Leptospirosis in Vietnam


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Abstract

Leptospirosis poses a serious public health problem in many countries because about 1 million people suffer annually from this severe, often fatal, infection. At present, its importance has been increasing due to development of integration processes, globalization and intensification of economic activities, inevitable anthropogenic transformation of landscapes as well as rise in number of people with occupational risk of pathogen exposure. The burden of human leptospirosis is expected to rise with demographic shifts and climate change that result in heavy rainfall and flooding. Regarding leptospirosis, Southeast Asia, including Vietnam, is among the most vulnerable global regions. The objective of the review was to analyze available published data on the spread of leptospirosis in Vietnam. More than 100 research articles were analyzed allowing to state that in Vietnam synanthropic rodents (rats), agricultural (buffaloes, cattle, pigs) and domestic animals (cats, dogs) are the main sources of leptospirosis infection in humans. It is essential that rats (cats and dogs also) in Vietnam are used for food. Among all farm animals, pigs are of maximal importance as a source of infection in humans. In Vietnam, Leptospira prevalence in pigs varies widely, up to 73%. It depends significantly on the location, farm size, age and gender of animals, etc. A large variety of Leptospira serovars have been identified in pigs in Vietnam: Tarassovi, Bratislava, Australis, Javanica, Autumnalis, Grippotyphosa, and some others. Official Vietnam reporting of leptospirosis cases based on clinical data does not reflect the real-life incidence rate in humans. However, the available seroprevalence studies reveal that, on average, about 10% of the Vietnamese population are infected with Leptospira. Work in agriculture is the dominant risk factor for acquiring this infection. The highest Leptospira seroprevalence rates were detected in farmers, 63.2%. Serovar diversity is typical for pathogenic Leptospira circulating in Vietnam. In humans, the most frequent are antibodies to Hebdomadis, Wolffi and Icterohaemorrhagiae, but the frequency varied markedly across the country depending on the site, possibly with relation to the environment, as well as with economic activity of the local population. In Vietnam, geographic, climatic and social differences between northern, central and southern regions contribute to the specificity of local leptospirosis epidemiology. This emphasizes the advisability of developing special measures for leptospirosis prevention taking into account regional peculiarities.

Full Text

Introduction

Leptospirosis is a globally widespread disease, largely due to the wide range of reservoir hosts of pathogenic leptospira and animals susceptible to them [9].

Thus, according to the Leptospirosis Burden Epidemiology Reference Group (LERG), the number of severe leptospirosis cases in humans exceeds 500,000 per year, though real incidence may be even much higher due to insufficient attention to this infection and difficulties of its diagnostics [78].

Some other researchers emphasize that leptospirosis is among the main global zoonoses, and it accounts for the number of deaths that exceeds mortality due to other causes of hemorrhagic fever. The annual number of leptospirosis cases exceeds one million, and 58,900 of fatal outcomes are recorded worldwide annually [26].

The highest leptospirosis incidence rate in humans is reported in subtropical and tropical climatic zones, e.g., in Seychelles, Malaysia, New Caledonia, Suriname: 20.0-100.0 per 100 thousand population [4], [31], [46], [86]. Vietnam is a country in Southeast Asia that is one of the most vulnerable regions in the world with regard to leptospirosis. The region ranks second in the world (next to Oceania) both for leptospirosis morbidity and mortality [26]. Moreover, possibly, it was in Southeast Asia, under conditions of high humidity and swampiness, long before the appearance of humans that certain species of leptospira adapted to parasitizing in the body of animals, primarily rodents [5]. Currently, leptospirosis poses a significant public health problem in many countries, including Russia [9], but Southeast Asia, Vietnam particularly, provides the most favorable conditions for the survival of leptospira as the pathogen prefers warm and humid climate. The essential social significance of leptospirosis lies in the occupational risk of infection to which people are exposed in connection with the work they perform [15]. The Government of Vietnam has recognized the priority of five zoonotic diseases, including leptospirosis, and established a framework to investigate and respond to these diseases through the One Health program [63].

The socio-economic importance of leptospirosis is increasing due to a number of drivers. The most important of them are as follows:

1. The development of integration processes due to globalization of the economy, international economic cooperation, trade including export/import of agricultural, domestic and wild animals, food and feed [60]. All this favors the introduction of pathogenic leptospira into virgin territories [2], [3]. Development of international tourism entails the growth in number of leptospirosis patients infected with leptospira abroad [57], [14], [45]. Several cases of leptospirosis, including those fatal, are reported for Russian tourists that had acquired the infection in Vietnam. [7], [10],[6].

