Congenital malformations caused by Akabane virus in porcine fetuses in southern Japan

Akabane virus (AKAV) is known as a major teratogenic agent of ruminant fetuses. In this study, we investigated the relationship between porcine abnormal deliveries and AKAV by serology, pathology, and virology investigations using specimens from 16 stillborn fetuses delivered in southern Japan between 2013 and 2015. The major clinical manifestations in stillborn fetuses were hydranencephaly, arthrogryposis, spinal curvature, and both skeletal muscle and subcutaneous edema. Histologic examination of the specimens identified atrophy of skeletal muscle fibers accompanied by adipose replacement. Nonsuppurative encephalomyelitis and decreased neuronal density in the ventral horn of the spinal cord were shown in two separate fetuses, respectively. Neutralizing antibody titers to AKAV were detected in most of the tested fetuses (13/16). The AKAV sequences detected in the affected fetuses in 2013 and 2015 were highly identical and closely related to Japanese AKAV isolates which were isolated in 2013 and sorted into genogroup I of AKAV. Immunohistochemistry visualized AKAV antigens in the neuronal cells of the central nervous system of the fetuses. These findings indicate that AKAV was involved in the birth of abnormal piglets at the affected farm. The clinical manifestations and histopathological features in the stillborn fetuses were very similar to those in ruminant neonates affected by AKAV. To avoid misdiagnosis and to evaluate the precise impact of AKAV on pig reproduction, AKAV should be considered in differential diagnoses of reproductive failures in pigs.

Mast Cell-Derived Proteases Induce Endothelial Permeability and Vascular Damage in Severe Fever with Thrombocytopenia Syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging hemorrhagic fever acquired by tick bites. Whether mast cells (MCs), the body's first line of defense against pathogens, might influence immunity or pathogenesis during SFTS virus (SFTSV) infection remained unknown. Here, we found that SFTSV can cause MC infection and degranulation, resulting in the release of the vasoactive mediators, chymase, and tryptase, which can directly act on endothelial cells, break the tight junctions of endothelial cells and threaten the integrity of the microvascular barrier, leading to microvascular hyperpermeability in human microvascular endothelial cells. Local activation of MCs (degranulation) and MC-specific proteases-facilitated endothelial damage were observed in mouse models. When MC-specific proteases were injected subcutaneously into the back skin of mice, signs of capillary leakage were observed in a dose-dependent manner. MC-specific proteases, chymase, and tryptase were tested in the serum collected at the acute phase of SFTS patients, with the higher level significantly correlated with fatal outcomes. By performing receiver operator characteristic curve (ROC) analysis, chymase was determined as a biomarker with the area under the curve value of 0.830 (95% CI = 0.745 to 0.915) for predicting fatal outcomes in SFTS. Our findings highlight the importance of MCs in SFTSV-induced disease progression and outcome. An emerging role for MCs in the clinical prognosis and blocking MC activation as a potential drug target during SFTSV infection was proposed. IMPORTANCE We revealed a pathogenic role for MCs in response to SFTSV infection. The study also identifies potential biomarkers that could differentiate patients at risk of a fatal outcome for SFTS, as well as novel therapeutic targets for the clinical management of SFTS. These findings might shed light on an emerging role for MCs as a potential drug target during infection of other viral hemorrhagic fever diseases with similar host pathology as SFTS.

Hazara virus and Crimean-Congo Hemorrhagic Fever Virus show a different pattern of entry in fully-polarized Caco-2 cell line

Crimean-Congo Hemorrhagic Fever Virus (CCHFV) and Hazara virus (HAZV) belong to the same viral serotype and family. HAZV has lately been used as a model system and surrogate to CCHFV. However, virus-host cell interaction and level of pathogenicity for these viruses are not well investigated nor compared. In this study, we compared HAZV and CCHFV infection of human polarized epithelial cells to shed light on similarities and differences in virus-host cell interaction between these two viruses. We investigated the pattern of infection of CCHFV and HAZV in fully polarized human cells, the Caco-2 cell line. Polarization of Caco-2 cells lead to difference in expression level and pattern of proteins between the apical and the basolateral membranes. We found that CCHFV virus, in contrast to HAZV, is more likely infecting polarized cells basolaterally. In addition, we found that cytokines/pro-inflammatory factors or other viral factors secreted from CCHFV infected moDC cells enhance the entry of CCHFV contrary to HAZV. We have shown that CCHFV and HAZV early in infection use different strategies for entry. The data presented in this study also highlight the important role of cytokines in CCHFV-host cell interaction.

Crimean-Congo Hemorrhagic Fever virus (CCHFV) is a tick-borne pathogen responsible for a severe acute fever disease in humans, requiring biosafety level 4 laboratory for handling. This is the reason why the molecular pathogenesis of CCHFV remains largely unknown. Hazara virus (HAZV), member of the same serogroup but nor responsible for human disease, is commonly used as surrogate model to study CCHFV in biosafety level 2 laboratory. As an important viral model, it is important to better understand its range of applicability. Using polarized Caco-2 cells, we showed HAZV doesn’t have the same pattern of infection in fully polarized cells than CCHFV. These data were confirmed using compounds able to modulate cell junctions: compounds leaded to opposite effect on respective virus infection capacity. All data together suggest that CCHFV and HAZV receptors have different localization on polarized Caco-2 cells. Moreover, using supernatant of HAZV or CCHFV infected monocyte-derived dendritic cells, we demonstrated that only factors released from CCHFV-infected moDCs are able to enhance CCHFV infection. To our knowledge, this study is the first one showing differences in HAZV and CCHFV entry into polarized target cells and in CCHFV infection modulation by a paracrine effect linked to infected dendritic cells.

Severe fever with thrombocytopenia syndrome virus infection during pregnancy in C57/BL6 mice causes fetal damage

BACKGROUND

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a novel tick-borne phlebovirus, which is listed in the most dangerous pathogens by the World Health Organization, and has 12-30% fatality rates. SFTSV antibodies were reported in minks that experienced abortion or reproductive failure. The aim of this study was to determine whether SFTSV infection causes an adverse pregnancy outcome in the fetus using a pregnant mouse model.

