Rickettsial seropositivity in Lao PDR smallholder livestock farms: Implications for animal and human health

Abstract

Rickettsioses are emerging zoonotic diseases in Southeast Asia caused by vector-borne, intracellular Rickettsia bacteria that threaten public health, animal welfare, and food security. Despite their importance to rural livelihoods, the epidemiology of rickettsial exposure in livestock remains poorly understood. This study used abattoir-based serology to evaluate livestock as sentinels of environmental exposure to Rickettsia in Lao PDR and to identify spatial hotspots and risk factors for seropositivity. Abattoir-based serological data were generated from cattle, pigs, and water buffalo samples collected in 18 provinces between January 2022 and April 2023. The immunofluorescence assay was used to detect antibodies against three rickettsial antigens: Scrub Typhus Group (Orientia tsutsugamushi), Typhus Group (R. typhi), and Spotted Fever Group (R. conorii, R. honei). Samples with IgG titres ≥1:100 were considered positive. Of 821 samples tested, 32 were seropositive: 25 cattle (9.9%), seven pigs (2.4%), and none of the buffalo. Breed and age were significant predictors, with non-native breeds and animals under one year old more likely to be positive (p < 0.05). Spatial-temporal analysis revealed one significant cluster in cattle (p = 0.0056) in southern Laos. These results represent the first nationwide serological assessment of Rickettsia exposure in Lao livestock.