The effect of dose and line on immunisation of cattle with lymphoblastoid cells infected with Theileria annulata

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.

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.

Genetic exchange and sub-structuring in Theileria annulata populations

Tropical theileriosis, caused by the tick-transmitted protozoan Theileria annulata, is a major disease of cattle in many regions of the developing world. Development and deployment of current and novel control strategies should take into account the potential diversity of parasite populations and therefore it is important that the nature and basis for this genetic variation is investigated and quantified. The recently completed genome sequence of T. annulata provided an opportunity to develop a panel of genetic markers for population studies. Bioinformatic screening of the genome sequence identified micro- and mini-satellite loci, which were PCR amplified from a series of diverse parasite stocks in order to characterise their polymorphism and determine their species-specificity. A panel of 10 polymorphic markers was then selected for population genetic studies and used to genotype both cloned and uncloned isolates maintained as cell lines of T. annulata isolated from different countries. Uncloned isolates comprised a multiplicity of genotypes, while cloned isolates showed evidence of a single haploid genome. Population genetic analysis revealed a high level of genotypic diversity both between and within countries, as measured by the number of distinct multilocus genotypes. Based on measures of genetic differentiation (F(ST) and Nei's genetic distance), the parasite populations are geographically sub-structured and these measurements positively correlate with geographical distance. To investigate whether genetic exchange occurs at random and the populations are panmictic, the level of linkage disequilibrium was measured using the index of association across all loci. Linkage disequilibrium was observed when isolates from all countries were treated as a single population but when the isolates from Tunisia were analysed separately, linkage equilibrium was observed.

Impact of field vaccination with a Theileria annulata schizont cell culture vaccine on the epidemiology of tropical theileriosis

Tropical theileriosis, caused by Theileria annulata, is an important tick-borne disease of cattle. A cell culture attenuated vaccine has been developed in our laboratory by long-term in vitro propagation of the schizont stage of the parasite. A longitudinal study was conducted at selected farms housing indigenous, cross-bred and exotic animals to investigate the effect of vaccination on the epidemiology of the disease. A total of 120 animals in 4 age groups were vaccinated with the vaccine before the onset of disease season. An equal number of age-matched animals were kept as controls at the same sites. Animals were monitored for 14 months at monthly intervals. The 97.5% vaccinated animals showed a rise in antibody titres 1 month post-vaccination, as determined by single dilution ELISA. The 78.3% of non-vaccinated animals became sero-positive over the period of observation. Mean antibody titres were significantly higher in vaccinated than non-vaccinated animals. Cross-bred animals showed higher antibody titres followed by exotic and indigenous animals in both the vaccinated and non-vaccinated groups. However, the antibody titres in animals of different ages were similar. The 36.7% vaccinated and 64.2% non-vaccinated animals became carriers (<0.5% piroplasms in erythrocytes) during the observation period. Clinical cases of theileriosis were recorded only in the non-vaccinated group suggesting that vaccinated animals were sufficiently immune to withstand field tick challenge for at least 14 months.

Vaccination against tropical theileriosis

Theileria annulata, the cause of tropical theileriosis is propagated in cattle with stage-to-stage transmission by Hyalomma ticks. Three stages in the life cycle of the parasite--tick-derived sporozoites, intramononuclear schizonts, and erythrocytic merozoites--infect cattle. When cattle are inoculated with schizont-infected cells, the parasite is transferred from the donor cell to the recipient. The main pathological damage in cattle is induced by the schizont stage. Each development stage of T. annulata elicits a specific immune response. Schizont-infected lymphoid cells can be grown indefinitely in culture and prolonged cultivation results in loss of virulence. Blood-derived schizonts induce stronger immunity than culture-derived schizonts, which suggests that restrictions on the parasite population or antigenic variation occur during prolonged cultivation. The duration of immunity following sporozoite or schizont infections has not yet been determined, but does not appear to be lifelong. The attenuated, culture-derived anti-theileria vaccine proved to be safe and effective in prevention of field theileriosis in large enzootic areas.

