Ostreid herpesvirus-1 microvariant surveillance in Pacific oysters (Magallana gigas, Thunberg, 1793) in Australia in 2011.

OBJECTIVE: To demonstrate that OsHV-1 microvariant was limited to the known infected areas in New South Wales at the time of the survey in 2011. DESIGN: A 2-stage survey to demonstrate probability of infection at 2% design prevalence within oyster growing regions and to detect at least one infected region (4% design prevalence) with 95% confidence. SAMPLE POPULATION: Magallana gigas in nominated oyster growing regions in New South Wales, South Australia and Tasmania as approved by the Aquatic Consultative Committee on Emergency Animal Diseases and documented in a national surveillance plan. PROCEDURE: Field sampling for active surveillance and laboratory selection of appropriate tissues using methods to minimize potential for cross contamination. Published methods for qPCR and conventional PCR for OsHV-1 microvariant. Stochastic analysis of survey results to demonstrate probability of detection in the areas tested. RESULTS AND CONCLUSIONS: OsHV-1 microvariant was not detected in a total 4121 samples according to the case definition developed for the survey. However, in NSW a screening qPCR for OsHV-1 detected 13 samples that reacted. These samples were negative at 2 laboratories in the qPCR and conventional PCR assays used in the case definition for the survey. We concluded that oyster production areas of Australia outside the infected area in NSW met the criteria for self-declaration of freedom at the time of the survey in 2011. CLINICAL RELEVANCE: This activity illustrated achievements in surveillance for an emerging emergency animal pathogen where epidemiological and test validation data were limited, but where data was required to inform the emergency disease response. It also illustrated the challenges faced by investigators in interpreting surveillance results using tests with limited validation. It was guided by and has informed improvements in surveillance and emergency disease preparedness.

Efficacy of bath and orally administered praziquantel and fenbendazole against Lepidotrema bidyana Murray, a monogenean parasite of silver perch, Bidyanus bidyanus (Mitchell).

We investigated the efficacy of praziquantel (PZQ) and fenbendazole (FBZ), each administered by bath and orally, against the monogenean Lepidotrema bidyana Murray, a gill parasite of the freshwater fish silver perch, Bidyanus bidyanus (Mitchell). PZQ and FBZ were each administered by bath at 10 mg L⁻¹ for 48 h and on surface-coated feed pellets at 75 mg kg⁻¹ per body weight (BW) per day for 6 days. Bath treatments of PZQ and FBZ had an efficacy of 99% and 91%, respectively, against adult L. bidyana. Oral treatments of PZQ and FBZ had an efficacy of 79% and 95%, respectively, against adult L. bidyana. Fish rejected feed pellets surface-coated with PZQ, suggesting that palatability of surface-coated PZQ-medicated feed is poor, which undermined efficacy. In all trials, some juvenile parasites were present on fish after treatment during efficacy assessment, indicating that efficacy may be lower against juvenile parasites or that recruitment occurred post-treatment, demonstrating that repeat treatments are necessary to effectively control L. bidyana in aquaculture.

Simulated aquatic animal disease outbreaks: a tool for improving responses to emergencies.

Simulated disease outbreaks are vital tools for preparing administrative and functional responses to emergencies. Three aquatic emergency response exercises conducted in Australia are summarised. The prinicipal lesson learned from these exercises was the need for coordination, improved communication and a whole-of-government approach. An enhanced understanding of the legislative instruments required for a response, insights into human factors such as staff rostering, training, counselling and provision of assistance packages were also obtained. Developing a sense of overconfidence about preparedness arrangements (as a result of having tested specific, planned scenarios) must be avoided. Emergencies occur infrequently and erratically; conducting exercises is a vital component of planning processes that ensure that responses to emergency events are effective.

Gross and histopathological characteristics of two lipomas and a neurofibrosarcoma detected in aquacultured southern bluefin tuna, Thunnus maccoyii (Castelnau), in South Australia.

Three visible lesions were examined from two specimens of southern bluefin tuna. The lesions were examined grossly and two were identified as lipomas, the third bore similarities to a schwannoma. Histopathology confirmed that two consisted of mature adipocytes consistent with a diagnosis of lipoma. The third lesion consisted of spindle cells in Antoni A and B patterns and was tentatively diagnosed as a malignant schwannoma. Immunohistochemistry identified both S100 and glial fibrillary acid protein expression within the lesion, which, together with the histopathological appearance, is consistent with a diagnosis of neurofibrosarcoma.

A parasite survey of farmed Southern bluefin tuna, Thunnus maccoyii (Castelnau).

