ATTEMPTS to vaccinate against a bug that affects fish brains and causes 鈥渕ad
fish disease鈥� in humans have backfired.
The bacterium, called Streptococcus iniae, affects fish throughout
the world. In the 1990s, S. iniae infected 20 people in Canada, killing
one.
Trout farmers in Israel began vaccinating their fish against it in 1995. But
despite this, in 1997 there were massive outbreaks of a particularly nasty form
of the disease that affected other organs besides the brain. Now Avi Eldar of
the Kimron Veterinary Institute in Israel and his colleagues have shown that the
outbreak was caused by a new vaccine-resistant strain of the disease (
Applied and Environmental Microbiology, vol 67, p 3758).
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This strain probably evolved because of the evolutionary pressure induced by
the vaccine, the researchers report. It鈥檚 not known if it will be harder on
humans too.