Further Assessment of Monkeypox Virus Infection in Gambian Pouched Rats (Cricetomys gambianus) Using In Vivo Bioluminescent Imaging

Monkeypox is a zoonosis clinically similar to smallpox in humans. Recent evidence has shown a potential risk of increased incidence in central Africa. Despite attempts to isolate the virus from wild rodents and other small mammals, no reservoir host has been identified. In 2003, Monkeypox virus (MPXV) was accidentally introduced into the U.S. via the pet trade and was associated with the Gambian pouched rat (Cricetomys gambianus). Therefore, we investigated the potential reservoir competence of the Gambian pouched rat for MPXV by utilizing a combination of in vivo and in vitro methods. We inoculated three animals by the intradermal route and three animals by the intranasal route, with one mock-infected control for each route. Bioluminescent imaging (BLI) was used to track replicating virus in infected animals and virological assays (e.g. real time PCR, cell culture) were used to determine viral load in blood, urine, ocular, nasal, oral, and rectal swabs. Intradermal inoculation resulted in clinical signs of monkeypox infection in two of three animals. One severely ill animal was euthanized and the other affected animal recovered. In contrast, intranasal inoculation resulted in subclinical infection in all three animals. All animals, regardless of apparent or inapparent infection, shed virus in oral and nasal secretions. Additionally, BLI identified viral replication in the skin without grossly visible lesions. These results suggest that Gambian pouched rats may play an important role in transmission of the virus to humans, as they are hunted for consumption and it is possible for MPXV-infected pouched rats to shed infectious virus without displaying overt clinical signs.     

Shedding of Infectious Borna Disease Virus-1 in Living Bicolored White-Toothed Shrews

Background

Many RNA viruses arise from animal reservoirs, namely bats, rodents and insectivores but mechanisms of virus maintenance and transmission still need to be addressed. The bicolored white-toothed shrew (Crocidura leucodon) has recently been identified as reservoir of the neurotropic Borna disease virus 1 (BoDV-1).

Principal Findings

Six out of eleven wild living bicoloured white-toothed shrews were trapped and revealed to be naturally infected with BoDV-1. All shrews were monitored in captivity in a long-term study over a time period up to 600 days that differed between the individual shrews. Interestingly, all six animals showed an asymptomatic course of infection despite virus shedding via various routes indicating a highly adapted host-pathogen interaction. Infectious virus and viral RNA were demonstrated in saliva, urine, skin swabs, lacrimal fluid and faeces, both during the first 8 weeks of the investigation period and for long time shedding after more than 250 days in captivity.

Conclusions

The various ways of shedding ensure successful virus maintenance in the reservoir population but also transmission to accidental hosts such as horses and sheep. Naturally BoDV-1-infected living shrews serve as excellent tool to unravel host and pathogen factors responsible for persistent viral co-existence in reservoir species while maintaining their physiological integrity despite high viral load in many organ systems.     

Comparison of Mucosal,Subcutaneous and Intraperitoneal Routes of Rat Leptospira Infection

Leptospirosis is a zoonosis found worldwide that is caused by a spirochete. The main reservoirs of Leptospira, which presents an asymptomatic infection, are wild rodents, including the brown rat (Rattus norvegicus). Experimental studies of the mechanisms of its renal colonization in rats have previously used an intraperitoneal inoculation route. However, knowledge of rat-rat transmission requires the use of a natural route of inoculation, such as a mucosal or subcutaneous route. We investigated for the first time the effects of subcutaneous and mucosal inoculation routes compared to the reference intraperitoneal route during Leptospira infection in adult rats. Infection characteristics were studied using Leptospira renal isolation, serology, and molecular and histological analyses. Leptospira infection was asymptomatic using each inoculation route, and caused similar antibody production regardless of renal colonization. The observed renal colonization rates were 8 out of 8 rats, 5 out of 8 rats and 1 out of 8 rats for the intraperitoneal, mucosal and subcutaneous inoculation routes, respectively. Thus, among the natural infection routes studied, mucosal inoculation was more efficient for renal colonization associated with urinary excretion than the subcutaneous route and induced a slower-progressing infection than the intraperitoneal route. These results can facilitate understanding of the infection modalities in rats, unlike the epidemiological studies conducted in wild rats. Future studies of other natural inoculation routes in rat models will increase our knowledge of rat-rat disease transmission and allow the investigation of infection kinetics.     

