Abortion and premature birth in cattle following vaccination with Brucella abortus strain RB51

A review of three decades of use of the cattle brucellosis rough vaccine Brucella abortus RB51: myths and facts

Cattle brucellosis is a severe zoonosis of worldwide distribution caused by Brucella abortus and B. melitensis. In some countries with appropriate infrastructure, animal tagging and movement control, eradication was possible through efficient diagnosis and vaccination with B. abortus S19, usually combined with test-and-slaughter (T/S). Although S19 elicits anti-smooth lipopolysaccharide antibodies that may interfere in the differentiation of infected and vaccinated animals (DIVA), this issue is minimized using appropriate S19 vaccination protocols and irrelevant when high-prevalence makes mass vaccination necessary or when eradication requisites are not met. However, S19 has been broadly replaced by vaccine RB51 (a rifampin-resistant rough mutant) as it is widely accepted that is DIVA, safe and as protective as S19. These RB51 properties are critically reviewed here using the evidence accumulated in the last 35 years. Controlled experiments and field evidence shows that RB51 interferes in immunosorbent assays (iELISA, cELISA and others) and in complement fixation, issues accentuated by revaccinating animals previously immunized with RB51 or S19. Moreover, contacts with virulent brucellae elicit anti-smooth lipopolysaccharide antibodies in RB51 vaccinated animals. Thus, accepting that RB51 is truly DIVA results in extended diagnostic confusions and, when combined with T/S, unnecessary over-culling. Studies supporting the safety of RB51 are flawed and, on the contrary, there is solid evidence that RB51 is excreted in milk and abortifacient in pregnant animals, thus being released in abortions and vaginal fluids. These problems are accentuated by the RB51 virulence in humans, lack diagnostic serological tests detecting these infections and RB51 rifampicin resistance. In controlled experiments, protection by RB51 compares unfavorably with S19 and lasts less than four years with no evidence that RB51-revaccination bolsters immunity, and field studies reporting its usefulness are flawed. There is no evidence that RB51 protects cattle against B. melitensis, infection common when raised together with small ruminants. Finally, data acumulated during cattle brucellosis eradication in Spain shows that S19-T/S is far more efficacious than RB51-T/S, which does not differ from T/S alone. We conclude that the assumption that RB51 is DIVA, safe, and efficaceous results from the uncritical repetition of imperfectly examined evidence, and advise against its use.

Histopathologic and immunohistochemical findings in the placentas and fetuses of domestic swine naturally infected with Brucella suis biovar 2

Porcine brucellosis, which is caused by Brucella suis biovar (bv) 2, is a re-emerging disease that causes reproductive problems in pigs in Europe. The pathogenesis and lesions of B. suis intrauterine infection are poorly characterized; characterization could facilitate the diagnosis and investigation of porcine brucellosis. We collected samples of placentas and fetuses for histologic and microbiologic studies during an outbreak of abortions on a pig-breeding farm in Spain. Brucella was cultured from the vaginal swabs obtained from sows that had aborted, some placentas, and fetal tissues (spleen, liver, lung, gastric content); molecular testing confirmed B. suis bv 2 infection. Histologically, there was necrotizing and hemorrhagic placentitis; suppurative hepatitis; lymphoid depletion and sinusoidal histiocytosis in the spleen, lymph nodes, and thymus; and bronchointerstitial pneumonia. Hemorrhages were observed in the umbilical cord, heart, kidneys, and brain. We detected Brucella by immunohistochemistry (IHC) in all of the placentas and fetal organs studied, specifically in the trophoblasts of the chorionic epithelium, in the cytoplasm of macrophages in the chorionic stroma, and extracellularly in necrotic debris. Furthermore, we assessed the lymphocyte population in the placentas through the use of IHC (anti-CD3, anti-Pax5 antibodies), revealing that the lymphocytic response was composed of T cells but not B cells.

