Vaccination against tropical theileriosis

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.

Comparative evaluation of cell-mediated immune response in calves immunized with live-attenuated and killed Theileria annulata vaccines

Tropical theileriosis is a tick-borne disease caused by the protozoan Theileria annulata and transmitted by numerous species of Ixodid ticks of the genus Hyalomma. The main clinical signs are fever, lymphadenopathy, and anemia responsible for heavy economic losses, including mortality, morbidity, vaccination failure, and treatment cost. Development of poor cell-mediated immunity (CMI) has been observed in the case of many bovine pathogens (bacteria, viruses, and parasites). Quantification of CMI is a prerequisite for evaluating vaccine efficacy against theileriosis caused by T. annulata. The current study evaluated the CMI in calves administered with two types of T. annulata vaccine (live attenuated and killed). We prepared a live attenuated T. annulata vaccine by attenuation in a rabbit model and also prepared killed vaccine from non-attenuated T. annulata. For the evaluation of immune response in experimental groups including control, 20 calves were divided into four different groups (A, B, C, and D). They were either inoculated subcutaneously with live rabbit-propagated-Theileria-infected RBCs (5 × 106) (group A) or with killed T. annulata vaccine (2 × 109 schizonts) with Freund's adjuvant (group B), along with an infected group (group C) and a healthy control group (group D). The protection of vaccinated calves was estimated with challenge infection. Our results showed that with a single shot of live-attenuated and killed vaccine with a booster dose elicited cell-mediated immune responses in immunized calves. We observed a significant elevation in CD4 + and CD8 + T cells in immunized calves. A significant difference in the CD8 + T cell response between the post-challenge stage of killed and live vaccine (p < 0.0001) was observed, whereas no other difference was found at both pre- and post-immunization stages. A similar finding was recorded for the CD4 + T cells at a post-challenge stage, where a significant difference was seen between killed and live vaccine (p < 0.0001). Another significant difference was observed between the CD8 + T cells and CD4 + T cells at the post-challenge stage in the live vaccine group, where there was a significantly higher induction of CD4 + T cell response (p < 0.0001).

Theileria annulata: Its Propagation in Rabbits for the Attenuation of Piroplasms in Cross-Bred Calves

Tropical theileriosis caused by the protozoan; Theileria annulata is a tick-borne disease (TBD) transmitted by ticks of genus Hyalomma; is clinically characterized by fever, anemia, and lymphadenopathy; and is responsible for heavy economic losses in terms of high morbidity and mortality rates with reduced production. Infected red blood cells of T. annulata were inoculated into rabbits intraperitoneally, and propagation of T. annulata has been investigated. The current study has shown an association between induced tropical theileriosis and variation of body temperature in rabbits. A significant rise in temperature (39.92 ± 0.33 °C) was seen on day 8 onwards, with the maximum temperature (40.27 ± 0.44 °C) on day 14 post-inoculation. In the current study, in vivo trials in susceptible cross-bred calves to investigate the attenuation and comparison with the infected group were also conducted. All the infected calves (n = 5) showed a significant rise in temperature (40.26 ± 0.05 °C) on day 10 onwards, with the maximum temperature (40.88 ± 0.05 °C) on day 16. The temperature of inoculated calves increased gradually post-inoculation, but the difference was not significant. A maximum parasitemia of 20% was observed in infected calves, but no piroplasm parasitemia was observed in inoculated calves. The prescapular lymph nodes of infected calves were enlarged, while the lymph nodes of inoculated calves remained normal throughout the trial. Analysis of clinical and parasitological responses of infected and inoculated calves showed a significant difference (p ≤ 0.05) in terms of temperature, parasitemia, and lymph node scoring between two groups. The current study was primarily aimed to attenuate T. annulata in rabbit and to check its virulence in susceptible calves. It is concluded that propagation of Theileria annulata in rabbits made it attenuated. Rabbit can be used as an in vivo model to weaken the virulence of T. annulata.

Prevention of tick-borne diseases: challenge to recent medicine

Abstract

Ticks represent important vectors and reservoirs of pathogens, causing a number of diseases in humans and animals, and significant damage to livestock every year. Modern research into protection against ticks and tick-borne diseases focuses mainly on the feeding stage, i.e. the period when ticks take their blood meal from their hosts during which pathogens are transmitted. Physiological functions in ticks, such as food intake, saliva production, reproduction, development, and others are under control of neuropeptides and peptide hormones which may be involved in pathogen transmission that cause Lyme borreliosis or tick-borne encephalitis. According to current knowledge, ticks are not reservoirs or vectors for the spread of COVID-19 disease. The search for new vaccination methods to protect against ticks and their transmissible pathogens is a challenge for current science in view of global changes, including the increasing migration of the human population.

