Current status of vaccine development against Theileria parasites

Isolation and propagation of an Egyptian Theileria annulata infected cell line and evaluation of its use as a vaccine to protect cattle against field challenge

Tropical theileriosis is an important protozoan tick-borne disease in cattle. Vaccination using attenuated schizont-infected cell lines is one of the methods used for controlling the disease. This study describes the production of attenuated schizont-infected cell lines from Egypt and an evaluation of its use as a vaccine to protect calves against clinical disease upon field challenge. Two groups of exotic and crossbred male calves were divided into vaccinated and control groups. The vaccinated groups were inoculated with 4 ml (1 × 106 cells/ml) of the attenuated cell line. Three weeks after vaccination, calves of both groups were transported to the New Valley Governorate (Egyptian oasis) where they were kept under field conditions and exposed to the natural Theileria annulata challenge. All animals in the control group showed severe clinical signs and died despite treatment with buparvaquone, which was administered after two days of persistent fever due to a severe drop in packed cell volume (PCV). Animals in the vaccinated group became seropositive without developing severe clinical signs other than transient fever. Post-mortem examinations revealed enlarged and fragile lymph nodes, spleen, and liver with necrosis and hemorrhages. These findings indicate that the Egyptian attenuated cell line was successful in protecting both exotic and crossbred animals against tropical theileriosis under field conditions.

In silico analysis of sporozoite surface antigen 1 of Theileria annulata (TaSPAG1) for multi-epitope vaccine design against theileriosis

Tropical theileriosis is a protozoan infection caused by Theileria annulata, which significantly affects cattle worldwide. This study was aimed to analyze the TaSPAG1 protein and design a novel multi-epitope vaccine candidate. Online tools were employed for the prediction of Physico-chemical properties, antigenicity, allergenicity, solubility, transmembrane domains and signal peptide, posttranslational modification (PTM) sites, secondary and tertiary structures as well as intrinsically disordered regions, followed by identification and screening of potential linear and conformational B-cell epitopes and those peptides having affinity to bind bovine major histocompatibility complex class I (MHC-I) molecules. Next, a multi-epitope vaccine construct was designed and analyzed. This 907-residue protein was hydrophilic (GRAVY: -0.399) and acidic (pI: 5.04) in nature, with high thermotolerance (aliphatic: 71.27). Also, 5 linear and 12 conformational B-cell epitopes along with 8 CTL epitopes were predicted for TaSPAG1. The 355-residue vaccine candidate had a MW of about 35 kDa and it was antigenic, non-allergenic, soluble and stable, which was successfully interacted with cattle MHC-I molecule and finally cloned into the pET28a(+) vector. Further wet studies are required to assess the vaccine efficacy in cattle.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40203-023-00153-5.

Molecular detection of Theileria annulata, Theileria mutans and Theileria velifera but no evidence of Theileria parva infected or vaccinated cattle in Nigeria despite extensive transboundary migrations

The extensive livestock management system predominant in Nigeria necessitates active disease surveillance for the early detection and prompt control of transboundary animal diseases. Theileriae are obligate intracellular protozoa which infect both wild and domestic bovidae throughout much of the world causing East Coast Fever (Theileria parva), Tropical or Mediterranean theileriosis (Theileria annulata) or benign theileriosis (Theileria mutans; Theileria velifera). This study aimed to detect and characterize Theileria spp. infecting cattle in Nigeria using conventional PCR and sequencing approach. Five hundred and twenty-two DNA samples obtained from different cattle blood samples were subjected to PCR targeting the 18S rRNA gene of piroplasmida and specifically, the p104 kDa and Tp1 genes for the evidence of infection or vaccination respectively, with T. parva. A total of 269 out of 522 (51.5%) of the cattle tested PCR- positive for DNA of piroplasmida. Nucleotide sequence and phylogenetic analyses showed that the cattle were infected with T. annulata, T. mutans and T. velifera. Piroplasmida DNA was associated with sex (ꭓ² = 7.2; p = 0.007), breed (ꭓ² = 115; p = 0.000002) of animals and the state where the samples were collected (ꭓ² = 78.8; p = 0.000002). None of the samples tested positive for T. parva DNA or showed evidence of vaccination (Tp1 gene). This is the first report on the molecular detection and characterization of T. annulata in the blood of cattle from Nigeria. Continuous surveillance of Nigerian cattle for East Coast Fever (ECF) is encouraged considering the recent report of the disease in cattle in the neighboring country, Cameroon, where unregulated transboundary cattle movement into Nigeria has been observed.

