Animal Studies of New H1N1 Show More Severe Lung Symptoms Than Seasonal Flus

July 5, 2009(LPAC)—Two new animal studies published today in the online edition of Science magazine indicate that the H1N1 (swine) influenza can cause more serious lung disease than seasonal flu strains.

According to the studies carried out at Erasmus Medical Center in the Netherlands and an MIT/Centers for Disease Control study in the U.S., the virus can shed infective material from the lung and throat tissue, where it reproduces at higher rates than ordinary seasonal flus.

The studies, carried out in ferrets and mice, may explain the appearance of severe pneumonia in autopsies of swine flu victims, as well as the rapid spread of the virus.

The Netherlands team found the new swine flu caused worse infection than seasonal flu in the laboratory animals, and warned of more severe clinical consequences in the human population, as the pandemic spreads. "Replication of seasonal A(H1N1) virus was confined to the nasal cavity of ferrets, but the 2009 A(H1N1) influenza virus also replicated in the trachea, bronchi, and bronchi oles," the study reports. "Virus shedding was more abundant from the upper respiratory tract for 2009 A(H1N1) influenza virus by comparison with seasonal virus, and transmission via aerosol or respiratory droplets was equally efficient."

The MIT/CDC team also found more severe lung infection among the laboratory ferrets infected with the new H1N1, as opposed to seasonal strains, but they found the rate of droplet transmission to be slightly lower for the new swine flu. They warned, however, that further changes could cause the H1N1 transmissibility to increase.

The fact that the H1N1 strain is already established in the Northern Hemisphere off-season, adds to its danger.