Airborne influenza PR8-A virus infections in actively immunized mice

Molecular and microscopic analysis of bacteria and viruses in exhaled breath collected using a simple impaction and condensing method

Exhaled breath condensate (EBC) is increasingly being used as a non-invasive method for disease diagnosis and environmental exposure assessment. By using hydrophobic surface, ice, and droplet scavenging, a simple impaction and condensing based collection method is reported here. Human subjects were recruited to exhale toward the device for 1, 2, 3, and 4 min. The exhaled breath quickly formed into tiny droplets on the hydrophobic surface, which were subsequently scavenged into a 10 µL rolling deionized water droplet. The collected EBC was further analyzed using culturing, DNA stain, Scanning Electron Microscope (SEM), polymerase chain reaction (PCR) and colorimetry (VITEK 2) for bacteria and viruses.Experimental data revealed that bacteria and viruses in EBC can be rapidly collected using the method developed here, with an observed efficiency of 100 µL EBC within 1 min. Culturing, DNA stain, SEM, and qPCR methods all detected high bacterial concentrations up to 7000 CFU/m(3) in exhaled breath, including both viable and dead cells of various types. Sphingomonas paucimobilis and Kocuria variants were found dominant in EBC samples using VITEK 2 system. SEM images revealed that most bacteria in exhaled breath are detected in the size range of 0.5-1.0 µm, which is able to enable them to remain airborne for a longer time, thus presenting a risk for airborne transmission of potential diseases. Using qPCR, influenza A H3N2 viruses were also detected in one EBC sample. Different from other devices restricted solely to condensation, the developed method can be easily achieved both by impaction and condensation in a laboratory and could impact current practice of EBC collection. Nonetheless, the reported work is a proof-of-concept demonstration, and its performance in non-invasive disease diagnosis such as bacterimia and virus infections needs to be further validated including effects of its influencing matrix.

Influenza virus in human exhaled breath: an observational study

Background

Recent studies suggest that humans exhale fine particles during tidal breathing but little is known of their composition, particularly during infection.

Methodology/Principal Findings

We conducted a study of influenza infected patients to characterize influenza virus and particle concentrations in their exhaled breath. Patients presenting with influenza-like-illness, confirmed influenza A or B virus by rapid test, and onset within 3 days were recruited at three clinics in Hong Kong, China. We collected exhaled breath from each subject onto Teflon filters and measured exhaled particle concentrations using an optical particle counter. Filters were analyzed for influenza A and B viruses by quantitative polymerase chain reaction (qPCR). Twelve out of thirteen rapid test positive patients provided exhaled breath filter samples (7 subjects infected with influenza B virus and 5 subjects infected with influenza A virus). We detected influenza virus RNA in the exhaled breath of 4 (33%) subjects–three (60%) of the five patients infected with influenza A virus and one (14%) of the seven infected with influenza B virus. Exhaled influenza virus RNA generation rates ranged from <3.2 to 20 influenza virus RNA particles per minute. Over 87% of particles exhaled were under 1 µm in diameter.

Conclusions

These findings regarding influenza virus RNA suggest that influenza virus may be contained in fine particles generated during tidal breathing, and add to the body of literature suggesting that fine particle aerosols may play a role in influenza transmission.

Exposure to ozone reduces influenza disease severity and alters distribution of influenza viral antigens in murine lungs

Exposure to ambient levels of ozone (0.5 ppm) was shown to alter the pathogenesis of respiratory infection after aerosol infection of mice with influenza A virus. A semiquantitative method for determination of the sites of virus replication by direct immunofluorescence indicated that exposure to ozone reduced the involvement of respiratory epithelium in the infectious process and resulted in a less widespread infection of the alveolar parenchyma. Furthermore, the ozone-mediated alteration in viral antigen distribution was consistent with significantly reduced influenza disease mortality and prolonged survival time, but only when the oxidant was present during the course of infection. Reduced disease severity in ozone-exposed animals appeared to be independent of peak pulmonary virus titers, pulmonary interferon titers, and pulmonary and serum-neutralizing antibody titers. These studies suggested that the distribution of influenza virus in the murine lung was a key factor in disease severity.

