Severity of pneumonia due to new H1N1 influenza virus in ferrets is intermediate between that due to seasonal H1N1 virus and highly pathogenic avian influenza H5N1 virus.
BACKGROUND
The newly emerged influenza A(H1N1) virus (new H1N1 virus) is causing the first influenza pandemic of this century. Three influenza pandemics of the previous century caused variable mortality, which largely depended on the development of severe pneumonia. However, the ability of the new H1N1 virus to cause pneumonia is poorly understood.


METHODS
The new H1N1 virus was inoculated intratracheally into ferrets. Its ability to cause pneumonia was compared with that of seasonal influenza H1N1 virus and highly pathogenic avian influenza (HPAI) H5N1 virus by using clinical, virological, and pathological analyses.


RESULTS
Our results showed that the new H1N1 virus causes pneumonia in ferrets intermediate in severity between that caused by seasonal H1N1 virus and by HPAI H5N1 virus. The new H1N1 virus replicated well throughout the lower respiratory tract and more extensively than did both seasonal H1N1 virus (which replicated mainly in the bronchi) and HPAI H5N1 virus (which replicated mainly in the alveoli). High loads of new H1N1 virus in lung tissue were associated with diffuse alveolar damage and mortality.


CONCLUSIONS
The new H1N1 virus may be intrinsically more pathogenic for humans than is seasonal H1N1 virus.
van den Brand
Judith M A
JM
Department of Virology, Erasmus Medical Centre, Rotterdam, The Netherlands.
Stittelaar
Koert J
KJ
van Amerongen
Geert
G
Rimmelzwaan
Guus F
GF
Simon
James
J
de Wit
Emmie
E
Munster
Vincent
V
Bestebroer
Theo
T
Fouchier
Ron A M
RA
Kuiken
Thijs
T
Osterhaus
Albert D M E
AD
D000704:Analysis of Variance; D000818:Animals; D001831:Body Temperature; D001835:Body Weight; D002460:Cell Line; D005260:Female; D005289:Ferrets / Q000821:virology*; D007150:Immunohistochemistry; D053118:Influenza A Virus, H1N1 Subtype / Q000472:pathogenicity*; D053124:Influenza A Virus, H5N1 Subtype / Q000472:pathogenicity*; D008168:Lung / Q000473:pathology / Q000821:virology; D008297:Male; D009929:Organ Size; D009976:Orthomyxoviridae Infections / Q000662:veterinary* / Q000821:virology; D011024:Pneumonia, Viral / Q000662:veterinary* / Q000821:virology; D012720:Severity of Illness Index; D019562:Viral Load