Polygenic control of Rhipicephalus microplus infestation in purebred and crossbred cattle revealed by GWAS.

The blue tick, Rhipicephalus microplus, threatens cattle production in most tropical and subtropical areas of the world. Delayed skin hypersensitivity reactions are thought to cause Nguni cattle to be more resistant to R. microplus than Bonsmara cattle yet the cellular mechanisms responsible for these differences have not been classified. Tick counts and inflammatory cell infiltrates in skin biopsies from feeding sites of adult R. microplus ticks were determined in 9-month-old Nguni and Bonsmara heifers to determine the cellular mechanisms responsible for tick immunity. Nguni heifers (1.7 ± 0.03) had lower (P < 0.05) tick counts than the Bonsmaras (2.0 ± 0.03). Parasitized sites in Nguni heifers had higher counts of basophils, mast and mononuclear cells than those in the Bonsmara heifers. Conversely, parasitized sites in Nguni heifers had lower neutrophil and eosinophil counts than those in the Bonsmara heifers. Tick count was negatively correlated with basophil and mast cell counts and positively correlated with eosinophil counts in both breeds. In the Bonsmara breed, tick count was positively correlated with mononuclear cell counts. Cellular responses to adult R. microplus infestations were different and correlated with differences in tick resistance in Nguni and Bonsmara cattle breeds. It is essential to further characterise the molecular composition of the inflammatory infiltrate elicited by adult R. microplus infestation to fully comprehend immunity to ticks in cattle.

BackgroundIn tropical countries, losses caused by bovine tick Rhipicephalus (Boophilus) microplus infestation have a tremendous economic impact on cattle production systems. Genetic variation between Bos taurus and Bos indicus to tick resistance and molecular biology tools might allow for the identification of molecular markers linked to resistance traits that could be used as an auxiliary tool in selection programs. The objective of this work was to identify QTL associated with tick resistance/susceptibility in a bovine F2 population derived from the Gyr (Bos indicus) × Holstein (Bos taurus) cross.ResultsThrough a whole genome scan with microsatellite markers, we were able to map six genomic regions associated with bovine tick resistance. For most QTL, we have found that depending on the tick evaluation season (dry and rainy) different sets of genes could be involved in the resistance mechanism. We identified dry season specific QTL on BTA 2 and 10, rainy season specific QTL on BTA 5, 11 and 27. We also found a highly significant genome wide QTL for both dry and rainy seasons in the central region of BTA 23.ConclusionsThe experimental F2 population derived from Gyr × Holstein cross successfully allowed the identification of six highly significant QTL associated with tick resistance in cattle. QTL located on BTA 23 might be related with the bovine histocompatibility complex. Further investigation of these QTL will help to isolate candidate genes involved with tick resistance in cattle.

Tick infestation is one of the main challenges in tropical beef cattle production, leading to significant economic losses. Knowledge of the molecular factors underlying natural tick resistance in cattle contributes to genetic selection through the identification of biomarkers that can be used to accurately identify animals resistant to ticks. Although several genes associated with resistance to ticks have been identified, the molecular mechanisms underlying tick resistance are yet to be elucidated. This study investigated the biological processes, pathways, and key proteins involved in the resistance to the tick Rhipicephalus (Boophilus) microplus in a tropically adapted beef cattle breed. Tick resistance was evaluated in 162 Caracu cows. Blood samples were collected from a subset of 16 extreme animals, including eight with a high tick load (SUS) and eight with a low tick load (RES), for proteomic analysis by LC-MS/MS. A total of 172 and 34 proteins were exclusively identified in plasma samples from the SUS and RES groups, respectively. In addition, 14,034 proteins were detected in the blood plasma of both groups, of which 51 and 101 proteins were significantly increased in plasma samples of the SUS and RES groups, respectively. Among the top 20 proteins with the highest absolute log-fold change values, those encoded by the RNASE1, TNS2, NOXO1, ZNRF3, APOA4, KMT2B, RPS6KA5, PON1, C4BPA, SETD2, HP, TMEM63A, MAST2, and SETD1B genes were highlighted based on their functions that may contribute to a response to tick infestation. Functional enrichment analysis revealed 36 biological processes, 35 molecular functions, and 16 pathways to be significant (P < 0.05), highlighting those related to hemostasis, vesicular transport, cell proliferation and migration, calcium, actin, lipids, scavenger receptors, hydrogen peroxide, tyrosine, and insulin-like growth factor, which may contribute to tick resistance. In addition, PPI network analysis revealed several proteins involved in complement and coagulation systems, hematopoiesis, and immune response as important nodes, based on their centrality and edges. The identification of differentially abundant proteins between RES and SUS animals, as well as their relationships and roles in key biological processes and molecular pathways detected, contribute to improving our understanding of the mechanisms underlying tick resistance in naturally adapted cattle breeds. Furthermore, the differentially abundant proteins detected in this study are potential biomarkers for the response to R. microplus infestation.

