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).

Development of a dual vaccine against East Coast fever and lumpy skin disease

East Coast fever is an acute bovine disease caused by the apicomplexan parasite Theileria parva and is regarded as one of the most important tick-vectored diseases in Africa. The current vaccination procedure has many drawbacks, as it involves the use of live T. parva sporozoites. As a novel vaccination strategy, we have constructed the recombinant lumpy skin disease virus (LSDV) named LSDV-SODis-p67HA-BLV-Gag, encoding a modified form of the T. parva p67 surface antigen (p67HA), as well as the bovine leukemia virus (BLV) gag gene for the formation of virus-like particles (VLPs) to potentially enhance p67 immunogenicity. In place of the native sequence, the chimeric p67HA antigen has the human tissue plasminogen activator signal sequence and the influenza hemagglutinin A2 transmembrane domain and cytoplasmic tail. p67HA was detected on the surface of infected cells, and VLPs comprising BLV Gag and p67HA were produced. We also show that higher multiple bands observed in western blot analysis are due to glycosylation of p67. The two vaccines, pMExT-p67HA (DNA) and LSDV-SODis-p67HA-BLV-Gag, were tested for immunogenicity in mice. p67-binding antibodies were produced by vaccinated animals, with higher titers detected in mice vaccinated with the recombinant LSDV. This candidate dual vaccine warrants further testing in cattle.

Molecular characterization and population genetics of Theileria parva in Burundi's unvaccinated cattle: Towards the introduction of East Coast fever vaccine

Theileria parva (T. parva) is a protozoan parasite that causes East Coast fever (ECF). The disease is endemic in Burundi and is a major constraint to livestock development. In this study, the parasite prevalence in cattle in six regions namely; Northern, Southern, Eastern, Western, Central and North Eastern was estimated. Furthermore, the sequence diversity of p67, Tp1 and Tp2 genes was assessed coupled with the population genetic structure of T. parva using five satellite markers. The prevalence of ECF was 30% (332/1109) on microscopy, 60% (860/1431) on ELISA and 79% (158/200) on p104 gene PCR. Phylogenetic analysis of p67 gene revealed that only allele 1 was present in the field samples. Furthermore, phylogenetic analysis of Tp1 and Tp2 showed that the majority of samples clustered with Muguga, Kiambu and Serengeti and shared similar epitopes. On the other hand, genetic analysis revealed that field samples shared only two alleles with Muguga Cocktail. The populations from the different regions indicated low genetic differentiation (FST = 0.047) coupled with linkage disequilibrium and non-panmixia. A low to moderate genetic differentiation (FST = 0.065) was also observed between samples and Muguga cocktail. In conclusion, the data presented revealed the presence of a parasite population that shared similar epitopes with Muguga Cocktail and was moderately genetically differentiated from it. Thus, use of Muguga Cocktail vaccine in Burundi is likely to confer protection against T. parva in field challenge trials.

Immunization with one Theileria parva strain results in similar level of CTL strain-specificity and protection compared to immunization with the three-component Muguga cocktail in MHC-matched animals

BACKGROUND

The tick-borne protozoan parasite Theileria parva causes a usually fatal cattle disease known as East Coast fever in sub-Saharan Africa, with devastating consequences for poor small-holder farmers. Immunity to T. parva, believed to be mediated by a cytotoxic T lymphocyte (CTL) response, is induced following natural infection and after vaccination with a live vaccine, known as the Infection and Treatment Method (ITM). The most commonly used version of ITM is a combination of parasites derived from three isolates (Muguga, Kiambu 5 and Serengeti-transformed), known as the "Muguga cocktail". The use of a vaccine comprising several strains is believed to be required to induce a broad immune response effective against field challenge. In this study we investigated whether immunization with the Muguga cocktail induces a broader CTL response than immunization with a single strain (Muguga).

RESULTS

Four MHC haplotype-matched pairs of cattle were immunized with either the trivalent Muguga cocktail or the single Muguga strain. CTL specificity was assessed on a panel of five different strains, and clonal responses to these strains were also assessed in one of the MHC-matched pairs. We did not find evidence for a broader CTL response in animals immunized with the Muguga cocktail compared to those immunized with the Muguga strain alone, in either the bulk or clonal CTL analyses. This was supported by an in vivo trial in which all vaccinated animals survived challenge with a lethal dose of the Muguga cocktail vaccine stabilate.

CONCLUSION

We did not observe any substantial differences in the immunity generated from animals immunized with either Muguga alone or the Muguga cocktail in the animals tested here, corroborating earlier results showing limited antigenic diversity in the Muguga cocktail. These results may warrant further field studies using single T. parva strains as future vaccine candidates.

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.

Vector ecology of equine piroplasmosis

Equine piroplasmosis is a disease of Equidae, including horses, donkeys, mules, and zebras, caused by either of two protozoan parasites, Theileria equi or Babesia caballi. These parasites are biologically transmitted between hosts via tick vectors, and although they have inherent differences they are categorized together because they cause similar pathology and have similar morphologies, life cycles, and vector relationships. To complete their life cycle, these parasites must undergo a complex series of developmental events, including sexual-stage development in their tick vectors. Consequently, ticks are the definitive hosts as well as vectors for these parasites, and the vector relationship is restricted to a few competent tick species. Because the vector relationship is critical to the epidemiology of these parasites, we highlight current knowledge of the vector ecology of these tick-borne equine pathogens, emphasizing tick transmissibility and potential control strategies to prevent their spread.

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.

Tropical theileriosis is a leukaemia-like disease of cattle caused by the Apicomplexa parasite Theileria annulata. Live attenuated vaccines are used to control the mortality and morbidity of tropical theileriosis and each endemic country produces its own vaccine by isolating a virulent clinical isolate and then growing the infected and transformed macrophages for many months in the laboratory. With time, virulence is progressively lost, and loss is evaluated from time to time by injecting infected macrophages into calves and monitoring any resulting pathology. If the calves demonstrate clinical symptoms, in vitro culture of vaccine lines continues, and eventually attenuation is achieved after approximately two years. The process is empirical, and with time in culture the infected macrophage lines lose their vaccine potential such that when cattle are injected the immune response to the vaccine can be compromised. To circumvent these problems we engineered the rapid loss of a host macrophage virulence trait and obtained complete attenuation of dissemination of T. annulata–transformed macrophages when tested in an immune-compromised mouse model. This rational, rather than empirical, approach now allows injecting into calves Theileria-infected macrophages engineered for attenuation to evaluate the role of Theileria-infected macrophage dissemination in the pathology of tropical theileriosis.