Safety and Efficacy of the East Coast Fever Muguga Cocktail Vaccine: A Systematic Review

Immunisation of livestock with high quality vaccines is considered an essential approach to controlling many animal diseases. The only currently available commercial vaccine to protect cattle from East Coast fever (ECF), a tick-borne disease caused by Theileria parva, is an unconventional “infection and treatment method” (ITM) involving administration of a combination of live T. parva isolates, referred to as the “Muguga cocktail”, and simultaneous treatment with long-acting oxytetracycline. Veterinary vaccine research and development typically involves studies designed to demonstrate vaccine quality, safety, and efficacy; however, as there were no such purpose-designed registration studies conducted for the Muguga cocktail, evidence for safety and efficacy is solely based on that which is available in the clinical literature. An extensive systematic review was conducted to analyse the evidence available in the literature in order to establish the safety and efficacy of the Muguga cocktail vaccine. A combination of meta-analyses and narrative summaries was conducted. A total of 61 studies met the criteria to be included in the systematic review. The majority of studies demonstrated or reported in favour of the vaccine with regards to safety and efficacy of the Muguga cocktail vaccine. Proximity to buffalo often resulted in reduced vaccine efficacy, and reports of shed and transmission of vaccine components affected the overall interpretation of safety. Better understanding of control options for this devastating livestock disease is important for policymakers and livestock keepers, enabling them to make informed decisions with regards to the health of their animals and their livelihoods.

Antigenic Diversity in Theileria parva Populations From Sympatric Cattle and African Buffalo Analyzed Using Long Read Sequencing

East Coast fever (ECF) in cattle is caused by the Apicomplexan protozoan parasite Theileria parva, transmitted by the three-host tick Rhipicephalus appendiculatus. The African buffalo (Syncerus caffer) is the natural host for T. parva but does not suffer disease, whereas ECF is often fatal in cattle. The genetic relationship between T. parva populations circulating in cattle and buffalo is poorly understood, and has not been studied in sympatric buffalo and cattle. This study aimed to determine the genetic diversity of T. parva populations in cattle and buffalo, in an area where livestock co-exist with buffalo adjacent to the Serengeti National Park, Tanzania. Three T. parva antigens (Tp1, Tp4, and Tp16), known to be recognized by CD8⁺ and CD4⁺ T cells in immunized cattle, were used to characterize genetic diversity of T. parva in cattle (n = 126) and buffalo samples (n = 22). Long read (PacBio) sequencing was used to generate full or near-full length allelic sequences. Patterns of diversity were similar across all three antigens, with allelic diversity being significantly greater in buffalo-derived parasites compared to cattle-derived (e.g., for Tp1 median cattle allele count was 9, and 81.5 for buffalo), with very few alleles shared between species (8 of 651 alleles were shared for Tp1). Most alleles were unique to buffalo with a smaller proportion unique to cattle (412 buffalo unique vs. 231 cattle-unique for Tp1). There were indications of population substructuring, with one allelic cluster of Tp1 representing alleles found in both cattle and buffalo (including the TpM reference genome allele), and another containing predominantly only alleles deriving from buffalo. These data illustrate the complex interplay between T. parva populations in buffalo and cattle, revealing the significant genetic diversity in the buffalo T. parva population, the limited sharing of parasite genotypes between the host species, and highlight that a subpopulation of T. parva is maintained by transmission within cattle. The data indicate that fuller understanding of buffalo T. parva population dynamics is needed, as only a comprehensive appreciation of the population genetics of T. parva populations will enable assessment of buffalo-derived infection risk in cattle, and how this may impact upon control measures such as vaccination.

Molecular investigation of bacterial and protozoal pathogens in ticks collected from different hosts in Turkey

Background

The emergence of tick-borne disease is increasing because of the effects of the temperature rise driven by global warming. In Turkey, 19 pathogens transmitted by ticks to humans and animals have been reported. Based on this, this study aimed to investigate tick-borne pathogens including Hepatozoon spp., Theileria spp., Babesia spp., Anaplasma spp., Borrelia spp., and Bartonella spp. in tick samples (n = 110) collected from different hosts (dogs, cats, cattle, goats, sheep, and turtles) by molecular methods.

Methods

To meet this objective, ticks were identified morphologically at the genus level by microscopy; after DNA isolation, each tick sample was identified at the species level using the molecular method. Involved pathogens were then investigated by PCR method.

