Field studies on the epidemiology of Venezuelan hemorrhagic fever: implication of the cotton rat Sigmodon alstoni as the probable rodent reservoir

A review of emerging health threats from zoonotic New World mammarenaviruses

Despite repeated spillover transmission and their potential to cause significant morbidity and mortality in human hosts, the New World mammarenaviruses remain largely understudied. These viruses are endemic to South America, with animal reservoir hosts covering large geographic areas and whose transmission ecology and spillover potential are driven in part by land use change and agriculture that put humans in regular contact with zoonotic hosts.We compiled published studies about Guanarito virus, Junin virus, Machupo virus, Chapare virus, Sabia virus, and Lymphocytic Choriomeningitis virus to review the state of knowledge about the viral hemorrhagic fevers caused by New World mammarenaviruses. We summarize what is known about rodent reservoirs, the conditions of spillover transmission for each of these pathogens, and the characteristics of human populations at greatest risk for hemorrhagic fever diseases. We also review the implications of repeated outbreaks and biosecurity concerns where these diseases are endemic, and steps that countries can take to strengthen surveillance and increase capacity of local healthcare systems. While there are unique risks posed by each of these six viruses, their ecological and epidemiological similarities suggest common steps to mitigate spillover transmission and better contain future outbreaks.

Land reversion and zoonotic spillover risk

Deforestation alters wildlife communities and modifies human-wildlife interactions, often increasing zoonotic spillover potential. When deforested land reverts to forest, species composition differences between primary and regenerating (secondary) forest could alter spillover risk trajectory. We develop a mathematical model of land-use change, where habitats differ in their relative spillover risk, to understand how land reversion influences spillover risk. We apply this framework to scenarios where spillover risk is higher in deforested land than mature forest, reflecting higher relative abundance of highly competent species and/or increased human-wildlife encounters, and where regenerating forest has either very low or high spillover risk. We find the forest regeneration rate, the spillover risk of regenerating forest relative to deforested land, and how rapidly regenerating forest regains attributes of mature forest determine landscape-level spillover risk. When regenerating forest has a much lower spillover risk than deforested land, reversion lowers cumulative spillover risk, but instaneous spillover risk peaks earlier. However, when spillover risk is high in regenerating and cleared habitats, landscape-level spillover risk remains high, especially when cleared land is rapidly abandoned then slowly regenerates to mature forest. These results suggest that proactive wildlife management and awareness of human exposure risk in regenerating forests could be important tools for spillover mitigation.

An updated review and current challenges of Guanarito virus infection, Venezuelan hemorrhagic fever

Guanarito virus (GTOV) is a member of the family Arenaviridae and has been designated a category A bioterrorism agent by the US Centers for Disease Control and Prevention. It is endemic to Venezuela's western region, and it is the etiological agent of "Venezuelan hemorrhagic fever" (VHF). Similar to other arenaviral hemorrhagic fevers, VHF is characterized by fever, mild hemorrhagic signs, nonspecific symptoms, thrombocytopenia, and leukopenia. Patients with severe disease usually develop signs of internal bleeding. Due to the absence of reference laboratories that can handle GTOV in endemic areas, diagnosis is primarily clinical and epidemiological. No antiviral therapies are available; thus, treatment includes only supportive analgesia and fluids. GTOV is transmitted by contact with the excreta of its rodent reservoir, Zygodontomys brevicauda. The main reasons for the emergence of the disease may be the increase in the human population, migration, and changes in land use patterns in rural areas. Social and environmental changes could make VHF an important cause of underdiagnosed acute febrile illnesses in regions near the endemic areas. Although there is evidence that GTOV circulates among rodents in different Venezuelan states, VHF cases have only been reported in the states of Portuguesa and Barinas. However, due to the increased frequency of invasions by humans into wildlife habitats, it is probable that VHF could become a public health problem in the nearby regions of Colombia and Brazil. The current Venezuelan political crisis is causing an increase in the migration of people and livestock, representing a risk for the redistribution and re-emergence of infectious diseases.

