Differential effects of aquatic anaesthetics on the pharmacokinetics of antibiotics: Examples using florfenicol in Nile tilapia (Oreochromis niloticus)

Anaesthetics are commonly applied in pharmacokinetic (PK) studies to assure smooth handling of experimental procedures or to promote animal welfare. However, the influence of anaesthetics on the PK of co-administered drug is generally unknown but assumes ignorable. The goal of the study was to investigate the effect of tricaine methanesulfonate (MS-222), 2-phenoxyethanol (2-PE) and eugenol (EUG) on the PK of florfenicol (FF) in Nile tilapia. Twenty-eight fish were repeatedly exposed to 90 ppm EUG, 300 ppm MS-222 or 900 ppm 2-PE before FF oral administration (15 mg/kg) and each successive blood sampling. The serum concentration-time profiles were analysed by a 2-compartmental model, and the generated parameters in the control (without anaesthetic) and anaesthetic groups were statistically compared. The results demonstrated that the serum concentrations of each anaesthetic were similar at every FF sampling times (70 μg/ml for MS-222; 277 μg/ml for 2-PE; and 61 μg/ml for EUG). In comparison with the control group, the repeated use of MS-222 did not result in a statistical difference in most of the PK parameters. In contrast, the elimination half-lives of the 2-PE and EUG groups were significantly longer whereas the absorption and distribution half-lives of the 2-PE group were significantly shorter than the control, resulting in altered optimal dosages in the simulation modelling. Whether or not the numbers and extent of PK parameters change mitigate subsequent estimations of other PK-derived secondary values such as dosing regimen and withdrawal time remains to be elucidated, but the auxiliary use of anaesthetics in PK studies should not assume uninfluential.

Impact of yellow head virus outbreaks in the whiteleg shrimp, Penaeus vannamei (Boone), in Thailand

Yellow head virus (YHV) is known as a major pathogen in the black tiger shrimp, Penaeus (Penaeus) monodon. It can also cause serious mortality in farmed whiteleg shrimp, Penaeus (Litopenaeus) vannamei. However, there is no published information on the economic and/or production impact of the disease in P. vannamei. Shrimp with gross signs of YHV disease (faded body colour and 60-70% mortality) were observed in 20 study farms rearing P. vannamei in the central part of Thailand from the end of 2007 through early 2008. The estimated economic loss for these farms according to the Thai Animal Aquaculture Association was approximately US$3 million. Detailed sequence analysis of RT-PCR amplicons from shrimp in all the study ponds revealed the presence of YHV Type 1b (YHV-1b) alone (characterized by a 162-bp deletion in the ORF3 region encoding the structural gene for gp116) and the absence of YHV Type 1a (YHV-1a), the original YHV type reported from Thailand. Despite the large 162-bp deletion (= 54 deduced amino acids) in the gp116 structural gene, histopathology of YHV-1b infections was identical to that of YHV-1a infections, and electron microscopy revealed that YHV-1b virions were morphologically indistinguishable from those previously reported for YHV-1a. In addition, an existing commercial RT-PCR detection kit and an immunochromatographic test strip for the detection of YHV were proven to have been valid tests for both YHV-1b and YHV-1a. The source of the virus for these outbreaks was unlikely to have been the post-larvae used to stock the ponds, as they were derived from domesticated specific pathogen-free stocks free of YHV. Thus, it is possible that they originated from an unknown, natural reservoir.

Chlorella viruses as a source of novel enzymes

A special advantage has been conferred upon Chlorella cells as tools in biotechnology when viruses (Phycodnaviridae) infecting Chlorella cells were discovered and isolated. The viruses are large icosahedral particles (150-200 nm in diameter), containing a giant, 330-380 kbp long, linear dsDNA genome. Recently, the nucleotide sequence of the 330,740-bp genome of PBCV-1, the prototype virus of Phycodnaviridae, was determined, and up to 702 open reading frames (ORFs) were identified along the genome. The possible genes present include those encoding a variety of enzymes involved in the modification of DNA, RNA, protein and polysaccharides as well as those involved in the metabolism of sugars, amino acids, lipids, nucleotides and nucleosides. Many of these genes are actually expressed during viral infection, with functional enzymes detected in the host cytoplasm or incorporated into the virion. The successful utilization of these viral enzymes as various DNA restriction and modification enzymes (Cvi enzymes) that are now commercially available is well documented. Also noteworthy are virion-associated chitinase and chitosanase activities that have potentially important applications in the recycling of natural resources. The virions of Chlorella viruses contain more than 50 different structural proteins, ranging in size from 10 to 200 kDa. Some of these proteins may be replaced with useful foreign proteins using recombinant DNA technology. The proteins of interest can be recovered easily from the viral particles, and collected by centrifugation after complete lysis of the host Chlorella cells.

A variable region on the chlorovirus CVK2 genome contains genes possibly involved in the host range determination

A 22.6-kbp variable region near the left end of the chlorovirus CVK2 genome which was characterized. This region contained a tandem array of 5 gene copies for Vp260-like protein, a viral surface glycoprotein. The authentic 104-kDa Vp260 was encoded at another site on the genome and contained 13 internally located, tandem repeats of 61-65 amino acids like the prominent Rickettsia surface antigen. By Northern and Western blot analyses, these genes were demonstrated to be expressed late in infection and the proteins were incorporated into virions. These results implied that the extra copies of Vp260-like proteins may be involved in host range in the natural environment.