Rhipicephalus (Boophilus) microplus tick causes large economic losses in beef cattle production, mainly in regions under tropical climates. The evaluation of tick resistance in breeding programs requires individual phenotype collection based on tick counts, which is an extremely laborious process. The knowledge of the genomic architecture of resistance to ticks can contribute to identify biomarkers, which could be used to identify animals resistant to tick. This study aimed to investigated key pathways and potential biomarkers involved in resistance against tick in Caracu. A total of 162 cows have their resistance to tick evaluated through direct counts of tick telogens during 18 months. A subset of 16 extreme animals, including the eight with high tick load (susceptible group) and eight with low tick load (resistant group), had their blood plasma samples used for proteomic analysis by liquid chromatography coupled to tandem mass spectrometry in a data-dependent acquisition mode. Proteins with fold-change ratios ≥ 2 and ≤ 0.5 were considered as differentially abundant (P &amp;lt; 0.05). The differentially abundant proteins were used to perform functional enrichment analysis by DAVID tool (P &amp;lt; 0.05). The protein-protein interaction (PPI) network of proteins differentially regulated was evaluated by STRING tool, with a medium confidence score (0.4). A total of 152 differentially abundant proteins were detected between the two experimental groups. Among the top proteins with the highest absolute log-fold change values, those encoded by the APOA4, C4BPA, HP, KMT2B, MAST2, NOXO1, PON1, RNASE1, RPS6KA5, SETD1B, SETD2, TMEM63A, TNS2, and ZNRF3 genes were highlighted based on their functions. The functional enrichment analysis revealed several Gene Ontology terms and pathways that may be associated with tick resistance, such as those linked to hemostasis, cell proliferation and migration, calcium, actin, and lipids. PPI network analysis also revealed several proteins acting in complement and coagulation systems, hematopoiesis, and immune response as important nodes based on their centrality and edges. The identification of differentially abundant proteins and its relationship, as well as of their roles in key pathways contribute to improve the knowledge of the mechanisms behind the tick resistance in naturally adapted cattle breeds. In addition, differently abundant proteins detected in this study are potential biomarkers for response to tick resistance.

Investigating volatile semiochemical production from Bos taurus and Bos indicus as a novel phenotype for breeding host resistance to ixodid ticks