Should we be concerned about Venezuelan hemorrhagic fever? – A reflection on its current situation in Venezuela and potential impact in Latin America amid the migration crisis

Venezuelan Haemorrhagic Fever is an endemic zoonosis exhibiting a high lethality. Discovered decades ago, it is still causing seasonal hemorrhagic fever outbreaks. With the ongoing migration crisis, transmission and spreading to other countries in Latin America remains a latent threat that should be monitored, particularly in light of recent cases.

Preserve a Voucher Specimen! The Critical Need for Integrating Natural History Collections in Infectious Disease Studies

Despite being nearly 10 months into the COVID-19 (coronavirus disease 2019) pandemic, the definitive animal host for SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2), the causal agent of COVID-19, remains unknown. Unfortunately, similar problems exist for other betacoronaviruses, and no vouchered specimens exist to corroborate host species identification for most of these pathogens. This most basic information is critical to the full understanding and mitigation of emerging zoonotic diseases. To overcome this hurdle, we recommend that host-pathogen researchers adopt vouchering practices and collaborate with natural history collections to permanently archive microbiological samples and host specimens. Vouchered specimens and associated samples provide both repeatability and extension to host-pathogen studies, and using them mobilizes a large workforce (i.e., biodiversity scientists) to assist in pandemic preparedness. We review several well-known examples that successfully integrate host-pathogen research with natural history collections (e.g., yellow fever, hantaviruses, helminths). However, vouchering remains an underutilized practice in such studies. Using an online survey, we assessed vouchering practices used by microbiologists (e.g., bacteriologists, parasitologists, virologists) in host-pathogen research. A much greater number of respondents permanently archive microbiological samples than archive host specimens, and less than half of respondents voucher host specimens from which microbiological samples were lethally collected. To foster collaborations between microbiologists and natural history collections, we provide recommendations for integrating vouchering techniques and archiving of microbiological samples into host-pathogen studies. This integrative approach exemplifies the premise underlying One Health initiatives, providing critical infrastructure for addressing related issues ranging from public health to global climate change and the biodiversity crisis.

Rodent-borne viruses survey in rural settlers from Central Brazil

Anthropogenic environmental changes arising from settlement and agriculture include deforestation and replacement of natural vegetation by crops providing opportunities for pathogen spillover from animals to humans. This study aimed to investigate the prevalence of rodent-borne virus infections in seven rural settlements from Midwestern Brazil. Of the 466 individuals tested 12 (2.57%) were reactive for orthohantavirus and 3 (0.64%) for mammarenavirus. These rural settlers lived under unfavorable infrastructure, socioeconomic disadvantages, and unsanitary conditions, representing a risk for rodent-borne infections. Development of public policies towards the improvement of health, sanitation and awareness of rodent-borne diseases in improvised camps and settlements is imperative, in order to reduce morbidity and mortality caused by these diseases.

[Epidemiology of Ebola virus disease and of other highly contagious, life-threatening diseases with low incidence in Germany]

Das Vorkommen von Ebolafieber, der Marburgvirus-Krankheit sowie von Lassa-Fieber ist – abgesehen von vereinzelten eingeschleppten Fällen – auf den afrikanischen Kontinent beschränkt. Hämorrhagisches Krim-Kongo-Fieber kommt in Südosteuropa, jedoch bisher nicht in Deutschland vor. Weitere hämorrhagische Fiebererkrankungen sind regional auf dem südamerikanischen Kontinent verbreitet. Die Lungenpest ist die bakterielle Infektionskrankheit mit der höchsten Kontagiösität und Letalität und ist vor allem in Madagaskar und Ostafrika, aber auch in vielen anderen Ländern beheimatet, wie z. B. in Indien und in den USA. Affenpocken haben in entlegenen Regionen des Kongobeckens zu Ausbrüchen geführt, die sich in Zukunft aufgrund der nicht mehr durchgeführten Pockenimpfung häufen könnten. Das 2002/2003 neu aufgetretene Severe Acute Respiratory Syndrome (SARS) ist eine weitere Erkrankung mit hohem epidemischen Potenzial. Typisch für diese hochkontagiösen Erreger ist, dass sie meist unerkannt zwischen Reservoirtieren abseits des Menschen zirkulieren. Durch sporadischen Kontakt zwischen infizierten Tieren und dem Menschen können diese übertragen werden. Die dann folgende Mensch-zu-Mensch-Übertragung kann zu ausgedehnten Epidemien, wie dem derzeitigen Ausbruch des Ebolafiebers in Westafrika, führen.

