Clinical Evaluation of Corridor Disease in Bos indicus (Boran) Cattle Naturally Infected With Buffalo-Derived Theileria parva

Characterization and identification of novel polymorphisms in the OR51H1 gene associated with resistance/tolerance to natural Theileria infection in Vechur (Bos indicus) and crossbred (B. taurus × B. indicus) cattle in a Theileria-endemic region

Theileriosis is a haemo protozoan disease affecting livestock, causing high mortality and production loss. Although therapeutic and vector control measures are available, selecting Theileria-resistant/tolerant animals is considered an alternate control measure for which the identification of genetic markers is essential. The present study screened dwarf Vechur (Bos indicus) and crossbred (B. taurus × B. indicus) cattle for natural infection to Theileria using peripheral blood smear and clinical and haematology evaluation. Polymorphisms in a previously identified candidate gene were screened in olfactory receptor family 51 sub-family H member-1 (OR51H1, single exon, 948 bp) associated with Theileria tolerance. The association of Theileria resistance/tolerance with different genotypes was also evaluated. Theileria was detected in 32.45 % of crossbred and 6 % of Vechur. Resistance and tolerance to Theileria infection varied significantly across breeds, and Vechur was found resistant (no parasites detected in the blood smear) compared to crossbred (Odds ratio-0.14, 95 % CI- 0.03-0.42, p < 0.01). The OR51H1 gene was characterised by sequencing in Vechur cattle, and putative single nucleotide variations (SNVs) were identified by pooled sample sequencing and genotyped using PCR-RFLP (polymerase chain reaction-restriction fragment length polymorphism). The five SNVs, T271C, C272T, T362C, G180A and T181G, exhibited polymorphic patterns. SNVs T271C and C272T were tolerant, while T362C, G180A and T181G were non-tolerant. The population was in Hardy-Weinberg equilibrium for SNV G180A in crossbred cattle and for SNVs T271C, C272T, and G180A in Vechur cattle. The SNVs T271C in crossbred and T362C, G180A and T181G in Vechur were significantly associated with Theileria tolerance. The identified SNVs also had moderate to high heterozygosity and polymorphic information content. The findings imply that these SNVs can be used as potential markers to select Theileria-resistant Vechur and tolerant crossbred cattle using marker-assisted selection.

Longitudinal transcriptome analysis of cattle infected with Theileria parva

The apicomplexan cattle parasite Theileria parva is a major barrier to improving the livelihoods of smallholder farmers in Africa, killing over one million cattle on the continent each year. Although exotic breeds not native to Africa are highly susceptible to the disease, previous studies have illustrated that such breeds often show innate tolerance to infection by the parasite. The mechanisms underlying this tolerance remain largely unclear. To better understand the host response to T. parva infection we characterised the transcriptional response over 15 days in tolerant and susceptible cattle (n = 29) naturally exposed to the parasite. We identify key genes and pathways activated in response to infection as well as, importantly, several genes differentially expressed between the animals that ultimately survived or succumbed to infection. These include genes linked to key cell proliferation and infection pathways. Furthermore, we identify response expression quantitative trait loci containing genetic variants whose impact on the expression level of nearby genes changes in response to the infection. These therefore provide an indication of the genetic basis of differential host responses. Together these results provide a comprehensive analysis of the host transcriptional response to this under-studied pathogen, providing clues as to the mechanisms underlying natural tolerance to the disease.

Inherited Tolerance in Cattle to the Apicomplexan Protozoan Theileria parva is Associated with Decreased Proliferation of Parasite-Infected Lymphocytes

Theileria parva is the causative agent of East Coast fever and Corridor disease, which are fatal, economically important diseases of cattle in eastern, central and southern Africa. Improved methods of control of the diseases are urgently required. The parasite transforms host lymphocytes, resulting in a rapid, clonal expansion of infected cells. Resistance to the disease has long been reported in cattle from T. parva-endemic areas. We reveal here that first- and second-generation descendants of a single Bos indicus bull survived severe challenge with T. parva, (overall survival rate 57.3% compared to 8.7% for unrelated animals) in a series of five field studies. Tolerant cattle displayed a delayed and less severe parasitosis and febrile response than unrelated animals. The in vitro proliferation of cells from surviving cattle was much reduced compared to those from animals that succumbed to infection. Additionally, some pro-inflammatory cytokines such as IL1β, IL6, TNFα or TGFβ which are usually strongly expressed in susceptible animals and are known to regulate cell growth or motility, remain low in tolerant animals. This correlates with the reduced proliferation and less severe clinical reactions observed in tolerant cattle. The results show for the first time that the inherited tolerance to T. parva is associated with decreased proliferation of infected lymphocytes. The results are discussed in terms of whether the reduced proliferation is the result of a perturbation of the transformation mechanism induced in infected cells or is due to an innate immune response present in the tolerant cattle.