Laboratory Diagnosis of Bovine Abortions Caused by Non-Maintenance Pathogenic Leptospira spp.: Necropsy, Serology and Molecular Study Out of a Belgian Experience

Abstract

: Bovine leptospirosis is a bacterial zoonotic disease caused by pathogenic Leptospira spp.. The pathology and epidemiology of this infection are influenced by the numerous existing serovars and their adaptation to specific hosts. Infections by host-maintained serovars such as Hardjo are well documented, unlike those from the incidental ones. In July 2014, an emerging phenomenon of an increased incidence of icteric abortions associated with leptospiral infection occurred in southern Belgium. First-line serological analyses targeting cattle-adapted serovars failed at initial diagnosis. This study provides a comprehensive description of laboratory findings-at the level of necropsy, serology and molecular diagnosis-regarding icteric and non-icteric abortions (n = 116) recorded during this time (years 2014-2015) and associated with incidental infection by serovars such as Grippotyphosa, Australis and Icterohaemorrhagiae. Based on these tests, a diagnostic pathway is proposed for these types of infection in cattle to establish an affordable but accurate diagnosis in the future. These investigations add insights into the understanding of the pathogenesis of bovine leptospirosis associated with serovars classically described as non-maintenance.

Keywords: Leptospira spp., cattle; MAT; PCR; abortion; lfb1-phylogeny; non-maintenance serovars; pathology.

Figure 1

lbf1-derived phylogeny of Leptospira-induced icteric abortions and reference strains. Red, green and rose circles indicate strains of L. interrogans, L.kirschneri and L. borgepetersenii species, respectively. Reference strains are listed with their serogroup, serovar and strain name. Abortuses are indicated with their fetus ID as in Table S1.

Figure 2

Recommended diagnostic approach for abortuses according to the results of necropsy, MAT on a dam’s serum and PCR on fetal organs performed in series, for a conclusion about Leptospira spp. as the cause of the abortion. NT: non tested, * did not occur in this study.