METHODOLOGY/PRINCIPAL FINDINGS

We found SFTSV in the fetus after infection in pregnant mice, and some dams showed adverse pregnancy outcomes after infection with SFTSV including placental damage, fetal reabsorption, and fetal intrauterine growth restriction (IUGR). SFTSV had obvious tropism characteristics in the placenta, especially in the labyrinth. In early-gestation, pregnant mice infected with SFTSV had fetal IUGR and a high viral load in the fetus. The virus widely spread in infected fetuses, including the hindbrain, thymus, heart, spinal cord, and liver.

CONCLUSIONS

Our study demonstrated that SFTSV was vertically transmitted to the fetus through the placental barrier of immunocompetent mice, and resulted in adverse pregnancy outcomes.

Pathophysiology of severe fever with thrombocytopenia syndrome and development of specific antiviral therapy

Severe fever with thrombocytopenia syndrome (SFTS) caused by SFTS virus (SFTSV), a novel phlebovirus, was reported to be endemic to central and northeastern PR China and was also to be endemic to South Korea and western Japan. SFTS is an emerging viral infection, which should be categorized as a viral hemorrhagic fever disease as Crimean-Congo hemorrhagic fever (CCHF) is caused by CCHF virus. SFTS is a tick-borne viral infection. SFTSV is maintained between several species of ticks and wild and domestic animals in nature. Patients with SFTS show symptoms of fever, general fatigue, and gastrointestinal symptoms such as bloody diarrhea. The severely ill SFTS patients usually show gastrointestinal hemorrhage and deteriorated consciousness. The case fatality rate of SFTS ranges from 5 to 40%. Pathological studies on SFTS have revealed that the mechanisms behind the high case fatality rate are virus infection-related hemophagocytic syndrome associated with cytokine storm, coagulopathy due to disseminated intravascular coagulation causing bleeding tendency, and multi-organ failure. Favipiravir was reported to show efficacy in the prevention and treatment of SFTSV infections in an animal model. A clinical study to evaluate the efficacy of favipiravir in the treatment of SFTS patients has been initiated in Japan. SFTSV is circulating in nature in PR China, Korea, and Japan, indicating that we cannot escape from the risk being infected with SFTSV. The development of specific therapy and preventive measures is a pressing issue requiring resolution to reduce the morbidity and mortality of SFTS patients.

Congenital Malformations of Calves Infected with Shamonda Virus, Southern Japan

In 2015 and 2016, we observed 15 malformed calves that were exposed to intrauterine infection with Shamonda virus, a Simbu serogroup orthobunyavirus, in Japan. Characteristic manifestations were arthrogryposis and gross lesions in the central nervous system. Our results indicate that this arbovirus should be considered a teratogenic virus in ruminants.

Heartland virus infection in hamsters deficient in type I interferon signaling: Protracted disease course ameliorated by favipiravir

Heartland virus (HRTV) is an emerging tick-borne virus (Bunyaviridae, Phlebovirus) that has caused sporadic cases of human disease in several central and mid-eastern states of America. Animal models of HRTV disease are needed to gain insights into viral pathogenesis and advancing antiviral drug development. Presence of clinical disease following HRTV challenge in hamsters deficient in STAT2 function underscores the important role played by type I interferon-induced antiviral responses. However, the recovery of most of the infected animals suggests that other mechanisms to control infection and limit disease offer substantial protection. The most prominent disease sign with HRTV infection in STAT2 knockout hamsters was dramatic weight loss with clinical laboratory and histopathology demonstrating acute inflammation in the spleen, lymph node, liver and lung. Finally, we show that HRTV disease in hamsters can be prevented by the use of favipiravir, a promising broad-spectrum antiviral in clinical development for the treatment of influenza.

Novel Clinical and Pathologic Findings in a Heartland Virus-Associated Death

We describe an investigation into a Heartland virus (HRTV)-associated death in Tennessee with novel clinical and pathologic findings. HRTV can cause rapidly fatal, widely disseminated infection with multisystem organ failure in patients without substantial comorbidities. We identified viral antigen in multiple organ tissues where it was not detected previously.

A simple and practical score model for predicting the mortality of severe fever with thrombocytopenia syndrome patients

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging disease with a high fatality rate. The risk factors for death are not clearly identified, and there is no clinical score model to predict the prognosis. We retrospectively collected the clinical information of clinical symptoms and laboratory parameters of SFTS patients on admission. After analyzing the clinical characteristics of 179 SFTS patients, we found that an elevated level of neurologic symptoms, respiratory symptoms, viral load, and a lower level of monocyte percentage were the critical risk factors for mortality. We used the 4 variables to assemble a score formula named the SFTS index [SFTSI = 5 × Neurologic symptoms-level + 4 × Respiratory symptoms-level + 3 × LG10 Viral load - 2 × LN Monocyte% - 7]. The AURC of this model was 0.964, which was higher than the AURC 0.913 of the viral load especially among the patients with higher viral loads (0.936 vs 0.821). We identified that the neurologic symptoms, respiratory symptoms, viral load, and monocyte percentage were the critical risk factors for SFTS mortality. The clinical score model of SFTSI provides a practical method for clinicians to stratify patients with SFTS and to adopt prompt effective treatment strategies.

[ZOOPATHOGENIC ORTHOBUNIAVIRUSES (ORTHOBUNYAVIRUS, BUNYAVIRIDAE)]

This work deals with the systematics and taxonomy of orthobunyaviruses, little-studied dangerous and new iruses Akabane, Aino, Schmallenberg, Cache Valley diseases, Oropouche fever. The significance of the reassortment mechanism of their origin and diversification is discussed.

