The requirement for early exposure of Haemonchus contortus larvae to Bacillus thuringiensis for effective inhibition of larval development

The potential for a nematocidal Bacillus thuringiensis (Bt) to target the free-living larval stages of Haemonchus contortus was examined using in vitro larval development and migration assays. Bt toxicity in larval development assays decreased as the time period between egg hatch and initial exposure to the Bt was increased; a time lag of 48 h resulted in a 350-fold increase in the IC(50) (from 2.6 ng/ml to 910 ng/ml). The effects on larval migration largely paralleled the effects on larval development, indicating that the larvae which reached the infective stage after exposure to Bt were generally as 'fit' as control worms in terms of migration ability. However, a comparison of the two assays also showed the presence of a level of Bt exposure which showed significantly more toxicity in migration assays than development assays, indicating that, in some cases, fully developed Bt-exposed larvae were less able to migrate than controls, and hence may be compromised in their ability to infect sheep. The rapid decrease in toxicity when exposure to the Bt is delayed highlights a significant issue concerning the use of Bt for control of the free-living larval stages of animal-parasitic nematodes. Targeting the larvae by delivering bacterial spores to the faeces through the host animal's digestive tract would require the spores to germinate upon defecation, grow through a vegetative phase, to then produce crystal toxin protein upon subsequent sporulation. This period of bacterial development will introduce a time lag between worm egg hatching and initial exposure of the larvae to the Bt, which, as demonstrated in the present study, may allow the worm larvae to develop to late larval stages which are relatively insensitive to the toxin.     

High-level pyrantel resistance in the hookworm Ancylostoma caninum

While anthelmintic resistance is now a widely recognized issue in the livestock industries, its existence within companion animal medicine has been rarely established conclusively. We undertook a placebo-controlled in vivo trial to measure the efficacy of pyrantel embonate against pooled isolates of the hookworm Ancylostoma caninum from Brisbane, Australia. A statistically significant fall in adult worm burden was observed among dogs in the pyrantel treatment group compared to the control dogs (178.0+/-24.5 versus 239.7+/-14.0; p=0.02), equating to an efficacy of just 25.7% (95% CI, 15.0-35.1%), as based upon reduction in mean worm burden. Analysis of faecal egg count trends through the course of the study revealed that egg counts rose in both control and pyrantel-treated dogs, with a greater rise observed in the latter group (11.6+/-8.3% versus 17.3+/-7.6%; p=0.04), despite the decrease in adult worm numbers in this group. Our results indicate that high-level anthelmintic resistance does occur in companion animal medicine, and highlight the need for greater vigilance and more judicious use of anthelmintics in small animal practice. They further indicate that the faecal egg count reduction test needs to be used with caution with this parasite.     

Pyrantel in small animal medicine: 30 years on

Pyrantel, a tetrahydropyrimidine nicotinic agonist anthelmintic, has been used in companion animal medicine since the 1970s to control two important nematode groups, the hookworms and the roundworms. Given the zoonotic potential of these parasites, pyrantel has served a dual role in helping to protect the health of both companion animals and the public for more than 30 years. This review describes the history and mechanism of action of this drug, and collates evidence that resistance to pyrantel has developed in at least one canine nematode, the hookworm Ancylostoma caninum. The role of in vitro diagnosis tests in managing anthelmintic resistance in companion animal parasites is discussed, as are management practices that may reduce the rate at which resistance develops.     

Landscape history,time lags and drivers of change: urban natural grassland remnants in Potchefstroom,South Africa

Context

The history of the landscape directly affects biotic assemblages, resulting in time lags in species response to disturbances. In highly fragmented environments, this phenomenon often causes extinction debts. However, few studies have been carried out in urban settings.

Objectives

To determine if there are time lags in the response of temperate natural grasslands to urbanization. Does it differ for indigenous species and for species indicative of disturbance and between woody and open grasslands? Do these time lags change over time? What are the potential landscape factors driving these changes? What are the corresponding vegetation changes?

Methods

In 1995 and 2012 vegetation sampling was carried out in 43 urban grassland sites. We calculated six urbanization and landscape measures in a 500 m buffer area surrounding each site for 1938, 1961, 1970, 1994, 1999, 2006, and 2010. We used generalized linear models and model selection to determine which time period best predicted the contemporary species richness patterns.

Results

Woody grasslands showed time lags of 20–40 years. Contemporary open grassland communities were, generally, associated with more contemporary landscapes. Altitude and road network density of natural areas were the most frequent predictors of species richness. The importance of the predictors changed between the different models. Species richness, specifically, indigenous herbaceous species, declined from 1995 to 2012.

Conclusions

The history of urbanization affects contemporary urban vegetation assemblages. This indicates potential extinction debts, which have important consequences for biodiversity conservation planning and sustainable future scenarios.

     

The genus Xiphinema in southern Africa. XI. Description of Xiphinema stockeri n. sp. from Botswana (Nematoda: Dorylaimida)

Xiphinema stocken 'n. sp. is described from Botswana The new species is characterized by an exceptionally long and conspicuous peg on the tail, and seems to be most closely related to X. mammatum Siddiqi, 1979, from which it can be distinguished by the a ratio, odontostyle and total stylet length, spicule length, the shape of the lip region and tail peg and the presence of a pseudo-z differentiation in X. stocken.     

Freshwater Nematodes from South Africa. 4. The Genus Monhystera Bastian, 1865

During a survey of freshwater nematodes in South Africa, five species of Monhystera Bastian, 1865, were encountered. The five species, three of which are new to science, are described and figured, viz. Monhystera taaiboschiensis n.sp., M. magnacephala n.sp., M. gabaza n.sp., M. filiformis Bastian, 1865 and M. somereni Allgen, 1952.     

Forest edge structure as a shaping factor of understorey vegetation in urban forests in Finland

We investigated the effects of edge structure (i.e. side-canopy openness based on tree, sapling and shrub characteristics, and the composition of tree species) on the understorey vegetation at mesic urban conifer-dominated forest edges in southern Finland. Forest edge structure had an effect on understorey vegetation, and on the spatial extent of the edge effect into the forests. At open edges the edge effect (in terms of the abundances of understorey vegetation) penetrated at least up to 30 m into the forest patches whereas closed edges may prevent these effects. A multilayered canopy with saplings and shrubs at the edge is important to alleviate the effects of the edge. We found that 225–250 m³ ha⁻¹ of trees (diameter at breast height (dbh) > 5 cm) is adequate to restrict the edge effect near the edge. However, the number of broad-leaved trees may be high at edges which, in turn, diminishes the abundance of mosses and favours herb species, thus changing the original natural understorey vegetation composition. Therefore we recommend that conifers be favoured at the edges of mesic conifer-dominated forest patches if the purpose is to restrict the extent of the effects of habitat edges. The appropriate proportion of conifers at these edges should be 80% or more.