Results

Seven different tick species were identified including Rhipicephalus sanguineus, R. turanicus, R. bursa, Hyalomma marginatum, H. anatolicum, H. aegyptium, and Haemaphysalis erinacei. Among the analyzed ticks, Hepatozoon spp., Theileria spp., Babesia spp., and Anaplasma spp. were detected at rates of 6.36%, 16.3%, 1.81%, and 6.36%, respectively while Borrelia spp. and Bartonella spp. were not detected. Hepatozoon spp. was detected in R. sanguineus ticks while Theileria spp., Babesia spp., and Anaplasma spp. were detected in R. turanicus and H. marginatum. According to the results of sequence analyses applied for pathogen positive samples, Hepatozoon canis, Theileria ovis, Babesia caballi, and Anaplasma ovis were identified.

Conclusion

Theileria ovis and Anaplasma ovis were detected for the first time to our knowledge in H. marginatum and R. turanicus collected from Turkey, respectively. Also, B. caballi was detected for the first time to our knowledge in ticks in Turkey.

Immune Response to Tick-Borne Hemoparasites: Host Adaptive Immune Response Mechanisms as Potential Targets for Therapies and Vaccines

Tick-transmitted pathogens cause infectious diseases in both humans and animals. Different types of adaptive immune mechanisms could be induced in hosts by these microorganisms, triggered either directly by pathogen antigens or indirectly through soluble factors, such as cytokines and/or chemokines, secreted by host cells as response. Adaptive immunity effectors, such as antibody secretion and cytotoxic and/or T helper cell responses, are mainly involved in the late and long-lasting protective immune response. Proteins and/or epitopes derived from pathogens and tick vectors have been isolated and characterized for the immune response induced in different hosts. This review was focused on the interactions between tick-borne pathogenic hemoparasites and different host effector mechanisms of T- and/or B cell-mediated adaptive immunity, describing the efforts to define immunodominant proteins or epitopes for vaccine development and/or immunotherapeutic purposes. A better understanding of these mechanisms of host immunity could lead to the assessment of possible new immunotherapies for these pathogens as well as to the prediction of possible new candidate vaccine antigens.

Dynamics and within-host interaction of Theileria lestoquardi and T. ovis among naive sheep in Oman

Mixed species infections of Theileria spp. are common in nature. Experimental and epidemiological data suggest that mixed species infections elicit cross-immunity that can modulate pathogenicity and disease burden at the population level. The present study examined within-host interactions, over a period of 13 months during natural infections with two Theileria spp., pathogenic (T. lestoquardi) and non-pathogenic (T. ovis), amongst a cohort of naive sheep in Oman. In the first two months after exposure to infection, a high rate of mortality was seen among sheep infected with T. lestoquardi alone. However, subsequently mixed-infections of T. lestoquardi and T. ovis prevailed, and no further death occurred. The overall densities of both parasite species were significantly higher as single infection vs mixed infection and the higher relative density of pathogenic T. lestoquardi indicated a competitive advantage over T. ovis in mixed infection. The density of both species fluctuated significantly over time, with no difference in density between the very hot (May to August) and warm season (September to April). A high degree of genotype multiplicity was seen among T. lestoquardi infections, which increased with rising parasite density. Our results illustrate a potential competitive interaction between the two ovine Theileria spp., and a substantial reduction in the risk of mortality in mixed parasite infections, indicating that T. ovis confers heterologous protection against lethal T. lestoquardi infection.

Theileria parva: a parasite of African buffalo, which has adapted to infect and undergo transmission in cattle

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Theileria parva parasites show extensive genotypic diversity and undergo frequent genetic recombination during tick transmission.

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Theileria parva maintained in cattle is much less genotypically diverse than the buffalo-maintained population.

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Theileria parva transmitted from buffalo to cattle usually fails to differentiate to the tick-transmissible stages in cattle.

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These differences have resulted in the parasites in the two hosts being maintained largely as separate populations.

The tick-borne protozoan parasite Theileria parva causes an acute, often fatal disease in cattle throughout a large part of eastern and southern Africa. Infection of African buffalo (Syncerus caffer) is also widespread in this region but does not cause clinical disease in this species. This difference most likely reflects the evolutionary history of the parasites in these species, in that cattle were only introduced into Africa within the last 8000 years. In both hosts, T. parva establishes a carrier state, involving persistence of small numbers of parasites for many months following the acute phase of infection. This persistence is considered important for maintaining the parasite populations. Although cattle and buffalo parasites both produce severe disease when transmitted to cattle, the buffalo-derived parasites are usually not transmissible from infected cattle. Recent studies of the molecular and antigenic composition of T. parva, in addition to demonstrating heterogeneity in the populations in both host species, have revealed that infections in individual animals are genotypically mixed. The results of these studies have also shown that buffalo T. parva exhibit much greater genotypic diversity than the cattle population and indicate that cattle parasites represent a subpopulation of T. parva that has adapted to maintenance in cattle. The parasites in cattle and buffalo appear to be maintained largely as separate populations. This insight into the genotypic composition of T. parva populations has raised important questions on how host adaptation of the parasite has evolved and whether there is scope for further adaptation of buffalo-maintained populations to cattle.