Virological and Serological Findings in Rousettus aegyptiacus Experimentally Inoculated with Vero Cells-Adapted Hogan Strain of Marburg Virus

The Egyptian fruit bat, Rousettus aegyptiacus, is currently regarded as a potential reservoir host for Marburg virus (MARV). However, the modes of transmission, the level of viral replication, tissue tropism and viral shedding pattern remains to be described. Captive-bred R. aegyptiacus, including adult males, females and pups were exposed to MARV by different inoculation routes. Blood, tissues, feces and urine from 9 bats inoculated by combination of nasal and oral routes were all negative for the virus and ELISA IgG antibody could not be demonstrated for up to 21 days post inoculation (p.i.). In 21 bats inoculated by a combination of intraperitoneal/subcutaneous route, viremia and the presence of MARV in different tissues was detected on days 2–9 p.i., and IgG antibody on days 9–21 p.i. In 3 bats inoculated subcutaneously, viremia was detected on days 5 and 8 (termination of experiment), with virus isolation from different organs. MARV could not be detected in urine, feces or oral swabs in any of the 3 experimental groups. However, it was detected in tissues which might contribute to horizontal or vertical transmission, e.g. lung, intestines, kidney, bladder, salivary glands, and female reproductive tract. Viremia lasting at least 5 days could also facilitate MARV mechanical transmission by blood sucking arthropods and infections of susceptible vertebrate hosts by direct contact with infected blood. All bats were clinically normal and no gross pathology was identified on post mortem examination. This work confirms the susceptibility of R. aegyptiacus to infection with MARV irrespective of sex and age and contributes to establishing a bat-filovirus experimental model. Further studies are required to uncover the mode of MARV transmission, and to investigate the putative role of R. aegyptiacus as a reservoir host.     

Patterns in size and shedding of Fasciola hepatica eggs by naturally and experimentally infected murid rodents

Using samples collected on the island of Corsica, a comparative study was done of the morphometry of Fasciola hepatica eggs shed by cattle and by naturally and experimentally infected murid rodents (wild Mus musculus and Rattus rattus and Rattus norvegicus Wistar laboratory strain). Eggs shed by murids are smaller in size than those shed by naturally infected cattle. A second study analyzed the number of F. hepatica eggs shed in murid feces at different time intervals, i.e., months, days, and 6-hr periods, by the Kato-Katz technique. Both experimentally and naturally infected black rats (R. rattus) were used, and Wistar rats were experimentally infected and included for comparison. The present studies prove that black rats R. rattus are able to shed eggs independently from the liver fluke isolate and that egg shedding occurs throughout the life of this host species, uninterrupted during all the months analyzed in a 2-yr period. Moreover, the results suggest that this shedding is continuous, with eggs appearing in the feces daily. The results on egg shedding by wild black rats R. rattus reach their maximum shedding in spring and autumn and a maximum during twilight hr. These chronobiological patterns appear to favor parasite transmission, both seasonally and daily.     

Dependence between penetration route and course of infection with Coxiella burnetii in mice]

This study was aimed at investigation of course of Coxiella burnetii infection in mice infected by these bacteria by different routes. The animals infected intranasally, perorally, intraperitoneally and intravaginally by suspension of C. burnetii cells. Mice were also infected via peritoneal and intravaginal route with spermatozoa derived from infected males. In all animals at the same time specific antibodies against phase I and phase II antigens of C. burnetii belonging to IgG and IgM classes of similar titers appeared and this was detected by dot-blot immunoenzymatic test. Independently of route of infection C. burnetii were present in the liver, spleen, testicles, prostate and spermatozoa of tested animals. The bacteria were detected in these organs for 18 days of infection, in the blood for 7 days only, whereas in urine they appeared as late as 14 days after infection. The course of infection with C. burnetii in mice in thus similar regardless of site of bacterial penetration. Infection with C. burnetii may be also transmitted by a sexual route from male to female animals. Infection of female mice occurs both after intravaginal application of live suspension of C. burnetii or spermatozoa derived from infected males.     

