A mini-review of Bunyaviruses recorded in India

Introduction

Globally, emerging viral infections constitute a major public health challenge. About 350 viruses, most of which are arthropod borne, are classified in the Bunyaviridae family. Bunyaviridae is one of the largest families of animal viruses. Individuals infected by different Bunyaviruses exhibit a range of mild-to-severe diseases i.e., febrile illness, encephalitis, haemorrhagic fever and acute respiratory illness. Earlier, many Bunyaviruses have been isolated and characterized at the serological level in India, for example, Ingwavuma virus (INGV), Thottapalayam virus (TPMV), Umbre (UMB), sandfly fever virus (SFV), Nairobi sheep disease virus/Ganjam virus (GANV), etc1234. There is a need to understand the members of this family at molecular level which may help to understand their disease profile in nature.

Bunyavirus is named after Bunyamwera, Uganda, where the virus was first found in mosquitoes5. The particles of Bunyaviridae family of viruses are spherical and of 80-120 nm in diameter. These have a common genetic organization of three segmented negative-stranded RNA (S, M and L segments). These are subdivided into five genera on the basis of antigenic, genetic and ecological relatedness. Except for the genus Tospovirus which is pathogenic in plants, Orthobunyavirus, Hantavirus, Nairovirus and Phlebovirus genera consist of enzootic viruses and some of these cause zoonotic diseases in humans. Of the more than 537 known arboviruses, more than 350 known viruses belong to these four genera. About 174 of these are listed under the genus Orthobunyavirus and include about half of the nearly 60 viruses of the family Bunyaviridae causing human diseases. Humans act as accidental dead-end hosts for these viruses in a zoonotic transmission cycle that alternates between arthropods and mammals (mostly rodents)67.

Chittoor Virus (Chitv)/batai Virus (Batv)

Chittoor virus (CHITV) was first isolated in 1957 from Anopheles barbirostris collected from Brahmanpalli, Chittoor district, Andhra Pradesh, India8. Subsequently, several isolates of this virus were obtained from Anopheles and Culex mosquitoes as well as from a piglet in India910. This virus was placed in Bunyamwera group based on serological characterization11. It was found to be antigenically related to Calovo virus and Batai virus (BATV) isolated from Slovakia and Malaysia, respectively12. Repeated isolations of CHITV and seroprevalence in several States suggest that the virus has been circulating in India for a many years13. However, this virus has not caused any outbreak or exhibited any disease symptoms involving humans. Its ability to replicate in vertebrates and mosquitoes may be the cause of concern for public health as it is related to severe fever with thrombocytopenia. A reassortant between Ngari virus and BATV was found to be associated with febrile human illness in Sudan14. This emphasizes that, though BATV on its own may not cause human or animal disease, it has the potential to cause febrile illness after reassortment with other viruses of the Bunyamwera group.

CHITV was isolated from Anopheles mosquitoes (An. barbirostris and An. subpictus from Andhra Pradesh and Karnataka, respectively), Culex mosquitoes (Cx. tritaeniorhynchus and Cx. pseudovishnui from Karnataka) and swine (Sus scrofa from Karnataka)15. A phylogenetic study based on S, M and L segments of CHITV isolated from India showed that a genetically uniform strain of CHITV is circulating in India, despite being isolated from different hosts i.e., mosquitoes and pigs. Moreover, the strains isolated in the 1960s and 1980s have not changed genetically, indicating the conserved nature of the virus even after several years of circulation in nature16.

A novel BATV NM/12 strain was isolated from bovine serum collected in inner Mongolia, China, and based on the L segment, it was found to be most closely related to the Chittoor strain17.

Umbre Virus (Umbv)

