Prevalence and spatial distribution of Brucella spp. seropositive equids from the state of Mato Grosso, Brazil.

Overview

• This study assessed the prevalence and spatial distribution of equine brucellosis caused by Brucella spp. in Mato Grosso, Brazil, finding a low and evenly spread prevalence among horses, mules, and donkeys across different biomes.

Background on Brucellosis in Equids

• Brucellosis is a chronic infectious disease affecting equids such as horses, mules, and donkeys.
• The disease typically causes suppurative (pus-forming) lesions in joints and bursae, which can impair animal performance.
• Brucellosis is also a concern for public health due to its zoonotic potential, meaning it can be transmitted from animals to humans.
• Understanding its prevalence and spatial distribution helps target control measures and epidemiological surveillance.

Objectives of the Study

• To determine the prevalence of Brucella spp. seropositive equids in the state of Mato Grosso, Brazil.
• To analyze the spatial distribution patterns of seropositive cases across different regions and environmental biomes in the state.
• To examine potential associations between seropositivity and factors like species, age, sex, management practices, and proximity to bovine brucellosis foci.

Methods

• Sample Collection:
  • 3,858 serum samples were collected from equids: 3,230 horses, 602 mules, and 26 donkeys.
  • Samples were collected throughout Mato Grosso, covering all municipalities and three major biomes: Amazon, Cerrado, and Pantanal.
• Diagnostic Tests:
  • Initial screening was done using the Buffered Acidified Antigen Test (AAT).
  • Confirmatory testing employed the Complement Fixation Test (CFT), per the Brazilian Ministry of Agriculture guidelines.
• Statistical and Spatial Analysis:
  • Prevalence rates with confidence intervals were calculated.
  • Associations between seropositivity and animal or management variables were assessed.
  • Spatial distribution was analyzed to detect any clustering or patterns of disease occurrence.
  • Analysis of potential links between equine brucellosis seropositivity and bovine brucellosis foci was performed.

Results

• Prevalence Rates:
  • Buffered Acidified Antigen Test (AAT) indicated 4.48% reactive animals (173 out of 3,858 samples).
  • Complement Fixation Test (CFT) confirmed 0.78% (30 out of 3,858) as true positives.
  • Overall estimated prevalence was 0.82% (95% Confidence Interval: 0.79-0.85%).
  • Prevalence by biome:
    • Amazon: 0.91%
    • Cerrado: 0.88%
    • Pantanal: 0.12%
• Associations:
  • No statistically significant relationship was found between seropositivity and:
    • Age
    • Sex
    • Species (horse, mule, donkey)
    • Management variables (type of husbandry, location, etc.)
  • No association between seropositive equids and bovine brucellosis foci was observed, suggesting separate infection dynamics.
• Spatial Distribution:
  • Spatial analysis showed no evidence of disease clustering.
  • The distribution of seropositive animals was homogeneous across the state, implying a diffuse and widespread presence rather than localized outbreaks.

Interpretation and Conclusions

• The low prevalence of seropositivity in equids suggests that brucellosis is present but not highly endemic in Mato Grosso.
• The homogeneous spatial pattern indicates no specific hotspots or clusters, reflecting a widespread but low-level exposure or infection.
• Since equids appear to be incidental hosts rather than main reservoirs, control efforts might focus more on primary hosts like cattle.
• The absence of association with bovine brucellosis foci reduces the likelihood of significant interspecies transmission to equids, although the potential risk merits ongoing surveillance.
• These findings highlight the importance of continuing epidemiological monitoring to detect any changes in prevalence or distribution that could impact animal health and public safety.