Safe Subunit Green Vaccines Confer Robust Immunity and Protection against Mucosal Brucella Infection in Mice

Brucellosis is a zoonotic disease that causes significant negative impacts on the animal industry and affects over half a million people worldwide every year. The limited safety and efficacy of current animal brucellosis vaccines, combined with the lack of a licensed human brucellosis vaccine, have led researchers to search for new vaccine strategies to combat the disease. To this end, the present research aimed to evaluate the safety and efficacy of a green vaccine candidate that combines Brucella abortus S19 smooth lipopolysaccharide (sLPS) with Quillaja saponin (QS) or QS-Xyloglucan mix (QS-X) against mucosal brucellosis in BALB/C mice. The results of the study indicate that administering two doses of either sLPS-QS or sLPS-QS-X was safe for the animals, triggered a robust immune response, and enhanced protection following intranasal challenge with S19. Specifically, the vaccine combinations led to the secretion of IgA and IgG1 in the BALF of the immunized mice. We also found a mixed IgG1/IgG2a systemic response indicating evidence of both Th1 and Th2 activation, with a predominance of the IgG1 over the IgG2a. These candidates resulted in significant reductions in the bioburden of lung, liver, and spleen tissue compared to the PBS control group. The sLPS-QS vaccination had conferred the greatest protection, with a 130-fold reduction in Brucella burdens in lung and a 55.74-fold reduction in the spleen compared to PBS controls. Vaccination with sLPS-QS-X resulted in the highest reduction in splenic Brucella loads, with a 364.6-fold decrease in bacterial titer compared to non-vaccinated animals. The study suggests that the tested vaccine candidates are safe and effective in increasing the animals’ ability to respond to brucellosis via mucosal challenge. It also supports the use of the S19 challenge strain as a safe and cost-effective method for testing Brucella vaccine candidates under BSL-2 containment conditions.

Molecular characterization of Brucella spp. from seropositive herds of cattle farmed at the wildlife-livestock-human interface in Rwanda

Seroprevalence studies showed that brucellosis is prevalent in cattle in Rwanda with no recent study on the characterization of Brucella spp. Therefore, this study aimed to characterize Brucella spp. in seropositive herds of cattle farmed at the wildlife–livestock–human interface. Whole blood samples (n = 118), milk (n = 41), and vaginal swabs (n = 51) were collected from 64 seropositive herds. All samples (n = 210) were inoculated onto modified Centro de Investigacion y Tecnologia Agroalimentaria (CITA) selective medium. Cultures were analyzed to detect Brucella spp. using 16S−23S ribosomal DNA interspacer region (ITS) PCR, the Brucella cultures were speciated using AMOS and Bruce-ladder PCR assays. Brucella spp. were detected in 16.7% (35/210) of the samples established from the samples using ITS-PCR. The AMOS PCR assay identified mixed Brucella abortus and B. melitensis (n = 6), B. abortus (n = 7), and B. melitensis (n = 1) from cultures from blood samples; mixed B. abortus and B. melitensis (n = 1) and B. abortus (n = 4) from cultures from milk samples; mixed B. abortus and B. melitensis (n = 6), B. abortus (n = 8), and B. melitensis (n = 1) from cultures from vaginal swabs. Bruce-ladder PCR assay confirmed B. abortus and B. melitensis cultures. The isolation of Brucella spp. was significantly associated with districts, with the Nyagatare district having more isolates than other districts (p = 0.01). This study identified single or mixed B. abortus and B. melitensis infections in cattle samples in Rwanda, which emphasizes the need to improve brucellosis control at the wildlife–livestock–human interface and raise the awareness of cattle keepers, abattoir workers, laboratory personnel, and consumers of cattle products.

