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July 2 (Bloomberg) -- Swine flu caused more-severe illness in ferrets than seasonal flu, according to two studies in the journal Science that help explain why the H1N1 virus causes symptoms not seen in regular flu such as nausea and vomiting.
The H1N1 swine flu virus went further into the ferrets’ lungs, and also penetrated the gastrointestinal tract while seasonal flu stayed in the nasal cavity, researchers from the U.S. and the Netherlands found. Ferrets are affected by flu viruses much as humans are, the researchers said.
Swine flu has struck at least 77,201 people in 113 nations worldwide, killing 332, according to laboratory-confirmed reports compiled by the World Health Organization, which has declared the first flu pandemic since 1968. While the virus causes little more than a fever and cough in most people, a previous study showed that about 40 percent of those infected have developed symptoms such as diarrhea, vomiting and nausea.
“These data suggest that the 2009 A(H1N1) influenza virus has the ability to persist in the human population, potentially with more severe clinical consequences,” wrote the Dutch study authors, led by Ron Fouchier at the Erasmus Medical Center in Rotterdam.
The two studies were published online today. Both groups found that ferrets infected with swine flu lost more weight than those exposed to seasonal flu, and that the swine flu virus was more widespread in the animals’ bodies.
When they examined the transmissibility of the virus, the two groups found conflicting evidence. Fouchier and colleagues, who used a strain of swine flu taken from the first person infected in the Netherlands, said ferrets passed it to each other through the air as easily as seasonal flu.
The U.S. researchers, led by Terrence Tumpey at the Atlanta-based Centers for Disease Control and Prevention, said the ferrets in their study didn’t transmit the swine flu strains they used, taken from patients in California, Texas and Mexico, as efficiently as seasonal flu strains.
Swine flu doesn’t latch on to healthy cells in the human respiratory tract as easily as seasonal flu because of a genetic mutation, the CDC researchers said.
Inefficient transmission suggests the virus would need to mutate to become as transmissible as seasonal flu or the 1918 pandemic virus, they said.