The Pathology of Pathogenic Theileriosis in African Wild Artiodactyls

The published literature on schizont-"transforming," or pathogenic theileriosis, in African wild artiodactyls is dated and based on limited information. Here the authors review the taxonomy, diagnosis, epidemiology, hematology, pathology, and aspects of control in various species. Molecular studies based on 18S and 16S rRNA gene sequences have shown that African wild artiodactyls are commonly infected with diverse Theileria spp., as well as nontheilerial hemoprotozoa and rickettsia-like bacteria, and coinfections with pathogenic and nonpathogenic Theileria species are often recorded. Although theileriosis is still confusingly referred to as cytauxzoonosis in many species, the validity of a separate Cytauxzoon genus in artiodactyls is debated. The epidemiology of theileriosis is complex; the likelihood of fatal disease depends on the interplay of parasite, vertebrate host, tick vector, and environmental factors. Roan calves (Hippotragus equinus) and stressed animals of all host species are more susceptible to fatal theileriosis. Even though regenerative anemia is common, peripheral blood piroplasm parasitemia does not correlate with disease severity. Other than anemia, common macroscopic lesions include icterus, hemorrhages (mucosal, serosal, and tissue), fluid effusions into body cavities, lung edema, and variably sized raised cream-colored foci of leukocyte infiltration in multiple organs. Histopathologic findings include vasocentric hyperproliferation and lysis of atypical leukocytes with associated intracellular schizonts, parenchymal necrosis, hemorrhage, thromboembolism, and edema. Immunophenotyping is required to establish the identity of the schizont-transformed leukocytes in wild ungulates. Throughout the review, we propose avenues for future research by comparing existing knowledge on selected aspects of theileriosis in domestic livestock with that in African wild artiodactyls.

Antigenicity assessment of the Theileria equi merozoite antigen (EMA-2) expressed in Pichia pastoris in mice and horses

Equine theileriosis is a severe equine disease caused by the protozoan Theileria equi, which is prevalent in tropical and subtropical areas. In this study, a recombinant equi merozoite antigen-2 (rEMA-2) of T. equi was used as an immunogen. Two groups of 10 mice each were divided into control and vaccinated groups. Sixty mares seronegative for theileriosis were divided in two groups, one vaccinated and another group as a control animal. Mice and mares of the vaccinated groups were inoculated with 150 μL of the vaccine containing 50 μg of rEMA-2 and 2 mL of the vaccine containing 200 μg of rEMA-2, respectively, at days 0 and 21. The immunogenicity of rEMA-2 was evaluated by ELISA and fluorescent antibody test (IFAT) using serum from vaccinated mice, mares and antigenicity in naturally infected horse. At every point throughout the ELISA study, there were significant differences between the vaccinated and control groups (p < 0.05). The vaccine induced 3- and 4-fold IgG increases in mice at the 14th and 28th day, respectively, compared to the control group. The horses' IgG dynamics showed a significant (p < 0.05) increase in the total IgG titer as early as day 7, which increased until day 28 at which time a more significant (p < 0.001) IgG titer was observed. In evaluating the isotypes, we observed a trend similar to that of total IgG, where IgG(T) (IgG3-5) were significantly (p < 0.05) more elevated than the other isotypes analyzed, followed by IgGb (IgG4-7) and IgGa (IgG1). Positive fluorescence was detected by IFAT, suggesting that the protein is immunogenic and conserves some epitopes identical to the native T. equi antigens present in the equine blood smear. Thus, our results suggest that rEMA-2 can be a promising vaccinal antigen.

Corridor disease (buffalo-associated Theileria parva) outbreak in cattle introduced onto a game ranch and investigations into their carrier-state

