Hantavirus Reservoirs: Current Status with an Emphasis on Data from Brazil
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Viruses 2014, 6, 1929-1973; doi:10.3390/v6051929 OPEN ACCESS viruses ISSN 1999-4915 www.mdpi.com/journal/viruses Review Hantavirus Reservoirs: Current Status with an Emphasis on Data from Brazil Renata Carvalho de Oliveira 1,*, Alexandro Guterres 1, Jorlan Fernandes 1, Paulo Sérgio D’Andrea 2, Cibele Rodrigues Bonvicino 2,3 and Elba Regina Sampaio de Lemos 1 1 Laboratório de Hantaviroses e Rickettsioses, Instituto Oswaldo Cruz, Fundação Oswaldo Cruz, Rio de Janeiro, 21040-360, RJ, Brazil; E-Mails: [email protected] (A.G.); [email protected] (J.F.); [email protected] (E.R.S.L.) 2 Laboratório de Biologia e Parasitologia de Mamíferos Silvestres Reservatórios, Instituto Oswaldo Cruz, Fundação Oswaldo Cruz, Rio de Janeiro, 21040-360, RJ, Brazil; E-Mails: [email protected] (P.S.D.); [email protected] (C.R.B.) 3 Programa de Genética, Instituto Nacional de Câncer, Ministério da Saúde, Rio de Janeiro, 20231-050, RJ, Brazil * Author to whom correspondence should be addressed; E-Mail: [email protected]; Tel./Fax: +55-21-2562-1727. Received: 25 November 2013; in revised form: 3 February 2014 / Accepted: 7 February 2014 / Published: 29 April 2014 Abstract: Since the recognition of hantavirus as the agent responsible for haemorrhagic fever in Eurasia in the 1970s and, 20 years later, the descovery of hantavirus pulmonary syndrome in the Americas, the genus Hantavirus has been continually described throughout the World in a variety of wild animals. The diversity of wild animals infected with hantaviruses has only recently come into focus as a result of expanded wildlife studies. The known reservoirs are more than 80, belonging to 51 species of rodents, 7 bats (order Chiroptera) and 20 shrews and moles (order Soricomorpha). More than 80genetically related viruses have been classified within Hantavirus genus; 25 recognized as human pathogens responsible for a large spectrum of diseases in the Old and New World. In Brazil, where the diversity of mammals and especially rodents is considered one of the largest in the world, 9 hantavirus genotypes have been identified in 12 rodent species belonging to the genus Akodon, Calomys, Holochilus, Oligoryzomys, Oxymycterus, Necromys and Rattus. Considering the increasing number of animals that have been implicated as reservoirs of different hantaviruses, the understanding of this diversity is important for evaluating the risk of distinct hantavirus species as human pathogens. Viruses 2014, 6 1930 Keywords: hantavirus; reservoirs; hantavirus pulmonary syndrome; haemorrhagic fever with renal syndrome 1. Introduction The genus Hantavirus, which consists of more than 80 genetically related viruses, was first identified as an agent of the human disease haemorrhagic fever with renal syndrome (HFRS) in the 1970s [1,2]. After characterization of the Hantaan virus prototype in samples from humans and the rodent reservoir Apodemus agrarius, other species linked to HFRS in Eurasia, such as Pummala, Seoul and Dobrava-Belgrado, were identified. The Dobrava-Belgrado species is thought to be responsible for the majority of deaths from hantaviruses in the Old World [3–5]. Hantavirus has been known to circulate throughout the Americas in the rodents Microtus pennsylvanicus (virus Prospect Hill) and Rattus novegicus (virus Seoul) since the 1980s. In 1993, the novel hantavirus Sin Nombre was identified, and researchers determined that infection by the genus Hantavirus causes hantavirus pulmonary syndrome (HPS) or hantavirus cardiopulmonary syndrome (HCPS), which is restricted to the Americas [6–9]. Since HPS was identified in the United States, the number of new hantaviruses discovered in rodent reservoirs and more recently in insectivorous and bats has grown steadily. Hantaviruses are considered infectious agents of great importance for public health and are broadly distributed around the globe. Hantaviruses are trisegmented RNA that belong to the genus Hantavirus and the family Bunyaviridae. Humans acquire HPS/HCPS and HFRS mainly by inhalation of viral particles present in aerosols that arise from rodent excretions and secretions [10,11]. Hantaviruses are distributed focally because transmission depends critically on the rodent reservoir in addition to human activity. With various clinical-epidemiological patterns depending on the human behavior, the natural history and the distribution of their reservoirs, the hantaviruses have been identified worldwide. In Asia and Europe, the hantaviruses that cause HFRS are responsible for approximately 150,000 to 200,000 cases per year with mortality rates ranging from <1% to 12%. There are approximately 200 cases of HPS per year in South America, with a mortality rate around 40% [12,13]. According