Molecular Epidemiological Survey of Leptospira Infection of Wild Rodents in the Urban Settlement of Cambodia

Leptospira infection and carrier survey on rats from wet market areas in Kuala Lumpur, Malaysia

BACKGROUND OBJECTIVES

Leptospirosis is an important zoonotic infection that has caused significant mortality and morbidity worldwide. This disease is endemic in Malaysia and as a developing tropical country, leptospirosis is concerning as it threatens Malaysian public health and the country's economic sectors. However, there is limited information on leptospirosis in Malaysia, especially regarding leptospiral seroepidemiology among carriers in Malaysia. Therefore, more epidemiological information on the source of the disease and reservoir are needed for better disease control and source intervention. The objectives of this study are to gather information on Leptospira infection and the carrier status of rats captured from selected wet markets of Kuala Lumpur metropolitan city in Malaysia.

METHODS

Live rat trappings were performed in four major wet markets in Kuala Lumpur, namely, Pudu, Chow Kit, Datuk Keramat, and Petaling Street. Animal samplings were performed for 12 months in 2017, where blood and kidney samples were collected and tested for anti-leptospiral antibodies via Microscopic Agglutination Test (MAT) and pathogenic Leptospira screening via Polymerase Chain Reaction (PCR) amplification offlaB gene.

RESULTS

MAT showed that 34.7% (n = 50/144) of the captured rats were positive for anti-leptospiral antibody of which the most prominent serovar was Malaya followed by a local strain, IMR LEP 175. In parallel, 50 rats were also positive for pathogenic Leptospira DNA.

INTERPRETATION CONCLUSION

This study showed that there are persistent Leptospira infections among rats in Kuala Lumpur wet markets and these rats are important reservoir hosts for the bacteria.

Identification of Leptospira Species in Environmental Soil of Urban Settlements in Cambodia

Background: Leptospirosis represents a major public health threat in Cambodia. To help establish preventive strategies for leptospirosis, we isolated and identified Leptospira from soil collected in Phnom Penh and its neighboring province during the dry and rainy seasons. Materials and Methods: Soil samples were collected from 15 sites in the Phnom Penh metropolitan area and Kandal Province in 2019 and 2020. A total of 120 soil samples were collected and analyzed after culturing. Cultured isolates were identified at the species level using 16S rRNA and gyrB gene sequencing analysis. Results: The positive culture rate for Leptospira was significantly higher for samples collected during the rainy season (31 out of 60 samples, 51.7%) than during the dry season (19 out of 60 samples; p < 0.05, chi-squared test). In terms of sampling area, 10 (35.7%) and 13 (46.9%) soil samples from Phnom Penh and 9 (28.1%) and 18 (56.3%) soil samples from Kandal Province were culture-positive when collected during the dry and rainy seasons, respectively. Three isolates from the Kandal samples collected during the dry season were categorized as pathogenic clade type P1 according to 16S rRNA and gyrB sequence analyses. In addition, samples collected during the rainy season from Phnom Penh and Kandal Province (three each) were categorized as clade type P1. The samples with isolates in clade type P1 were collected from riverbanks during both the dry and rainy seasons and from a hospital garden during the rainy season. Conclusions: This is the first report on the isolation of clade P1 Leptospira species in environmental soil samples from Cambodia. Environmental soil appears to be a reservoir for Leptospira in the capital city and surrounding areas of Cambodia. This study contributes to the understanding of Leptospira species distribution in Asian countries.

Comparative genomic analysis of Leptospira spp. isolated from Rattus norvegicus in Indonesia

Leptospirosis is one of the most prevalent zoonotic diseases caused by pathogenic spirochetes of Leptospira spp. The disease has become a public health concern in urban localities in the tropics, where rats serve as significant reservoir animals for leptospirosis transmission. In Indonesia, the occurrence of leptospirosis is underestimated, and information on the causative Leptospira genotypes and serotypes is limited. This study reports the isolation of Leptospira spp. from rats captured in urban areas of Bogor, Indonesia. Serogroups and genotypes, sequence types (STs), or multiple-locus variable-number tandem repeat analysis (MLVA) types using 11 loci, were determined for the isolates. Furthermore, whole genome sequencing (WGS) was performed on 11 Indonesian isolates and 24 isolates from other Asian countries. Ninety small mammals, including 80 Rattus norvegicus and ten Suncus murinus, were captured and, 25 Leptospira spp. were isolated solely from R. norvegicus (31.3%). The isolates were identified as Leptospira borgpetersenii serogroup Javanica with ST 143 (four strains) and Leptospira interrogans serogroup Bataviae with the same MLVA type as isolates from other Asian countries (19); the serogroup of the two L. interrogans with ST252 could not be identified. The core genome SNP-based phylogenetic tree revealed that Indonesian isolates were genetically related to L. borgpetersenii serogroup Javanica strains widely distributed in Asian countries but formed a different cluster from other strains. The phylogenetic tree of L. interrogans serogroup Bataviae isolates from Indonesia, the Philippines, Taiwan, and Vietnam revealed that isolates were grouped into five clusters based on their geographic locations. This study discovered a high carriage rate of Leptospira spp. among R. norvegicus in Bogor, Indonesia, indicating a potential risk of rat-borne leptospirosis in the area. Besides L. borgpetersenii serogroup Javanica, WGS on L. interrogans serogroup Bataviae illustrated the geographical structuring of genetic diversity in Leptospira spp.