Weekly counts of Boophilus microplus (Canestrini) on 30 Australian Illawarra Shorthorn heifers enabled the cattle to be ranked in order of tick infestation, with highly significant correlations between counts of two observers and between counts of one observer on different occasions. In May 1960, when the heifers were 1½–2 years old, 12 were selected as relatively tick-resistant and 12 as relatively tick-susceptible. Each of these groups was divided at random into herds of six, and the four herds were then allotted randomly to separate paddocks, each onequarter of the area previously grazed. A herd was sprayed with 0.5% DDT emulsion when its average count of ticks (adult females over 5 mm in length) on one side of the animals exceeded 40. During the ensuing tick season, from October 5, 1960, to June 7, 1961, the sums of average weekly tick counts, and the numbers of sprayings (in parenthesis) were: susceptible herds 4853 (5) and 5962 (6): resistant herds 718 (0) and 1073 (1). Counts of tick larvae on defined body areas showed that, in the summer after segregation, resistant herds carried fewer larvae than the susceptible herds, apparently because fewer mature ticks fell from the resistant cattle in the preceding spring and winter. As a consequence of this, counts of adult ticks were comparatively lower after than before segregation. There was little or no 'spring rise' of tick infestation on the resistant herds. There was no significant correlation between tick resistance and coat score, sweat gland dimensions, or total skin thickness, but a correlation of -0.53 with follicle depth was significant at the 1% level. There was no evidence of adaptation of cattle ticks to the resistant animals, either in the field experiment or in observations on stalled cattle. The experiment draws attention to the appreciable proportion of tick-resistant animals within the Australian Illawarra Shorthorn breed, which has largely been overlooked in past discussions on tick-resistant breeds of cattle. It also suggests a technique for estimating the improvement in tick control that may be obtained by a given degree of selection within any breed, for any given environment.

Strategic control of Rhipicephalus (Boophilus) microplus infestation on beef cattle grazed in Panicum maximum grasses in a subtropical semi-arid region of Argentina

Approximately 80% of the world's cattle are raised in regions with a high risk of tick-borne diseases, resulting in significant economic losses due to parasitism by Rhipicephalus (Boophilus) microplus. However, the lack of a systemic biology approach hampers a comprehensive understanding of tick-host interactions that mediate tick resistance phenotypes. Here, we conducted a genome-wide association study (GWAS) of 2933 Braford cattle and found 340 single-nucleotide polymorphisms (SNPs) associated with tick counts. Gene expression analyses were performed on skin samples obtained from previously tick-exposed heifers with extremely high or low estimated breeding values for R. microplus counts. Evaluations were performed both before and after artificial infestation with ticks. Differentially expressed genes were found within 1-Mb windows centered at significant SNPs from GWAS. A total of 330 genes were related to the breakdown of homeostasis that was induced by larval attachment to bovine skin. Enrichment analysis pointed to a key role of proteolysis and signal transduction via JAK/STAT, NFKB and WNT/beta catenin signaling pathways. Integrative analysis on matrixEQTL revealed two cis-eQTLs and four significant SNPs in the genes peptidyl arginine deiminase type IV (PADI4) and LOC11449251. The integration of genomic data from QTL maps and transcriptome analyses has identified a set of twelve key genes that show significant associations with tick loads. These genes could be key candidates to improve the accuracy of genomic predictions for tick resistance in Braford cattle.

Resistance to Rhipicephalus microplus infestation in cattle has many effector mechanisms, each of which is likely to be modulated by complex, interacting factors. Some of the mechanisms of host resistance and their modulating factors have been identified and quantified, although much remains to be explained. The variation in resistance to tick infestation is most marked between Bos taurus and Bos indicus cattle, taurine cattle given the same exposure carrying between five and 10 times as many ticks as indicine cattle. Tick resistance is mostly manifest against attaching larvae, which attempt to feed often and without success, death occurring mostly within 24 h of finding a host. There is evidence of innate and adaptive immune response to tick infestation, and it appears that the relative importance of each differs between indicine and taurine cattle. There is conflicting information regarding the role of humoral immunity in tick resistance, and recent studies indicate that strong IgG responses to tick antigens are not protective. A strong T-cell-mediated response directed against larval stages, as mounted by indicine cattle, seems to be protective. Variation in the extracellular matrix of skin (epidermal growth factors, collagens and other matrix components such as lumican) also contributes to variation in host resistance.