Akabane virus infection

Akabane virus is a Culicoides-borne orthobunyavirus that is teratogenic to the fetus of cattle and small ruminant species. Depending upon the stage of gestation atwhich infection occurs, and the length of gestation of the mammalian host, a range of congenital defects may be observed. The developing central nervous system is usually the most severely affected, with hydranencephaly and arthrogryposis most frequently observed. Less commonly, some strains of Akabane virus can cause encephalitis in the neonate or, rarely, adult cattle. Akabane viruses are known to be widespread in temperate and tropical regions of Australia, Southeast Asia, the Middle East and some African countries. Disease is infrequently observed in regions where this virus is endemic and the presence of the virus remains unrecognised in the absence of serological surveillance. In some Asian countries, vaccines are used to minimise the occurrence of disease.

[Infection of the Severe Fever with Thrombocytopenia Syndrome Virus in Balb/C Mice and Hamsters]

The severe fever with thrombocytopenia syndrome virus (SFTSV) is the causative pathogen of an emerging infectious disease severe fever with thrombocytopenia syndrome and a new member in the genus Phlebovirus of family Bunyaviridae. Immune responses and pathological lesions in SFTSV-infected Balb/C mice and hamsters were evaluated by inoculation of SFTSV at 105 TCID50 or 103 TCID50 per animal through four different routes of infection, including intravenous, intramuscular, intraperitoneal, and intracerebral injections. The vehicle control groups were also included. At different time points after the inoculation blood and plasma samples were collected. Blood cell counts, blood viral RNA copies, and plasma antibodies were detected by automatic blood cell counters, real-time PCR, and luminex assays, respectively. At two weeks post inoculation, the animals were sacrificed. Tissues including heart, liver, spleen, lung, kidney, intestine, muscle, and brain, were collected for pathological analyses. Results showed that the SFTSV could infect Balb/C mice and hamsters with SFTSV-specific immunoglobulin (Ig) M and IgG antibodies detected in plasma samples on day 7 post inoculation. The SFTSV-specific IgM levels peaked on day 7 post inoculation and then decreased, whereas the SFTSV-specific IgG levels started to increase on day 7 and then peaked on day 14 post inoculation. Pathological analyses indicated significant pathological lesions in liver and kidney tissues. In conclusion, SFTSV could can infect different strains of rodent animals and cause similar immunological and pathological responses.

Spread of Oropouche virus into the central nervous system in mouse

Oropouche virus (OROV) is an important cause of arboviral illness in Brazil and other Latin American countries, with most cases clinically manifested as acute febrile illness referred to as Oropouche fever, including myalgia, headache, arthralgia and malaise. However, OROV can also affect the central nervous system (CNS) with clinical neurological implications. Little is known regarding OROV pathogenesis, especially how OROV gains access to the CNS. In the present study, neonatal BALB/c mice were inoculated with OROV by the subcutaneous route and the progression of OROV spread into the CNS was evaluated. Immunohistochemistry revealed that OROV infection advances from posterior parts of the brain, including the periaqueductal gray, toward the forebrain. In the early phases of the infection OROV gains access to neural routes, reaching the spinal cord and ascending to the brain through brainstem regions, with little inflammation. Later, as infection progresses, OROV crosses the blood-brain barrier, resulting in more intense spread into the brain parenchyma, with more severe manifestations of encephalitis.

[Pathologic-anatomical changes in newborn goats caused by an intrauterine Schmallenberg virus infection]

A complex of various malformations in newborns was observed to an increased extent in sheep farms in the 2011/2012 lambing season. An intrauterine Schmallenberg virus (SBV) infection was identified as the cause of these malformations. To date, a detailed pathological description of the deformity complex has only been given for bovine and ovine newborns.The aim of this study was therefore to provide a description of pathologic-anatomical congenital malformations in goat kids caused by intrauterine SBV infection. To this end, pathologic-anatomical and molecular biological investigations by PCR were carried out on 37 goat kids and 457 lambs from 238 sheep and goat farms in order to carry out an interspecies comparison. Of the 37 goat kids dissected, it was possible to identify a SBV infection in twelve animals (32.4%) by RT-PCR. In nine animals (24.3%) displaying pathological-anatomical malformations SBV could not be detected by PCR. The following malformations were observed: athrogryposis, deformation of spinal column, torticollis, asymmetry of the skull, brachygnathia inferior, cerebellar hypoplasia, cerebellar aplasia and internal hydrocephalus. Arthogryposis was the most common malformation, both in animals with positive PCR results and those with negative PCR results. This study documents congenital malformations caused by an intrauterine SBV infection for the first time on a large number of newborn goats.

Immunophenotyping of inflammatory cells associated with Schmallenberg virus infection of the central nervous system of ruminants

Schmallenberg virus (SBV) is a recently discovered Bunyavirus associated mainly with abortions, stillbirths and malformations of the skeletal and central nervous system (CNS) in newborn ruminants. In this study, a detailed immunophenotyping of the inflammatory cells of the CNS of affected animals was carried out in order to increase our understanding of SBV pathogenesis. A total of 82 SBV-polymerase chain reaction (PCR) positive neonatal ruminants (46 sheep lambs, 34 calves and 2 goat kids) were investigated for the presence of inflammation in the brain and spinal cord. The study focused on 15 out of 82 animals (18.3%) showing inflammation in the CNS. All 15 neonates displayed lymphohistiocytic meningoencephalomyelitis affecting most frequently the mesencephalon and the parietal and temporal lobes. The majority of infiltrating cells were CD3-positive T cells, followed by CD79α-positive B cells and CD68-positive microglia/macrophages. Malformations like por- and hydranencephaly, frequently found in the temporal lobe, showed associated demyelination and axonal loss. SBV antigen was detected in 37 out of 82 (45.1%) neonatal brains by immunohistochemistry. In particular, SBV antigen was found in 93.3% (14 out of 15 ruminants) and 32.8% (22 out of 67 ruminants) of animals with and without encephalitis, respectively. Highest amounts of virus-protein expression levels were found in the temporal lobe. Our findings suggest that: (i) different brain regions display differential susceptibility to SBV infection; (ii) inflammatory cells in the CNS are found only in a minority of virus infected animals; (iii) malformations occur in association with and without inflammation in the CNS; and (iv) viral antigen is strongly associated with the presence of inflammation in naturally infected animals. Further studies are required to explore the cell tropism and pathogenesis of SBV infection in ruminants.

