During the last two decades, more than 100 cattle deaths have been
reported from 11 alpine sites in south-eastern Switzerland.
Pathological findings and the histological examination of their organs
strongly indicated acute hepatotoxicosis. Clinical symptoms
suggestive of neurotoxicity were also observed in some cases. To elucidate the
etiology of these poisonings, different water bodies in
one of the affected alpine pastures were investigated for cyanobacterial toxins.
The waters were highly oligotrophic, cold and turbid, and
the ice-free period was limited to 3–4 months. The algal community in
these waters consisted mostly of benthic cyanobacteria forming
dense mats on the surface of sediments and on submerged rocks. Oscillatoria
limosa and Phormidium konstantinosum (=Oscillatoria tenuis)
dominated these populations, but occasionally other species of
Oscillatoria, Phormidium, Tychonema and
Pseudanabaena also occurred in the
mats. Samples from the cyanobacterial mats yielded positive results in a
protein phosphatase inhibition assay, reacted with antibodies
against microcystins in an enzyme-linked immunosorbent assay and were
hepatotoxic in a mouse bioassay. The same cyanobacterial
material also included neurological effects in mice. High-performance
liquid chromatography was used to identify a microcystin, in these
cyanobacterial samples as well as in the corresponding lake water. To our
knowledge, this is the first documented example of
hepatotoxicity associated with benthic cyanobacteria, and the first report
of toxic cyanobacteria from the remote, oligotrophic alpine environment.
