Fatal encephalitis due to Nipah virus among pig-farmers in Malaysia

BACKGROUND

Between February and April, 1999, an outbreak of viral encephalitis occurred among pig-farmers in Malaysia. We report findings for the first three patients who died.

METHODS

Samples of tissue were taken at necropsy. Blood and cerebrospinal-fluid (CSF) samples taken before death were cultured for viruses, and tested for antibodies to viruses.

FINDINGS

The three pig-farmers presented with fever, headache, and altered level of consciousness. Myoclonus was present in two patients. There were signs of brainstem dysfunction with hypertension and tachycardia. Rapid deterioration led to irreversible hypotension and death. A virus causing syncytial formation of vero cells was cultured from the CSF of two patients after 5 days; the virus stained positively with antibodies against Hendra virus by indirect immunofluorescence. IgM capture ELISA showed that all three patients had IgM antibodies in CSF against Hendra viral antigens. Necropsy showed widespread microinfarction in the central nervous system and other organs resulting from vasculitis-induced thrombosis. There was no clinical evidence of pulmonary involvement. Inclusion bodies likely to be of viral origin were noted in neurons near vasculitic blood vessels.

INTERPRETATION

The causative agent was a previously undescribed paramyxovirus related to the Hendra virus. Close contact with infected pigs may be the source of the viral transmission. Clinically and epidemiologically the infection is distinct from infection by the Hendra virus. We propose that this Hendra-like virus was the cause of the outbreak of encephalitis in Malaysia.

Prevalence and clinical symptoms of human metapneumovirus infection in hospitalized patients

During a 17-month period, we performed retrospective analyses of the prevalence of and clinical symptoms associated with human metapneumovirus (hMPV) infection, among patients in a university hospital in The Netherlands. All available nasal-aspirate, throat-swab, sputum, and bronchoalveolar-lavage samples (N=1515) were tested for hMPV RNA by reverse-transcriptase polymerase chain reaction. hMPV RNA was detected in 7% of samples from patients with respiratory tract illnesses (RTIs) and was the second-most-detected viral pathogen in these patients during the last 2 winter seasons. hMPV was detected primarily in very young children and in immunocompromised individuals. In young children, clinical symptoms associated with hMPV infection were similar to those associated with human respiratory syncytial virus (hRSV) infection, but dyspnea, feeding difficulties, and hypoxemia were reported more frequently in hRSV-infected children. Treatment with antibiotics and corticosteroids was reported more frequently in hMPV-infected children. From these data, we conclude that hMPV is an important pathogen associated with RTI.

Nipah virus infection: pathology and pathogenesis of an emerging paramyxoviral zoonosis

In 1998, an outbreak of acute encephalitis with high mortality rates among pig handlers in Malaysia led to the discovery of a novel paramyxovirus named Nipah virus. A multidisciplinary investigation that included epidemiology, microbiology, molecular biology, and pathology was pivotal in the discovery of this new human infection. Clinical and autopsy findings were derived from a series of 32 fatal human cases of Nipah virus infection. Diagnosis was established in all cases by a combination of immunohistochemistry (IHC) and serology. Routine histological stains, IHC, and electron microscopy were used to examine autopsy tissues. The main histopathological findings included a systemic vasculitis with extensive thrombosis and parenchymal necrosis, particularly in the central nervous system. Endothelial cell damage, necrosis, and syncytial giant cell formation were seen in affected vessels. Characteristic viral inclusions were seen by light and electron microscopy. IHC analysis showed widespread presence of Nipah virus antigens in endothelial and smooth muscle cells of blood vessels. Abundant viral antigens were also seen in various parenchymal cells, particularly in neurons. Infection of endothelial cells and neurons as well as vasculitis and thrombosis seem to be critical to the pathogenesis of this new human disease.