Vaccinia virus Transmission through Experimentally Contaminated Milk Using a Murine Model

Bovine vaccinia (BV) is a zoonosis caused by Vaccinia virus (VACV), which affects dairy cattle and humans. Previous studies have detected the presence of viable virus particles in bovine milk samples naturally and experimentally contaminated with VACV. However, it is not known whether milk contaminated with VACV could be a route of viral transmission. However, anti-Orthopoxvirus antibodies were detected in humans from BV endemic areas, whom had no contact with affected cows, which suggest that other VACV transmission routes are possible, such as consumption of contaminated milk and dairy products. Therefore, it is important to study the possibility of VACV transmission by contaminated milk. This study aimed to examine VACV transmission, pathogenesis and shedding in mice orally inoculated with experimentally contaminated milk. Thirty mice were orally inoculated with milk containing 10⁷ PFU/ml of VACV, and ten mice were orally inoculated with uncontaminated milk. Clinical examinations were performed for 30 consecutive days, and fecal samples and oral swabs (OSs) were collected every other day. Mice were euthanized on predetermined days, and tissue and blood samples were collected. Nested-PCR, plaque reduction neutralization test (PRNT), viral isolation, histopathology, and immunohistochemistry (IHC) methods were performed on the collected samples. No clinical changes were observed in the animals. Viral DNA was detected in feces, blood, OSs and tissues, at least in one of the times tested. The lungs displayed moderate to severe interstitial lymphohistiocytic infiltrates, and only the heart, tonsils, tongue, and stomach did not show immunostaining at the IHC analysis. Neutralizing antibodies were detected at the 20^th and 30^th days post infection in 50% of infected mice. The results revealed that VACV contaminated milk could be a route of viral transmission in mice experimentally infected, showing systemic distribution and shedding through feces and oral mucosa, albeit without exhibiting any clinical signs.     

Indirect Transmission of Influenza A Virus between Pig Populations under Two Different Biosecurity Settings

Respiratory disease due to influenza virus is common in both human and swine populations around the world with multiple transmission routes capable of transmitting influenza virus, including indirect routes. The objective of this study was to evaluate the role of fomites in influenza A virus (IAV) transmission between pig populations separated by two different biosecurity settings. Thirty-five pigs were divided into four experimental groups: 10 pigs (1 replicate) were assigned to the infected group (I), 10 pigs (2 replicates of 5 pigs) were assigned to the low biosecurity sentinel group (LB), 10 pigs (2 replicates of 5 pigs) were assigned to the medium biosecurity sentinel group (MB), and 5 pigs (1 replicate) were assigned to the negative control group (NC). Eight of 10 pigs in the infected group were inoculated with IAV and 36 hours following inoculation, personnel movement events took place in order to move potentially infectious clothing and personal protective equipment (PPE) to sentinel pig rooms. Following contact with the infected group, personnel moved to the MB group after designated hygiene measures while personnel moved directly to the LB group. Nasal swabs and blood samples were collected from pigs to assess IAV infection status and fomites were sampled and tested via RRT-PCR. All experimentally inoculated pigs were infected with IAV and 11 of the 144 fomite samples collected following contact with infected pigs were low level positive for IAV genome. One replicate of each sentinel groups LB and MB became infected with IAV and all five pigs were infected over time. This study provides evidence that fomites can serve as an IAV transmission route from infected to sentinel pigs and highlights the need to focus on indirect routes as well as direct routes of transmission for IAV.     

