Genetic exchange and sub-structuring in Theileria annulata populations

Molecular characterization of Hyalomma scupense and its vector-borne pathogen Theileria annulata in Ksar El Boukhari (Medea, Algeria)

This study analyzed the molecular and phylogenetic profiles of Theileria annulata, the causative agent of tropical theileriosis in cattle, and its tick vector Hyalomma scupense in Algeria. Forty H. scupense ticks were collected in Medea, with 5 testing positive for Theileria spp. based on partial COXIII gene sequences. Positive ticks were further analyzed using COX1 and 12S rRNA genes. Two novel H. scupense 12S rRNA haplotypes and one novel COX1 haplotype were identified. One T. annulata haplotype previously reported in Algerian cattle was detected. This represents the first molecular characterization of T. annulata from H. scupense ticks in Algeria, providing insights into the genetic diversity of the parasite vector in this region. Overall, the study reveals new haplotypes for both the tick vector and parasite, furthering our understanding of their molecular profiles and phylogenetics in Algeria.

Genetic diversity of Hyalomma marginatum in Tunisia is not influenced by the bio-climate

Ticks are important ectoparasites responsible for the transmission of several pathogens with significant medical, veterinary, and economic impacts. Climate and social changes have generated substantial changes in ticks' distribution, abundance, and activity patterns, including ticks belonging to the Hyalomma marginatum species. Knowledge on the genetic structure and dynamics of H. marginatum populations might contribute to a better understanding of their current and future evolution under the effects of anthropogenic factors and eco-climatic changes. In the present study, we investigated the genetic structure and phylogenetic distribution of H. marginatum across three bioclimatic regions in Tunisia using two mitochondrial markers (16S and 12S rRNA). The molecular investigations were based on 47 adult H. marginatum ticks collected from humid, upper semi-arid, and sub-humid regions of Tunisia. Our results revealed a genetic diversity of 0.278% and 0.809% using the 16S and 12S markers, respectively. The low genetic diversity that we observed raises the hypothesis of a bottleneck event occasioned by a reduction in the size of the tick population under the effects of environmental factors and/or human activities. This hypothesis is supported by the population's demographic history analysis, which revealed a clear deviation from neutrality and supports the occurrence of a bottleneck event followed by a demographic expansion. The fact that most 16S and 12S variability was present in the ticks from the humid bioclimatic zone may suggest that those ticks represent the ancestral population. Overall, the analysis has shown that the phylogenetic clusters do not correspond to the bioclimatic zones.

Phylogenetic analysis of Babesia gibsoni isolates of south India using apical membrane antigen, 50 kDa surface antigen, and 70 kDa heat shock protein genes

The prevalence of canine babesiosis due to Babesia gibsoni has increased throughout the world including in southern India. The polymerase chain reaction (PCR) based molecular characterization of B. gibsoni in dogs of Kerala, south India, targeting three specific genes viz., apical membrane antigen (AMA1), 50 kDa surface antigen (P50), and heat shock protein (HSP70) was undertaken in this study. Out of 297 blood samples collected from clinically suspected animals, microscopy detected piroplasms of B. gibsoni in 60 (20.20 per cent), while the PCR targeting the BgP50 gene detected 85 (28.61 per cent). Polymerase chain reaction targeting the BgAMA1 and BgHSP70 detected a lesser number of samples (60 and 65 respectively) as positive. The phylogenetic analysis of BgHSP70 gene sequences did not reveal genetic heterogeneity among the B. gibsoni isolates of South India and from other countries, while the BgP50 gene differentiated the Indian isolates from Japanese isolates. When BgAMA1 was used for phylogenetic analysis, genetic variation was not observed among Indian and Taiwanese isolates, however, differentiated them from the Japanese isolates.

Selection of genotypes harbouring mutations in the cytochrome b gene of Theileria annulata is associated with resistance to buparvaquone

Buparvaquone remains the only effective therapeutic agent for the treatment of tropical theileriosis caused by Theileria annulata. However, an increase in the rate of buparvaquone treatment failures has been observed in recent years, raising the possibility that resistance to this drug is associated with the selection of T. annulata genotypes bearing mutation(s) in the cytochrome b gene (Cyto b). The aim of the present study was: (1) to demonstrate whether there is an association between mutations in the T. annulata Cyto b gene and selection of parasite-infected cells resistant to buparvaquone and (2) to determine the frequency of these mutations in parasites derived from infected cattle in the Aydın region of Türkiye. Susceptibility to buparvaquone was assessed by comparing the proliferative index of schizont-infected cells obtained from cattle with theileriosis before and/or after treatment with various doses of buparvaquone, using the 3-(4,5-dimethyl thiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) colourimetric assay. The DNA sequence of the parasite Cyto b gene from cell lines identified as resistant or susceptible was determined. A total of six nonsynonymous and six synonymous mutations were identified. Two of the nonsynonymous mutations resulted in the substitutions V135A and P253S which are located at the putative buparvaquone binding regions of cytochrome b. Allele-specific PCR (AS-PCR) analyses detected the V135A and P253S mutations at a frequency of 3.90% and 3.57% respectively in a regional study population and revealed an increase in the frequency of both mutations over the years. The A53P mutation of TaPIN1 of T. annulata, previously suggested as being involved in buparvaquone resistance, was not detected in any of the clonal cell lines examined in the present study. The observed data strongly suggested that the genetic mutations resulting in V135A and P253S detected at the putative binding sites of buparvaquone in cytochrome b play a significant role in conferring, and promoting selection of, T. annulata genotypes resistant to buparvaquone, whereas the role of mutations in TaPIN1 is more equivocal.

Analysis of genetic diversity and population structure of Babesia gibsoni

Babesia gibsoni is a tick-borne apicomplexan protozoan causing canine babesiosis. This parasite has diploid sexual reproduction in ticks, during which genetic exchanges can occur leading to increased genetic diversity, which is an important factor in adapting to environmental changes. Exploring the genetic variation of B. gibsoni population can provide a foundation for understanding the patterns of disease transmission and developing babesiosis control strategies. Partial 18S rRNA fragment sequences were obtained from 11 B. gibsoni isolates collected from different regions in China and 117 publicly available sequences were from 12 geographical areas including China. The genetic variation, demographic expansion and population structure were examined. A total of 34 haplotypes were identified among B. gibsoni populations. Analysis of molecular variance, pairwise Fst and structure analysis showed that high genetic variation within populations, low genetic differentiation and obvious mixture haplotype were apparent in a single continent, but higher genetic differentiation was detected across different continents. Neutrality tests implied that B. gibsoni populations had experienced population extension. These findings will contribute to understand the genetics and evolution of B. gibsoni and will be useful for formulating effective management strategies to prevent and control this parasite.

