INTRODUCTION
Leptospirosis is one of the most widespread zoonotic infections worldwide. Leptospirosis is caused by pathogenic Leptospira, an infectious disease that is often overlooked [1–3]. Leptospira belongs to the genus Leptospira, family Leptospiraceae, and order Spirochaetales. The causative genospecies that are the leading cause of leptospirosis in humans and animals globally include L. interrogans, L. kirschneri, L. noguchii, L. borgpetersenii, L. weilii, L. santarosai, L. alexanderi, L. kmetyi, and L. alstonii, with the L. interrogans genospecies being the most common [4]. Leptospirosis is a naturally occurring disease, in which rodents serve as the primary reservoir host, with wild boars, domestic pigs, cattle, horses, sheep, dogs, and other wildlife and domestic animals also being important transmission hosts when infected [2, 3, 5–7]. Leptospira can colonize the kidneys of animals, is excreted in the urine, contaminates water and soil, and survives for months in water or wet soil [8–11]. Globally, >500,000 people are infected with Leptospira each year with a case fatality rate of >15% [1]. It has been reported that a wide range of animals are natural carriers of pathogenic Leptospira and 67 species of wild and domestic animals have been identified as hosts for pathogenic species [12–14]. Therefore, leptospirosis endangers the development of animal husbandry and threatens public health and the safety of the global community.
Chinese scientists published the first complete genome sequence of L. interrogans Lai strain (56601) in Nature in 2003 [15]. The sequence provides an essential scientific basis for studying the Leptospira genome. Molecular epidemiologic investigations of key outbreak sites of leptospirosis in Jiangxi and Fujian Provinces (China) have revealed that two genotypes, L. interrogans and L. borgpetersenii, are predominantly prevalent [5, 16–18]. There have been several outbreaks of leptospirosis in China, most of which occurred after floods. Although the incidence of leptospirosis in China has decreased significantly in recent years compared to the last century, leptospirosis is still a zoonotic infection that cannot be ignored [13, 19].
With globalization of the economy, the development of tourist attractions in China, and the abundance of outdoor activities, the spread of leptospirosis is often no longer limited to one epidemiologic factor [20–23]. In the context of One Health, animal, environmental, social, and human factors can all influence the occurrence and spread of leptospirosis.
Therefore, the objectives of this review were to examine the development and changes of leptospirosis in China in recent years, the animal and environmental factors in the transmission of leptospirosis in China, and the results of the molecular epidemiologic survey of Leptospira in China in recent years.
MATERIALS AND METHODS
Country of study
China has a sizeable north-south span and a complex and varied climate with several tropical, subtropical, and temperate heat zones. From the southeast coast to the northwest interior, the continental character of the environment gradually increases with humid, semi-humid, semi-arid, and arid climatic zones appearing in that order. The monsoon strongly influences the climate, and the average annual temperature ranges from 4.4°C in the north to 23.8°C in the south [19]. The annual precipitation in the coastal areas of southeastern China ranges from 1500–2000 millimeters. The annual precipitation ranges from 100–200 millimeters in the inland regions of northwestern China and the annual precipitation decreases from the coast-to-the inland areas and from southeast-to-northwest. The rainy, humid, and warm climate of the tropical and subtropical regions in the southern part of the country is suitable for the survival of pathogenic Leptospira and the host animals, so leptospirosis is a relatively common zoonosis in south China. A map of climatic zones in China is shown in Fig. 1.

A map of climatic zones in China (The available data was provided by The Resource and Environmental Science Data Platform (www.resdc.cn).
Literature search and ethics
A bibliographic search was performed using the following electronic literature databases: PubMed; ScienceDirect; and China National Knowledge Infrastructure. The published literature related to leptospirosis in Chinese and international journals was investigated. A combination of the following terms was screened in any given order: leptospirosis; Leptospira; China; epidemiologic investigation; animal factors; environmental factors; strain isolation and identification; and prevention strategies. The published literatures were reviewed with anonymous data, so this study did not require bioethical approval.
RESULTS
Published literature
Forty-one articles were identified, of which 15 (36.59%), 16 (39.02%), 5 (12.20%), and 3 (7.32%) involved human infections, animal infections, the environment, and genotyping of L.interrogans prevalent in China, respectively. There were 35 (85.37%) and 6 (14.63%) English and Chinese original articles, respectively. From the perspective of One Health research, the 41 publications involving humans, animals, and the environment cover detailed information on leptospirosis research in China over the past 30 years.