Comparative pathology of the diseases caused by Hendra and Nipah viruses

Information on the pathogenesis and transmissibility of Hendra and Nipah viruses was obtained by comparing their histopathology. Both viruses induced syncytial cells in vascular tissues and they were primarily vasotropic and/or neurotropic, generating interstitial pneumonia or encephalitis. Nipah virus in pigs was also epitheliotropic in respiratory epithelium and thus contagious.

Experimental Nipah virus infection in pigs and cats

A human isolate of Nipah virus from an outbreak of febrile encephalitis in Malaysia that coincided with a field outbreak of disease in pigs was used to infect eight 6-week-old pigs orally or subcutaneously and two cats oronasally. In pigs, the virus induced a respiratory and neurological syndrome consistent with that observed in the Malaysian pigs. Not all the pigs showed clinical signs, but Nipah virus was recovered from the nose and oropharynx of both clinically and sub-clinically infected animals. Natural infection of in-contact pigs, which was readily demonstrated, appeared to be acute and self-limiting. Subclinical infections occurred in both inoculated and in-contact pigs. Respiratory and neurological disease was also produced in the cats, with recovery of virus from urine as well as from the oropharynx. The clinical and pathological syndrome induced by Nipah virus in cats was comparable with that associated with Hendra virus infection in this species, except that in fatal infection with Nipah virus there was extensive inflammation of the respiratory epithelium, associated with the presence of viral antigen. Viral shedding via the nasopharynx, as observed in pigs and cats in the present study, was not a regular feature of earlier reports of experimental Hendra virus infection in cats and horses. The findings indicate the possibility of field transmission of Nipah virus between pigs via respiratory and oropharyngeal secretions.

A 1-year experience with human metapneumovirus in children aged <5 years

Human metapneumovirus (hMPV) is a recently discovered respiratory pathogen. We tested respiratory specimens for the presence of hMPV by reverse-transcription polymerase chain reaction. These specimens were obtained over a 1-year period from children aged <5 years and had negative results by the direct fluorescent antibody test for respiratory syncytial virus, influenza A and B, parainfluenza viruses 1-3, and adenovirus. Overall, 54 (8.1%) of 668 individuals tested positive for hMPV. During March and April of the study period, hMPV was detected in 17.6% and 25.0% of specimens tested, respectively. At least 2 distinct genotypes of hMPV circulated during the study period. Fever, tachypnea, cough, rhinorrhea, retractions of the chest wall, and wheezing were common findings. Of hMPV-positive children, 60.4% were aged <12 months. hMPV accounted for a small but significant proportion of respiratory-tract disease in infants and children.

Relapsed and late-onset Nipah encephalitis

An outbreak of infection with the Nipah virus, a novel paramyxovirus, occurred among pig farmers between September 1998 and June 1999 in Malaysia, involving 265 patients with 105 fatalities. This is a follow-up study 24 months after the outbreak. Twelve survivors (7.5%) of acute encephalitis had recurrent neurological disease (relapsed encephalitis). Of those who initially had acute nonencephalitic or asymptomatic infection, 10 patients (3.4%) had late-onset encephalitis. The mean interval between the first neurological episode and the time of initial infection was 8.4 months. Three patients had a second neurological episode. The onset of the relapsed or late-onset encephalitis was usually acute. Common clinical features were fever, headache, seizures, and focal neurological signs. Four of the 22 relapsed and late-onset encephalitis patients (18%) died. Magnetic resonance imaging typically showed patchy areas of confluent cortical lesions. Serial single-photon emission computed tomography showed the evolution of focal hyperperfusion to hypoperfusion in the corresponding areas. Necropsy of 2 patients showed changes of focal encephalitis with positive immunolocalization for Nipah virus antigens but no evidence of perivenous demyelination. We concluded that a unique relapsing and remitting encephalitis or late-onset encephalitis may result as a complication of persistent Nipah virus infection in the central nervous system.

An outbreak of severe respiratory tract infection due to human metapneumovirus in a long-term care facility

BACKGROUND

Human metapneumovirus (hMPV) is a newly described paramyxovirus that is mainly associated with bronchiolitis in children. We sought to describe the epidemiological, virological, and histopathological findings associated with a large outbreak of hMPV infection in a long-term care facility.