新型H7N9病毒在同居小鼠中的传播途径

目的进一步了解新型H7N9流感病毒的致病性、传播能力以及通过何种途径进行传播。方法 H7N9病毒感染小鼠后与同居小鼠合笼,研究同居小鼠的临床变化指征、病毒复制情况、病毒在组织中的分布以及病理变化。以同居小鼠分泌物接种其他小鼠,观察同居小鼠通过何种途径传播病毒。结果 H7N9病毒可以在肺组织、肠组织和脑组织中复制,并可以在同居小鼠中传播。H7N9病毒感染小鼠其咽、眼分泌物以及粪便均具有感染性,其中尤以咽拭子的传播风险最高。结论 H7N9病毒可以不通过适应就感染小鼠,并引起小鼠间传播。被感染小鼠分泌物具有感染性。     

Transmission study of Andes hantavirus infection in wild sigmodontine rodents

Our study was designed to contribute to an understanding of the timing and conditions under which transmission of Andes hantavirus in Oligoryzomys longicaudatus reservoir populations takes place. Mice were caged in test habitats consisting of steel drums containing holding cages, where seronegative rodents were exposed to wild seropositive individuals by freely sharing the same cage or being separated by a wire mesh. Tests were also performed for potential viral transmission to mice from excrement-tainted bedding in the cages. Andes virus transmitted efficiently; from 130 attempts with direct contact, 12.3% resulted in virus transmission. However, if we consider only those rodents that proved to be infectious, from 93 attempts we obtained 16 infected animals (17.2%). Twelve of them resulted from intraspecies O. longicaudatus encounters where male mice were differentially affected and 4 resulted from O. longicaudatus to Abrothrix olivaceus. Experiments using Abrothrix longipilis as receptors were not successful. Transmission was not observed between wire mesh-separated animals, and mice were not infected from excrement-tainted bedding. Bites seemed not to be a requisite for oral transmission. Genomic viral RNA was amplified in two out of three saliva samples from seropositive rodents, but it was not detected in urine samples obtained by vesicle puncture from two other infected rodents. Immunohistochemistry, using antibodies against Andes (AND) hantavirus proteins, revealed strong reactions in the lung and salivary glands, supporting the possibility of oral transmission. Our study suggests that AND hantavirus may be principally transmitted via saliva or saliva aerosols rather than via feces and urine.     

Nipah virus transmission in a hamster model

Based on epidemiological data, it is believed that human-to-human transmission plays an important role in Nipah virus outbreaks. No experimental data are currently available on the potential routes of human-to-human transmission of Nipah virus. In a first dose-finding experiment in Syrian hamsters, it was shown that Nipah virus was predominantly shed via the respiratory tract within nasal and oropharyngeal secretions. Although Nipah viral RNA was detected in urogenital and rectal swabs, no infectious virus was recovered from these samples, suggesting no viable virus was shed via these routes. In addition, hamsters inoculated with high doses shed significantly higher amounts of viable Nipah virus particles in comparison with hamsters infected with lower inoculum doses. Using the highest inoculum dose, three potential routes of Nipah virus transmission were investigated in the hamster model: transmission via fomites, transmission via direct contact and transmission via aerosols. It was demonstrated that Nipah virus is transmitted efficiently via direct contact and inefficiently via fomites, but not via aerosols. These findings are in line with epidemiological data which suggest that direct contact with nasal and oropharyngeal secretions of Nipah virus infected individuals resulted in greater risk of Nipah virus infection. The data provide new and much-needed insights into the modes and efficiency of Nipah virus transmission and have important public health implications with regards to the risk assessment and management of future Nipah virus outbreaks.     

