Experimental infection of Neotoma albigula (Muridae) with Whitewater Arroyo virus (Arenaviridae)

Inoculation route-dependent Lassa virus dissemination and shedding dynamics in the natural reservoir - Mastomys natalensis

Lassa virus (LASV), a Risk Group-4 zoonotic haemorrhagic fever virus, affects sub-Saharan African countries. Lassa fever, caused by LASV, results in thousands of annual deaths. Although decades have elapsed since the identification of the Natal multimammate mouse (Mastomys natalensis) as a natural reservoir of LASV, little effort has been made to characterize LASV infection in its reservoir. The natural route of infection and transmission of LASV within M. natalensis remains unknown, and the clinical impact of LASV in M. natalensis is mostly undescribed. Herein, using an outbred colony of M. natalensis, we investigate the replication and dissemination dynamics of LASV in this reservoir following various inoculation routes. Inoculation with LASV, regardless of route, resulted in a systemic infection and accumulation of abundant LASV-RNA in many tissues. LASV infection in the Natal multimammate mice was subclinical, however, clinical chemistry values were transiently altered and immune infiltrates were observed histologically in lungs, spleens and livers, indicating a minor disease with coordinated immune responses are elicited, controlling infection. Intranasal infection resulted in unique virus tissue dissemination dynamics and heightened LASV shedding, compared to subcutaneous inoculation. Our study provides important insights into LASV infection in its natural reservoir using a contemporary infection system, demonstrating that specific inoculation routes result in disparate dissemination outcomes, suggesting intranasal inoculation is important in the maintenance of LASV in the natural reservoir, and emphasizes that selection of the appropriate inoculation route is necessary to examine aspects of viral replication, transmission and responses to zoonotic viruses in their natural reservoirs.

Density dependence and persistence of Morogoro arenavirus transmission in a fluctuating population of its reservoir host

A key aim in wildlife disease ecology is to understand how host and parasite characteristics influence parasite transmission and persistence. Variation in host population density can have strong impacts on transmission and outbreaks, and theory predicts particular transmission-density patterns depending on how parasites are transmitted between individuals. Here, we present the results of a study on the dynamics of Morogoro arenavirus in a population of multimammate mice (Mastomys natalensis). This widespread African rodent, which is also the reservoir host of Lassa arenavirus in West Africa, is known for its strong seasonal density fluctuations driven by food availability. We investigated to what degree virus transmission changes with host population density and how the virus might be able to persist during periods of low host density. A seven-year capture-mark-recapture study was conducted in Tanzania where rodents were trapped monthly and screened for the presence of antibodies against Morogoro virus. Observed seasonal seroprevalence patterns were compared with those generated by mathematical transmission models to test different hypotheses regarding the degree of density dependence and the role of chronically infected individuals. We observed that Morogoro virus seroprevalence correlates positively with host density with a lag of 1-4 months. Model results suggest that the observed seasonal seroprevalence dynamics can be best explained by a combination of vertical and horizontal transmission and that a small number of animals need to be infected chronically to ensure viral persistence. Transmission dynamics and viral persistence were best explained by the existence of both acutely and chronically infected individuals and by seasonally changing transmission rates. Due to the presence of chronically infected rodents, rodent control is unlikely to be a feasible approach for eliminating arenaviruses such as Lassa virus from Mastomys populations.

Prevalence of Wēnzhōu virus in small mammals in Yunnan Province, China

Background

Mammarenaviruses are associated with human hemorrhagic fever diseases in Africa and America. Recently, a rodent mammarenavirus, Wēnzhōu virus (WENV) and related viruses, have been reported in China, Cambodia, and Thailand. Moreover, in Cambodia, these viruses were suspected to be associated with human disease. In China, Yunnan Province is famous for its abundant animal and plant diversity and is adjacent to several South-eastern Asia countries. Therefore, it is necessary to know whether WENV-related viruses, or other mammarenaviruses, are prevalent in this province.

