Rapid transmission of Bonamia exitiosa by cohabitation causes mortality in Ostrea angasi

Abstract

The haplosporidian Bonamia was first detected in Australian shellfish in 1991. Australian isolates in Ostrea angasi Sowerby, 1871 were identified as Bonamia exitiosa Hine, Cochennac and Berthe, 2001, which threatens development of an O. angasi aquaculture industry. European field data suggest that Bonamia ostreae Pichot, Comps, Tigé, Grizel and Rabouin, 1980 infections in Ostrea edulis Linnaeus, 1758 build slowly, but infection dynamics of B. exitiosa in O. angasi are unknown. We investigated B. exitiosa infection in O. angasi by cohabiting uninfected juvenile O. angasi with adults infected with B. exitiosa. Oysters were sampled at 10, 21 and 40 days after cohabitation, and B. exitiosa prevalence and intensity were assessed. Bonamia exitiosa rapidly infected and caused disease in O. angasi. Mortalities began at 12 days, with ˜50% mortality by day 21 and >85% mortality by day 40. Mortalities displayed pathology consistent with clinical B. exitiosa infection. Time to first infection is likely influenced by a combination of parasite infectivity, host exposure and host immune capacity. Host death is not required for transmission, but probably facilitates release of parasites from decaying tissue. Understanding B. exitiosa transmission informs design and interpretation of field studies and aids development of management strategies for oyster aquaculture.

Bonamia exitiosa in European Flat Oyster (Ostrea edulis) on the Croatian Adriatic Coast from 2016 to 2020

“…However, outside hemocytes, there was a lower abundance of cells with two nuclei. This corresponds to the previously described imprints findings of Bonamia exitiosa in flat oysters [31][32][33][34]. Histopathological examination of positive PCR samples of B. exitiosa confirmed Bonamia-like cells in one-third of samples.…”

Infection dynamics of Bonamia exitiosa on intertidal Ostrea angasi farms

“…Survival assessment at the end of the experiment showed that survival after one year was low (17%–33%). Bonamia exitiosa infection intensities were lower (3.01–7.02 cells/heart smear) than described for O. angasi experiencing clinical B. exitiosa disease and mortality (15.40–24.20 cells/heart smear) by Buss et al (2019a). It is therefore unlikely that oysters were dying from clinical B. exitiosa infection in this study.…”

“…was identified in Australia in the early 1990s in farmed and wild populations of the Native Oyster ( Ostrea angasi , Sowerby, 1871) (see Hine & Jones, ). Extensive investigations including genome sequencing have identified all southern Australian Bonamia isolates as Bonamia exitiosa Hine, Cochennac and Berthe, 2001 (see Bradley, ; Buss, Harris, Tanner, Wiltshire, & Deveney, 2019a). Handlinger et al () reported that histological surveys of wild O. angasi across SA in 1992–93 did not detect Bonamia .…”