Fatal Neurotoxicosis in Dogs Associated with Tychoplanktic, Anatoxin-a Producing Tychonema sp. in Mesotrophic Lake Tegel, Berlin

Abstract

In May 2017, at least 12 dogs showed signs of acute neurotoxicosis after swimming in or drinking from Lake Tegel, a mesotrophic lake in Berlin, Germany, and several of the affected dogs died shortly afterwards despite intensive veterinary treatment. Cyanobacterial blooms were not visible at the water surface or the shorelines. However, detached and floating water moss (Fontinalis antipyretica) with high amounts of Tychonema sp., a potential anatoxin-a (ATX) producing cyanobacterium, was found near the beaches where the dogs had been swimming and playing. Necropsies of two of the dogs revealed no specific lesions beside the anamnestic neurotoxicosis. ATX was detected in concentrations up to 8700 µg L^-1 in the stomach contents, while other (neuro)toxic substances were not found. In the aqueous fraction of Fontinalis/Tychonema clumps sampled after the casualties, ATX was found in concentrations up to 1870 µg L^-1. This is the first report of a dense population of Tychonema sp. in stands of Fontinalis resulting in high ATX contents. This case emphasizes the need for further investigation of potentially toxic, non-bloom forming cyanobacteria in less eutrophic water bodies and underlines the novel challenge of developing appropriate surveillance schemes for respective bathing sites.

Keywords: Tychonema; anatoxin-a; cyanobacteria; cyanotoxins; macrophytes; neurotoxicosis.

Figure 1

(a) Water moss (Fontinalis antipyretica) floating on the surface of Lake Tegel (2 June 2017); (b–d) Tychonema sp. filaments within water moss clumps (b: 2 June 2017; c-d: 6 June 2017; b: ×100; c: ×400, d: ×1000); (e) Tychonema sp. filament observed in the stomach contents of a dead dog (×200).

Figure 2

Reconstructed LC-MS/MS chromatograms of (a) certified reference standards; (b) the aqueous fraction from Fontinalis/Tychonema clumps from Reiherwerder, 6 June 2017 (WT1, Table 2); (c) the stomach contents of dog D1 (Table 2). The blue lines show the transitions indicative for cylindrospermopsin; red, orange and yellow lines show transitions for anatoxin-a.