The actual incidence of leptospirosis in the Asia Pacific region is not well-documented, similar to the situation in many regions worldwide. Aside from underreporting, incidence data are further compromised by the unavailability of laboratory diagnosis [10
]. Within the Asia Pacific region, Southeast Asia and Oceania appear to have the highest incidence of leptospirosis [11
Major outbreaks of the disease in South-East Asia due to flooding were reported in Orrisa (1999), Jakarta (2003) and Mumbai (2005). It has been a continuing and significant problem in the densely populated, flood-prone low lying areas of India.
, the disease has been found more commonly associated with natural disasters especially during the monsoon period at which times acute epidemics may eventuate [13
]. A multi-centric study in India showed that leptospirosis accounts for about 12.7% of cases of acute febrile illness responsible for attendance at hospitals [14
]. Carrier animals include rats, pigs, cattle, bandicoots and dogs. The predominant serovars are Copenhageni, Autumnalis, Pyrogenes, Grippotyphosa, Canicola, Australis, Javanica, Sejroe, Louisiana, and Pomona. Outbreaks of leptospirosis have increasingly been reported from Kerala, Gujarat, Tamil Nadu and Karnataka and sporadic cases have been reported from Goa, Andhra Pradesh and Assam [13
Leptospirosis has been known to be endemic since the early part of 20th
century on the Andaman and Nicobar Islands, where serovars Ratnapura, Valbuzzi and Grippotyphosa have been recently documented as causes of severe epidemics [15
]. Highest rates occur during October to November, with seroprevalence of up to 55% in the general population [8
]. Interestingly, the predominance of leptospirosis in coastal regions is most likely correlated with the presence of semi-domestic brown rats. In the inland urban regions, other serovars with other host animals/rodents were presumed to cause the 'mild' leptospirosis that is usually unrecognized or misdiagnosed. The Maldives
reported their first confirmed case of human leptospirosis in November 2000. Since then, the disease is under national surveillance (Geela Ali-personal communication. Director, Center for Community Health and Disease Control, Maldives).
, countries with similar environmental and sanitary conditions to those in India, the problem of overcrowding also contributes to the burden of disease [16
]. A serological survey in a rural flood prone district of Bangladesh in 1994 showed 38% seropositivity in 89 samples of human sera tested, indicating that the rural population is at high risk of leptospiral infection [18
]. In 2000, acute-phase serum specimens from 359 dengue-negative patients in Dhaka were assessed for leptospirosis; Leptospira
was detected by PCR in 63 (18%) of them. Poverty and poor education were implicated as conditions leading to rodent-borne transmissions [16
]. A number of serological studies carried out in Nepal during the last decade showed the presence of antibodies against major Leptospira
spp. prevalent in Asia. [17
]. There are no published human leptospirosis data for Bhutan
. However, suspected leptospirosis human cases have been reported from Chukha district during summer season after flooding in 2008. Cases commonly present with a history of fever for 10 days and autopsy reports indicate organ failure or pulmonary hemorrhage as cause of death. The National Center for Animal Health has detected leptospirosis cases among pigs based on positive serology. (Karma Lhazeen - personal communication. Programme Officer, Vector-borne Disease Control Programme, Gelephu, Bhutan)
Increasing numbers of leptospirosis cases have been observed over recent years in Sri Lanka
despite the implementation of a set of strategies for its control and prevention. It has a reported annual incidence of approximately 14/100,000. Over 19 leptospiral serovars belonging to over 7 serogroups have been isolated and incriminated as the causative agents of leptospirosis in humans and/or animals throughout the country [21
]. Peak incidence is associated with the rice paddy-harvesting seasons wherein an increase in the rodent population in and around the fields is observed. The majority of patients [43.5%] had been exposed in the paddy fields, indicating occupational exposure among the farmers [21
]. In 2007, a total of 2195 cases was reported, 40% more than in the previous year. An unusually high case fatality rate and high reporting were noted in districts not previously identified as high risk areas [22
]. This alarming trend has cautioned the Ministry of Health to re-assess its on-going strategies on leptospirosis.
, data from disease notification reports indicated an increase in the incidence rate from less than 0.3 per 100,000 in 1995 to 23.7 in 2000, with a drop in subsequent years. The vast majority of the cases [90%] was reported in the Northeast region, primarily as a result of flooding [23
] and the emergence of a highly virulent clone [24
]. A recent seroprevalence study at a hospital on the Thai-Myanmar border revealed that 17% of patients who sought treatment for fever were diagnosed with leptospirosis [25
]. Most infections occur in agricultural workers, primarily rice producers, whose bare-footed activity during work in rice fields constitutes the main risk. Outbreaks of leptospirosis correspond with the rainy season, with an increase in cases beginning in August and decreasing in November. In Myanmar
, veterinary investigations have reported the presence of leptospirosis in the animal population [26
] while data for human leptospiral cases are not available.