2. Intensification of economic activity, leading to anthropogenic transformation of landscapes and growth in number of the threatened professionals. More than 50% of Vietnam population are employed in the agricultural sector [24]. Back in the last century, it was noted that the cultivation of rice provides favorable conditions both for survival of leptospira in the environment and for the habitat of the pathogen potential carriers [1]. Rice is the main agricultural crop in Vietnam, its production and export increase steadily. According to the Ministry of Agriculture and Rural Development of the Socialist Republic of Vietnam, the country’s rice output in 2021 reached over 43.86 million tons, up 1.1 million tons compared to 2020 [85]. In 2020, Vietnam exported $2.74 billion worth of rice to many countries, making it the third largest rice exporter in the world [66]. Leptospirosis in Vietnam (in Mekong delta, first of all) may be considered as an environmentally linked disease. Obviously, the spread of leptospirosis is underestimated in Southeast Asia and, possibly, in other rice-growing countries [81]. Animal husbandry is an important sector of Vietnam national economy, and livestock is potentially an important reservoir for pathogenic leptospira [36]. Significant changes have recently taken place in this sector Vietnam that resulted both in notable increase in the number of farm animals (pigs only about 29 million heads), and improvement of technologies of meat processing and trade in supermarkets. However, infection with some leptospira serovars may reduce one live pig born per litter, equivalent to 8% loss of production [18].

  1. Global climate change soon can result in that Vietnam is among the countries most affected by global climate change [53], [31]. It means more extensive flooding of agricultural land during the rainy season and increased salinization during the dry season as a result of the sea level rise and higher river flooding. In the Mekong Delta, about 590,000 hectares of rice land would be lost due to flooding and salinization, that is about 13 percent of rice growing fields in the region [87]. And leptospirosis is commonly considered as flood-related infection [47]. Some findings support the hypothesis that soils may be the original habitat of the genus Leptospiraand a possible environmental reservoir or at least a temporary carrier of pathogenic strains [75], [76],  

[23] Rains wash the surface of the soil, transferring particles, leptospira involving, into suspension [70], [74]. Thus, leptospira penetrate freshwater bodies, where it survives even under unfavorable conditions [77] and can infect people on rice plantations. On the other hand, during the dry season salinity will grow due both to sea level rise and higher river flooding.

The objective of this review was to analyze the literature data on the spread of leptospirosis infection in Vietnam.

 

Materials

Articles were sought from Web of Science and international databases: Medline (through PubMed), Science Direct and https://scholar.google.com/. We used a combination of the following search terms: [Leptospirosis AND Vietnam)]. The total number of references exceeded 100, but we excluded  those non-essential and added a number of important references (mostly in Russian) not available in those databases.

 

Geography

Vietnam is situated at the southeastern tip of the Indochinese Peninsula. On the east side, Vietnam is washed by the South China Sea. The geographical position of Vietnam has a pronounced elongated meridional character. The state stretches along the 105th meridian in a narrow strip. This specific feature of the Vietnam geography together with alternation of highlands and lowlands, results in significant variety of its climatic conditions.

Vietnam has both a tropical climate zone and a temperate climate zone, with all of the country experiencing the effects of the annual monsoon. Rainy seasons correspond to monsoon circulations, which bring heavy rainfall in the north and south from May to October, and in the central regions from September to January. In the northern regions, average temperatures range from 22–27.5°C in summer to 15–20°C in winter, while the southern areas have a narrower range of 28–29°C in summer to 26–27°C in winter. Vietnam’s climate is also impacted by the El Niño Southern Oscillation (ENSO), which influences monsoonal circulation, and drives complex shifts in rainfall and temperature patterns which vary spatially at a sub-national level. Due to so different geographical and climatic features, which to a certain extent determine their socio-economic characteristics, Northern, Central and Southern Vietnam are usually considered separately. This prompted researchers to analyze the impact of abiotic, biotic and social factors on the spread of leptospirosis infections in those different regions of Vietnam [54].