Incidence of leptospirosis in China
Leptospirosis has been monitored by the Chinese Center for Disease Control and Prevention since 1955 [13, 19]. As a new type of zoonotic infectious disease, leptospirosis is like many febrile diseases with respect to early-stage symptoms and is often ignored by individuals who are infected. According to the available data provided by The Data-center of China Public Health Science (www.phsciencedata.cn), the total number of confirmed cases of leptospirosis from 2004–2023 was 10,581, with the highest number of cases recorded in 2004 and 2005 and the lowest number of cases in 2017. The average annual incidence of leptospirosis is 0.03691 cases/100,000 cases, which decreased significantly in 2011. It is worth noting that The incidence of leptospirosis between 2013 and 2023 (0.022 cases/100,000 cases) was lower than 2004–2012 (0.061 cases/100,000 cases).
Over the past two decades, changes in ecological and social conditions in China may have had an essential role in the epidemiology of leptospirosis. Improvements in China’s rural human settlement environment may have helped reduce the risk of leptospirosis transmission [24]. During the construction of large-scale water conservancy projects, significant anthropogenic changes in the ecological environment have occurred and rodent densities have declined and remained low, which effectively controlled the spread of the disease by rodents [25]. In addition, improvement in waste management and on-farm biosecurity in the livestock sector of China may have contributed to lowering the transmission of Leptospira [13].
Therefore, the incidence of leptospirosis in China during recent years has generally shown a decreasing trend and there may be a few cases that have not been counted. The incidence of leptospirosis in China from 2004–2023 is shown in Fig. 2.
Epidemic and transmission of Leptospira in China
The epidemic and transmission of Leptospira in China are described in terms of animal and environmental factors. Animal factors include infection sources, transmission routes, and susceptible populations. Ecological factors are expressed in terms of natural geographic and socio-human factors.
Animal factors
Source of infection
The host animals for Leptospira are more diverse with mammals dominating. Large mammals infected with Leptospira mainly include cattle, sheep, and pigs, which are primarily farmed. Wild rodents dominate among small mammals and epidemiologic investigations have shown that bats also carry Leptospira [2].
Leptospirosis in large mammals can cause acute fever and jaundice for a short length of time and even cause death. Leptospirosis in female animals can lead to reproductive disorders, abortions, stillbirths, mummified fetuses, reduced milk production, and decreased farming productivity, which can cause significant losses to the farming industry [3]. Animals infected with Leptospira can become carrier hosts. For example, cattle are the maintenance host of L. borgpetersenii serovar and the urine of infected animals can contaminate soil and nearby water sources for a long time [6]. An epidemiologic survey of leptospirosis in cattle, sheep, and swine on a large provincial scale has not been conducted in China and there are only small epidemiologic surveys of swine and cattle in early individual leptospirosis endemic provinces.
The spread of leptospirosis is associated with small mammalian rodents [7]. Small mammals, predominantly rodents, tend to be maintenance hosts for Leptospira. Rodents infected with Leptospira in the urogenital tract can be a source of infection, contaminating soil and water sources. Leptospira serotypes in one area of China are related to local rodent species [16]. The main rodent species carrying Leptospira are Apodemus agrarius, Rattus norvegicus, R. losea, and Mus musculus. The differences in Leptospira serogroups may be influenced by differences in rodents from place-to-place because of geographic factors, such as environment, climate, and altitude [5, 20]. The regions with a high prevalence of leptospirosis are mainly tropical and subtropical regions [21]. Epidemiologic investigations in recent years based on RT-PCR, nested PCR, and MLST have shown that Leptospira isolated from wild rodents are mainly L. interrogans and L. borgpetersenii [26] and the prevalence of Leptospira infections in rodents ranges from 4.8%–31.9% [26, 27]. South China has the highest prevalence of rodent leptospirosis infection and a high prevalence of leptospirosis in the Yangtze River basin [28].
In addition rodents, dogs, and cats serve as host animals for Leptospira. For example, 1053 serum samples from dogs were collected in Changchun, China and the positive rate was 19.1% based on MAT in these cases [29]. Dogs and cats excrete Leptospira through the urine and humans may be at risk for Leptospira infection.
It has also been reported that bats may be essential carriers of Leptospira. In 2019, sixty bats were captured in rural Xianning City, Hubei Province. Testing showed that 57% (34/60) of the bats were positive for Leptospira [12].
Routes of transmission
The transmission of leptospirosis is mainly by direct contact with Leptospira spp. Leptospira can be eliminated from the body in the urine of wild and domestic mammals, which contaminates the environment. Leptospira may invade the organisms and the animals may become infected with Leptospira [30]. The detection and isolation of Leptospira from aborted fetuses, placenta, milk, and amniotic fluid suggest that Leptospira may also be vertically transmissible [31].
Susceptible population
Specific occupational activities (e.g., agriculture, veterinary workers, and military training), recreational immersion in water, harsh living conditions, and seasonal rainfall in the tropics are often associated with leptospirosis. In general, human leptospirosis is more prevalent in tropical and subtropical regions. Leptospsirosis patients are usually 30–45 years of age, with a significantly higher incidence in men than women and the at-risk occupations are farming, outdoor work, livestock farming, and butchering [19, 32–34]. Workers in these occupations will inevitably have skin injuries in their work and have a greater likelihood of exposure to contaminants and becoming infected with Leptospira, which increases the risk of the disease.