Highlights

• Tick-borne diseases have an increasing incidence due to climate change and increased human migration

• To date, there is no evidence of transmission of coronavirus COVID-19 by tick as a vector

• To date, there are only a few modern, effective, and actively- used vaccines against ticks or tick-borne diseases

• Neuropeptides and their receptors expressed in ticks may be potentially used for vaccine design

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.

Ticks and tick-borne diseases of bovines in a smallholder livestock context: The Pakistani example

Ticks and tick-borne diseases (TTBDs) substantially affect the health and production of ruminants, particularly in resource-poor, small-scale farming systems worldwide. However, to date, there has been no critical appraisal of the current state of knowledge of TTBDs in such farming systems. In this article, we systematically reviewed the situation in Pakistan-as an example of a country that is highly reliant on agriculture to sustain its economy, particularly smallholder livestock farms, which are continually faced with challenges associated with TTBDs. The main aims of this review were to gain improved insights into the current status of TTBDs in small-scale farming systems, and to identify knowledge gaps, through the systematic evaluation of published literature on this topic from Pakistan, and to recommend future research directions. We searched publicly available literature from three databases (i.e. Web of Science, Google Scholar, and PubMed) on bovine TTBDs in Pakistan. Of 11,224 published studies identified, 185 were eligible for inclusion; these studies were published between August 1947 and June 2021. A critical analysis of these 185 studies revealed that the diagnosis of ticks and tick-borne pathogens (TBPs) in Pakistan has been based largely on the use of traditional methods (i.e. 'morpho-taxonomy'). At least 54 species of tick have been recorded, most of which belong to the genera Haemaphysalis, Hyalomma and Rhipicephalus. The prevalence of ticks was higher, particularly in young, exotic and crossbred female cattle, during the summer season. Major TBPs include species of Anaplasma, Babesia and Theileria, with prevalences being higher in cattle than buffaloes. Additionally, pathogens of zoonotic potential, including species of Anaplasma, Borrelia, the Crimean-Congo haemorrhagic fever virus, Coxiella, Ehrlichia and Rickettsia, have been recorded in both tick and bovine populations. Information on risk factors, spatial-temporal distribution, genetic diversity, and control of ticks and TBPs is limited, the vector potential of ticks and the distribution patterns of ticks and TBPs in relation to climate remains largely unexplored. Future research should focus on addressing these knowledge gaps and the key challenges of poverty, food security and disease outbreaks in a small-scale livestock farming context in order to provide sustainable, environment-friendly control measures for TTBDs.

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.

Targeted Next-Generation Sequencing and Informatics as an Effective Tool to Establish the Composition of Bovine Piroplasm Populations in Endemic Regions

Protists of the genera Babesia and Theileria (piroplasms) cause some of the most prevalent and debilitating diseases for bovines worldwide. In this study, we established and used a next-generation sequencing-informatic approach to explore the composition of Babesia and Theileria populations in cattle and water buffalo in a country (Pakistan) endemic for these pathogens. We collected individual blood samples from cattle (n = 212) and water buffalo (n = 154), extracted genomic DNAs, PCR-amplified the V4 hypervariable region of 18S small subunit rRNA gene from piroplasms, sequenced amplicons using Illumina technology, and then analysed data using bioinformatic platforms. The results revealed piroplasms in 68.9% (252/366) samples, with overall occurrence being markedly higher in cattle (85.8%) than in water buffaloes (45.5%). Babesia (B.) occultans and Theileria (T.) lestoquardi-like species were recorded for the first time in Pakistan, and, overall, T. annulata was most commonly detected (65.8%) followed by B. bovis (7.1%), B. bigemina (4.4%), and T. orientalis (0.5%), with the genetic variability within B. bovis being pronounced. The occurrence and composition of piroplasm species varied markedly across different agro-ecological zones. The high detection of T. annulata in asymptomatic animals suggested a relatively high level of endemic stability of tropical theileriosis in the bovine population.