 

Leptospira reservoirs

Small synanthropic mammals, rats first of all, are the most important reservoirs of pathogenic leptospira. The principal feature of their behavior is living close to humans, in residential premises or commercial facilities (livestock farms, enterprises for the processing of animal raw materials, warehouses, etc.). Moreover, rats penetrate natural foci, easily contact wild animals, and can exchange leptospira. Infection in rodents proceeds mostly in chronic, non-fatal forms, but causes very long, often lifelong, excretion of the pathogen in the animal urine. In Vietnam, the risk of human infection with leptospira from those animals is especially high, since rats, including those imported from abroad, are traditionally used for food [41]. In 1962 in the south of Vietnam, in Saigon (currently: Ho Chi Minh City), leptospira were isolated from rats Rattus norvegicus. Those leptospira were assigned to L. bataviae by the cross agglutination lysis and cross absorption tests, although they were not antigenically identical to the reference strain or its variant subserotype [40]. Those synanthropic mammals perform as an important source of human infection in the cities of Vietnam, as leptospira prevalence in rats is high. Thus, in January 2011 in Northern Vietnam (urban areas of Hanoi and Hai Phong) 22% of studied 100 rats were found to have antibodies to L. Interrogans [44]. In a later study another group of researchers in Vietnam not only confirmed so high infection prevalence in rats, but also isolated leptospira from 3 [43] and from 144 rats (135 - R. norvegicus, 8 - R. rattus, 1 - R. argentiventer) captured in Vietnam. In total 17 L. interrogans were isolated, of which 16 isolates belonged to the Bataviae serogroup [42]. More recent studies conducted in southwestern Vietnam used not only serological but also molecular genetic methods (using RT-PCR for the lipL32 gene, confirmed by 16S rRNA, as well as by the microscopic agglutination test- MAT). The results also bear witness to high prevalence of leptospira in those synanthropic animals. Antibodies to leptospira were detected in 18.3% of rats, namely in Rattus norvegicus (33.0%), Bandicota indica (26.5%), Rattus tanezumi (24.6%), Rattus exulans (14.3%) and Rattus argentiventer (7.1%). The most common serovars, in descending order, were: Javanica (4.6% of rats), Lousiana (4.2%), Copenageni (4.2%), Cynopterie (3.7%), Pomona (2.9%) and Icterohaemorrhagiae (2.5%). A total of 16 rats (5.8%) tested positive by RT-PCR. There was considerable agreement between the MAT and PCR, although significantly more rats were positive by MAT. The seroprevalence to leptospira in rats caught during the rainy season was higher than in those caught in the dry season [52].

The results of a study performed by a Russian-Vietnamese group of researchers in seven northern provinces of Vietnam (Dien Bien, Laitiau, Lao Cai, Ha Giang, Lang Son, Cao Bang and Quang Ninh) confirmed the high infection of small wild mammals with leptospira. So, PCR-based study of lungs and kidneys suspensions of 158 animals revealed 16S rRNA of pathogenic leptospira in 22 (13.9%) samples [8]. Another Russian-Vietnamese group investigated by real-time PCR 133 rodents (of 25 species) trapped in 2010, 2013, 2014, and 2018 in three provinces of northern Vietnam (Ha Giang, Cao Bang and Lao Cai) and found that 24 rodents (18%) were positive for Leptospira. Those were: Callosciurus erythraeus, Bandicota savilei, Berylmys bowersi, Niviventer fulvescens, Rattus nitidus, Rattus cf. rattus, Rattus tanezumi. The Tanezumi rat (Rattus tanezumi), also known as the Asian rat or Asian house rat, dominated: 11 of 44 animals (33.1%) were infected [12]. When comparing the results of a study on sera of 156 rats from different provinces of Vietnam: it was found that leptospira seroprevalence in the southern province (Can Tho) was higher than in the central (Ha Tinh) or in the northern (Tai Binh): 24.6%, 10.0% and 11.4% respectively; the average value being 16.0%.[54]. Therefore, leptospira prevalence in rats was close to those obtained in earlier studies conducted in the Mekong Delta region [52], [58], [17]. And their findings were at the level of those for other countries of Southeast Asia, such as Thailand, Lao PDR and Cambodia: the mean prevalence was about 7.1% [25]. However, it should be mentioned that in Southeast Asia, Vietnam including, the prevalence of leptospira in rats was found to be rather low as compared to other southern countries. The highest leptospira prevalence in rats (>70%) was reported in Brazil [62], [29], [26], [27], Mexico [59], Egypt [69] or some other countries [17]. The study conducted in three provinces of Vietnam [54] revealed that the seroprevalence in animals other than rats was much higher: 44.2% in buffalo (n= 52), 32.9% in dogs (n=219), 24.9% in cattle (n=233), while only 12.2% in cats (n=164), and 10.2% in pigs (n=381). In total it means that leptospira seroprevalence in animals in the northern province (Tai Binh) was higher than in the central (Ha Tinh) or the southern (Can Tho): 25.9%, 13.3% and 19.8% respectively. However, consideration of seroprevalence in individual animal species clarifies significantly our knowledge about the infection of animals with leptospira in different regions of Vietnam. It should be noted that the sera of buffaloes, in the samples of which antibodies to leptospira were found more often than in other animal species, were not examined in Can Tho, as buffalo are not common in this province. Naturally, the lack of data on those animals in the southern Vietnam had an impact on the total seroprevalence in animals of the region. Moreover, it was found that in Can Tho leptospira seroprevalence in cattle (n=69) was higher than in Tai Binh (n=80) or Hatin (n= 84): 30.4%, 22.5% and 22.6% respectively. While leptospira seroprevalence in dogs, cats and pigs in Tai Binh exceeded that in both other provinces. Thus, in dogs it was 46.7% in Tai Binh (n=60), 15.2% in Hatin (n=79), and 40.0% in Can Tho (n=32). The same figures for cats were 25.0% in Tai Binh (n=60), 4.8% in Hatin (n= 42) and 4.8% in Can Tho (n=62).  Leptospira seroprevalence in pigs was 20.5% in Tai Binh (n=122), 3.3% in Hatin (n=121) and 7.2% in Can Tho (n=138).

