Persistent High Leptospiral Shedding by Asymptomatic Dogs in Endemic Areas Triggers a Serious Public Health Concern

Domestic dogs in indigenous Amazonian communities: key players in Leptospira cycling and transmission?

Background

Leptospirosis is the world's most common zoonotic disease. Mitigation and control rely on pathogen identification and understanding the roles of potential reservoirs in cycling and transmission. Underreporting and misdiagnosis obscure the magnitude of the problem and confound efforts to understand key epidemiological components. Difficulties in culturing hamper the use of serological diagnostics and delay the development of DNA detection methods. As a result, especially in complex ecosystems, we know very little about the importance of different mammalian host species in cycling and transmission to humans.

Methodology/Principal Findings

We sampled five indigenous Kichwa communities living in the Yasuní National Park in the Ecuadorian Amazon basin. Blood and urine samples from domestic dogs were collected to assess the exposure of these animals to Leptospira, and to identify the circulating species. Microscopic Agglutination Tests with a panel of 22 different serovars showed anti-leptospira antibodies in 36 sampled dogs (75%), and 10 serotypes were detected. Two DNA-based detection assays revealed pathogenic Leptospira DNA in 18 of 19 dog urine samples (94.7%). Amplicon sequencing and phylogenetic analysis of 16s rDNA and SecY genes from 15 urine samples revealed genetic diversity within two of three different Leptospira species: noguchii (n=7), santarosai (n=7), and interrogans (n=1).

Conclusions/Significance

The high prevalence of antibodies and Leptospira DNA provides strong evidence for high rates of past and current infections. Such high prevalence has not been previously reported for dogs. These dogs live in the peridomestic environment in close contact with humans, yet they are free-ranging animals that interact with wildlife. This complex web of interactions may explain the diverse types of pathogenic Leptospira observed in this study. Our results suggest that domestic dogs are likely to play an important role in the cycling and transmission of Leptospira. Future studies in areas with complex ecoepidemiology will enable better parsing of the significance of genotypic, environmental, and host characteristics.

Molecular Epidemiology of Pathogenic Leptospira spp. Infecting Dogs in Latin America

Canine leptospirosis is a bacterial disease caused by spirochetes of the genus Leptospira. Infections can vary from asymptomatic and chronic infections to clinical acute diseases. The disease is endemic in tropical areas, such as Latin American countries, but a broad understanding of the dynamics of circulation of strains, based on molecular data, has not yet been performed. Based on in silico analyses, the present study aims to analyze the genetic diversity and circulation patterns of haplotypes from pathogenic leptospires infecting dogs in Latin America. DNA sequences were obtained from GenBank platform, curated, and aligned. Genetic distances were calculated, and a maximum likelihood tree and haplotype network were constructed. According to the inclusion criteria adopted, a total of 148 sequences were identified. Most of the records were from Brazil, including sequences from L. interrogans serogroup Icterohaemorrhagiae. Phylogenetic analysis showed a genetically closely related cluster, consisting of a larger haplogroup that includes the reference strain Fiocruz L1-130, known to be the major circulating strain in humans. Moreover, no genetic variations were observed according to clinical history and/or geographical localization. We described the molecular epidemiology of leptospires circulating among dogs in Latin America and demonstrated a very genetically homogeneous group, elucidating its ubiquitous circulation pattern and drawing attention to the important role of dogs in the One Health transmission dynamics of leptospirosis.

Potential Drivers for the Re-Emergence of Canine Leptospirosis in the United States and Canada

Canine leptospirosis is an important zoonotic disease in many countries. This review examines potential drivers for increased diagnoses of canine leptospirosis in the United States and Canada, using the epidemiologic triad of agent-environment-host as a template. Leptospira spp. are classified into more than 250 serovars, but in many laboratories only 6 are routinely tested for in serologic agglutination tests of canine sera. Leptospiral infections in dogs may potentially go undetected with unemployed or currently employed diagnostic methods. Disease transmission from infected reservoir hosts usually occurs via urine-contaminated environmental sources such as water. Direct contact between infected and susceptible individuals, environmental factors such as climate changes in temperature and/or rainfall, and increasing number and urbanization of reservoir hosts may greatly increase dog exposure risks. A dog's lifestyle may influence exposure risk to leptospirosis, but vaccination based on proper identification of circulating serogroups dramatically reduces post-exposure infections. Regrettably, resistance to vaccination by veterinarians and dog owners leaves a large number of dogs at risk for this zoonotic disease.

Pathogenesis and Genomic Analysis of a Virulent Leptospira Interrogans Serovar Copenhageni Isolated from a Dog with Lethal Infection

Dogs are highly susceptible to leptospirosis and are a public health concern due to their important role as a source of spreading disease, particularly in urban settings. In this study, we present the pathogenesis, serological characterization, and complete genome sequencing of a virulent Brazilian strain (NEG7) of L. interrogans serovar Copenhageni isolated from the urine of a dog that died due to acute leptospirosis. Clinical investigation showed that the dog was presented with icteric mucous membranes, weakness, dehydration, anorexia, and kidney and liver failures. Necropsy followed by histopathological evaluation revealed lesions compatible with liver and kidney leptospirosis. The leptospires recovered from the urine were further characterized by genome analysis, which confirmed that the isolate belonged to L. interrogans serogroup icterohaemorrhagiae serovar Copenhageni. Multiple bioinformatics tools were used to characterize the genomic features, and comparisons with other available Copenhageni strains were performed. Characterization based on absence of an INDEL in the gene lic12008, associated with phylogenetic and ANI (99.99% identity) analyses, confirmed the genetic relatedness of the isolate with L. interrogans serovar Copenhageni. A better understanding of the diversity of the pathogenic Leptospira isolates could help in identifying genotypes responsible for severe infections. Moreover, it can be used to develop control and prevention strategies for Leptospira serovars associated with particular animal reservoirs.