Ecological characterization of murine gammaherpesvirus 68 and it’s epidemiological implications

Murine gammaherpesvirus 68 (MHV-68) is a natural pathogen of free-living murid rodents, isolated from a bank vole (Clethrionomys glareolus) in Slovakia. It belongs to the family Herpesviridae, the genus Rhadinovirus, the species Murid herpesvirus 4. Neutralizing serum MHV-68 antibodies were found in animals of other species living with infected rodents in the same biotope (fallow deer, wild boars, deer, sheep, foxes, and mouflons) as well as in humans (laboratory personnel working with MHV-68 or wild rodents, hunters, general population). In this study, the shedding of MHV-68 in the nature was investigated on the model of laboratory mice experimentally infected with the virus. The virus was first detected in breast milk and lactic glands at day 4, in urine and salivary glands at day 9, and in saliva and tear glands at day 14 p.i. Out of intranasal, peroral, intramuscular, intraperitoneal, and subcutaneous routes of infection the first two proved most effective.     

Experimental congenital toxoplasmosis in Wistar and Holtzman rats

Congenital toxoplasmosis was evaluated in Wistar and Holtzman rats using two strains of Toxoplasma gondii isolated in Brazil. Pregnant rats were inoculated by subcutaneous or intraperitoneal routes with 10(6) or 8 x 10(6) tachyzoites of N strain (virulent for mice) and by subcutaneous or oral routes with 10(2) or 1.2 x 10(3) cysts of P strain (avirulent for mice). The tissues of rat pups born from these rats were bioassayed for T. gondii infection. T. gondii was not observed in the pups born from rats inoculated with N strain. In the animals inoculated with P strain, congenital toxoplasmosis occurred in 22.8% (Wistar rats inoculated with 10(2) cysts by the subcutaneous route), 11.4% (Wistar rats inoculated with 10(2) cysts by the oral route), 21.2% (Wistar rats inoculated with 1.2 x 10(3) cysts by the oral route) and 2.9% of fetal infection (Holtzman rats inoculated with 10(2) cysts by the oral route). None of the pups born from chronically infected mother were infected with T. gondii.     

Detection of Coxiella burnetii DNA on small-ruminant farms during a Q fever outbreak in the Netherlands

During large Q fever outbreaks in the Netherlands between 2007 and 2010, dairy goat farms were implicated as the primary source of human Q fever. The transmission of Coxiella burnetii to humans is thought to occur primarily via aerosols, although available data on C. burnetii in aerosols and other environmental matrices are limited. During the outbreak of 2009, 19 dairy goat farms and one dairy sheep farm were selected nationwide to investigate the presence of C. burnetii DNA in vaginal swabs, manure, surface area swabs, milk unit filters, and aerosols. Four of these farms had a positive status during the Coxiella burnetii bulk milk monitoring program in 2009 and additionally reported abortion waves in 2008 or 2009. Eleven farms were reported as having positive bulk milk only, and five selected (control) farms had a bulk milk-negative status in 2009 and no reported Q fever history. Screening by quantitative PCR (qPCR) revealed that on farms with a history of abortions related to C. burnetii and, to a lesser extent, on farms positive by bulk milk monitoring, generally higher proportions of positive samples and higher levels of C. burnetii DNA within positive samples were observed than on the control farms. The relatively high levels of C. burnetii DNA in surface area swabs and aerosols sampled in stables of bulk milk-positive farms, including farms with a Q fever-related abortion history, support the hypothesis that these farms can pose a risk for the transmission of C. burnetii to humans.     

Real-Time PCR Investigation of Potential Vectors, Reservoirs, and Shedding Patterns of Feline Hemotropic Mycoplasmas