METHODS

An investigation of the outbreak was performed by public health authorities, who used standardized questionnaires to collect relevant clinical information from all residents of the facility. Nasopharyngeal samples were obtained from a subset of patients who had influenza-like illnesses for testing by viral culture and reverse-transcriptase polymerase chain reaction. Lung tissue samples from a patient whose case was fatal were available for molecular, histopathological, and immunohistochemical testing.

RESULTS

A total of 96 (27%) of 364 residents of a long-term care facility presented with respiratory or constitutional symptoms between 1 January 2006 and 15 February 2006. The attack rate in the most affected ward was 72% (31 of 43 patients), which included 4 of the 6 polymerase chain reaction-confirmed cases of hMPV infection. In contrast, viral culture results were positive for hMPV in only 2 of the 5 polymerase chain reaction-positive samples tested. The most reported diagnosis was an upper respiratory tract infection or an influenza-like illness, although 21% of residents in 1 of the 3 wards that had confirmed cases of hMPV infection had lower respiratory tract infections. The fatality rate was 50% (3 of 6 patients) among confirmed cases and 9.4% (9 of 96 patients) among patients with possible cases. A patient with a fatal case had histopathological findings that confirmed the presence of hMPV RNA and proteins in the bronchiolar epithelium of affected lobes. Phylogenetic analysis revealed the presence of 2 distinct strains of hMPV circulating simultaneously on different wards.

CONCLUSION

hMPV can be associated with important outbreaks of acute respiratory tract infection in elderly institutionalized persons.

Respiratory disease due to parainfluenza virus in adult bone marrow transplant recipients

We reviewed the frequency and clinical course of parainfluenza virus (PIV) infections in 1,173 adult bone marrow transplant (BMT) recipients cared for at The University of Texas M.D. Anderson Cancer Center (Houston). Between January 1991 and September 1994, PIV was isolated from the respiratory secretions of 61 (5.2%) of these patients. Thirty-four (56%) of the 61 patients had uncomplicated upper respiratory tract illnesses and survived. The remaining 27 patients (44%) developed pneumonia, and the associated mortality was 37% (10 of 27 patients). Twenty-three (85%) of the patients with pneumonia had had preceding upper respiratory illnesses. Of the 10 patients who died, nine died within 100 days after transplantation. Histopathologic examination of lung tissue from seven patients revealed intracytoplasmic viral inclusions in six, a finding consistent with invasive PIV pneumonia, and viral changes in the seventh patient. Seven of the 10 patients who died had other serious concurrent infections. Of 42 patients who developed PIV infection early after transplantation (i.e., < 100 days), the frequency of pneumonia was higher among the 18 allogeneic BMT recipients (61%) than among the 24 autologous BMT recipients (42%), and the associated mortality was also higher (55% vs. 30%, respectively). PIVs are an important cause of life-threatening pneumonia in adult BMT recipients, particularly patients who have recently undergone allogeneic bone marrow transplantation.

Experimental hendra virus infectionin pregnant guinea-pigs and fruit Bats (Pteropus poliocephalus)

Antibodies to Hendra virus (HeV) have been found in a high percentage of fruit bats (Pteropus spp.) in Australia, indicating a possible reservoir for the virus. The aim of the experiments reported here was to investigate transplacental infection as a possible mode of transmission of the virus in fruit bats and other animals. In a first experiment, 18 pregnant guinea-pigs in the mid-stage of gestation were inoculated with HeV, as an experimental model in a conventional laboratory animal. Nine developed HeV disease as confirmed by viral isolation, histopathology and immunohistochemistry. In five of the nine clinically affected guinea-pigs there was necrosis and strong positive immunostaining in the placentas in an indirect immunoperoxidase (IPX) test for HeV antigen. One of these five guinea-pigs aborted and HeV was isolated from its three fetuses, one of which was also positive to the IPX test. In three other sick guinea-pig dams, virus was isolated from fetuses, and there was positive immunostaining in two of the latter. In a second experiment, four fruit bats were inoculated with a similar dose of HeV. (A further four guinea-pigs inoculated at the same time developed severe disease, indicating adequate virulence.) Two bats were killed at 10 days post-inoculation and two were killed at 21 days. In these bats, no overt clinical disease was observed, but subclinical disease occurred, as indicated by viral isolation, seroconversion, vascular lesions and positive immunostaining. Transplacental transmission was indicated by positive immunostaining in two placentas and confirmed by isolation of virus from one of the associated fetuses.