Schmallenberg virus pathogenesis, tropism and interaction with the innate immune system of the host

Schmallenberg virus (SBV) is an emerging orthobunyavirus of ruminants associated with outbreaks of congenital malformations in aborted and stillborn animals. Since its discovery in November 2011, SBV has spread very rapidly to many European countries. Here, we developed molecular and serological tools, and an experimental in vivo model as a platform to study SBV pathogenesis, tropism and virus-host cell interactions. Using a synthetic biology approach, we developed a reverse genetics system for the rapid rescue and genetic manipulation of SBV. We showed that SBV has a wide tropism in cell culture and “synthetic” SBV replicates in vitro as efficiently as wild type virus. We developed an experimental mouse model to study SBV infection and showed that this virus replicates abundantly in neurons where it causes cerebral malacia and vacuolation of the cerebral cortex. These virus-induced acute lesions are useful in understanding the progression from vacuolation to porencephaly and extensive tissue destruction, often observed in aborted lambs and calves in naturally occurring Schmallenberg cases. Indeed, we detected high levels of SBV antigens in the neurons of the gray matter of brain and spinal cord of naturally affected lambs and calves, suggesting that muscular hypoplasia observed in SBV-infected lambs is mostly secondary to central nervous system damage. Finally, we investigated the molecular determinants of SBV virulence. Interestingly, we found a biological SBV clone that after passage in cell culture displays increased virulence in mice. We also found that a SBV deletion mutant of the non-structural NSs protein (SBVΔNSs) is less virulent in mice than wild type SBV. Attenuation of SBV virulence depends on the inability of SBVΔNSs to block IFN synthesis in virus infected cells. In conclusion, this work provides a useful experimental framework to study the biology and pathogenesis of SBV.

Schmallenberg virus (SBV) was discovered in Germany (near the town of Schmallenberg) in November 2011 and since then has been found to be the cause of malformations and stillbirths in ruminants. SBV has spread very rapidly to many European countries including the Netherlands, Belgium, France and the United Kingdom. Very little is known about the biological properties of this virus and there is no vaccine available. In this study (i) we developed an approach (called reverse genetics) that allows the recovery of “synthetic” SBV under laboratory conditions; (ii) we developed a mouse model of infection for SBV; (iii) we showed that SBV replicates in neurons of experimentally infected mice similar to naturally infected lambs and calves; (iv) we developed viral mutants that are not as pathogenic as the original virus due to the inability to counteract the host cell defenses; and v) we identified mutations that are associated with increased virulence. This work provides the experimental tools to understand how this newly emerged virus causes disease in ruminants. In addition, it will now be possible to manipulate the SBV genome in order to develop highly effective vaccines.

Toscana meningoencephalitis: a comparison to other viral central nervous system infections

BACKGROUND

Toscana virus (TOSV) is an emerging pathogen causing central nervous system (CNS) infection in Mediterranean countries, mostly during summer season.

OBJECTIVES

To compare the clinical and laboratory characteristics of Toscana CNS infections to the most common viral pathogens seen in the United States.

STUDY DESIGN

We performed a case series of patients with 41 TOSV infection and compared the clinical characteristics, laboratory findings, imaging results and clinical outcomes to the most commonly recognized viral causes of meningoencephalitis in the US [enterovirus (n=60), herpes simplex virus (n=48), and West Nile virus (n=30)] from our multi-center study of patients with aseptic meningoencephalitis syndromes in the Greater Houston area.

RESULTS

TOSV infection occurs in different age groups compared to enterovirus, HSV, and WNV. All infections most frequently occur during summer-fall except HSV which distributes throughout the year. All patients with TOSV had history of travel to endemic areas. There are differences in clinical presentation and CSF findings comparing TOSV and enterovirus, HSV, and WNV infection. There are no significant differences in outcomes of each infection except WNV meningoencephalitis which had a poorer outcome compared to TOSV infection.

CONCLUSIONS

TOSV is an emerging pathogen that should be considered in the differential diagnosis of patients with CNS infections and a recent travel history to endemic areas.

Organ distribution of Schmallenberg virus RNA in malformed newborns

A novel orthobunyavirus was first detected in German dairy cows in autumn 2011 and was subsequently found in the brains of malformed lambs, kids and calves in the Netherlands, Germany, Belgium, France, Italy, Great Britain, Luxembourg and Spain. For rapid detection of this novel virus, named Schmallenberg virus, a real time quantitative reverse transcription PCR (RT-qPCR) was developed at the Friedrich-Loeffler-Institut and provided to the federal veterinary state laboratories in Germany. For diagnostic purposes, the organ distribution of this new virus was analyzed in several organs and body fluids of 15 lambs and two calves showing typical malformations. Spleen, cerebrum, meconium, spinal cord, rib cartilage, umbilical cord, placental fluid out of the stomach as well as external placental fluid scraped from the coat of the foetuses were collected during necropsy. All animals were tested RT-qPCR positive in the external placental fluid, and all but one were also RT-qPCR positive in the cerebrum, the umbilical and the spinal cord. Our results suggest that both the external placental fluid and the umbilical cord could be suitable sample materials for the confirmation of an infection with Schmallenberg virus in malformed newborns, at least in lambs. This is of special interest since those samples can be collected very easily on the farm without the need of a necropsy.

Oropouche virus experimental infection in the golden hamster (Mesocrisetus auratus)

Oropouche virus (OROV), of the family Bunyaviridae, is the second most frequent arbovirus causing febrile disease in Brazil. In spite of this, little is known about pathogenesis of OROV infection. This report describes an experimental model of OROV in golden hamster (Mesocricetus auratus). Following subcutaneous inoculation of OROV, over 50% of the animals developed disease characterized by lethargy, ruffled fur, shivering, paralysis, and approximately one third died. Animals were sacrificed on days 1, 3, 5, 8 and 11 post-inoculation to collect tissue samples from brain, heart, liver, lung, spleen, muscle and blood for virus titration, histology and OROV immunohistochemistry. OROV was detected in high titers in blood, liver and brain, but not in the other organs. Histopathology revealed meningoencephalitis and hepatitis, with abundant OROV antigen detected in liver and brain. Diffuse galectin-3 immunostaining in brain and liver supports microglial and Kupfer cells activation. This is the first description of an experimental model for OROV infection and should be helpful to study pathogenesis and possibly to test antiviral interventions such as drugs and vaccine candidates.