Three hemotropic mycoplasmas have been identified in pet cats: Mycoplasma haemofelis, “Candidatus Mycoplasma haemominutum,” and “Candidatus Mycoplasma turicensis.” The way in which these agents are transmitted is largely unknown. Thus, this study aimed to investigate fleas, ticks, and rodents as well as saliva and feces from infected cats for the presence of hemotropic mycoplasmas, to gain insight into potential transmission routes for these agents. DNA was extracted from arthropods and from rodent blood or tissue samples from Switzerland and from salivary and fecal swabs from two experimentally infected and six naturally infected cats. All samples were analyzed with real-time PCR, and some positive samples were confirmed by sequencing. Feline hemotropic mycoplasmas were detected in cat fleas and in a few Ixodes sp. and Rhipicephalus sp. ticks collected from animals but not in ticks collected from vegetation or from rodent samples, although the latter were frequently Mycoplasma coccoides PCR positive. When shedding patterns of feline hemotropic mycoplasmas were investigated, “Ca. Mycoplasma turicensis” DNA was detected in saliva and feces at the early but not at the late phase of infection. M. haemofelis and “Ca. Mycoplasma haemominutum” DNA was not amplified from saliva and feces of naturally infected cats, despite high hemotropic mycoplasma blood loads. Our results suggest that besides an ostensibly indirect transmission by fleas, direct transmission through saliva and feces at the early phase of infection could play a role in the epizootiology of feline hemotropic mycoplasmas. Neither the investigated tick nor the rodent population seems to represent a major reservoir for feline hemotropic mycoplasmas in Switzerland.     

Monkeypox disease transmission in an experimental setting: prairie dog animal model

Monkeypox virus (MPXV) is considered the most significant human public health threat in the genus Orthopoxvirus since the eradication of variola virus (the causative agent of smallpox). MPXV is a zoonotic agent endemic to forested areas of Central and Western Africa. In 2003, MPXV caused an outbreak in the United States due to the importation of infected African rodents, and subsequent sequential infection of North American prairie dogs (Cynomys ludovicianus) and humans. In previous studies, the prairie dog MPXV model has successfully shown to be very useful for understanding MPXV since the model emulates key characteristics of human monkeypox disease. In humans, percutaneous exposure to animals has been documented but the primary method of human-to-human MPXV transmission is postulated to be by respiratory route. Only a few animal model studies of MPXV transmission have been reported. Herein, we show that MPXV infected prairie dogs are able to transmit the virus to naive animals through multiple transmission routes. All secondarily exposed animals were infected with MPXV during the course of the study. Notably, animals secondarily exposed appeared to manifest more severe disease; however, the disease course was very similar to those of experimentally challenged animals including inappetence leading to weight loss, development of lesions, production of orthopoxvirus antibodies and shedding of similar levels or in some instances higher levels of MPXV from the oral cavity. Disease was transmitted via exposure to contaminated bedding, co-housing, or respiratory secretions/nasal mucous (we could not definitively say that transmission occurred via respiratory route exclusively). Future use of the model will allow us to evaluate infection control measures, vaccines and antiviral strategies to decrease disease transmission.     

Comparison of virulence between two strains of Rattus serotype hemorrhagic fever with renal syndrome (HFRS) virus in newborn rats

Two strains of hemorrhagic fever with renal syndrome (HFRS) virus from Rattus, SR-11 and KI-262, showed virtually identical antigenicity but differed from prototype strain Hantaan 76-118 (Apodemus origin) in a neutralization test. Wistar newborn rats inoculated intraperitoneally (i.p.) with SR-11, which was isolated from a laboratory rat associated with an outbreak of HFRS, developed clinical signs such as ataxia and limb paralysis and died at about 18 days after inoculation. The LD50 of SR-11 in 1-day-old rats was 10(1.2) focus-forming units (FFU). In contrast, the animals inoculated i.p. or intracerebrally with 10(4) FFU of KI-262, which was from a wild rat in a dumping-ground area--an enzootic focus where no human cases have been recorded--did not show any significant clinical signs. The susceptibility of rats to SR-11 fatal infection was age-dependent. Virus titers in brains, lungs, kidneys, and livers of the rats inoculated with SR-11 were significantly higher than those in the same organs of the animals infected with KI-262. Necrosis of neurons in the brain tissue occurred in the rats infected with SR-11, while it was mild in the animals infected with KI-262.     

