Eimeria tenella: Construction of a recombinant fowlpox virus expressing rhomboid gene and its protective efficacy against homologous infection

Innovative prevention and control of coccidiosis: targeting sporogony for new control agent development

Coccidiosis is one of the most significant diseases affecting the poultry industry, with recent estimates indicating that it causes annual losses exceeding £10 billion globally. Increasing concerns over drug residues and resistance have elevated the importance of safe and effective vaccines as the primary method for controlling coccidiosis and other animal diseases. However, current commercial live vaccines for coccidiosis can negatively impact the feed conversion rates of young broilers and induce subclinical symptoms of coccidiosis, limiting their widespread adoption. Eimeria species, the causative agents of coccidiosis, exhibit unique biological characteristics. Their life cycle involves 2 or more generations of schizogony and 1 generation of gametogony within the host, followed by sporogony in a suitable external environment. Sporogony is crucial for Eimeria oocysts to become infectious and propagate within the host. Focusing on the sporogony process of Eimeria presents a promising approach to overcoming technical challenges in the efficient control of coccidiosis, addressing the urgent need for sustainable and healthy farming practices. This paper systematically reviews existing control strategies for coccidiosis, identifies current challenges, and emphasizes the research progress and future directions in developing control agents targeting sporogony. The goal is to provide guidance for the formulation of scientific prevention and control measures for coccidiosis.

Vaccination Against Poultry Parasites

The complexity of parasites and their life cycles makes vaccination against parasitic diseases challenging. This review highlights this by discussing vaccination against four relevant parasites of poultry. Coccidia, i.e., Eimeria spp., are the most important parasites in poultry production, causing multiple billions of dollars of damage worldwide. Due to the trend of antibiotic-free broiler production, use of anticoccidia vaccines in broilers is becoming much more important. As of now, only live vaccines are on the market, almost all of which must be produced in birds. In addition, these live vaccines require extra care in the management of flocks to provide adequate protection and prevent the vaccines from causing damage. Considerable efforts to develop recombinant vaccines and related work to understand the immune response against coccidia have not yet resulted in an alternative. Leucozytozoon caulleryi is a blood parasite that is prevalent in East and South Asia. It is the only poultry parasite for which a recombinant vaccine has been developed and brought to market. Histomonas meleagridis causes typhlohepatitis in chickens and turkeys. The systemic immune response after intramuscular vaccination with inactivated parasites is not protective. The parasite can be grown and attenuated in vitro, but only together with bacteria. This and the necessary intracloacal application make the use of live vaccines difficult. So far, there have been no attempts to develop a recombinant vaccine against H. meleagridis. Inactivated vaccines inducing antibodies against the poultry red mite Dermanyssus gallinae have the potential to control infestations with this parasite. Potential antigens for recombinant vaccines have been identified, but the use of whole-mite extracts yields superior results. In conclusion, while every parasite is unique, development of vaccines against them shares common problems, namely the difficulties of propagating them in vitro and the identification of protective antigens that might be used in recombinant vaccines.

Protective Efficacy Induced by the Common Eimeria Antigen Elongation Factor 2 against Challenge with Three Eimeria Species in Chickens