Umbre virus (UMBV) was first isolated in 1955 from Cx. vishnui group of mosquitoes, collected at Umbre, in Kolar district of Maharashtra, India1819, and was classified as Orthobunyavirus (Turlock serogroup which includes three other viruses, namely, M'opoko virus from Africa, Lednice virus from Europe and Turlock virus from America; https://wwwn.cdc.gov/arbocat/VirusDetails.aspx?ID=499&SID=5). Even though UMB virus is classified as a Bunyavirus, it cross-reacts by complement fixation (CF) and haemagglutinin inhibition (HI) assays with Barmah forest virus, an alpha virus from Australia18. Eight isolates obtained from Culex mosquitoes were characterized based on partial glycoprotein (G2) gene. The differences within these isolates at nucleotide and amino acid levels were 26 and 17 per cent, respectively. Phylogenetic analysis of 345 bp of glycoprotein gene G2, of UMBV and other Orthobunyaviruses, showed six distinct lineages, namely, Bunyamwera, Simbu, California encephalitis, Group C, Kaeng Khoi (KK) and UMBV. On comparing partial M gene, four lineages, excluding Group C viruses and Simbu group of viruses, were seen suggesting that UMBV represents a distinct group within the genus Orthobunyavirus19. UMBV has so far not been isolated from humans or animals and it is not known whether it causes any disease in humans or animals.

Kaikalur Virus

This virus was isolated from a mosquito pool comprising 100 Cx. tritaeniorhynchus collected in a cattle shed at Kaikalur town, Krishna district, Andhra Pradesh, in 197120. The virus belongs to Simbu group and is closely related to Shuni virus isolated in Nigeria by CF and neutralization tests. In 2008, it was shown by Yamakawa et al21, that Aino virus isolated from Japan was closely related to Kaikalur virus. Aino and Kaikalur viruses were found to be indistinguishable by CF or neutralization tests22. These results indicate a broader global distribution pattern of the virus. Although Aino virus is known to cause developmental disorders in foetus of ruminants2324, the pathogenic potential of Kaikalur virus to humans and animals is not reported.

Thimiri Virus

This was isolated from North Arcot district (currently named Vellore district), Tamil Nadu, in 1962 from Ardeola grayii, paddy bird25. Based on serology and sequencing data of partial S gene, though this virus was found to belong to Simbu serogroup of arboviruses26, it was not closely related to other Simbu viruses and was placed in its own complex. Thimiri virus is associated with birds in south India, Egypt and midges in Australia27. The pathogenic potential of Kaikalur virus to humans and animals is not known.

Sathuperi Virus (Satv)

This virus was isolated from a pool of Cx. vishnui in 1957 from a place called Sathuperi village, North Arcot district, Tamil Nadu, India27. This virus has been registered in the International Arboviruses catalogue and has been shown to belong to Simbu group28. Sathuperi virus (SATV) was also identified in Japan in 1999, isolated from cattle and Culicoides biting midges29. During an outbreak investigation of ruminants in Northern Europe caused by Schmallenberg virus, sequencing of genomic RNA segments of the virus showed that the M gene RNA of Schmallenberg virus was very similar to SATV. Phylogenetic analysis further indicated that Schmallenberg virus is a reassortant, with the M gene RNA segment from SATV29. Human disease caused by SATV virus is not known so far.

Ingwavuma Virus

In India, INGV was isolated in 1963 from a paddy bird A. grayii (Sykes) (from Balagodu village) in Shimoga district in the then Mysore state (at present Karnataka) of South India1. The isolations from pig were made from Tumkur district, whereas the isolations from humans were made from Kolar district in Karnataka State. However, no studies have been done to understand its epidemiology in this country1. Human disease caused by INGV is not known so far.

INGV belongs to Simbu serogroup in genus Orthobunyavirus. It was first isolated in 1959 on the banks of ‘Ingwavuma river’ near the village of Ndumu, South Africa, from a passerine bird Hyphanturgus (Ploceus) ocularis and from mosquitoes such as Ae. circumluteolus, Cx. guiarti, Cx. neavei and Cx. vishnui30. Later on, its presence was recorded from several countries in Africa and Asia1313233. Pigs are considered to be the natural vertebrate host in Thailand, but isolations from wild birds in Africa and India suggested a natural bird-mosquito cycle also27.

In spite of many reports of INGV worldwide, complete genome sequence of INGV is not available till date. No information is available about the disease caused, natural cycle of the virus or its molecular characterization. The study of virus pathology and its role in involvement in human disease is needed.

Phylogenetic study of nucleocapsid gene and glycoprotein gene of four viral isolates from India showed that Simbu viruses have evolved into at least five lineages and INGV from India had been clustered into third lineage16.