Hebdomadis, Louisiana and Javanica were the most common serovars detected in buffalo, while in pigs it was Castelloni, and in rats Louisiana. In cattle 15 different serovars were detected, Hebdomadis and Canicola being the most frequent; 13 serovars were identified in dogs, but Hardjobovis was the most frequently detected; 6 serovars were detected in cats, and Louisiana, Hebdomadis and Castellonis dominated.

Using a low dilution threshold for sera containing antibodies to leptospira (1:100), 17 leptospira serovars were detected in the studied animals, of which Hebdomadis (2.3%), Molasses (1.6%), Castelloni (1.5%) and Javanika (1.4%) were the most frequent.  Panama, Tarassovi, Australis and Autumnalis were found in all three provinces, while Bratislava was found only in Can Tho. It should be underlined that all 17 Leptospira serovars were available in Can Tho, while only 12 and 8 serovars were found in Taibin and Hatin, respectively [54].

In Vietnam infection of humans with leptospira occurs not only through direct contacts with dogs and cats or the use of water or food contaminated by them, but also through consumption of their meat, as those animals are used for food [13], [11].

Pigs are of great importance in Vietnam because of their contribution to human nutrition, their role in agricultural production systems and their economic function. Vietnam’s pig herd is the largest in Southeast Asia [51]. In 2020 it exceeded 27 mln head, and about 7 millions of Vietnamese people were involved in pigs raising in 2016 [34]. Therefore pigs are considered as the main source of leptospirosis in humans. Besides, leptospirosis in pigs leads to large economic losses due to abortion and infertility of animals [48]. In Vietnam the leptospira seroprevalence in pigs ranged up to 73% among sows (n=424) in Mekong delta, where leptospirosis is endemic. [18]. High leptospira prevalence in pigs was also confirmed by the pathogen detection in pig kidneys. Thus, in the Mekong Delta (south of Vietnam), leptospira were detected by immunofluorescence in 22 of 32 pigs (69%), and leptospira serovar Bratislava was isolated from the kidney of one pig [19]. A serological survey was conducted among sows in the Mekong delta in southern Vietnam in 1999 to investigate variations in leptospiral seroprevalence over a one-year period. In this region, leptospirosis is endemic and a high leptospiral seroprevalence has been shown in the pig population [20]. However, rather low prevalence rate (8.17%) was detected in the seraprevalence study in pigs (n=1959), randomly selected in five provinces: Son La, Hanoi, Nghe An, Dak Lak and An Giang [48]. The low leptospira prevalence, according to those authors, was due to a number of reasons. - Serum was sampled during dry or early wet seasons, when seroprevalence is likely to be lower than in the rainy season [71];

- Most of other studies were conducted in the Mekong Delta of southern Vietnam, relatively close to riverine areas, which provide more exposure to contaminated water and hence higher levels of leptospira prevalence.

- Sera was sampled at slaughterhouses, from rather young animals (aged 6–9 months), while older pigs are more likely to be infected with leptospira [18].

- Animals chosen for slaughter usually look healthy and probably are less infected with leptospira.