Avian coccidiosis arises from co-infection involving multiple Eimeria species, which could give rise to substantial economic losses in the global poultry industry. As a result, multivalent anticoccidial vaccines containing common Eimeria antigens offer considerable promise for controlling co-infection in clinical practice. In our previous study, Elongation factor 2 (EF2) was deemed as an immunogenic common antigen across various Eimeria species. This current investigation aimed to further assess the immunogenicity and protective efficacy of EF2 in recombinant subunit vaccine format against three Eimeria species. The EF2 gene cloned from Eimeria maxima (E. maxima) cDNA was designated as EF2 of E. maxima (EmEF2). The immunogenicity of the recombinant protein EmEF2 (rEmEF2) was assessed through Western blot analysis. The evaluation of the vaccine-induced immune response encompassed the determination of T lymphocyte subset proportions, cytokine mRNA transcription levels, and specific IgY concentrations in rEmEF2-vaccinated chickens using flow cytometry, quantitative real-time PCR (qPCR), and indirect enzyme-linked immunosorbent assay (ELISA). Subsequently, the protective efficacy of rEmEF2 was evaluated through vaccination and challenge experiments. The findings demonstrated that rEmEF2 was effectively recognized by the His-tag monoclonal antibody and E. maxima chicken antiserum. Vaccination with rEmEF2 increased the proportions of CD4+ and CD8+ T lymphocytes, elevated IL-4 and IFN-γ mRNA transcription levels, and enhanced IgY antibody levels compared to the control groups. Moreover, compared to the control groups, vaccination with rEmEF2 led to decreased weight loss, reduced oocyst outputs, and alleviated enteric lesions. Furthermore, in the rEmEF2-immunized groups, challenges with E. maxima and E. acervulina resulted in anticoccidial index (ACI) scores of 166.35 and 185.08, showing moderate-to-excellent protective efficacy. Nevertheless, challenges with E. tenella and mixed Eimeria resulted in ACI scores of 144.01 and 127.94, showing low protective efficacy. In conclusion, EmEF2, a common antigen across Eimeria species, demonstrated the capacity to induce a significant cellular and humoral immune response, as well as partial protection against E. maxima, E. acervulina, and E. tenella. These results highlight EmEF2 as a promising candidate antigen for the development of multivalent vaccines targeting mixed infections by Eimeria species.

Construction of recombinant SAG22 Bacillus subtilis and its effect on immune protection of coccidia

Avian coccidiosis causes huge economic losses to the global poultry industry. Vaccine is an important means to prevent and control coccidiosis. In this study, Bacillus subtilis was selected as the expression host strain to express anti Eimeria tenella surface protein SAG22. The synthesized surface protein SAG22 gene fragment of E. tenella was ligated with Escherichia coli-bacillus shuttle vector GJ148 to construct the recombinant vector SAG22-GJ148. And then the recombinant Bacillus strain SAG22-DH61 was obtained by electrotransfer. The results of SDS-PAGE and Western Blot showed that the recombinant protein SAG22 was successfully expressed intracellularly. The immunoprotective effect of recombinant Bacillus strain SAG22-DH61 on broiler chickens was evaluated in 3 identically designed animal experiments. The birds were infected with E. tenella on d 14, 21, and 28, respectively. Each batch of experiments was divided into 4 groups: blank control group (NC), blank control group + infected E. tenella (CON), addition of recombinant SAG22-DH61 strain + infected with E. tenella (SAG22-DH61), addition of recombinant empty vector GJ148-DH61 strain + infected with E. tenella (GJ148-DH61). The animal experiments results showed that the average weight gain of the SAG22-DH61 group was higher than that of the infected control group, and the difference was significant in the d 14 and 28 attack tests (P < 0.05); the oocyst reduction rate of the SAG22-DH61 group was much higher than that of the GJ148-DH61 group (P < 0.05); the intestinal lesion count score of the SAG22-DH61 group was much lower than that of the GJ148-DH61 group (P < 0.05). In addition, the SAG22-DH61 group achieved highly effective coccidia resistance in the d 14 attack test and moderately effective coccidia resistance in both the d 21 and 28 attack tests. In summary, recombinant SAG22 B. subtilis has the potential to become one of the technological reserves in the prevention and control of coccidiosis in chickens in production.

Comparative Degradome Analysis of the Bovine Piroplasmid Pathogens Babesia bovis and Theileria annulata

Babesia bovis and Theileria annulata are tick-borne hemoprotozoans that impact bovine health and are responsible for considerable fatalities in tropical and subtropical regions around the world. Both pathogens infect the same vertebrate host, are closely related, and contain similar-sized genomes; however, they differ in invertebrate host specificity, absence vs. presence of a schizont stage, erythrocyte invasion mechanism, and transovarial vs. transstadial transmission. Phylogenetic analysis and bidirectional best hit (BBH) identified a similar number of aspartic, metallo, and threonine proteinases and nonproteinase homologs. In contrast, a considerably increased number of S54 serine rhomboid proteinases and S9 nonproteinase homologs were identified in B. bovis, whereas C1A cysteine proteinases and A1 aspartic nonproteinase homologs were found to be expanded in T. annulata. Furthermore, a single proteinase of families S8 (subtilisin-like protein) and C12 (ubiquitin carboxyl-terminal hydrolase), as well as four nonproteinase homologs, one with dual domains M23-M23 and three with S9-S9, were exclusively present in B. bovis. Finally, a pronounced difference in species-specific ancillary domains was observed between both species. We hypothesize that the observed degradome differences represent functional correlates of the dissimilar life history features of B. bovis and T. annulata. The presented improved classification of piroplasmid proteinases will facilitate an informed choice for future in-depth functional studies.