Culture-derived parasites in vaccination of cattle against tick-borne diseases

The major economically important tick-borne diseases of cattle are theileriosis, babesiosis, anaplasmosis, and cowdriosis. Culture-derived attenuated schizonts of Theileria annulata have proved to be safe for all types of cattle and they protect against tick-borne theileriosis. T. parva was also successfully grown in vitro; however, inoculation of cattle with allogeneic schizont-infected cells resulted in rejection and destruction of the parasites together with the host cells. The number of schizont-infected cells needed for immunization is greater than for T. annulata theileriosis. Culture-propagated Babesia bovis and B. bigemina were used for large scale vaccination in the field. An avirulent population of Babesia spp. was obtained by in vitro cloning; inoculation of cattle did not induce clinical babesiosis, but produced specific antibodies. Culture-derived exoantigens of Babesia spp. proved to be completely safe for cattle, however, they conferred less protection than live parasites. Cell-cultured Cowdria ruminantium was highly infective for susceptible animals but, attenuated in vitro, could offer a potential source for vaccination. Anaplasma marginale, successfully grown in tick cell culture, may be developed for vaccines. Factors that should be considered in the developing of vaccines against tick-borne diseases include: the protective immune response to the pathogenic parasite developmental stages, virulence, immunological strain differences, and antigenic variations in cattle and in culture.

Live vaccines against hemoparasitic diseases in livestock

Live vaccines against hemoparasitic diseases in livestock are based on parasites derived from culture (Theileria annulata), from blood of infected animals (Babesia bovis, Babesia bigemina, Anaplasma centrale, (attenuated) Anaplasma marginale and Cowdria ruminantium), and from ticks (Theileria parva). The T. annulata attenuated cultured schizont vaccine is safe for all varieties of cattle. Blood derived vaccines are recommended mainly for young cattle, the age limit varying with the different vaccines and breeds of cattle. In older animals, monitoring of the individual response is needed. Immunization against T. parva requires simultaneous or postinoculation chemotherapy. The potential for accidental transmission of disease agents exists with all blood derived vaccines. Various degrees of resistance to field infection have been reported in animals immunized with live vaccines. Nevertheless, all of them engender a level of protection against natural challenge that justifies their use in field vaccination. Chemotherapy or chemoprophylaxis may prevent establishment of infection with the vaccinal parasites, and thus may interfere with elaboration of immunity. Outbreaks of disease in vaccinated herds, caused by antigenic variants among the tick-transmitted parasites, have been observed mainly in Babesia infections. In recent years, the main efforts towards improvement of live vaccines have been in the direction of replacing blood- and tick-derived parasites by those cultured in vitro under controlled standardized conditions.

Theileria annulata sporozoite targets

Bovine peripheral blood mononuclear cells (PBM) infected in vitro with Theileria annulata sporozoites have previously been characterized as MHC class II+ mature macrophages. The ability of T. annulata sporozoites to infect different subpopulations of MHC class II+ bovine monocytes was investigated. Cells were labelled with monocyte specific monoclonal antibodies (MoAb) and isolated using magnetic cell sorting (MACS). Sporozoites infected both immature and mature monocytes, but more readily infected the mature population. A potential ligand for sporozoite entry is the elastin receptor which is expressed mainly on the immature population of monocytes and not on B cells or T cells. T. annulata sporozoites infected elastin receptor positive and negative cell populations equally well. Infected immature cells lost the expression of elastin receptors and the immature marker, subsequently expressing the mature marker. All monocytes lost the expression of CD14 (the LPS receptor) upon infection with sporozoites. The infection of specific populations and subsequent alterations in phenotype may alter the function of these cells and play an important role in disease pathogenesis.

