethyl, 2-fluoro, 3,4-difluoro, 2-fluoro-3-trifluoromethyl, 4-chloro, 3-methoxy, 3-chloro, 2-nitro, 2-methoxy-5-nitro, 4-methoxycarbonyl, 3-cyano, or 4-(2,3,4-thiadiazolyl), wherein R 60 is wherein R 70 is wherein R 80 is or wherein R 90 is or or a pharmaceutically acceptable salt thereof. wherein R 40 is H, 2-methyl, 4-phenyl, 3-fluoro, 2,4-difluoro, 2-chloro, 3-methoxy, or 4-cyano, wherein R 50 is H, 2-methyl, 4-methyl, 2,4,6-trimethyl, 2-fluoro, 3,4-difluoro, 2-fluoro-3-trifluoromethyl, 4-chloro, 3-methoxy, 3-chloro, 2-nitro, 2-methoxy-5-nitro, 4-methoxycarbonyl, 3-cyano, or 4-(2,3,4-thiadiazolyl), wherein R 60 is wherein R 70 is wherein R 80 is or wherein R 90 is or