Eimeria maxima Rhomboid-like Protein 5 Provided Partial Protection against Homologous Challenge in Forms of Recombinant Protein and DNA Plasmid in Chickens

Eimeria maxima (E. maxima) is one of the most prevalent species that causes chicken coccidiosis on chicken farms. During apicomplexan protozoa invasion, rhomboid-like proteins (ROMs) cleave microneme proteins (MICs), allowing the parasites to fully enter the host cells, which suggests that ROMs have the potential to be candidate antigens for the development of subunit or DNA vaccines against coccidiosis. In this study, a recombinant protein of E. maxima ROM5 (rEmROM5) was expressed and purified and was used as a subunit vaccine. The eukaryotic expression plasmid of pVAX-EmROM5 was constructed and was used as a DNA vaccine. Chickens who were two weeks old were vaccinated with the rEmROM5 and pVAX-EmROM5 vaccines twice, with a one-week interval separating the vaccination periods. The transcription and expression of pVAX-EmROM5 in the injected sites were detected through reverse transcription PCR (RT-PCR) and Western blot (WB) assays. The cellular and humoral immune responses that were induced by EmROM5 were determined by detecting the proportion of CD4⁺ and CD8⁺ T lymphocytes, the cytokine levels, and the serum antibody levels. Finally, vaccination-challenge trials were conducted to evaluate the protective efficacy of EmROM5 in forms of the recombinant protein (rEmROM5) and in the DNA plasmid (pVAX-EmROM5) separately. The results showed that rEmROM5 was about 53.64 kDa, which was well purified and recognized by the His-Tag Mouse Monoclonal antibody and the chicken serum against E. maxima separately. After vaccination, pVAX-EmROM5 was successfully transcribed and expressed in the injected sites of the chickens. Vaccination with rEmROM5 or pVAX-EmROM5 significantly promoted the proportion of CD4⁺/CD3⁺ and CD8⁺/CD3⁺ T lymphocytes, the mRNA levels of the cytokines IFN-γ, IL-2, IL-4, IL-17, TNF SF15, and IL-10, and specific IgG antibody levels compared to the control groups. The immunization also significantly reduced the weight loss, oocyst production, and intestinal lesions that are caused by E. maxima infection. The anticoccidial index (ACI)s of the vaccinated groups were beyond 160, showing moderate protection against E. maxima infection. In summary, EmROM5 was able to induce a robust immune response and effective protection against E. maxima in chickens in the form of both a recombinant protein and DNA plasmid. Hence, EmROM5 could be used as a candidate antigen for DNA vaccines and subunit vaccines against avian coccidiosis.

Protective Efficacy of Rhomboid-Like Protein 3 as a Candidate Antigen Against Eimeria maxima in Chickens

Avian coccidiosis brings tremendous economic loss to the poultry industry worldwide. The third generation vaccine, including subunit and DNA vaccines, exhibited promising developmental prospects. In a previous study, we found rhomboid-like protein 3 of Eimeria maxima (EmROM3) was involved in infections by Eimeria species. However, the protective efficacy of EmROM3 against Eimeria maxima (E. maxima) remains unknown. In this study, chickens were intramuscularly immunized with the recombinant protein EmROM3 (rEmROM3) or pVAX1-EmROM3 to determine the EmROM3-induced immune response. The induced humoral immune response was determined by measuring serum IgG antibody levels in immunized chickens. The induced cellular immune response was detected by measuring the transcription level of immune related cytokines and the proportion of T cell subsets of the immunized chickens. Finally, the protective efficacy of the EmROM3 vaccine against E. maxima was evaluated by immunization-challenge trials. Results revealed that the purified rEmROM3 reacted with chicken anti-E. maxima serum. The recombinant plasmid of pVAX1-EmROM3 was transcribed and translated in the injected muscle from the vaccinated chickens. In experimental groups, the IgG titers, proportions of CD4⁺ and CD8⁺ T cells, and transcription level of splenic cytokines were significantly increased compared with the control groups. The immunization-challenge trial revealed that immunization with rEmROM3 or pVAX1-EmROM3 led to restored weight gain, alleviated enteric lesion, decreased oocyst output as well as the higher anticoccidial index (ACI), indicating partial protection against E. maxima. These results indicate that EmROM3 is an effective candidate antigen for developing novel vaccines against infection by E. maxima.

