6-halogeno-[1,2,4]-triazolo[1,5-a]-pyrimidine compound of the general formula I wherein X is halogen; R 1 is hydrogen, halogen, OH, CN, C 1 -C 10 -alkyl, C 1 -C 10 -haloalkyl, C 1 -C 10 -alkoxy, C 1 -C 6 -alkoxy-C 1 -C 6 -alkyl, C 1 -C 4 -alkoxy-C 1 -C 4 -alkoxy, C 1 -C 4 -alkoxy-C 1 -C 4 -alkoxy-C 1 -C 4 -alkoxy, C 1 -C 10 -alkylthio, C 1 -C 10 -alkylsulfinyl, C 1 -C 10 -alkylsulfonyl, C 1 -C 10 -alkylamino, di(C 1 -C 10 -alkyl)amino, C 2 -C 10 -alkenyl, phenyl, phenoxy, benzyloxy, C 2 -C 10 -alkenyloxy, C 2 -C 10 -alkynyloxy or C 2 -C 10 -alkynyl, wherein C 1 -C 10 -alkylthio, C 1 -C 10 -alkylsulfinyl and C 1 -C 10 -alkylsulfonyl may be unsubstituted or partially or completely substituted with halogen, C 1 -C 4 -alkoxy, C 1 -C 4 -alkoxycarbonyl or COOH; R 2 is C 1 -C 10 -alkyl, C 1 -C 10 -haloalkyl, C 1 -C 6 -alkoxy-C 1 -C 6 -alkyl, C 3 -C 10 -cycloalkyl, C 2 -C 10 -alkenyl or C 2 -C 10 -alkynyl; R 3 is hydrogen, C 1 -C 10 -alkyl, C 1 -C 10 -haloalkyl, C 1 -C 6 -alkoxy-C 1 -C 6 -alkyl, C 1 -C 10 -alkylcarbonyl, C 1 -C 10 -alkoxycarbonyl or arylcarbonyl; A is a single bond or a C 1 -C 6 -alkylene chain, wherein one methylene group may be substituted by one heteroatom selected from oxygen or sulfur; R 4 is C 3 -C 10 -cycloalkyl, phenyl, naphthyl, or 3- to 7-membered heterocyclyl, being unsubstituted or substituted with 1, 2 or 3 radicals which are selected from the group consisting of halogen, cyano, nitro, hydroxy, C 1 -C 10 -alkyl, C 1 -C 10 -alkoxy, C 1 -C 10 -haloalkyl, C 1 -C 10 -haloalkoxy, amino, C 1 -C 10 -alkylamino, di(C 1 -C 10 -alkyl)amino, C 1 -C 10 -alkylthio, C 1 -C 10 -alkylsulfinyl, C 1 -C 10 -alkylsulfonyl, C 3 -C 8 -cycloalkyl, C 3 -C 8 -cycloalkyl-C 1 -C 4 -alkyl, phenyl, phenyl-C 1 -C 4 -alkoxy and phenyloxy, wherein the five last-mentioned radicals for their part may be unsubstituted or may carry one, two or three substituents which are selected from the group consisting of C 1 -C 4 -alkyl, C 1 -C 4 -alkoxy and halogen, and wherein the 3 to 7 membered heterocyclyl contains 1, 2 or 3 heteroatoms selected from the group consisting of oxygen, sulfur, nitrogen and a group NR a, it being also possible for C 3 -C 10 -cycloalkyl, phenyl and 3- to 7-membered heterocyclyl to be fused to a 5- to 7-membered saturated, unsaturated or aromatic carbocyclic ring or to a 5- to 7-membered heterocyclic ring and said fused ring may be unsubstituted or may itself carry one, two, three, four, five or six substituents which are selected from the group consisting of halogen and C 1 -C 4 -alkyl; wherein R a is hydrogen, C 1 -C 6 -alkyl, C 3 -C 6 -alkenyl or C 3 -C 6 -alkynyl; and/or an enantiomer, diastereomer or veterinarily acceptable salt thereof for use in treating, controlling, preventing or protecting against infestation or infection by parasites wherein the compound is for