Comparison of depopulation and S19-RB51 vaccination strategies for control of bovine brucellosis in high prevalence areas

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.

Modelling the control of bovine brucellosis in India

Brucellosis imposes substantial impacts on livestock production and public health worldwide. A stochastic, age-structured model incorporating herd demographics was developed describing within- and between-herd transmission of Brucella abortus in dairy cattle herds. The model was fitted to data from a cross-sectional study conducted in Punjab State of India and used to evaluate the effectiveness of control strategies under consideration. Based on model results, stakeholder acceptance and constraints regarding vaccine supply, vaccination of replacement calves in large farms should be prioritized. Test and removal applied at early stages of the control programme where seroprevalence is high would not constitute an effective or acceptable use of resources because significant numbers of animals would be 'removed' (culled or not used for breeding) based on false positive results. To achieve sustained reductions in brucellosis, policymakers must commit to maintaining vaccination in the long term, which may eventually reduce frequency of infection in the livestock reservoir to a low enough level for elimination to be a realistic objective. This work provides key strategic insights into the control of brucellosis in India, which has the largest cattle population globally, and a general modelling framework for evaluating control strategies in endemic settings.

Brucellosis control methods with an emphasis on vaccination: a systematic review

INTRODUCTION

Brucellosis is considered as one of the main zoonotic infections and a major public health concern worldwide. The aim of the present study was to evaluate various strategies for controlling brucellosis with an especial emphasis on efficacy of vaccination.

AREAS COVERED

International databanks (Web of Science, PubMed, Embase) were searched for potentially relevant studies published from January 1, 2011 to March 25, 2021 using the following keywords: "Brucella", "Brucella abortus", "Brucella melitensis", "Brucella canis", "Brucella suis", "brucellosis", "Bang disease", "undulant fever", "Malta fever", "vaccination", "vaccine", and "immunization". The literature search was restricted to original articles published in English.

EXPERT OPINION

Various methods are employed to prevent and control brucellosis, such as removing sick animals by slaughtering, separating sick animals from the herd, and vaccination. Preventing, controlling, and eradicating brucellosis requires a lot of financial support, perseverance, and time. In order to conduct a detailed study, it is recommended that more studies be conducted in developing countries and different parts of the world.

Extraction and characterisation of Brucella abortus strain RB51 rough lipopolysaccharide

Brucellosis is an important zoonotic disease with considerable impacts on human and animal health. Brucella abortus strain RB51 vaccine is used for prevention of bovine brucellosis in Iran. Due to strain roughness, available serological tests cannot detect vaccinated animals. Detection of serological responses to the vaccine is important to monitor accurate vaccination implementation. Rough lipopolysaccharide (RLPS) of RB51 strain was extracted and characterised to develop serological tests for diagnosis of vaccinated animals. RLPS was extracted using phenol-chloroform-petroleum ether and evaluated by limulus amebocyte lysate (LAL) assay, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and agar gel immunodiffusion (AGID). According to our results, the extracted RLPS caused positive reaction in LAL assay. In SDS-PAGE, a band with a molecular weight around 14 kDa was identified after specific staining using silver nitrate. Double AGID of the RLPS with a hyperimmune serum resulted in a precipitation line formation. Our study showed that the method can be successfully used to extract RLPS from Brucella abortus strain RB51 as confirmed by LAL assay, PAGE and AGID.

PLGA (85:15) nanoparticle based delivery of rL7/L12 ribosomal protein in mice protects against Brucella abortus 544 infection: A promising alternate to traditional adjuvants

There is a compelling need for the development of suitable adjuvants for human use to enhance the efficacy of the upcoming vaccines for the prevention of life threatening infections. In the current study, we have tried to explore the immunogenic potential of nanoparticles (NPs) made of PLGA (poly lactic-co-glycolic acid), a biodegradable and biocompatible polymer approved by FDA for human use after entrapping rL7/L12 protein, an immunodominant antigen of Brucella. Adjuvant properties were exhibited by the formulation as it elicited high IgG antibody titers just after first immunization which increased significantly after the booster administration. A good elicitation of the Th1 cytokines especially IFN-γ was recorded. Amongst the IgG antibody subclasses, IgG1 remained the predominant subclass to be elicited in mice serum after immunization; however IgG1/2a ratio showed a mixed profile of Th1/Th2 response. Lymphocyte proliferation assay as a marker of amplification in cellular immunity demonstrated that the splenocytes of the immunized mice had a high proliferation index with reference to the control, revealing that L7/L12 entrapping PLGA nanoparticles are potent inducer of inflammatory cell response indispensable to combat Brucella infection. Enumeration of splenic CFU after 14 days of infection with Brucella abortus 544 showed a significant reduction in log CFU of splenic bacteria in the vaccinated mice as compared to the control group. Therefore it is evident that PLGA nano formulations delivering the entrapped vaccine candidate in mice elicit specific humoral as well as cellular responses specific to the entrapped Brucella antigen. So there is much promise in this approach and this work by highlighting the adjuvant properties of the PLGA nanospheres will accelerate the development of improved vaccines safe for human as well as veterinary use.