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.

Rat trade and leptospirosis: Molecular epidemiology of Leptospira species in rats exported from Cambodia to Vietnam

Rats are an important maintenance host of Leptospira spp., the causative agents of leptospirosis, a zoonotic disease with worldwide distribution. Rats are traded as food in the Mekong Delta, where Cambodia exports tons of rats to Vietnam. Handling wild rats is a potential health risk, but the information on Leptospira spp. carried by rats traded in the region remains limited. In this study, we investigated the carriage of Leptospira spp. in rats exported from Cambodia to Vietnam using bacterial culture, nested PCR and DNA sequencing. Isolates were then assessed using serological analysis and whole-genome sequencing (WGS), and Leptospira DNA detected in rat kidney tissues was also analysed by multilocus sequence typing (MLST). Seventy-two rats (2 Bandicota indica, 57 Rattus argentiventer, 11 R. losea, 1 R. norvegicus and 1 R. rattus) were subjected to bacterial culture, and three L. borgpetersenii serogroup Javanica isolates were obtained from R. argentiventer (5.3%). WGS revealed that although Cambodian isolates were genetically related to L. borgpetersenii serogroup Javanica strains widely distributed in East and South-East Asian countries, they formed a different cluster from other strains. In addition to the three L. borgpetersenii sequences, the flaB sequence of L. interrogans was detected in 18 R. argentiventer and 7 R. losea kidney tissue samples (38.9%) using nested PCR followed by DNA sequencing. The L. interrogans flaB-positive samples were further analysed by MLST, revealing that seven housekeeping genes (glmU, pntA, sucA, tpiA, pfkB, mreA and caiB) contained novel sequences with distinct lineages from other sequence types. This study revealed a high prevalence of Leptospira spp. among rats exported from Cambodia to Vietnam, indicating a potential risk to people engaging in rat trade and demonstrating that a fastidious L. interrogans strain circulates among Cambodian rats.

First record of Leptospira and Blastocystis infections in captive flying squirrels (Trogopterus xanthipes) from Enshi County, China

In traditional Chinese medicine, the feces of flying squirrels have long been used to promote blood circulation and relieve bodily stasis. However, the excrement of flying squirrels may harbor zoonotic agents that could be hazardous to public health. To understand the occurrence of bacterial and parasitic infections in this species, we investigated selected zoonotic pathogens including Leptospira and Blastocystis in the urine and feces of flying squirrels in China. Urine and fecal samples from flying squirrels were collected from a family-owned flying squirrel farm located in Enshi County, Hubei Province in China. Leptospira and Blastocystis DNA was extracted from the urine and feces of flying squirrels, and used as targets for PCR amplification, using different specific primers. PCR amplification and DNA sequencing showed that 4.4% (3/69) of flying squirrels were positive for Leptospira, while 30.4% (21/69) of the animals were positive for Blastocystis. Notably, 1.4% (1/69) of flying squirrels were found to be co-infected with Leptospira and Blastocystis. Sequence analyses allowed for the detection of 3 Blastocystis subtypes (ST1, ST3 and ST13), and mixed infections of Blastocystis subtype 1 and subtype 3 were found in 4.4% (3/69) of flying squirrels. Phylogenetic analysis of the 16S ribosomal RNA gene (rrs2), the flagellin B gene (flaB), and outer membrane lipoprotein lipL32 gene (LipL32) sequences indicated that the Leptospira species detected in the study was L. interrogans. We concluded that flying squirrels from central China were infected with Leptospira and Blastocystis, suggesting that these animals can be a source of infection for their owners, and using fresh excrement from this animal as traditional medicine could be risky to human health. To the best of our knowledge, this is the first report of Leptospira and Blastocystis infection in flying squirrels from Enshi County, China. Our findings provide new data on the epidemiology of these pathogens in this region.