Effect of Vaccination against Leptospira on Shelter Asymptomatic Dogs Following a Long-Term Study

(1) Background: Vaccination of dogs against leptospirosis is of paramount importance, as they ideally must provide not only long-term protection, but also against the renal carrier state of leptospires. This study assessed the post-vaccine humoral response against Leptospira in naturally exposed dogs and effects on renal carrier status. (2) Methods: A total of 118 dogs were studied for 365 days, separated into Group A (vaccinated, n = 94) and Group B (non-vaccinated, n = 24). Group A was subdivided into three groups: A1 with 32 dogs immunized with the vaccine #1; A2 by 32 dogs with #2; and A3 30 dogs with #3. Serology (MAT and IgG-ELISA) and urinary PCR were conducted. (3) Results: Seroreactivity increased at D15 post-vaccination and, regardless of vaccine brand, remained high up to D180, with antibody switch to IgG after D30. A total of 46.8% of animals from Group A were PCR-positive at least once, in contrast to 75% in Group B, regardless of vaccine brand (p < 0.05; OR: 0.3). (4) Conclusions: All commercial vaccines succeeded at eliciting a long-term IgG-based response and were partially effective at protecting against kidney infection.

Role of Diagnostics in Epidemiology, Management, Surveillance, and Control of Leptospirosis

A One Health approach to the epidemiology, management, surveillance, and control of leptospirosis relies on accessible and accurate diagnostics that can be applied to humans and companion animals and livestock. Diagnosis should be multifaceted and take into account exposure risk, clinical presentation, and multiple direct and/or indirect diagnostic approaches. Methods of direct detection of Leptospira spp. include culture, histopathology and immunostaining of tissues or clinical specimens, and nucleic acid amplification tests (NAATs). Indirect serologic methods to detect leptospiral antibodies include the microscopic agglutination test (MAT), the enzyme-linked immunosorbent assay (ELISA), and lateral flow methods. Rapid diagnostics that can be applied at the point-of-care; NAAT and lateral flow serologic tests are essential for management of acute infection and control of outbreaks. Culture is essential to an understanding of regional knowledge of circulating strains, and we discuss recent improvements in methods for cultivation, genomic sequencing, and serotyping. We review the limitations of NAATs, MAT, and other diagnostic approaches in the context of our expanding understanding of the diversity of pathogenic Leptospira spp. Novel approaches are needed, such as loop mediated isothermal amplification (LAMP) and clustered regularly interspaced short palindromic repeats (CRISPR)-based approaches to leptospiral nucleic acid detection.

Are Small Animal Practitioners Occupationally Exposed to Leptospirosis? Results of a Serological Survey

Leptospirosis is a worldwide zoonosis frequently responsible for clinical disease in dogs and rarely reported in human people. The risk of human exposure to Leptospira has been investigated in a sample population working in the northeast of Italy, a geographical area with high endemicity of canine leptospirosis. Two-hundred twenty-one human serum samples were analyzed for Leptospira microagglutination test (MAT): 112 clinical freelance small animal practitioners (exposed subjects) and 109 people not occupationally exposed to Leptospira-infected animals (unexposed subjects) were voluntarily enrolled. Despite the previously reported serological detection of antibodies vs. Leptospira in people in different Italian regions, this study did not detect any reactivity in the investigated population. This study shows that veterinarians do not appear to be at a greater risk of leptospirosis than the reference population. This may be due to both veterinarian awareness of the Leptospira zoonotic risk and the efficiency of the preventive measures and management of patients. Moreover, it could be the result of the relatively low excretion of Leptospira in symptomatic dogs, which can be considered as an environmental sentinel for Leptospira presence rather than a vehicle of transmission.

Leptospira noguchii associated to reproductive disease in ruminants

Leptospirosis is known to determine reproductive disorders on livestock, and Leptospira interrogans and Leptospira borgpetersenii are the most frequently reported species. Leptospira noguchii is an emerging pathogen, but its association with reproductive disease is unclear. We have detected L. noguchii as the agent of an outbreak with reproductive disorders in a Brazilian dairy goat flock. In the kidding season, five out of 10 Saanen had abortions in the final month of pregnancy and two newborn kids had acute clinical signs. After necropsy of three foetuses and one newborn kid, fragments of liver, lung and kidney were submitted to lipL32-PCR. It yielded positive results in at least one fragment from each animal. After, a nested secY-PCR, followed by sequencing, could identify L. noguchii, with 99-100% of identity with sequences obtained from cattle in the same region. For the first time, L. noguchii was detected in goats and, most importantly, the association of this leptospiral species with reproductive failures in ruminants has been demonstrated.