Common and stage-specific antigens of Theileria annulata

Western blot analysis of Theileria annulata antigens was carried out using sera collected from cattle which had been immunised and challenged with either T. annulata sporozoites or schizont-infected cells. Three antigens between 71 and 73 kDa proved to be common to the three stages of parasite studied: sporozoites, schizonts and piroplasms. An antigen was found at 32 kDa which was specific to T. annulata piroplasms. Results were reproducible using sera from Morocco and the UK. At least one of the proteins at 71-73 kDa, but not that at 32 kDa were also recognised by sera from animals infected with Babesia species.

Tropical theileriosis in Bos taurus and Bos taurus cross Bos indicus calves: response to infection with graded doses of sporozoites of Theileria annulata

This work extends basic knowledge of tropical theileriosis in taurine and crossbred cattle. Infection of Bos taurus and Bos taurus cross Bos indicus (Sahiwal) calves with graded doses of sporozoites of Theileria annulata (Hissar), an Indian stock of the parasite, showed the following to be dose dependent in both cattle types: the time to appearance and population size of macroschizonts, microschizonts and piroplasms, time and severity of pyrexia, anaemia manifested by erythrocyte counts and haematocrit. All infections were accompanied by a prompt and severe panleucopenia. This effect was dose related in both the taurine and the Sahiwal crossbred calves. Lymphocyte counts returned to preinfection levels in the blood of animals which recovered, but death from theileriosis was characteristically accompanied by a persistent and severe lymphocytopenia. Flow cytometry using monoclonal antibodies to bovine mononuclear cells was used to identify the lymphocyte subsets involved in lymphocytopenia. The outcome of infection was dose dependent in the crossbred calves but not in taurine calves. Although the results obtained did not differ qualitatively between the two cattle types, they provided some preliminary evidence for resistance to tropical theileriosis in Sahiwal crossbred calves.

The epidemiology of tropical theileriosis (Theileria annulata infection in cattle) in an endemic area of Morocco

A longitudinal study of tropical theileriosis was performed on 12 farms in the Doukkala region of Morocco during 1990. Adult Hyalomma detritum detritum were collected between March and early October and a peak in numbers was observed at the end of June. Nineteen percent (24/127) were infected with Theileria species and, amongst these, over 50% had five or more sporoblasts in their salivary glands (range 1-151). Hyalomma d detritum larvae and nymphs were found on cattle between September and early December with the highest numbers in late October. The prevalence of T. annulata piroplasm carriers at the beginning of the year was 48.5% (47 positive out of 97) and there were 14 new infections during the disease season (March to September) of which five developed into clinical cases. The incidence rates of new infection and clinical disease were 0.156 and 0.056 per animal-season, respectively. Differences were observed between age categories of cattle in both tick and parasite infections. A significantly lower number of adult H.d. detritum were collected from calves than from adult cattle. The prevalences of piroplasm carriers before the disease season were 0%, 36% and 76%, respectively, in (a) calves which had been born since the previous disease season, (b) calves born before then and (c) adults. However, the incidence rates of infection and disease for uninfected animals in the two categories of calves were approximately the same: 0.299 and 0.378 new infections, and 0.085 and 0.126 clinical cases per animal-season for (a) and (b), respectively. The date predicted for the appearance of adult H.d. detritum, based on published tick development times and local temperature records, was within 2 weeks of the study visit when the highest number of adults were collected from cattle. However, the date predicted for the appearance of larvae was 6 weeks earlier than the observed peak populations and may indicate that H.d. detritum delays either egg laying in the summer or larval host searching in the autumn.

Anti-lymphocyte antibodies generated in animals immunised with Theileria annulata-infected cells

Complement fixing antibodies were measured in sera from animals immunised with either Theileria annulata sporozoites or autologous or allogeneic schizont-infected mononuclear cells using a complement-mediated micro-cytotoxicity test. The test demonstrated the presence of anti-lymphocyte antibodies in allogeneic cell-immunised animals, which were not detectable in autologous cell- or sporozoite-immunised animals; also that these antibodies were directed to T. annulata-infected and (MHC) class I antigens. Their potential importance in repeated immunisations is discussed.