East Coast fever (Theileria parva infection in cattle) was eradicated from South Africa in the mid-1900. However, another form named Corridor disease (CD), associated with T. parva carrier buffaloes exists and outbreaks have increased in endemic areas. The occurrence of a CD carrier state in cattle under field situations has not been demonstrated but remains a subject of controversy. The current study investigated the T. parva carrier state following a severe outbreak in cattle introduced onto a game ranch. Monitoring of the outbreak included clinical signs, mortality, microscopy, serology, real-time PCR and xenodiagnoses. The herd of cattle received block treatment using oxytetracyclines (OTC) by the farmer during the outbreak. Cattle were sampled early during the outbreak and twice within the following 75 days. All buffaloes were tested for a T. parva carrier state. Two batches of questing adult R. appendiculatus were collected at the time of disease occurrence and a year later. These ticks were fed on susceptible cattle under controlled conditions and monitored for disease transmission. Ticks infected with a buffalo-derived stock of T. parva were fed on one bovine under controlled conditions and simultaneously injected with OTC, simulating the infection and treatment method of vaccination and was used as a positive control. Clean R. appendiculatus nymphs were fed on four recovered PCR positive cattle from the outbreak and on the positive control animal. The adult ticks were tested for infectivity by xenodiagnoses on susceptible bovines. For the initial outbreak the CD prevalence was 62.3% with a mortality rate of 29.5%. However, the outbreak was contained by block OTC treatment of the herd since only 3.4% cattle subsequently died until the end of the investigations. Adult ticks fed on one field bovine and the laboratory established T. parva carrier both transmitted fatal infections to susceptible cattle. Ticks fed on two field cattle transmitted T. taurotragi and one failed to transmit any infection. Questing adult R. appendiculatus collected during the outbreak transmitted fatal CD to two bovines while ticks collected a year later transmitted T. taurotragi. These findings demonstrated the effectiveness of disease control either by cattle treatment using OTC simulating the ITM or by intensive cattle dipping following the outbreak or by both interventions. The potential risk of creating carrier cattle by OTC treatment during CD outbreaks should be considered, supporting the continued control measures of segregation of cattle and buffalo herds.

Gene gun DNA immunization of cattle induces humoral and CD4 T-cell-mediated immune responses against the Theileria parva polymorphic immunodominant molecule

Theileria parva kills over one million cattle annually in sub-Saharan Africa. Parasite genetic complexity, cellular response immunodominance, and bovine MHC diversity have precluded traditional vaccine development. One potential solution is gene gun (GG) immunization, which enables simultaneous administration of one or more DNA-encoded antigens. Although promising in murine, porcine, and human vaccination trials, bovine GG immunization studies are limited. We utilized the model T. parva antigen, polymorphic immunodominant molecule (PIM) to test bovine GG immunization. GG immunization using a mammalian codon optimized PIM sequence elicited significant anti-PIM antibody and cell-mediated responses in 7/8 steers, but there was no difference between immunized and control animals following T. parva challenge. The results suggest immunization with PIM, as delivered here, is insufficient to protect cattle from T. parva. Nonetheless, the robust immune responses elicited against this model antigen suggest GG immunization is a promising vaccine platform for T. parva and other bovine pathogens.

Establishment of a mouse-tick infection model for Theileria orientalis and analysis of its transcriptome

Oriental theileriosis caused by Theileria orientalis is an economically significant disease in cattle farming. The lack of laboratory animal models and in vitro culture systems is a major obstacle in the drive to better understand the biology of this parasite. Notably, research on the sporozoite stage of T. orientalis has rarely been undertaken, although such investigations are of paramount importance for vaccine development based on blocking sporozoite invasion of its host animals. In the present study, we established a mouse-tick infection model for propagating T. orientalis in mice and for producing the sporozoite stage in tick salivary glands. Splenectomized severe combined immunodeficient mice transfused with bovine erythrocytes were infected with T. orientalis. The larval ticks of Haemaphysalis longicornis were then fed on the T. orientalis-infected mice. The piroplasm and sporozoite stages were microscopically observed in the mouse blood and nymphal salivary glands, respectively. The transcriptomics data generated from the piroplasm and sporozoite stages revealed a stage-specific expression pattern for the parasite genes. The mouse-tick infection model and the transcriptomics data it has provided will contribute to a better understanding of T. orientalis biology and will also provide much needed information for the design of effective control measures targeting oriental theileriosis.

Ancient diversity and geographical sub-structuring in African buffalo Theileria parva populations revealed through metagenetic analysis of antigen-encoding loci