Molecular insights into the population structure and haplotype network of Theileria annulata based on the small-subunit ribosomal RNA (18S rRNA) gene

The present study was conducted to elucidate the population genetic diversity and haplotype network of Theileria annulata based on all available nearly complete 18S rRNA gene sequences in the GenBank™. In total, 52 sequences of the nuclear 18S rRNA gene used to assess the relationship of T. annulata with their country of origin identified 34 haplotypes. Haplotype 4 was widespread, occurring in India, China, Turkey and Iran, while the remaining haplotypes were singleton and unique to one country. Haplotype 4 displayed numerous single haplotypes around it and the stellate shape of the network suggested a rapid population expansion. India exhibited the largest number of haplotypes (h = 25) followed by Turkey (h = 6), China (h = 4), and Iran and Italy (h = 1). No geographical clustering of haplotypes was recorded. Nucleotide diversity was the highest in the Turkish followed by the Indian and Chinese populations. Similarly, haplotype diversity was the highest in China followed by Turkey, and the lowest in India. The overall dataset exhibited a low nucleotide diversity (0.00253 ± 0.00035), but high haplotype diversity (0.917 ± 0.034). It suggested the presence of only minor differences (01-11 nucleotide) between haplotypes which was also evident from the haplotype network. A high level of genetic diversity was documented within the Indian, Chinese and Turkish populations of T. annulata, whereas little genetic differentiation was noticed among these populations with a very high level of gene flow. Analysis of molecular variance (AMOVA) of T. annulata sequences revealed higher genetic variation within countries (83.58%) as compared to the variation among countries (16.42%). Neutrality indices, viz., Tajima's D, Fu and Li's F, Fu's F_s, and R_2, along with the unimodal mismatch distributions demonstrated a recent population expansion of T. annulata in India and the overall dataset. However, the non-significant values of Tajima's D, Fu and Li's F, and Fu's F_s for the Chinese population along with a bimodal mismatch distribution signified a constant population size. For the Turkish population, the neutrality and mismatch distribution tests either indicated a constant or a slight increase in population size. The present study provides novel insights into the population genetics and haplotype network of T. annulata based on the 18S rRNA gene for the first time.

Diversity and Genetic Structure of Theileria annulata in Pakistan and Other Endemic Sites

Background: Theileria annulata is a tick-borne protozoan parasite responsible for bovine theileriosis, a disease that impacts cattle population in many developing countries. Development and deployment of effective control strategies, based on vaccine or therapy, should consider the extent of diversity of the parasite and its population structure in different endemic areas. In this study, we examined T. annulata in Pakistan and carried out a comparative analysis with similar data garneted in other areas, to provide further information on the level of parasite diversity and parasite genetic structure in different endemic areas. Methods: The present study examined a set of 10 microsatellites/minisatellites and analyzed the genetic structure of T. annulata in cattle breeds from Pakistan (Indian sub-continent) and compared these with those in Oman (Middle East), Tunisia (Africa), and Turkey (Europe). Result: A high level of genetic diversity was observed among T. annulata detected in cattle from Pakistan, comparable to that in Oman, Tunisia, and Turkey. The genotypes of T. annulata in these four countries form genetically distinct groups that are geographically sub-structured. The T. annulata population in Oman overlapped with that in the Indian Subcontinent (Pakistan) and that in Africa (Tunisia). Conclusions: The T. annulata parasite in Pakistan is highly diverse, and genetically differentiated. This pattern accords well and complements that seen among T. annulata representing the global endemic site. The parasite population in the Arabian Peninsula overlapped with that in the Indian-Subcontinent (India) and that in Africa (Tunisia), which shared some genotypes with that in the Near East and Europe (Turkey). This suggests some level of parasite gene flow, indicative of limited movement between neighboring countries.

Population Genetic Analysis and Sub-Structuring of Theileria annulata in Sudan

Theileria annulata, which causes tropical theileriosis, is a major impediment to improving cattle production in Sudan. Tropical theileriosis disease is prevalent in the north and central regions of Sudan. Outbreaks of the disease have been observed outside the known endemic areas, in east and west regions of the country, due to changes in tick vector distribution and animal movement. A live schizont attenuated vaccination based on tissue culture technology has been developed to control the disease. The parasite in the field as well as the vaccine strain need to be genotyped before the vaccinations are practiced, in order to be able to monitor any breakthrough or breakdown, if any, after the deployment of the vaccine in the field. Nine microsatellite markers were used to genotype 246 field samples positive for T. annulata DNA and the vaccine strain. North and central populations have a higher multiplicity of infection than east and west populations. The examination of principal components showed two sub-structures with a mix of all four populations in both clusters and the vaccine strain used being aligned with left-lower cluster. Only the north population was in linkage equilibrium, while the other populations were in linkage disequilibrium, and linkage equilibrium was found when all samples were regarded as single population. The genetic identity of the vaccine and field samples was 0.62 with the north population and 0.39 with west population. Overall, genetic investigations of four T. annulata populations in Sudan revealed substantial intermixing, with only two groups exhibiting regional origin independence. In the four geographically distant regions analyzed, there was a high level of genetic variation within each population. The findings show that the live schizont attenuated vaccine, Atbara strain may be acceptable for use in all Sudanese regions where tropical theileriosis occurs.

A comparative study of single Theileria lestoquardi and mixed infections with Theileria ovis

Background

Epidemiological surveys in Oman have revealed a high prevalence of the co-occurrence of the pathogenic Theileria lestoquardi and the non-pathogenic Theileria ovis among sheep in the Barka region, Oman. Our most recent data illustrated an interaction and reduced mortality risk in animals co-infected with T. lestoquardi and T. ovis, suggesting that the latter confers protection against pathogenicity of T. lestoquardi. The present study extends the above findings and examines disease outcomes; clinical markers, hematological parameters, and parasite density in mixed and single T. lestoquardi infections.

Methods

A total of 390 blood samples were collected from 16 sheep pens located in Barka, Oman between July and November 2019. Theileria spp. were detected and quantified using qPCR assay targeting 18S rRNA, and the extent of genetic diversity was estimated by a panel of T. lestoquardi specific micro- and mini-satellites. The association of some disease markers with the presence of Theileria spp. and genetic diversity was tested.

Results

Theileria spp. were detected in 75 (19.2%) sheep; of these 65 (86.7%) had mixed infections (T. lestoquardi plus T. ovis), 8 (10.6%) were infected with T. lestoquardi alone, and 2 (2.7%) with only T. ovis. Exotic breeds had a higher risk for Theileria spp. infection. The density (18S rRNA gene copies) of both parasites was higher in single infection against mixed infection, and there was a relatively lower density of T. lestoquardi in mixed infections. However, there was no difference in hematological indices between single T. lestoquardi and mixed infections. High genetic diversity was observed among T. lestoquardi in Barka, with no differences of T. lestoquardi in single and mixed infections. The extent of diversity seen in Barka was higher (He = 0.772) than that reported in Oman in 2019 (He = 0.582), with distinct T. lestoquardi genotypes.

Conclusion

The lower density of T. lestoquardi as mixed infection with T. ovis compared to single infection supports the hypothesis that T. ovis confers protection against lethal T. lestoquardi infection. However, there were no differences in disease correlations (clinical markers, hematological parameters, and density of parasites) or the extent of diversity of T. lestoquardi between the two types of infection. The presence of distinct T. lestoquardi genotypes in Barka, compared to that reported earlier in Oman, likely reflects movement of carrier animals and highlights the need for further analysis of the parasite populations to inform novel approaches for controlling malignant ovine theileriosis.