Environmental factors
Natural factors
Natural environmental factors have been associated with the spread of Leptospira, with warm and humid climates and soil environments being more favorable for Leptospira survival [8, 9, 35]. Macrogenomic sequencing of soil from Tuo Lake in Bengbu, Anhui Province revealed that the risk of leptospiral pathogenicity is higher in submerged lands than dry lands [10]. Lake Taihu, one of the largest freshwater lakes in China, is an essential source of drinking water with pathogenic Leptospira detected in 33% and 13% of water and sediment samples, respectively [11]. Occupational workers engaged in agriculture are more likely than other occupations to be exposed to waterlogged soil for long periods, and the probability of developing leptospirosis increases.
Severe natural disasters are also likely to increase the risk of leptospirosis, such as a significant increase in the prevalence of leptospirosis after floods. This finding may be related to the alteration of rivers and lakes, contamination of water resources, and subsequent small-scale migration of host animals [36, 37].
Geographic factors
The spread of leptospirosis in China has a distinct regional distribution, mainly in the southern part of China, in some provinces located in the Yangtze River basin, and in cities in provinces with tropical and subtropical climates [21, 38, 39]. Epidemiologic surveys in northern regions have also shown a high rate of Leptospira positivity in rodents [40, 41]. There are many substantial rivers and lakes with abundant water resources in the southern region of China, which may be contaminated by the faeces of host animals of pathogenic Leptospira and contaminated water increases the risk of infection in humans by direct contact with broken skin or by facilitating diffusion into the soil.
Social and human factors
Changing ecological and social conditions in China have a role in the prevalence of leptospirosis with the modernization of traditional farming and animal husbandry, increasing mechanized inputs into production, reduced probability of being able to access germ-carrying host animals and contaminated soils, and a reduction in the number of workers relying on traditional human labor, which has led to a decrease in the prevalence of leptospirosis. The prevalence of leptospirosis is related to local transport, farming practices, economic and traditional activities, and local physical geography [22].
There has been an increased risk of importing and exporting pathogenic host animals and disease vectors with the globalization of trade, which has increased the risk of zoonotic diseases, such as leptospirosis [23]. In recent years, the incidence of leptospirosis in China has decreased compared to the last century [13, 42–44]. However, leptospirosis should not be ignored because leptospirosis is still a significant zoonotic disease.
Prevalence of Leptospira in China in recent years
Leptospirosis is a zoonotic disease caused by pathogenic Leptospira and is one of the critical infectious diseases under surveillance in China. There are many serotypes of Leptospira and inactivated vaccines have poor or no cross-protection effect between different serotypes.
Therefore, understanding the recent results of the isolation and identification of Leptospira in China can help in understanding the epidemiology of Leptospira and in preventing and controlling leptospirosis. The results of isolation and characterization of Leptospira in recent years are shown in Table 1.
A separate table summarises the results of the identification of Leptospira in China in recent years.
Region | Epidemiologic survey time | Host animal | Detection method | Positivity rate | Leptospira identification or isolation results |
---|---|---|---|---|---|
Hubei province [26] | 2021 | Rodent | Nested PCR | 4.77% (46/964) | L. interrogans, L. borgpetersenii |
Zhejiang province [14] | 2020 | Rodent | QPCR | 7.36% (99/1345) | L. interrogans |
Fujian province [5] | 2018-2020 | Rodent | 16S rDNA gene sequencing, MAT, and MLST | 23.26% (90/387) | L. borgpetersenii serogroup javanica strains (ST143), L. interrogans serogroup icterohaemorrhagiae strains (ST1 and ST17), L. interrogans serogroup bataviae strains (ST96 and ST333) and L. interrogans serogroup pyrogenes strains (ST332) |
Jiangxi province [17] | 2007-2015 | Rodent | 16S rRNA gene sequencing, MLST, and MAT | 9.35% (330/3531) | L. icterohaemorrhagiae (61.1%), javanica (19.20%), and australis (9.73%) |
Yunnan province [45] | 2017-2021 | Bat | Nested PCR and MLST | 6.16% (17/276) | L. kirschneri (FMAS_PN5) and L. interrogans (56639) |
Shandong province [46] | 2015 | Bat | Nested PCR and MLST | 50% (62/124) | L. borgpetersenii and L. kirschneri |
Changchun city [29] | 2020-2021 | Dog | MAT | 19.08% (201/1053) | L. icterohaemorrhagiae (8.1%), L. canicola (7.6%), L. australis (5.3%), L. ballum (4.7%), and L. pyrogenes (4.2%) |
Guangzhou city [27] | 2020-2021 | Rattus norvegicus | RT-PCR | 31.93% (38/119) | L. interrogans |
Guangzhou city [47] | 2020 | Rodent | Nested PCR | 9.46% (28/296) | L. interrogans, L. borgpetersenii, and L. kirschneri |
Guangzhou city [48] | 2018-2019 | Rattus norvegicus and Rattus flavipectus | PCR | Rattus norvegicus: 57.89% (66/114) | L. interrogans and L. borgpetersenii |
Risk factors and preventive strategies
In the last decade, the incidence of leptospirosis in China has declined significantly relative to the beginning of the 21st century, which is due to improved living conditions, improvements in the environment, and increased health awareness of the population [13, 19]. However, the threat of leptospirosis has not disappeared with the emergence of global warming, the destruction of animal habitats, and tourism development. There are many rats in the city and rats often carry pathogens, including Leptospira, the urine of which is a source of infection [9, 11, 14, 28]. From July-to-September each year, people working in agriculture and outdoor activities have more exposure to contaminated water sources, which increases the risk of contracting leptospirosis [49–51].