Rhomboid protein 2 of Eimeria maxima provided partial protection against infection by homologous species

Rhomboid-like proteases (ROMs) are considered as new candidate antigens for developing new-generation vaccines due to their important role involved in the invasion of apicomplexan protozoa. In prior works, we obtained a ROM2 sequence of Eimeria maxima (EmROM2). This study was conducted to evaluate the immunogenicity and protective efficacy of EmROM2 recombinant protein (rEmROM2) and EmROM2 DNA (pVAX1-EmROM2) against infection by Eimeria maxima (E. maxima). Firstly, Western blot assay was conducted to analyze the immunogenicity of rEmROM2. The result showed that rEmROM2 was recognized by chicken anti-E. maxima serum. Reverse transcription-polymerase chain reaction (RT-PCR) and Western blot assay revealed apparent transcription and expression of EmROM2 at the injection site. qRT-PCR (quantitative real-time PCR), flow cytometry and indirect ELISA indicated that vaccination with rEmROM2 or EmROM2 DNA significantly upregulated the transcription level of cytokines (IFN-γ, IL-2, IL-4, IL-10, IL-17, TGF-β and TNF SF15), the proportion of CD8⁺ and CD4⁺ T lymphocytes and serum IgG antibody response. Ultimately, a vaccination-challenge trial was performed to evaluate the protective efficacy of rEmROM2 and pVAX1-EmROM2 against E. maxima. The result revealed that vaccination with rEmROM2 or pVAX1-EmROM2 significantly alleviated enteric lesions, weight loss, and reduced oocyst output caused by challenge infection of E. maxima, and provided anticoccidial index (ACI) of more than 160, indicating partial protection against E. maxima. In summary, vaccination with rEmROM2 or pVAX1-EmROM2 activated notable humoral and cell-mediated immunity and provided partial protection against E. maxima. These results demonstrated that EmROM2 protein and DNA are promising vaccine candidates against E. maxima infection.

In vitro effects of 5 recombinant antigens of Eimeria maxima on maturation, differentiation, and immunogenic functions of dendritic cells derived from chicken spleen

Eimeria maxima possesses integral families of immunogenic constituents that promote differentiation of immune cells during host-parasite interactions. Dendritic cells (DCs) have an irreplaceable role in the modulation of the host immunity. However, the selection of superlative antigen with immune stimulatory efficacies on host DCs is lacking. In this study, 5 recombinant proteins of E. maxima (Em), including Em14-3-3, rhomboid family domain containing proteins (ROM) EmROM1 and EmROM2, microneme protein 2 (EmMIC2), and Em8 were identified to stimulate chicken splenic derived DCs in vitro. The cultured populations were incubated with recombinant proteins, and typical morphologies of stimulated DCs were obtained. DC-associated markers major histocompatibility complex class II, CD86, CD11c, and CD1.1, showed upregulatory expressions by flow cytometry assay. Immunofluorescence assay revealed that recombinant proteins could bind with the surface of chicken splenic derived DCs. Moreover, quantitative real-time PCR results showed that distinct gene expressions of Toll-like receptors and Wnt signaling pathway were upregulated after the coincubation of recombinant proteins with DCs. The ELISA results indicated that the DCs produced a significant higher level of interleukin (IL)-12 and interferon-γ secretions after incubation with recombinant proteins. While transforming growth factor-β was significantly increased with rEmROM1, rEmROM2, and rEmMIC2 as compared to control groups, and IL-10 did not show significant alteration. Taken together, these results concluded that among 5 potential recombinant antigens, rEm14-3-3 could promote immunogenic functions of chicken splenic derived DCs more efficiently, which might represent an effective molecule for inducing the host Th1-mediated immune response against Eimeria infection.