Crystal structure of Venezuelan hemorrhagic fever virus fusion glycoprotein reveals a class 1 postfusion architecture with extensive glycosylation

Guanarito virus (GTOV) is an emergent and deadly pathogen. We present the crystal structure of the glycosylated GTOV fusion glycoprotein to 4.1-Å resolution in the postfusion conformation. Our structure reveals a classical six-helix bundle and presents direct verification that New World arenaviruses exhibit class I viral membrane fusion machinery. The structure provides visualization of an N-linked glycocalyx coat, and consideration of glycan dynamics reveals extensive coverage of the underlying protein surface, following virus-host membrane fusion.

Ocozocoautla de espinosa virus and hemorrhagic fever, Mexico

Arenavirus RNA was isolated from Mexican deer mice (Peromyscus mexicanus) captured near the site of a 1967 epidemic of hemorrhagic fever in southern Mexico. Analyses of nucleotide and amino acid sequence data indicated that the deer mice were infected with a novel Tacaribe serocomplex virus (proposed name Ocozocoautla de Espinosa virus), which is phylogenetically closely related to Tacaribe serocomplex viruses that cause hemorrhagic fever in humans in South America.

Natural host relationships of hantaviruses native to western Venezuela

Strains of Caño Delgadito virus (CADV) and Maporal virus (MAPV) were isolated from 25 (8.9%) of the 280 rodents captured on farms in 1997 in western Venezuela. The results of analyses of laboratory and zoographic data indicated that Alston's cotton rat (Sigmodon alstoni) is the principal host of CADV, horizontal virus transmission is the dominant mode of CADV transmission in Alston's cotton rat in nature, a pygmy rice rat (Oligoryzomys sp.) is the principal host of MAPV, and the natural host relationships of CADV and MAPV are highly specific.

Genetic diversity between and within the arenavirus species indigenous to western Venezuela

The results of analyses of Z, RNA-dependent RNA polymerase, glycoprotein precursor, and nucleocapsid protein gene sequence data suggested that Guanarito virus was the most common cause of Venezuelan hemorrhagic fever in a 7-year period in the 1990s and that the evolution of Pirital virus in association with Sigmodon alstoni (Alston's cotton rat) has occurred at a significantly higher rate than the evolution of Guanarito virus in association with Zygodontomys brevicauda (short-tailed cane mouse) on the plains of western Venezuela. The results of analyses of the primary structures of the glycoproteins of the 8 strains of Guanarito virus isolated from humans suggested that these strains would be highly cross-reactive in neutralization assays. Thus, passive antibody therapy may prove beneficial in the treatment of human disease caused by strains of Guanarito virus that are enzootic in the region in which Venezuelan hemorrhagic fever is endemic.

Arenaviruses

The Arenaviridae family contains 22 recognized virus species, each of them strongly associated with a rodent species (except Tacaribe virus which is associated with a species of bat), suggesting an ancient co-evolutionary process. Although the concept of co-evolution between rodents and arenaviruses is now largely accepted, little has been uncovered in terms of dating the phenomenon and the mechanisms of evolution, including speciation and pathogenicity. These questions are targeted in the present chapter. Old World arenaviruses are associated with the Eurasian rodents in the family Muridae. New World arenaviruses are associated with American rodents in the subfamily Sigmodontinae. The correlation between the rodent host phylogeny and the viruses suggests a long association and a co-evolutionary process. Furthermore, three distinct New World arenaviruses share a common ancestor, demonstrating a unique recombination event that probably occurred in that ancestor. This shows that recombination among arenaviruses of different lineages might occur in nature. Recombination and co-evolutionary adaptation appear as the main mechanisms of arenavirus evolution, generating a high degree of diversity. The diversity among rodent host reservoir and virus species and the potential to exchange genomic material provide a basis for the emergence of new viruses and the risk of these becoming pathogenic for humans.