Maternal antibody uptake, duration and influence on survival and growth rate in a cohort of indigenous calves in a smallholder farming system in western Kenya

The passive transfer of antibodies from dams to offspring via colostrum is believed to play an important role in protecting neonatal mammals from infectious disease. The study presented here investigates the uptake of colostrum by 548 calves in western Kenya maintained under smallholder farming, an important agricultural system in eastern Africa. Serum samples collected from the calves and dams at recruitment (within the first week of life) were analysed for the presence of antibodies to four tick-borne haemoparasites: Anaplasma marginale, Babesia bigemina, Theileria mutans and Theileria parva. The analysis showed that at least 89.33% of dams were seropositive for at least one of the parasites, and that 93.08% of calves for which unequivocal results were available showed evidence of having received colostrum. The maternal antibody was detected up until 21 weeks of age in the calves. Surprisingly, there was no discernible difference in mortality or growth rate between calves that had taken colostrum and those that had not. The results are also important for interpretation of serosurveys of young calves following natural infection or vaccination.

Ethnoknowledge of Bukusu community on livestock tick prevention and control in Bungoma district, western Kenya

ETHNOPHARMACOLOGICAL RELEVANCE

To date, nomadic communities in Africa have been the primary focus of ethnoveterinary research. The Bukusu of western Kenya have an interesting history, with nomadic lifestyle in the past before settling down to either arable or mixed arable/pastoral farming systems. Their collective and accumulative ethnoveterinary knowledge is likely to be just as rich and worth documenting.

AIM OF THE STUDY

The aim of the present study was to document indigenous knowledge of the Bukusu on the effect of livestock ticks and ethnopractices associated with their management. It was envisaged that this would provide a basis for further research on the efficacy of these practices that could also lead to the discovery of useful tick-control agents.

MATERIALS AND METHODS

Non-alienating, dialogic, participatory action research (PAR) and participatory rural appraisal (PRA) approaches involving 272 women and men aged between 18 and 118 years from the Bukusu community were used.

RESULTS

Ticks are traditionally classified and identified by colour, size, host range, on-host feeding sites, and habitat preference. Tick-associated problems recognised include kamabumba (local reference to East Coast fever, Anaplasmosis or Heartwater diseases transmitted by different species of livestock ticks) and general poor performance of livestock. Traditional methods of controlling ticks include handpicking, on-host use of ethnobotanical suspensions (prepared from one or more of over 150 documented plants) to kill the ticks and prevent re-infestation, fumigation of infested cattle with smoke derived from burning ethnobotanical products, burning pastures, rotational grazing ethnopractices, and livestock quarantine.

CONCLUSIONS

The study confirms that the Bukusu have preserved rich ethnoveterinary knowledge and practices. It provides some groundwork for elucidating the efficacy of some of these ethnopractices in protecting livestock from tick disease vectors, particularly those involving the use of ethnobotanicals, which may lead to the discovery of useful ant-tick agents.

[Prevalence of tropical theileriosis in cattle in the Aydin Region and determination of efficacy of attenuated Theileria annulata vaccine]

The present study was carried out to find out the prevalence of tropical theileriosis in the Aydin region and to determine immune status of cattle vaccinated with Theileria annulata schizont vaccine using the indirect fluorescence antibody test (IFAT) during and after the disease season. A total of 236 out of 466 cattle found to be seronegative with IFAT were vaccinated in the Aydin region (Cine, Incirliova, Nazilli, and Centrum) before the disease season (March). The remaining cattle (230/466) served as controls. Blood samples were collected from all cattle following the vaccination once in each month of April, June, September, and December (a total of 4 times) to determine the incidence of the disease using microscopic and serologic evaluations. Results indicated that the incidence of the disease varied among the regions. Clinical theileriosis was found in a total of 22 cattle (10 vaccinated, 12 unvaccinated) during the disease season.

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.

Comparison of the survival on ice of thawed Theileria parva sporozoites of different stocks cryoprotected by glycerol or sucrose

Stabilates of Theileria parva sporozoites are mostly delivered in liquid nitrogen tanks to the East Coast fever immunization points. Using an in vitro titration model, we assessed the loss of infectivity of several stabilates when they are stored in ice baths for up to 24 h. Comparisons, with respect to rates of loss of infectivity, were made between T. parva stocks (Chitongo and Katete), cryoprotectants (sucrose and glycerol) and method of assessment (in vivo and in vitro techniques). Chitongo and Katete stabilates showed similar loss dynamics. The losses were 1-4% (depending on parasite stock) and 3% per hour of storage for glycerol and sucrose stabilates respectively, and the loss rates were not significantly different. The results suggest that Chitongo stabilates and sucrose cryoprotected suspensions can be delivered on ice as is done for Katete. A graphical relationship of in vitro effective dose at 50% infectivity (ED50) and in vivo protection rate was made. The relationship showed a 35% loss of protection for a relatively low corresponding increase of ED50 from 0.006 to 0.007 tick equivalent.

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.

Current status of vaccine development against Theileria parasites

The tick-borne protozoan parasites Theileria parva and Theileria annulata cause economically important diseases of cattle in tropical and sub-tropical regions. Because of shortcomings in disease control measures based on therapy and tick control, there is a demand for effective vaccines against these diseases. Vaccines using live parasites have been available for over two decades, but despite their undoubted efficacy they have not been used on a large scale. Lack of infrastructure for vaccine production and distribution, as well as concerns about the introduction of vaccine parasite strains into local tick populations have curtailed the use of these vaccines. More recently, research has focused on the development of subunit vaccines. Studies of immune responses to different stages of the parasites have yielded immunological probes that have been used to identify candidate vaccine antigens. Immunisation of cattle with antigens expressed in the sporozoite, schizont or merozoite stages has resulted in varying degrees of protection against challenge. Although the levels of protection achieved have not been sufficient to allow exploitation for vaccination, there are clearly further lines of investigation, relating to both the choice of antigens and the antigen delivery systems employed, that need to be pursued to fully explore the potential of the candidate vaccines. Improved knowledge of the molecular biology and immunology of the parasites gained during the course of these studies has also opened up opportunities to refine and improve the quality of live vaccines.

