Antibody-dependent enhancement of Murray Valley encephalitis virus virulence in mice

Enhancement of flavivirus infection in vitro in the presence of subneutralizing concentrations of homologous or heterologous antiserum has been well described. However, the importance of this phenomenon in the enhancement of flavivirus infection in vivo has not been established. In order to study antibody- mediated enhancement of flavivirus infection in vivo, we investigated the effect of passive immunization of mice with Japanese encephalitis virus (JE) antiserum on the outcome of infection with Murray Valley encephalitis virus (MVE). We show that prior treatment of mice with subneutralizing concentrations of heterologous JE antiserum resulted in an increase in viraemia titres and in mortality following challenge with wild-type MVE. Our findings support the hypothesis that subneutralizing concentrations of antibody may enhance flavivirus infection and virulence in vivo. These findings are of potential importance for the design of JE vaccination programs in geographic areas in which MVE co-circulates. Should subneutralizing concentrations of antibody remain in the population following JE vaccination, it is possible that enhanced disease may be observed during MVE epidemics.

Rates of spread of marine pathogens

Epidemics of marine pathogens can spread at extremely rapid rates. For example, herpes virus spread through pilchard populations in Australia at a rate in excess of 10 000 km year(-1), and morbillivirus infections in seals and dolphins have spread at more than 3000 km year(-1). In terrestrial environments, only the epidemics of myxomatosis and calicivirus in Australian rabbits and West Nile Virus in birds in North America have rates of spread in excess of 1000 km year(-1). The rapid rates of spread of these epidemics has been attributed to flying insect vectors, but flying vectors have not been proposed for any marine pathogen. The most likely explanation for the relatively rapid spread of marine pathogens is the lack of barriers to dispersal in some parts of the ocean, and the potential for long-term survival of pathogens outside the host. These findings caution that pathogens may pose a particularly severe problem in the ocean. There is a need to develop epidemic models capable of generating these high rates of spread and obtain more estimates of disease spread rate.

Introduced mammals in Australian rangelands: Future threats and the role of monitoring programmes in management strategies

In the present paper, we have provided an initial assessment of the current and future threats to biodiversity posed by introduced mammals (predators and herbivores) inhabiting the Australian rangelands, exploring trends in populations and options for management. Notably, rabbits have declined in recent years in the wake of rabbit haemorrhagic disease, populations of feral camels have increased dramatically and foxes appear to have moved northwards, thereby threatening native fauna within an expanded range. Following on, we developed a framework for monitoring the impacts of introduced mammals in the Australian rangelands. In doing so, we considered the key issues that needed to be considered in designing a monitoring programme for this purpose and critically evaluated the role of monitoring in pest animal management. Finally we have provided a brief inventory of current best-practice methods of estimating the abundance of introduced mammal populations in the Australian rangelands with some comments on new approaches and their potential applications.

Simultaneous detection and differentiation of human Polyomaviruses JC and BK by a rapid and sensitive PCR-ELAHA assay and a survey of the JCV subtypes within an Australian population

Human polyomaviruses JCV and BKV can cause several clinical manifestations in immunocompromised hosts, including progressive multifocal leukoencephalopathy (PML) and haemorrhagic cystitis. Molecular detection by polymerase chain reaction (PCR) is recognised as a sensitive and specific method for detecting human polyomaviruses in clinical samples. In this study, we developed a PCR assay using a single primer pair to amplify a segment of the VP1 gene of JCV and BKV. An enzyme linked amplicon hybridisation assay (ELAHA) using species-specific biotinylated oligonucleotide probes was used to differentiate between JCV and BKV. This assay (VP1-PCR-ELAHA) was evaluated and compared to a PCR assay targeting the human polyomavirus T antigen gene (pol-PCR). DNA sequencing was used to confirm the polyomavirus species identified by the VP1-PCR-ELAHA and to determine the subtype of each JCV isolate. A total of 297 urine specimens were tested and human polyomavirus was detected in 105 specimens (35.4%) by both PCR assays. The differentiation of JCV and BKV by the VP1-PCR-ELAHA showed good agreement with the results of DNA sequencing. Further, DNA sequencing of the JCV positive specimens showed the most prevalent JCV subtype in our cohort was 2a (27%) followed by 1b (20%), 1a (15%), 2c (14%), 4 (14%) and 2b (10%). The results of this study show that the VP1-PCR-ELAHA is a sensitive, specific and rapid method for detecting and differentiating human polyomaviruses JC and BK and is highly suitable for routine use in the clinical laboratory. (C) 2004 Wiley-Liss, Inc.

Suspected hexamine intoxication in a dog

An eight-month-old Labrador Retriever was presented with urinary incontinence and haematuria. Recent history suggested that the dog had access to solid fuel hexamine tablets, ingesting a dose of 6g/kg. Clinical signs, laboratory investigation and ultrasonographic findings were supportive of chemically-induced cystitis and a diagnosis of suspected hexamine intoxication was made. The dog recovered uneventfully and it is unlikely that the insult will be carcinogenic.

Ebola virus glycoprotein GP is not cytotoxic when expressed constitutively at a moderate level

Transient expression of Ebola virus (EBOV) glycoprotein GP causes downregulation of surface proteins, cell rounding and detachment, a phenomenon believed to play a central role in the pathogenicity of the virus. In this study, evidence that moderate expression of GP does not result in such morphological changes was provided. It was shown that GP continuously produced in 293T cells from the Kunjin virus replicon was correctly processed and transported to the plasma membrane without affecting the surface expression of beta 1 and alpha 5 integrins and major histocompatibility complex I molecules. The level of GIP expression in Kunjin replicon GP-expressing cells was similar to that observed in cells infected with EBOV early in infection and lower than that produced in cells transfected with plasmid DNA, phCMV-GP(1) expressing GP from a strong promoter. Importantly, transient transfection of Kunjin replicon GIP-expressing cells with GIP-coding plasmid DNA resulted in overexpression of GP, which lead to the downregulation of surface molecules and massive rounding and detachment of transfected cells. Here, it was also demonstrated that cell rounding and downregulation of the surface markers are the late events in EBOV infection, whereas synthesis and massive release of virus particles occur at early steps and do not cause significant cytotoxic effects. These findings indicate that the synthesis of EBOV GP in virus-infected cells is controlled well by several mechanisms that do not allow GP overexpression and hence the early appearance of its cytotoxic properties.

PCR detection and analysis of Pasteurella multocida from the tonsils of slaughtered pigs in Vietnam

A total of 36 tonsil swab samples were collected from healthy swine prior to slaughter at the abattoirs in Can tho and Tien giang provinces of Southern Vietnam, The presence of Pasteurella multocida in these samples was detected by the combination of direct cultivation and isolation, mouse inoculation and the polymerase chain reaction (PM-PCR). P. multocida was detected in 16 samples by PCR, with 17 strains ultimately isolated. All samples were negative for serogroup B by HSB-PCR and conventional serotyping, with isolates identified as A:3, D:1 or D:3. In addition, all samples were determined to be negative for the P. multocida toxin (PMT). Characterisation of isolated P, multocida by REP-PCR and biotyping revealed nine distinct REP profiles and seven biotypes among the 17 isolates. Some correlation was seen with P. multocida isolated from a previous Australian outbreak of acute swine pasteurellosis, and those isolated from fowl cholera outbreaks in Vietnamese poultry. (C) 2000 Elsevier Science B.V. All rights reserved.