Construction and evaluation of a pertactin-deficient live attenuated pertussis vaccine candidate BPZE1 derivative

Pertussis, mainly caused by Bordetella pertussis, is a severe respiratory disease that can be fatal, especially in young infants. Vaccines, massively implemented since the middle of the last century, have substantially reduced the pertussis incidence, but have not been able to fully control the disease. One of the shortcomings of current pertussis vaccines is their inability to prevent infection by and transmission of B. pertussis, in contrast to immunity following natural infection. We have developed the live attenuated nasal vaccine BPZE1 and have shown that it prevents both disease and B. pertussis infection in preclinical models. This vaccine is now in clinical development. However, the initial clinical studies have suggested that vaccine take is hampered by pre-existing antibodies to pertactin. Here, we have constructed a pertactin-deficient BPZE1 derivative called BPZE1P in order to overcome this limitation. BPZE1P colonized the murine respiratory tract as efficiently as BPZE1 and induced antibodies at levels similar to those elicited by BPZE1. In the presence of pre-existing antibodies induced by acellular pertussis vaccination, BPZE1P colonized the mouse respiratory tract more efficiently than BPZE1. Both vaccines protected equally well the murine lungs and noses from challenge with laboratory and clinical strains of B. pertussis, including pertactin-deficient strains, against which current acellular pertussis vaccines are less efficient. BPZE1P may thus be an interesting alternative to BPZE1 to overcome vaccine take limitations due to pre-existing antibodies to pertactin.

Rabbit Enteropathies on Commercial Farms in the Iberian Peninsula: Etiological Agents Identified in 2018-2019

Simple Summary

Digestive disorders are the main cause of economic damage in rabbit farms and, usually, antibiotic treatment is the first choice to control them. Nevertheless, a broad range of infectious agents can be involved in such disorders, as we have observed in our diagnosis work as a veterinary diagnostic laboratory. In this study, a global and updated overview of the frequency of detection of those etiological agents is provided. We have seen differences depending on the age of the affected rabbits, with young rabbits (<15 days old) being the most affected by enteropathogenic Escherichia coli strains, while in preweaning and growing rabbits, a coinfection of two or three pathogens is the most prevalent situation. Clostridium spiroforme and E. coli are the main bacterial agents detected in preweaning rabbits, but enterotoxigenic Bacteroides fragilis has just appeared as a new possible emergent pathogen. Coinfections between bacteria (C. spiroforme and E. coli), parasites (Eimeria spp.), and viruses (rotavirus) are much more frequent than simple infections in growing rabbits; for this reason, complete laboratory studies are required to establish on-farm disease control measures.

Abstract

Digestive disorders are the main cause of economic damage to rabbit farms. This article provides a global and updated overview of the diverse etiological agents causing them, since 757 clinical cases were analyzed during 2018 and 2019—Ninety-five from young rabbits (<15 days old), 117 from preweaning rabbits (15–35 days old), and 545 from growing rabbits. Etiological diagnosis was carried out by bacteriological culture and a set of real time polymerase chain reaction (qPCR) tests for the detection of enteropathogenic Escherichia coli (EPEC), Clostridium spiroforme, C. perfringens, rotavirus A, Bacteroides fragilis, and Eimeria spp. Also, 40 EPEC and 38 non EPEC isolates were investigated for the presence of other colonization factors (afr2, ral, liftA, and paa) by qPCR. EPEC is the most prevalent agent in young rabbits, and although different virulence profiles have been found among EPEC isolates, the liftA+, ral+, and paa+ profile is the most prevalent. C. spiroforme and EPEC are the more frequently detected pathogens in preweaning rabbits, but B. fragilis appears to be a new possible emergent pathogen. In growing rabbits, diverse co-infections between C. spiroforme, Eimeria spp., EPEC, and rotavirus are much more frequent than infections due to only one of them. Other pathogens detected in very few cases are Salmonella spp. and Enterococcus hirae.

