But even exit screening, he says, is unlikely to have much effect because of the virus' long incubation period.

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One security watcher saw a long-term effect of the Melissa virus.

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Limiting travel and imposing travel restrictions would have very little effect on stopping the virus from spreading, but would be highly disruptive to the global community.

UNESCO: CONFINTEA VI

The Israeli acute paralysis virus (and, perhaps, the mystery virus) may have had such a devastating effect there because of the presence of a parasite called the varroa mite.

ECONOMIST: A virus may help explain colony collapse disorder

And third, by failing to breast-feed, a mother in many parts of Africa is in effect announcing that she has the virus, and thus exposing herself to both stigma and discrimination.

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Worse, the worm can "lobotomize" anti-virus software, Corman says, so that it appears to be running but has no effect.

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LONDON, England (CNN) -- British airlines have put into effect measures to stop people with swine flu boarding flights in a bid to prevent the virus from spreading further.

CNN: Airlines stop swine flu victims flying

Separately they have little effect, but together they prevent hep-C from spreading by causing it to make defective virus cells.

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