How should pathogen transmission be modelled?

Host-pathogen models are essential for designing strategies for managing disease threats to humans, wild animals and domestic animals. The behaviour of these models is greatly affected by the way in which transmission between infected and susceptible hosts is modelled. Since host-pathogen models were first developed at the beginning of the 20th century, the 'mass action' assumption has almost always been used for transmission. Recently, however, it has been suggested that mass action has often been modelled wrongly. Alternative models of transmission are beginning to appear, as are empirical tests of transmission dynamics.

Wolbachia-mediated sperm modification is dependent on the host genotype in Drosophila

Estimates of Wolbachia density in the eggs, testes and whole flies of drosophilid hosts have been unable to predict the lack of cytoplasmic incompatibility (CI) expression in so-called mod(-) variants. Consequently, the working hypothesis has been that CI expression, although related to Wolbachia density, is also governed by unknown factors that are influenced by both host and bacterial genomes. Here, we compare the behaviour of the mod(-) over-replicating Wolbachia popcorn strain in its native Drosophila melanogaster host to the same strain transinfected into a novel host, namely Drosophila simulans. We report that (i) the popcorn strain is a close relative of other D. melanogaster infections, (ii) the mod(-) status of popcorn in D. melanogaster appears to result from its inability to colonize sperm bundles, (iii) popcorn is present in the bundles in D. simulans and induces strong CI expression, which demonstrates that the bacterial strain does not lack the genetic machinery for inducing CI and that there is host-species-specific control over Wolbachia tissue tropism, and (iv) infection of sperm bundles by the mod(-) D. simulans wCof strain indicates that there are several independent routes by which a strain can be a CI non-expressor.

Pasture grazing by black-striped wallabies (Macropus dorsalis) in central Queensland

Black-striped wallabies (Macropus dorsalis) are uncommon to rare in most of their former range, yet in parts of central Queensland where they are still locally common they are regarded as a serious pasture pest. There is considerable pressure from cattle graziers to reduce their density because of the putative damage that they cause to cattle pasture. Here we examined the effects of this species and other herbivores on pasture by monitoring vegetation cover between 1993 and 1998 in exclosures in brigalow, and poplar box communities on three grazing properties in the Maranoa region. The exclosures selectively allowed access to either: all vertebrate grazers including cattle; rabbits, bettongs, and wallabies; rabbits and bettongs; no vertebrate grazers. The greatest effects on the structure and species composition of pasture were caused by cattle, but wallabies did consume commercially important quantities of grass at some times of the year. This conflicts with local opinion that sees wallabies as the major cause of pasture degradation. Herein lies the management problem that sees continued reduction in wallaby habitat, and fragmentation of the species.

Wolbachia pipientis in Australian spiders

Wolbachia pipientis is an endosymbiotic bacterium common to arthropods and filarial nematodes. This study presents the first survey and characterization of Wolbachia pipientis that infect spiders. All spiders were collected from Queensland, Australia during 2002-2003 and screened for Wolbachia infection using PCR approaches. The Wolbachia strains present in the spiders are diverse, paraphyletic, and for the most part closely related to strains that infect insects. We have also identified several spider Wolbachia strains that form a lineage outside the currently recognized six main Wolbachia supergroups (A-F). Incongruence between spider and Wolbachia phylogenies indicates a history of horizontal transmission of the bacterium in these host taxa. Like other arthropods, spiders are capable of harboring multiple Wolbachia strains.

Factors affecting akinete differentiation in Cylindrospermopsis raciborskii (Nostocals, Cyanobacteria)

1. Cylindrospermopsis raciborskii is a potentially toxic freshwater cyanobacterium which can produce akinetes (reproductive spores) that on germinating can contribute to future populations. To further understand factors controlling the formation of these specialised cells, the effects of diurnal temperature fluctuations (magnitude and frequency), in combination with different light intensities and phosphorus concentrations were investigated under laboratory conditions. 2. Akinete differentiation was affected by the frequency of temperature fluctuations. Maximum akinete concentrations were observed in cultures that experienced multiple diurnal temperature fluctuations. 3. Akinete concentrations increased with increasing magnitude of temperature fluctuation. A maximum akinete concentration was achieved under multiple diurnal temperature fluctuations with a magnitude of 10degreesC (25degreesC to 15degreesC). 4. A fourfold increase in light intensity (25-100 mumol m(-2) s(-1)) resulted in an approximate 14-fold increase in akinete concentration. 5. High filterable reactive phosphorus (FRP) concentrations (> 70 mug L-1) in the medium, combined with a multiple diurnal temperature fluctuation of 10degreesC, supported the development of the highest akinete concentration.

Gastrointestinal transit in the common brushtail possum measured by gamma scintigraphy

This paper reports an example of the application of pharmaceutical technology to wildlife management, specifically the design of an oral delivery system for the common brushtail possum in New Zealand. Designing an oral delivery system requires a knowledge of the time taken for particulates to reach target sites within the gastrointestinal tract (GIT). The transit time for fluid and indigestible particles of two different size ranges was determined in the common brushtail possum (Trichosurus vulpecula). Technetium-labelled (Tc-99m) anion exchange resin particles (75-125 or 500-700 mu m diameter) or solution (Tc-99m-labelled diethylenetriamine pentaacetic acid, Tc-99m-DTPA) was administered orally. At predetermined times after dosing (3, 6, 12, 24 or 32 h), the distribution of radioactivity throughout excised gastrointestinal tracts was determined by gamma scintigraphy. The transit profile was similar for the three formulations investigated. Unlike other closely related hindgut fermenting marsupials, there was no evidence to support the presence of a colonic separating mechanism in the common brushtail possum. Gastrointestinal transit was independent of body mass, gender and time of day that the dose is given. To target the hindgut for oral delivery of protein and peptide biocontrol agents, the formulation Would need to protect the bioactive for approximately 12 h prior to release. (c) 2005 Elsevier B.V. All rights reserved.

A physiological product-release model for baculovirus infected insect cells

Existing models describe the product release from baculovirus infected insect cells as an unspecific protein leakage occurring in parallel with protein production. The model presented here shows that the observed product release of normally non-secreted proteins can be described through cell death alone. This model avoids the implicit non-physiological assumption of previous models that cells permeable to recombinant protein as well as trypan blue continue to produce protein. (c) 2005 Wiley Periodicals, Inc.

Rotary atomizer drop size distribution database

Wind tunnel measurements of drop Size distributions from Micronair A U4000 and A U5000 rotary atomizers were collected to develop a database for model use. The measurements varied tank mix, flow rate, air speed, and blade angle conditions, which were correlated by multiple regressions (average R-2 = 0.995 for A U4000 and 0.988 for AU5000). This database replaces an outdated set of rotary atomizer data measured in the 1980s by the USDA Forest Service and fills in a gap in data measured in the 1990s by the Spray Drift Task Force. Since current USDA Forest Service spray projects rely on rotary atomizers, the creation of the database (and its multiple regression interpolation) satisfies a need seen for ten years.