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Epidemiological Dynamics of Bovine Brucellosis in India Gloria J. Kang1,2, L. Gunaseelan3, Kaja M. Abbas2 1Biomedical
and Veterinary Sciences, 2Department of Population Health Sciences, Virginia Tech, Blacksburg, VA, USA 3Department of Veterinary Public Health and Epidemiology, Madras Veterinary College, Tamil Nadu Veterinary and Animal Sciences University, Chennai, India
ABSTRACT
Data collection and analysis was conducted at Madras Veterinary College in Chennai, India. We developed a deterministic, susceptible-infected-recovered model to simulate brucellosis transmission dynamics in cattle in India, calibrated to current endemically stable levels of bovine brucellosis prevalence (13.5%). We then analyzed the epidemiological benefits at various rates of transmission reduction and mass vaccination.
Findings While test-and-slaughter is an effective control strategy, socio-cultural constrains in India forbid culling of cattle on religious grounds. Reducing transmission rates lowered disease prevalence correspondingly, and a one-time vaccination initially lowered prevalence but increased with influx of new susceptible births over time. Reducing transmission among cattle either by restricting movement and contact rate or through vaccination decreases the burden of brucellosis in India.
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Transmission
• Routes: ingestion of infected tissues/body fluids, contact with mucous membranes, direct inoculation, inhalation, and fomites • Symptoms: spontaneous abortion, premature birth, retained placenta, low milk yield; otherwise insidious and nondescript presentation
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• Bovine brucellosis is caused by Brucella abortus bacterium in cattle
Reduced Transmission Rate 0% 20% 40% 60% 80%
Bovine brucellosis in India
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Time (years)
• Major veterinary and public health problem • Indian Council of Agricultural Research estimate seroprevalence of ~13.5% and at a stable, endemic equilibrium [1]
Figure 1. Epidemiological impact of reducing transmission rate Prevalence decreases over time by reducing transmission rate by 20%, 40%, 60%, and 80% below the transmission rate at endemic stability (0%).
• No disease management practices in place; strict governmental ban on cow slaughter; and weak surveillance
Vaccination 0.15
Methods
Reducing Transmission Rate
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Bovine brucellosis is a worldwide, zoonotic, disease with significant economic and global health impact. As a predominantly agrarian society, India faces many healthrelated and socioeconomic challenges in managing livestock disease. Mathematical modeling of livestock diseases in developing regions can provide valuable insight into infectious disease dynamics and disease management strategies; these findings help decision-makers in improving public health policy. Our objective was to develop an epidemiological model of brucellosis transmission dynamics among cattle in India, and to estimate the impact of various control strategies. Control strategies include test-andslaughter, reducing transmission rate, and mass vaccination.
• Brucellosis is a complex zoonotic disease with significant epidemiological, economic, and global health impact. Recent reemergence of brucellosis has necessitated innovative approaches to epidemiological study and intervention design, specifically mathematical modeling. Prevalence
Background
RESULTS
INTRODUCTION
Public health significance • Risk factors: farm management, vaccination status, sanitation, and hygiene
OBJECTIVES • Develop an epidemiological model of brucellosis transmission dynamics among livestock cattle in India • Estimate the impact of various prevention and control strategies
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METHODS 0
Epidemic model • We developed a system dynamics model of bovine brucellosis transmission with births and deaths. Mass action mixing of susceptible and infected cattle lead to new infections; and at the time of vaccination, susceptible cattle move into the immune compartment
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Figure 2. Epidemiological impact of one-time vaccination Vaccinating 20%, 40%, 60%, 80%, and 100% of cattle initially reduces brucellosis prevalence correspondingly. Over time however, infections rebound due to the influx of new susceptible births into the population.
Vaccination
Birth
Susceptible
Transmission
DISCUSSION Infected
Recovered
Death
Death
• One-time vaccination
Ordinary differential equations • We adapted the susceptible – infected – recovered (SIR) epidemic model, where • S0 = initial susceptible population
[1] H. Rahman, “DBT Network Project on Brucellosis,” Indian Council of Agricultural Research, Project Monitoring Unit, Project Directorate on Animal Disease Monitoring and Surveillance, Annual Report, Sep. 2013.
50 Time (Years)
Death
• Transmission rate reduction
REFERENCES
Proportion Vaccinated 0% 20% 40% 60% 80% 100%
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• In addition to zoonotic threat of spillover into human populations, infected herds can cause significant economic losses for those dependent on agrarian practices
Prevalence
Vaccination is an effective strategy to eliminate bovine brucellosis in India, but it must be implemented at regular intervals. One potential management strategy may be restricting herd density, although further study is necessary to establish densitydependent effects on disease transmission. A main limitation of this study is lacking data on disease prevalence and population dynamics of livestock. The governmental ban on cow slaughter presents a significant obstacle within this analysis as well as potential management outcomes; nonexistent records of cattle off-take and the impossibility of test-and-slaughter implementation stress dire need of further mathematical modeling and analysis. Although this epidemiological model is a generalized representation of brucellosis transmission dynamics in cattle, this study illustrates the comparative public health impact of various prevention and control strategies for India. Low resource availability, weak infrastructure, and unique cultural beliefs in India emphasize the demand for enhanced inter-sectoral collaboration in research and policy.
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Interpretation
• β = transmission rate
𝑆0 = 𝑆0 − 𝑝𝑣𝑆0 𝑑𝑆 = 𝜇 − 𝛽𝑆𝐼 − 𝜇𝑆 𝑑𝑡 𝑑𝐼 = 𝛽𝑆𝐼 − 𝜇𝐼 𝑑𝑡 𝑑𝑅 = 𝑝𝑣𝑆0 − 𝜇𝑅 𝑑𝑡
• Summary: Mass vaccination and reducing transmission rates of susceptible and infected cattle are effective strategies in controlling bovine brucellosis in India. • Future research: However, challenges remain in implementing feasible practices without enhanced systems-based research through transdisciplinary collaborations among the fields of population health, public policy, and mathematical sciences.
Questions for public health policy through mathematical modeling What is the epidemiological impact: prevalence, incidence, mortality, morbidity? What is the geographic and spatial distribution? What is the demographic distribution?
Model parameters and values
CONTACT
• Model parameters reflect brucellosis transmission at endemic stability Gloria Kang
[email protected]
ACKNOWLEDGEMENTS •
How reliable is surveillance?
We thank the students, faculty, and scientists of the Department of Veterinary Public Health and Epidemiology at Madras Veterinary College for their assistance and feedback on this study.
• Initial conditions: 13.5% cattle infected and 86.5% cattle susceptible
How to conduct hypothesis testing of different scenarios for risk and potential for spread and transmission dynamics? What interventions are warranted for prevention and control? When to introduce interventions? What is the quantum and period of interventions?
Parameter Susceptible proportion (S) - endemic stability Infected proportion (I) - endemic stability Transmission rate (β) Birth/Death rates (μ) Vaccine efficacy (v) Proportion vaccinated (p)
Value 0.865 0.135 0.1156 /year 0.1 /year 70% 0 - 100%
• Limitations: No cattle mortality data due to sociocultural constraints, lacking seroprevalence data, and limited understanding of livestock population dynamics.