Encephalomyelitis of cattle caused by Akabane virus in southern Japan in 2006

Six calves, aged between 55 days and 15 months, were presented between September and November 2006 with neurological signs including limb weakness and circling. Microscopical examination of the brain and spinal cord revealed the presence of non-suppurative encephalitis in all animals. Perivascular cuffing of lymphocytes and macrophages and diffuse gliosis was prominent in the cerebrum and degeneration and/or necrosis of neurons with vacuolation of the neuropil was present in the brainstem. Neuronal necrosis and neuronophagia were noted in the ventral horn of the spinal cord. The distribution of the lesions was closely related to the clinical signs displayed by each calf. Five calves presenting with astasia with low head carriage or torticollis had lesions throughout the central nervous system (CNS). The oldest calf displayed astasia caused by weakness of the "hindlimb" one word and had lesions largely restricted to the caudal spinal cord. Akabane virus (AKAV) antigens were detected immunohistochemically within neurons and axons in lesional tissue. Virus was not isolated from CNS tissue but the AKAV S gene was detected in this tissue from five calves by reverse transcriptase polymerase chain reaction (RT-PCR). It is suggested that AKAV infection is likely to have occurred during the early life period in the calves of this study.

Comparison of Akabane virus isolated from sentinel cattle in Japan

Adult cows, ewes, and goats infected with Akabane virus (AKAV) of the genus Orthobunyavirus of the family Bunyaviridae do not present any clinical signs; however, in utero infections may result in abortion, premature birth, stillbirth, and congenital deformities such as arthrogryposis-hydranencephaly syndrome in cattle, sheep, and goats. In contrast, the Iriki strain, a variant of AKAV isolated from a calf with nervous signs and encephalitis, causes encephalitis in experimentally inoculated calves. Two AKAV field isolates, named Okayama2001 and Okayama2004, were isolated from blood specimens of sentinel calves and characterized by cross-neutralization testing, genetic analyses of the S and M RNA segments, and experimental intraperitoneal infection in mice. Although a genetic relationship was established between Okayama2001 and the Iriki strain, their antigenic characteristics differ. Okayama2001 was avirulent in mice, as was the OBE-1 strain, which was isolated from an aborted bovine fetus. In contrast, Okayama2004 was antigenically and genetically related to the OBE-1 strain, but was virulent in mice, similar to the Iriki strain. These results indicate that the isolates mutated antigenically or pathogenically and suggest that AKAV mutates frequently in the field. Although attenuated and inactivated vaccines have been developed for disease prevention, an outbreak may occur due to variant viruses arising from mutation.

Apoptosis of hepatocytes caused by Punta Toro virus (Bunyaviridae: Phlebovirus) and its implication for Phlebovirus pathogenesis

Experimental infection of hamsters with Punta Toro virus (PTV) produces a disease with clinical and pathological similarities to the severe human hemorrhagic fever caused by Rift Valley fever virus (RVFV), thus providing an animal model for RVFV pathogenesis. In this model, hepatocytic apoptosis is the main pathological component of liver injuries that are responsible for severe hemorrhagic manifestations. To further elucidate whether viral replication in hepatocytes directly causes apoptosis, we studied the morphological and biochemical changes of apoptosis in HepG2 cells at different time points after PTV infection. Cellular viability began to decrease 12 hours after infection compared with controls. Caspases 3/7 were activated significantly at 48 and 72 hours after infection, and phosphatidylserine translocation and DNA fragmentation were also detected at 48 and 72 hours. Cell cycle analysis by flow cytometry showed that infected HepG2 cells were arrested at G(0)/G(1) phase. Furthermore, virus titer increased with apoptosis progression, suggesting that viral replication is necessary for the apoptotic process. These results indicate that PTV infection alone, without a secondary inflammatory cellular reaction, induces hepatocytic apoptosis and suggest that future therapeutics for RVFV hemorrhagic disease might target inhibition of cellular apoptotic pathways during the acute infection.

Development of a mouse model for the study of Toscana virus pathogenesis

Toscana virus (TOSV) has recently been recognized as an emerging virus transmitted by phlebotomus vectors, responsible for acute neurological diseases in Mediterranean countries. In our study, we demonstrated that adult Balb/c mice were susceptible to TOSV when infected intracerebrally (i.c.) or subcutaneously (s.c.) with a neuroadapted strain of the virus. We have shown that by performing serial passages of a wild type human isolate of TOSV in mouse brains, selection occurs for a highly virulent variant which replicates efficiently in the central nervous system (CNS) of i.c.-injected mice, causing acute encephalitis and death. Immunohistochemical analysis and TUNEL assay of post-mortem organs showed that TOSV replication was highly restricted to neurons in which it induced apoptotic death; however, virus antigen-positivity was also observed in the spleen and lymph nodes. In s.c.-injected mice, virus was detectable in the spleen and lymph nodes, whereas only few meningeal cells and neurons were affected, allowing for the mouse survival the infection. The presence of TOSV in spleen and lymph node cells in both s.c.- and i.c.-treated mice suggests their possible involvement in the diffusion of the infection. This animal model may be helpful for the development of prophylactic measures against TOSV infections.

Induction of severe disease in hamsters by two sandfly fever group viruses, Punta toro and Gabek Forest (Phlebovirus, Bunyaviridae), similar to that caused by Rift Valley fever virus

Adult golden hamsters inoculated subcutaneously with either of two sandfly fever group viruses, Punta Toro and Gabek Forest (Phlebovirus, Bunyaviridae), developed a fulminating fatal illness characterized by hepatic and splenic necrosis and interstitial pneumonitis. Most animals died within three days after infection; this was accompanied by high levels of viremia. Necropsy and histopathologic examination of the infected animals revealed pathologic changes involving multiple organs that resembled those described in Rift Valley fever. These two hamster-phlebovirus systems may serve as alternative animal models for Rift Valley fever and should be useful in studying the pathogenesis of severe phlebovirus infection and for testing potential therapeutic agents.

