Abstract
During an epidemiological survey following a mortality event of freshwater mussels in
2018 in the Embarrass River, Wisconsin, USA, we identified a novel microsporidian parasite in the
ovaries of mucket (Actinonaias ligamentina), plain pocketbook (Lampsilis cardium), and fatmucket
(Lampsilis siliquoidea) (Unionidae). Histopathology showed round-to-oval microsporidian spores in
the cytoplasm of oocytes in 60% (3/5) of female mucket, 100% (4/4) of female plain pocketbook, and
50% (1/2) of female fatmucket. Using transmission electron microscopy, we found that mature spores
were round-to-oval and measured 4.13 ± 0.64 µm (3.14–5.31) long by 2.88 ± 0.37 µm (2.36–3.68)
wide. The spores had a thin electron-dense exospore with a spiky “hairy” coat, a thick electron lucent
endospore, diplokaryotic nuclei, a polar vacuole, and 27–28 polar filaments arranged in 1–3. Sequencing of the small subunit rRNA produced a 1356 bp sequence most similar to that of Pseudonosema
cristatellae (92%), and phylogenetic analysis grouped it within the freshwater Neopereziida. Genetic,
morphological, and ultrastructural characteristics did not closely match those of other Pseudonosema
spp., and a new genus and species, Hirsutonosema embarrassi n. gen. n. sp., were designated. Additional studies could evaluate host susceptibility, distribution, seasonality, transmission, and lethal or
sub-lethal effects of this parasite on freshwater mussels.
2018 in the Embarrass River, Wisconsin, USA, we identified a novel microsporidian parasite in the
ovaries of mucket (Actinonaias ligamentina), plain pocketbook (Lampsilis cardium), and fatmucket
(Lampsilis siliquoidea) (Unionidae). Histopathology showed round-to-oval microsporidian spores in
the cytoplasm of oocytes in 60% (3/5) of female mucket, 100% (4/4) of female plain pocketbook, and
50% (1/2) of female fatmucket. Using transmission electron microscopy, we found that mature spores
were round-to-oval and measured 4.13 ± 0.64 µm (3.14–5.31) long by 2.88 ± 0.37 µm (2.36–3.68)
wide. The spores had a thin electron-dense exospore with a spiky “hairy” coat, a thick electron lucent
endospore, diplokaryotic nuclei, a polar vacuole, and 27–28 polar filaments arranged in 1–3. Sequencing of the small subunit rRNA produced a 1356 bp sequence most similar to that of Pseudonosema
cristatellae (92%), and phylogenetic analysis grouped it within the freshwater Neopereziida. Genetic,
morphological, and ultrastructural characteristics did not closely match those of other Pseudonosema
spp., and a new genus and species, Hirsutonosema embarrassi n. gen. n. sp., were designated. Additional studies could evaluate host susceptibility, distribution, seasonality, transmission, and lethal or
sub-lethal effects of this parasite on freshwater mussels.
| Original language | English |
|---|---|
| Pages (from-to) | 184-198 |
| Number of pages | 15 |
| Journal | Parasitologia |
| Volume | 4 |
| Issue number | 2 |
| DOIs | |
| Publication status | Published - 7 Jun 2024 |