Purification of macroschizonts of a Sudanese isolate of Theileria lestoquardi (T. lestoquardi [Atbara])

Research on malignant theileriosis is affected by the limited access to biological materials required for studies aiming at controlling the disease through the establishment of diagnostic tools and vaccines. The main aims of this work were to isolate, establish, and characterize a Theileria lestoquardi-infected cell culture (line) as a source of biological material and to generate a schizont cDNA library for further studies aiming at the identification of antigenic proteins. The T. lestoquardi isolate used originated from a sheep showing typical signs of malignant theileriosis in Atbara town in northern Sudan, and was maintained as an infected cell culture. A high-quality representative schizont cDNA library was established by isolating and purifying the schizonts using a nocodazole/aerolysin protocol followed by Percoll gradient ultracentrifugation. As a parameter to assess the quality of the schizont library, a provisional estimation of the percentage of recombinant phage clones originating from T. lestoquardi (Atbara) was undertaken. Ten clones with inserts ranging in size between 600 and 1200 bp were selected randomly, sequenced, and subjected to BLAST similarity searches. As 6 of the 10 sequenced clones showed similarities to T. parva, T. annulata, and other apicomplexan genes, it was concluded that the majority of the library phage clones originated from the parasite and not from host cell transcripts. The cDNA library will be used for screening of antigenic proteins using sera from infected sheep.

Theileria parva live vaccination: parasite transmission, persistence and heterologous challenge in the field

The 'Muguga cocktail' live vaccine, delivered by an infection and treatment protocol, has been widely deployed in Eastern, Central and Southern Africa to protect cattle against East Coast fever, caused by Theileria parva. The vaccine contains 3 component stocks (Muguga, Serengeti-transformed and Kiambu 5). In a previous study, parasites from vaccinated and unvaccinated animals were genotyped with a panel of micro- and minisatellite markers (Oura et al. 2004a) and it was shown that only the Kiambu 5 stock establishes a long-term carrier state but there was no evidence for the transmission of this stock. Also parasite genotypes different from the 3 component vaccine stocks were identified in vaccinated animals. We now report a follow-up study on the same farm, some 4 years after the initial vaccination, aimed at establishing the source of the novel parasite genotypes identified in vaccinated cattle, determining the longevity of the carrier state established by the Kiambu 5 vaccine stock and re-examining whether vaccine transmission can occur over a longer time-scale. To do this, samples were taken from vaccinated and unvaccinated cattle and the parasites were genotyped with a series of micro- and minisatellite markers. The data indicate that the vaccine stabilates contain at least 6 parasite genotypes, the Kiambu 5 stock can be detected in many but not all vaccinated cattle for up to 4 years and can be transmitted to unvaccinated cattle which share grazing and that some of the vaccinated animals become infected with local genotypes without causing overt disease.

Vaccination of calves with an attenuated cell line of Theileria annulata and the sporozoite antigen SPAG-1 produces a synergistic effect

The sporozoite surface antigen, SPAG-1 and the attenuated schizont infected Tunisian line CL1 of Theileria annulata have been shown, in previous studies, to induce variable levels of protection against homologous and heterologous sporozoite challenge, respectively. We report here the result of a vaccination trial comparing the protection level induced by the SPAG-1 antigen (as a recombinant full length His tagged protein) and the attenuated cell line, used singly or in combination. The results, after challenge of immunised calves with a lethal dose of sporozoites, show that SPAG-1 provides limited protection (one out of seven calves surviving), while the attenuated cell line provides moderate protection (three out of seven calves recovered). The combination of SPAG-1 and the attenuated cell line induced the best protection as indicated by the survival of all the vaccinated calves. These results, together with a range of parasitological and clinical parameters, demonstrate the enhanced protection provided by combining sporozoite and schizont antigens in vaccination against tropical theileriosis.

Identification of Homologous Genes ofT. annulataProteins in the Genome ofTheileriasp. (China)

Homologues to previously described Theileria (T.) annulata genes (T. annulata surface protein [TaSP], putative T. annulata membrane protein [TaD]) were successfully amplified by polymerase chain reaction (PCR) from Theileria sp. (China) merozoite cDNA, with 88% identity to TaD; TcSP partial cDNA, 94% identity to TaSP. Moreover, homologues to a secretory protein of T. annulata (TaSE), with a sequence identity of 99% on the cDNA level (TcSE partial cDNA) and to a potential membrane protein of T. lestoquardi (Clone-5), with a sequence identity of 100% on the genomic level (Tc Clone-5) but lacking an intron at positions 1894-1928 were identified.

An outbreak of East Coast Fever on the Comoros: a consequence of the import of immunised cattle from Tanzania?

In 2003 and 2004, a severe epidemic decimated the cattle population on Grand Comore, the largest island of the Union of Comoros. Fatalities started soon after the import of cattle from Tanzania. Theileria parva and its vector, Rhipicephalus appendiculatus, could be identified as the main culprits of the epidemic. Characterisation by multilocus genotyping revealed that the T. parva parasites isolated on the Comoros were identical to the components of the Muguga cocktail vaccine used in Tanzania to immunise cattle. Therefore, it is believed that East Coast Fever reached the Comoros while some of the imported livestock got infected in Tanzania by ticks of which the immature stadia fed on Muguga cocktail vaccinated animals. Since the Comorian government neither has the financial means nor the competent staff to pursue an adequate epidemiosurveillance, the danger exists that without external assistance and in a context of continuing globalisation more transboundary diseases will affect the Comorian livestock sector in the future.

Infectivity of Theileria parva sporozoites following cryopreservation in four suspension media and multiple refreezing: evaluation by in vitro titration

Theileria parva sporozoite stabilates are used for immunizing cattle against East Coast fever and in in vitro sporozoite neutralization assays. In this study, we attempted to identify a cheaper freezing medium and quantified the infectivity loss of sporozoites due to refreezing of stabilates, using an in vitro technique. Pools of stabilates prepared using Minimum Essential Medium (MEM), Roswell Park Memorial Institute (RPMI 1640), foetal calf serum (FCS) and phosphate-buffered saline (PBS) were compared. All were supplemented with bovine serum albumin except the FCS. RPMI 1640 was as effective as MEM in maintaining sporozoite infectivity while the infectivity in PBS and FCS reached only 59% and 67%, respectively. In a second experiment, a stabiiate based on MEM was subjected to several freeze-thaw cycles including various holding times on ice between thawing and refreezing. Refrozen stabilate gave an average sporozoite infectivity loss of 35% per cycle. The results indicate that RPMI can be used as a cheaper freezing medium for T. parva stabilates and that refrozen stabilate doses need to be adjusted for the 35% loss of infectivity.