Experimental human metapneumovirus infection of cynomolgus macaques (Macaca fascicularis) results in virus replication in ciliated epithelial cells and pneumocytes with associated lesions throughout the respiratory tract

A substantial proportion of hitherto unexplained respiratory tract illnesses is associated with human metapneumovirus (hMPV) infection. This virus also was found in patients with severe acute respiratory syndrome (SARS). To determine the dynamics and associated lesions of hMPV infection, six cynomolgus macaques (Macaca fascicularis) were inoculated with hMPV and examined by pathological and virological assays. They were euthanized at 5 (n = 2) or 9 (n = 2) days post-infection (dpi), or monitored until 14 dpi (n = 2). Viral excretion peaked at 4 dpi and decreased to zero by 10 dpi. Viral replication was restricted to the respiratory tract and associated with minimal to mild, multi-focal erosive and inflammatory changes in conducting airways, and increased numbers of macrophages in alveoli. Viral expression was seen mainly at the apical surface of ciliated epithelial cells throughout the respiratory tract, and less frequently in type 1 pneumocytes and alveolar macrophages. Both cell tropism and respiratory lesions were distinct from those of SARS-associated coronavirus infection, excluding hMPV as the primary cause of SARS. This study demonstrates that hMPV is a respiratory pathogen and indicates that viral replication is short-lived, polarized to the apical surface, and occurs primarily in ciliated respiratory epithelial cells.

Human metapneumovirus persists in BALB/c mice despite the presence of neutralizing antibodies

Human metapneumovirus (HMPV) has emerged as an important human respiratory pathogen causing upper and lower respiratory tract infections in young children and older adults. Recent epidemiological evidence indicates that HMPV may cocirculate with respiratory syncytial virus, and HMPV infection has been associated with other respiratory diseases. In this study, we show that BALB/c mice are susceptible to HMPV infection, the virus replicates in the lungs with biphasic growth kinetics in which peak titers occur at days 7 and 14 postinfection (p.i.), and infectious HMPV can be recovered from lungs up to day 60 p.i. In addition, we show that genomic HMPV RNA can be detected in the lungs for >/=180 days p.i. by reverse transcription-PCR; however, neither HMPV RNA nor infectious virus can be detected in serum, spleen, kidneys, heart, trachea, and brain tissue. Lung histopathology revealed prevalent mononuclear cell infiltration in the interstitium beginning at day 2 p.i. and peaking at day 4 p.i. which decreased by day 14 p.i. and was associated with airway remodeling. Increased mucus production evident at day 2 p.i. was concordant with increased bronchial and bronchiolar inflammation. HMPV-specific antibodies were detected by day 14 p.i., neutralizing antibody titers reached >/=6.46 log(2) end-point titers by day 28 p.i., and depletion of T cells or NK cells resulted in increased HMPV titers in the lungs, suggesting some immune control of viral persistence. This study shows that BALB/c mice are amenable for HMPV studies and indicates that HMPV persists as infectious virus in the lungs of normal mice for several weeks postinfection.

