HANTAVIRUS SPECIES IN INDIA: A RETROSPECTIVE STUDY

Identification of Novel Rodent-Borne Orthohantaviruses in an Endemic Area of Chronic Kidney Disease of Unknown Etiology (CKDu) in Sri Lanka

We reported the genetic evidence of circulating hantaviruses from small mammals captured in a chronic kidney disease of unknown etiology (CKDu) hotspot area of Sri Lanka. The high seroprevalence of anti-hantavirus antibodies against Thailand orthohantavirus (THAIV) has been reported among CKDu patients and rodents in Sri Lankan CKDu hotspots. We captured 116 small mammals from CKDu endemic regions in the Polonnaruwa District of Sri Lanka. Seven animals (five out of 11 Mus booduga and two out of 99 Rattus rattus) were PCR-positive for the hantavirus. A rat-borne sequence was grouped with a THAIV-like Anjozorobe virus. In contrast, Mus-borne sequences belonged to the THAIV lineage, suggesting a novel orthohantavirus species according to the phylogenetic analyses and whole-genome comparisons. Our genetic evidence indicates the presence of two THAIV-related viruses circulating in this CKDu endemic area, suggesting a basis for further investigations to identify the infectious virus in patients with CKDu and the CKDu induction mechanism of these viruses.

[Hantavirus infection as a risk for chronic kidney disease of unknown etiology (CKDu) in Sri Lanka]

Chronic kidney disease of unknown etiology (CKDu) has emerged in endemic areas of Sri Lanka since the 1990s. The disease is a chronic but fatal disease. Until now, heavy metals and agrochemicals have been suspected as the cause of CKDu, but it has been still unknown. Recently, we have found a high seroprevalence to hantavirus in CKDu patients and reported that hantavirus infection is a risk of CKDu. Hantaviruses are rodent-borne zoonotic viruses. Here, I would like to introduce a story of the research from sero-epidemiology to the search for host animals.

Serological Evidence of Thailand Orthohantavirus or Antigenically Related Virus Infection Among Rodents in a Chronic Kidney Disease of Unknown Etiology Endemic Area, Girandurukotte, Sri Lanka

We have reported high seroprevalence to Thailand orthohantavirus (THAIV) or THAIV-related orthohantavirus (TRHV) among patients with chronic kidney disease of unknown etiology in Girandurukotte, Sri Lanka. THAIV or TRHV infection is considered to be transmitted by rodent hosts in this area, but its reservoir rodents have not yet been identified. Hence, 116 rodents were captured, and seroprevalences were examined by indirect immunofluorescent antibody assay (immunofluorescence assay [IFA]) using antigens of THAIV strain Thai749-infected Vero E6 cells and recombinant nucleocapsid protein of THAIV expressed in Vero E6 cell. Molecular biological species identification of rodents was carried out by sequencing rag1, irbp, and mitochondrial cytb genes. The majority (112/116) of the captured rodents were lineage Ib of black rats (Rattus rattus). Among them, 19.6% (22/112) of the rats possessed antibodies against THAIV. Also, a lesser bandicoot rat (Bandicota bengalensis), which belongs to the Sri Lankan endemic genetic lineage, was seropositive (1/1). Two Mus booduga and one Murinae sp. were seronegative. Rodent sera showed less cross-reactivities to antigens of Vero E6 cells infected with Hantaan orthohantavirus (HTNV), Seoul orthohantavirus (SEOV), and Puumala orthohantavirus (PUUV) in IFA. These results suggest that the hantavirus present in rodents in Sri Lanka is related to THAIV or TRHV rather than to SEOV, HTNV, or PUUV. However, it might be serologically distinct from the prototype THAIV strain, Thai749, used in this study. This study revealed that black rats and lesser bandicoot rats belonging to Sri Lankan endemic lineages are possible reservoirs for THAIV or TRHV in Girandurukotte. Further multiple geographical studies are needed to confirm the THAIV or TRHV reservoir status of black and lesser bandicoot rats in Sri Lanka.

Globally emerging hantaviruses: An overview

Hantaviruses are known to cause haemorrhagic fever with renal syndrome in Eurasia and hantavirus cardiopulmonary syndrome in the Americas. They are globally emerging pathogens as newer serotypes are routinely being reported. This review discusses hantavirus biology, clinical features and pathogenesis of hantavirus disease, its diagnostics, distribution and mammalian hosts. Hantavirus research in India is also summarised.

