A safety assessment of a fowlpox-vectored Mycoplasma gallisepticum vaccine in chickens

Immune Evasion of Mycoplasma gallisepticum: An Overview

Mycoplasma gallisepticum is one of the smallest self-replicating organisms. It causes chronic respiratory disease, leading to significant economic losses in poultry industry. Following M. gallisepticum invasion, the pathogen can persist in the host owing to its immune evasion, resulting in long-term chronic infection. The strategies of immune evasion by mycoplasmas are very complex and recent research has unraveled these sophisticated mechanisms. The antigens of M. gallisepticum exhibit high-frequency changes in size and expression cycle, allowing them to evade the activation of the host humoral immune response. M. gallisepticum can invade non-phagocytic chicken cells and also regulate microRNAs to modulate cell proliferation, inflammation, and apoptosis in tracheal epithelial cells during the disease process. M. gallisepticum has been shown to transiently activate the inflammatory response and then inhibit it by suppressing key inflammatory mediators, avoiding being cleared. The regulation and activation of immune cells are important for host response against mycoplasma infection. However, M. gallisepticum has been shown to interfere with the functions of macrophages and lymphocytes, compromising their defense capabilities. In addition, the pathogen can cause immunological damage to organs by inducing an inflammatory response, cell apoptosis, and oxidative stress, leading to immunosuppression in the host. This review comprehensively summarizes these evasion tactics employed by M. gallisepticum, providing valuable insights into better prevention and control of mycoplasma infection.

Infection, Transmission, Pathogenesis and Vaccine Development against Mycoplasma gallisepticum

Mycoplasma sp. comprises cell wall-less bacteria with reduced genome size and can infect mammals, reptiles, birds, and plants. Avian mycoplasmosis, particularly in chickens, is primarily caused by Mycoplasma gallisepticum (MG) and Mycoplasma synoviae. It causes infection and pathology mainly in the respiratory, reproductive, and musculoskeletal systems. MG is the most widely distributed pathogenic avian mycoplasma with a wide range of host susceptibility and virulence. MG is transmitted both by horizontal and vertical routes. MG infection induces innate, cellular, mucosal, and adaptive immune responses in the host. Macrophages aid in phagocytosis and clearance, and B and T cells play critical roles in the clearance and prevention of MG. The virulent factors of MG are adhesion proteins, lipoproteins, heat shock proteins, and antigenic variation proteins, all of which play pivotal roles in host cell entry and pathogenesis. Prevention of MG relies on farm and flock biosecurity, management strategies, early diagnosis, use of antimicrobials, and vaccination. This review summarizes the vital pathogenic mechanisms underlying MG infection and recapitulates the virulence factors of MG-host cell adhesion, antigenic variation, nutrient transport, and immune evasion. The review also highlights the limitations of current vaccines and the development of innovative future vaccines against MG.

Designing of novel chimeric PvpA-pMGA protein of Mycoplasma gallisepticum, applicable for indirect ELISA

Background

Mycoplasma gallisepticum is the primary agent of chronic respiratory disease in chickens creating important economic losses in poultry industry. pMGA and pvpA genes encode major surface proteins in M. gallisepticum containing pathogenic, antigenic, and immune evasion characteristics. The objective of the present study was to design, express, and purify the recombinant chimeric PvpA-pMGA protein from M.gallisepticum for using in serological diagnostic test.

Methods

Antigenic regions of PvpA and pMGA proteins were predicted for designing chimeric pvpA-pMGA gene construct. The codon optimized sequence was cloned into the expression vector pET32a+ and transformed into the Escherichia coli strain BL21 (DE3). The pET32a-PvpA-pMGA recombinant plasmid was expressed and confirmed by SDS-PAGE and immunoblotting. PvpA-pMGA recombinant protein (20μg and 50μg), ts-11 vaccine strain, and S6 strain that formulated by montanide adjuvant and two control groups (PBS and adjuvant) were injected subcutaneously to six groups of chickens.