Theileria: intracellular protozoan parasites of wild and domestic ruminants transmitted by ixodid ticks

Theileria are economically important, intra-cellular protozoa, transmitted by ixodid ticks, which infect wild and domestic ruminants. In the mammalian host, parasites infect leukocytes and erythrocytes. In the arthropod vector they develop in gut epithelial cells and salivary glands. All four intra-cellular stages of Theileria survive free in the cytoplasm. The schizont stages of certain Theileria species induce a unique, cancer-like, phenotype in infected host leukocytes. Theileria undergoes an obligate sexual cycle, involving fusion of gametes in the tick gut, to produce a transiently diploid zygote. The existence of sexual recombination in T. parva has been confirmed in the laboratory, and is presumed to contribute to the extensive polymorphism observed in field isolates. Key parameters in T. parva population dynamics are the relative importance of asymptomatic carrier cattle and animals undergoing severe disease, in transmission of the parasite to ticks, and the extent of transmission by nymphs as compared to adult ticks. Tick populations differ in vector competence for specific T. parva stocks. Recombinant forms of T. parva and T. annulata sporozoite surface antigens induce protection against parasite challenge in cattle. In future, vaccines might be improved by inclusion of tick peptides in multivalent vaccines.

Comparative evaluation of antibody positive titer by ELISA and IFA in Theileria annulata vaccinated cattle in Iran

An enzyme linked immunosorbent assay (ELISA) was used to evaluate antibody positive titer in vaccinated and non-vaccinated cattle using schizont infected myeloid cells as an antigen. The result was compared with indirect fluorescent antibody level in the same animals. For this study 116 milking cows, 95 vaccinated and 21 non-vaccinated, were bleeded in order to prepare sera. They were tested with both ELISA and IFA tests. 94 sera had positive antibody titer and 22 sera were negative through ELISA test but, with IFA test, only 89 sera showed positive antibody titer and 27 were negative. Thereby, it was concluded that the sensitivity and specificity of ELISA test in comparison with IFA test was 95.5% and 66.6% respectively. This study generally indicated that ELISA could be an effective test for sero-epidemiological investigations of bovine tropical theileriosis, and it is considered to be valid as an additional test to distinguish the vaccinated from the non vaccinated cattle in order to schedule vaccination programs.

Infection of calves with Theileria annulata in Tunisia: Economic analysis and evaluation of the potential benefit of vaccination

A field study aiming to estimate the costs of tropical theileriosis was carried out in an endemic region of the North of Tunisia. Three farms were monitored for two successive summer seasons. A total number of 56 calves and 12 sentinel cows were monitored. Calves were ranked into four groups: non infected animals, diseased animals with clinical tropical theileriosis, sub-clinical Theileria annulata infected animals with anaemia and sub-clinical T. annulata infected animals without anaemia. The total costs due to disease and infection were estimated to be 15,115.058 TD (Euro 9388.20). A high proportion of these costs (50.81%) is accounted for by asymptomatic infection. Sub-clinical infections with anaemia showed the highest losses in live weight, while disease cases (prevalence 42.86%) are responsible for 23.64% of the losses with death as the most important element. A cost-benefit analysis of vaccination using a Tunisian attenuated cell line vaccine was also undertaken. Considering that the vaccine would cost 5 TD (Euro 3.10), the cost-benefit ratio of vaccination is 23.7. Sensitivity analysis of the vaccination costs shows that the indifference decision point is around 118 TD (Euro 73.29).

Reduction of Theileria annulata infection in ticks fed on calves immunized with purified larval antigens of Hyalomma anatolicum anatolicum

Larval antigen of Hyalonmma anatolicum anatolicum, the vector of Theileria annulata, was purified by two-step affinity chromatography using anti-tick gut-specific rabbit IgG and IgG from immunized cattle. The purified antigen showed the presence of a single polypeptide of 37 kDa (GHLAgP) on SDS-PAGE. Two groups (I and II) of naive crossbred calves (Bos taurus x B. indicus) were immunized with I mg of GHLAgP in three divided doses. Immunized calves of group I were also infected with a sublethal dose of T annulata along with a group of non-immunized calves (group III). Animals in groups I, II, III as well a control group (group IV) were challenged with live nymphs of H. a. anatolicum on the 10th day of immunization. There was a significant reduction in the number of emerging adults of 56.9% +/- 1.67%, in calves of group I (p < 0.01) and 63.09% +/- 1.26% in calves of group II (p < 0.001) compared to the controls. The calves of groups I and II showed antibody responses to tick antigen up to day 70 post immunization. Infection with T. annulata was determined in the salivary glands of adult ticks that developed from the nymphs used for challenge infection. In ticks taken from group I calves, there was a 75.0% +/- 0.00% infection compared with only 85.0 +/- 2.88% infection in ticks taken from calves of group III. Using PCR, a lower infection (83.33% +/- 3.33%) was detected in ticks that developed from calves of group I compared with calves from group III (90.00% +/- 2.88%). The ground-up tick supernatants (GUTS) of the ticks taken from calves of group III yielded higher infection rate and exhibited higher infectivity titre in in vitro infection assay of bovine mononuclear cells than the GUTS of the ticks taken from calves of group I. The results suggest a partial reduction in growth rate of T. annulata in ticks feeding on calves immunized with GHLAgP.

Perception of cattle farmers of the efficacy of east coast fever immunization in Southern Zambia

A study using a structured questionnaire was conducted to assess the perception of cattle farmers of the efficacy of East Coast fever (ECF) immunization in southern Zambia. One hundred and seventy-nine farmers from five districts in southern Zambia were interviewed. The majority of farmers (85%) perceived ECF immunization as being very effective and about half of them (51.4%) preferred immunization to other ECF control strategies. The study showed that the number of calves immunized was strongly associated with the farmer's perception of the benefits of immunization. There was no association between the number of calves immunized and the number of veterinary assistants in a given district or their transport situation. Overall mortality in ECF-immunized calves from various causes stood at 4.2%. Based on farmers' reports, the majority of these deaths seemed to have been caused by anaplasmosis, another tick-borne disease, and might have resulted from relaxation of tick control after ECF immunization. The reasons identified by farmers for not immunizing their animals included failure by immunizing teams to reach certain areas, not having calves of immunization age, and lack of money. These findings provide valuable information on how livestock farmers perceive and adopt new animal disease control strategies and the information could be useful in their planning and implementation.

