Genetic variants associated with trypanotolerance trait in cattle.

Abstract

Animal trypanosomiasis (Nagana), a protozoan disease, is the source of huge productivity losses to small scale farmers in sub-Saharan Africa. Nagana affects wild animals, sheep, goats, camels and cattle reducing their productivity or causing death in severe cases. Several interventions for the disease have been developed and applied including vector control using insecticides and the use of trypanocides. However, these control measures have been ineffective with the trypanosomes developing resistance to the existing trypanocides. Ineffective interventions to Nagana necessitate the need to advance a better disease control strategy. The use of the trypanotolerance trait that is expressed by some West African cattle breeds is promising because infected cattle don’t develop the severe form of the disease that reduces productivity. Trypanotolerance trait can be introduced to cattle breeds that show no tolerance through breeding. This study sought to understand trypanotolerance trait by identifying the key genes involved in the trypanotolerance trait. The sample size used was n=1199 cattle from 44 cattle breeds which were organized into 4 case-control groups of African indigenous and hybrid cattle. A GWAS was performed on each of the four groups to identify the significant SNPs after quality control. A total of 36 genes were found to contain the significant SNPs in all the case-control groups. All cases groups (Sheko, N’Dama, Boran and N’DamaXBoran) were compared to the same set of controls, n=993 cattle. This control group consisted of 3 cattle breeds from Africa (n=108), 31 cattle breeds from Europe (n=693), 2 cattle breeds from South America (n=27), 2 cattle breeds from Asia (n=49), 1 cattle breed from North America (n=105) and 1 cattle breed from Australia (n=11). Separate comparison of the case groups to the same control set highlighted 6, 4, 9 and 17 genes in the Sheko, N’Dama, Boran and N’DamaXBoran comparisons respectively. The roles of some of these genes in several pathways have also been individually described in previous studies. This study suggests that the key genes responsible for the trypanotolerance trait are SUSD1, DPF3, COL19A1 and SLC19A3 among others that are found in the N’Dama and Sheko cattle breeds that are mainly involved in the molecular mechanism that may lead to reduced parasitemia.