Towards the successful control of the invasive <Emphasis Type="Italic">Pseudorasbora parva</Emphasis> in the UK

The aim of this paper is to detail a control programme of the invasive Asian cyprinid fish Pseudorasbora parva in the UK that was initiated in March 2005. Described as Europe’s most invasive fish, P. parva presents a risk to native fishes through the transmission of a novel pathogen and undesirable impacts arising from processes including increased inter-specific competition. Populations have been recorded in 32 UK waters since their first recording outside of aquaculture in 1996; the majority are lakes <5 ha used for recreational angling in England. The aims of the control programme were to develop a basic evaluation framework that assesses populations by risk (high, medium and low), determine commensurate management actions according to that risk and then execute those actions. For populations assessed as ‘high-risk’, for example those that could result in P. parva dispersal into a river catchment, eradication was determined as the commensurate management action and six operations have since been completed, principally using rotenone, and all have been successful to date. For P. parva populations in sites evaluated as lower risk, techniques such as biomanipulation were determined as more appropriate actions and have been used to successfully reduce their abundance by >99%. To date, the total direct cost of this programme of sustained and on-going P. parva control is approximately ￡190,000.     

The introduced <Emphasis Type="Italic">Micropterus salmoides</Emphasis> in an equatorial lake: a paradoxical loser in an invasion meltdown scenario?

Micropterus salmoides is a North American piscivorous fish on the IUCN list of 100 of the world’s worst invasive alien species. Introduced into Lake Naivasha (Kenya) in 1929, their current population abundance is significantly depressed in a lake that has recently become dominated by fishes of the Cyprinidae family; the introduced cyprinid Cyprinus carpio now dominates catches in the commercial fishery and Barbus paludinous is now numerically dominant in the fish community. Long-term diet studies of M. salmoides based on gut contents analysis (GCA) have defined their diet spectrum, feeding preferences and ontogenetic dietary shifts. Between 1987 and 1991, diet was size-structured; fish <260 mm were mainly insectivorous and fish >260 mm fed mainly on invasive crayfish Procambarus clarkia with B. paludinosus rarely taken. More recent GCA data revealed that up to 2003, these size-structured trophic relationships were still evident, but there has been a subsequent shift to their feeding almost exclusively on small (<100 mm) B. paludinosus, coincident with a size-related functional switch whereby M. salmoides >120 mm were now piscivorous. However, a Bayesian stable isotope mixing model (SIAR) suggested M. salmoides diet actually remained relatively varied in 2006 and 2007; it indicated P. clarkii were still contributing more to their diet than B. paludinosus in fish <260 mm and provided only partial support for the functional shift. The consequence of the M. salmoides depressed population abundance is their predation pressure on prey fishes is limited and preventing top-down effects. This is in contrast to their invasive populations elsewhere in the world and the likely result of invasion meltdown processes in Naivasha involving the introduced C. carpio and P. clarkii that have produced sub-optimal foraging conditions for M. salmoides.     

Systemic FasL and TRAIL neutralisation reduce leishmaniasis induced skin ulceration

Cutaneous leishmaniasis (CL) is caused by Leishmania infection of dermal macrophages and is associated with chronic inflammation of the skin. L. aethiopica infection displays two clinical manifestations, firstly ulcerative disease, correlated to a relatively low parasite load in the skin, and secondly non-ulcerative disease in which massive parasite infiltration of the dermis occurs in the absence of ulceration of epidermis. Skin ulceration is linked to a vigorous local inflammatory response within the skin towards infected macrophages. Fas ligand (FasL) and Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) expressing cells are present in dermis in ulcerative CL and both death ligands cause apoptosis of keratinocytes in the context of Leishmania infection. In the present report we show a differential expression of FasL and TRAIL in ulcerative and non-ulcerative disease caused by L. aethiopica. In vitro experiments confirmed direct FasL- and TRAIL-induced killing of human keratinocytes in the context of Leishmania-induced inflammatory microenvironment. Systemic neutralisation of FasL and TRAIL reduced ulceration in a model of murine Leishmania infection with no effect on parasitic loads or dissemination. Interestingly, FasL neutralisation reduced neutrophil infiltration into the skin during established infection, suggesting an additional proinflammatory role of FasL in addition to direct keratinocyte killing in the context of parasite-induced skin inflammation. FasL signalling resulting in recruitment of activated neutrophils into dermis may lead to destruction of the basal membrane and thus allow direct FasL mediated killing of exposed keratinocytes in vivo. Based on our results we suggest that therapeutic inhibition of FasL and TRAIL could limit skin pathology during CL.     