Nipah virus encephalitis outbreak in Malaysia

Emerging infectious diseases involving zoonosis have become important global health problems. The 1998 outbreak of severe febrile encephalitis among pig farmers in Malaysia caused by a newly emergent paramyxovirus, Nipah virus, is a good example. This disease has the potential to spread to other countries through infected animals and can cause considerable economic loss. The clinical presentation includes segmental myoclonus, areflexia, hypertension, and tachycardia, and histologic evidence includes endothelial damage and vasculitis of the brain and other major organs. Magnetic resonance imaging has demonstrated the presence of discrete high-signal-intensity lesions disseminated throughout the brain. Nipah virus causes syncytial formation in Vero cells and is antigenically related to Hendra virus. The Island flying fox (Pteropus hypomelanus; the fruit bat) is a likely reservoir of this virus. The outbreak in Malaysia was controlled through the culling of >1 million pigs.

Detection of severe human metapneumovirus infection by real-time polymerase chain reaction and histopathological assessment

BackgroundInfections with common respiratory tract viruses can cause high mortality, especially in immunocompromised hosts, but the impact of human metapneumovirus (hMPV) in this setting was previously unknown

MethodsWe evaluated consecutive bronchoalveolar lavage and bronchial wash fluid samples from 688 patients—72% were immunocompromised and were predominantly lung transplant recipients—for hMPV by use of quantitative real-time polymerase chain reaction (PCR), and positive results were correlated with clinical outcome and results of viral cultures, in situ hybridization, and lung histopathological assessment

ResultsSix cases of hMPV infection were identified, and they had a similar frequency and occurred in a similar age range as other paramyxoviral infections. Four of 6 infections occurred in immunocompromised patients. Infection was confirmed by in situ hybridization for the viral nucleocapsid gene. Histopathological assessment of lung tissue samples showed acute and organizing injury, and smudge cell formation was distinct from findings in infections with other paramyxoviruses. Each patient with high titers of hMPV exhibited a complicated clinical course requiring prolonged hospitalization

ConclusionsOur results provide in situ evidence of hMPV infection in humans and suggest that hMPV is a cause of clinically severe lower respiratory tract infection that can be detected during bronchoscopy by use of real-time PCR and routine histopathological assessment

Fusion properties of cells persistently infected with human parainfluenza virus type 3: participation of hemagglutinin-neuraminidase in membrane fusion

Cells persistently infected with human parainfluenza virus type 3 (HPF3) exhibit a novel phenotype. They are completely resistant to fusion with each other but readily fuse with uninfected cells. We demonstrate that the inability of these cells to fuse with each other is due to a lack of cell surface neuraminic acid. Neuraminic acid is the receptor for the HPF3 hemagglutinin-neuraminidase (HN) glycoprotein, the molecule responsible for binding of the virus to cell surfaces. Uninfected CV-1 cells were treated with neuraminidase and then tested for their ability to fuse with the persistently infected (pi) cells. Neuraminidase treatment totally abolished cell fusion. To extend this result, we used a cell line deficient in sialic acid and demonstrated that these cells, like the neuraminidase-treated CV-1 cells, were unable to fuse with pi cells. We then tested whether mimicking the agglutinating function of the HN molecule with lectins would result in cell fusion. We added a panel of five lectins to the neuraminic acid-deficient cells and showed that binding of these cells to the pi cells did not result in fusion; the lectins could not substitute for interaction of neuraminic acid with the HN molecule in promoting membrane fusion. These results provide compelling evidence that the HN molecule of HPF3 and its interaction with neuraminic acid participate in membrane fusion and that cell fusion is mediated by an interaction more complex than mere juxtaposition of the cell membranes.

Human metapneumovirus infection induces long-term pulmonary inflammation associated with airway obstruction and hyperresponsiveness in mice

BACKGROUND

Human metapneumovirus (hMPV) is a newly described paramyxovirus that is associated with bronchiolitis, pneumonia, and asthma exacerbation. The objective of the present work was to study the duration of pulmonary inflammation and the functional consequences of infection with hMPV by use of a BALB/c mouse model.

