Intracerebral pathogenicity for chickens of avian influenza viruses isolated from free-living waterfowl in Japan

Neuraminidase-associated plasminogen recruitment enables systemic spread of natural avian Influenza viruses H3N1

Repeated outbreaks due to H3N1 low pathogenicity avian influenza viruses (LPAIV) in Belgium were associated with unusually high mortality in chicken in 2019. Those events caused considerable economic losses and prompted restriction measures normally implemented for eradicating high pathogenicity avian influenza viruses (HPAIV). Initial pathology investigations and infection studies suggested this virus to be able to replicate systemically, being very atypical for H3 LPAIV. Here, we investigate the pathogenesis of this H3N1 virus and propose a mechanism explaining its unusual systemic replication capability. By intravenous and intracerebral inoculation in chicken, we demonstrate systemic spread of this virus, extending to the central nervous system. Endoproteolytic viral hemagglutinin (HA) protein activation by either tissue-restricted serine peptidases or ubiquitous subtilisin-like proteases is the functional hallmark distinguishing (H5 or H7) LPAIV from HPAIV. However, luciferase reporter assays show that HA cleavage in case of the H3N1 strain in contrast to the HPAIV is not processed by intracellular proteases. Yet the H3N1 virus replicates efficiently in cell culture without trypsin, unlike LPAIVs. Moreover, this trypsin-independent virus replication is inhibited by 6-aminohexanoic acid, a plasmin inhibitor. Correspondingly, in silico analysis indicates that plasminogen is recruitable by the viral neuraminidase for proteolytic activation due to the loss of a strongly conserved N-glycosylation site at position 130. This mutation was shown responsible for plasminogen recruitment and neurovirulence of the mouse brain-passaged laboratory strain A/WSN/33 (H1N1). In conclusion, our findings provide good evidence in natural chicken strains for N1 neuraminidase-operated recruitment of plasminogen, enabling systemic replication leading to an unusual high pathogenicity phenotype. Such a gain of function in naturally occurring AIVs representing an established human influenza HA-subtype raises concerns over potential zoonotic threats.

The nucleoprotein is responsible for intracerebral pathogenicity of A/duck/Mongolia/47/2001 (H7N1) in chicks

Avian influenza viruses A/duck/Mongolia/47/2001 (H7N1) (47/01) and A/duck/Mongolia/867/2002 (H7N1) (867/02) were defined as low-pathogenic avian influenza viruses (LPAIVs) using an intravenous pathogenicity test in chickens. On the other hand, the intracerebral pathogenicity indices of 47/01 and 867/02 were 1.30 and 0.00, respectively. A series of reassortant viruses were generated between 47/01 and 867/02, and their intracerebral pathogenicity was compared in one-day-old chicks to identify the protein(s) responsible for the intracerebral pathogenicity of 47/01. The results indicate that the amino acids at positions 50 and 98 of the nucleoprotein are related to the pathogenicity of 47/01 in chicks by intracerebral inoculation. A significant association was found between mortality of the chicks inoculated intracerebrally with 47/01 and virus replication in the lungs and/or brain. These results indicate that the NP of avian influenza viruses may be responsible for intracerebral pathogenicity in the host.

Development of a new disinfectant with very strong anti-influenza viral activity: a preliminary report

OBJECTIVES

We evaluated the effectiveness and safety of a disinfectant newly developed by our laboratories for use against influenza viruses.

METHODS

The effectiveness of our new disinfectant against avian, swine and human influenza viruses was tested in ovo. The acute toxicity of this disinfectant to two different cultured cell lines was investigated.

RESULTS

This new disinfectant showed very strong anti-influenza viral activity in the in ovo tests. All of the influenza viruses tested were inactivated very quickly. Following exposure to the disinfectant, the infectivity of all viral strains tested had been eliminated within ≤10 min. The infectant showed a weak acute toxicity in vitro.

CONCLUSION

This new disinfectant is expected to be useful for preventing viral infection during a new influenza pandemic.

The infection of primary avian tracheal epithelial cells with infectious bronchitis virus

Here we introduce a culture system for the isolation, passaging and amplification of avian tracheal epithelial (ATE) cells. The ATE medium, which contains chicken embryo extract and fetal bovine serum, supports the growth of ciliated cells, goblet cells and basal cells from chicken tracheas on fibronectin- or matrigel-coated dishes. Non-epithelial cells make up less than 10% of the total population. We further show that ATE cells support the replication and spread of infectious bronchitis virus (IBV). Interestingly, immunocytostaining revealed that basal cells are resistant to IBV infection. We also demonstrate that glycosaminoglycan had no effect on infection of the cells by IBV. Taken together, these findings suggest that primary ATE cells provide a novel cell culture system for the amplification of IBV and the in vitro characterization of viral cytopathogenesis.