Methodology/Principal findings

Small mammals were trapped, euthanized, and sampled. Mammarenavirus RNA was detected using a nested reverse transcription polymerase chain reaction (RT-PCR) and quantified by real-time RT-PCR. A total of 1040 small mammals belonging to 13 genera and 26 species were trapped in Yunnan Province. WENV-related mammarenaviruses were detected in 41 rodent liver samples, mainly in brown rats (Rattus norvegicus) and oriental house rats (R. tanezumi).Viral nucleocapsid protein was detected in liver sections by indirect immunofluorescence assay. Full-length-genomes were amplified by RT-PCR and used for phylogenetic analysis with the MEGA package. Recombination analysis was performed using the SimPlot and Recombination Detection Program.

Conclusions/Significance

WENV related viruses circulated in small mammals in Yunnan Province. Whole genome sequence analysis of five selected viral strains showed that these viruses are closely related to WENVs discovered in Asia and form an independent branch in the phylogenetic tree in the WENV clade. Paying attention to investigate the influence of these viruses to public health is essential in the epidemic regions.

Rodents are natural reservoirs of mammarenavirus. Lymphocytic choriomeningitis virus (LCMV), isolated in Asian countries during the 1990s, has a worldwide distribution and was the first mammarenavirus isolated. In 2014, a second mammarenavirus, Wēnzhōu virus (WENV), was identified in rodents in Zhejiang Province of China and later in Guangdong, Shandong, and Hainan Provinces. Most importantly, WENV or related viruses were reported in Thailand and Cambodia. In Cambodia, the isolated virus was associated with human respiratory diseases. In this study, we detected WENV or related viruses in Yunnan Province and found a high prevalence in rats of two species (Rattus norvegicus and R. tanezumi). Phylogenetic analysis of the complete L and S segments of five strains showed that these viruses form an independent phylogenetic branch in WENV clade most closely related to WENVs found in China and Cambodia. Considering the wide spread distribution of rats and altered distribution patterns due to ecological changes, we propose that these viruses may have a wider prevalence and be found in countries from South-eastern Asia to China. Given that WENV may be associated with human diseases, it is necessary to improve surveillances of these viruses in their natural reservoirs and in humans.

Serological evidence of arenavirus circulation among fruit bats in Trinidad

Tacaribe virus (TCRV) was isolated in the 1950s from artibeus bats captured on the island of Trinidad. The initial characterization of TCRV suggested that artibeus bats were natural reservoir hosts. However, nearly 60 years later experimental infections of Jamaican fruit bats (Artibeus jamaicensis) resulted in fatal disease or clearance, suggesting artibeus bats may not be a reservoir host. To further evaluate the TCRV reservoir host status of artibeus bats, we captured bats of six species in Trinidad for evidence of infection. Bats of all four fruigivorous species captured had antibodies to TCRV nucleocapsid, whereas none of the insectivore or nectarivore species did. Many flat-faced fruit-eating bats (A. planirostris) and great fruit-eating bats (A. literatus) were seropositive by ELISA and western blot to TCRV nucleocapsid antigen, as were two of four Seba’s fruit bats (Carollia perspicillata) and two of three yellow-shouldered fruit bats (Sturnira lilium). Serum neutralization tests failed to detect neutralizing antibodies to TCRV from these bats. TCRV RNA was not detected in lung tissues or lung homogenates inoculated onto Vero cells. These data indicate that TCRV or a similar arenavirus continues to circulate among fruit bats of Trinidad but there was no evidence of persistent infection, suggesting artibeus bats are not reservoir hosts.

