Biochemie

These hubs and nodes, they said, are so concentrated and yet so connected that eradicating any
sexually transmitted disease requires concentrated efforts at the hubs. As in any computer network -- or a
chain of Christmas lights --interrupting the flow of information or electricity at a hub can cause flows to
cease network wide.
So too, Barabasi and Deszo claim, with AIDS. Slow or stop the disease at a hub, they said, and you
severely reduce its ability to spread anywhere else.
"We are indeed familiar with the results by Barabasi and co-workers and are certainly excited by all the
developments coming out," Luis Amaral told United Press International. "We believe that the new focus
on the possibility of characterizing the structure of networks could help the understanding of epidemics
both for human and animal diseases."
The discovery of this new pattern of epidemic transmission is a major step in a worldwide effort. Amaral
and Stanley revealed humans engage in "scale-free" patterns of intimacy: A very few individuals have the
largest number of sexual contacts.
Sociologists and epidemiologists previously had taken for granted the idea that human sexual activity
followed a standard bell-shaped curve: The largest clusters of people would have an average number of
sexual contacts with very few people engaging in either very few or very many sexual encounters at
either ends of the curve.
Instead, the Boston researchers found a curve that gradually curves upward and keeps rising. Most
surprising, a very few 10 percent of men have 48 percent of all sexual encounters, a pattern more like the
distribution of wealth where 1 percent of people control 95 percent of all assets.
Capitalizing on this discovery, Spanish scientists Yamir Moreno, Romualdo Pastor-Satorras and
Alessandro Vespignani showed that "scale-free" transmission patterns allow even the weakest infective
diseases to spread unchecked. The frightening upshot is that given the scale-free pattern of human
sexual contact, "short of a cure or vaccine available to all, the HIV virus will eventually reach the so far
uninfected segments of the population exposed to the disease," Barabasi explained in a recent paper on
the topic.
Now Barabasi imposes a network architecture on AIDS transmission patterns. "Epidemics spread without
a threshold on a scale-free network thanks to hubs and nodes with an unexpectedly large number of
links," Barabasi said. "Once infected, hubs offer an efficient conduit for disease spreading by reaching an
unusually high percentage of other nodes."
As a result, anything less than attacking the disease at its hub represents random treatments that cannot
contain the epidemic because, Barabasi said, they "leave the scale-free nature of the network unaltered."
Mit Netzwerksimulationen konnte man nachweisen, dass grosse Knoten im
Luftverkehrsnetz, wie London, New York oder Frankfurt, für eine rapide weltweite
Ausbreitung einer Epidemie verantwortlich sind - und das weitest gehend unabhängig
vom Ort des ersten Auftretens eines Krankheitserregers. Dabei ist die Kapazität des
Flughafens an einem Knotenpunkt viel weniger entscheidend als der Grad seiner
Vernetzung.
Strategie der Natur:
Sie Stoffwechselprozesse der Natur müssen sehr stabil sein, daher sind Scale-Free-
Netzwerke häufig anzutreffen.
Bewährte Strukturen sind in den Hubs immer wieder anzutreffen, wie z.B. die
Hämgruppe in Hämoglobin, Myoglobin, Cytochrom, Catalase etc..
Chemie, 6sm
33