Graphical Abstract

First report of Theileria annulata in Nigeria: Findings from cattle ticks in Zamfara and Sokoto States

Background

Ticks and tick-borne pathogens (TBPs) represent a significant economic burden to cattle farming in sub-Saharan Africa including Nigeria. However, in the northern part of this country, where the largest livestock population resides, little is known about the contemporary diversity of ticks and TBPs. This area is particularly vulnerable to climate change, undergoing marked transformation of habitat and associated flora and fauna that is also likely to include ticks. This study aimed to document the occurrence of tick species and Apicomplexan TBPs in cattle from north-western Nigeria.

Methods

In 2017, ticks were collected from cattle in Zamfara and Sokoto States and identified morphologically. Additionally, a subset of ticks was screened molecularly for the detection of apicomplexan DNA.

Results

A total of 494 adult ticks were collected from 80 cattle in Zamfara and 65 cattle in Sokoto State. Nine tick species were encountered, among which the presence of one, Hyalomma turanicum, had not previously been recorded in Nigeria. Hyalomma rufipes was the most prevalent tick infesting cattle in Zamfara State (76%), while Hyalomma dromedarii was the most prevalent in Sokoto State (44%), confirming the widespread transfer of this species from camels onto livestock and its adaptation to cattle in the region. Of 159 ticks screened, 2 out of 54 (3.7%) from Zamfara State and 29 out of 105 (27.6%) from Sokoto State harboured DNA of Theileria annulata, the agent of tropical theileriosis.

Conclusions

This study confirms the presence of a broad diversity of tick species in cattle from north-western Nigeria, providing the first locality records for Zamfara State. The occurrence of H. turanicum indicates a distribution of this tick beyond northern Africa. This study provides the first report for T. annulata in Nigerian ticks. Given its enormous burden on livestock farming in north Africa and across Asia, further investigations are needed to better understand its epidemiology, vector transmission and potential clinical significance in cattle from northern Nigeria and neighbouring Sahelian countries.

Graphical abstract

Population Genetic Analysis of the Theileria annulata Parasites Identified Limited Diversity and Multiplicity of Infection in the Vaccine From India

Background: Apicomplexan parasite Theileria annulata causes significant economic loss to the livestock industry in India and other tropical countries. In India, parasite control is mainly dependent on the live attenuated schizont vaccine and the drug buparvaquone. For effective disease control, it is essential to study the population structure and genetic diversity of the Theileria annulata field isolates and vaccine currently used in India. Methodology/Results: A total of 125 T. annulata isolates were genotyped using 10 microsatellite markers from four states belonging to different geographical locations of India. Limited genetic diversity was observed in the vaccine isolates when compared to the parasites in the field; a level of geographical substructuring was evident in India. The number of genotypes observed per infection was highest in India when compared to other endemic countries, suggesting high transmission intensity and abundance of ticks in the country. A reduced panel of four markers can be used for future studies in these for surveillance of the T. annulata parasites in India. Conclusion: High genetic variation between the parasite populations in the country suggests their successful spread in the field and could hamper the disease control programs. Our findings provide the baseline data for the diversity and population structure of T. annulata parasites from India. The low diversity in the vaccine advocates improving the current vaccine, possibly by increasing its heterozygosity. The reduced panel of the markers identified in this study will be helpful in monitoring parasite and its reintroduction after Theileria eradication.

Contrasting population genetics of co-endemic cattle- and buffalo- derived Theileria annulata

A study was designed to improve understanding of the genetics of Theileria annulata populations in sympatric cattle and Asian buffalo (Bubalus bubalus). The study was undertaken in the Punjab province of Pakistan, where the prevalence of tropical theileriosis is high. Parasite materials were collected from infected animals in defined regions, where cattle and Asian buffalo are kept together. Six satellite DNA markers and a mitochondrial cytochrome b marker were used to explore the multiplicity of T. annulata infection and patterns of emergence and spread of different parasite genotypes. The results show differences in the numbers of unique satellite locus alleles, suggesting that T. annulata is genetically more diverse in cattle- than in buffalo-derived populations. Heterozygosity (H_e) indices based on satellite and cytochrome b loci data show high levels of genetic diversity among the cattle- and buffalo-derived T. annulata populations. When considered in the context of high parasite transmission rates and frequent animal movements between different regions, the predominance of multiple T. annulata genotypes and multiple introductions of infection may have practical implications for the spread of parasite genetic adaptations; such as those conferring vaccine cross-protection against different strains affecting cattle and Asian buffalo, or resistance to antiprotozoal drugs.

The impact of tick-borne pathogen infection in Indian bovines is determined by host type but not the genotype of Theileria annulata

Tick-borne pathogens (TBP) are a major source of production loss and a welfare concern in livestock across the globe. Consequently, there is a trade-off between keeping animals that are tolerant to TBP infection, but are less productive than more susceptible breeds. Theileria annulata is a major TBP of bovines, with different host types (i.e. exotic and native cattle breeds, and buffalo) displaying demonstrable differences in clinical susceptibility to infection. However, the extent to which these differences are driven by genetic/physiological differences between hosts, or by different parasite populations/genotypes preferentially establishing infection in different host breeds and species is unclear. In this study, three different bovine host types in India were blood sampled to test for the presence of various TBP, including Theileria annulata, to determine whether native cattle (Bos indicus breeds), crossbreed cattle (Bos taurus x Bos indicus breeds) or water buffalo (Bubalus bubalis) differ in the physiological consequences of infection. Population genetic analyses of T. annulata isolated from the three different host types was also performed, using a panel of mini- and micro-satellite markers, to test for sub-structuring of the parasite population among host types. We discovered that compared to other host types, “carrier” crossbreed cattle showed a higher level of haematological pathology when infected with T. annulata. Despite this finding, we found no evidence for differences in the genotypes of T. annulata infecting different host types, although buffalo appeared to harbour fewer mixed parasite genotype infections, indicating they are not the major reservoir of parasite diversity. The apparent tolerance/resistance of native breed cattle and buffalo to the impacts of T. annulata infection is thus most likely to be driven by host genotype, rather than differences in the parasite population. Our results suggest that an improved understanding of the genetic factors that underpin disease resistance could help to ameliorate future economic loss due to TBP or tropical theileriosis.

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Theileria annulata infection has different consequences in crossbreed cattle, native cattle and water buffalo in India

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Crossbreed Bos taurus x Bos indicus cattle showed reductions in haematological parameters when infected with T. annulata

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We found no evidence for infection-mediated physiological change in native cattle breeds or water buffalo

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We found no sub-structuring of the T. annulata population between different host types using microsatellite analysis

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Buffalo were not a major reservoir of genetically diverse T. annulata infecting cattle, contrasting the epidemiology of T. parva

Genetic characterization of Theileria species infecting bovines in India

Genetic characterization of Theileria species infecting bovines in India was attempted targeting the 18S ribosomal RNA region of the parasite. Blood samples of bovines (n = 452), suspected for haemoprotozoan infections, from 9 different states of the country were microscopically examined for Theileria species infection. Four Theileria spp. positive blood samples from each state were randomly utilized for PCR amplification of the 18S rRNA gene (approx. 1529 bp) followed by cloning and sequencing. The sequence data analysis of all the 36 isolates revealed that 33 isolates had high sequence similarity with published sequences of T. annulata, whereas 3 isolates (MF287917, MF287924 and MF287928) showed close similarity with published sequences of T. orientalis. Sequence homology within the isolates ranged between 95.8 and 100% and variation in the length of targeted region was also noticed in different isolates (1527-1538 nt). Phylogenetic tree created for T. annulata sequences revealed that a total of 24 Indian isolates formed a major clade and grouped together with isolates originating from countries like China, Spain, Turkey and USA. Remaining 09 isolates clustered in a separate group and were closely related to the TA5 isolate of T. annulata (a new genotype) originating from India and also with the isolates from East Asian countries like Japan and Malaysia. All the three T. orientalis isolates had minimal intraspecific variation (99-100% homology) amongst themselves. Further, in the phylogenetic analysis T. orientalis Indian isolates were found to cluster away from other 14 isolates of T. buffeli/sergenti/orientalis originating from different countries (Australia, China, Indonesia and Spain). However, these 3 isolates clustered together with the T. buffeli Indian isolate (EF126184). Present study confirmed the circulation of different genotypes of T. annulata in India, along with T. orientalis isolates.