An infection and treatment protocol involving infection with a mixture of three parasite isolates and simultaneous treatment with oxytetracycline is currently used to vaccinate cattle against Theileria parva. While vaccination results in high levels of protection in some regions, little or no protection is observed in areas where animals are challenged predominantly by parasites of buffalo origin. A previous study involving sequencing of two antigen-encoding genes from a series of parasite isolates indicated that this is associated with greater antigenic diversity in buffalo-derived T. parva. The current study set out to extend these analyses by applying high-throughput sequencing to ex vivo samples from naturally infected buffalo to determine the extent of diversity in a set of antigen-encoding genes. Samples from two populations of buffalo, one in Kenya and the other in South Africa, were examined to investigate the effect of geographical distance on the nature of sequence diversity. The results revealed a number of significant findings. First, there was a variable degree of nucleotide sequence diversity in all gene segments examined, with the percentage of polymorphic nucleotides ranging from 10% to 69%. Second, large numbers of allelic variants of each gene were found in individual animals, indicating multiple infection events. Third, despite the observed diversity in nucleotide sequences, several of the gene products had highly conserved amino acid sequences, and thus represent potential candidates for vaccine development. Fourth, although compelling evidence for population differentiation between the Kenyan and South African T. parva parasites was identified, analysis of molecular variance for each gene revealed that the majority of the underlying nucleotide sequence polymorphism was common to both areas, indicating that much of this aspect of genetic variation in the parasite population arose prior to geographic separation.

Approaches to vaccination against Theileria parva and Theileria annulata

Despite having different cell tropism, the pathogenesis and immunobiology of the diseases caused by Theileria parva and Theileria annulata are remarkably similar. Live vaccines have been available for both parasites for over 40 years, but although they provide strong protection, practical disadvantages have limited their widespread application. Efforts to develop alternative vaccines using defined parasite antigens have focused on the sporozoite and intracellular schizont stages of the parasites. Experimental vaccination studies using viral vectors expressing T. parva schizont antigens and T. parva and T. annulata sporozoite antigens incorporated in adjuvant have, in each case, demonstrated protection against parasite challenge in a proportion of vaccinated animals. Current work is investigating alternative antigen delivery systems in an attempt to improve the levels of protection. The genome architecture and protein-coding capacity of T. parva and T. annulata are remarkably similar. The major sporozoite surface antigen in both species and most of the schizont antigens are encoded by orthologous genes. The former have been shown to induce species cross-reactive neutralizing antibodies, and comparison of the schizont antigen orthologues has demonstrated that some of them display high levels of sequence conservation. Hence, advances in development of subunit vaccines against one parasite species are likely to be readily applicable to the other.

Livestock vaccinations translate into increased human capital and school attendance by girls

To fulfill the United Nation's Sustainable Development Goals (SDGs), it is useful to understand whether and how specific agricultural interventions improve human health, educational opportunity, and food security. In sub-Saharan Africa, 75% of the population is engaged in small-scale farming, and 80% of these households keep livestock, which represent a critical asset and provide protection against economic shock. For the 50 million pastoralists, livestock play an even greater role. Livestock productivity for pastoralist households is constrained by multiple factors, including infectious disease. East Coast fever, a tick-borne protozoal disease, is the leading cause of calf mortality in large regions of eastern and Southern Africa. We examined pastoralist decisions to adopt vaccination against East Coast fever and the economic outcomes of adoption. Our estimation strategy provides an integrated model of adoption and impact that includes direct effects of vaccination on livestock health and productivity outcomes, as well as indirect effects on household expenditures, such as child education, food, and health care. On the basis of a cross-sectional study of Kenyan pastoralist households, we found that vaccination provides significant net income benefits from reduction in livestock mortality, increased milk production, and savings by reducing antibiotic and acaricide treatments. Households directed the increased income resulting from East Coast fever vaccination into childhood education and food purchase. These indirect effects of livestock vaccination provide a positive impact on rural, livestock-dependent families, contributing to poverty alleviation at the household level and more broadly to achieving SDGs.

In Vitro Screening of the Open-Source Medicines for Malaria Venture Malaria Box Reveals Novel Compounds with Profound Activities against Theileria annulata Schizonts

Intracellular schizonts of the apicomplexans Theileria annulata and Theileria parva immortalize bovine leukocytes and thereby cause fatal diseases. The hydroxynaphthoquinone buparvaquone is currently the only option for the treatment of theileriosis, and resistance development has been reported. It is therefore tempting to investigate the repurposing of compounds effective against related apicomplexan parasites, such as Plasmodium Here, we present the results of a screen of 400 compounds included in the open-access Medicines for Malaria Venture (MMV) malaria box on TaC12 cells, a macrophage-derived cell line immortalized by T. annulata schizonts. Using a combination of the classical alamarBlue vitality assay and a recently developed quantitative reverse transcriptase real-time PCR method based on the Theileria TaSP gene, we have identified 5 compounds, characterized their effects on the ultrastructure of TaC12 cells, and investigated whether they easily induce resistance formation. Two compounds, the quinolinols MMV666022 and MMV666054, have 50% inhibitory concentrations (IC50s) of 0.5 and 0.2 μM on TaC12 cells and 5.3 and 5.2 μM on BoMac cells, respectively. Thus, with therapeutic indexes of 11 and 18, they represent promising leads for further development of antitheilerial chemotherapeutics.

