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

Emerging zoonotic diseases in Southeast Asia in the period 2011-2022: a systematic literature review

As COVID-19 has shown, pandemics and outbreaks of emerging infections such as Zika, Nipah, monkeypox and antimicrobial-resistant pathogens, especially emerging zoonotic diseases, continue to occur and may even be increasing in Southeast Asia. In addition, these infections often result from environmental changes and human behaviour. Overall, public health surveillance to identify gaps in the literature and early warning signs are essential in this region. A systematic review investigated the prevalence of emerging zoonotic diseases over 11 years from 2011 to 2022 in Southeast Asia to understand the status of emerging zoonotic diseases, as well as to provide necessary actions for disease control and prevention in the region. During the 2011-2022 period, studies on pigs, poultry, ruminants, companion animals and wildlife in Southeast Asia were reviewed thoroughly to assess the quality of reporting items for inclusion in the systematic review. The review was performed on 26 studies of pigs, 6 studies of poultry, 21 studies of ruminants, 28 studies of companion animals and 25 studies of wildlife in Southeast Asia, which provide a snapshot of the prevalence of the emerging zoonotic disease across the country. The findings from the review showed that emerging zoonotic diseases were prevalent across the region and identified a few zoonotic diseases associated with poultry, mainly stemming from Cambodia and Vietnam, as high priority in Southeast Asia.Clinical relevance: Appropriate prevention and control measures should be taken to mitigate the emerging zoonotic diseases in Southeast Asia.

Immunological Responses to Seoul Orthohantavirus in Experimentally and Naturally Infected Brown Rats (Rattus norvegicus)

To clarify the mechanism of Seoul orthohantavirus (SEOV) persistence, we compared the humoral and cell-mediated immune responses to SEOV in experimentally and naturally infected brown rats. Rats that were experimentally infected by the intraperitoneal route showed transient immunoglobulin M (IgM) production, followed by an increased anti-SEOV immunoglobulin G (IgG) antibody response and maturation of IgG avidity. The level of SEOV-specific cytotoxic T lymphocytes (CTLs) peaked at 6 days after inoculation and the viral genome disappeared from serum. In contrast, naturally infected brown rats simultaneously had a high rate of SEOV-specific IgM and IgG antibodies (28/43). Most of the IgM-positive rats (24/27) had the SEOV genome in their lungs, suggesting that chronic SEOV infection was established in those rats. In female rats with IgG avidity maturation, the viral load in the lungs was decreased. On the other hand, there was no relationship between IgG avidity and viral load in the lungs in male rats. A CTL response was not detected in naturally infected rats. The difference between immune responses in the experimentally and naturally infected rats is associated with the establishment of chronic infection in natural hosts.

Hemorrhagic Fever With Renal Syndrome in Vladivostok City, Russia

Hemorrhagic fever with renal syndrome (HFRS) is a public health problem in Vladivostok city, Russia. From 1997 to 2019, a study of hantaviruses in Norway rats (Rattus norvegicus), a natural reservoir of Seoul virus (SEOV), and in HFRS patients was conducted. We demonstrated the presence of SEOV in the local population of Norway rats and detected SEOV in 10, Amur virus (AMRV) in 4 and Hantaan virus (HTNV) in 1 out of 15 HFRS patients. Genetic analysis based on partial S, M and L segment sequences revealed that the Russian SEOV strains were related most closely to strains from Cambodia and Vietnam. We postulate that the SEOV strains found in the port city of Vladivostok have been spread from South-East Asia as a result of distribution of rats during standard shipping trade activities. Moreover, we suggest that city residents may have acquired AMRV and HTNV infection during visits to rural areas.

Serological methods for detection of infection with shrew-borne hantaviruses: Thottapalayam, Seewis, Altai, and Asama viruses

The infectivity of shrew-borne hantaviruses to humans is still unclear because of the lack of a serodiagnosis method for these viruses. In this study, we prepared recombinant nucleocapsid (rN) proteins of Seewis orthohantavirus, Altai orthohantavirus (ALTV), Thottapalayam thottimvirus (TPMV), and Asama orthohantavirus. Using monospecific rabbit sera, no antigenic cross-reactivity was observed. In a serosurvey of 104 samples from renal patients and 271 samples from heathy controls from Sri Lanka, one patient serum and two healthy control sera reacted with rN proteins of ALTV and TPMV, respectively. The novel assays should be applied to investigate potential infectivity of shrew-borne hantaviruses to humans.

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.

