The effect of age on the pathogenesis of a highly pathogenic avian influenza (HPAI) H5N1 virus in Pekin ducks (Anas platyrhynchos) infected experimentally

Abstract

Background Highly pathogenic avian influenza (HPAI) H5N1 viruses have recently displayed increased virulence for wild waterfowl. Objectives To study the effect of host age on the shedding and tissue dissemination of a HPAI H5N1 virus in infected Pekin ducks. Methods Pekin ducks in two age‐matched groups (n = 18), 8 and 12 weeks old (wo) were each infected with 106 EID50/0·1 ml of HPAI A/turkey/Turkey/1/05 (H5N1, clade 2·2). Each day for 5 days, birds were monitored clinically, and cloacal and oropharyngeal swabs collected, before three birds from each group were selected randomly for post‐mortem examination. Tissue samples were collected for examination by real‐time RT‐PCR, histopathology and immunohistochemistry (IHC). Results Severe clinical signs, including incoordination and torticollis were observed in the 8 wo group resulting in 100% mortality by 4 dpi. Mild clinical signs were observed in the 12 wo group with no mortality. Real‐time RT‐PCR and IHC results demonstrated the systemic spread of H5N1 virus in birds of both age groups. Higher levels of virus shedding were detected in oropharyngeal swabs than in cloacal swabs, with similar levels of shedding detected in both age groups. Variations in level and temporal dissemination of virus within tissues of older ducks, and the presence of the virus in brain and heart were observed, which coincided with the appearance of clinical signs preceding death in younger birds. Conclusions These results are consistent with reports of natural infections of wild waterfowl and poultry possibly indicating an age‐related association with dissemination and clinical outcome in ducks following infection with H5N1 HPAI virus.

The Effect of the PB2 Mutation 627K on Highly Pathogenic H5N1 Avian Influenza Virus Is Dependent on the Virus Lineage

“…Domesticated ducks are a known avian host of modern H5N1 HPAIVs. Ty/05/K WT virus was previously shown to readily infect 12-week-old Pekin ducks and was not lethal in birds of this age, although this virus was 100% lethal to 4-week-old Pekin ducks (45,48). Therefore, twelve 12-week-old Pekin ducks were infected with 10 6 EID 50 units of either Ty/05/K or Ty/05/E and five 4-week-old naive contact sentinel Pekin ducks were cohoused at 1 d.p.i.…”

“…At postmortem, tissue samples (including nasal turbinates, air sac, bursa, spleen, and gonad) were harvested and fixed in 10% buffered formalin. Four-micrometer-thick sections were stained with hematoxylin-eosin or used for immunohistochemical detection of influenza A virus nucleoprotein as previously described (48). Briefly, sections for immunohistochemistry (IHC) were dewaxed in xylene and passed through graded alcohols to Tris-buffered saline (TBS) solution (0.005 M Tris, pH 7.6, 0.85% [wt/vol] NaCl).…”

Pathogenicity and Transmission of H5 and H7 Highly Pathogenic Avian Influenza Viruses in Mallards

“…Although the Ws/Mongolia/05 (H5N1) virus belongs to the clade 2.2 H5N1 viruses that spread from Asia into Europe in 2005, it is not representative of all viruses from this clade. Viruses from clade 2.2 were reported to cause mortality in wild waterfowl (6,7,57), but differences in pathogenicity have been described between viruses examined experimentally in domestic ducks (53,(57)(58)(59)(60)(61), indicating that ducks could become infected with these viruses and not necessarily show clinical signs but still shed large amounts of virus and transmit virus efficiently.…”

Effect of species, breed and route of virus inoculation on the pathogenicity of H5N1 highly pathogenic influenza (HPAI) viruses in domestic ducks

“…Trying to emulate natural exposure, ducks were infected by inoculating virus simultaneously via the cloaca, trachea, throat, nares and eyes [7,45,46]. Simultaneous inoculation by the IN and intraocular (IO) routes, or IN, IO and through the mouth, has also been used to infect ducks with H5N1 HPAI virus [1,47,48], and wild ducks were infected with a H5N1 HPAI virus after simultaneous inoculation by the intratracheal and intraesophageal routes [9]. Infection with a H5N1 HPAI virus caused morbidity and mortality in domestic ducks after ingestion of infected meat and inoculation by the intragastric and IN routes [49].…”