Ganjam Virus (Ganv)

Ganjam virus was initially isolated from adult Haemaphysalis intermedia and H. wellingtoni ticks and Cx. vishnui mosquitoescollected from goats in Ganjam district, Odisha, Shimoga district, Karnataka, and Vellore, North Arcot district, Tamil Nadu, respectively34. The presence of GANV was again reported in 1977 during an investigation of acute febrile illness shown by fever, anorexia and lumbar paralysis of sheep in Chittoor district of Andhra Pradesh, India35. GANV was isolated from adult H. intermedia and R. hemaphysaloides ticks infecting domestic animals in some villages near Pune, Maharashtra, between 2000 and 200235.

Based on the documented evidence of isolation of GANV from ticks, mosquitoes, sheep and humans, it can be stated that the virus is prevalent in different parts of India. In addition, GANV antibodies were detected in sheep and goat serum samples in Verrapuram during an episode of febrile illness in 199436. Neutralizing antibodies for the virus were found in human samples based on serological surveys conducted in Tamil Nadu and Jammu and Kashmir. Human laboratory-acquired infection of GANV with febrile illness, abdominal pain, back pain, headache, nausea, vomiting and conjunctival infection has been reported36.

The genome S RNA segment of Nairobi sheep disease virus (NSD) and GANVs has been shown to differ by only 10.1 and 3.3 per cent at the nucleotide and amino acid levels, respectively. Therefore, GANV may be an Asian variant of NSD virus. Further, GANV and NSD are more closely related than other characterized Nairoviruses, no evidence of reassortment was found37.

Crimean-Congo Haemorrhagic Fever (Cchf) Virus

CCHF virus causes severe acute febrile illness and haemorrhagic fever with an overall case fatality of 9-50 per cent. It belongs to family Bunyaviridae and genus Nairovirus. CCHF was first detected in the Crimean peninsula in the mid-1940s38. It was first isolated from a patient in Kisangani, the Democratic Republic of Congo, in 195638. Direct exposure to blood or other secretions resulting in person-to-person transmission and instances of nosocomial transmission has been documented. Ixodid ticks, particularly those belonging to the genus Hyalomma, are known vectors of CCHF. The virus is capable of persisting in the tick throughout its life cycle by transstadial transmission. It can also be passed onto the offspring by transovarial transmission38. Cattle and goats play an important role in the natural cycle of the virus. CCHFV replicates to high titres in the lung, liver, spleen and reticuloendothelial system in other organs in these animals. Unlike humans, it generally causes only subclinical disease in cattle. Human infections show high levels of viral replication occurring in all major organs, including the liver accompanied by haemorrhagic manifestations38.

Although CCHF had been detected in neighbouring countries such as Pakistan and China, it was confirmed for the first time in India in 201139. Nosocomial human infections with haemorrhagic manifestations were reported from a tertiary care hospital in Ahmadabad, Gujarat, in 201139. Domestic animals from Kolat and Ahmadabad were also found to be positive for anti-CCHF IgG antibodies. The possible sources of CCHFV infection were virus-infected Hyalomma ticks and livestock at the rural residence of the index case. In addition, a retrospective sample analysis showed the prevalence of CCHFV in Gujarat and Rajasthan before this outbreak40. So far, there is no evidence of circulation of multiple strains of the virus in the country. Though the 2011 outbreak may not have resulted from a very recent introduction, the probability of a recent re-introduction from any of the neighbouring countries during thoroughfare of livestock needs to be considered41.

In addition, a CCHF case was also confirmed from Sirohi, Rajasthan State, in 2014, and during 2015, a nosocomial outbreak was recorded in a private hospital of Rajasthan which affected nursing staff. This indicated that trade of livestock and consequent movements of domestic animals infested with infected ticks may be the reason for the spread of CCHFV to newer areas42. Further, a cross-sectional serosurvey of CCHFV in livestock from 22 States and one Union Territory reported that this virus was widespread in the livestock population of India43. With the increasing spread of CCHFV to newer regions of the country, it becomes imperative to conduct regular surveillance programmes for human and animals. Increased awareness about the disease and its spread among at-risk population such as abattoir workers, people working in proximity with livestock and medical personnel working in CCHF-endemic areas is needed.