Still naïve or primed: Anticoccidial vaccines call for memory

Despite decades of investigation to clarify protective mechanisms of anticoccidial responses, one crucial field is neglected, that is, protective memory responses in primed birds. Protective memory immunity is critical for host resistance to reinfection and is the basis of modern vaccinology, especially in developing successful subunit vaccines. There are important differences between the immune responses induced by infections and antigens delivered either as killed, recombinant proteins or as live, replicating vector vaccines or as DNA vaccines. Animals immunized with these vaccines may fail to develop protective memory immunity, and is still naïve to Eimeria infection. This may explain why limited success is achieved in developing next-generation anticoccidial vaccines. In this review, we try to decipher the protective memory responses against Eimeria infection, assess immune responses elicited by various anticoccidial vaccine candidates, and propose possible approaches to develop rational vaccines that can induce a protective memory response to chicken coccidiosis.

Construction of Lactococcus lactis expressing secreted and anchored Eimeria tenella 3-1E protein and comparison of protective immunity against homologous challenge

Two novel plasmids pTX8048-SP-Δ3-1E and pTX8048-SP-NAΔ3-1E-CWA were constructed. The plasmids were respectively electrotransformed into L. lactis NZ9000 to generate strain of L. lactis/pTX8048-SP-Δ3-1E in which 3-1E protein was expressed in secretion, and L. lactis/pTX8048-SP-NAΔ3-1E-CWA on which 3-1E protein was covalently anchored to the surface of bacteria cells. The expression of target proteins were examined by Western blot. The live lactococci expressing secreted 3-1E protein, anchored 3-1E protein, and cytoplasmic 3-1E protein was administered orally to chickens respectively, and the protective immunity and efficacy were compared by animal experiment. The results showed oral immunization to chickens with recombinant lactococci expressing anchored 3-1E protein elicited high 3-1E-specific serum IgG, increased high proportion of CD4⁺ and CD8α⁺ cells in spleen, alleviated average lesion score in cecum, decreased the oocyst output per chicken compared to lactococci expressing cytoplasmic or secreted 3-1E protein. Taken together, these findings indicated the surface anchored Eimeria protein displayed by L. lacits can induce protective immunity and partial protection against homologous infection.

The evolution of poxvirus vaccines

After Edward Jenner established human vaccination over 200 years ago, attenuated poxviruses became key players to contain the deadliest virus of its own family: Variola virus (VARV), the causative agent of smallpox. Cowpox virus (CPXV) and horsepox virus (HSPV) were extensively used to this end, passaged in cattle and humans until the appearance of vaccinia virus (VACV), which was used in the final campaigns aimed to eradicate the disease, an endeavor that was accomplished by the World Health Organization (WHO) in 1980. Ever since, naturally evolved strains used for vaccination were introduced into research laboratories where VACV and other poxviruses with improved safety profiles were generated. Recombinant DNA technology along with the DNA genome features of this virus family allowed the generation of vaccines against heterologous diseases, and the specific insertion and deletion of poxvirus genes generated an even broader spectrum of modified viruses with new properties that increase their immunogenicity and safety profile as vaccine vectors. In this review, we highlight the evolution of poxvirus vaccines, from first generation to the current status, pointing out how different vaccines have emerged and approaches that are being followed up in the development of more rational vaccines against a wide range of diseases.

A novel recombinant BCG vaccine encoding eimeria tenella rhomboid and chicken IL-2 induces protective immunity against coccidiosis

A novel recombinant Bacille Calmette-Guerin (rBCG) vaccine co-expressed Eimeria tenella rhomboid and cytokine chicken IL-2 (chIL-2) was constructed, and its efficacy against E. tenella challenge was observed. The rhomboid gene of E. tenella and chIL-2 gene were subcloned into integrative expression vector pMV361, producing vaccines rBCG pMV361-rho and pMV361-rho-IL2. Animal experiment via intranasal and subcutaneous route in chickens was carried out to evaluate the immune efficacy of the vaccines. The results indicated that these rBCG vaccines could obviously alleviate cacal lesions and oocyst output. Intranasal immunization with pMV361-rho and pMV361-rho-IL2 elicited better protective immunity against E. tenella than subcutaneous immunization. Splenocytes from chickens immunized with either rBCG pMV361-rho and pMV361-rho-IL2 had increased CD4⁺ and CD8⁺ cell production. Our data indicate recombinant BCG is able to impart partial protection against E. tenella challenge and co-expression of cytokine with antigen was an effective strategy to improve vaccine immunity.

