New Parasite Discovered in the European Sardine, One of the Most Widely Consumed Species in the Atlantic

A team of researchers from the University of Navarra has identified, for the first time, the presence of a microsporidian of the genus Glugea infecting the European sardine (Sardina pilchardus), one of the most commercially and nutritionally important fish species in the Atlantic.

The finding, published in the journal *Life*, describes a new association detected in sardines from an Atlantic fishery. The researchers observed whitish cysts measuring between 5 and 20 mm in the fish’s visceral cavity, containing millions of spores of a microorganism belonging group —intracellular parasites capable of infecting a wide variety of animals.

To characterize the organism, the team combined optical microscopy, histology, electron microscopy, and molecular analysis. The results show that the parasite shares some characteristics with other species of the genus Glugea, but exhibits unique morphological and ultrastructural features that distinguish it from the taxa described to date.

“This work for the first time the presence of a microsporidian from this group the European sardine and expands our knowledge the parasites that affect a species of great ecological and commercial importance,” says Enrique Baquero, researcher the BIOMA Institute for Biodiversity and the Environment at the University of Navarra.

research implications for Economics health
This finding have implications for the fishing industry. Various species of the genus Glugea have historically been linked to health problems in populations of other fish species, and even to the decline of commercial fisheries. The researchers emphasize that the emergence of infections in species caught in the open ocean warrants special monitoring, as controlling them is much more complex than in aquaculture systems.

The study also addresses the potential implications from a One Health perspective, approach that recognizes that the health of people, animals, and the environment are closely interconnected and interdependent. Although there is no evidence that Glugea species cause disease in humans, the authors note that other microsporidia are recognized pathogens and can cause infections in immunocompromised individuals.

“The results highlight the need to continue researching these microorganisms from an integrated perspective that takes into account both the health of marine ecosystems and food quality, as well as the protection of the most vulnerable populations,” notes Gabriel Reina, a specialistwith the Microbiology Service at the Clínica Universidad de Navarra.

Researchers believe that this finding new avenues of work for understanding the parasite's geographic distribution, its prevalence in sardine populations, and its potential impact on fish health and the food chain.

Furthermore, the authors believe that phenomena such as ocean warming and the increasing incidence of diseases in aquatic organisms make it increasingly important to strengthen surveillance of this subject pathogens.

reference letter
Baquero, E., Reina, G., & Jordana, R. (2026). A New Host–Parasite Association: A Glugea sp. (Microsporidia) Infecting the Commercial Fish Sardina pilchardus from an Atlantic Fishery. Life, 16(5), 733. https://doi.org/10.3390/life16050733