A parasite that was considered 'harmless' for years just suddenly wiped out half of a massive clam population.
April 17, 2026
Original Paper
First Report of Perkinsus olseni-Induced Mass Mortality in Manila Clams (Ruditapes philippinarum) in China
SSRN · 6591903
The Takeaway
In marine biology, the parasite Perkinsus olseni was generally seen as a minor nuisance, but not a killer. That changed when it caused a 'mass mortality event,' killing off 50% of the Manila clams in a single area in China. This is a huge shock because it shatters the 'benign parasite' paradigm that scientists had relied on for management. It shows that parasites we think are safe can suddenly turn lethal, likely due to environmental stress or mutation. For regular people, this is a warning sign of how fragile our food systems are; a 'harmless' bug today could be the reason your seafood prices double tomorrow.
From the abstract
Perkinsus olseni infections in Chinese mollusks have historically shown high prevalence but low intensity with no associated mortality. In August 2025, mass mortality (~50%) occurred in cultured Manila clams (Ruditapes philippinarum) in Nantong, China. Affected clams exhibited significantly higher infection intensity (mean >2.0 vs. 1.0; P < 0.01) and lower condition index (P < 0.0001) than healthy clams. Histopathology confirmed trophozoite aggregation in vital tissues. ITS sequencing identified