Farmed Southern bluefin tuna (SBT) were examined for parasites. Samples of harvest fish, mortalities and some fish showing clinical signs of disease were investigated. Targeted screening was conducted for a scuticociliate, Uronema nigricans, the myxosporean Kudoa sp. and a sanguinicolid digenean, Cardicola forsteri. General parasitological investigation revealed a diverse parasite community of didymozoid digeneans, two species of copepods, a polyopisthocotylean monogenean and larval cestodes. Targeted screening for U. nigricans exposed a low prevalence, most probably due to a lack of sensitivity in the test method. Few of the parasites examined pose a risk to the health of farmed SBT.

Gill histopathology of wild marine fish in Tasmania: potential interactions with gill health of cultured Atlantic salmon, Salmo salar L.

This study surveyed conditions in the gills of wild marine fish in Tasmania to determine potential interactions between wild and cultured fish. Wild marine fish of 12 species were captured from three Atlantic salmon farm sites and three reference sites around Tasmania. The survey concentrated on three species, red cod, Pseudophycis bachus, sand flathead, Platycephalus bassensis, and jack mackerel, Trachurus declivus. Seventy-six per cent of salmon pens contained wild fish species. The number of species found in a pen ranged from one to nine and the number of individuals ranged from one to 23. Trichodinids were prevalent and occurred on seven of the 13 species examined. Trichodina occurred on the gills of all but one specimen of red cod. Monogenean gill flukes were observed on all three major species sampled and were abundant on sand flathead. Other parasites and conditions observed in the survey included metacercariae of digenean trematodes, epitheliocystis and cysts of unknown origin. Infestations of trichodinids on red cod and monogenean gill flukes on sand flathead were significantly more intense at farm sites than at reference sites. Atlantic salmon sampled at the same time from the farms were only affected by amoebic gill disease and isopods.

A preliminary phylogenetic analysis of the Capsalidae (Platyhelminthes: Monogenea: Monopisthocotylea) inferred from large subunit rDNA sequences.

Phylogenetic relationships within the Capsalidae (Monogenea) were examined using large subunit ribosomal DNA sequences from 17 capsalid species (representing 7 genera, 5 subfamilies), 2 outgroup taxa (Monocotylidae) plus Udonella caligorum (Udonellidae). Trees were constructed using maximum likelihood, minimum evolution and maximum parsimony algorithms. An initial tree, generated from sequences 315 bases long, suggests that Capsalinae, Encotyllabinae, Entobdellinae and Trochopodinae are monophyletic, but that Benedeniinae is paraphyletic. Analyses indicate that Neobenedenia, currently in the Benedeniinae, should perhaps be placed in a separate subfamily. An additional analysis was made which omitted 3 capsalid taxa (for which only short sequences were available) and all outgroup taxa because of alignment difficulties. Sequence length increased to 693 bases and good branch support was achieved. The Benedeniinae was again paraphyletic. Higher-level classification of the Capsalidae, evolution of the Entobdellinae and issues of species identity in Neobenedenia are discussed.

First published record of the pathogenic monogenean parasite Neobenedenia melleni (Capsalidae) from Australia.

The monogenean Neobenedenia melleni (MacCallum, 1927) Yamaguti 1963 is a well-known and virulent pathogen in culture conditions recorded from the skin of many teleost fish species worldwide. Until now, N. melleni has not been reported from wild or cultured fish in Australian waters. This study documents a recent outbreak of N. melleni that occurred on Lates calcarifer (barramundi) cultivated in sea cages in Hinchinbrook Channel between Hinchinbrook Island and mainland Queensland, Australia, which resulted in the loss of 200,000 fish (50 tonnes). The origin of this outbreak is unclear because N. melleni has not been recorded from any wild host species in Australia and strict quarantine regulations exclude the possibility of its introduction on imported fish. We propose that N. melleni occurs naturally on wild populations of some teleost species in Australian waters and that the few surveys of wild fish conducted along the east coast have failed to report this species. The possibility that uncharacteristically low water temperatures led to the outbreak is discussed.

A technique for preserving pigmentation in some capsalid monogeneans for taxonomic purposes.

A technique is described to preserve the pigment found in the bodies and the intestine of some brightly coloured and darkly pigmented benedeniine capsalid monogeneans. Previous studies of these pigmented capsalids have proven difficult because the pigmentation usually disappears when the worms are fixed using preservatives containing concentrations of formalin over 5% and/or ethanol, acetic acid, chromic acid, picric acid and mercuric chloride. The technique developed here uses a fixative comprising glycerol, acetone and formalin (GAF). After fixation under light coverslip compression for three minutes, specimens are transferred to absolute acetone for three minutes and cleared in a mixture of nine parts cedar wood oil and one part absolute acetone before mounting in Canada balsam. Processing must be carried out quickly, as these chemicals will cause the pigments to fade if the specimens are exposed to them for too long. Pigmented benedeniines processed using this technique retain the distribution, intensity and colour observed in live worms. The colour and distribution of pigmentation in monogeneans may be of taxonomic importance and this technique aids preparation of whole-mounts suitable for registration as type-material.