Spatial and seasonal distribution of Leptospira spp. seropositive horses in the Northeast region of Brazil.

Overview

• This study investigated the prevalence, distribution, and risk factors of Leptospira spp. infection in horses in Northeast Brazil.
• It aimed to identify seasonal variations, spatial clusters of infection, serogroups involved, and associated demographic factors over a three-year period.

Background

• Leptospirosis is a bacterial disease caused by Leptospira spp., important for both public health and the economy due to its zoonotic nature.
• Horses often carry the bacteria asymptomatically, serving as silent reservoirs and potential transmission sources to humans.
• Understanding the distribution and prevalence of Leptospira in horses helps in formulating control measures to reduce transmission risks.

Objectives

• Determine the prevalence of Leptospira spp. seropositive horses in four states of Northeast Brazil: Paraíba, Pernambuco, Rio Grande do Norte, and Ceará.
• Identify the serogroups of Leptospira circulating and the antibody titers in horses.
• Examine seasonal (rainy vs dry) and spatial distribution patterns of seropositive cases.
• Identify demographic factors of horses associated with higher seropositivity.

Methodology

• Samples: 1152 equine serum samples collected from 225 municipalities across four states over three years (2017-2019).
• Seasons: Samples were collected during the rainy season (May and June) and the dry season (October and November).
• Testing Method: Microscopic Agglutination Test (MAT) was used to detect anti-Leptospira antibodies.
• Data Analysis: Prevalence rates, serogroup distributions, spatial clustering, and correlations with demographic data were evaluated.

Key Findings

• Overall seroprevalence was 23.9% over the three-year period.
• Higher prevalence in the rainy season (30.4%) compared to the dry season (17.4%).
• During the rainy season, the Ballum serogroup was predominant, while Sejroe serogroup was more common in the dry season.
• Age was a significant factor: horses aged 6 years and older had increased seropositivity.
• Geographically, Pernambuco state had higher seropositivity, especially in border municipalities and large urban centers.
• A spatial cluster with 2.8 times higher relative risk of infection was identified during the dry season of 2018.

Interpretation and Implications

• The findings highlight seasonal variation in Leptospira infections, likely influenced by environmental conditions favoring bacterial survival and host exposure.
• Higher seropositivity in older horses may reflect cumulative exposure over time.
• The detection of spatial clusters suggests focal areas where transmission risk is intensified, especially in border zones and urban settings.
• Dominance of different serogroups in different seasons suggests potential shifts in reservoir hosts or environmental conditions affecting bacterial ecology.
• Rodents and wild animals are important reservoirs; thus, rodent control and limiting contact in horse farming are critical.
• Shared pastures with cattle could facilitate cross-species transmission, necessitating integrated management approaches.
• Immunoprophylaxis (vaccination) is recommended to reduce infection and transmission potential.

Conclusions

• Leptospira spp. infections are widespread among horses in Northeast Brazil, with marked seasonal and spatial patterns.
• Preventive measures focusing on rodent control, minimizing contact with wildlife, careful pasture management, and vaccination can help control leptospirosis in horses.
• Monitoring and surveillance should continue, especially in high-risk areas and seasons, to protect both animal and human health.