Turlock-like bunyavirus associated with encephalomyelitis and myocarditis in an ostrich chick

In the fall of 1995, a 20-day-old female ostrich chick, 1 of a group of 20, was presented live with clinical signs of 2 days duration characterized by unsteady gait, circling to the left, and walking backward. Another bird with similar clinical signs had died and another had recovered. The bird was euthanized and examined at necropsy. Twenty-five milliliters of serous fluid was in the abdominal cavity and there was increased pericardial fluid. Histopathology of the brain revealed mild to moderate nonsuppurative encephalitis characterized by mild multifocal malacia, perivascular cuffing by lymphocytes, and gliosis. The heart had multifocal infiltrations of lymphocytes mixed with macrophages and a few plasma cells throughout the myocardium. Cytopathic effects were observed in primary chicken embryo liver cells following inoculation with a tissue homogenate prepared from the brain of the affected ostrich. Virus particles the size and morphology of the family Bunyaviridae were observed in cell culture lysate by negative-stain electron microscopy. Viral characterization demonstrated that the virus isolate is a previously unknown serotypic variant (subtype) of Turlock virus. Twelve of 65 sera collected over a 3-year period from ostriches aged from 1 month to 4 years were positive for neutralizing antibody to both the Turlock prototype strain and the new subtype of Turlock virus described in this report.

Encephalomyelitis associated with akabane virus infection in adult cows

Between August and September 2000, five 2-7-year-old cows in Korea exhibited neurologic signs and were diagnosed as infected with Akabane virus based on the results of histopathology, immunohistochemistry, serology, and reverse transcription polymerase chain reaction (RT-PCR) analysis. Immunohistochemistry and RT-PCR were equally effective and sensitive for diagnosing Akabane virus infection during the early stage of infection. Typical lymphohistiocytic inflammation characterized by perivascular mononuclear cell infiltration, gliosis, neuronophagia, and neuronal loss was noted in the brain and the ventral horn gray matter of the spinal cord. The lesions in the brain were most prominent in the pons and medulla oblongata. Akabane virus antigen was detected in the brain and spinal cord, mainly in degenerating neurons and glial cells. RT-PCR analysis revealed a target band of expected size in four cows. This is the first report on an outbreak of natural Akabane virus infection in adult cattle.

Chizé virus, a new phlebovirus isolated in France from Ixodes (Trichotoixodes) frontalis

A new phlebovirus (Bunyaviridae family, Phlebovirus genus), provisionally designed Chizé virus, was isolated from a nymph of Ixodes (Trichotoixodes) frontalis collected on a wren (Troglodytes troglodytes) found dead in the Chizé forest, western France. Chizé virus produced a lethal encephalitis in one-day-old mice and cytopathic effect (CPE) in Vero cells. Extracellular particles with a mean diameter of 105 nm with surface spikes characteristic of Uukuniemi (UUK) serogroup viruses were observed in Vero cells. Chizé virus reacted in complement-fixation test with several UUK serogroup viruses but was readily distinguished from all registered viruses in the serogroup. I. frontalis is highly specific for birds and unlikely to transmit Chizé virus to humans or domestic animals; the pathogenicity of the new virus to wild birds remains to be clarified.

Aino virus antigen in brain lesions of a naturally aborted bovine fetus

A bovine fetus aborted at 187 days of gestation was serologically and immunohistopathologically examined. Serum and cerebrospinal fluid samples had high titers of virus-neutralizing antibody for Aino virus. A severe necrotizing encephalopathy was noted. Aino virus antigen was demonstrated in neuroglial cells within the brain lesion. The destruction of developing neuronal cells appeared to be a significant feature of the pathogenesis of lesions due to Aino virus infection in the central nervous system.

Hydranencephaly, cerebellar hypoplasia, and myopathy in chick embryos infected with aino virus

Pathogenesis of Aino virus (AIV), a suspected causative agent of congenital abnormalities of calves, has not yet been established by experimental infection of dams. To investigate the pathogenesis, 10(3) median tissue culture infective doses per 0.2 ml of AIV strain JaNAr 28 was inoculated into the yolk sac of 8-day-old chick embryos. At 4, 7, 10, and 13 days post-inoculation (PI) 20 eggs were opened and macro- and microscopic studies combined with virus recovery and immunohistochemical detection of the virus antigen were performed. At 7 to 13 days PI chick embryos manifested marked hydranencephaly, cerebellar hypoplasia, arthrogryposis, and scoliosis, with the highest incidences of 86.7%, 73.3%, 80.0%, and 20.0%, respectively. At 4 days PI the viral antigen was found in nerve cells, gitter cells in mild necrotic foci of the central nervous system (CNS), degenerative myotubules, and macrophages in the interstitium, which was associated with the early phase of AIV-induced encephalitis and polymyositis, with occasional accompanying hemorrhage and clumping of myotubular fragments. From 7 to 10 days PI, AIV antigen increased markedly in the liquefactive necrosis and in both degenerative and normal-looking myotubules in conjunction with developing hydranencephaly and arthrogryposis. The encephalitis and myositis had a tendency to mitigate by 10 days PI, coincident with a slight decrease in amount of AIV antigen. At 13 days PI there was almost no detectable AIV antigen in CNS and skeletal muscles, probably due to depletion of cells having affinity to AIV.

