BRUCELLOSIS AT THE HUMAN–ANIMAL INTERFACE: COMPARATIVE IMMUNOGENICITY OF KILLED VS LIVE VACCINES IN RUMINANTS AND ABATTOIR WORKERS

Abstract

Brucellosis remains a major zoonotic disease in endemic regions, sustained by infected ruminant reservoirs and amplified at occupational interfaces such as abattoirs. In Pakistan—particularly Punjab—livestock movement, variable vaccination practice, and limited workplace biosafety create conditions that perpetuate human exposure and hinder disease control. While live attenuated vaccines remain widely used in ruminants, killed/inactivated platforms continue to be explored for safety, yet their comparative immunogenicity under real-world endemic conditions remains insufficiently documented.

Objective

To compare immune responses induced by killed versus live brucellosis vaccines in ruminants and to evaluate serological evidence of exposure among abattoir workers, thereby assessing cross-species immunogenicity patterns and occupational risk at the human–animal interface in Punjab, Pakistan.

Study Type: Zoonotic Immunology / Vaccine Evaluation

Methods

A comparative immunogenicity and occupational exposure evaluation was conducted through a tertiary care hospital in Punjab, Pakistan, with linked sampling of ruminants entering abattoir supply chains. Human participants included abattoir workers (n=180) and non-exposed controls (n=120). Animal sampling involved ruminants (n=880) categorized into live vaccine, killed/inactivated vaccine, and unvaccinated groups across cattle, buffalo, sheep, and goats. Human serological screening was performed using RBPT with confirmatory serology. In ruminants, humoral immune response was quantified via IgG ELISA (mean OD values), and a subset underwent IFN-γ analysis as a surrogate marker of Th1-driven cellular immunity. Occupational risk factors were assessed through structured exposure histories and modeled using adjusted odds ratios.

Results

Human seropositivity was significantly higher among abattoir workers (17.8%) compared with controls (5.0%), supporting substantial occupational exposure. Risk modeling showed strong associations between seropositivity and lack of gloves, absence of respiratory protection, frequent cut injuries, raw milk consumption, and ≥5 years of abattoir employment, indicating both direct-contact and aerosol-related transmission pathways.

In ruminants, live attenuated vaccination generated immune patterns more consistent with protective immunity. IFN-γ responses were markedly higher in the live vaccine groups, reflecting stronger Th1 cellular activation, while killed/inactivated vaccines produced moderate and more variable cellular signaling. Unvaccinated animals demonstrated the highest IgG ELISA values, suggesting ongoing endemic infection pressure rather than vaccine-induced immunity. Species-level visualization showed consistent elevation of antibody signals in unvaccinated groups across cattle, buffalo, sheep, and goats, indicating sustained circulation of Brucella in supply-chain animals.

Conclusion

This study demonstrates that live attenuated brucellosis vaccines induce stronger cellular immune signatures in ruminants compared with killed/inactivated platforms, aligning more closely with the immune requirements for controlling intracellular Brucella. Simultaneously, abattoir workers in Punjab exhibit substantially higher seropositivity than non-exposed controls, driven by modifiable workplace factors and cumulative exposure. These findings support a One Health approach combining high-coverage livestock vaccination using immunologically robust platforms with strengthened abattoir biosafety measures, targeted occupational surveillance, and risk-based prevention to reduce zoonotic spillover and protect high-risk workers in endemic settings.