Results

High yield of protein was purified amount 138 mg/L by affinity batch formation method. Indirect ELISA showed the levels of antibodies in rPvpA-pMGA was significantly higher than ts-11 and S6 groups (p<0.05). The results indicated that antigen-specific response was successfully elicited by the rpMGA-PvpA in chickens. The result of the ELISA with sera collected from ts-11 and S6 groups showed that indirect PvpA-pMGA-ELISA is appropriate candidate for detection of specific antibodies against M. gallisepticum with 100% sensitivity and specificity.

Conclusions

The rPvpA-pMGA is a highly candidate immunogenic protein which induced high amount of humoral immune response. Novel rPvpA-pMGA protein could be useful for evaluation of antibody level in vaccinated poultry flocks.

Review of Poultry Recombinant Vector Vaccines

The control of poultry diseases has relied heavily on the use of many live and inactivated vaccines. However, over the last 30 yr, recombinant DNA technology has been used to generate many novel poultry vaccines. Fowlpox virus and turkey herpesvirus are the two main vectors currently used to construct recombinant vaccines for poultry. With the use of these two vectors, more than 15 recombinant viral vector vaccines against Newcastle disease, infectious laryngotracheitis, infectious bursal disease, avian influenza, and Mycoplasma gallisepticum have been developed and are commercially available. This review focuses on current knowledge about the safety and efficacy of recombinant viral vectored vaccines and the mechanisms by which they facilitate the control of multiple diseases. Additionally, the development of new recombinant vaccines with novel vectors will be briefly discussed.

Clinical expression, epidemiology and monitoring of Mycoplasma gallisepticum and Mycoplasma synoviae: an update

Mycoplasma gallisepticum (MG) and Mycoplasma synoviae (MS) are of clinical and economic importance for the global poultry industry. Many countries and integrations are involved in monitoring programs to control both mycoplasma species. This review provides an extensive historic overview of the last seven decades on the development of the knowledge regarding the factors that influence the clinical expression of the disease, the epidemiology and monitoring of both MG and MS. This includes the detection of new virulent strains, studies unravelling the transmission routes, survival characteristics and the role of other avian hosts. Also the role of molecular typing tests in unravelling epidemiology, and factors that complicate the interpretation of test results such as heterologous mycoplasma infections, use of heterologous oil-emulsion vaccines, use of antibiotic treatments, occurrence of MG and MS strains with low virulence, and last but not least the use of live and/or inactivated MG and MS vaccines are discussed.

Current status of vaccine research, development, and challenges of vaccines for Mycoplasma gallisepticum

Mycoplasma gallisepticum (MG) is an important avian pathogen that causes significant economic losses in the poultry industry. Surprisingly, the limited protection and adverse reactions caused by the vaccines, including live vaccines, bacterin-based (killed) vaccines, and recombinant viral vaccines is still a major concern. Mycoplasma gallisepticum strains vary in infectivity and virulence and infection may sometimes unapparent and goes undetected. Although extensive research has been carried out on the biology of this pathogen, information is lacking about the type of immune response that confers protection and selection of appropriate protective antigens and adjuvants. Regardless of numerous efforts focused on the development of safe and effective vaccine for the control of MG, the use of modern DNA vaccine technology selected in silico approaches for the use of conserved recombinant proteins may be a better choice for the preparation of novel effective vaccines. More research is needed to characterize and elucidate MG products modulating MG-host interactions. These products could be used as a reference for the preparation and development of vaccines to control MG infections in poultry flocks.

Chitosan-adjuvanted Mycoplasma gallisepticum bacterin via intraocular administration enhances Mycoplasma gallisepticum protection in commercial layers