Golgi complex localization of the Punta Toro virus G2 protein requires its association with the G1 protein

The glycoproteins of bunyaviruses accumulate in membranes of the Golgi complex, where virus maturation occurs by budding. In this study we have constructed a series of full length or truncated mutants of the G2 glycoprotein of Punta Toro virus (PTV), a member of the Phlebovirus genus of the Bunyaviridae, and investigated their transport properties. The results indicate that the hydrophobic domain preceding the G2 glycoprotein can function as a translocational signal peptide, and that the hydrophobic domain near the C-terminus serves as a membrane anchor. A G2 glycoprotein construct with an extra hydrophobic sequence derived from the N-terminal NSM region was stably retained in the ER, and was unable to be transported to the Golgi complex. The full-length G2 glycoprotein, when expressed on its own, was transported out of the ER and expressed on the cell surface, whereas the G1 and G2 proteins when expressed together are retained in the Golgi complex. A truncated anchor-minus form of the G2 glycoprotein was found to be secreted into the culture medium, but was retained in the Golgi complex when coexpressed with the G1 glycoprotein. These results indicate that the G2 membrane glycoprotein is a class I membrane protein which does not contain a signal sufficient for Golgi retention, and suggest that its Golgi localization is a result of association with the G1 glycoprotein.

Experimental labyrinthitis in guinea pigs caused by a hantavirus

Hantavirus-induced acute viral infection of the inner ear of guinea pigs is reported. Guinea pigs were inoculated directly into the inner ear through the round window, or intraperitoneally with hantavirus (B-1 strain), and the cochlea was examined using an immunohistochemical technique for the localization of viral antigens. Virus-specific antigens were detected prominently in the stria vascularis and to a lesser degree in other inner ear structures of the infected guinea pigs. The morphological changes in the inner ear structures of these guinea pigs were observed. Virus was isolated from the blood of some infected guinea pigs. These data suggest that hantavirus can infect the inner ear of the guinea pig via viremia. The effect of immunosuppression by ciclosporin A or cyclophosphamide is discussed.

Role of hepatocytes and Kupffer cells in age-dependent murine hepatitis caused by a phlebovirus, Punta Toro

Punta Toro virus (PTV) infection of C57BL/6 mice results in fulminant hepatic necrosis and death in 3-week-old susceptible mice, but survival with minimal hepatocellular necrosis in 8-week-old resistant mice. Susceptibility in 3-week-old mice is associated with an earlier rise of viral titers in liver and serum than that occurring in 8-week-old resistant mice. There is also an earlier and more rapid accumulation of infectious progeny in serum vs. liver after PTV infection in both age groups, suggesting that the virus may replicate in extrahepatic sites as well as the liver. PTV infection of isolated hepatocytes and Kupffer cells from 3- and 8-week-old mice demonstrates a significant age-related difference in the ability of these cells to support replication of PTV in vitro (P less than 0.05). The age-related difference in liver cell-PTV interaction appears to be an inherent difference in the liver cells themselves, since there are no age-related differences in viral adsorption, morphogenesis, cytopathic effect, or interferon action within these cells. Thus, age-related differences in PTV replication or dissemination at extrahepatic sites, and the ability of the virus to replicate in intrahepatic sites, may be additive factors in the expression of age-related susceptibility to PTV in C57BL/6 mice.

Pathogenesis of a phleboviral infection (Punta Toro virus) in golden Syrian hamsters

The hamster, Mesocricetus auratus, was examined as a possible model for investigating the poorly defined pathogenesis of the family Bunyaviridae, genus Phlebovirus. Punta Toro virus (PTV) isolates from Eastern Panama were highly virulent for two outbred and five inbred hamster strains, while isolates from western Panama were of low virulence. The Adames strain (eastern Panama) of PTV (LD50 approximately 1 PFU, sc) caused an acute fatal disease (average survival time, 3.8 days) in 10-week-old Lak: LVG (SYR) hamsters. Severe necrosis of the liver, spleen, and small intestine was associated with extensive expression of viral antigen in these organs. The Balliet strain (western Panama) of PTV (LD50 greater than 6 log10 PFU, subcutaneously) caused a mild hepatocellular infection with peak viral liver titers of 3-4 log10 PFU/g compared to 8-9 log10 PFU/g for the Adames strain. We observed histological lesions in the red pulp of the spleen or the lamina propria of the small intestine with the Adames strain. Lesions in the hamsters had characteristics of disseminated intravascular coagulation (DIC). The PTV-hamster model shares similarities to Rift Valley fever (phleboviral disease), which causes fatal disease in man and domesticated ruminants.

Encephalitis of cattle caused by Iriki isolate, a new strain belonging to Akabane virus

A disease characterized by nervous signs was found in 10 calves in two districts in Kagoshima Prefecture, Japan, from October to November, 1984. Histopathological changes of nonpurulent encephalitis were found in every case. An agent, named Iriki isolate, was isolated from the cerebellum of a calf in HmLu-1 cell cultures. All of the affected calves possessed neutralizing antibody to the virus. A high seropositive rate to the virus in cohabiting cattle and cattle kept in the epizootic area, and seroconversion to the virus in 1984, were disclosed. Experimental infection of calves with Iriki isolate produced severe nervous signs and histopathological changes similar to those of the natural infection. These seroepidemiological findings and animal experiments established that Iriki isolate is the causative agent of the disease. Iriki isolate was considered as a variant of Akabane virus since the virus showed cross reaction with Akabane virus in virus neutralization tests.

Akabane disease in sheep

Perinatal lamb mortality, associated with malformations of the CNS due to Akabane viral infection, occurred in 4 of 9 flocks of ewes lambing on 3 farms between 26 May and 14 November, 1976. Cases were restricted to ewes conceiving prior to the second week of March and lambing between 26 May and 19 July. As judged by seroconversion in sentinel flocks on 2 of the farms, field infection with Akabane virus occurred mainly between mid-February and mid-April. Malformations of the CNS occurred in 42.5%, 51.2%, 100% and 31.0% of the dead lambs examined in the affected flocks respectively. Prevalence in the 4 affected flocks, expressed as the proportion of ewes lambing which delivered at least one malformed foetus, was 6.1%, 8.4%, 88.9% and 5.7% respectively. Lamb mortality due to malformations of the CNS was 7.1%, 5.5%, 92.3% and 5.7% of lambs born. Age-specific prevalence was calculated for 3 of the 4 flocks and 2-year-old ewes accounted for 71.4% and 76.9% of total cases respectively in 2 flocks, whereas in one flock malformations occurred at equivalent frequencies throughout several older age groups. Birthweights of affected lambs were usually significantly lighter than those of unaffected lambs of similar sex and birth-type, and their mean duration of gestation was slightly, and significantly, prolonged. Micrencephaly (88.1% of cases) and hydrocephalus (68.7% of cases) were the outstanding pathological features of the malformations with hydranencephaly, microgyria, porencephaly and attenuation of the spinal cord occurring at much lower frequencies.(ABSTRACT TRUNCATED AT 250 WORDS)