The spread and persistence of influenza viruses in normal and cyclophosphamide-treated mice

The persistence and extrapulmonary spread of three strains of influenza virus, the mouse neuro-adapted A/NWS virus, the wild-type strain A/Victoria/75, and a recombinant virus RIT4050, bearing surface antigens derived from A/Victoria/75, were studied in both normal and cyclophosphamide-treated CBA mice following either intranasal or intracerebral inoculation. All three viruses showed increased lethality in mice in the presence of cyclophosphamide but exhibited distinctive patterns of replication and spread. The recombinant virus RIT4050 showed a reduced ability to replicate, persist, and spread in CBA mice compared to either A/NWS or A/Victoria/75 viruses, and in general, the A/NWS virus persisted to a greater extent than the A/Victoria/75 virus in both normal and treated mice. However, in the presence of cyclophosphamide, no extrapulmonary spread of A/NWS virus was observed. The reasons for the differences are discussed.

Effects of low- and high-passage influenza virus infection in normal and nude mice

A human isolate of type A Hong Kong influenza virus (H3N2) was adapted to mice by serial passage. Lung homogenates from mice who received low passage levels contained about the same quantity of virus (10(6.2-6.95) 50% tissue culture infective doses/ml) as those from mice who received high passage levels (10(5.95-6.45) 50% tissue culture infective doses/ml); however, death occurred only in animals given high-passage virus. Passage 3 (P3) and passage 9 (P9) viruses were selected as representative of low-passage and high-passage viruses, respectively. Although minimal differences were detected in infectivity for rhesus monkey kidney tissue cultures and mice, P9 virus was at least 10,000 times more lethal for mice (mean lethal dose = 10(4.2)). Infection with P3 virus was accompanied by minimal bronchitis and bronchiolitis only, whereas P9-infected animals exhibited marked bronchitis, bronchiolitis, and pneumonia. Striking thymic cortical atrophy was also demonstrable in the P9-infected animals and, although virus was more commonly recovered from thymuses from these animals, immunofluorescent studies revealed only a few cells containing influenza virus antigens. To further explore the participation of thymus-derived lymphocytes in influenza, athymic nude mice and furred immunocompetent littermates were given 500 50% mouse infectious doses of P9 virus. Nude mice exhibited an increased survival time and, in contrast to the extensive lung pathology seen in furred littermates, manifested minimal cellular infiltration and no tissue destruction in lungs. Brains from nude mice exhibited encephalomalacia with lymphocytic perivascular cuffing, which was not seen in furred animals. Virus was recovered from brains of 6 of 13 nude mice and 1 of 10 furred animals. The contrasting models suggest that thymus-dependent cells play a significant role in the inflammatory response to influenza virus infection and should prove useful for probing host-virus interactions which characterize influenza virus virulence.

The destruction of type 2 pneumocytes by airborne influenza PR8-A virus; its effect on surfactant and lecithin content of the pneumonic lesions of mice

Influenzal pneumonia has been studied in mice subjected to sublethal doses of airborne PR8-A influenza virus. Electron microscopy revealed that the virus propagated in and at the same time destroyed the ciliated and nonciliated bronchial cells and the types 1 and 2 alveolar pneumocytes. The regenerating bronchial membranes were metaplastic and grew peripherally into the surrounding alveolar ducts and alveoli to form epithelial nodules which caused obstruction and collapse of the involved lobes. The development of the lung lesions was correlated with phospholipid (lecithin) levels in consolidated and unconsolidated infected and normal lungs. As the lungs became more and more consolidated, there was a corresponding and significant decrease in the amount of phospholipid (dipalmitoyl lecithin) compared to the amount of normal or unconsolidated infected tissue. The destruction of the type 2 pneumocytes by the influenza virus and their failure to regenerate is considered to be the reason for the low phospholipid levels in the involved lobes, and thus an important cause of post-influenzal collapse in mice. The above adds additional evidence to the view that the type 2 pneumocytes are a major source of surfactant in mammalian lungs.