Mycoplasma gallisepticum (MG) causes respiratory signs and economic losses in the poultry industry. MG vaccination is one of the effective prevention and control measures that have been used around the world. Our previous study demonstrated that chitosan-adjuvanted MG bacterin could effectively reduce pathological lesions induced by MG and that chitosan could be used as an adjuvant in MG bacterin. The present study determining the efficacy of MG bacterins against the Thai MG strain was based on vaccine programs. Seven groups (25 layers/group) were received MG bacterins containing 0.5% chitosan or a commercial bacterin via intramuscular (IM) or intraocular (IO) route at 6 and 10 wk of age. Sham-negative and sham-positive controls were groups 1 and 2, respectively. Group 3: IM route of chitosan bacterin followed by IM route of chitosan bacterin; group 4: commercial bacterin via IM route followed by chitosan bacterin via IO route; group 5: commercial bacterin via IM route followed by commercial bacterin via IM route; group 6: chitosan bacterin via IM followed by chitosan bacterin via IO route; and group 7: chitosan bacterin via IO route followed by chitosan bacterin via IO route were determined. At 16 wk of age, all groups, excluding group 1, were challenged intratracheally with 0.1 mL containing Thai MG strain 107 colony-forming unit. At 17, 18, and 20 wk of age, 5 birds in each group were bled for serological testing and swabbed at the choanal cleft for the quantitative real-time PCR assay, the euthanized and necropsied. The results showed that birds vaccinated with a commercial intramuscular bacterin followed by an intraocularly chitosan adjuvant bacterin showed the best protection against the MG challenge. The study indicated that chitosan could be the effective mucosal adjuvant and increased the effectiveness of MG bacterin.

Development and evaluation of novel recombinant adenovirus-based vaccine candidates for infectious bronchitis virus and Mycoplasma gallisepticum in chickens

Avian infectious bronchitis caused by the infectious bronchitis virus (IBV), and mycoplasmosis caused by Mycoplasma gallisepticum (MG) are two major respiratory diseases in chickens that have resulted in severe economic losses in the poultry industry. We constructed a recombinant adenovirus that simultaneously expresses the S1 spike glycoprotein of IBV and the TM-1 protein of MG (pBH-S1-TM-1-EGFP). For comparison, we constructed two recombinant adenoviruses (pBH-S1-EGFP and pBH-TM-1-EGFP) that express either the S1 spike glycoprotein or the TM-1 protein alone. The protective efficacy of these three vaccine constructs against challenge with IBV and/or MG was evaluated in specific pathogen free chickens. Groups of seven-day-old specific pathogen free chicks were immunized twice, two weeks apart, via the oculonasal route with the pBH-S1-TM-1-EGFP, pBH-S1-EGFP, or pBH-TM-1-EGFP vaccine candidates or the commercial attenuated infectious bronchitis vaccine strain H52 and MG vaccine strain F-36 (positive controls), and challenged with virulent IBV or MG two weeks later. Interestingly, by days 7 and 14 after the booster immunization, pBH-S1-TM-1-EGFP-induced antibody titre was significantly higher (P < 0.01) compared to attenuated commercial IBV vaccine; however, there was no significant difference between the pBH-S1-TM-1-EGFP and attenuated commercial MG vaccine groups (P > 0.05). The clinical signs, the gross, and histopathological lesions scores of the adenovirus vaccine constructs were not significantly different from that of the attenuated commercial IBV or MG vaccines (positive controls) (P > 0.05). These results demonstrate the potential of the bivalent pBH-S1-TM-1-EGFP adenovirus construct as a combination vaccine against IB and mycoplasmosis.

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.

Avipoxviruses: infection biology and their use as vaccine vectors

Avipoxviruses (APVs) belong to the Chordopoxvirinae subfamily of the Poxviridae family. APVs are distributed worldwide and cause disease in domestic, pet and wild birds of many species. APVs are transmitted by aerosols and biting insects, particularly mosquitoes and arthropods and are usually named after the bird species from which they were originally isolated. The virus species Fowlpox virus (FWPV) causes disease in poultry and associated mortality is usually low, but in flocks under stress (other diseases, high production) mortality can reach up to 50%. APVs are also major players in viral vaccine vector development for diseases in human and veterinary medicine. Abortive infection in mammalian cells (no production of progeny viruses) and their ability to accommodate multiple gene inserts are some of the characteristics that make APVs promising vaccine vectors. Although abortive infection in mammalian cells conceivably represents a major vaccine bio-safety advantage, molecular mechanisms restricting APVs to certain hosts are not yet fully understood. This review summarizes the current knowledge relating to APVs, including classification, morphogenesis, host-virus interactions, diagnostics and disease, and also highlights the use of APVs as recombinant vaccine vectors.