Serum-free in vitro cultivation of Theileria annulata and Theileria parva schizont-infected lymphocytes

Theileriosis is a tick-borne disease caused by intracellular protozoa of the genus Theileria. The most important species in cattle are Theileria annulata and Theileria parva. Both species transform leucocyte host cells, resulting in their uncontrolled proliferation and immortalization. Vaccination with attenuated T. annulata-infected cell lines is currently the only practical means of inducing immunity in cattle. Culture media for Theileria spp. typically contain 10%-20% foetal bovine serum (FBS). The use of FBS is associated with several disadvantages, such as batch-to-batch variation, safety and ethical concerns. In this study, the suitability of serum-free media for the cultivation of Theileria-transformed cell lines was examined. Three commercial serum-free media (HL-1, ISF-1 and Hybridomed DIF 1000) were evaluated for their ability to support growth of the T. annulata A288 cell line. The generation doubling times were recorded for each medium and compared with those obtained with conventional FBS-containing RPMI-1640 medium. ISF-1 gave the shortest generation doubling time, averaging 35.4 ± 2.8 hr, significantly shorter than the 52.2 ± 14.9 hr recorded for the conventional medium (p = .0011). ISF-1 was subsequently tested with additional T. annulata strains. The doubling time of a Moroccan strain was significantly increased (65.4 ± 15.9 hr) compared with the control (47.7 ± 7.5 hr, p = .0004), whereas an Egyptian strain grew significantly faster in ISF-1 medium (43.4 ± 6.5 hr vs. 89.3 ± 24.8 hr, p = .0001). The latter strain also showed an improved generation doubling time of 73.7 ± 21.9 hr in an animal origin-free, serum-free, protein-free medium (PFHM II) compared with the control. Out of four South African T. parva strains and a Theileria strain isolated from roan antelope (Hippotragus equinus), only one T. parva strain could be propagated in ISF-1 medium. The use of serum-free medium may thus be suitable for some Theileria cell cultures and needs to be evaluated on a case-by-case basis. The relevance of Theileria cultivation in serum-free media for applications such as vaccine development requires further examination.

Optimization of a suspension culture for a Theileria annulata-infected bovine cell line

Theileria annulata schizont transformed bovine lymphocytes show the feature of permanent proliferation in vitro culture. In this study, we optimized a suitable culture medium for transformed cells to ensure a high yield of quality cells in suspension culture. As the basis for the optimized medium, we combined 75% Gibco (GB) and 25% RPMI-1640 medium. Glucose, lactic acid, ammonia, growth factors and several kinds of amino acids at specific concentrations play important roles in maintaining the maximum growth rate and the quality of cells. The metabolic flow of 17 amino acids, glucose and nutrients was determined with high-performance liquid chromatography (HPLC) and cell viability analysis. The genetic stability of the TaSP and TaSE genes at different passages of the cell line in suspension culture was determined using PCR amplification. The optimal concentrations or tolerated levels of glucose, lactic acid and ammonia were 10-14, 2-5.5 and 3.5-5.5 mmol/L, respectively. Our data demonstrated that the potential utility of the medium optimized here to yield high quality cells compared with basal (normally used) medium. The medium also facilitated the easy maintenance of transformed cells with high yields and excellent quality for in vitro studies. This study also provides insight into the processes of optimization and vaccine development.

A review of reverse vaccinology approaches for the development of vaccines against ticks and tick borne diseases

The field of reverse vaccinology developed as an outcome of the genome sequence revolution. Following the introduction of live vaccinations in the western world by Edward Jenner in 1798 and the coining of the phrase 'vaccine', in 1881 Pasteur developed a rational design for vaccines. Pasteur proposed that in order to make a vaccine that one should 'isolate, inactivate and inject the microorganism' and these basic rules of vaccinology were largely followed for the next 100 years leading to the elimination of several highly infectious diseases. However, new technologies were needed to conquer many pathogens which could not be eliminated using these traditional technologies. Thus increasingly, computers were used to mine genome sequences to rationally design recombinant vaccines. Several vaccines for bacterial and viral diseases (i.e. meningococcus and HIV) have been developed, however the on-going challenge for parasite vaccines has been due to their comparatively larger genomes. Understanding the immune response is important in reverse vaccinology studies as this knowledge will influence how the genome mining is to be conducted. Vaccine candidates for anaplasmosis, cowdriosis, theileriosis, leishmaniasis, malaria, schistosomiasis, and the cattle tick have been identified using reverse vaccinology approaches. Some challenges for parasite vaccine development include the ability to address antigenic variability as well the understanding of the complex interplay between antibody, mucosal and/or T cell immune responses. To understand the complex parasite interactions with the livestock host, there is the limitation where algorithms for epitope mining using the human genome cannot directly be adapted for bovine, for example the prediction of peptide binding to major histocompatibility complex motifs. As the number of genomes for both hosts and parasites increase, the development of new algorithms for pan-genomic mining will continue to impact the future of parasite and ricketsial (and other tick borne pathogens) disease vaccine development.