Arenavirus Dynamics in Experimentally and Naturally Infected Rodents

Infectious diseases of wildlife are typically studied using data on antibody and pathogen levels. In order to interpret these data, it is necessary to know the course of antibodies and pathogen levels after infection. Such data are typically collected using experimental infection studies in which host individuals are inoculated in the laboratory and sampled over an extended period, but because laboratory conditions are controlled and much less variable than natural conditions, the immune response and pathogen dynamics may differ. Here, we compared Morogoro arenavirus infection patterns between naturally and experimentally infected multimammate mice (Mastomys natalensis). Longitudinal samples were collected during three months of bi-weekly trapping in Morogoro, Tanzania, and antibody titer and viral RNA presence were determined. The time of infection was estimated from these data using a recently developed Bayesian approach, which allowed us to assess whether the natural temporal patterns match the previously observed patterns in the laboratory. A good match was found for 52% of naturally infected individuals, while most of the mismatches can be explained by the presence of chronically infected individuals (35%), maternal antibodies (10%), and an antibody detection limit (25%). These results suggest that while laboratory data are useful for interpreting field samples, there can still be differences due to conditions that were not tested in the laboratory.

Epizootiology of Tacaribe serocomplex viruses (Arenaviridae) associated with neotomine rodents (Cricetidae, Neotominae) in southern California

The objective of this study was to advance our knowledge of the epizootiology of Bear Canyon virus and other Tacaribe serocomplex viruses (Arenaviridae) associated with wild rodents in California. Antibody (immunoglobulin G [IgG]) to a Tacaribe serocomplex virus was found in 145 (3.6%) of 3977 neotomine rodents (Cricetidae: Neotominae) captured in six counties in southern California. The majority (122 or 84.1%) of the 145 antibody-positive rodents were big-eared woodrats (Neotoma macrotis) or California mice (Peromyscus californicus). The 23 other antibody-positive rodents included a white-throated woodrat (N. albigula), desert woodrat (N. lepida), Bryant's woodrats (N. bryanti), brush mice (P. boylii), cactus mice (P. eremicus), and deer mice (P. maniculatus). Analyses of viral nucleocapsid protein gene sequence data indicated that Bear Canyon virus is associated with N. macrotis and/or P. californicus in Santa Barbara County, Los Angeles County, Orange County, and western Riverside County. Together, analyses of field data and antibody prevalence data indicated that N. macrotis is the principal host of Bear Canyon virus. Last, the analyses of viral nucleocapsid protein gene sequence data suggested that the Tacaribe serocomplex virus associated with N. albigula and N. lepida in eastern Riverside County represents a novel species (tentatively named "Palo Verde virus") in the genus Arenavirus.

Shedding dynamics of Morogoro virus, an African arenavirus closely related to Lassa virus, in its natural reservoir host Mastomys natalensis

Arenaviruses can cause mild to severe hemorrhagic fevers. Humans mainly get infected through contact with infected rodents or their excretions, yet little is known about transmission dynamics within rodent populations. Morogoro virus (MORV) is an Old World arenavirus closely related to Lassa virus with which it shares the same host species Mastomys natalensis. We injected MORV in its host, and sampled blood and excretions at frequent intervals. Infection in adults was acute; viral RNA disappeared from blood after 18 days post infection (dpi) and from excretions after 39 dpi. Antibodies were present from 7 dpi and never disappeared. Neonatally infected animals acquired a chronic infection with RNA and antibodies in blood for at least 3 months. The quantified excretion and antibody patterns can be used to inform mathematical transmission models, and are essential for understanding and controlling transmission in the natural rodent host populations.