Maporal virus, a hantavirus associated with the fulvous pygmy rice rat (Oligoryzomys fulvescens) in western Venezuela

Oryzomine rodents in the southeastern United States, Panama, and southern South America are natural hosts of 6 of the 13 viruses known to cause hantavirus pulmonary syndrome. The purpose of this study was to extend our knowledge of the geographical distribution and genetic diversity of the hantaviruses associated with oryzomine rodents in South America. An infectious hantavirus was isolated from two fulvous pygmy rice rats captured in western Venezuela. Analyses of complete nucleocapsid protein and glycoprotein precursor sequences indicated that the isolates are strains of a novel hantavirus (proposed name "Maporal") which is phylogenetically most closely related to the viruses known to cause hantavirus pulmonary syndrome in southern South America.

The cotton rat: an underutilized animal model for human infectious diseases can now be exploited using specific reagents to cytokines, chemokines, and interferons

The cotton rat represents the best or only animal model for a large number of human infectious diseases, and it may be unique among small laboratory animals in its susceptibility to several potential agents of bioterrorism. Although the cotton rat is a reliable model to define pathologic changes produced during infection with human pathogens, the lack of specific reagents has precluded a more extensive analysis of the molecular basis of pathogenesis. Here, we report the cloning of 24 cotton rat genes encoding various cytokines, chemokines, and interferons (IFNs). Analysis of the expression of most of these genes was performed by RT-PCR in cotton rat macrophages during treatment with lipopolysaccharide (LPS) and in cotton rat lungs after infection with influenza virus. The availability of these reagents will provide the tools for molecular analysis of pathogenesis and immune responses to a wide variety of pathogens and set the basis for the development of new prophylactic and therapeutic strategies against human infectious diseases.

Viral hemorrhagic fevers including hantavirus pulmonary syndrome in the Americas

The term viral hemorrhagic fever refers to an acute systemic illness with a propensity for bleeding and shock. The viral hemorrhagic fevers endemic in the Americas include yellow fever, dengue hemorrhagic fever, the South American hemorrhagic fevers, hantavirus pulmonary syndrome, and hemorrhagic fever with renal syndrome. Because these diseases are primarily zoonotic, the distribution of any given virus is generally restricted by the distribution of its natural reservoir or arthropod vector. A high index of suspicion, detailed investigation of the travel and exposure history of the patient, and a basic understanding of the incubation periods and distributions of the various reservoirs of hemorrhagic fever viruses are imperative, as are prompt notification and laboratory confirmation. Clinical management is largely supportive, with a special emphasis on safe nursing practices to prevent nosocomial transmission.

Extreme genetic diversity among Pirital virus (Arenaviridae) isolates from western Venezuela

Pirital-like virus isolates from rodents collected in a variety of habitats within a six-state area of central Venezuela were analyzed genetically by amplifying a portion of the nucleocapsid protein gene using RT-PCR. Comparisons of the sequences from 30 selected Pirital-like virus isolates demonstrated up to 26% divergence in nucleotide sequences and up to 16% divergence in deduced amino acid sequences. Within the Pirital monophyletic group, 14 distinct lineages or genotypes, differing by at least 6% in nucleotide sequences, were identified. Although sample sizes were small for some lineages, many of the different genotypes were sampled in only one region or locality, suggesting allopatric divergence. Complement fixation tests with representatives of the most divergent Pirital virus lineages failed to delineate multiple species or subtypes within the Pirital clade. These results indicate that the previously proposed 12% nucleocapsid protein amino acid sequence divergence cutoff value for delineating arenavirus species is not appropriate for the entire family. When individual clones were examined from PCR amplicons, a mean of 0.17% sequence diversity vs the consensus sequences was detected, suggesting diverse quasispecies populations within infected rodent hosts. Possible explanations for the extreme genetic diversity within and among Pirital virus populations in infected rodents are discussed.

Rodent-borne emerging viral zoonosis. Hemorrhagic fevers and hantavirus infections in South America

Hantaviruses and arenaviruses are naturally occurring viruses of rodents. Four South American hemorrhagic fevers caused by arenaviruses have emerged in the last 5 decades. All have similar clinical manifestations, with a case-fatality rate as high as 15% to 30%. Hantavirus infections have been increasingly recognized in South America since the description in 1993 of Hantavirus pulmonary syndrome. Given the diversity of rodent species in the region, it can be foreseen that many other viruses will be discovered, and some of them will be causing human illnesses of high public health impact.