Genetic Profiling Reveals High Allelic Diversity, Heterozygosity and Antigenic Diversity in the Clinical Isolates of the Theileria annulata From India

Tropical theileriosis caused by Theileria annulata infection is a significant livestock disease affecting cattle health and productivity resulting in substantial monetary losses in several countries. Despite the use of an effective vaccine for disease control still, a high incidence of infection is reported from India. One of the many reasons behind the ineffective disease control can be the existence of genetically diverse T. annulata parasite population in India. Therefore, studies focusing on understanding the genotypes are warranted. In this study, we have performed a genetic analysis of the Indian T. annulata field cell lines and the vaccine line using microsatellite markers, Genotyping based sequencing (GBS) and tams1 gene polymorphism. The degree of allelic diversity and multiplicity of the infection was determined to be high in the Indian population. No geographical sub-structuring and linkage disequilibrium were observed in the population. High population diversity was found which were similar with countries like Oman, Tunisia, and Turkey in contrast to Portugal and China. The presence of multiple genotypes as determined by microsatellite marker genotyping, GBS analysis and tams1 gene polymorphism point toward a panmictic parasite population in India. These findings are the first report from India which would help in understanding the evolution and diversity of the T. annulata population in the country and can help in designing more effective strategies for controlling the disease.

Molecular detection and genetic diversity of Theileria orientalis in cattle in China

The apicomplexan parasite Theileria orientalis is a tick-borne intracellular protozoan parasite that is widely distributed throughout China. It causes bovine theileriosis in infected cattle, which results in huge economic losses to the cattle industry. In this study, the infection status of T. orientalis was determined in 260 blood samples from cattle from seven provinces across China. Results of a major piroplasm surface protein (MPSP)-PCR assay revealed that an average of 36.5% (95/260) of cattle was positive for T. orientalis infection. Based on the MPSP gene sequences, phylogenetic analysis revealed that these isolates of T. orientalis comprised of eight MPSP types, 1, 2, 3, 4, 5, 7, N1, and N2. This is the first report of new T. orientalis MPSP genotypes N1 and N2 in cattle in China.

Theileria lestoquardi in Sudan is highly diverse and genetically distinct from that in Oman

Malignant ovine theileriosis is a severe tick-borne protozoan disease of sheep and other small ruminants which is widespread in sub-Saharan Africa and the Middle East. The disease is of considerable economic importance in Sudan as the export of livestock provides a major contribution to the gross domestic product of this country. Molecular surveys have demonstrated a high prevalence of sub-clinical infections of Theileria lestoquardi, the causative agent, among small ruminants. No information is currently available on the extent of genetic diversity and genetic exchange among parasites in different areas of the country. The present study used a panel of T. lestoquardi specific micro- and mini-satellite genetic markers to assess diversity of parasites in Sudan (Africa) and compared it to that of the parasite population in Oman (Asia). A moderate level of genetic diversity was observed among parasites in Sudan, similar to that previously documented among parasites in Oman. However, a higher level of mixed-genotype infection was identified in Sudanese animals compared to Omani animals, consistent with a higher rate of tick transmission. In addition, the T. lestoquardi genotypes detected in these two countries form genetically distinct groups. The results of this work highlight the need for analysis of T. lestoquardi populations in other endemic areas in the region to inform on novel approaches for controlling malignant theileriosis.

Population Genetic Analysis of Theileria annulata from Six Geographical Regions in China, Determined on the Basis of Micro- and Mini-satellite Markers

Theileria annulata, a tick-borne apicomplexan protozoan, causes a lymphoproliferative disease of cattle with high prevalence in tropical and sub-tropical regions. Understanding the genetic diversity and structure of local populations will provide more fundamental knowledge for the population genetics and epidemics of protozoa. In this study, 78 samples of T. annulata collected from cattle/yaks representing 6 different geographic populations in China were genotyped using eight micro- and mini-satellite markers. High genetic variation within population, moderate genetic differentiation, and high level of diversity co-occurring with significant linkage disequilibrium were observed, which indicates there is gene flow between these populations in spite of the existence of reproductive and geographical barriers among populations. Furthermore, some degree of genetic differentiation was also found between samples from China and Oman. These findings provide a first glimpse of the genetic diversity of the T. annulata populations in China, and might contribute to the knowledge of distribution, dynamics, and epidemiology of T. annulata populations and optimize the management strategies for control.

Genotyping of Theileria lestoquardi from sheep and goats in Sudan to support control of Malignant Ovine Theileriosis

Theileriosis, caused by parasitic protozoa of the genus Theileria parasites, are among the major tick-borne diseases of ruminant livestock. The largest economic losses are attributed in particular to those caused by the leukoproliferative species of Theileria: T. parva, T. annulata and T. lestoquardi. Theileria lestoquardi is transmitted by Hyalomma ticks and causes malignant ovine theileriosis (MOT), a disease that is particularly prevalent in Sudan. The disease is considered of a high economic importance in Sudan, where export of sheep is a major component of the national economy. A live vaccine based on a Sudanese isolate of T. lestoquardi (Atbara strain) was previously developed for the control of MOT in Sudan, but not yet deployed in the field. The present study aims to genetically characterize and compare samples of T. lestoquardi circulating in Sudan as well as the live vaccine isolate in order to understand vaccine breakthroughs and failure that may occur. Sheep and goats blood samples were collected from six regions in Sudan that are known to be endemic for T. lestoquardi infection or have experienced outbreaks of MOT. Blood samples infected with T. lestoquardi were identified by PCR or RLB. Genotyping was carried out by (1) sequencing the homologues of two T. parva CD8⁺ T cell antigen genes, Tp1 and Tp2, and (2) using a panel of seven micro- and mini-satellite markers. A total of 100 T. lestoquardi positive field samples and the T. lestoquardi (Atbara) vaccine were genotyped. The results showed that all samples had mixed genotypes, with several alleles identified at one or more loci. The gene diversity ranged from 0.7840 (TS8) to 0.2133 (TS12) with mean values of 0.5470. PCA revealed three clusters of the parasite in Sudan; interestingly one independent cluster was clearly seen, corresponding to the vaccine isolate. The T. lestoquardi Tp1 homologue showed higher homology with T. annulata than with T. parva sequences included the defined single CD8⁺ T cell target epitope region. The result indicates that multiple genotypes are a common feature of T. lestoquardi infection in Sudan. Both genotyping and the sequencing results clearly showed that the vaccine isolate is highly distinct from the field samples. This finding raised the question whether vaccination with the prepared lived vaccine will effectively protect animals against challenges by the field isolates of T. lestoquardi. The results of this work will inform on the best approach for controlling MOT in Sudan.