The Role of Mucosal Immunity in Pertussis

Pertussis or whooping cough, mainly caused by Bordetella pertussis, is a severe respiratory disease that can affect all age groups but is most severe and can be life-threatening in young children. Vaccines against this disease are widely available since the 1950s. Despite high global vaccination coverage, the disease is not under control in any country, and its incidence is even increasing in several parts of the world. Epidemiological and experimental evidence has shown that the vaccines fail to prevent B. pertussis infection and transmission, although they are very effective in preventing disease. Given the high infection rate of B. pertussis, effective control of the disease likely requires prevention of infection and transmission in addition to protection against disease. With rare exceptions B. pertussis infections are restricted to the airways and do not usually disseminate beyond the respiratory epithelium. Therefore, protection at the level of the respiratory mucosa may be helpful for an improved control of pertussis. Yet, compared to systemic responses, mucosal immune responses have attracted relatively little attention in the context of pertussis vaccine development. In this review we summarize the available literature on the role of mucosal immunity in the prevention of B. pertussis infection. In contrast to vaccination, natural infection in humans and experimental infections in animals induce strong secretory IgA responses in the naso-pharynx and in the lungs. Several studies have shown that secretory IgA may be instrumental in the control of B. pertussis infection. Furthermore, studies in mouse models have revealed that B. pertussis infection, but not immunization with current acellular pertussis vaccines induces resident memory T cells, which may also contribute to protection against colonization by B. pertussis. As these resident memory T cells are long lived, vaccines that are able to induce them should provide long-lasting immunity. As of today, only one vaccine designed to induce potent mucosal immunity is in clinical development. This vaccine is a live attenuated B. pertussis strain delivered nasally in order to mimic the natural route of infection. Due to its ability to induce mucosal immunity it is expected that this approach will contribute to improved control of pertussis.

Distinct virulence ranges for infection of mice by Bordetella pertussis revealed by engineering of the sensor-kinase BvgS

The whooping cough agent Bordetella pertussis coordinately regulates the expression of its virulence factors with the two-component system BvgAS. In laboratory conditions, specific chemical modulators are used to trigger phenotypic modulation of B. pertussis from its default virulent Bvg⁺ phase to avirulent Bvg^- or intermediate Bvgⁱ phases, in which no virulence factors or only a subset of them are produced, respectively. Whether phenotypic modulation occurs in the host remains unknown. In this work, recombinant B. pertussis strains harboring BvgS variants were tested in a mouse model of infection and analyzed using transcriptomic approaches. Recombinant BP-Bvg_Δ65, which is in the Bvgⁱ phase by default and can be up-modulated to the Bvg⁺ phase in vitro, could colonize the mouse nose but was rapidly cleared from the lungs, while Bvg⁺-phase strains colonized both organs for up to four weeks. These results indicated that phenotypic modulation, which might have restored the full virulence capability of BP-Bvg_Δ65, does not occur in mice or is temporally or spatially restricted and has no effect in those conditions. Transcriptomic analyses of this and other recombinant Bvgⁱ and Bvg⁺-phase strains revealed that two distinct ranges of virulence gene expression allow colonization of the mouse nose and lungs, respectively. We also showed that a recombinant strain expressing moderately lower levels of the virulence genes than its wild type parent was as efficient at colonizing both organs. Altogether, genetic modifications of BvgS generate a range of phenotypic phases, which are useful tools to decipher host-pathogen interactions.

Characterization of a Bvg-regulated fatty acid methyl-transferase in Bordetella pertussis

The whooping cough agent Bordetella pertussis controls the expression of its large virulence regulon in a coordinated manner through the two-component signal transduction system BvgAS. In addition to the genes coding for bona fide virulence factors, the Bvg regulon comprises genes of unknown function. In this work, we characterized a new Bvg-activated gene called BP2936. Homologs of BP2936 are found in other pathogenic Bordetellae and in several other species, including plant pathogens and environmental bacteria. We showed that the gene product of BP2936 is a membrane-associated methyl-transferase of free fatty acids. We thus propose to name it FmtB, for fatty acid methyl-transferase of Bordetella. The role of this protein was tested in cellular and animal models of infection, but the loss of BP2936 did not appear to affect host-pathogen interactions in those assays. The high level of conservation of BP2936 among B. pertussis isolates nevertheless argues that it probably plays a role in the life cycle of this pathogen.