Guanarito virus (Arenaviridae) isolates from endemic and outlying localities in Venezuela: sequence comparisons among and within strains isolated from Venezuelan hemorrhagic fever patients and rodents

Despite intensive surveillance, Venezuelan hemorrhagic fever (VHF), caused by Guanarito (GTO) virus, has been detected in only a small region of western Venezuela. To determine whether VHF is associated with a particular regional GTO virus strain(s), 29 isolates from rodents and humans throughout the surrounding regions were analyzed by partial sequencing of the nucleocapsid protein gene. Phylogenetic trees delineated nine distinct GTO genotypes that differ by 4-17% in nucleotides and up to 9% in amino acid sequences; most appeared to be restricted to discrete geographic regions, although a few genotypes were isolated in several locations. Each genotype included at least one strain recovered from a rodent, but only two genotypes were isolated from VHF cases. The presence outside of the endemic/epidemic region of two genotypes isolated also from VHF cases suggests that human pathogenic viruses occur outside of the endemic zone, but do not frequently infect people and/or cause apparent disease there. VHF does not appear to be associated with a GTO virus genotype that is restricted to a certain rodent species. When quasispecies diversity was examined, rodent isolates had higher sequence variation than human isolates. One rodent isolate included a mixture of two phylogenetically distinct genotypes, suggesting a dual infection.

Isolation, characterization and geographic distribution of Caño Delgadito virus, a newly discovered South American hantavirus (family Bunyaviridae)

Rodents collected from the Venezuelan llanos (plains) during field studies of viral hemorrhagic fever were tested for evidence of hantavirus infection. Hantavirus antibody was found in one (7.7%) of 13 Oryzomys bicolor, one (3.4%) of 29 Rattus rattus, 10 (6.0%) of 166 Sigmodon alstoni and one (2.2%) of 45 Zygodontomys brevicauda. Hantavirus-specific RNA was detected in lung tissues from four antibody-positive rodents: two S. alstoni from Portuguesa State and one S. alstoni each from Cojedes and Barinas States. A hantavirus isolate (herein identified as VHV-574) was recovered from lung tissue from a hantavirus RNA-positive S. alstoni collected from Portuguesa State. The results of serological tests and analyses of small and medium RNA segment nucleotide sequence data indicated that VHV-574 represents a novel hantavirus (proposed name 'Caño Delgadito') that is distinct from all previously characterized hantaviruses. The results of analyses of nucleotide sequence data from the four hantavirus RNA-positive S. alstoni suggested that Caño Delgadito virus is widely distributed in the Venezuelan llanos.

Definition of cotton rat immunoglobulins: sigmodon species differ in expression of IgG isotypes and production of respiratory syncytial virus antibody

The cotton rat (Sigmodon species) is the preferred animal model for experiments with a number of human pathogens, especially the respiratory viruses. The cotton rat is classified in the family Cricetidae (with hamsters and gerbils) and is a distant cousin of the common laboratory rat (Rattus) classified in the family Muridae (with the common laboratory mouse, Mus). Antibody reagents that are specific for cotton rat immunoglobulins have not been described. To enhance the usefulness of this model, four immunoglobulins in Sigmodon serum were characterized (IgG1, IgG2, IgA, IgM) and antisera specific for each immunoglobulin were made. Sera from three different species of Sigmodon were examined, S. hispidus (SH), S. arizoni (SA) and S. fulviventer (SF). Although IgA and IgM appeared similar in all three species, the IgG were expressed differently because normal serum levels of IgG2 were deficient in SH when compared with SA and SF and to other rodents. Similarly, IgG2 antibody response to purified protein antigen was deficient in SH although the IgG1 antibody response was superior to that in SF and SA. The three cotton rat species were infected with respiratory syncytial virus, and the kinetics of the antibody response was measured. Neutralizing antibody developed faster and to a higher titre in SH than in SA and SF. The enhanced immunoresponsiveness in SH may compensate for the IgG2 deficiency in SH and these changes appear to be relatively recent events in the evolution of this most populous species of Sigmodon.