Real-time PCR investigation of potential vectors, reservoirs, and shedding patterns of feline hemotropic mycoplasmas

Three hemotropic mycoplasmas have been identified in pet cats: Mycoplasma haemofelis, "Candidatus Mycoplasma haemominutum," and "Candidatus Mycoplasma turicensis." The way in which these agents are transmitted is largely unknown. Thus, this study aimed to investigate fleas, ticks, and rodents as well as saliva and feces from infected cats for the presence of hemotropic mycoplasmas, to gain insight into potential transmission routes for these agents. DNA was extracted from arthropods and from rodent blood or tissue samples from Switzerland and from salivary and fecal swabs from two experimentally infected and six naturally infected cats. All samples were analyzed with real-time PCR, and some positive samples were confirmed by sequencing. Feline hemotropic mycoplasmas were detected in cat fleas and in a few Ixodes sp. and Rhipicephalus sp. ticks collected from animals but not in ticks collected from vegetation or from rodent samples, although the latter were frequently Mycoplasma coccoides PCR positive. When shedding patterns of feline hemotropic mycoplasmas were investigated, "Ca. Mycoplasma turicensis" DNA was detected in saliva and feces at the early but not at the late phase of infection. M. haemofelis and "Ca. Mycoplasma haemominutum" DNA was not amplified from saliva and feces of naturally infected cats, despite high hemotropic mycoplasma blood loads. Our results suggest that besides an ostensibly indirect transmission by fleas, direct transmission through saliva and feces at the early phase of infection could play a role in the epizootiology of feline hemotropic mycoplasmas. Neither the investigated tick nor the rodent population seems to represent a major reservoir for feline hemotropic mycoplasmas in Switzerland.     

Study of hantavirus infection in captive breed colonies of wild rodents

Wild sigmondontine rodents are known to be the reservoir of several serotypes of New World hantaviruses. The mechanism of viral transmission is by aerosol inhalation of the excreta from infected rodents. Considering that the captive breed colonies of various wild mammals may present a potential risk for hantaviral transmission, we examined 85 specimens of Thrichomys spp. (Echimyidae) and 17 speciemens of Nectomys squamipes (Sigmodontinae) from our colony for the presence of hantavirus infections. Blood samples were assayed for the presence of antibodies to Andes nucleocapsid antigen using enzyme-linked immunosorbent assay (ELISA). Additionally, serum samples from workers previously exposed to wild rodents, in the laboratories where the study was conducted, were also tested by ELISA to investigate prevalence of anti-hantavirus IgG antibodies. All blood samples were negative for hantavirus antibodies. Although these results suggest that those rodent's colonies are hantavirus free, the work emphasizes the need for hantavirus serological monitoring in wild colonized rodents and secure handling potentially infected rodents as important biosafety measures.     

Generation of defective virus after infection of newborn rats with reovirus.

When 2-day-old rats were inoculated subcutaneously with the R2 strain of reovirus type 3 or with a class B (352) or class C (447) temperature-sensitive (ts) mutant, 5 to 10% of the animals died from acute encephalitis within 12 days. Approximately half of the survivors recovered rapidly and grew normally, but the remainder became runted. Two phases of infection are distinguished in the animals: an acute phase during which infectious virus reaches a maximum titer in brain and other tissues by 10 days p.i. and thes runting of the rats and the slow disappearance of virus from their brains over a period of 2 months or so. Virus isolated from chronically infected brains generally retained the genetic character (ts or wild type) of the inoculated virus, but two exceptions to this are described. Defective virions lacking the L1 segment of the viral genome (L1 defectives) were generated in rat brains during the acute phase of infection. Defective virus was also generated during the chronic phase, but during this period defectives were found with multiple segments deleted from the genome in addition to L1 defectives. In another type of experiment defective virus exerted a marked protective effect when inoculated intracerebrally with R2 virus. In the absence of defectives all animals died, but in their presence 17 of 23 animals survived and 15 of 23 became runted and chronically infected. The formation and evolution of defective particles in the brains of these rats were similar to those found in rats chronically infected after subcutaneous inoculation of reovirus. We conclude that the formation of defective virus particles may play a role in the initiation and maintenance of chronic neutropic infections with reovirus.