Leptospirosis probably poses a severe and highly underestimated continuous health problem in Indonesia
. In 2001, 139 human serum samples were tested out of which 18.7% were positive, indicating predominantly presumptive serovar Bataviae infections [27
]. In the wake of massive flooding in Indonesia in January 2002, a leptospirosis outbreak occurred, notably in the capital Jakarta on Java. In this outbreak, 12.0% out of 418 samples were seropositive against serovars Bataviae or Hardjo [27
]. During this outbreak, high seropositivity rates were detected among potential domestic infection reservoirs such as cats, dogs and cattle. There has been a nationwide increase in the number of reported human cases since 2006. Out of 667 reported human cases in 2007, 93% were laboratory confirmed. The case fatality rate was 8%. In the first quarter of 2008, 269 cases have been detected [Asri Mohammad - personal communication. WHO country office, Indonesia].
A suspected clinical case of leptospirosis was recorded during the flooding season in Timor-Leste in 2006 but it could not be confirmed [Sidartha Yuwono - Personal communication. WHO country office, Timor-Leste].
For the year 2008, the total number of notifications for Australia
was 112 cases [28
]. This is the lowest number of reported cases in over ten years and represents a downward trend since a peak in 1999. This reduction has been attributed to persistent drought conditions over the last few years. The northern state of Queensland accounts for most of the leptospirosis cases in the country [71.2%], with serovars Zanoni, Australis and Hardjo accounting for 58.9% of these. The disease has been mainly an occupational hazard of livestock and agricultural workers. Serovars Arborea and Topaz have recently emerged as significant causes of human leptospirosis. In the southern temperate climate states, serovar Hardjo acquired from cattle constitutes the main infecting serovar.
Leptospirosis is the most common occupationally acquired infectious disease in New Zealand
. The great majority of cases of leptospirosis occurs among livestock farm workers and meat processing workers [29
]. An assessment of human leptospiral epidemiology in New Zealand, conducted by Thornley et al. [30
] from 1990 to1998, showed an annual incidence of 4.4 per 100,000 population. However, the analysis of trends over this 9-year period revealed that a changing epidemiological pattern was evident, with the emergence of L. borgpetersenii
serovar Ballum as a more frequent cause of human infection.
faces a serious problem of leptospirosis. Poor sanitation and the increase in urban slums along with frequent typhoons and expansion of flooding areas in the country have exacerbated the risk of infection [31
]. Information on the prevalent Leptospira
serovars among humans in the Philippines dates back to the late 1960s and 1970s, when antibodies against serovars Pyrogenes, Bataviae, Pomona, Grippotyphosa, Manilae and Javanica were detected among high-risk workers such as abattoir employees, dog pound workers and fish inspectors in Manila. Outbreaks of leptospirosis due to flooding were reported in prisons, penal farms and in many parts of the country [32
]. Yanagihara et al. [7
] performed a seroepidemiological survey from 1998 to 2001, showing that 70% of suspected leptospirosis patients (1,200) were seropositive. They also isolated leptospires from humans and rats (both house and field) in metropolitan Manila and nearby provinces, and also in the city of Iloilo. In 1999, the Department of Health listed leptospirosis as a notifiable disease in the country.
