ORIGINAL ARTICLE Infection of Chickens Caused by Avian Influenza Virus A/H5N1 Delivered by Aerosol and Other Routes Ar. A. Sergeev 1 , O. K. Demina 1 , O. V. Pyankov 1,2 , O. G. Pyankova 1,2 , A. P. Agafonov 1 , S. A. Kiselev 1 , I. E. Agranovski 2 , Al. A. Sergeev 1 , A. N. Shikov 1 , L. N. Shishkina 1 , A. S. Safatov 1 and A. N. Sergeev 1 1 State Research Centre of Virology and Biotechnology ‘‘Vector’’, Koltsovo, Novosibirsk region, Russia 2 Griffith School of Engineering, Griffith University, Brisbane, Qld, Australia Introduction Avian influenza virus (AIV) A subtype H5N1 has been the cause of mass death of wild birds and fatalities in humans [The Writing Committee of the World Health Organization (WHO) Consultation on Human Influenza A/H5 (2005)]. This subtype can potentially infect a broad range of species of wild birds and poultry (Chen et al., 2009). The disease severity can vary depending on avian species affected (Kim et al., 2009; Saito et al., 2009; Spackman et al., 2009). In chickens, AIV causes a severe disease with multi-organ affection and lethal outcome (Chen et al., 2009; Muramoto et al., 2006; Nakamura et al., 2008). The AIV transmission is quite efficient from infected chickens to healthy ones, resulting in rapid disease spread within poultry farms (Chen et al., 2009). Also, some authors have highlighted the risk of the virus transmis- sion from chickens to humans; in the latter, the disease is very severe and has a lethal outcome in more than 60% of cases (Shortridge et al., 1998; Vong et al., 2008; WHO, 2009). In addition, there is a danger of emergence of new AIV variants because of the high rate of mutation, which could increase the efficiency of transmission from human to human (Swayne and Slemons, 2008). Among the known ways of virus transmission, aerosol and faecal–oral routes are considered to be the most effi- cient as they allow the virus to quickly spread across the population (Mims et al., 2001; Pantin-Jackwood and Swayne, 2009; Rohani et al., 2009). Recently, Kwon and Swayne, 2010 demonstrated that chickens and ducks were more susceptible to the intranasal delivery of AIV H5N1 compared with the alimentary routes of inoculation (in- tragastric or oral-fed infected chicken meat). Some authors do not exclude the importance of aerosol trans- mission of this virus within chicken populations (Antara- sena et al., 2006; Shortridge et al., 1998). A number of studies showed that AIV could be accumulated in Keywords: Avian influenza; respiratory transmission; A/ H5N1 aerosol infecting dose Correspondence: I. E. Agranovski, Griffith School of Engineering, Griffith University, Brisbane, 4111 Qld, Australia. Tel.: +617 3735 7923; Fax: +617 3735 7459; E-mail: i.agranovski@griffith.edu.au Received for publication January 10, 2012 doi:10.1111/j.1865-1682.2012.01329.x Summary This study presents results of the study of infectivity of avian influenza virus (AIV) A subtype H5N1 strains isolated from agricultural birds across the terri- tory of the Russian Federation and CIS countries. The results of the susceptibil- ity of chickens to the AIV isolates delivered by the aerosol route and the dissemination of the virus in the organs of infected birds are presented. As was observed, the sensitivity of birds to AIV by the aerosol route of infection is 30 times higher than by intranasal route, 500 times higher than by the oral route and 10 000 times higher than by the intragastric route of infection, which is indicative of higher permissivity of respiratory organs to AIV. The highest titres of AIV A subtype H5N1(A/Chicken/Kurgan/05/2005 strain) in aerosol-infected chickens were found in nasal cavity mucosa, lungs, cloaca, serum and kidney, where viable virus accumulation was detected by 18 h post-infection (p.i.). The highest virus titres were observed 54 h p.i. in lungs, serum and kidney, reach- ing the value of 8.16 lg EID 50 /g(ml) in the lungs. The results showed that birds infected by the aerosol route developed higher titres of virus than those infected by other routes. Transboundary and Emerging Diseases ª 2012 Blackwell Verlag GmbH • Transboundary and Emerging Diseases. 1