METHODS

BALB/c mice were inoculated with 1 x 10(8) TCID(50) of hMPV type A (C-85473), and viral persistence in lungs was assessed by reverse-transcription polymerase chain reaction for 154 days after infection. Pulmonary inflammation was characterized in histopathological experiments by use of a validated scoring system, and periodic acid-Schiff (PAS) staining of lung sections was used to document increased mucus production, also until day 154. Finally, respiratory functions were analyzed by taking plethysmographic measurements until day 70.

RESULTS

Persistence of viral RNA and significant pulmonary inflammation were noted until day 154, whereas the findings for PAS staining suggested that mucus production was increased only until day 12. Maximal breathing difficulties occurred on day 5, and airway obstruction and hyperresponsiveness were still significant until at least day 70.

CONCLUSION

Acute hMPV infection in BALB/c mice is associated with long-term pulmonary inflammation that leads to significant obstructive disease of the airways. This animal model will be of a great benefit in the evaluation of novel therapeutic and prophylactic modalities.

Effect of ribavirin and glucocorticoid treatment in a mouse model of human metapneumovirus infection

Human metapneumovirus (hMPV)-infected BALB/c mice were treated with ribavirin (40 mg/kg of body weight twice a day intraperitoneally), corticosterone (0.2 mg/ml in water), or both modalities. Ribavirin significantly decreased both hMPV replication in lungs (by 5 log10) and global pulmonary inflammation on day 5 postinfection, whereas glucocorticoids reduced only alveolar and interstitial inflammation, compared to controls.

MR imaging features of Nipah encephalitis

OBJECTIVE

The newly discovered Nipah virus causes an acute febrile encephalitic illness in humans that is associated with a high mortality. The purpose of this study is to describe the MR imaging findings of Nipah encephalitis.

MATERIALS AND METHODS

MR imaging of the brain was performed in 31 patients with Nipah encephalitis divided into three groups. The first group (14 patients) underwent MR imaging during the acute phase of the illness and the second group (10 patients) during the later phase of the acute illness. The third group consisted of six patients who underwent MR imaging because they experienced neurologic relapse and one patient who had late-onset encephalitis. Spin-echo T1- and T2-weighted sequences and T2-weighted fluid attenuated inversion recovery (FLAIR) sequences were performed. Contrast-enhanced MR imaging was performed in four patients.

RESULTS

The FLAIR sequences revealed abnormalities in all patients studied. MR imaging findings in both the acute and later phases of encephalitis were similar; the main feature of both phases was the presence of discrete high-signal-intensity lesions, measuring 2-7 mm, disseminated throughout the brain, mainly in the subcortical and deep white matter of the cerebral hemispheres. Neither mass effect nor cerebral edema was seen. There was no correlation with the focal neurologic signs, depth of coma, and outcome of the patients. The lesions were attributed to widespread microinfarctions from underlying vasculitis of cerebral small vessels. Features found on MR imaging in relapsed and late-onset encephalitis differed from the features in acute encephalitis in that confluent cortical involvement was the prominent finding in the former, as opposed to discrete focal lesions in the subcortical and deep white matter in the latter.

CONCLUSION

MR imaging is a sensitive and specific diagnostic tool for evaluating Nipah encephalitis.

Pneumotropism of Sendai virus in relation to protease-mediated activation in mouse lungs

The pneumotropism of Sendai virus in mice was studied in relation to the activation and replication of the virus in the lung. Inactive Sendai virus grown in LLC-MK(2) cells, which possessed an uncleaved precursor glycoprotein, F, and was noninfectious to tissue culture cells, neither grew nor caused pathological changes in the lung of mice. When trypsin treatment was made which cleaved F into F(1) and F(2) subunits, the virus became activated so that it could initiate replication in the bronchial epithelium of the lung. In this case, the progeny virus was produced in the activated form and multiple-cycle replication occurred successively. A parallel relationship was found between the degree of the viral replication and that of clinical signs of the respiratory disease, body weight loss, and histopathological changes in the lung. A protease mutant, TR-2, which was able to be activated only by chymotrypsin but not by trypsin, could also initiate replication in the bronchial epithelium, when activated by chymotrypsin before inoculation into mice. The progeny virus, however, remained inactive, and the replication was limited to a single cycle, which resulted in the limited lung lesion. The overall results suggest that some activating mechanism for the progeny virus of wild-type Sendai virus exists in the lung of mice and the principle (activator) responsible for this phenomenon has a character similar to trypsin. The possible location of the activator is discussed.

