Enhanced Neuropathogenicity of Avian Influenza A Virus by Passages through Air Sac and Brain of Chicks.

Abstract

ABSTRACT. 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 postinoculation (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. -KEY WORDS: avian influenza virus, chick, neuropathogenicity, passaged-strain.

Primary target cells of virulent strains of type A influenza virus in chicken embryos

“…The major gross pathological findings in chickens infected with highly pathogenic influenza viruses are petechial to ecchymotic haemorrhages in the skin and on the serosa of visceral organs, widespread subcutaneous oedema, and ischaemic necrosis of the comb and wattles (Easterday et al, 1997). Histologically, these chickens show severe injuries to the vascular system including necrosis, vasculitis, and thrombosis (Acland et al, 1984;Brown et al, 1992;Hooper et al, 1995;Kobayashi et al, 1996;Silvano et al, 1997). In our study, although the embryos infected with virulent viruses Primary target cells of AIV 271 did not show the pathological changes seen in chickens, the tropism of the virulent viruses for vascular endothelial cells is common to both embryos and chickens.…”

“…Each group of 21 embryos was inoculated intra-allantoically with 0.1 ml (10 4 median embryo infective dose (EID 5 0 /ml) of one of four strains of virulent influenza virus: A/tern/South Africa/61 (H5N3; Tern/ SA) (Uys & Becker;1967), A/whistling swan/Shimane/499/83 (H5N3; 24a5b) (Silvano et al, 1997), A/Hong Kong/483/97 (H5N1; HK483) or A/Hong Kong/156/97 (H5N1; HK156) (Suarez et al, 1998). Fourteen embryos were inoculated with 0.1 ml (10 4 EID 5 0 /ml) of the avirulent strain A/duck/Pennsylvania/10128/84 (H5N2; Dk/Penn).…”

Encephalitis in Mice Inoculated Intranasally with an Influenza Virus Strain Originated from a Water Bird.

“…This virus was passaged in the brain of chicks five times after 24 serial passages in the air sac of chicks (strain 24a5b). The strain 24a5b produced 100% mortality in chicks [12]. Virulence of the 24a5b was compared with the original virus passaged in embryonated eggs four times (4e).…”

Evaluation of the Reverse Transcription Loop-Mediated Isothermal Amplification (RT-LAMP) as a Screening Method for the Detection of Influenza Viruses in the Fecal Materials of Water Birds

“…However, highly pathogenic avian influenza viruses (HPAIVs) replicate in multiple tissues and lead to a high mortality in chickens. HPAIVs are selected during multiple transmissions in chicken populations [1,10,13,15,25]. When highly pathogenic avian influenza (HPAI) outbreaks occur in poultry, depopulation of affected flocks is the standard strategy for the control of HPAI.…”