oral, topical or parenteral administration to an animal. R 1 is hydrogen, halogen, OH, CN, C 1 -C 10 -alkyl, C 1 -C 10 -haloalkyl, C 1 -C 10 -alkoxy, C 1 -C 6 -alkoxy-C 1 -C 6 -alkyl, C 1 -C 4 -alkoxy-C 1 -C 4 -alkoxy, C 1 -C 4 -alkoxy-C 1 -C 4 -alkoxy-C 1 -C 4 -alkoxy, C 1 -C 10 -alkylthio, C 1 -C 10 -alkylsulfinyl, C 1 -C 10 -alkylsulfonyl, C 1 -C 10 -alkylamino, di(C 1 -C 10 -alkyl)amino, C 2 -C 10 -alkenyl, phenyl, phenoxy, benzyloxy, C 2 -C 10 -alkenyloxy, C 2 -C 10 -alkynyloxy or C 2 -C 10 -alkynyl, wherein C 1 -C 10 -alkylthio, C 1 -C 10 -alkylsulfinyl and C 1 -C 10 -alkylsulfonyl may be unsubstituted or partially or completely substituted with halogen, C 1 -C 4 -alkoxy, C 1 -C 4 -alkoxycarbonyl or COOH; R 2 is C 1 -C 10 -alkyl, C 1 -C 10 -haloalkyl, C 1 -C 6 -alkoxy-C 1 -C 6 -alkyl, C 3 -C 10 -cycloalkyl, C 2 -C 10 -alkenyl or C 2 -C 10 -alkynyl; R 3 is hydrogen, C 1 -C 10 -alkyl, C 1 -C 10 -haloalkyl, C 1 -C 6 -alkoxy-C 1 -C 6 -alkyl, C 1 -C 10 -alkylcarbonyl, C 1 -C 10 -alkoxycarbonyl or arylcarbonyl; A is a single bond or a C 1 -C 6 -alkylene chain, wherein one methylene group may be substituted by one heteroatom selected from oxygen or sulfur; R 4 is C 3 -C 10 -cycloalkyl, phenyl, naphthyl, or 3- to 7-membered heterocyclyl, being unsubstituted or substituted with 1, 2 or 3 radicals which are selected from the group consisting of halogen, cyano, nitro, hydroxy, C 1 -C 10 -alkyl, C 1 -C 10 -alkoxy, C 1 -C 10 -haloalkyl, C 1 -C 10 -haloalkoxy, amino, C 1 -C 10 -alkylamino, di(C 1 -C 10 -alkyl)amino, C 1 -C 10 -alkylthio, C 1 -C 10 -alkylsulfinyl, C 1 -C 10 -alkylsulfonyl, C 3 -C 8 -cycloalkyl, C 3 -C 8 -cycloalkyl-C 1 -C 4 -alkyl, phenyl, phenyl-C 1 -C 4 -alkoxy and phenyloxy, wherein the five last-mentioned radicals for their part may be unsubstituted or may carry one, two or three substituents which are selected from the group consisting of C 1 -C 4 -alkyl, C 1 -C 4 -alkoxy and halogen, and wherein the 3 to 7 membered heterocyclyl contains 1, 2 or 3 heteroatoms selected from the group consisting of oxygen, sulfur, nitrogen and a group NR a, it being also possible for C 3 -C 10 -cycloalkyl, phenyl and 3- to 7-membered heterocyclyl to be fused to a 5- to 7-membered saturated, unsaturated or aromatic carbocyclic ring or to a 5- to 7-membered heterocyclic ring and said fused ring may be unsubstituted or may itself carry one, two, three, four, five or six substituents which are selected from the group consisting of halogen and C 1 -C 4 -alkyl; wherein R a is hydrogen, C 1 -C 6 -alkyl, C 3 -C 6 -alkenyl or C 3 -C 6 -alkynyl; and/or an enantiomer, diastereomer or veterinarily acceptable salt thereof for use in treating, controlling, preventing or protecting against infestation or infection by parasites wherein the compound is for oral, topical or parenteral administration to an animal.