, the number of leptospirosis cases had increased, reaching more than 200 reported deaths annually until 1960 [34
], mostly in rice-field farmers. Since then, this number has decreased rapidly, primarily due to the mechanization of agriculture in this country, farmers' use of rubber boots when working in the fields and the use of an inactivated vaccine [7
]. Currently, less than 20 human cases are reported annually, mostly contracted during recreational activities or imported from Southeast Asian countries, or by contact with imported infected animals [7
]. Serovars Icterohaemorrhagiae, Copenhageni, Autumnalis, Hebdomadis and Australis have been recognized as major causes of human leptospirosis. Most current cases are confined to the southernmost islands, the Okinawa archipelago [7
The first leptospiral case in Korea
was documented in 1984, and since then, it has become recognized as a major public health problem [37
]. Serovars Lai, Copenhageni and Canicola were isolated from 1984-1990 [38
]. A leptospiral vaccination programme was initiated in 1988, targeting high risk groups in the rural areas and may have been responsible for the reduction of cases in the succeeding years. However, during the last decade, cases have been increasing slightly. In the year 2007, 208 cases of human leptospirosis were recorded. The bulk of cases consisted predominantly of rice field farmers, occurred in the rural areas of Jeonnam and Jeonbuk (Sang-Hee Park - personal communication, NIH, Korea Center for Disease Control & Prevention. [39
To date, 37 serovars from humans and animals have been isolated in Malaysia
]. Human infections in the 1950s, depicted as febrile cases, were commonly observed in military personnel and civilians [40
]. Succeeding investigations revealed that the disease is an occupational hazard mostly for people engaged in agricultural and livestock activities, such as cattle farmers, veterinary staff, tin miners, farmers and paddy planters [40
]. Recent studies reported a high enzootic incidence in the animal population [40
]. In 2000, a recreational event-related outbreak of leptospirosis originated in Malaysia [42
have been considered endemic for leptospirosis. In 2002, a study by Laras and colleagues [43
] confirmed the endemicity of the disease in many areas in these countries. In this study, Hurstbridge, Bataviae and Icterohaemorrhagiae were reported to be the predominant serovars identified in patients with clinical jaundice. Serovar Bataviae, on the other hand, was most frequently isolated from patients with non-malarial febrile illness. Pyrogenes and Hurstbridge were the principal serogroups identified among patients with hemorrhagic fever. Recent seroprevalence studies conducted in flood-prone rural areas in Laos [44
] and in southern Vietnamese children [45
] showed an overall seroprevalence of 23.9% and 12.8%, respectively. In a human seroprevalence study conducted in the Mekong Delta of Vietnam (1998), Bataviae was identified as the most common serogroup [46
]. Meanwhile, the highest seroprevalence rate among sows in the same area was recorded with serovar Bratislava [47
]. A study in Takeo province, Cambodia estimated an annual incidence of 7.65 per 100,000 population [48
] with Javanica and Australis as the main serogroups.
Leptospirosis has been notifiable since 1955 in People's Republic of China
. Accumulated evidence from 1955-1993 showed an annual incidence of 7.1 per 100,000 with a mortality rate of 1.0% in 26 provinces across the mainland [Gu J-W, Jiang X-G, Guo X-K, unpublished]. Cases were concentrated in July to October, particularly in August and September. Icterohaemorrhagiae and Pomona are the dominant serogroups frequently associated with leptospirosis in the country [Gu J-W, Jiang X-G, Guo X-K, unpublished]. From January 2002 to October 2007, the Ministry of Health reported about 1,500 confirmed cases and 50 deaths in mainland China [49
]. There is a low incidence of leptospirosis in Hong Kong SAR
. There was only 1 local case in 2001, 2 local cases in 2002, 1 imported case in 2003 and 1 imported and 5 local cases in 2004, 7 in 2005 and 1 in 2006 [50
]. Although no published reports on human leptospirosis in Mongolia
can be found, the disease is most likely endemic, as numerous seroprevalence studies indicate a high incidence of animal leptospirosis [51
In a regional human leptospirosis survey conducted in the Western Pacific Islands
], among 263 cases of suspected leptospirosis cases from September 2003 to December 2005, 69 were confirmed from 7 islands: Futuna, Raiatea and the Marquesas Islands, where outbreaks were apparent, and Vanuatu, Fiji, Palau and Wallis where sporadic cases indicated the presence of the disease. Icterohaemorrhagiae and Australis were the dominant presumptive serogroups, indicating linkage to a rodent reservoir. The rate of exposure has more often been related to normal daily activities than following a specific occupational exposure. According to World Organisation for Animal Health (OIE) data, the disease is enzootic in French Polynesia
and New Caledonia
. In a retrospective study of 192 cases of human leptospirosis in New Caledonia from 1989 to 1993, the annual incidence rate was estimated to be 30 per 100,000 population [53
]. Serovar Icterohaemorrhagiae was the most prominent among the forty isolates obtained. The annual incidence between 2002 and 2008 has varied from 6.1 to 92 per 100,000, with a large increase in incidence in 2008 (92/100,000) and with signs that this will increase further in 2009. Notifications up to 8 June 2009 were 134, which would equate to an overall figure of over 150/100,000 if the trend continues for the remainder of the year.
Leptospirosis has been considered endemic in the Commonwealth of the Northern Mariana Islands
], although its actual incidence is unknown. Serological evidence in Palau
indicates that up to 8 percent of "viral syndrome" cases (fever of unknown origin in an adult) were related to acute leptospirosis [55
reported its first laboratory-confirmed human case in April 2003. A year later, a seroprevalence survey was conducted, showing that 17% of the enrolled adults have had prior infection, with Bratislava as the dominant serovar [56
]. Leptospirosis in Papua New Guinea
dates back to the 1970s; however, data collection on the disease is scarce. A recent investigation in livestock found a dominance of serovar Hardjo [57
The incidence of leptospirosis in the region is summarized in Table .
Summary of incidence of leptospirosis in the Asia Pacific region.