The Ecology and Phylogeny of Hosts Drive the Enzootic Infection Cycles of Hantaviruses

Hantaviruses (Family: Hantaviridae; genus: Orthohantavirus) and their associated human diseases occur globally and differ according to their geographic distribution. The structure of small mammal assemblages and phylogenetic relatedness among host species are suggested as strong drivers for the maintenance and spread of hantavirus infections in small mammals. We developed predictive models for hantavirus infection prevalence in rodent assemblages using defined ecological correlates from our current knowledge of hantavirus-host distributions to provide predictive models at the global and continental scale. We utilized data from published research between 1971–2014 and determined the biological and ecological characteristics of small mammal assemblages to predict the prevalence of hantavirus infections. These models are useful in predicting hantavirus disease outbreaks based on environmental and biological information obtained through the surveillance of rodents.

Wild Rats, Laboratory Rats, Pet Rats: Global Seoul Hantavirus Disease Revisited

Recent reports from Europe and the USA described Seoul orthohantavirus infection in pet rats and their breeders/owners, suggesting the potential emergence of a “new” public health problem. Wild and laboratory rat-induced Seoul infections have, however, been described since the early eighties, due to the omnipresence of the rodent reservoir, the brown rat Rattus norvegicus. Recent studies showed no fundamental differences between the pathogenicity and phylogeny of pet rat-induced Seoul orthohantaviruses and their formerly described wild or laboratory rat counterparts. The paucity of diagnosed Seoul virus-induced disease in the West is in striking contrast to the thousands of cases recorded since the 1980s in the Far East, particularly in China. This review of four continents (Asia, Europe, America, and Africa) puts this “emerging infection” into a historical perspective, concluding there is an urgent need for greater medical awareness of Seoul virus-induced human pathology in many parts of the world. Given the mostly milder and atypical clinical presentation, sometimes even with preserved normal kidney function, the importance of simple but repeated urine examination is stressed, since initial but transient proteinuria and microhematuria are rarely lacking.

Global Diversity and Distribution of Hantaviruses and Their Hosts

Rodents represent 42% of the world's mammalian biodiversity encompassing 2,277 species populating every continent (except Antarctica) and are reservoir hosts for a wide diversity of disease agents. Thus, knowing the identity, diversity, host-pathogen relationships, and geographic distribution of rodent-borne zoonotic pathogens, is essential for predicting and mitigating zoonotic disease outbreaks. Hantaviruses are hosted by numerous rodent reservoirs. However, the diversity of rodents harboring hantaviruses is likely unknown because research is biased toward specific reservoir hosts and viruses. An up-to-date, systematic review covering all known rodent hosts is lacking. Herein, we document gaps in our knowledge of the diversity and distribution of rodent species that host hantaviruses. Of the currently recognized 681 cricetid, 730 murid, 61 nesomyid, and 278 sciurid species, we determined that 11.3, 2.1, 1.6, and 1.1%, respectively, have known associations with hantaviruses. The diversity of hantaviruses hosted by rodents and their distribution among host species supports a reassessment of the paradigm that each virus is associated with a single-host species. We examine these host-virus associations on a global taxonomic and geographical scale with emphasis on the rodent host diversity and distribution. Previous reviews have been centered on the viruses and not the mammalian hosts. Thus, we provide a perspective not previously addressed.

Genetic characterization of hantaviruses isolated from rodents in the port cities of Heilongjiang, China, in 2014

Background

Hantavirus is a tripartite negative-sense RNA virus. It can infect humans through contaminated rodent excreta and causes two types of fatal human diseases: hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS). China exhibits the highest HFRS occurrence rate in the world, and the Heilongjiang area is one of the most severely infected regions.

Results

To obtain additional insights into the genetic characteristics of hantaviruses in the port cities of the Heilongjiang area in China, a molecular epidemiological investigation of hantaviruses isolated from rodents was performed in 2014. A total of 649 rodents (11 murine species and 1 shrew species) were caught in 12 port cities in Heilongjiang. Among these rodents, the most common species was A. agrarius, and the second-most common was R. norvegicus. A viral gene PCR assay revealed the presence of two specific genotypes of hantavirus, referred to as Hantaan virus (HTNV) and Seoul virus (SEOV), and the positive SEOV infection rate was higher than that for HTNV. A genetic analysis based on partial M segment sequences indicated that all of the isolates belonging to SEOV could be assigned to two genetic lineages, whereas the isolate belonging to HTNV could be assigned to only one genetic lineage.

Conclusions

These results suggested that HTNV and SEOV are circulating in A. agrarius and R. norvegicus in the port cities in the area of Heilongjiang, but SEOV may be the dominant common hantavirus.

Prevalence of antibodies against Ehrlichia spp. and Orientia tsutsugamushi in small mammals around harbors in Taiwan

BACKGROUND

Tick-borne ehrlichiosis and mite-borne scrub typhus represent important emerging zoonotic rickettsial diseases. Although scrub typhus has been recognized by the Taiwanese public health system, information on ehrlichial infections is scarce in Taiwan. In this study, the risk of spread of ectoparasites on rodents through aerial and marine transportation was assessed in international and domestic harbors. Here, we report the first systematic surveillance of seroprevalence against Ehrlichia spp. in small mammals on the main island of Taiwan.

