Frio Nature Conservancy
H1N1 Flu (Swine Flu)

The virus is being transmitted person to person.
The Frio Nature Conservancy is reviewing and tracking the virus for any indication
that it is being transmitted by mosquitoes.
The information, below, is that being reported by the CDC and World Health
Organization and is provided here for your information.
either humans or animals. Although firm conclusions cannot be reached at present, scientists anticipate
that pre-existing immunity to the virus will be low or non-existent, or largely confined to older population

H1N1 appears to be more contagious than seasonal influenza. The secondary attack rate of seasonal
influenza ranges from 5% to 15%. Current estimates of the secondary attack rate of H1N1 range from 22% to

With the exception of the outbreak in Mexico, which is still not fully understood, the H1N1 virus tends to
cause very mild illness in otherwise healthy people. Outside Mexico, nearly all cases of illness, and all
deaths, have been detected in people with underlying chronic conditions.

In the two largest and best documented outbreaks to date, in Mexico and the United States of America, a
younger age group has been affected than seen during seasonal epidemics of influenza. Though cases
have been confirmed in all age groups, from infants to the elderly, the youth of patients with severe or
lethal infections is a striking feature of these early outbreaks.

In terms of population vulnerability, the tendency of the H1N1 virus to cause more severe and lethal
infections in people with underlying conditions is of particular concern.

For several reasons, the prevalence of chronic diseases has risen dramatically since 1968, when the last
pandemic of the previous century occurred. The geographical distribution of these diseases, once
considered the close companions of affluent societies, has likewise shifted dramatically. Today, WHO
estimates that 85% of the burden of chronic diseases is now concentrated in low- and middle-income
countries. In these countries, chronic diseases show an earlier average age of onset than seen in more
affluent parts of the world.

In these early days of the outbreaks, some scientists speculate that the full clinical spectrum of disease
caused by H1N1 will not become apparent until the virus is more widespread. This, too, could alter the
current disease picture, which is overwhelmingly mild outside Mexico.

Apart from the intrinsic mutability of influenza viruses, other factors could alter the severity of current
disease patterns, though in completely unknowable ways, if the virus continues to spread.

Scientists are concerned about possible changes that could take place as the virus spreads to the
southern hemisphere and encounters currently circulating human viruses as the normal influenza season
in that hemisphere begins.
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