Bhanja Virus (Bhav)

Bhanja virus (BHAV) was first isolated from a pool of ticks H. intermedia collected from a goat displaying lumbar paralysis in Bhanjanagar (district Ganjam, Odisha, India) in 1954. It was named based on the region of the isolation44. BHAV causes fever and symptoms indicating the central nervous system affection in young ruminants (lambs, kids, and calves). Bhanja virus has been isolated in India, various parts of Africa, former USSR and Europe45. Metastriate ticks of the genera Haemaphysalis, Dermacentor, Hyalomma, Rhipicephalus, Boophilus and Amblyomma transmit this arbovirus. Sheep, goat, cattle, African hedgehog Atelerix albiventris and African ground squirrel Xerus erythropus are vertebrate hosts of BHAV. It is so far not known to cause disease in humans. The complete genome sequence of BHAV has helped in phylogenetically placing the virus in the genus Phlebovirus in the Bunyaviridae family45.

Sandfly Fever Virus (Sfv)

The activity of SFV in India was suspected for many years on the basis of clinical diagnosis. Twenty isolates of this virus were obtained from India out of which 11 were identified as Naples and nine as Sicilian type, from human serum samples and wild caught sandflies46. The disease is usually self-limiting. However, sometimes, neurological involvement resulting in morbidity is seen47. New antigenically distinct serotypes have been identified from Europe, Southeast Asia, central Asia and Africa48.

Malsoor Virus (Mv)

Malsoor virus (MV) was isolated from Mahabaleshwar, Maharashtra, from bats belonging to Rousettus species. Malsoor is the first Phlebovirus to be isolated from Rousettus bat species. So far, this virus is not known to cause human infections. The virus infects several different mammalian cell types49.

Experimental studies showed pan cytotrophic property of the virus for different mammalian and insect cell lines in vitro. High-resolution transmission electron microscopy studies have been carried out to characterize the fine structure and morphogenesis of this novel Phlebovirus50. Detailed ultrastructural studies on MV particles showed heterogeneous morphology. Majority of the virions (80%) were round, having well-defined envelope projections (6±1 nm) with an average size of 70 nm. A subclass of virions (15%) showed pleomorphism. Interestingly, the envelope projections on the virions were tightly packed and not fragile to staining. Virus-infected cells showed several interesting features not commonly reported for Bunyaviruses. These included frequent detection of multiple inclusion bodies, distinct cytoplasmic membrane-associated virus replication sites and presence of autophagy50. Recently, a human serosurvey was conducted in Mahabaleshwar region (the region from which the virus was first isolated), Maharashtra State, India to detect the presence of anti-Malsoor IgG antibodies, and all the tested samples were found to be negative for the same (NIV unpublished data).

Hantavirus

Hantavirus are a family of rodent-borne viruses (roboviruses) and are responsible for haemorrhagic fever with renal syndrome in Europe and Asia and Hantavirus cardiopulmonary syndrome in America. Hantavirus cases have not been reported from India515253. A pilot study from south India conducted with serum samples obtained from individuals with acute febrile illness and voluntary blood donors indicated 14.7 per cent of samples positive for anti-Hantavirus IgM antibodies5455. This indicated that Hantavirus infections may be present in population and further studies need to be conducted to understand its seroprevalence. In another study, the presence of Hantavirus-specific IgG antibodies was evaluated in 661 individuals. The individuals included tribal population, warehouse workers, patients with chronic renal disease and voluntary blood donors. Nearly 74 per cent of the tested samples were positive for anti-Hantavirus IgG antibodies56. These reports are an indication of Hantavirus prevalence in the country, and further studies need to be conducted to assess the threat of the disease.

Thottapalayam Virus (Tpmv)

TPMV (family Bunyaviridae and genus Hantavirus) was isolated from an Asian house shrew (Suncus murinus) in Tamil Nadu, India2. In fact, this was the first Hantavirus to be isolated in cell culture. Except TPMV, all other known Hantavirus members have been isolated or detected in murid rodents. Whether the shrew (S. murinus) is a primary reservoir or a ‘spillover’ host infected through contact with a primary host is not known. TPMV has also been reported from Nepal57 and China58.

The complete genome sequence analyses of S, M and L segments has confirmed that TPMV is a distinct virus in all the three segments compared to other Hantavirus members. Phylogenetic tree of all the three segments showed that this virus was unique compared to other rodent-borne Hantavirus members (Sigmodontinae, Muridae and Arvicolinae)59.