Facing the Human and Animal Brucellosis Conundrums: The Forgotten Lessons

Brucellosis is a major zoonotic disease caused by Brucella species. Historically, the disease received over fifty names until it was recognized as a single entity, illustrating its protean manifestations and intricacies, traits that generated conundrums that have remained or re-emerged since they were first described. Here, we examine confusions concerning the clinical picture, serological diagnosis, and incidence of human brucellosis. We also discuss knowledge gaps and prevalent confusions about animal brucellosis, including brucellosis control strategies, the so-called confirmatory tests, and assumptions about the primary-binding assays and DNA detection methods. We describe how doubtfully characterized vaccines have failed to control brucellosis and emphasize how the requisites of controlled safety and protection experiments are generally overlooked. Finally, we briefly discuss the experience demonstrating that S19 remains the best cattle vaccine, while RB51 fails to validate its claimed properties (protection, differentiating infected and vaccinated animals (DIVA), and safety), offering a strong argument against its current widespread use. These conundrums show that knowledge dealing with brucellosis is lost, and previous experience is overlooked or misinterpreted, as illustrated in a significant number of misguided meta-analyses. In a global context of intensifying livestock breeding, such recurrent oversights threaten to increase the impact of brucellosis.

Challenges in Veterinary Vaccine Development

Animals provide food and clothing in addition to other value-added products. Changes in diet and lifestyle have increased the consumption and the use of animal products. Infectious diseases in animals are a major threat to global animal health and its welfare; their effective control is crucial for agronomic health, for safeguarding food security and also alleviating rural poverty. Development of vaccines has led to increased production of healthy poultry, livestock, and fish. Animal production increases have alleviated food insecurity. In addition, development of effective vaccines has led to healthier companion animals. However, challenges remain including climate change that has led to enhancement in vectors and pathogens that may lead to emergent diseases in animals. Preventing transmission of emerging infectious diseases at the animal-human interface is critically important for protecting the world population from epizootics and pandemics. Hence, there is a need to develop new vaccines to prevent diseases in animals. This review describes the broad challenges to be considered in the development of vaccines for animals.

Clinical Presentations of Brucellosis Over a Four-Year Period at Sultan Qaboos University Hospital and Armed Forces Hospital, Muscat, Oman

Objectives

Brucellosis is a highly contagious zoonotic disease which can have serious health implications for affected humans and livestock. This study aimed to evaluate the clinical presentation, geographical distribution and risk factors of brucellosis cases admitted over a four-year period to two hospitals in Muscat, Oman.

Methods

This observational study was conducted from January 2015 to December 2018 at the Sultan Qaboos University Hospital and Armed Forces Hospital in Muscat. All patients with probable or definitive diagnoses of brucellosis according to the diagnostic criteria of the World Health Organization were included. Relevant data were gathered from the patients’ medical records, including results from standard agglutination tests, Brucella enzyme-linked immunosorbent assays, bacterial blood or tissue/aspirate cultures and Brucella polymerase chain reaction tests.

Results

A total of 64 patients were diagnosed with brucellosis over the study period. The median age was 31.5 years and 73.4% were male. The majority (95.2%) presented with fever, followed by weight loss (51%), transaminitis (48.4%), peripheral arthritis/arthralgia (15.9%) and back pain (spondylodiscitis/sacroiliitis; 23.4%). Overall, 75.5% reported having consumed raw dairy products, while only 25.9% gave a positive history of animal contact.

Conclusion

Patients with brucellosis presented with a wide range of clinical features, the most predominant of which was fever. The majority of patients were residents of or had recently visited Salalah and had consumed raw dairy products. These findings highlight the need for healthcare practitioners to maintain a high index of suspicion for this diagnosis. Moreover, further regulatory measures are necessary to oversee the sale of raw/unpasteurised dairy products.