METHODS

In total, 1648 small mammals were trapped from 8 international ports, 18 domestic fishing harbors, and 7 local public health centers around Taiwan from November 2004 to December 2008. Sera were analyzed using indirect immunofluorescence assays to detect IgG antibodies against Ehrlichia chaffeensis and Orientia tsutsugamushi. A serum titer of ≧1:80 was considered positive.

RESULTS

Antibodies against Ehrlichia spp. and O. tsutsugamushi were detected in 3.28% and 4.92% of small mammals active around harbors, respectively. The seropositive rate against Ehrlichia was higher in northern Taiwan from 2005 to 2008. However, O. tsutsugamushi infections increased in southern Taiwan during this period. The serological evidence of ehrlichial and O. tsutsugamushi infections in all international ports were included in the study. No significant differences were found among the seropositive rates of Ehrlichia spp. and O. tsutsugamushi in small mammals trapped between international and local harbors.

CONCLUSIONS

The overall prevalence of Ehrlichia spp. and O. tsutsugamushi infections in small mammals active around harbors was 3.28% and 4.92%, respectively. The results provided serological evidence supporting the potential risks of transporting pathogens through air and maritime traffic. This study highlights serious issues of the emergence and spread of rickettsial diseases in Taiwan. The incidence of human ehrlichiosis requires further investigation.

Rodents and risk in the Mekong Delta of Vietnam: seroprevalence of selected zoonotic viruses in rodents and humans

In the Mekong Delta in southern Vietnam, rats are commonly traded in wet markets and sold live for food consumption. We investigated seroprevalence to selected groups of rodent-borne viruses among human populations with high levels of animal exposure and among co-located rodent populations. The indirect fluorescence antibody test (IFAT) was used to determine seropositivity to representative reference strains of hantaviruses (Dobrava virus [DOBV], Seoul virus [SEOV]), cowpox virus, arenaviruses (lymphocytic choriomeningitis virus [LCMV]), flaviviruses (tick-borne encephalitis virus [TBEV]), and rodent parechoviruses (Ljungan virus), using sera from 245 humans living in Dong Thap Province and 275 rodents representing the five common rodent species sold in wet markets and present in peridomestic and farm settings. Combined seropositivity to DOBV and SEOV among the rodents and humans was 6.9% (19/275) and 3.7% (9/245), respectively; 1.1% (3/275) and 4.5% (11/245) to cowpox virus; 5.4% (15/275) and 47.3% (116/245) for TBEV; and exposure to Ljungan virus was 18.8% (46/245) in humans, but 0% in rodents. Very little seroreactivity was observed to LCMV in either rodents (1/275, 0.4%) or humans (2/245, 0.8%). Molecular screening of rodent liver tissues using consensus primers for flaviviruses did not yield any amplicons, whereas molecular screening of rodent lung tissues for hantavirus yielded one hantavirus sequence (SEOV). In summary, these results indicate low to moderate levels of endemic hantavirus circulation, possible circulation of a flavivirus in rodent reservoirs, and the first available data on human exposures to parechoviruses in Vietnam. Although the current evidence suggests only limited exposure of humans to known rodent-borne diseases, further research is warranted to assess public health implications of the rodent trade.

Biodiversity and evolution of Imjin virus and Thottapalayam virus in Crocidurinae shrews in Zhejiang Province, China

The recent discovery of numerous hantaviruses in insectivores has provided a new view of hantavirus biodiversity and evolution. To determine the presence and genetic diversity of Imjin virus (MJNV) and Thottapalayam virus (TPMV) in insectivores in Zhejiang Province, China, we captured and performed virus screening of 32 Ussuri white-toothed shrews (Crocidura lasiura) and 105 Asian house shrews (Suncus murinus) in different coastal regions. Hantavirus genome (S, M, and L segments) sequences were successfully recovered from one Ussuri white-toothed shrew and seven Asian house shrews. Phylogenetic analysis revealed that the virus carried by the Ussuri white-toothed shrew was most closely related to MJNV, but with >15% nucleotide sequence difference, suggesting that it represents a new subtype. The hantaviruses carried by Asian house shrews were closely related to the TPMV variants found in the same geographic area, but more distantly related to those sampled in India and Nepal. Additionally, the TPMV sequences obtained in this study, as well as those found previously in this area, could be divided into three lineages reflecting their geographic origins, indicative of largely allopatric evolution. Overall, our data highlights the high genetic diversity of insectivore-borne hantaviruses in China, suggesting that more may be discovered in the future.