Diversity among Tacaribe serocomplex viruses (Family Arenaviridae) associated with the southern plains woodrat (Neotoma micropus)

The southern plains woodrat (Neotoma micropus) is the principal host of Catarina virus in southern Texas and a natural host of other North American Tacaribe serocomplex viruses. The objectives of this study were to increase our knowledge of the genetic diversity among Tacaribe serocomplex viruses associated with N. micropus and to define better the natural host relationships of these viruses. Pairwise comparisons of complete glycoprotein precursor gene sequences and complete nucleocapsid protein gene sequences revealed a high level of genetic diversity among Tacaribe serocomplex viruses associated with N. micropus in western Oklahoma, southern New Mexico, and northern and southern Texas. Collectively, the results of Bayesian analyses of nucleotide sequences and pairwise comparisons of amino acid sequences confirmed that the arenaviruses associated with N. micropus in Oklahoma and New Mexico should be included in the Whitewater Arroyo species complex, and indicated that that the arenaviruses associated with N. micropus in northern Texas are strains of a novel arenaviral species--tentatively named "Middle Pease River virus". Together, the results of assays for arenavirus and assays for anti-arenavirus antibody in 54 southern plains woodrats and 325 other rodents captured at 2 localities suggested that the southern plains woodrat is the principal host of Middle Pease River virus in northern Texas.

Antibodies to Tacaribe serocomplex viruses (family Arenaviridae, genus Arenavirus) in cricetid rodents from New Mexico, Texas, and Mexico

Blood samples from 4893 cricetid rodents were tested for antibody (immunoglobulin G) to Whitewater Arroyo virus and Amaparí virus to extend our knowledge of the natural host range and geographical distribution of Tacaribe serocomplex viruses in North America. Antibodies to arenaviruses were found in northern pygmy mice (Baiomys taylori), woodrats (Neotoma spp.), northern grasshopper mice (Onychomys leucogaster), oryzomys (Oryzomys spp.), deermice (Megadontomys nelsoni and Peromyscus spp.), harvest mice (Reithrodontomys spp.), and cotton rats (Sigmodon spp.) captured in New Mexico, Texas, or Mexico. Comparison of endpoint antibody titers to Whitewater Arroyo virus and Amaparí virus in individual blood samples indicated that the Tacaribe complex viruses enzootic in Texas and Mexico are antigenically diverse.

Genetic evidence for a tacaribe serocomplex virus, Mexico

We isolated arenavirus RNA from white-toothed woodrats (Neotoma leucodon) captured in a region of Mexico in which woodrats are food for humans. Analyses of nucleotide and amino acid sequence data indicated that the woodrats were infected with a novel Tacaribe serocomplex virus, proposed name Real de Catorce virus.

Genistein, a general kinase inhibitor, as a potential antiviral for arenaviral hemorrhagic fever as described in the Pirital virus-Syrian golden hamster model

Arenaviruses are rodent-borne negative strand RNA viruses and infection of these viruses in humans may result in disease and hemorrhagic fever. To date, supportive care, ribavirin, and in some cases immune plasma remain the foremost treatment options for arenaviral hemorrhagic fever. Research with the hemorrhagic fever causing-arenaviruses usually requires a Biosafety level (BSL)-4 environment; however, surrogate animal model systems have been developed to preliminarily study and screen various vaccines and antivirals. The Syrian golden hamster-Pirital virus (PIRV) surrogate model of hemorrhagic fever provides an opportunity to test new antivirals in an ABSL-3 setting. Thus, we challenged hamsters, implanted with telemetry, with PIRV and observed viremia and tissue viral titers, and changes in core body temperature, hematology, clinical chemistry, and coagulation parameters. Physical signs of disease of the PIRV-infected hamsters included weight loss, lethargy, petechial rashes, epistaxis, ocular orbital and rectal hemorrhage, and visible signs of neurologic disorders. However, treating animals with genistein, a plant derived isoflavone and general kinase inhibitor, resulted in increased survival rates and led to an improved clinical profile. In all, the results from this study demonstrate the potential of a general kinase inhibitor genistein as an antiviral against arenaviral hemorrhagic fever.