The candidate vaccine strain Brucella ovis ∆abcBA is protective against Brucella melitensis infection in mice

Brucellosis is a major zoonotic disease, and Brucella melitensis is the species most often associated with human infection. Vaccination is the most efficient tool for controlling animal brucellosis, with a consequent decrease of incidence of human infections. Commercially available live attenuated vaccines provide some degree of protection, but retain residual pathogenicity to human and animals. In this study, Brucella ovis ∆abcBA (Bo∆abcBA), a live attenuated candidate vaccine strain, was tested in two formulations (encapsulated with alginate and alginate plus vitelline protein B [VpB]) to immunize mice against experimental challenge with B. melitensis strain 16M. One week after infection, livers and spleens of immunized mice had reduced numbers of the challenge strain B. melitensis 16M when compared with those of nonimmunized mice, with a reduction of approximately 1-log₁₀ of B. melitensis 16M count in the spleens from immunized mice. Moreover, splenocytes stimulated with B. melitensis antigens in vitro secreted IFN-γ when mice had been immunized with Bo∆abcBA encapsulated with alginate plus VpB, but not with alginate alone. Body and liver weights were similar among groups, although spleens from mice immunized with Bo∆abcBA encapsulated with alginate were larger than those immunized with Bo∆abcBA encapsulated with alginate plus VpB or nonimmunized mice. This study demonstrated that two vaccine formulations containing Bo∆abcBA protected mice against experimental challenge with B. melitensis.

Immunological pathways of macrophage response to Brucella ovis infection

As the molecular mechanisms of Brucella ovis pathogenicity are not completely clear, we have applied a transcriptome approach to identify the differentially expressed genes (DEGs) in RAW264.7 macrophage infected with B. ovis. The DEGs related to immune pathway were identified by Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) functional enrichment analysis. Quantitative real-time PCR (qRT-PCR) was performed to validate the transcriptome sequencing data. In total, we identified 337 up-regulated and 264 down-regulated DEGs in B. ovis-infected group versus mock group. Top 20 pathways were enriched by KEGG analysis and 20 GO by functional enrichment analysis in DEGs involved in the molecular function, cellular component, and biological process and so on, which revealed multiple immunological pathways in RAW264.7 macrophage cells in response to B. ovis infection, including inflammatory response, immune system process, immune response, cytokine activity, chemotaxis, chemokine-mediated signaling pathway, chemokine activity, and CCR chemokine receptor binding. qRT-PCR results showed Ccl2 (ENSMUST00000000193), Ccl2 (ENSMUST00000124479), Ccl3 (ENSMUST00000001008), Hmox1 (ENSMUST00000005548), Hmox1 (ENSMUST00000159631), Cxcl2 (ENSMUST00000075433), Cxcl2 (ENSMUST00000200681), Cxcl2 (ENSMUST00000200919), and Cxcl2 (ENSMUST00000202317). Our findings firstly elucidate the pathways involved in B. ovis-induced host immune response, which may lay the foundation for revealing the bacteria–host interaction and demonstrating the pathogenic mechanism of B. ovis.

Vaccine safety studies of Brucella abortus S19 and S19ΔvjbR in pregnant swine

Brucellosis in swine is caused by Brucella suis, a bacterial infection of nearly worldwide distribution. Brucella suis is also transmissible to humans, dogs and cattle and is considered a reemerging disease of public health concern. To date, there is no effective vaccine for swine. This prompted us to investigate the potential use of the commercially available vaccine for cattle or the live attenuated vaccine candidate S19ΔvjbR. As the first step, we sought to study the safety of the vaccine candidates when administered in pregnant sows, since one of the major drawbacks associated with vaccination using Live Attenuated Vaccines (LAV) is the induction of abortions when administered in pregnant animals. Fifteen pregnant gilts at mid-gestation were divided into four groups and subsequently vaccinated subcutaneously using different formulations containing 2.0 ± 0.508 × 109 CFU of either S19 or S19ΔvjbR. Vaccination in pregnant animals with the vaccine candidates did not induce abortion, stillbirths or a reduction in litter size. Multiple tissues in the gilts and piglets were examined at the time of delivery to assess bacterial colonization and histopathological changes. There was no evidence of vaccine persistence in the gilts or bacterial colonization in the fetuses. Altogether, these data suggest that both vaccine candidates are safe for use in pregnant swine. Analysis of the humoral responses, specifically anti-Brucella IgG levels measured in serum, demonstrated a robust response induced by either vaccine, but of shorter duration (4-6 weeks post-inoculation) compared to that observed in cattle or experimentally infected mice. Such a transient humoral response may prove to be beneficial in cases where the vaccine is used in eradication campaigns and in the differentiation of vaccinated from infected animals. This study provides evidence to support future efficacy studies of both vaccine candidates in swine.