Identification and Analysis of Immunodominant Antigens for ELISA-Based Detection of Theileria annulata

Tropical or Mediterranean theileriosis, caused by the protozoan parasite Theileria annulata, remains an economically important bovine disease in North Africa, Southern Europe, India, the Middle East and Asia. The disease affects mainly exotic cattle and imposes serious constraints upon livestock production and breed improvement programmes. While microscopic and molecular methods exist which are capable of detecting T. annulata during acute infection, the identification of animals in the carrier state is more challenging. Serological tests, which detect antibodies that react against parasite-encoded antigens, should ideally have the potential to identify carrier animals with very high levels of sensitivity and specificity. However, assays developed to date have suffered from a lack of sensitivity and/or specificity and it is, therefore, necessary to identify novel parasite antigens, which can be developed for this purpose. In the present study, genes encoding predicted antigens were bioinformatically identified in the T. annulata genome. These proteins, together with a panel of previously described antigens, were assessed by western blot analysis for immunoreactivity, and this revealed that four novel candidates and five previously described antigens were recognised by immune bovine serum. Using a combination of immunoprecipitation and mass spectrophotometric analysis, an immunodominant protein (encoded by TA15705) was identified as Ta9, a previously defined T cell antigen. Western blotting revealed another of the five proteins in the Ta9 family, TA15710, also to be an immunodominant protein. However, validation by Enzyme-Linked Immunosorbent Assay indicated that due to either allelic polymorphism or differential immune responses of individual hosts, none of the novel candidates can be considered ideal for routine detection of T. annulata-infected/carrier animals.

Theileria lestoquardi displays reduced genetic diversity relative to sympatric Theileria annulata in Oman

The Apicomplexan parasites, Theileria lestoquardi and Theileria annulata, the causative agents of theileriosis in small and large ruminants, are widespread in Oman, in areas where cattle, sheep and goats co-graze. Genetic analysis can provide insight into the dynamics of the parasite and the evolutionary relationship between species. Here we identified ten genetic markers (micro- and mini-satellites) spread across the T. lestoquardi genome, and confirmed their species specificity. We then genotyped T. lestoquardi in different regions in Oman. The genetic structures of T. lestoquardi populations were then compared with previously published data, for comparable panels of markers, for sympatric T. annulata isolates. In addition, we examined two antigen genes in T. annulata (Tams1 and Ta9) and their orthologues in T. lestoquardi (Tlms1 and Tl9). The genetic diversity and multiplicity of infection (MOI) were lower in T. lestoquardi (He=0.64-0.77) than T. annulata (He=0.83-0.85) in all populations. Very limited genetic differentiation was found among T. lestoquardi and T. annulata populations. In contrast, limited but significant linkage disequilibrium was observed within regional populations of each species. We identified eight T. annulata isolates in small ruminants; the diversity and MOI were lower among ovine/caprine compared to bovine. Sequence diversity of the antigen genes, Tams1 and Ta9 in T. annulata (π=0.0733 and π=0.155 respectively), was 10-fold and 3-fold higher than the orthologous Tlms1 and Tl9 in T. lestoquardi (π=0.006 and π=0.055, respectively). Despite a comparably high prevalence, T. lestoquardi has lower genetic diversity compared to sympatric T. annulata populations. There was no evidence of differentiation among populations of either species. In comparison to T. lestoquardi, T. annulata has a larger effective population size. While genetic exchange and recombination occur in both parasite species, the extent of diversity, overall, is less for T. lestoquardi. It is, therefore, likely that T. lestoquardi evolved from an ancestor of present day T. annulata and that this occurred either once or on a limited number of occasions.

Tageldin M, Weir W, Al-Fahdi A, Johnson EH, Bobade P, Alqamashoui B, Beja-Pereira A, Thompson J, Kinnaird J, Shiels B, Tait A, Babiker H. Genetic Diversity and Population Structure of Theileria annulata in Oman

Background

Theileriosis, caused by a number of species within the genus Theileria, is a common disease of livestock in Oman. It is a major constraint to the development of the livestock industry due to a high rate of morbidity and mortality in both cattle and sheep. Since little is currently known about the genetic diversity of the parasites causing theileriosis in Oman, the present study was designed to address this issue with specific regard to T. annulata in cattle.

Methods

Blood samples were collected from cattle from four geographically distinct regions in Oman for genetic analysis of the Theileria annulata population. Ten genetic markers (micro- and mini-satellites) representing all four chromosomes of T. annulata were applied to these samples using a combination of PCR amplification and fragment analysis. The resultant genetic data was analysed to provide a first insight into the structure of the T. annulata population in Oman.

Results

We applied ten micro- and mini-satellite markers to a total of 310 samples obtained from different regions (174 [56%] from Dhofar, 68 [22%] from Dhira, 44 [14.5%] from Batinah and 24 [8%] from Sharqia). A high degree of allelic diversity was observed among the four parasite populations. Expected heterozygosity for each site ranged from 0.816 to 0.854. A high multiplicity of infection was observed in individual hosts, with an average of 3.3 to 3.4 alleles per locus, in samples derived from Batinah, Dhofar and Sharqia regions. In samples from Dhira region, an average of 2.9 alleles per locus was observed. Mild but statistically significant linkage disequilibrium between pairs of markers was observed in populations from three of the four regions. In contrast, when the analysis was performed at farm level, no significant linkage disequilibrium was observed. Finally, no significant genetic differentiation was seen between the four populations, with most pair-wise F_ST values being less than 0.03. Slightly higher F_ST values (G_ST’ = 0.075, θ = 0.07) were detected when the data for T. annulata parasites in Oman was compared with that previously generated for Turkey and Tunisia.

Conclusion

Genetic analyses of T. annulata samples representing four geographical regions in Oman revealed a high level of genetic diversity in the parasite population. There was little evidence of genetic differentiation between parasites from different regions, and a high level of genetic diversity was maintained within each sub-population. These findings are consistent with a high parasite transmission rate and frequent movement of animals between different regions in Oman.

Engineering attenuated virulence of a Theileria annulata-infected macrophage

Live attenuated vaccines are used to combat tropical theileriosis in North Africa, the Middle East, India, and China. The attenuation process is empirical and occurs only after many months, sometimes years, of in vitro culture of virulent clinical isolates. During this extensive culturing, attenuated lines lose their vaccine potential. To circumvent this we engineered the rapid ablation of the host cell transcription factor c-Jun, and within only 3 weeks the line engineered for loss of c-Jun activation displayed in vitro correlates of attenuation such as loss of adhesion, reduced MMP9 gelatinase activity, and diminished capacity to traverse Matrigel. Specific ablation of a single infected host cell virulence trait (c-Jun) induced a complete failure of Theileria annulata-transformed macrophages to disseminate, whereas virulent macrophages disseminated to the kidneys, spleen, and lungs of Rag2/γC mice. Thus, in this heterologous mouse model loss of c-Jun expression led to ablation of dissemination of T. annulata-infected and transformed macrophages. The generation of Theileria-infected macrophages genetically engineered for ablation of a specific host cell virulence trait now makes possible experimental vaccination of calves to address how loss of macrophage dissemination impacts the disease pathology of tropical theileriosis.