Epidemiological aspects and economic impact of bovine theileriosis (East Coast fever) and its control: a preliminary assessment with special reference to Kibaha district, Tanzania

A cross-sectional study based on clinical examination, inspection of herd health records and a questionnaire was designed to determine the epidemiology, economics and potential impact of immunisation against theileriosis in Tanzania. The results showed annual theileriosis costs to be US$ 205.40 per head, whereas the introduction of immunisation reduced this by 40-68% depending on the post immunisation dipping strategy adopted. Morbidity risk due to theileriosis was 0.048 in immunised and 0.235 in non-immunised cattle, and the difference was significant (chi(2)=66.7; P=0.000). The questionnaire results indicated that immunised cattle had a significantly (chi(2)=6; P=0.015) higher risk of anaplasmosis compared with non-immunised cattle, whereas the risk of bovine babesiosis did not differ significantly (chi(2)=0.06; P=0.807) between the two groups. Mortality risk due to anaplasmosis was 0.046 in immunised and 0.018 in non-immunised cattle and this difference was statistically significant (chi(2)=4.48; P=0.043). The theileriosis mortality risk was 0.203 in the non-immunised cattle, while the risk was 0.009 in the immunised cattle and these differences were also significant (chi(2)=103; P=0.000). It was concluded that farmers who have immunised their cattle may cautiously cut down acaricide application by 50% for extensively grazed herds and by 75% for zero grazed animals depending on the level of tick challenge at the herd level.

Novel baculovirus-derived p67 subunit vaccines efficacious against East Coast fever in cattle

Two novel baculovirus-derived recombinant Theileria parva p67 constructs were tested for their vaccine potential against East Coast fever. Boran calves were immunized with a his-GFP-p67 fusion protein (GFP:p67deltaSS) or with GP64:p67C, a protein fusion between a C-terminal domain of p67 and the baculovirus envelope protein GP64. Both GFP:p67deltaSS and GP64:p67C induced antibodies with high ELISA titers that neutralized T. parva sporozoites with high efficiency. Upon challenge, a correlation was observed between the in vitro neutralizing capacity and the reduction in severe ECF for individual animals. A protection level upto 85% was obtained. This level of protection was achieved with only two inoculations of 100 microg per dose, which is a major improvement over previous recombinant p67 products.

Bovine leukocyte antigen major histocompatibility complex class II DRB3*2703 and DRB3*1501 alleles are associated with variation in levels of protection against Theileria parva challenge following immunization with the sporozoite p67 antigen

Initial laboratory trials of an experimental subunit vaccine against Theileria parva based on the 67-kDa major sporozoite surface antigen revealed a range of responses to challenge. We have analyzed convergence in seven sets of monozygotic twins which suggests that genetic factors may have an influence in determining the degree of protection provided by p67 immunization. In addition, we have examined whether allelic diversity at major histocompatibility complex class II loci influences protection. Analysis of bovine leukocyte antigen DRB3 diversity in 201 animals identified significant associations with vaccine success (DRB3*2703; P = 0.027) and vaccine failure (DRB3*1501; P = 0.013). Furthermore, DRB3*2703 was associated with the likelihood of immunized animals showing little to no clinical signs of disease following challenge. We discuss the acquired and innate immune mechanisms that may be behind the associations described here.

Improved immunogenicity of novel baculovirus-derived Theileria parva p67 subunit antigens

East Coast fever (ECF) in cattle is caused by the tick-borne protozoan parasite Theileria parva. The major sporozoite surface antigen of T. parva (p67) is an important candidate for inclusion in a subunit vaccine. Recently, we reported the expression and production of different parts of p67 as fusions to either GFP or to the baculovirus GP64 envelope glycoprotein in insect cells, which resulted in stable proteins recognized by a monoclonal specific for native p67. The immunogenicity of these fusion proteins was examined in out-bred mice and cattle. In mice, the full length p67 molecule without its signal peptide and transmembrane region, but fused to GFP (GFP:p67deltaSS) was the best immunogen followed by the C-terminus of p67 fused to GP64 (GP64:p67C). These two immunogens also provoked a high level of sero-conversion in cattle when formulated in a water-in-oil or saponin-derived adjuvant with only 100 microg of protein and a single booster. The vaccine-elicited antibodies efficiently inhibited the infectivity of T. parva sporozoites in in vitro neutralization assays. This study demonstrated that these new baculovirus-derived p67 vaccines were highly immunogenic, and that in combination with a suitable adjuvant, they have a clear potential to induce protective immunity in cattle.

Lyophilisation and resuscitation of sporozoites of Theileria parva: preliminary experiments

Lyophilisation of Theileria parva sporozoite stabilates used for immunisation of cattle against East Coast fever would greatly improve vaccine storage and delivery. We report three attempts to lyophilise and resuscitate the sporozoites of T. parva. Sporozoites survived lyophilisation and were effective for immunisation. Lyophilised stabilate survived for 2 weeks at 5 degrees C and for 12 weeks at -20 degrees C. Although the viability of the stabilates was severely reduced during lyophilisation, this work suggests that this method has potential and should be considered for other Apicomplexan parasites such as Babesia sp. or Plasmodium sp.

In vitro titration of Theileria parva tick derived stabilates

Immunization against the protozoan Theileria parva by infection and treatment has proved to be very efficient for the control of East Coast fever, an acute and often-fatal lymphoproliferative tick-borne disease of cattle in Eastern, Central and Southern Africa. The immunizing dose of live T. parva sporozoites used in this method is usually determined by in vivo titration. An alternative in vitro method of quantification of sporozoites in whole tick-derived stabilates is proposed. The method consists of incubating serially diluted T. parva stabilates with bovine peripheral blood lymphocytes, the host cell that is infected naturally. Allowing the cultures to incubate undisturbed for the full cultivation period (10 days) reduced the variability among replicate titrations. Fungal contaminations were avoided by centrifuging stabilates at 400 g prior to the incubation, which did not precipitate sporozoites significantly. Fungistatics, Nystatin and Flucytosine, did not appear to interfere with the in vitro development of T. parva but their effect on fungal growth was limited. In vitro titration data were compared to in vivo infection data for 2 stabilates. In vitro titration of T. parva sporozoites should allow more ethical and efficient research on the preparation and storage of T. parva tick-derived stabilates.