Brucellosis in India: results of a collaborative workshop to define One Health priorities

Brucellosis is an important zoonosis worldwide. In livestock, it frequently causes chronic disease with reproductive failures that contribute to production losses, and in humans, it causes an often-chronic febrile illness that is frequently underdiagnosed in many low- and middle-income countries, including India. India has one of the largest ruminant populations in the world, and brucellosis is endemic in the country in both humans and animals. In November 2017, the International Livestock Research Institute invited experts from government, national research institutes, universities, and different international organizations to a one-day meeting to set priorities towards a "One Health" control strategy for brucellosis in India. Using a risk prioritization exercise followed by discussions, the meeting agreed on the following priorities: collaboration (transboundary and transdisciplinary); collection of more epidemiological evidence in humans, cattle, and in small ruminants (which have been neglected in past research); Economic impact studies, including cost effectiveness of control programmes; livestock vaccination, including national facilities for securing vaccines for the cattle population; management of infected animals (with the ban on bovine slaughter, alternatives such as sanctuaries must be explored); laboratory capacities and diagnostics (quality must be assured and better rapid tests developed); and increased awareness, making farmers, health workers, and the general public more aware of risks of brucellosis and zoonoses in general. Overall, the meeting participants agreed that brucellosis control will be challenging in India, but with collaboration to address the priority areas listed here, it could be possible.

Safety of vaccination against brucellosis with the rough strain in pregnant cattle

Brucellosis is an infectious and contagious disease that profoundly impacts public health. However, in many countries, disease prevention is restricted to the vaccination of calves, and there is no prophylactic strategy for pregnant heifers and cows. The aim of this study was to evaluate the safety of the rough strain vaccine against brucellosis in pregnant cattle. Crossbred cows (N = 96) at three gestational periods (early, mid, or late pregnancy) were randomly allocated into the vaccine treatment group or to the control group. We then compared the percentage of pregnancies reaching full term, live calves 60 days after delivery, and seropositive calves. There was no effect of vaccination in any of the gestational periods on the evaluation endpoints. In conclusion, vaccination against brucellosis with the rough strain is safe for pregnant cattle at all gestational periods.

Characterization of Brucella abortus mutant strain Δ22915, a potential vaccine candidate

Brucellosis, caused by Brucella spp., is an important zoonosis worldwide. Vaccination is an effective strategy for protection against Brucella infection in livestock in developing countries and in wildlife in developed countries. However, current vaccine strains including S19 and RB51 are pathogenic to humans and pregnant animals, limiting their use. In this study, we constructed the Brucella abortus (B. abortus) S2308 mutant strain Δ22915, in which the putative lytic transglycosylase gene BAB_RS22915 was deleted. The biological properties of mutant strain Δ22915 were characterized and protection of mice against virulent S2308 challenge was evaluated. The mutant strain Δ22915 showed reduced survival within RAW264.7 cells and survival in vivo in mice. In addition, the mutant strain Δ22915 failed to escape fusion with lysosomes within host cells, and caused no observable pathological damage. RNA-seq analysis indicated that four genes associated with amino acid/nucleotide transport and metabolism were significantly upregulated in mutant strain Δ22915. Furthermore, inoculation of ∆22915 at 105 colony forming units induced effective host immune responses and long-term protection of BALB/c mice. Therefore, mutant strain ∆22915 could be used as a novel vaccine candidate in the future to protect animals against B. abortus infection.