Leptospira infection in rats: A literature review of global prevalence and distribution

Background

The role of rodents in Leptospira epidemiology and transmission is well known worldwide. Rats are known to carry different pathogenic serovars of Leptospira spp. capable of causing disease in humans and animals. Wild rats (Rattus spp.), especially the Norway/brown rat (Rattus norvegicus) and the black rat (R. rattus), are the most important sources of Leptospira infection, as they are abundant in urban and peridomestic environments. In this study, we compiled and summarized available data in the literature on global prevalence of Leptospira exposure and infection in rats, as well as compared the global distribution of Leptospira spp. in rats with respect to prevalence, geographic location, method of detection, diversity of serogroups/serovars, and species of rat.

Methods

We conducted a thorough literature search using PubMed without restrictions on publication date as well as Google Scholar to manually search for other relevant articles. Abstracts were included if they described data pertaining to Leptospira spp. in rats (Rattus spp.) from any geographic region around the world, including reviews. The data extracted from the articles selected included the author(s), year of publication, geographic location, method(s) of detection used, species of rat(s), sample size, prevalence of Leptospira spp. (overall and within each rat species), and information on species, serogroups, and/or serovars of Leptospira spp. detected.

Findings

A thorough search on PubMed retrieved 303 titles. After screening the articles for duplicates and inclusion/exclusion criteria, as well as manual inclusion of relevant articles, 145 articles were included in this review. Leptospira prevalence in rats varied considerably based on geographic location, with some reporting zero prevalence in countries such as Madagascar, Tanzania, and the Faroe Islands, and others reporting as high as >80% prevalence in studies done in Brazil, India, and the Philippines. The top five countries that were reported based on number of articles include India (n = 13), Malaysia (n = 9), Brazil (n = 8), Thailand (n = 7), and France (n = 6). Methods of detecting or isolating Leptospira spp. also varied among studies. Studies among different Rattus species reported a higher Leptospira prevalence in R. norvegicus. The serovar Icterohaemorrhagiae was the most prevalent serovar reported in Rattus spp. worldwide. Additionally, this literature review provided evidence for Leptospira infection in laboratory rodent colonies within controlled environments, implicating the zoonotic potential to laboratory animal caretakers.

Conclusions

Reports on global distribution of Leptospira infection in rats varies widely, with considerably high prevalence reported in many countries. This literature review emphasizes the need for enhanced surveillance programs using standardized methods for assessing Leptospira exposure or infection in rats. This review also demonstrated several weaknesses to the current methods of reporting the prevalence of Leptospira spp. in rats worldwide. As such, this necessitates a call for standardized protocols for the testing and reporting of such studies, especially pertaining to the diagnostic methods used. A deeper understanding of the ecology and epidemiology of Leptospira spp. in rats in urban environments is warranted. It is also pertinent for rat control programs to be proposed in conjunction with increased efforts for public awareness and education regarding leptospirosis transmission and prevention.

The role of rodents in the transmission of many diseases, including leptospirosis, is widely known. Rats abundant in urban and peridomestic environments are the most important reservoirs and sources of Leptospira infection in humans and animals. Leptospirosis is a significant but neglected disease of humans and animals that is increasing in incidence in regions affected by natural disasters. This paper summarizes the global prevalence and distribution of Leptospira infection in rats and will add to the literature that supports research, education, and public awareness regarding leptospirosis transmission and prevention.

Molecular epidemiology of Leptospira interrogans in Rattus norvegicus in Hanoi, Vietnam