Detection and genetic characterization of Seoul virus from commensal brown rats in France

Background

Hantaviruses are single-stranded RNA viruses, which are transmitted to humans primarily via inhalation of aerosolised virus in contaminated rodent urine and faeces. Whilst infected reservoir hosts are asymptomatic, human infections can lead to two clinical manifestations, haemorrhagic fever with renal syndrome (HFRS) and hantavirus cardiopulmonary syndrome (HCPS), with varying degrees of clinical severity. The incidence of rodent and human cases of Seoul virus (SEOV) in Europe has been considered to be low, and speculated to be driven by the sporadic introduction of infected brown rats (Rattus norvegicus) via ports.

Methods

Between October 2010 and March 2012, 128 brown rats were caught at sites across the Lyon region in France.

Results

SEOV RNA was detected in the lungs of 14% (95% CI 8.01 – 20.11) of brown rats tested using a nested pan-hantavirus RT-PCR (polymerase gene). Phylogenetic analysis supports the inclusion of the Lyon SEOV within Lineage 7 with SEOV strains originating from SE Asia and the previously reported French & Belgian SEOV strains. Sequence data obtained from the recent human SEOV case (Replonges) was most similar to that obtained from one brown rat trapped in a public park in Lyon city centre. We obtained significantly improved recovery of virus genome sequence directly from SEOV infected lung material using a simple viral enrichment approach and NGS technology.

Conclusions

The detection of SEOV in two wild caught brown rats in the UK and the multiple detection of SEOV infected brown rats in the Lyon region of France, suggests that SEOV is circulating in European brown rats. Under-reporting and difficulties in identifying the hantaviruses associated with HFRS may mask the public health impact of SEOV in Europe.

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.

Phylogeny and origins of hantaviruses harbored by bats, insectivores, and rodents

Hantaviruses are among the most important zoonotic pathogens of humans and the subject of heightened global attention. Despite the importance of hantaviruses for public health, there is no consensus on their evolutionary history and especially the frequency of virus-host co-divergence versus cross-species virus transmission. Documenting the extent of hantavirus biodiversity, and particularly their range of mammalian hosts, is critical to resolving this issue. Here, we describe four novel hantaviruses (Huangpi virus, Lianghe virus, Longquan virus, and Yakeshi virus) sampled from bats and shrews in China, and which are distinct from other known hantaviruses. Huangpi virus was found in Pipistrellus abramus, Lianghe virus in Anourosorex squamipes, Longquan virus in Rhinolophus affinis, Rhinolophus sinicus, and Rhinolophus monoceros, and Yakeshi virus in Sorex isodon, respectively. A phylogenetic analysis of the available diversity of hantaviruses reveals the existence of four phylogroups that infect a range of mammalian hosts, as well as the occurrence of ancient reassortment events between the phylogroups. Notably, the phylogenetic histories of the viruses are not always congruent with those of their hosts, suggesting that cross-species transmission has played a major role during hantavirus evolution and at all taxonomic levels, although we also noted some evidence for virus-host co-divergence. Our phylogenetic analysis also suggests that hantaviruses might have first appeared in Chiroptera (bats) or Soricomorpha (moles and shrews), before emerging in rodent species. Overall, these data indicate that bats are likely to be important natural reservoir hosts of hantaviruses.

Host mTORC1 signaling regulates andes virus replication

Hantavirus pulmonary syndrome (HPS) is a severe respiratory disease characterized by pulmonary edema, with fatality rates of 35 to 45%. Disease occurs following infection with pathogenic New World hantaviruses, such as Andes virus (ANDV), which targets lung microvascular endothelial cells. During replication, the virus scavenges 5'-m(7)G caps from cellular mRNA to ensure efficient translation of viral proteins by the host cell cap-dependent translation machinery. In cells, the mammalian target of rapamycin (mTOR) regulates the activity of host cap-dependent translation by integrating amino acid, energy, and oxygen availability signals. Since there is no approved pharmacological treatment for HPS, we investigated whether inhibitors of the mTOR pathway could reduce hantavirus infection. Here, we demonstrate that treatment with the FDA-approved rapamycin analogue temsirolimus (CCI-779) blocks ANDV protein expression and virion release but not entry into primary human microvascular endothelial cells. This effect was specific to viral proteins, as temsirolimus treatment did not block host protein synthesis. We confirmed that temsirolimus targeted host mTOR complex 1 (mTORC1) and not a viral protein, as knockdown of mTORC1 and mTORC1 activators but not mTOR complex 2 components reduced ANDV replication. Additionally, primary fibroblasts from a patient with tuberous sclerosis exhibited increased mTORC1 activity and increased ANDV protein expression, which were blocked following temsirolimus treatment. Finally, we show that ANDV glycoprotein Gn colocalized with mTOR and lysosomes in infected cells. Together, these data demonstrate that mTORC1 signaling regulates ANDV replication and suggest that the hantavirus Gn protein may modulate mTOR and lysosomal signaling during infection, thus bypassing the cellular regulation of translation.