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.

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.

Resistance and susceptibility to a protozoan parasite of cattle—Gene expression differences in macrophages from different breeds of cattle

Cattle infected with the tick-borne protozoan, Theileria annulata, usually undergo severe morbidity, and mortality ensues in a high proportion of animals. However, we have shown that a Bos indicus breed, the Sahiwal, which originates in a T. annulata endemic area, is more resistant to the parasite. Although Sahiwals become infected, the breed exhibits fewer clinical signs and recovers from a dose of parasite which is fatal in the Holstein B. taurus breed. The Sahiwals have a significantly lower fever response, and lower levels of parasite than the Holsteins. One unusual feature of this disease is the production of acute phase proteins (APP), indicating that the parasite induces high systemic levels of pro-inflammatory cytokines. In the Holsteins there is prolonged production of the APP, alpha1-glycoprotein, which, in contrast, is only slightly elevated in the Sahiwals. As the parasite infects macrophages (mphi), our hypothesis is that the Sahiwals can control the excessive production of pro-inflammatory cytokines in response to infection, and that this control is expressed at the level of the mphi. We thus reasoned that the genes underlying the observed difference in resistance to tropical theileriosis, might be identified by investigating gene expression differences in mphi from both breeds. It is possible that relevant polymorphisms might in themselves result in gene expression differences, so initially we targeted likely candidates. However, we detected no differences in expression of the pro-inflammatory cytokines, tumour necrosis factor-alpha (TNFalpha), interleukin-1beta (IL-1beta) or IL-6, in infected mphi. As it is more likely that polymorphisms in candidate genes influence the expression of other genes involved in interrelated pathways, we undertook a more global approach. We designed a bovine mphi specific cDNA microarray, which contains representatives of 5000 different genes expressed in mphi, and investigated the transcriptional responses of mphi from both breeds in response to a variety of stimuli, including infection with T. annulata. Our results indicate that there are fundamental differences in gene expression in mphi from both breeds in the way they respond to infection, and even in their pre-infection resting state.

Current status of veterinary vaccines

The major goals of veterinary vaccines are to improve the health and welfare of companion animals, increase production of livestock in a cost-effective manner, and prevent animal-to-human transmission from both domestic animals and wildlife. These diverse aims have led to different approaches to the development of veterinary vaccines from crude but effective whole-pathogen preparations to molecularly defined subunit vaccines, genetically engineered organisms or chimeras, vectored antigen formulations, and naked DNA injections. The final successful outcome of vaccine research and development is the generation of a product that will be available in the marketplace or that will be used in the field to achieve desired outcomes. As detailed in this review, successful veterinary vaccines have been produced against viral, bacterial, protozoal, and multicellular pathogens, which in many ways have led the field in the application and adaptation of novel technologies. These veterinary vaccines have had, and continue to have, a major impact not only on animal health and production but also on human health through increasing safe food supplies and preventing animal-to-human transmission of infectious diseases. The continued interaction between animals and human researchers and health professionals will be of major importance for adapting new technologies, providing animal models of disease, and confronting new and emerging infectious diseases.

Economical impact of tropical theileriosis in the Cappadocia region of Turkey

This study was initiated to investigate the economical impact of vaccination against tropical theileriosis in cattle in Cappadocia in Turkey. A total of 554 vaccinated and non-vaccinated animals were monitored for Theileria annulata infection using microscopic examination serology by measuring the antibody response of the animals by the indirect immunofluorescence antibody test (IFAT). The prevalence of T. annulata infection, morbidity and mortality were significantly higher in unvaccinated than in vaccinated cattle, whereas the seropositivity was significantly lower in the unvaccinated group. Acute tropical theileriosis cases were diagnosed in 156 of 554 (27.61%) cattle, and 86 of 156 (56.21%) died from the disease. The total economic losses because of tropical theileriosis were estimated at US $598,133 for 2 years.

Attenuated vaccines for tropical theileriosis, babesiosis and heartwater: the continuing necessity

Overwhelming evidence has accumulated of the effectiveness of immunization with live attenuated vaccines to control tick-borne diseases of livestock. Despite several disadvantages, vaccination with live attenuated organisms against tropical theileriosis, babesiosis and possibly heartwater constitutes one of the most cost-effective intervention strategies. Although great advances have been made through genomics and proteomics research, this has not yet translated into effective non-living vaccines. As a result, there is a continuing necessity to use available live vaccines in tick and tick-borne disease-control strategies adapted to conditions prevailing in many parts of the world.