Protective immunity induced by a DNA vaccine encoding Eimeria tenella rhomboid against homologous challenge

Rhomboid protein in Apicomplexa was associated with the process of host cell invasion. To evaluate the potential of the protein in eliciting protective immunity against challenge, a DNA vaccine pVAX1-Rho encoding Eimeria tenella rhomboid was constructed. Recombinant protein was expressed in Hela cells and verified by indirect immunofluorescence and western blotting analysis. In vivo experiments, 1-week-old chickens were randomly divided into three groups. Experimental group of chickens were immunized with DNA vaccines while control group of chickens were injected with pVAX1 plasmid alone or sterile water. Two weeks following the booster dose, all chickens were inoculated orally with 5 × 10(4) sporulated oocysts of E. tenella. The host immunity and protective efficacy of this vaccine against E. tenella challenge in broilers were evaluated. Results showed that specific antibody, the levels of interleukin-2 (IL-2), interferon-γ (IFN-γ), and the percentages of CD4(+) and CD8(+) T lymphocyte cells were significantly increased in the pVAX1-Rho group. Challenge experiments demonstrated that pVAX1-Rho vaccination could reduce oocyst excretion, decrease cecal lesion, increase bodyweight gains and provide chickens with oocysts decrease ratio around 75.8 %. These results suggest that the pVAX1-Rho was able to induce humoral and cellular responses and generate protective immunity against E. tenella infection.

Efficacy of Eimeria tenella rhomboid-like protein as a subunit vaccine in protective immunity against homologous challenge

The immune responses and protective efficacy against homologous challenge in chickens elicited by recombinant proteins of a rhomboid-like gene (ETRHO1) from Eimeria tenella was investigated in the present study. When chickens were immunized with the recombinant rhomboid antigen, specific antibody was generated by ELISA assay. In comparison with the PBS group, the expression levels of interleukin-2, interferon-γ, as well as the percentages of CD4⁺ and CD8⁺ cells in the group immunized with the recombinant rhomboid proteins were significantly increased (p < 0.01, p < 0.05, and p < 0.05, respectively). These results suggest that rhomboid was capable of eliciting humoral and cell-mediated immunity response in birds. Challenge experiments demonstrated that the recombinant rhomboid protein could provide chickens with a protection rate around 77.3%. Numbers of oocysts and cecal lesion from chickens in the group immunized with recombinant rhomboid proteins decreased significantly, and the body weight increased significantly when compared with chickens in the PBS group (p < 0.05). These results suggested that the recombinant rhomboid antigen was able to impart partial protection against homologous challenge in chicken and could be a potential candidate for an E. tenella vaccine development.

New insights into parasite rhomboid proteases

The rhomboid-like proteins constitute a large family of intramembrane serine proteases that are present in all branches of life. First studied in Drosophila, these enzymes catalyse the release of the active forms of proteins from the membrane and hence trigger signalling events. In protozoan parasites, a limited number of rhomboid-like proteases have been investigated and some of them are associated to pathogenesis. In Apicomplexans, rhomboid-like protease activity is involved in shedding adhesins from the surface of the zoites during motility and host cell entry. Recently, a Toxoplasma gondii rhomboid was also implicated in an intracellular signalling mechanism leading to parasite proliferation. In Entamoeba histolytica, the capacity to adhere to host cells and to phagocytose cells is potentiated by a rhomboid-like protease. Survey of a small number of protozoan parasite genomes has uncovered species-specific rhomboid-like protease genes, many of which are predicted to encode inactive enzymes. Functional investigation of the rhomboid-like proteases in other protozoan parasites will likely uncover novel and unexpected implications for this family of proteases.