Molecular typing of isolates obtained from aborted foetuses in Brucella-free Holstein dairy cattle herd after immunisation with Brucella abortus RB51 vaccine in Egypt

Bovine brucellosis is endemic in Egypt in spite of application of surveillance and control measures. An increase of abortions was reported in a Holstein dairy cattle herd with 600 animals in Damietta governorate in Egypt after immunisation with Brucella (B.) abortus RB51 vaccine. Twenty one (10.6%) of 197 vaccinated cows aborted after 3 months. All aborted cows had been tested seronegative for brucellosis in the past 3 years. B. abortus was isolated from four foetuses. Conventional biochemical and bacteriological identification and polymerase chain reaction (PCR) confirmed two B. abortus biovar (bv.) 1 smooth and two B. abortus rough strains. None of the B. abortus isolates were identified as RB51. Genotyping analysis by multiple locus of variable number tandem repeats analysis based on 16 markers (MLVA-16) revealed two different profiles with low genetic diversity. B. abortus bv1 was introduced in the herd and caused abortions.

The Case for Live Attenuated Vaccines against the Neglected Zoonotic Diseases Brucellosis and Bovine Tuberculosis

Vaccination of humans and animals with live attenuated organisms has proven to be an effective means of combatting some important infectious diseases. In fact, the 20th century witnessed tremendous improvements in human and animal health worldwide as a consequence of large-scale vaccination programs with live attenuated vaccines (LAVs). Here, we use the neglected zoonotic diseases brucellosis and bovine tuberculosis (BTb) caused by Brucella spp. and Mycobacterium bovis (M. bovis), respectively, as comparative models to outline the merits of LAV platforms with emphasis on molecular strategies that have been pursued to generate LAVs with enhanced vaccine safety and efficacy profiles. Finally, we discuss the prospects of LAV platforms in the fight against brucellosis and BTb and outline new avenues for future research towards developing effective vaccines using LAV platforms.

Use of serology and real time PCR to control an outbreak of bovine brucellosis at a dairy cattle farm in the Nile Delta region, Egypt

Background

Bovine brucellosis remains one of the most prevalent zoonotic infections affecting dairy cattle in developing countries where the applied control programs often fail. We analyzed the epidemiologic pattern of bovine brucellosis in a dairy cattle herd that showed several cases of abortions after regular vaccination with RB51 (B. abortus vaccine). In 2013 thirty dairy cows, from a Holstein-Friesian dairy herd with a population of 600 cattle, aborted five months post vaccination by a regular RB51 vaccine. Blood samples were drawn from milking cows and growing heifers, as well as heifers and cows pregnant up to 6 months. These samples were collected in June 2013 (n = 257) and May 2014 (n = 263) and were tested by real time (rt)-PCR as well as serological tests, in particular Rose Bengal Test (RBT), Enzyme-Linked Immunosorbent Assays (ELISA) and Fluorescence Polarization Assay. Tissue specimens were also collected from an aborted fetus and cultured. Isolates were subjected to bacteriological typing tests at the genus and species levels.

Results

Five months post vaccination with RB51 vaccine, Brucella (B.) DNA was detected in blood samples of cows by rt-PCR. The serological tests also revealed the spread of Brucella field strains within the herd in 2013. Four Brucella isolates were recovered from specimens collected from the aborted fetus. These isolates were typed as follows: one B. abortus RB51 vaccine strain and three isolates of B. abortus field strain. The seropositive cows with positive rt-PCR might indicate an infection by the Brucella field strain; while the positive rt-PCR results from seronegative animals may either be due to circulating RB51 vaccine DNA in vaccinated animals or to circulating field strain in infected animals before seroconversion.

Conclusion

The results herein suggest that PCR can be a good supplementary tool in an outbreak situation, if an assay is available that can differentiate vaccine and field strains with a high analytical sensitivity. We recommend using RBT and ELISA in parallel in outbreak situations, to identify as many infected animals as possible during the initial screenings. This test procedure should be repeated for at least three successive negative tests, with one month interval.