Co-infections determine patterns of mortality in a population exposed to parasite infection

Many individual hosts are infected with multiple parasite species, and this may increase or decrease the pathogenicity of the infections. This phenomenon is termed heterologous reactivity and is potentially an important determinant of both patterns of morbidity and mortality and of the impact of disease control measures at the population level. Using infections with Theileria parva (a tick-borne protozoan, related to Plasmodium) in indigenous African cattle [where it causes East Coast fever (ECF)] as a model system, we obtain the first quantitative estimate of the effects of heterologous reactivity for any parasitic disease. In individual calves, concurrent co-infection with less pathogenic species of Theileria resulted in an 89% reduction in mortality associated with T. parva infection. Across our study population, this corresponds to a net reduction in mortality due to ECF of greater than 40%. Using a mathematical model, we demonstrate that this degree of heterologous protection provides a unifying explanation for apparently disparate epidemiological patterns: variable disease-induced mortality rates, age-mortality profiles, weak correlations between the incidence of infection and disease (known as endemic stability), and poor efficacy of interventions that reduce exposure to multiple parasite species. These findings can be generalized to many other infectious diseases, including human malaria, and illustrate how co-infections can play a key role in determining population-level patterns of morbidity and mortality due to parasite infections.

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.

A quantitative reverse-transcriptase PCR assay for the assessment of drug activities against intracellular Theileria annulata schizonts

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Quantitative RT real time PCR was used to assess metabolic impairment of Theileria schizonts.

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The method was validated with buparvaquone.

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Buparvaquone acts directly and rapidly on the parasite within 1 h of treatment.

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Electron microscopy confirmed these findings.

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A series of anti-parasitic compounds and antibiotics acted primarily on the host cells.

Intracellular schizonts of the apicomplexans Theileria annulata and Theileria parva immortalize bovine leucocytes thereby causing fatal immunoproliferative diseases. Buparvaquone, a hydroxynaphthoquinone related to parvaquone, is the only drug available against Theileria. The drug is only effective at the onset of infection and emerging resistance underlines the need for identifying alternative compounds. Current drug assays employ monitoring of proliferation of infected cells, with apoptosis of the infected host cell as a read-out, but it is often unclear whether active compounds directly impair the viability of the parasite or primarily induce host cell death. We here report on the development of a quantitative reverse transcriptase real time PCR method based on two Theileria genes, tasp and tap104, which are both expressed in schizonts. Upon in vitro treatment of T. annulata infected bovine monocytes with buparvaquone, TaSP and Tap104 mRNA expression levels significantly decreased in relation to host cell actin already within 4 h of drug exposure, while significant differences in host cell proliferation were detectable only after 48–72 h. TEM revealed marked alterations of the schizont ultrastructure already after 2 h of buparvaquone treatment, while the host cell remained unaffected. Expression of TaSP and Tap104 proteins showed a marked decrease only after 24 h. Therefore, the analysis of expression levels of mRNA coding for TaSP and Tap104 allows to directly measuring impairment of parasite viability. We subsequently applied this method using a series of compounds affecting different targets in other apicomplexan parasites, and show that monitoring of TaSP- and Tap104 mRNA levels constitutes a suitable tool for anti-theilerial drug development.

The role of nuclear technologies in the diagnosis and control of livestock diseases--a review

Nuclear and nuclear-related technologies have played an important role in animal health, particularly in relation to disease diagnosis and characterization of pathogenic organisms. This review focuses primarily on how and where nuclear technologies, both non-isotopic and isotopic methods, have made their impact in the past and where it might be expected they could have an impact in the future. The review outlines the extensive use of radiation attenuation in attempts to create vaccines for a multiplicity of pathogenic organisms and how the technology is being re-examined in the light of recent advances in irradiation techniques and cryopreservation/lyophilization that might obviate some of the problems of maintenance of viable, attenuate vaccines and their transport and use in the field. This approach could be used for a number of parasitic diseases where vaccination has been problematic and where investigations into the development of molecular vaccines have still failed to deliver satisfactory candidates for generating protective immune responses. Irradiation of antigens or serum samples also has its uses in diagnosis, especially when the samples need to be transported across international boundaries, or when handling the pathogens in question when carrying out a test presents serious health hazards to laboratory personnel. The present-day extensive use of enzyme immunoassays and molecular methods (e.g., polymerase chain reaction) for diagnosis and characterization of animal pathogens has its origins in the use of isotope-labeled antigens and antibodies. These isotopic techniques that included the use of 75Se, 32P, 125I, and 35S isotopes enabled a level of sensitivity and specificity that was hitherto unrealized, and it is prescient to remind ourselves of just how successful these technologies were, in spite of their infrequent use nowadays. Finally, the review looks at the potential for stable isotope analysis for a variety of applications--in the tracking of animal migrations, where the migrant are potential carriers of transboundary animal diseases, and where it would be useful to determine the origins of the carrier, e.g., Highly Pathogenic Avian Influenza and its dissemination by wild water fowl. Other applications could be in monitoring sequestered microbial culture (e.g., rinderpest virus) where in the case of accidental or deliberate release of infective culture it would be possible to identify the laboratory from which the isolate originated.