We herein describe zebuine cattle tick infestation in a farm in southeast Brazil with an examination accurate enough to detect tick immatures and species other than R. microplus. Cattle were inspected monthly for ticks from May 2015 to May 2017 and 7604 ticks were collected along 276 bovine inspections. Rhipicephalus microplus was the dominant species (7197 specimens, 94.5% from the total), but Amblyomma sculptum was also collected (407/5.5%). Horse tick infestations were evaluated for comparison purposes of A. sculptum infestations of a primary host sharing pastures with bovines. Ticks were counted on the left side of 4-12 horses every 3months from October 2015 to October 2017. Overall, 68 horse inspections were performed and 1702 ticks were collected: Dermacentor nitens (805 specimens/47.3% of the total), A. sculptum (733/43.1%) and R. microplus (164/9.6%). Overall mean tick abundance on bovines was low if compared to that of taurine cattle and counting revealed four annual generations of R. microplus. The interval between infestation peaks was 3months, irrespective of the season, and an increase in tick counts from spring onward, as described in the south of Brazil, was not seen. Amblyomma sculptum infestation abundance was minor but constant and in high prevalence. Cattle infestation with A. sculptum seems to depend on pasture sharing with other domestic and wild hosts that are its primary hosts and provide engorged females to complete their life cycle. The impact of such tick sharing among several host species on tick-borne pathogen transmission remains to be elucidated.

Boophilus microplus, an ectoparasite of bovines has immense importance in South Asian countries like Pakistan. These are cosmopolitans and affect cattle herds drastically worldwide and are involved in direct and indirect harm to the bovine species. In this regard, trichlorfon is widely used to control ticks in bovines along with its sprays to control different pests, which leads to resistance in ticks against these acaricides in different parts of the world. Therefore, the present study aims to investigate the resistance and prevailing genomic mutations in Boophilus microplus ticks against trichlorfon. Molecular characterization was carried out and heterozygous mutations were observed in the adult tick samples collected from two different zones of the Khyber Pakhtunkhwa (KPK) province of Pakistan. After the identification of ticks, in vitro studies were performed which showed resistance in ticks against trichlorfon drug. To assess genomic mutation in the samples, DNA was extracted through a kit, and PCR was performed to evaluate the mutation in the samples. After in-vitro studies, almost 104 (54%) ticks samples were found resistant and run through PCR in which 3 and 4 samples from zone-I and zone-II, were identified mutated while the remaining samples were found non-mutated. Boophilus microplus acetylcholinesterase genes were sequenced and compared with the control group. All these findings suggest a continuous monitoring of heterozygous mutations in the Boophilus microplus ticks and the strategic application of trichlorfon against Boophilus microplus ticks, to enable improvement in drug efficacy and tick control strategies.

An Australian Illawarra Shorthorn herd of 24 cows was mated in three consecutive years with an AIS bull. The cows and their progeny were rated for tick resistance at frequent intervals from August 1959 to December 1965 by counting the numbers of semiengorged female ticks on the right side. The mean of log counts for all counts on a particular animal was adopted as the reference value for its degree of susceptibility. The ranking of cattle generally showed a high level of consistency with mean repeatability of counts (r = 0.47, P &lt; 0.01). Discrimination between animals was more reliable (P &lt; 0.01) in summer (r = 0.52) than in winter (r = 0.27). The repeatability of tick counts increased with mean count, from r = 0.27 when the mean count was 3 to r = 0.67 when it was 100. The reliability of counts on the cows decreased with age and with lactation. Supplementary information on a larger herd showed no effect of pregnancy on mean count or on discrimination between susceptible and resistant animals, but showed that there was a partial breakdown of resistance during lactation. In calves infested naturally, no effects of age or sex on tick counts or their repeatability were detected, though male calves yielded significantly larger numbers of ticks than females when infested artificially. The mean yield of mature female ticks on the cows following two artificial infestations with known numbers of larvae ranged from 0.2 to 27.4% of the potential. Natural and artificial assessments of susceptibility were closely correlated. The rank of the bull was similar to that of the more resistant cows. Mean estimates of the heritability of tick resistance based on single counts were 39 % from dam-calf correlations and 49 % from full-sib correlations. Estimates based on summer counts only were 42 and 64% respectively. These results provide strong encouragement for selecting for tick resistance.

