Description of a hepatopancreatic rickettsia-like organism in the redclaw crayfish Cherax quadricarinatus

Abstract

ABSTRACT. Basovhilic, Gram-neaative, nucrocolonies of rick- Rickettsia-like organisms (RLO) infect a range of aquahc crustaceans mcludmg amphpods, crabs, prawns and freshwater crayfish (Federici et al. 1974, Bonami & Pappalardo 1980, Johnson 1984, Sparks et al. 1985, Brock et al. 1986, Anderson et al. 1987, Krol et al. 1991, Ketterer et al. 1992, Owens et al. 1992, Bower et al. 1996. The decapod-infecting RLOs are either confined to the hepatopancreatic tubule epithelium, or are systemic. The systemic RLOs never have been observed to infect endodermal enteric tissues. The RLO infecting the redclaw freshwater crayfish Cherax quadricarinatus, and originally described by Ketterer et al. (1992) and Owens et al. (1992), is in the systemic category. A RLO was observed exclusively in the hepatopancreatic tubule epithelium of one moribund C. quadricarinatus during a n investigation of chronic low-grade mortality at a farm in north Queensland. Histopathology, cytopathology and basic morphology of this organism are reported here. Materials and methods. The moribund Cherax'Present address: Animal Quarantine Policy Branch, Australian Quarantine and Inspection Service, GPO Box 858, Canberra, ACT 2601, Australia. E-mail: brett.edgerton@aqis.gov.au ing haematoxylin and eosin staining of sections. Special stains (Culling et al. 1985) included Brown and Brenn Gram, phloxine and tartrazine, and Periodic Acid Schiff (PAS).Unstained, 5 pm thick sections of paraffin embedded tissues were processed for electron microscopy by a method adapted from Bhatnagar et al. (1977). Briefly, lesions were located on the paraffin section. Excess tissue was removed, and the remainder was deparaffinised, rehydrated, refixed in glutaraldehyde, postfixed in osmium tetroxide and dehydrated in a graduated acetone series. Infiltration with increasing concentrations of Spurr's resin was carried out on the slide, using a short section cut from a plastic pipette to create a dam of resin over the section. After overnight polymerisation at 60°C the plastic dam was cut away, the slide gently warmed and the resin stub with attached section eased off the glass slide. Ultrathin sections stained with uranyl acetate and lead citrate were examined with a Philips CM 10 TEM.Results. Basophilic inclusions were observed in the cytoplasm of hepatopancreatocytes in adjacent tubules. Nearly all hepatopancreatocytes in cross-sectioned tubules contained the inclusions (Fig. 1). The inclusions were Gram-negative, moderately PAS positive, intensely phloxophilic, and often had a clear central zone containing faint eosinophilic material. Intracytoplasmic, Gram-negative microcolonies were not observed in any other tissues. Sectioning for special stains went beyond the focus of infection, and the 0 Inter-Research 1999Resale of full a r t~c l e not permitted

Hazard Analysis of Exotic Pathogens of Potential Threat to European Freshwater Crayfish.

“…At least two prokaryotic rickettsia-like organisms have been reported to infected freshwater crayfish (KETTERER et al, 1992;OWENS et al, 1992;JIMÉNEZ and ROMERO, 1997;EDGERTON and PRIOR, 1999). One of the RLOs is known to cause serious disease in Cherax quadricarinatus in farms.…”

Infectivity, transmission and 16S rRNA sequencing of a rickettsia, Coxiella cheraxi sp. nov., from the freshwater crayfish Cherax quadricarinatus

“…Similarly, Edgerton et al (1995) found the presence of 2 species of rickettsiae, 1 in the cytoplasm of hepatopancreatic cells (Edgerton & Prior 1999) with mortalities up to 80% in several farms (Jimenez & Romero 1997). The bacteria exhibited morphology and characteristics similar to those reported by Edgerton et al (1995).…”

Molecular detection methods developed for a systemic rickettsia-like bacterium (RLB) in Penaeus monodon (Decapoda: Crustacea)

“…To survive and reproduce, the rickettsia organism must enter the eucaryotic host cell, multiply within the cell, exit and reestablish this cycle in another cell (Winkler 1990). Rickettsia-like microorganisms infect a wide range of aquatic crustaceans including amphipods, crabs, freshwater crayfish and prawns (Federici et al 1974, Harshbarger et al 1977, Bonami & Pappalardo 1980, Larrson 1982, Johnson 1984, Brock et al 1986, Anderson et al 1987, Krol et al 1991, Frelier et al 1992, Fryer & Lan-nan 1994, Bower et al 1996, Jimenez & Romero 1997, Edgerton & Prior 1999, Wang & Gu 2002.…”