Progress towards understanding the immunobiology of Theileria parasites

The pathogenic Theileria species Theileria parva and T. annulata infect bovine leukocytes and erythrocytes causing acute, often fatal lymphoproliferative diseases in cattle. The parasites are of interest not only because of their economic importance as pathogens, but also because of their unique ability to transform the leukocytes they infect. The latter property allows parasitized leukocytes to be cultured as continuously growing cell lines in vitro, thus providing an amenable in vitro system to study the parasite/host cell relationship and parasite-specific cellular immune responses. This paper summarizes important advances in knowledge of the immunobiology of these parasites over the last 40 years, focusing particularly on areas of relevance to vaccination.

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.

Expression analysis of the Theileria parva subtelomere-encoded variable secreted protein gene family

Background

The intracellular protozoan parasite Theileria parva transforms bovine lymphocytes inducing uncontrolled proliferation. Proteins released from the parasite are assumed to contribute to phenotypic changes of the host cell and parasite persistence. With 85 members, genes encoding subtelomeric variable secreted proteins (SVSPs) form the largest gene family in T. parva. The majority of SVSPs contain predicted signal peptides, suggesting secretion into the host cell cytoplasm.

Methodology/Principal Findings

We analysed SVSP expression in T. parva-transformed cell lines established in vitro by infection of T or B lymphocytes with cloned T. parva parasites. Microarray and quantitative real-time PCR analysis revealed mRNA expression for a wide range of SVSP genes. The pattern of mRNA expression was largely defined by the parasite genotype and not by host background or cell type, and found to be relatively stable in vitro over a period of two months. Interestingly, immunofluorescence analysis carried out on cell lines established from a cloned parasite showed that expression of a single SVSP encoded by TP03_0882 is limited to only a small percentage of parasites. Epitope-tagged TP03_0882 expressed in mammalian cells was found to translocate into the nucleus, a process that could be attributed to two different nuclear localisation signals.

Conclusions

Our analysis reveals a complex pattern of Theileria SVSP mRNA expression, which depends on the parasite genotype. Whereas in cell lines established from a cloned parasite transcripts can be found corresponding to a wide range of SVSP genes, only a minority of parasites appear to express a particular SVSP protein. The fact that a number of SVSPs contain functional nuclear localisation signals suggests that proteins released from the parasite could contribute to phenotypic changes of the host cell. This initial characterisation will facilitate future studies on the regulation of SVSP gene expression and the potential biological role of these enigmatic proteins.

The biological and practical significance of antigenic variability in protective T cell responses against Theileria parva

The evolution of antigenically distinct pathogen strains that fail to cross-protect is well documented for pathogens controlled primarily by humoral immune responses. Unlike antibodies, which recognise native proteins, protective T cells can potentially recognise epitopes in a variety of proteins that are not necessarily displayed on the pathogen surface. Moreover, individual hosts of different MHC genotypes generally respond to different sets of epitopes. It is therefore less easy to envisage how strain restricted immunity can arise for pathogens controlled by T cell responses, particularly in antigenically complex parasites. Nevertheless, strain restricted immunity is clearly a feature of a number of parasitic infections, where immunity is known to be mediated by T cell responses. One such parasite is Theileria parva which induces potent CD8 T cell responses that play an important role in immunity. CD8 T cells specific for parasitized lymphoblasts exhibit strain specificity, which appears to correlate with the ability of parasite strains to cross-protect. Studies using recently identified T. parva antigens recognised by CD8 T cells have shown that the strain restricted nature of immunity is a consequence of the CD8 T cell response in individual animals being focused on a limited number of dominant polymorphic antigenic determinants. Responses in animals of different MHC genotypes are often directed to different parasite antigens, indicating that, at the host population level, a larger number of parasite proteins can serve as targets for the protective T cell response. Nevertheless, the finding that parasite strains show overlapping antigenic profiles, probably as a consequence of sexual recombination, suggests that induction of responses to an extended but limited set of antigens in individual animals may overcome the strain restricted nature of immunity.