However, some other researchers do not share the conclusion about favorable conditions for infection of pigs with leptospira in the Mekong Delta. Thus, in a study of 2000 sera from 10 provinces, the average leptospira seroprevalence was 21.05%, while that of the samples from three provinces lying in the Mekong Delta was much lower: 10.0% in Soc Trang and 11.5% in Dong Thap, while the maximal detected seroprevalence was 37.5% in Quang Ngai (Central region), 32.5% in Binh Duong (South) and 30.5% in Bac Giang (North) [49]. There is probably some impact of the amount of precipitation, that already had been proved in Brazil [68], India [71], and Korea [39]. Further to above mentioned drivers of leptospira prevalence in pigs, it is likely that animal gender should be taken into account as well [48]. The size of the farms involved into the study is also important as well as possible movements of herd [50].

Some downtrend in letospira prevalence in pigs may be due to co-infection and reduction in number of those animals due to the outbreak of African swine fever in 2019, which led to culling and death of approximately 5.9 million pigs (about 22%) [21],[88]. In 2021 ASF outbreaks were ongoing in 48 out of 63 provinces in Vietnam, resulting in the death and culling of nearly 280,000 pigs with a total weight of about 11,678 metric tons (MT), about 3.6 times higher than the culled numbers in the same period of 2020 [22].

A wide variety of leptospira serovars were identified in pigs: Tarassovi, Bratislava, Australis, Javanica, Autumnalis, Grippotyphosa, etc. [18], [19], [20]. In particular, Pyogenes and Panama serovars were isolated [49], that already had been detected in cattle in some other countries [56], [61], [33]. It should be noted that the Pyrogenes serovar was detected in Quang Ngai, the province known for its large herd of cattle. One may assume the cattle to be a source of leptospira in local pigs. In addition, it has been suggested that since leptospira of Bratislava and Tarasovi serovars are common in wild boars [37], [80] those animals may also contribute to the pathogen transmission to farm pigs [50].

 

Leptospirosis in humans

Leptospirosis was first identified in Vietnam in 1930 [82], [28]. At the end of XX century the prevalence in humans was rather high: 18.8% of the inhabitants in the Mekong Delta aged 15-60 years had antibodies to leptospira [81]. Moreover, it should be underlined that by now leptospirosis is underdiagnosed in many countries, Vietnam including. Due to significant polymorphism of its clinical course and shortcomings in laboratory diagnostics leptospirosis is often misdiagnosed as some other febrile illnesses such as dengue, scrub typhus, and chikungunya [30], [32], [38], [65]. In Vietnam the national-wide reporting on infectious diseases is carried out by the General Department of Preventive Medicine of the Ministry of Health. Their statistics is built on the basis of clinical information, resulting in significant underdiagnosis of leptospirosis. Therefore in 2014-2017 Vietnam Ministry of Health reported about less than 20 cases nationwide per year. In 2018 both morbidity and mortality due to leptospirosis were reported to be zero. [35], [84].