Characterization of efferent lymph cells and their function following immunization of cattle with an allogenic Theileria annulata infected cell line

Immunization of cattle with in vitro propagated bovine mononuclear cells infected with Theileria annulata induces a protective immune response. Activation and effector function of T cells exiting the lymph node draining the site of cell line immunization were investigated to understand the mechanisms involved in the generation of immunity. Immunized animals exhibited a biphasic immune response in efferent lymph as well as peripheral blood. The first phase corresponded to allogenic responses against MHC antigens of the immunizing cell line and the second was associated with parasite specific responses. An increase in the output of CD2(+) cells and MHC class II(+) cells in efferent lymph was observed after cell line immunization with a corresponding decrease in WC1(+) cells. Although the percentage of CD4(+) T cells did not change significantly over the course of the experiment, they became activated. Both CD25 and MHC class II expressing CD4(+) T cells were detected from day 7 onwards, peaking around day 13. Efferent lymph leukocytes (ELL) exhibited sustained responses to IL-2 in vitro following cell line immunization. Antigen specific proliferation was also detected first to the immunizing cell line and then to parasite antigens. The two peaks of CD2(+) cells were observed, which corresponded to similar peaks of CD8(+) cells. The increase in CD8(+) cells was more pronounced during the second parasite specific phase than the first allogenic phase. Activated CD8(+) T cells mainly expressed MHC class II and some expressed CD25. Significantly the peak of activated CD4(+) T cells preceded the peak of activated CD8(+) T cells, highlighting the role of T. annulata specific CD4(+) T cells in inducing parasite specific CD8(+) cytotoxic responses. A biphasic cytotoxic response also appeared in efferent lymph and peripheral blood, the first directed against MHC antigens of the immunizing cell line followed by MHC class I restricted parasite specific cytotoxicity. The cytotoxic responses in efferent lymph appeared earlier than peripheral blood, suggesting that activated CD8(+) cells exiting the draining lymph node following immunization with T. annulata infected schizonts play an important role in the development of protective immune responses.

Immunity to East Coast fever in cattle induced by a polypeptide fragment of the major surface coat protein of Theileria parva sporozoites

Full-length recombinant versions of p67, the 709 amino acid major surface protein of Theileria parva sporozoites, induce immunity to East Coast fever (ECF) in cattle. We show that a soluble Escherichia coli recombinant version of p67 (p67(635)), in which a prokaryotic signal peptide replaces the eukaryotic one, confers protection comparable to that induced by the full-length molecule, but is unstable. Peptides encoding 80 (p67C) and 205 (p67N) amino acid fragments of p67, containing epitopes recognised by sporozoite neutralising monoclonal antibodies, exhibit improved stability in E. coli. Antibodies raised against the central region of p67 (p67M) neutralise sporozoite infectivity in vitro. The p67C peptide induced immunity against ECF in cattle, at a level equivalent to p67(635), suggesting that a synthetic peptide vaccine might be achievable.

Immunisation against Theileria parva in eastern Zambia: influence of maternal antibodies and demonstration of the carrier status

Immunisation of calves by the infection and treatment method (I & T) has been extensively used in the eastern province of Zambia to control East Coast fever (ECF), a protozoan tick-borne disease. This paper presents the results of a field longitudinal study, which included a total of 148 Angoni calves. After immunisation against ECF, they were monitored for a full rainy season, coinciding with the main peak of activity of the vector of Theileria parva, the tick Rhipicephalus appendiculatus. Dysimmunisation (acute reaction generated by I & T immunisation), seroconversion and mortality are among the parameters recorded. The effect of maternal antibodies on these parameters was analysed and also studied in experimental conditions on two calves. Before immunisation, young calves had a higher seroprevalence than older animals (maternal antibodies) but their post-immunisation seroprevalence was lower. There was no evidence that their immunoprotection was weaker but this indicates that the post-immunisation seroconversion is probably not a reliable tool to monitor the efficacy of calf immunisation. The carrier state of cattle after immunisation was investigated in experimental conditions on three bovines whereas in the field, the infection prevalence in the ticks was estimated using the relation between the tick burden and the T. parva contacts with the calves. The ability of larval and nymphal R. appendiculatus ticks to pick-up T. parva from carriers and to transmit it to naïve animals after moulting was assessed. It was found that both instars are able to transmit clinical and lethal ECF but that the prevalence of T. parva infection in nymphs is much lower than in adults, confirming the primary role of adults in the transmission of ECF in endemic conditions. Similar results were obtained from the field whereby the ECF peak corresponds with the peak of adult R. appendiculatus activity. The infection prevalence in the ticks was however much lower in the field than in experimental conditions indicating that an important proportion of them feed on alternative hosts. Old ticks seemed to have lost part of their infectivity.

Buffalo-associated Theileria parva: the risk to cattle of buffalo translocation into the Highveld of Zimbabwe

There has been an increase in the introduction of game animals, including African buffaloes, into the Highveld of Zimbabwe to establish private game reserves on condition that they are confined in separate and secured paddocks. Owing to shortages of pastures cattle were grazed in buffalo-grazed paddocks resulting in outbreaks of buffalo-derived theileriosis. This paper reports the results of epidemiological observations carried out on two game reserves to assess the risk of buffalo translocation. The infection rate with Theileria parasites in ticks collected from buffalo-grazed pastures was high and produced fatal theileriosis in susceptible cattle. Similarly, adult R. appendiculatus ticks artificially fed as nymphs on the buffaloes produced fatal infections in susceptible cattle. Theileria parva (Boleni), the vaccine used to immunize cattle against theileriosis, and a buffalo-derived T. parva stabilate (BV-1) were inoculated in naïve buffaloes to study the Theileria carrier-state in these animals. The two buffaloes that had received the Boleni stabilate showed no clinical theileriosis reaction; however, the ticks derived from them produced a subclinical reaction in one susceptible calf. The buffalo which had received stabilate BV-1 developed fever, high schizont parasitosis for 10 days and 15% piroplasms parasitemia. R. appendiculatus ticks fed as nymphs on this buffalo produced fatal theileriosis reaction in a susceptible calf.