Therefore, the following strategies should be implemented to prevent leptospirosis: workers in agriculture, and outdoor activities and people at high risk of leptospirosis should be vaccinated against leptospirosis; contact with fresh water and soil that may be contaminated by the urine of infected animals (especially rodents, such as rats, mice, pigs, dogs, and cows) should be avoided; keep food and water away from these animals that can easily carry the disease; and if symptoms consistent with leptospirosis occur in areas with a high incidence of leptospirosis, seek medical attention promptly.
DISCUSSION
The present review describes the current status of leptospirosis in China and provides insights into leptospirosis from the perspectives of animal and environmental factors. The review also focuses on the theme of One Health. Specifically, leptospirosis is still an infectious disease that cannot be ignored in China. Leptospirosis is a legally classified Class B infectious disease in China, which indicates that leptospirosis is a contagious disease with a degree of risk and is a significant public health problem.
Epidemiologic investigations have revealed that leptospirosis is endemic in most urban areas in southern China, from tiny wild rodents-to-large domesticated animals, such as cattle, sheep, and pigs [28, 52–54]. The prevalence of leptospirosis in southern China is closely related to climate [21, 22]. China is a large agricultural country. The Yangtze River basin to the south has more water resources, high precipitation in the summer and autumn, and a hot and humid climate, which are ideal for the growth of pathogenic Leptospira [14, 21, 28]. Agriculture and animal husbandry workers tend to be infected with Leptospira and are at greater risk of exposure [55–58].
Therefore, the best measure to reduce leptospirosis is to prevent infection with Leptospira. However, wild rodents are highly abundant in the urban areas of China and carry many pathogens, including Leptospira, that are difficult to eradicate [28, 40, 47, 48]. Animals carrying pathogens, including Leptospira, may be imported and exported to-and-from the coast with the globalization of trade, which further increases the risk of transmission [23]. Tourism development in some areas of China may have caused ecological damage and an influx of wildlife into urban areas, which also increases the risk of exposure to leptospirosis [5, 14, 17, 26, 27, 45–48]. Traditional manual agricultural work is still practiced in some areas of China and workers are more likely to be exposed to Leptospira in the summer, autumn and the rainy season [20]. Therefore, the best way to prevent leptospirosis is to vaccinate occupational groups susceptible to leptospirosis with the Leptospira vaccine [13, 19]. However, there are many serotypes of Leptospira and there is little cross-protection between Leptospira vaccines targeting specific serotypes [59, 60].
Leptospirosis is prevalent in subtropical and tropical areas of China. Epidemiologic survey results were integrated based on the theme of One Health, which showed that the two main endemic species in China are L. interrogans and L. borgpetersenii. In future scientific studies, it will be crucial to identify one or more proteins that L. interrogans and L. borgpetersenii share and are conserved and immunogenic to facilitate development of a Leptospira vaccine based on this protein that provides good protection against Leptospira.
Finally, although the incidence of leptospirosis in China has decreased in recent years, due to the diversity of pathogenic Leptospira species, the wide distribution of host animals, and the natural environment suitable for pathogenic Leptospira and host animals, leptospirosis is still an infectious disease that cannot be ignored in China.
CONCLUSIONS
Leptospirosis is an emerging zoonosis of global public concern but the symptoms of leptospirosis are like the symptoms of many febrile illnesses and are often overlooked. From the One Health perspective, leptospirosis transmission causes are multifactorial and related to animal, environmental, and socio-human factors. The best preventive measures against leptospirosis are to raise awareness of leptospirosis prevention in leptospirosis-prone areas of China and to vaccinate against Leptospira. Developing a Leptospira vaccine with cross-immunoprotection is essential for further prevention and control of leptospirosis.