Myopathy and encephalopathy in chick embryos experimentally infected with Akabane virus

Chick embryos infected with Akabane virus by the yolk sac route at 6 days of incubation developed polymyositis and encephalitis. At 3 to 7 days after inoculation, skeletal muscles had myotubule degeneration, clumping of muscle cell nuclei, and infiltration of heterophils; dysplasia and aplasia were evident at 9 to 15 days after inoculation. Changes in the cerebral neostriatum and optic lobes at 2 to 11 days after inoculation included necrosis of primordial nervous tissue, hemorrhages, and hyperplasia of the vascular endothelial cells. Cavities were in nervous tissue subsequent to encephalitis. Hydranencephaly and vascular wall thickening were found 13 and 15 days after inoculation. Embryos infected intravenously at 15 days incubation had foci of encephalitis 3 to 6 days after inoculation, including neuronal degeneration, neuroglial hyperplasia, vascular endothelial proliferation, and heterophil infiltration.

Punta Toro virus infection of C57BL/6J mice: a model for phlebovirus-induced disease

Punta Toro virus infections of inbred strains of mice have been characterized and evaluated as a model in which to study various aspects of the host response to phlebovirus infections and the requirements for protective immunity. The Adames strain of Punta Toro virus was found to be strongly hepatotropic and lymphotropic and the outcome of infection was largely a function of age. C57BL/6J mice of less than 5 weeks of age uniformly developed fulminant hepatocellular necrosis with mean survival times of 4.2 days. Resistance to lethal infection increased with age such that greater than 95% of 8-week-old mice survived challenge. The kinetics of viremia, antibody production, and hematological changes in 4- and 8-week animals indicated that the survival of the older animals is related to their ability to delay virus replication and the development of hepatic lesions during the initial 48 h of infection and their ability to terminate virus replication and clear virus from the circulation 4 to 5 days after infection. The mechanisms responsible for this resistance were studied using anti-interferon serum, immunosuppression, and passive immunization.

Avalon virus, Sakhalin group (Nairovirus, Bunyaviridae) from the seabird tick Ixodes (Ceratixodes) uriae White 1852 in France

Nine strains of Avalon virus were isolated from Ixodes uriae ticks collected in the Cape Sizun seabird reserve, Brittany, from 1979 to 1985, during a longitudinal study of consequences of tick-borne infections for kittiwakes (Rissa tridactyla). Avalon virus strains isolated in France proved difficult to study owing to the weak infectious titres they exhibited in suckling mice or cultured cells. However, some interesting data concerning the ecology of virus infection and the morphology of the virions were obtained and are discussed.

Cell fusion by haemorrhagic fever with renal syndrome (HFRS) viruses and its application for titration of virus infectivity and neutralizing antibody

Haemorrhagic fever with renal syndrome viruses, are members of the family Bunyaviridae. They cause cell to cell fusion from within under acidic conditions. This phenomenon was found to occur under a pH range of between 4.9 to 6.3 for all the viruses examined. The pH range which causes cell fusion was similar to that reported for the La Crosse virus of the Bunyaviridae, hence indicating that this property is a common biological characteristic among this family of viruses. Titration of virus infectivity and neutralizing antibody was done by counting the number of fused cell foci produced in infected Vero cell monolayers after low pH treatment. This method was simpler and more rapid than the ordinary plaque formation method or that of counting infected cell foci by IFA or immunoenzyme assay. In addition, this method may also be applicable in the detection of other enveloped viruses which do not cause a typical cytopathic effect.

[Pathogenic properties of the LEIV23 Astrakhan strain of Batai virus for primates]

Pathogenic properties of Batai virus, LEIV23 Astrakhañ strain, isolated from Aedes vexans mosquitoes in Astrakhañ region were studied comparatively. The degree of susceptibility to the virus of green monkeys and rodents (white mice, Syrian hamsters), and the pattern of lesions produced by the virus in organs of these animals were established. The virus was shown to have a comparatively wide host range affecting phylogenetically far distant animals. Monkeys were found to have virus-carrier state for 50 days (the observation period). The virus is pantropic. Apparently mammals may be virus hosts in nature, but human infection cannot be ruled out. This requires further study in an epidemiological experiment.

Experimental intrauterine infection of akabane virus. Pathological studies of skeletal muscles and central nervous system of newborn hamsters with relevances to the Fukuyama type congenital muscular dystrophy

A vertical infection system in hamsters produced by inoculating with Akabane virus was established as an experimental model of congenital muscular dystrophy (Fukuyama type) (FCMD) and arthrogryposis multiplex congenita (AMC) in humans. Swollen fetuses, mummified fetuses, arthrogryposis and cranial deformities were produced in 13 of 415 newborn hamsters inoculated transplacentally (3.1%). The incidence was significantly higher than that in the control group (p less than 0.05). Eight cases presenting apparent abnormalities were examined histologically and virologically. Pictures of skeletal muscles showing such immature features as chains of internal nuclei and myotubular muscle fibers were demonstrated in all cases. In addition, perivascular infiltration of small round cells and thickening of vascular walls were seen in 5 cases, while myogenic changes such as broken myofibrils, small muscle fibers and changes in fiber size were observed in 6 cases. In the anterior horn of the spinal cord, swelling and loss of nuclei and cell matrices were noticed in 4 cases. In the cerebral cortex, disarrangement of cell layers, edematous changes and loss of nerve cells were revealed in 5 cases. In 4 cases virus particles were found on electron microscopy in the cerebral cortex. The authors considered that this experimental system of intrauterine viral infection would be useful for the etiological study of FCMD and AMC in humans in which not only skeletal muscles but also the central nervous system is affected congenitally.