Leptospirosis is a zoonotic disease that is caused by pathogenic spirochaetes of Leptospira spp. and it has become a public health concern in urban localities in the tropics. Rats are important reservoir animals for the transmission of leptospirosis in urban areas. Leptospirosis is considered endemic in Vietnam. However, information on the causative Leptospira genotypes and serotypes in the country is limited. We investigated the carrier status of Leptospira spp. in rats captured in Hanoi by culturing and DNA detection. Isolates were characterized using a serological method and multiple-locus variable-number tandem repeat analysis (MLVA). We captured 144 rats (1 Rattus argentiventer, 135 R. norvegicus, and 8 R. rattus) and obtained 17 L. interrogans, determined by rrs sequencing, from R. norvegicus (12.6%). Sixteen of the isolates were serogroup Bataviae. Five of the 16 isolates exhibited an MLVA type identical to that of the serovar Bataviae reference strain Van Tienen, while there were nine repeats for the other 11 isolates at VNTR31 compared with the reference strain. The remaining isolate grew poorly, and we were unable to determine its serogroup. However, it had an MLVA type matching those of serogroup Pomona strains isolated from R. norvegicus in Japan. Three different flaB sequences were detected in 23 out of 81 R. norvegicus kidney tissue samples (28.4%) using nested PCR followed by DNA sequencing. Two of the sequences were identical with those of serogroups Bataviae and Pomona, and no strain with another sequence was detected in the present study. The present study reveals a high prevalence rate of L. interrogans among R. norvegicus in Hanoi, Vietnam, indicating a potential risk of rat-borne leptospirosis in the area. The present study also demonstrates that a fastidious L. interrogans strain circulates among rats and that molecular detection is crucial in facilitating the accurate determination of reservoir animals.

Association of rodent-borne Leptospira spp. with urban environments in Malaysian Borneo

Although leptospirosis is traditionally considered a disease of rural, agricultural and flooded environments, Leptospira spp. are found in a range of habitats and infect numerous host species, with rodents among the most significant reservoirs and vectors. To explore the local ecology of Leptospira spp. in a city experiencing rapid urbanization, we assessed Leptospira prevalence in rodents from three locations in Malaysian Borneo with differing levels of anthropogenic influence: 1) high but stable influence (urban); 2) moderate yet increasing (developing); and 3) low (rural). A total of 116 urban, 122 developing and 78 rural rodents were sampled, with the majority of individuals assigned to either the Rattus rattus lineage R3 (n = 165) or Sundamys muelleri (n = 100). Leptospira spp. DNA was detected in 31.6% of all rodents, with more urban rodents positive (44.8%), than developing (32.0%) or rural rodents (28.1%), and these differences were statistically significant. The majority of positive samples were identified by sequence comparison to belong to known human pathogens L. interrogans (n = 57) and L. borgpetersenii (n = 38). Statistical analyses revealed that both Leptospira species occurred more commonly at sites with higher anthropogenic influence, particularly those with a combination of commercial and residential activity, while L. interrogans infection was also associated with low forest cover, and L. borgpetersenii was more likely to be identified at sites without natural bodies of water. This study suggests that some features associated with urbanization may promote the circulation of Leptospira spp., resulting in a potential public health risk in cities that may be substantially underestimated.

Leptospirosis is a significant zoonotic disease that is found in a range of environments worldwide, most notably tropical regions prone to flooding. The bacterial agents of this disease, Leptospira spp., are most often associated with rodents, including species frequently found in urban areas. In cities, rodent populations are often larger and denser than those found in natural environments, which can lead to higher rates of contact with people and impact human disease risk. To investigate the impacts of urbanization on Leptospira spp., we sampled rodents at locations with differing levels of human influence, from highly urbanized to rural, surrounding a city in Malaysian Borneo. We found that 31.6% of all rodents were positive for Leptospira spp. DNA, and that two primary species were present, L. interrogans and L. borgpetersenii, both of which are known human pathogens. Statistical analyses revealed that infected animals were more common in areas with higher levels of human influence, and were more likely to occur at sites with limited forest cover, and mixed commercial and residential activity. Our study adds to a growing body of evidence suggesting that there is a significant yet underappreciated risk of leptospirosis for people living in urban environments.

Pathogenic Leptospira species are widely disseminated among small mammals in Atlantic Forest biome

Leptospirosis is a common worldwide bacterial zoonosis and has been studied in One Health approaches. Small mammals are described as the most important maintenance reservoirs of several pathogens in nature, including leptospires. The aim of this study was to identify infection by leptospires among small mammals on the Atlantic forest biome and evaluate their potential as carriers of these spirochetes. A total of 153 small mammals belonging to orders Rodentia and Didelphimorphia (distributed on 17 genera and 22 species) were captured. Blood and kidney samples were collected from animals and a conventional PCR targeted on lipL32 gene was conducted on renal tissues. Species identification was performed in eight samples by sequencing of rrs gene. A total of 28% of the animals presented lipL32 PCR-positive, and four pathogenic Leptospira species (L. interrogans, L. borgpetersenii, L. santarosai and L. noguchii) were identified. This study highlights the role of small mammals as carriers of leptospires on the Atlantic Forest representing a potential source of pathogenic Leptospira spp infection for both humans and domestic animals.