Theileria parva epidemics: a case study in eastern Zambia

This paper presents the results of the follow-up of three sentinel herds between 1994 and 2000 during an East Coast fever (ECF) epidemic in eastern Zambia. The animals of the sentinel herds were closely monitored clinically and serologically together with detailed Rhipicephalus appendiculatus counts. Peaks of disease incidence occurred in the rainy season (December-February) and the dry months of May-July with nymph-to-adult tick transmission dominating the infection dynamics. A second wave of adult R. appendiculatus at the start of the dry season is essential for the occurrence of a full-blown epidemic while the size of the susceptible cattle population acts as a most important limiting factor. The majority of adult cattle of the sentinel herds became infected less than 2 years after the introduction of the disease. The median age at first contact for calves born towards the end of the study (1999) was about 6 months. The case-fatality ratio (including sub-clinical cases) is estimated at 60%. It is argued that part of the so-called 'natural mortality' is actually due to ECF and that ECF occurrence and mortality are systematically underestimated. The direct financial cost of the epidemic, based on loss of animals and cost of treatment only and calculated over 4 years running, is estimated at about 6 US dollars per year per animal at risk. The value of the traditional seroprevalence survey as a tool for monitoring ECF epidemiology is put in question and the prevalence of maternal antibodies in new-born calves, reflecting the immune status of the dam population, is introduced as an alternative. It is demonstrated that an efficient immunisation campaign should concentrate its efforts in the period of low adult R. appendiculatus abundance (July-October).

A dual role for immunosuppressor mechanisms in infection with Theileria annulata: well-regulated suppressor macrophages help in recovery from infection; profound immunosuppression promotes non-healing disease

There is increasing evidence that immune mechanisms are involved in the pathogenesis of many parasitic infections, including infections with the tick-borne protozoan Theileria annulata. The initial stages of tropical theileriosis are characterised by the induction of a non-specific lymphoproliferation by schizont-infected cells which is believed to disrupt antigen recognition and interfere with protective immune responses. This study examined the possibility that cattle do not always succumb to infection because macrophages suppress this non-specific lymphoproliferation. The results provide evidence that lymphoproliferation in cattle may be controlled by two types of suppressor macrophages. The first type occurs in infected cattle and acts via a feedback loop well documented in other parasitic infections. This loop involves macrophages, apparently activated by high levels of gamma interferon produced by proliferating lymphocytes, which suppress lymphocyte proliferation via a prostaglandin-mediated pathway. The properties of a suppressor activity seen in immunised and challenged animals suggested that cattle also possess a type of novel suppressor macrophage recently described in filarial infections. This second type of suppressor macrophage does not seem to act via prostaglandin; its activity appeared to be linked to a suppressor epitope on the sporozoite antigen SPAG-1. Differences in the nature of the schizont-infected cells of the Friesian and Sahiwal calves used in one section of this work, in the in vitro and in vivo lymphoproliferative responses of the two groups of calves and in the behaviour of their suppressor macrophages suggested several reasons why the outcome of Theileria infections differed in the two cattle breeds. This study has extended our knowledge of the pluripotential activities of macrophages in T. annulata infections to include immunosuppression as well as anti-parasite responses and confirmed the view that the outcome of infection with T. annulata, as with many parasitic infections, depends upon the final balance of the protective and pathological properties of the immune system.

Prime-boost: the way forward for recombinant vaccines against apicomplexan parasites. A Theileria perspective

A good CD8+ response is required for immunity to many intracellular pathogens. Traditional antigen delivery using isolated sub-units or killed pathogens and adjuvant stimulates strong antibody responses but weak T-cell reactivity. Attenuated vaccines are usually more effective. The prime-boost delivery system based on immunisation with a naked DNA antigen-gene construct followed by boosting with an attenuated vaccinia virus expressing the same antigen is proving to be a powerful way to stimulate antigen-specific CD8 responses. Success using single epitopes is possible in malaria and we believe this approach holds much promise for other apicomplexan parasites such as Theileria spp.

A field test on the treatment of ovine theileriosis with an injection of Kangjiaoming

A compound effective for the treatment of ovine theileriosis was selected and a slow-release preparation (named Kangjiaoming) was prepared. A total of 1,172 sheep and goats in Zhangjiachuan, Lintan and Yuzhong Counties, Gansu Province, where small ruminants are seriously affected by theileriosis, were injected with this preparation at a dosage of 5 mg/kg body weight. The infection rate of the control group in each of the above-mentioned counties was 98.5%, 85% and 80%, respectively. None of the treated animals became sick due to theileriosis. This drug proved to be useful for the treatment of carrier cases, although its effect was apparently slower than in acute theileriosis. The effect of the preparation on some weak animals was not satisfactory.

Advances and prospects for subunit vaccines against protozoa of veterinary importance

Protozoa are responsible for considerable morbidity and mortality in domestic and companion animals. Preventing infection may involve deliberate exposure to virulent or attenuated parasites so that immunity to natural infection is established early in life. This is the basis for vaccines against theilerosis and avian coccidiosis. Vaccination may not be effective or practical with diseases, such as cryptosporidiosis, that primarily afflict the immune-compromised or individuals with an incompletely developed immune system. Strategies for combating these diseases often rely on passive immunotherapy using serum or colostrums containing antibodies to parasite surface proteins. Subunit vaccines offer an attractive alternative to virulent or attenuated parasites for several reasons. These include the use of bacteria or lower eukaryotes to produce recombinant proteins in batch culture, the relative stability of recombinant proteins compared to live parasites, and the flexibility to incorporate only those antigens that elicit "protective" immune responses. Although subunit vaccines offer many theoretical advantages, our lack of understanding of immune mechanisms to primary and secondary infection and the capacity of many protozoa to evade host immunity remain obstacles to developing effective vaccines. This review examines the progress made on developing recombinant proteins of Eimeria, Giardia, Cryptosporidium, Toxoplasma, Neospora, Trypanosoma, Babesia, and Theileria and attempts to use these antigens for vaccinating animals against the associated diseases.

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.