Efficacy of novel hemagglutinin-neuraminidase inhibitors BCX 2798 and BCX 2855 against human parainfluenza viruses in vitro and in vivo

Human parainfluenza viruses are important respiratory tract pathogens, especially of children. However, no vaccines or specific therapies for infections caused by these viruses are currently available. In the present study we characterized the efficacy of the novel parainfluenza virus inhibitors BCX 2798 and BCX 2855, which were designed based on the three-dimensional structure of the hemagglutinin-neuraminidase (HN) protein. The compounds were highly effective in inhibiting hemagglutinin (HA) and neuraminidase (NA) activities and the growth of hPIV-1, hPIV-2, and hPIV-3 in LLC-MK(2) cells. The concentrations required to reduce the activity to 50% of that of a control ranged from 0.1 to 6.0 micro M in HA inhibition assays and from 0.02 to 20 micro M in NA inhibition assays. The concentrations required to inhibit virus replication to 50% of the level of the control ranged from 0.7 to 11.5 micro M. BCX 2798 and BCX 2855 were inactive against influenza virus HA and NA and bacterial NA. In mice infected with a recombinant Sendai virus whose HN gene was replaced with that of hPIV-1 [rSV(hHN)], intranasal administration of BCX 2798 (10 mg/kg per day) and of BCX 2855 (50 mg/kg per day) 4 h before the start of infection resulted in a significant reduction in titers of virus in the lungs and protection from death. Treatment beginning 24 h after the start of infection did not prevent death. Together, our results indicate that BCX 2798 and BCX 2855 are effective inhibitors of parainfluenza virus HN and may limit parainfluenza virus infections in humans.

Mucin gene expression in rat airways following infection and irritation

Airway mucus hypersecretion occurs in response to infection and irritation and poses an important and poorly understood clinical problem. In order to gain insight into its pathogenesis, we have focused on an mRNA encoding the major mucus glycoprotein, mucin. Northern blots showed that mucin mRNA was abundant in the intestine of specific pathogen free rats whereas it was undetectable in the airways of these rats until pathogen-free conditions were suspended and rats acquired Sendai (Parainfluenza I) virus infections. Airway mucin hybridization signals in rats that were both infected with Sendai virus and exposed to SO2 were more intense than those in rats with infection alone. These results suggest that pathogen-and irritant-induced hypersecretion may be partly controlled at the level of mucin mRNA.

Cytotoxic T-lymphocyte epitope vaccination protects against human metapneumovirus infection and disease in mice

Human metapneumovirus (hMPV) has emerged as an important human respiratory pathogen causing upper and lower respiratory tract infections in young children and older adults. In addition, hMPV infection is associated with asthma exacerbation in young children. Recent epidemiological evidence indicates that hMPV may cocirculate with human respiratory syncytial virus (hRSV) and mediate clinical disease similar to that seen with hRSV. Therefore, a vaccine for hMPV is highly desirable. In the present study, we used predictive bioinformatics, peptide immunization, and functional T-cell assays to define hMPV cytotoxic T-lymphocyte (CTL) epitopes recognized by mouse T cells restricted through several major histocompatibility complex class I alleles, including HLA-A*0201. We demonstrate that peptide immunization with hMPV CTL epitopes reduces viral load and immunopathology in the lungs of hMPV-challenged mice and enhances the expression of Th1-type cytokines (gamma interferon and interleukin-12 [IL-12]) in lungs and regional lymph nodes. In addition, we show that levels of Th2-type cytokines (IL-10 and IL-4) are significantly lower in hMPV CTL epitope-vaccinated mice challenged with hMPV. These results demonstrate for the first time the efficacy of an hMPV CTL epitope vaccine in the control of hMPV infection in a murine model.