Evolution and genetic diversity of Theileria

Theileria parasites infect a wide range of domestic and wild ruminants worldwide, causing diseases with varying degrees of severity. A broad classification, based on the parasite's ability to transform the leukocytes of host animals, divides Theileria into two groups, consisting of transforming and non-transforming species. The evolution of transforming Theileria has been accompanied by drastic changes in its genetic makeup, such as acquisition or expansion of gene families, which are thought to play critical roles in the transformation of host cells. Genetic variation among Theileria parasites is sometimes linked with host specificity and virulence in the parasites. Immunity against Theileria parasites primarily involves cell-mediated immune responses in the host. Immunodominance and major histocompatibility complex class I phenotype-specificity result in a host immunity that is tightly focused and strain-specific. Immune escape in Theileria is facilitated by genetic diversity in its antigenic determinants, which potentially results in a loss of T cell receptor recognition in its host. In the recent past, several reviews have focused on genetic diversity in the transforming species, Theileriaparva and Theileriaannulata. In contrast, genetic diversity in Theileriaorientalis, a benign non-transforming parasite, which occasionally causes disease outbreaks in cattle, has not been extensively examined. In this review, therefore, we provide an outline of the evolution of Theileria, which includes T. orientalis, and discuss the possible mechanisms generating genetic diversity among parasite populations. Additionally, we discuss the potential implications of a genetically diverse parasite population in the context of Theileria vaccine development.

Population genetics of Trypanosoma brucei rhodesiense: clonality and diversity within and between foci

African trypanosomes are unusual among pathogenic protozoa in that they can undergo their complete morphological life cycle in the tsetse fly vector with mating as a non-obligatory part of this development. Trypanosoma brucei rhodesiense, which infects humans and livestock in East and Southern Africa, has classically been described as a host-range variant of the non-human infective Trypanosoma brucei that occurs as stable clonal lineages. We have examined T. b. rhodesiense populations from East (Uganda) and Southern (Malawi) Africa using a panel of microsatellite markers, incorporating both spatial and temporal analyses. Our data demonstrate that Ugandan T. b. rhodesiense existed as clonal populations, with a small number of highly related genotypes and substantial linkage disequilibrium between pairs of loci. However, these populations were not stable as the dominant genotypes changed and the genetic diversity also reduced over time. Thus these populations do not conform to one of the criteria for strict clonality, namely stability of predominant genotypes over time, and our results show that, in a period in the mid 1990s, the previously predominant genotypes were not detected but were replaced by a novel clonal population with limited genetic relationship to the original population present between 1970 and 1990. In contrast, the Malawi T. b. rhodesiense population demonstrated significantly greater diversity and evidence for frequent genetic exchange. Therefore, the population genetics of T. b. rhodesiense is more complex than previously described. This has important implications for the spread of the single copy T. b. rhodesiense gene that allows human infectivity, and therefore the epidemiology of the human disease, as well as suggesting that these parasites represent an important organism to study the influence of optional recombination upon population genetic dynamics.

Trypanosomes are single-celled organisms transmitted by the biting tsetse fly, which cause sleeping sickness in humans in sub-Saharan Africa, but also infect livestock and other mammals. Most trypanosomes cannot infect humans as they die in human serum, but two mutants of Trypanosoma brucei have evolved the ability to survive in human serum. This survival in human serum is conferred by the presence of one gene in the East African human-infective T. b. rhodesiense. How often trypanosomes exchange genetic material (they can mate in the tsetse fly) is debated, but will impact upon the spread of genes (e.g. that which confers human infectivity) through a population. We studied T. b. rhodesiense populations from different geographic locations (Malawi and two locations in Uganda), and over time (Uganda), to see if the populations are stable over time and space, using a panel of variable genetic markers enabling assessment of diversity. Our results suggest that there is significant difference in diversity between locations; those in Uganda are very closely related, increasingly so over time, whereas the Malawi population is very genetically diverse, consistent with the trypanosomes mating. These findings suggest that a greater understanding of T. b. rhodesiense population evolution will inform on sleeping sickness epidemiology.

Population genetic analysis and sub-structuring of Theileria parva in the northern and eastern parts of Zambia

BACKGROUND

Theileriosis, caused by Theileria parva, is an economically important disease in Africa. It is a major constraint to the development of the livestock industry in some parts of eastern, central and southern Africa. In Zambia, theileriosis causes losses of up to 10,000 cattle annually.

METHODS

Cattle blood samples were collected for genetic analysis of Theileria parva from Isoka and Petauke districts in Zambia. Microsatellite analysis was then performed on all Theileria parva positive samples for PCR using a panel of 9 microsatellite markers. Microsatellite data was analyzed using microsatellite toolkit, GenAlEx ver. 6, Fstat ver. 2.9.3.2, and LIAN computer softwares.

RESULTS

The combined percentage of positive samples in both districts determined by PCR using the p104 gene primers was 54.9% (95% CI: 46.7 - 63.1%, 78/142), while in each district, it was 44.8% (95% CI: 34.8 - 54.8%) and 76.1% (95% CI = 63.9 - 88.4%) for Isoka and Petauke districts, respectively. We analyzed the population genetic structure of Theileria parva from a total of 61 samples (33 from Isoka and 28 from Petauke) using a panel of 9 microsatellite markers encompassing the 4 chromosomes of Theileria parva. Wright's F index (FST = 0.178) showed significant differentiation between the Isoka and Petauke populations. Linkage disequilibrium was observed when populations from both districts were treated as a single population. When analyzed separately, linkage disequilibrium was observed in Kanyelele and Kalembe areas in Isoka district, Isoka district overall and in Petauke district. Petauke district had a higher multiplicity of infection than Isoka district.

CONCLUSION

Population genetic analyses of Theileria parva from Isoka and Petauke districts showed a low level of genotype exchange between the districts, but a high level of genetic diversity within each district population, implying genetic and geographic sub-structuring between the districts. The sub-structuring observed, along with the lack of panmixia in the populations, could have been due to low transmission levels at the time of sampling. However, the Isoka population was less diverse than the Petauke population.