to the International committee on the taxonomy of viruses (ICTV), four criteria are used to classification hantavirus species [14]. Thus, a virus under study is considered a novel hantavirus species when the following criteria are met: (i) belongs to a unique ecological niche, such as targeting a distinct rodent species or subspecies as the primary reservoir; (ii) exhibits at least 7% difference in the amino acid sequence of surface glycoproteins (Gn and Gc) of the viral nucleoprotein; (iii) shows at least a four-fold difference in the antibody titre in cross-neutralization tests; and (iv) does not form natural rearrangements with other hantavirus species [15]. Of the various hantaviruses described worldwide, 24 have been officially accepted and classified as species by the ICTV [16,17]. Referred to by different authors as species, variants, genotypes, strains, lineages or serotypes, despite the four species-defining criteria established by the ICTV the continuing identification of hantaviruses exhibits a lack of agreement with respect to naming terminology. Firth et al. recently Viruses 2014, 6 1931 suggested that newly identified hantaviruses that do not meet the species criteria and are related to other pre-existing viruses should be classified as genotypes according to a previously established standard, whereby the abbreviated hantavirus name is followed sequentially by a number [18]. With the on-going identification of novel hantaviruses in rodents that may or may not be associated with human disease, these viral agents will be recognized together with arenaviruses as the rodent-borne ―Robo‖ viruses [19]. However, nearly 40 years after the initial description of the Thottapalayam (TPM) hantavirus, which was isolated in 1964 [20] from an Asian house shrew species (Suncus murinus) captured in India and classified as a member of the genus in 1989 [21], novel hantaviruses that are genetically distant from the hantaviruses associated with rodents were identified in other vertebrate species, leading to the adoption of terms such as ―InBo-viruses‖ and ―RaInBo-viruses‖ [22–28]. Despite the identification of novel hantaviruses in samples from human cases, rodents, insectivores (families Sociridae and Talpidae) and bats (families Vespertilionidae and Nycteridae) that are not associated with human disease, the information obtained to date is insufficient to understand the numerous particularities with respect to the interactions between hantaviruses and their vertebrate reservoirs during the transmission cycles that occur in the wild [29–31]. Given the importance of correct taxonomic identification of reservoirs for a complete understanding of hantavirus transmission cycles and for assessing their potential as host transmitters of hantavirus to humans, certain factors that increase our understanding of the virus-host interaction dynamics and the risk of human infection must be identified. These factors include the following: (i) geographical distribution of the host to map the maximum area where the hantavirus species is distributed and, consequently, where the hantavirus species that colonizes this host may occur; (ii) abundance of the reservoir species in the natural environment, which is considered a strong indicator of greater risk for human infection based on the fact that hantaviruses are zoonosis whose transmission depends on host population density; (iii) how the agent interacts with the host reservoir, which is a critical factor for understanding the spread and maintenance of hantaviruses in the environment. Lack of illness in the reservoir and the establishment of prolonged infection that may persist for the entire lifetime of the reservoir animal ensure that the hantavirus will remain in the environment throughout the lifespan of the reservoir animals and ensures transmission among rodents and; (iv) host/reservoir habits in natural and anthropic environments. For example, the tendency of rodents to enter homes is an important factor in hantavirus epidemiology because this occurrence allows these reservoirs to come into close contact with humans. Despite the issues stated above, other factors associated with the process of anthropisation are related to the risk of hantavirus transmission. These factors include disruption of rodent habitats, which can be caused by deforestation and extensive agriculture and can favor opportunist or generalist species that can serve as hantavirus reservoirs. Environmental changes that reduce rodent diversity is another important factor because environmental changes permit aggressive encounters between animals, thereby increasing interactions between host species that can trigger a cascade of greater viral transmission within a single species or across different rodent species and can lead to greater risk of Viruses