Glucocorticoids inhibit neurogenic plasma extravasation and prevent virus-potentiated extravasation in the rat trachea

Capsaicin increases the permeability of blood vessels in the rat tracheal mucosa through a mechanism involving the release of tachykinins from sensory nerves. This capsaicin-induced increase in vascular permeability is potentiated by viral infections of the respiratory tract. The present study was done to determine whether this "neurogenic plasma extravasation" can be inhibited by glucocorticoids, to learn the time course of this inhibition, and to determine whether glucocorticoids can prevent the potentiating effect of viral respiratory infections on neurogenic plasma extravasation. Groups of pathogen-free F344 rats were treated with dexamethasone for 2 or 8 h (4 mg/kg i.p.) or 48 or 120 h (0.5-4 mg/kg per d i.p.). Another group of rats was treated with dexamethasone for 120 h following the intranasal inoculation of Sendai virus. The magnitude of plasma extravasation produced by capsaicin or substance P was assessed after this treatment by using Monastral blue pigment and Evans blue dye as intravascular tracers. We found that dexamethasone reduced, in a dose-dependent fashion, the magnitude of plasma extravasation produced in the rat trachea by capsaicin and substance P. Significant inhibition was produced by a dose of dexamethasone as small as 0.5 mg/kg i.p. The effect of dexamethasone had a latency of several hours and reached a maximum after 2 d of treatment. Furthermore, dexamethasone prevented the potentiation of neurogenic plasma extravasation usually present after 5 d of Sendai virus respiratory infection.

Pathology of human metapneumovirus infection: insights into the pathogenesis of a newly identified respiratory virus

Human metapneumovirus (hMPV) is a recently discovered human virus that causes significant respiratory infections. Pathologic features of hMPV infection have not been described. A total of 1257 pediatric respiratory samples submitted for routine clinical virologic testing were additionally tested for hMPV by reverse transcriptase polymerase chain reaction (PCR). Pathology specimens, available in 6 of 53 hMPV-positive patients, were examined by light and electron microscopy and included 6 bronchoalveolar lavage (BAL) and 3 lung biopsy specimens from 6 patients (3 girls and 3 boys) ranging in age from 1 to 16 years. BAL from three patients performed within 4 days of the positive hMPV assay showed epithelial degenerative changes and eosinophilic cytoplasmic inclusions within epithelial cells, multinucleate giant cells, and histiocytes. Inclusions were not seen in three patients with BAL performed = 1 month from the time of their positive assay. Lung biopsy, performed in three patients, all = 1 month from the time of their positive assay, showed chronic airway inflammation and intraalveolar foamy and hemosiderin-laden macrophages; all three patients had an underlying pulmonary/systemic disorder. Our findings delineate the clinicopathologic features in hMPV-infected patients undergoing anatomic sampling, which may provide diagnostic guidance to a practicing pathologist. Further, they contribute toward understanding the pathogenesis of hMPV infection.

The fusion and hemagglutinin-neuraminidase glycoproteins of human parainfluenza virus 3 are both required for fusion

Recombinant vaccinia viruses, VF and VHN, expressing the fusion (F) and hemagglutinin-neuraminidase (HN) glycoproteins of human parainfluenza virus 3 (HPIV3) were constructed. Infection of HeLa T4 cells with VF and VHN led to the synthesis of glycoproteins, with the correct apparent molecular weights, that were recognized by monoclonal antibodies specific for HPIV3F and HN. The HN glycoprotein was present on the surface of cells infected with VHN and these cells demonstrated both hemadsorbing and neuraminidase activities. The F glycoprotein was present in cleaved and uncleaved forms and was also expressed on the surface of VF-infected cells. Fusion activity, however, as evidenced by syncytium formation and lysis of human erythrocytes, could only be demonstrated when HeLa T4 cells were coinfected with VF and VHN. Fusion events that are mediated by HPIV3, therefore, require both the F and HN glycoproteins.