Infection by intracellular bacterium in red claw crayfish, Cherax quadricarinatus (Von Martens), in Ecuador

Abstract

An intracellular bacterium was detected on several occasions in commercial farms in Ecuador culturing red claw crayfish, Cherax quadricarinatus (Von Martens). Cases A, B and C presented mortality rates of 80%, 45% and 80%, respectively. Each incident occurred in grow-out ponds. Moribund crayfish were observed at the edge of the ponds in some cases. Affected crayfish presented no external differences from healthy ones, except their smaller size. Histological examination of affected red claw crayfish revealed that the cytoplasm of cells in the hepatopancreas, cuticular epithelium, and connective tissue of all organs had been replaced by massive granular and basophilic material. In the hepatopancreas, the tubules were intact but the intertubular connective tissue was replaced by Gram-negative microcolonies. Columnar cells in the cuticular epithelium also contained Gram-negative microcolonies and were necrotic. The heart and nerve cords also contained basophilic material. Transmission electron microscopy showed that the microcolonies consisted of a rod-shaped, obligately intracellular bacterium. The bacterium was delimited by a cell membrane that was composed of two electron-dense zones. Cells contained a single, compact, cytoplasmic condensation that was circumscribed by an electron-lucent halo. The bacterium replicated within the cytoplasm of host cells, which is pathognomic of rickettsiales infections. No host cell nuclei were infected.