However, some scientific publications on the seroprevalence of leptospira in humans contradict the official statistics on leptospirosis in Vietnam [46],[83]. In 2019 (November-December) a serological examination of 600 practically healthy residents of three provinces representing North, Central North and South Vietnam has revealed antibodies to leptospira in 9.5% of them. The antibodies to leptospira serovars Hebdomadis (14.0%), Pomona (14.0%), Saxkoebing (12.3%) and Panama (8.8%) were most frequently detected. The leptospira seroprevalence rates varied significantly: from 5.5%, in Can Tho City to 9.0% in Thai Binh and 14% in Ha Tinh province. The highest rate of leptospira seroprevalence, 63.2%, was found in farmers. [79]. The seropositivity in Vietnam seemed rather low as compared to other Southeast Asian countries. For instance, in Malaysia the seroprevalence of leptospiral antibodies in high-risk groups was up to 28.6% (in planters), and 33.6% (wet market workers) [64],[67]. However, the difference may be related to the choice of humans under study. The difference in prevalence might be due to the fact that in Malaysia the occupationally high-risk group was examined, while in Vietnam they "randomly" selected healthy residents aged above four, and the highest rate of seroprevalence to leptospira (63.2%) was revealed in farmers [79]. In our opinion, the detection of antibodies to leptospira in almost 10% of healthy humans in three different provinces clearly indicated that the official data on the registration of leptospirosis do not reflect the real spread of this infection in Vietnam. This is confirmed by the results of a study of sera sampled from 3815 patients with suspected leptospirosis. The patients were examined in 11 public hospitals, from three provinces: Thai Binh, Ha Tinh and Can Tho, representing three different geographical and climatic zones of Vietnam. The result proved that the conclusions of the authors about the unsatisfactory diagnosis of leptospirosis were valid not only for individual territories, but for the whole of Vietnam. [55]. The surveillance has revealed that in 68 (1.8%) and 248 (6.5%) cases, the diagnosis of leptospirosis was confirmed or regarded, according to the microscopic agglutination test (MAT) and enzyme immunoassay (ELISA-IgM), as probable, respectively. In addition, more than 30% of the patients' blood sera contained, according to ELISA data, IgM antibodies to leptospira. The number of laboratory-confirmed leptospirosis cases was maximal in Thai Binh (2.3%), somewhat less in Ha Tinh (2.0%) and Can Tho (1.0%). Laboratory values considered as “probable for leptospirosis” were even higher: 8.5% in Ha Tinh, 7.1% in Can Tho and 7.0% in Thai Binh. In 3 provinces, 20 different serovars with a titer threshold of 1:100 to 1:400 were detected using (MAT), indicating diversification of leptospira serovars circulating in Vietnam. Of those 20 serovars, 17 were found in Hatin, 16 in Taibin, and 12 in Can Tho. In general, the serovars Wolffi (14.2%), Hebdomadis (13.8%) and Icterohaemorrhagiae (12.6%) prevailed, but their incidence varied significantly in the three provinces. Castellonis (12.3%), Djasiman (12.3%) and Wolffi (12.3%) dominated in Taibin, Icterohaemorrhagiae (19%) and Wolffi (15%) in Khatin, while Hebdomadis (23.6%) and Wolffi (15.3%) prevailed in Can Tho. According to the aggregate findings in those three provinces leptospirosis was more common in women (57.9%) than in men (42.1%). It is not typical for most countries and may be explained by the fact that 85.9% of women in Vietnam are employed in agriculture. Of the probable and confirmed cases of leptospirosis, approximately two-thirds were farmers, and most of them were involved in raising agriculture or domestic animals. Working in agriculture is probably the main risk factor for leptospirosis contracting in Vietnam. Thus, 53.5% and 83.2% of patients with probable or confirmed leptospirosis were farmers in Taibin and Hatin, respectively. About two thirds of patients with leptospirosis were people of working age, 24 to 60 years [55].

Although the adults are more frequently infected with leptospira due to their professional activities, children also acquire this pathogen. Thus, a serological study of children in the south of Vietnam revealed the average leptospira prevalence of 12.8% [72]. It ranged from 11% in 7 years-old up to 25% in 12 year-old children [73]. It is possible that walking barefoot in the mud, swimming in polluted water, etc. may cause leptospira infection in children [55].

There is evidence that virulent leptospira survive in the environment for several months [16].

Conclusion

The main sources of leptospirosis infection in Vietnam are synanthropic rodents (rats), agricultural animals (buffaloes, cattle, pigs) and domestic animals (cats and dogs). Among all farm animals, pigs are the most important source of leptospira in Vietnam, as about 7 million of the country population work in pig breeding sector. The seroprevalence of leptospirosis in pigs is up to 73% in some locations (Mekong Delta), though it varies significantly depending on the territory, the farm size, the animal age and gender, the amount of precipitation, etc. A specific and essential feature of the infection in Vietnam is human consumption of cats, dogs and rats.

Official reporting of leptospirosis cases based on clinical data does not reflect the actual number of patients in Vietnam. On average, about 10% of population was found to be infected with leptospira. Work in the agriculture sector is the dominant risk factor for acquiring the infection. The most high leptospira seroprevalence was detected in farmers. Women are infected more often than men. About two thirds of patients with leptospirosis were people of working age: 24 to 60 years; but antibodies to leptospira were also detected in 12.8% of children. A very wide variety of pathogenic leptospira serovars was detected in Vietnam. The list of pathogenic leptospira varies significantly depending on the region, due to variation of environment, landscape and climatic features of the territory, and also due to the economic profile of the province.

Geographical, climatic and social differences in the northern, central and southern regions of Vietnam largely determine the epidemiological features of leptospirosis within the territory and argue the advisability of developing measures to prevent this infection at each region, taking into account their specifics.

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About the authors

Nikolay Konstantinovich Tokarevich

Saint-Petersburg pasteur institute

Email: zoonoses@mail.ru

Head of the Laboratory of Zooaptroponous Infections, Doctor of Medical Sciences, Professor

Russian Federation

Olga Vladimirovna Blinova

St.Petersburg Pasteur Institute

Author for correspondence.
Email: zoonoses@mail.ru

кхн, младший научный сотрудник 

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