Many shrew-borne Hantavirus members have been reported from different parts of the world, suggesting that shrews may play a greater role in the ecology and transmission of zoonotic diseases60. Virus sequences were obtained from two Asian house shrews captured in Indonesia60. In addition, anti-TPMV antibodies were detected from a febrile patient from Thailand60. In the light of recent reports of Hantavirus seropositivity, careful surveillance of TPMV is required in different States of India to ascertain whether this virus is involved in causing diseases in humans. The proximity of Asian house shrews with human habitation may result in TPMV infection in humans.

Kaisodi Virus

The Kaisodi virus was isolated from ectoparasite of birds H. turturis, H. spinigera and H. wellingtoni61. This virus was isolated from Kyasanur forest disease (KFD)-affected area (Mysore, Karnataka State). Some cross-reactivity has been observed between Kaisodi and Malayan viruses isolated from Ixodes granulatus61.CF and HI tests confirmed it to be an Arbovirus. No human disease is known so far.

Wanowrie Virus (Wan)

Wanowrie (WAN) virus is an ungrouped Arbovirus having morphogenetic characteristics in common with Bunyavirus. It was isolated for the first time in 1955 from a pool of four adult ticks; Hyalomma marginatum isacci collected from sheep at Wanowrie, near Pune, Maharashtra62, and was subsequently isolated from a human sample. Isolation of the virus was also reported from the human brain suspension at the Virus Research Centre, Pune, in 196662.

No haemagglutinin was produced, but the virus was sensitive to sodium deoxycholate. Wanowrie virus was pathogenic in suckling mice by the intracerebral and intraperitoneal routes but produced only occasional deaths in adult mice inoculated intracerebrally. The virus was pathogenic for seven day old chick embryos and produced cytopathic effects in Baby Hamster Kidney 21 cell line cultures, but no cytopathic effect or evidence of virus multiplication was elicited in an Ae. albopictus larval cell line. Wanowrie virus had no serological relationship to a very large variety of arboviruses. Only two of the 116 goat serum samples had evidence of neutralizing antibodies against the virus; no antibodies were detected in sheep, cow and buffalo serum62. A brief summary of all Bunyaviruses isolated in India is given in the Table. The Figure shows the places from where these Bunyaviruses were first isolated.

Table I A brief summary of various Bunyaviruses isolated in India

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Figure

Places from where the Bunyaviruses were first isolated in India. Source: Refs 1, 2, 8, 20, 25, 28, 34, 39, 44, 46, 49, 61–63.

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Conclusion

With advanced knowledge and technologies, many viruses have been identified and placed taxonomically in family Bunyaviridae. Under proactive research, the presence of CCHF and MV was detected from humans and animals, respectively43. Several Bunyaviruses are known worldwide for causing severe infections, diseases and mortality in humans and animals. Many of these cause severe economic loss (CCHFV, Rift Valley fever virus, SFTS virus, La Crosse encephalitis virus, etc.). In India, though many Bunyaviruses do not cause disease in humans or animals, their genetic similarity to other disease-causing viruses of the same family is of concern, especially in case of formation of reassortant viruses. On the other side of the spectrum are diseases such as CCHF and sandfly fever which cause severe disease in humans. The clinical signs and symptoms of CCHF are very similar to other viral haemorrhagic fevers such as Omsk haemorrhagic fever, dengue and KFD38. Therefore, proximity to livestock, presence of ticks or travel to endemic regions are factors which play a role in suspecting CCHFV infection. With the CCHF, it is necessary to understand bunyavirus prevalence in India.

Most of the viruses described have been discovered during the 1960s/1970s. With better understanding of biosafety concerns, the work regarding discovery and identification of newer viruses began after the establishment of biosafety level three laboratory (BSL3) at the National Institute of Virology (NIV), Pune, in 200563. Viruses such as CCHFV and MV have been identified in India after the establishment of BSL3 and BSL4. Further systematic searches for identification of viruses are ongoing and are necessary for understanding the emerging infectious diseases and identification of disease hot spots. A special emphasis needs to be laid on exploring animal, bird, arthropod and human viruses.

The current review is an attempt to concisely present information about various Bunyaviruses that were isolated from various insects, birds and animals and are circulating in the country. This information would help in preparedness in case of emergence of novel infections. Timely action could also be taken in case infections from these viruses are seen in either human or animal population. The available information will help not only in making new diagnostic tools but also in monitoring the emergence of diseases.