Babesia: a world emerging

Babesia are tick-transmitted hemoprotozooans that infect mammals and birds, and which are acknowledged for their major impact on farm and pet animal health and associated economic costs worldwide. Additionally, Babesia infections of wildlife can be fatal if associated with stressful management practices; and human babesiosis, also transmitted by blood transfusion, is an increasing public-health concern. Due to the huge diversity of species reported to serve as Babesia hosts, all vertebrates might be potential carriers, as long as they are adequate hosts for Babesia-vector ticks. We here provide a comprehensive overview of the most relevant Babesia species, and a discussion of the classical taxonomic criteria. Babesia, Cytauxzoon and Theileria parasites are closely related and collectively referred to as piroplasmids. A possible scenario for the history of piroplasmids is presented in the context of recent findings, and its implications for future research avenues are outlined. Phylogenetic trees of all available 18S rRNA and hsp70 genes were generated, based on which we present a thoroughly revised molecular classification, comprising five monophyletic Babesia lineages, one Cytauxzoon clade, and one Theileria clade. Updated 18S rRNA and beta-tubulin gene trees of the B. microti isolates agree with those previously reported. To reconcile estimates of the origin of piroplasmids and ticks (~300 Ma, respectively), and mammalian radiation (60 Ma), we hypothesize that the dixenous piroplasmid life cycle evolved with the origin of ticks. Thus, the observed time gap between tick origin and mammalian radiation indicates the existence of hitherto unknown piroplasmid lineages and/or species in extant vertebrate taxa, including reptiles and possibly amphibians. The development and current status of the molecular taxonomy of Babesia, with emphasis on human-infecting species, is discussed. Finally, recent results from population genetic studies of Babesia parasites, and their implications for the development of pathogenicity, drug resistance and vaccines, are summarized.

Demonstration of strain-specific CD8 T cell responses to Theileria annulata

The present study set out to examine the nature and specificity of the bovine CD8 T cell response at the clonal level in a group of eight animals immunized with a cloned population of Theileria annulata. The results demonstrated that immunized animals generated parasite-specific CD8 T cells that produced IFNγ in response to parasite stimulation but had highly variable levels of cytotoxicity for parasitized cells. The study also demonstrated that these parasite-specific CD8 T cells could be propagated and cloned in vitro from the memory T cell pool of cattle immunized with live T. annulata parasites. Within the small group of animals studied, there was evidence that responses were preferentially directed to antigens presented by an A10⁺ class I major histocompatibility complex (MHC) haplotype, suggesting that responses restricted by products of this haplotype may be dominant. The A10-restricted responses showed differential recognition of different parasite isolates and clones. By using a cloned population of parasites both for immunization of the animals and for in vitro analyses of the responses, we obtained unambiguous evidence that at least a proportion of CD8 T cells restricted by one MHC haplotype were parasite strain restricted.

Emergence of new types of Theileria orientalis in Australian cattle and possible cause of theileriosis outbreaks

Theileria parasites cause a benign infection of cattle in parts of Australia where they are endemic, but have, in recent years, been suspected of being responsible for a number of outbreaks of disease in cattle near the coast of New South Wales. The objective of this study was to identify and characterize the species of Theileria in cattle on six farms in New South Wales where disease outbreaks have occurred, and compare with Theileria from three disease-free farms in Queensland that is endemic for Theileria. Special reference was made to sub-typing of T. orientalis by type-specific PCR and sequencing of the small subunit (SSU) rRNA gene, and sequence analysis of the gene encoding a polymorphic merozoite/piroplasm surface protein (MPSP) that may be under immune selection. Nucleotide sequencing of SSU rRNA and MPSP genes revealed the presence of four Theileria genotypes: T. orientalis (buffeli), T. orientalis (ikeda), T. orientalis (chitose) and T. orientalis type 4 (MPSP) or type C (SSU rRNA). The majority of animals showed mixed infections while a few showed single infection. When MPSP nucleotide sequences were translated into amino acids, base transition did not change amino acid composition of the protein product, suggesting possible silent polymorphism. The occurrence of ikeda and type 4 (type C) previously not reported to occur and silent mutation is thought to have enhanced parasite evasion of the host immune response causing the outbreak.

Population genetic analysis and sub-structuring in Babesia bovis

The tick-borne protozoan parasite, Babesia bovis is one of the causes of bovine babesiosis, an economically important disease of cattle in tropical and sub-tropical countries. Using the recently published genome sequence of the parasite, we developed a panel of eight mini- and micro-satellite markers and used these to investigate the role of genetic exchange in the population structure and diversity of the parasite using isolates from Zambia and Turkey. This population genetic analysis showed that genetic exchange occurs and that there are high levels of genetic diversity, with geographical sub-structuring quantified using Wright's F Index. Linkage disequilibrium was observed when isolates from both countries were treated as one population, but when isolates from Zambia were analysed separately linkage equilibrium was observed. The Turkish isolates were sub-structured, containing two genetically distinct sub-groups, both of which appeared to be in linkage equilibrium. The results of the Zambian study suggest that a sub-set of the parasite population is responsible for the westward spread of babesiosis into the previously disease-free central region of the country. The Zambian isolates had a significantly higher number of genotypes per sample than those from Turkey and age was found to be a significant predictor of the multiplicity of infection. The high levels of diversity seen in the Zambian and Turkish B. bovis populations have implications in the development of subunit vaccines against the disease and the spread of drug resistance.

Extensive polymorphism and evidence of immune selection in a highly dominant antigen recognized by bovine CD8 T cells specific for Theileria annulata

Although parasite strain-restricted CD8 T cell responses have been described for several protozoa, the precise role of antigenic variability in immunity is poorly understood. The tick-borne protozoan parasite Theileria annulata infects leukocytes and causes an acute, often fatal lymphoproliferative disease in cattle. Building on previous evidence of strain-restricted CD8 T cell responses to T. annulata, this study set out to identify and characterize the variability of the target antigens. Three antigens were identified by screening expressed parasite cDNAs with specific CD8 T cell lines. In cattle expressing the A10 class I major histocompatibility complex haplotype, A10-restricted CD8 T cell responses were shown to be focused entirely on a single dominant epitope in one of these antigens (Ta9). Sequencing of the Ta9 gene from field isolates of T. annulata demonstrated extensive sequence divergence, resulting in amino acid polymorphism within the A10-restricted epitope and a second A14-restricted epitope. Statistical analysis of the allelic sequences revealed evidence of positive selection for amino acid substitutions within the region encoding the CD8 T cell epitopes. Sequence differences in the A10-restricted epitope were shown to result in differential recognition by individual CD8 T cell clones, while clones also differed in their ability to recognize different alleles. Moreover, the representation of these clonal specificities within the responding CD8 T cell populations differed between animals. As well as providing an explanation for incomplete protection observed after heterologous parasite challenge of vaccinated cattle, these results have important implications for the choice of antigens for the development of novel subunit vaccines.

Population diversity and multiplicity of infection in Theileria annulata

The tick-borne apicomplexan parasite Theileria annulata is endemic in many sub-tropical countries and causes the bovine disease tropical theileriosis. Although the parasite is known to be highly diverse, detailed information is lacking on the genetic structure of natural populations and levels of multiplicity of infection in the cattle host. With the widespread deployment of live attenuated vaccines and the emergence of drug-resistant parasites in the field, it is vital to appreciate the factors which shape genetic diversity of the parasite both within individual hosts and in the wider population. This study addresses these issues and represents an extensive genetic analysis of T. annulata populations in two endemic countries utilising a high-throughput adaptation of a micro- and mini-satellite genotyping system. Parasite material was collected from infected cattle in defined regions of Turkey and Tunisia to allow a variety of analyses to be conducted. All animals (n=305) were found to harbour multiple parasite genotypes and only two isolates shared an identical predominant multi-locus profile. A modelling approach was used to demonstrate that host age, location and vaccination status play a measurable role in determining multiplicity of infection in an individual animal. Age was shown to positively correlate with multiplicity of infection and while positive vaccination status exerted a similar effect, it was shown to be due not simply to the presence of the immunising genotype. Importantly, no direct evidence was found for the immunising genotype spreading or recombining within the local parasite community. Genetic analysis confirmed the tentative conclusion of a previous study that the parasite population appears to be, in general, panmictic. Nevertheless, evidence supporting linkage disequilibrium and a departure from panmixia was uncovered in some localities and a number of explanations for these findings are advanced.

