Abstract:
Trypanosoma congolense is the most important agent of nagana, a wasting livestock trypanosomosis in
sub-Saharan Africa. This species is a complex of three subgroups (Savannah, Forest and Kilifi) that differ
in virulence, pathogenicity, drug resistance, vectors, and geographical distribution. Congopain, the major
Cathepsin L-like cysteine protease (CP2) of T. congolense, has been extensively investigated as a pathogenic
factor and target for drugs and vaccines, but knowledge about this enzyme is mostly restricted
to the reference strain IL3000, which belongs to the Savannah subgroup. In this work we compared
sequences of congopain genes from IL3000 genome database and isolates of the three subgroups of T. congolense.
Results demonstrated that the congopain genes diverged into three subclades consistent with the
three subgroups within T. congolense. Laboratory and field isolates of Savannah exhibited a highly polymorphic
repertoire both inter- and intra-isolates: sequences sharing the archetypical catalytic triad clustered
into SAV1–SAV3 groups, whereas polymorphic sequences that, in general, exhibited unusual
catalytic triad (variants) assigned to SAV4 or not assigned to any group. Congopain homologous genes
from Forest and Kilifi isolates showed, respectively, moderate and limited diversity. In the phylogenetic
tree based on congopain and homologues, Savannah was closer to Forest than to Kilifi. All T. congolense
subgroup nested into a single clade, which together with the sister clade formed by homologues from
Trypanosoma simiae and Trypanosoma godfreyi formed a clade supporting the subgenus Nannomonas. A
single PCR targeting congopain sequences was developed for the diagnosis of T. congolense isolates of
the three subgroups. Our findings demonstrated that congopain genes are valuable targets for the diagnosis,
genotyping, and phylogenetic and taxonomic inferences among T. congolense isolates and other
members of the subgenus Nannomonas.