Diversity among tacaribe serocomplex viruses (family Arenaviridae) naturally associated with the white-throated woodrat (Neotoma albigula) in the southwestern United States

Bayesian analyses of glycoprotein precursor and nucleocapsid protein gene sequences indicated that arenaviruses naturally associated with white-throated woodrats in central Arizona are phylogenetically closely related to the Whitewater Arroyo virus prototype strain AV 9310135, which originally was isolated from a white-throated woodrat captured in northwestern New Mexico. Pairwise comparisons of glycoprotein precursor and nucleocapsid protein amino acid sequences revealed extensive diversity among arenaviruses isolated from white-throated woodrats captured in different counties in central Arizona and extensive diversity between these viruses and Whitewater Arroyo virus strain AV 9310135. It was concluded that the viruses isolated from the white-throated woodrats captured in Arizona represent 2 novel species (Big Brushy Tank virus and Tonto Creek virus) and that these species should be included with Whitewater Arroyo virus in a species complex within the Tacaribe serocomplex (family Arenaviridae, genus Arenavirus).

GENETIC VARIATION IN MULTILOCUS MICROSATELLITE GENOTYPES IN TWO SPECIES OF WOODRATS (NEOTOMA MACROTIS AND N. FUSCIPES) FROM CALIFORNIA

Five microsatellite loci were used to develop multilocus genotypes for Neotoma macrotis (n = 128) and N. fuscipes (n = 29). Several statistical analyses were used to estimate genetic structure, levels of genetic variability, and degree of relatedness within groups of these 2 species. Samples of N. macrotis represented 2 groups and 4 population clusters throughout southern California. Samples of N. fuscipes represented 2 regions in northern and southern California. Genetic structure was detected among samples of N. macrotis and N. fuscipes at a regional level. Both species displayed moderate to high genetic diversity in terms of mean expected heterozygosity (0.939 and 0.804 for N. macrotis and N. fuscipes, respectively) and mean polymorphic information content (0.930 and 0.761 for N. macrotis and N. fuscipes, respectively). Mean relatedness values within regions and populations of N. macrotis indicated 4th-order levels of relatedness within groups (e.g., distant-cousin relationships). Mean relatedness values within regions of N. fuscipes indicated 2nd-order (e.g., half-sibling) relationships within the northern region and 3rd-order (e.g., cousin) relationships in the southern region. One locus in particular (Nma04) was determined to be diagnostic in distinguishing between these 2 species.

Pathology of Whitewater Arroyo viral infection in the white-throated woodrat (Neotoma albigula)

The white-throated woodrat is a principal host of Whitewater Arroyo (WWA) virus, an arenavirus, in the western United States. The purpose of the present study was to investigate the pathology of WWA infection in this species. Twenty-one animals (eight newborn, seven juvenile, and six adult) were inoculated with WWA virus and killed at varying intervals after inoculation. The most striking histological findings were lymphocytic meningitis and perivascular lymphocytic cuffing in the brains of the animals killed on day 85, 113 or 121. Arenaviral antigen was detected immunohistochemically in the brain of each affected animal, suggesting that the inflammatory lesions in the brain were caused by WWA virus. Comparisons of the results of tests for infectious virus and antigen in brain and other solid tissues indicated that immunohistochemistry may be a useful method for detection of WWA viral antigen in post-mortem specimens.

Bear Canyon virus: an arenavirus naturally associated with the California mouse (Peromyscus californicus)

Thirty-four rodents captured in southern California were studied to increase our knowledge of the arenaviruses indigenous to the western United States. An infectious arenavirus was isolated from 5 of 27 California mice but none of the 7 other rodents. Analyses of viral nucleocapsid protein gene sequence data indicated that the isolates from the California mice are strains of a novel Tacaribe serocomplex virus (proposed name "Bear Canyon") that is phylogenetically most closely related to Whitewater Arroyo and Tamiami viruses, the only other Tacaribe serocomplex viruses known to occur in North America. The discovery of Bear Canyon virus is the first unequivocal evidence that the virus family Arenaviridae is naturally associated with the rodent genus Peromyscus and that a Tacaribe serocomplex virus occurs in California.