Identification of a target population for immunisation against East Coast fever in coastal Kenya

Two experiments were carried out to identify the target population of cattle for immunisation against East Coast fever (ECF) using the infection-and-treatment method. Firstly, a sentinel-calf study was used to determine the age window for ECF immunisation by determining ages at clinical detection of infection with Theileria parva. Six groups of five naive cross-bred (Bos taurus/Bos indicus) male calves, introduced at intervals of 2 months at a mean age of 26 days, were exposed to natural tick challenge on a high ECF-risk, small-holder farm in the coastal lowland, coconut-cassava agro-ecological zone of coastal Kenya. Secondly, a challenge study evaluated the relationship between the presence of T. parva antibodies and immunity. Ten indigenous adult Zebu cattle and nine Zebu young stock purchased from farmers in the same zone, and eight cross-bred calves (survivors of the sentinel-calf study) were challenged with 10 times the immunising dose of T. parva Marikebuni stock. Twenty-four of these 27 cattle had high antibody titres before challenge. Two cross-bred calves, obtained from an ECF-free area and seronegative to T. parva schizont antigen, also were challenged and used as susceptible controls. Twenty-five (83%) of the 30 sentinel calves contracted ECF over an age range of 36-116 days (mean 72 days). The remaining five calves died of other causes within 2 months of arrival on the farm. Fourteen of the 25 calves survived the infection and developed antibodies to T. parva. Despite tick control, seven of these 14 calves had a second episode of ECF and two died. In total, 13 of the 25 calves that contracted ECF died. Only one of 19 indigenous Zebu animals developed clinical ECF when challenged with T. parva Marikebuni (mild clinical signs with spontaneous recovery). Of the eight cross-bred survivors from the first experiment, only one succumbed to ECF when challenged and it died. Both susceptible cross-bred calves developed severe clinical signs of ECF and one died. The experimental studies show that in the high ECF-risk areas of the coconut-cassava zone of coastal Kenya, immunisation against ECF in cross-bred (B. taurus/B. indicus) cattle should be targeted at an early age (preferably within 1-2 months of birth).

Immunization of cattle against East Coast fever using Theileria parva (Marikebuni) and relaxation of tick control in North Rift, Kenya

A total of 90 animals was immunized against East Coast fever (ECF) using Theileria parva (Marikebuni) stock on three large-scale farms in Kiminini Division, Trans-Nzoia District, North Rift, Kenya. Another 90 cattle served as non-immunized controls. Following immunization the number of cattle with significant indirect fluorescent antibody (IFA) titres increased from 43.9% to 84.4% and 6.7% of the cattle developed clinical ECF reactions. Two months after immunization, the immunized and non-immunized cattle were divided into two groups one of which was dipped every 3 weeks and the other dipped when total full body tick counts reached 100. All the animals were monitored for 51 weeks for incidences of ECF and other tick-borne diseases. Twenty-four cases of ECF were diagnosed among the non-immunized cattle compared to four cases among the immunized cattle; a difference that was significant (P > 0.05). There was no significant difference in the incidences of babesiosis and anaplasmosis between the immunized and non-immunized cattle.

Exposure of cattle immunized with different stocks of Theileria parva to buffalo-associated Theileria challenge on two game parks in Zimbabwe

Eight cattle immunized with cattle-derived Theileria parva Boleni stabilate together with six susceptible controls were released in Dombawera Game Park on the Highveld of Zimbabwe. This coincided with Rhipicephalus appendiculatus nymphal activity. The cattle grazed together with African buffaloes (Syncerus caffer) and were not treated against tick infestation. The nymphal tick infestation was high, and seven of the eight immunized cattle and three of the controls had severe and fatal reactions. Subsequently, two stocks of Theileria parva to be tested for their immunizing abilities were prepared-one from adult ticks which were fed as nymphs on one of the sick control animals (Dom 268) and the other from adult ticks collected from pastures grazed by buffaloes (Bv-1). Two groups of cattle were immunized with either the Dom 268-derived strain (eight animals) or the Bv-1-derived strain (four animals). These together with three non-immunized controls, were released in Bally Vaughaun Game Park in the Highveld, where buffaloes are present, during the season of nymphal tick activity. A third group of five cattle, immunized with stabilate Bv-1, and three non-immunized controls were released at the same site during the season of adult tick activity. The nymphal and adult tick infestations of the cattle were large and more than 2000 nymphs and 1000 adult ticks were counted per animal. Cattle were treated with a pyrethroid pour-on preparation to control the tick infestation and screw-worm strike. The immunized cattle in the three groups survived the theileriosis challenge for a period of 18 months, but the non-immunized control cattle suffered a severe and fatal theileriosis 19-23 days after being placed on the pasture.

Immunisation against East Coast fever by the infection and treatment method: evaluation of the use of ice baths for field delivery and appraisal of an acid formulation of long-acting tetracycline

Immunisation by the infection and treatment method using the Katete strain is currently the most efficient prophylactic technique to control East Coast fever (ECF) in the endemic areas of the Eastern Province of Zambia. The maintenance of the cold chain in liquid nitrogen up to the time of inoculation and the cost of the reference long-acting oxytetracycline (Terramycin LA, Pfizer) are the main drawbacks of the method. The work presented in this paper aims at reducing the cost of immunisation against ECF by using an ice bath for the field delivery and a cheaper long-acting oxytetracycline formulation as chemotherapeutic agent. In experimental conditions, the results from 40 calves immunised after various periods of storage on ice ranging from 4 to 32 h indicate that deferred immunisation performed with a stabilate kept on ice for up to 6h after thawing has an efficiency of 90%. Moreover, sporozoites kept on ice were still surviving 32 h after thawing. In a field trial, 91 calves were inoculated with a stabilate kept for 3.5-5.5 h after thawing and dilution whereas 86 calves were immunised using the standard method. Clinical and parasitological reactions to immunisation were monitored as well as the seroconversion. In the field trial, the deferred immunisation was more efficient than the standard method. The acid formulation of oxytetracycline that was tested was found as suitable as the reference alkaline formulation for the chemotherapeutic control of the Katete strain in ECF immunisation. One indoor trial was carried out on 10 animals and a field trial involved 93 calves.

Epitope-Mapping of antigen-specific T lymphocyte in cattle immunized with recombinant major piroplasm surface protein of Theileria sergenti

The cellular immune responses against major piroplasm surface protein (MPSP) of Theileria sergenti were characterized. Three cattle were immunized with recombinant MPSP (C type) encapsulated by mannan-coated liposome. The proliferative responses of peripheral blood mononuclear cells (PBMC) against MPSP were detected in all immunized animals. Reverse transcriptase polymerase chain reaction (RT-PCR) analysis revealed that T cell lines derived from each animal expressed relatively high levels of interferon (IFN)-gamma mRNA, low levels of interleukin (IL)-2, IL-10, and tumor necrosis factor (TNF)-alpha mRNAs, but no detectable level of IL-4 mRNA. From the results of T cell epitope-mapping, T-cell lines from two animals responded to DTSKFTPTVAHRLKHAEDLF (residues 61 to 80), while other animal responded to GTGKVYDFVGNFKVTKVKFE (residues 141 to 160). The MPSP-type specific response of a T-cell line was observed in the latter region of MPSP. These data suggest that immunization with cocktail vaccine consisting of different types of MPSP may be necessary in the field trial.