An Australian Illawarra Shorthorn herd of 24 cows was mated in three consecutive years with an AIS bull. The cows and their progeny were rated for tick resistance at frequent intervals from August 1959 to December 1965 by counting the numbers of semiengorged female ticks on the right side. The mean of log counts for all counts on a particular animal was adopted as the reference value for its degree of susceptibility. The ranking of cattle generally showed a high level of consistency with mean repeatability of counts (r = 0.47, P &lt; 0.01). Discrimination between animals was more reliable (P &lt; 0.01) in summer (r = 0.52) than in winter (r = 0.27). The repeatability of tick counts increased with mean count, from r = 0.27 when the mean count was 3 to r = 0.67 when it was 100. The reliability of counts on the cows decreased with age and with lactation. Supplementary information on a larger herd showed no effect of pregnancy on mean count or on discrimination between susceptible and resistant animals, but showed that there was a partial breakdown of resistance during lactation. In calves infested naturally, no effects of age or sex on tick counts or their repeatability were detected, though male calves yielded significantly larger numbers of ticks than females when infested artificially. The mean yield of mature female ticks on the cows following two artificial infestations with known numbers of larvae ranged from 0.2 to 27.4% of the potential. Natural and artificial assessments of susceptibility were closely correlated. The rank of the bull was similar to that of the more resistant cows. Mean estimates of the heritability of tick resistance based on single counts were 39 % from dam-calf correlations and 49 % from full-sib correlations. Estimates based on summer counts only were 42 and 64% respectively. These results provide strong encouragement for selecting for tick resistance.

BackgroundThe present study aimed to evaluate the effects of different treatment strategies using a new commercial formulation containing pour-on fluralaner on Rhipicephalus microplus infestation in cattle and in pastures in a tropical climate region where up to five generations of this tick species can occur per year.MethodsForty-five naturally infested cattle were divided into three experimental groups: T01, treated with fluralaner (2.5 mg/kg) pour-on every 42 days; T02, the cattle received the first treatment with fluralaner on Day 0 but the next treatment involved a weekly visual evaluation; T03, control, received palliative treatment with a spray formulation when the group mean was ≥ 30 ticks. Counts of female R. microplus were performed weekly until day 343, and larval counts on pasture were performed on Days 0, 30, and 60 and every 30 days until Day 330.ResultsUsing fluralaner, six applications were performed in Group T01, and four were performed in Group T02. In the control group (T03), it was necessary to perform eight palliative acaricide treatments with the spray formulation. The animals in T01 and T02 showed lower mean tick counts (p ≤ 0.05) than the control group (T03) on 28 and 27 of the 49 evaluated dates, respectively. In the paddock where the animals were kept as controls, the R. microplus larvae counts increased to 1458. In the paddocks where the animals were treated with fluralaner, the number was ≤ 19 per paddock during the study.ConclusionsThe different strategic treatment protocols performed with pour-on fluralaner (2.5 mg/kg) over a year in taurine cattle in a tropical region with a history of up to five annual generations of cattle ticks were effective, maintaining levels of R. microplus infestations in animals and in pastures close to zero in most of the study. Depending on the retreatment criterion adopted, the number of applications per year may be lower, resulting in a reduction in the mean cost of acaricide treatment per year and lower exposure of R. microplus populations to the active ingredient, resulting in lower resistance and selection pressure.Graphical

Relationships between tick counts and coat characteristics in Nguni and Bonsmara cattle reared on semiarid rangelands in South Africa