Studies on construction of a recombinant Eimeria tenella SO7 gene expressing Escherichia coli and its protective efficacy against homologous infection

Eimeria spp. are the causative agents of coccidiosis, a major disease affecting the poultry industry. A recombinant non-antibiotic Escherichia coli that expresses the Eimeria tenella SO7 gene was constructed and its protective efficacy against homologous infection in chickens was determined. The three-day-old chickens were orally immunized with the recombinant non-antibiotic SO7 gene expressing E. coli and boosted two weeks later. Four weeks after the second immunization, the chickens were challenged with 5 × 10(4) homologous sporulated oocysts. The protective effects of the recombinant non-antibiotic E. coli were determined by measuring body weight change, mortality, histopathology, lesion scores, oocyst counts, the specific antibody response and the frequency of CD4(+) and CD8(+) lymphocytes in peripheral blood. The results showed that immunization with SO7 expressing E. coli resulted in significantly improved body weight gain, reduced lesion scores and oocyst shedding in immunized chickens compared to controls. Furthermore, administration of recombinant SO7 expressing E. coli leads to a significant increase in serum antibody, CD4(+) and CD8(+) T cells in peripheral blood of chickens. These results, therefore, suggest that the recombinant non-antibiotic E. coli that expresses the SO7 gene is able to effectively stimulate host protective immunity as evidenced by the induction of development of both humoral and cell-mediated immune responses against homologous challenge in chickens.

Cross immunity of DNA vaccine pVAX1-cSZ2-IL-2 to Eimeria tenella, E. necatrix and E. maxima

The study describes cross protection experiments with chimeric DNA vaccine pVAX1-cSZ2-IL-2 to determine its efficacy against four important Eimeria species. Seven-day-old chickens were randomly divided into nine groups; group 1 negative control, groups 2, 3, 4, 5 positive controls; and groups 6, 7, 8 and 9 experimental groups. On days 7 and 14, groups 1-5 were injected with TE buffer, and groups 6-9 with the vaccine. At 21 days of age, all chickens were inoculated with 5 x 10(4) sporulated oocysts except for the negative control. Groups 2 and 6 were inoculated with Eimeria tenella, groups 3 and 7 with Eimerianecatrix, groups 4 and 8 with Eimeria acervulina and groups 5 and 9 with Eimeria maxima. Seven days later, all chickens were weighed and slaughtered to obtain intestinal samples. Efficacy of immunization was evaluated on the basis of oocyst decrease ratio, lesion score, body-weight gain and anti-coccidial index. The results indicated that the recombinant plasmid can induce host immune responses by alleviating intestinal lesions, body weight loss and oocyst ratio and imparting good protection against E. tenella and E.acervulina, medium protection against E. necatrix but little effect against E. maxima. It is concluded that the conserved antigen can provide cross protection and should be explored further.

Past and future: vaccination againstEimeria

Eimeriaspp. are the causative agents of coccidiosis, a major disease affecting many intensively-reared livestock, especially poultry. The chicken is host to 7 species ofEimeriathat develop within intestinal epithelial cells and produce varying degrees of morbidity and mortality. Control of coccidiosis by the poultry industry is dominated by prophylactic chemotherapy but drug resistance is a serious problem. Strongly protective but species-specific immunity can be induced in chickens by infection with any of theEimeriaspp. At the Institute of Animal Health in Houghton, UK in the 1980s we showed that all 7Eimeriaspp. could be stably attenuated by serial passage in chickens of the earliest oocysts produced (i.e. the first parasites to complete their endogenous development) and this process resulted in the depletion of asexual development. Despite being highly attenuated, the precocious lines retained their immunizing capacity. Subsequent work led to the commercial introduction of the first live attenuated vaccine, Paracox®, that has now been in use for 20 years. As much work still remains to be done before the development of recombinant vaccines becomes a reality, it is likely that reliance upon live, attenuated vaccines will increase in years to come.

Construction of EGFP-tagged rBCG of E.tenella and distribution in chickens

Chicken coccidiosis is a major parasitic disease with substantial economic burden to the poultry industry. Enhanced green fluorescent protein (EGFP) tagged recombinant Bacille Calmette-Guerin (rBCG), as a fusion protein with coccidian rhomboid antigen was constructed to track rBCG in vivo in chickens in this study. Immunization of chickens with one dose of rBCG pMV361-Rho/EGFP induced humoral immune response. The colonization of rBCG in liver, spleen, lung, kidney and caecum was observed by laser confocal microscopy. Real-time quantitative RT-PCR showed a rise expression level of rhomboid protein on the 7th day and a peak on the 14th day and disappearance on the 28th day after immunization. These results have significant implications for the development of rBCG vaccines against avian coccidiosis.