Hantavirus seropositivity in rodents in relation to habitat heterogeneity in human-shaped landscapes of Southeast Asia

To establish how the conversion of natural habitats for agricultural purposes may impact the distribution of hantaviruses in Southeast Asia, we tested how habitat structure affects hantavirus infection prevalence of common murine rodents that inhabit human-dominated landscapes in this region. For this, we used geo-referenced data of rodents analysed for hantavirus infection and land cover maps produced for the seven study sites in Thailand, Cambodia and Lao PDR where they were collected. Rodents were tested by serological methods that detect several hantaviruses, including pathogenic ones. Rodents with a seropositive status were more likely to be found near to agriculture on steep land, and also in environments with a high proportion of agriculture on steep land. These results suggest that in Southeast Asia, hantaviruses, which are often associated with generalist rodent species with a preference for agricultural land, may benefit from land conversion to agriculture.

Epidemiology of hantavirus infection in Thousand Islands regency of Jakarta, Indonesia

Hemorrhagic fever with renal syndrome (HFRS) is a rodent-borne zoonotic disease caused by hantavirus infection. Many HFRS cases have been reported in East Asia and North Europe, while the situation in Southeast Asia remains unclear. In this study, the prevalence of hantavirus infection in rodents and humans in Thousand Islands regency, which is close to the port of Jakarta, one of the largest historic ports in Indonesia, was investigated. A total of 170 rodents were captured in 2005, and 27 (15.9%) of the rodents were antibody-positive against Hantaan virus antigen in an immunofluorescence assay (IFA) and Western blotting. Despite the high prevalence in rodents, human sera collected from 31 patients with fever of unknown origin and 20 healthy volunteers in the islands in 2009 did not show positive reaction to the antigen in IFA. To identify the virus in rodents genetically, a total of 59 rodents were captured in 2009. Sera from the rodents were screened for antibody by ELISA, and lung tissues were subjected to RT-PCR. 20 (33.9%) of the 59 rodents were antibody-positive, and 3 of those 20 rodents were positive for S and M genome segments of hantaviruses. Genetic analysis showed that the viruses belonged to Seoul virus and formed a cluster with those in Vietnam and Singapore. These results suggest that a unique group of Seoul viruses has spread widely in Southeast Asia.

Hantavirus infection among wild small mammals in Vellore, south India

Wild indigenous small mammals including 83 rodents (bandicoot and black rats, and house mice) and a shrew captured from multiple sites in Vellore, south India, were tested for serological and molecular evidence of hantavirus infection. Indirect immunofluorescence assay (IFA) using Hantaan virus (HTNV) antigen indicated hantavirus-reactive antibodies in 16 (19.3%) of 83 rodents (bandicoot and black rats). Western blot (WB) using Thailand virus (THAIV) antigen confirmed hantavirus-reactive antibodies in nine of the 16 HTNV IFA-positive rodents. Reverse transcription polymerase chain reaction (RT-PCR) of lung and kidney tissue of captured mammals resulted in the detection of partial S segment sequence in a bandicoot rat. This study complements our earlier reports on hantavirus epidemiology in south India and documents first laboratory evidence for rodent-associated hantaviruses in south India.

Studies on hantavirus infection in small mammals captured in southern and central highland area of Vietnam

To investigate the distribution of hantaviruses among animals in Southern and Central Highland area of Vietnam, a total of 1311 serum samples were obtained from rats and Asian house shrews (Suncus murinus) captured at 11 locations between 2006 and 2009. A total of 1066 serum samples from rats were examined for IgG antibodies against Hantaan virus, and there were 30 antibody-positive serum samples from rats that had been captured mainly in a port area and urban area in Ho Chi Minh City (HCMC) (2.8%). All of the antibody-positive rats were Rattus norvegicus, and they had Seoul virus (SEOV) genome in their lungs. SEOV sequences detected from rats captured in Southern Vietnam belonged to the same lineage as those from rats captured at Haiphong Port and a market area in Hanoi City. SEOV strain CSG5 was isolated from a rat captured at Saigon Harbor. Strain CSG5 showed a cross-neutralization pattern almost the same as that of a representative strain of SEOV. A total of 245 Asian house shrews were captured in the Central Highland area and near HCMC. Sera were examined for IgG antibodies against Thottapalayam virus (TPMV), and 32 (13.1%) of the antibody-positive shrews were mainly from the Central Highland area and showed a neutralizing antibody against TPMV. These results indicated that SEOV is distributed among R. norvegicus inhabiting harbor and urban areas of Southern Vietnam and that TPMV or an antigenically related virus is distributed among Asian house shrews in Central Highland area.