Genotypic diversity of merozoite surface antigen 1 of Babesia bovis within an endemic population

Multiple genetically distinct strains of a pathogen circulate and compete for dominance within populations of animal reservoir hosts. Understanding the basis for genotypic strain structure is critical for predicting how pathogens respond to selective pressures and how shifts in pathogen population structure can lead to disease outbreaks. Evidence from related Apicomplexans such as Plasmodium, Toxoplasma, Cryptosporidium and Theileria suggests that various patterns of population dynamics exist, including but not limited to clonal, oligoclonal, panmictic and epidemic genotypic strain structures. In Babesia bovis, genetic diversity of variable merozoite surface antigen (VMSA) genes has been associated with disease outbreaks, including in previously vaccinated animals. However, the extent of VMSA diversity within a defined population in an endemic area has not been examined. We analyzed genotypic diversity and temporal change of MSA-1, a member of the VMSA family, in individual infected animals within a reservoir host population. Twenty-eight distinct MSA-1 genotypes were identified within the herd. All genotypically distinct MSA-1 sequences clustered into three groups based on sequence similarity. Two thirds of the animals tested changed their dominant MSA-1 genotypes during a 6-month period. Five animals within the population contained multiple genotypes. Interestingly, the predominant genotypes within those five animals also changed over the 6-month sampling period, suggesting ongoing transmission or emergence of variant MSA-1 genotypes within the herd. This study demonstrated an unexpected level of diversity for a single copy gene in a haploid genome, and illustrates the dynamic genotype structure of B. bovis within an individual animal in an endemic region. Co-infection with multiple diverse MSA-1 genotypes provides a basis for more extensive genotypic shifts that characterizes outbreak strains.

Evolution and diversity of secretome genes in the apicomplexan parasite Theileria annulata

Background

Little is known about how apicomplexan parasites have evolved to infect different host species and cell types. Theileria annulata and Theileria parva invade and transform bovine leukocytes but each species favours a different host cell lineage. Parasite-encoded proteins secreted from the intracellular macroschizont stage within the leukocyte represent a critical interface between host and pathogen systems. Genome sequencing has revealed that several Theileria-specific gene families encoding secreted proteins are positively selected at the inter-species level, indicating diversification between the species. We extend this analysis to the intra-species level, focusing on allelic diversity of two major secretome families. These families represent a well-characterised group of genes implicated in control of the host cell phenotype and a gene family of unknown function. To gain further insight into their evolution and function, this study investigates whether representative genes of these two families are diversifying or constrained within the T. annulata population.

Results

Strong evidence is provided that the sub-telomerically encoded SVSP family and the host-nucleus targeted TashAT family have evolved under contrasting pressures within natural T. annulata populations. SVSP genes were found to possess atypical codon usage and be evolving neutrally, with high levels of nucleotide substitutions and multiple indels. No evidence of geographical sub-structuring of allelic sequences was found. In contrast, TashAT family genes, implicated in control of host cell gene expression, are strongly conserved at the protein level and geographically sub-structured allelic sequences were identified among Tunisian and Turkish isolates. Although different copy numbers of DNA binding motifs were identified in alleles of TashAT proteins, motif periodicity was strongly maintained, implying conserved functional activity of these sites.

Conclusions

This analysis provides evidence that two distinct secretome genes families have evolved under contrasting selective pressures. The data supports current hypotheses regarding the biological role of TashAT family proteins in the management of host cell phenotype that may have evolved to allow adaptation of T. annulata to a specific host cell lineage. We provide new evidence of extensive allelic diversity in representative members of the enigmatic SVSP gene family, which supports a putative role for the encoded products in subversion of the host immune response.

Modulation of NF-kappaB activation in Theileria annulata-infected cloned cell lines is associated with detection of parasite-dependent IKK signalosomes and disruption of the actin cytoskeleton

Apicomplexan parasites within the genus Theileria have the ability to induce continuous proliferation and prevent apoptosis of the infected bovine leukocyte. Protection against apoptosis involves constitutive activation of the bovine transcription factor NF-kappaB in a parasite-dependent manner. Activation of NF-kappaB is thought to involve recruitment of IKK signalosomes at the surface of the macroschizont stage of the parasite, and it has been postulated that additional host proteins with adaptor or scaffolding function may be involved in signalosome formation. In this study two clonal cell lines were identified that show marked differences in the level of activated NF-kappaB. Further characterization of these lines demonstrated that elevated levels of activated NF-kappaB correlated with increased resistance to cell death and detection of parasite-associated IKK signalosomes, supporting results of our previous studies. Evidence was also provided for the existence of host- and parasite-dependent NF-kappaB activation pathways that are influenced by the architecture of the actin cytoskeleton. Despite this influence, it appears that the primary event required for formation of the parasite-dependent IKK signalosome is likely to be an interaction between a signalosome component and a parasite-encoded surface ligand.

Discovery of mating in the major African livestock pathogen Trypanosoma congolense

The protozoan parasite, Trypanosoma congolense, is one of the most economically important pathogens of livestock in Africa and, through its impact on cattle health and productivity, has a significant effect on human health and well being. Despite the importance of this parasite our knowledge of some of the fundamental biological processes is limited. For example, it is unknown whether mating takes place. In this paper we have taken a population genetics based approach to address this question. The availability of genome sequence of the parasite allowed us to identify polymorphic microsatellite markers, which were used to genotype T. congolense isolates from livestock in a discrete geographical area of The Gambia. The data showed a high level of diversity with a large number of distinct genotypes, but a deficit in heterozygotes. Further analysis identified cryptic genetic subdivision into four sub-populations. In one of these, parasite genotypic diversity could only be explained by the occurrence of frequent mating in T. congolense. These data are completely inconsistent with previous suggestions that the parasite expands asexually in the absence of mating. The discovery of mating in this species of trypanosome has significant consequences for the spread of critical traits, such as drug resistance, as well as for fundamental aspects of the biology and epidemiology of this neglected but economically important pathogen.

Bovine immunity - a driver for diversity in Theileria parasites?

Theileria parva and Theileria annulata are tick-borne parasites of cattle that infect and transform leukocytes, causing severe and often fatal parasitic leukoses. Both species provoke strong immunity against subsequent infection. However, considerable diversity is observed in field populations of each parasite and protection is only assured against homologous challenge. The life cycles of these parasites are complex and involve prolonged exposure to host and vector defence mechanisms. Although the relevant vector mechanisms are poorly defined, protective responses of cattle seem to be tightly focused and variable in their specificity between individuals. This review considers whether bovine immunity acts as a driver for diversity in T. parva and T. annulata and explores other factors that might underlie genetic variation in these parasites.