Pathogenesis of pancreatic atrophy by avian influenza a virus infection

Specific-pathogen-free (SPF), 2-day-old chicks were inoculated with type A influenza virus (A/whistling swan/Shimane/499/83/(H5N3)) into their caudal thoracic air sac. The original isolate of the virus was of low virulence (ICPI 0. 20 to 0.40), and was passaged 10 times through the respiratory organs of SPF chicks. Most of the chicks inoculated with the passaged virus (strain 499) showed respiratory and alimentary signs. Three of 30 chicks died on days 2, 6 and 7 post-inoculation (p.i.). Almost half of the infected chicks showed poor growth, and the variation of body size in the flock became prominent from day 10 p.i. Infected chicks consistently had pathological changes in the pancreas, liver, kidneys and respiratory tracts, and occasionally in the brain, duodenum and bone marrow. Positive immunoreaction to avian influenza virus (AIV) antigen and recovery of the virus persisted for longer period in the pancreas than in other organs. The pancreatic lesions were caused by a direct, lytic virus infection of the acinar cells and contributed to poor growth of the chicks.

Strong antiviral activity of heated and hydrated dolomite--preliminary investigation

Heated and hydrated naturally occurring dolomite showed very strong antiviral activity. Infectivity of avian and human influenza, avian infectious bronchitis (coronavirus), Newcastle disease (paramyxovirus) and avian laryngotracheitis (herpesvirus) viruses dropped at least 1,000 fold following contact with the dolomite for five minutes at 4 degrees C. Dolomite is expected to be useful to inhibit the incidence of emerging and re-emerging infectious diseases.

Generation of a highly pathogenic avian influenza A virus from an avirulent field isolate by passaging in chickens

Highly virulent avian influenza viruses can arise from avirulent strains maintained in poultry, but evidence to support their generation from viruses in wild birds is lacking. The most likely mechanism for the acquisition of virulence by benign avian viruses is the introduction of mutations by error-prone RNA polymerase, followed by the selection of virulent viruses. To investigate whether this mechanism could apply to wild waterfowl, we studied an avirulent wild-swan virus that replicates poorly in chickens. After 24 consecutive passages by air sac inoculation, followed by five passages in chicken brain, the avirulent virus became highly pathogenic in chickens, producing a 100% mortality rate. Sequence analysis at the hemmaglutinin cleavage site of the original isolate revealed a typical avirulence type of sequence, R-E-T-R, which progressed incrementally to a typical virulence type of sequence, R-R-K-K-R, during repeated passages in chickens. These results demonstrate that avirulent viruses maintained in wild waterfowl in nature and bearing the consensus avirulence type sequence R-E-T-R have the potential to become highly pathogenic while circulating in chickens.

Encephalitis in mice inoculated intranasally with an influenza virus strain originated from a water bird

Five-week-old ddY mice were inoculated intranasally with a low virulent (4e) or highly virulent (24a5b) avian influenza virus strain originated from a water bird. None of mice in the 4e group showed clinical signs and brain lesions. Of the 24a5b group, two mice died and one mouse was killed at a moribund state at day 7 post-inoculation (PI). Four mice of the 24a5b group necropsied at day 5 or 7 PI had mild to severe encephalitis in the brain stem and the cerebellar white matter. Influenza virus antigen was detected in neurons, glial cells and vascular endothelium in the lesions. The distribution of the lesions seems to indicate the transneuronal invasion of the virus via cranial nerve fibers into the brain.

Avian influenza A virus induced stunting syndrome-like disease in chicks

Two-day-old specific-pathogen free chicks were inoculated with type A influenza virus (A/whistling swan/Shimane/499/83 (H5N3) through the air sac. Inoculated chicks showed mild to severe diarrhea and lesions of pancreatitis and atrophy of the pancreas, thymus and bursa of Fabricius. One chick died on each of days 4, 6 and 14 postinoculation (PI). Reduced weight gain was conspicuous from day 22 PI. Positive immunoreaction to the virus antigen was detected in the pancreas, kidneys, liver, lungs and air sacs, and cecal lamina propria. Virus recovery persisted longer in the pancreas. Some of these findings conformed to those of stunting syndrome.

Enhanced neuropathogenicity of avian influenza A virus by passages through air sac and brain of chicks

Three-day-old, specific-pathogen-free (SPF) chicks were inoculated with the strains of influenza A/whistling swan/Shimane/ 499/83 (H5N3) via the air sac route. The strains had been passaged through air sacs or air sacs and brains of SPF chicks. Two experiments were undertaken to examine the pathogenicity of these strains and the development of brain lesions based on time-interval changes. In experiment 1, original strain (4e) showed low pathogenicity with mild respiratory signs and zero mortality. Air sac passaged strains (18a and 24a) of 4e demonstrated mortalities of 50% and 67%, respectively, and inoculated chicks showed hemorrhages and necrotic lesions in major organs. Air sac-brain passaged strain (24a5b) of 4e produced 100% mortality and severe nervous signs. Severe circulatory disturbance with multiple foci of necrosis in major organs including the brain was found in chicks inoculated with 24a5b. The 24a5b was analogous to highly pathogenic avian influenza virus in regard to its pathogenicity to chicks. Hence, low pathogenic influenza virus (4e) gradually aggravated its pathogenicity to highly pathogenic virus (24a5b) by air sac and brain passages. In experiment 2, chicks were inoculated with 24a5b, and the earliest histological lesion was the enlargement of the vascular endothelial cells at 18 hr post-inoculation (PI) followed by necrotizing encephalitis at 24 to 48 hr PI. Immunohistological staining revealed avian influenza virus antigen initially in the vascular endothelial cells and then in the astrocytes, neurons and ependyma.