Medaka (Oryzias latipes) as a sentinel species for aquatic animals: Medaka cells exhibit a similar genotoxic response as North Atlantic right whale cells

Hexavalent chromium (Cr(VI)) is emerging as a major concern for aquatic environments, particularly marine environments. Medaka (Oryzias latipes) has been used as a model species for human and aquatic health, including the marine environment, though few studies have directly compared toxicological responses in medaka to humans or other aquatic species. We used a medaka fin cell line to compare the genotoxic response of medaka to Cr(VI) to the response observed in North Atlantic right whale cells to see if responses in medaka were similar to those of other aquatic species, particularly aquatic mammals. We used the production of chromosomal aberrations as a measure of genotoxicity. We found that in medaka cells, concentrations of 1, 5 and 10 microM sodium chromate damaged 17, 32 and 43% of metaphases, respectively and these same concentrations 1, 2.5, 5 and 10 microM sodium chromate damaged 14, 24 and 49% of metaphases, respectively, in North Atlantic right whale lung cells and 11, 32 and 41% of metaphases, respectively, in North Atlantic right whale testes cells. These data show that genotoxic responses in medaka are comparable to those seen in North Atlantic right whale cells, consistent with the hypothesis that medaka are a useful model for other aquatic species.     

Using Caenorhabditis elegans for functional analysis of genes of parasitic nematodes

Information on the functional genomics of Caenorhabditis elegans has increased significantly in the last few years with the development of RNA interference. In parasitic nematodes, RNA interference has shown some success in gene knockdown but optimisation of this technique will be required before it can be adopted as a reliable functional genomics tool. Comparative studies in C. elegans remain an appropriate alternative for studying the function and regulation of some parasite genes and will be extremely useful for fully exploiting the increasing parasite genome sequence data becoming available.     

Iron Imports. VI. HFE and regulation of intestinal iron absorption

The majority of clinical cases of iron overload is caused by mutations in the HFE gene. However, the role that HFE plays in the physiology of intestinal iron absorption remains enigmatic. Two major models have been proposed: 1) HFE exerts its effects on iron homeostasis indirectly, by modulating the expression of hepcidin; and 2) HFE exerts its effects directly, by changing the iron status (and therefore the iron absorptive activity) of intestinal enterocytes. The first model places the primary role of HFE in the liver (hepatocytes and/or Kupffer cells). The second model places the primary role in the duodenum (crypt cells or villus enterocytes). These models are not mutually exclusive, and it is possible that HFE influences the iron status in each of these cell populations, leading to cell type-specific downstream effects on intestinal iron absorption and body iron distribution.     

Modelling the Use of Wolbachia to Control Dengue Fever Transmission

Experiments and field trials have shown that the intracellular bacterium Wolbachia may be introduced into populations of the mosquito Aedes aegypti, the primary vector for dengue fever. In the absence of Wolbachia, a mosquito acquiring the dengue virus from an infected human enters an exposed (infected but not infectious) period before becoming infectious itself. A Wolbachia-infected mosquito that acquires dengue (i) may have a reduced lifespan, so that it is less likely to survive the exposed period and become infectious, and (ii) may have a reduced ability to transmit dengue, even if it has survived the exposed period. Wolbachia introduction has therefore been suggested as a potential dengue control measure. We set up a mathematical model for the system to investigate this suggestion and to evaluate the desirable properties of the Wolbachia strain to be introduced. We show that Wolbachia has excellent potential for dengue control in areas where R ₀ is not too large. However, if R ₀ is large, Wolbachia strains that reduce but do not eliminate dengue transmission have little effect on endemic steady states or epidemic sizes. Unless control measures to reduce R ₀ by reducing mosquito populations are also put in place, it may be worth the extra effort in such cases to introduce Wolbachia strains that eliminate dengue transmission completely.