Infectivity and virulence of leptospiral strains of serogroup Sejroe other than Hardjo on experimentally infected hamsters

Standardization of chronic uterine infection of hamsters by Leptospira santarosai serovar Guaricura, from serogroup Sejroe

Leptospirosis is an important zoonosis that in cattle is characterized as a reproductive disease. It is well reported that the main agent of bovine leptospirosis worldwide is Sejroe serogroup serovar Hardjo. Reproductive disease in cattle has several gaps in its knowledge and studies with Golden Syrian hamsters, experimentally infected, are limited. Therefore, a protocol that could reproduce the chronic genital disease in hamsters would be extremely valuable for the advance of the knowledge of that syndrome. The aim of this study was to establish an experimental protocol for chronic non-lethal genital infection of female hamsters by L. santarosai serovar Guaricura (Sejroe serogroup), strain 2013_VF52. For this, two concentrations (1.0 × 108 leptospires/mL and 1.0 × 104 leptospires/mL) were used intraperitoneally in female hamsters of 06-08 weeks of age. Hamsters that survived for up to forty days after inoculation were euthanized. Uterine and renal tissues were collected to evaluate leptospires' presence by PCR and culture. The protocol demonstrated that 1.0 × 104 leptospires/mL of the strain determined chronic genital leptospirosis in the hamster model. The standardization of a protocol for chronic genital leptospirosis in hamsters can be extremely useful for the understanding of the physiopathology of the infection, as the distribution of leptospires in the uterus and the agent-host interactions.

Leptospira interrogans Serovar Icterohaemorrhagiae Failed to Establish Distinct Infection in Naïve Gilts: Lessons Learned from a Preliminary Experimental Challenge

Leptospira is a pathogen involved in fertility problems in pigs. Nevertheless, little information is available on pathogenicity, transmission, tissue tropism, and immune response. The objective of this preliminary study was to induce a diagnostically detectable infection in naïve gilts using Leptospira interrogans serovar Icterohaemorrhagiae to gain the knowledge required for designing a large-scale trial. Eight seronegative fertile gilts were divided into three groups: control (n = 2), challenge (n = 3; 10 mL of 10⁸ leptospires/mL intravenously), and contact (n = 3). A daily clinical examination and periodic sampling of blood, urine, and vaginal swabs were performed until four weeks after infection when necropsy was undertaken. Seroconversion of infected animals was detected first by a microscopic agglutination test (MAT) between four and seven days after inoculation. No clinical signs were observed except pyrexia. Laboratory data primarily remained within reference intervals. Leptospira were undetectable in all groups by real-time PCR (sera, urine, vaginal swabs, and tissue samples) and bacterial culture (urine and tissue samples). However, histologic evidence for tubulo-interstitial nephritis could be found. Based on the study results and limitations, questions to be solved and approaches to be reconsidered are raised for the conduction of further experimental studies to understand the pathogenesis and the role of Icterohaemorrhagiae in pig health.

Investigating the Immunological and Biological Equilibrium of Reservoir Hosts and Pathogenic Leptospira: Balancing the Solution to an Acute Problem?

Leptospirosis is a devastating zoonotic disease affecting people and animals across the globe. Pathogenic leptospires are excreted in urine of reservoir hosts which directly or indirectly leads to continued disease transmission, via contact with mucous membranes or a breach of the skin barrier of another host. Human fatalities approach 60,000 deaths per annum; though most vertebrates are susceptible to leptospirosis, complex interactions between host species and serovars of Leptospira can yield disease phenotypes that vary from asymptomatic shedding in reservoir hosts, to multi-organ failure in incidental hosts. Clinical symptoms of acute leptospirosis reflect the diverse range of pathogenic species and serovars that cause infection, the level of exposure, and the relationship of the pathogen with the given host. However, in all cases, pathogenic Leptospira are excreted into the environment via urine from reservoir hosts which are uniformly recognized as asymptomatic carriers. Therefore, the reservoir host serves as the cornerstone of persistent disease transmission. Although bacterin vaccines can be used to abate renal carriage and excretion in domestic animal species, there is an urgent need to advance our understanding of immune-mediated host–pathogen interactions that facilitate persistent asymptomatic carriage. This review summarizes the current understanding of host–pathogen interactions in the reservoir host and prioritizes research to unravel mechanisms that allow for colonization but not destruction of the host. This information is required to understand, and ultimately control, the transmission of pathogenic Leptospira.

Identification of Pathogenic Leptospira Species in the Urogenital Tract of Water Buffaloes (Bubalus bubalis) From the Amazon River Delta Region, Brazil

In the current context of deforestation and fire in the Amazon, buffaloes could be a cost-effective and sustainable alternative for cattle production in the region, as they can convert low-quality foods and be raised in floodplain areas. However, little is known about the reproductive diseases that affect these animals; thus, the purpose of this study was to perform the molecular characterization of Leptospira spp. in the urogenital tract of water buffaloes (Bubalus bubalis) raised in the Amazon River Delta region in Brazil. Samples were collected from 114 kidneys, 204 ovaries, and 160 uterine swabs of slaughtered buffaloes in the Macapá microregion of Amapá State (Brazil) and were subjected to PCR to detect bacterial DNA. Positive amplicons were sequenced to identify Leptospira species. Among the total samples, 11/473 were PCR positive (2.3%), including 10 kidney samples and one uterine swab sample. DNA sequencing identified two pathogenic species from the kidney samples: L. interrogans, accounting for 60.0% (6/10) of these samples, and L. borgpetersenii, accounting for 20.0% (2/10), while 20.0% (2/10) were identified only at the genus level. The bacterium in the uterine swab sample was identified as L. interrogans with genetic proximity to strains belonging to the serovar Hardjo. This is the first report of leptospires species identified in buffaloes from the Amazon River Delta region and revealed that these animals may be carriers of different pathogenic Leptospira species, similar to bovines, including showing genital colonization.

Development of a pooled antigen for use in the macroscopic slide agglutination test (MSAT) to detect Sejroe serogroup exposure in cattle

This study aimed to develop and evaluate a pooled antigen for use in the macroscopic slide agglutination test (MSAT) to detect cattle positive for the Sejroe serogroup. To this end, 193 bovine serum samples from different Pará State regions (Amazonia) were subjected to a reference microscopic agglutination test (MAT) for the serological diagnosis of leptospirosis using 11 serovars representing the Sejroe serogroup: Hardjo-prajitno; Hardjo-bovis; Sejroe; Wolffi; Guaricura (Bov.G.); Guaricura (M4/98); Ricardi; Gorgas; Recreo; Polonica and Medanensis. The three most prevalent serovars in the MAT were selected for the development of a pooled antigen for use in MSAT; subsequently, the 193 serum were assessed with the macroscopic slide agglutination test (MSAT) containing the developed antigen. The Kappa test was used to determine the general agreement between the MAT and MSAT results. As a result, of the 193 serum samples, 155 (80.3%) were reactive, and 38 (19.7%) were non-reactive in the MAT; Hardjo-prajitno, Wolffi and Medanensis were the three most prevalent serovars. Of the 193 serum samples tested in the MSAT using the developed pooled antigen, 114 were reactive (59.0%), and 79 (41.0%) were non-reactive; the Kappa coefficient was 0.52 (CI 95%, 0.40-0.63), indicating moderate agreement between the two tests. The MSAT with the pooled antigen including the most prevalent serovars detected bovines with the Sejroe serogroup exposure, mainly in animals with high titters in the MAT, and could be used to screen herds suspected of acute infection by this serogroup in Pará State.