Post-ruminal protein supply and N retention of weaner sheep fed on a basal diet of lucerne hay (Medicago sativa) with increasing levels of quebracho tannins

The ability of low to moderate levels (

Effectiveness of introduced biocontrol insects on the weed Parthenium hysterophorus (Asteraceae) in Australia

Six species of insects and a rust fungus have been successfully established for biocontrol of the weed Parthenicum hysterophorus L. in Queensland, Australia. Effectiveness of biocontrol insects was evaluated at two properties in Queensland during 1996-97 based on an exclusion experiment using insecticides. Parthenium-infested plots with and without biocontrol insects were sampled at monthly intervals and the impact of biocontrol insects on parthenium at individual plant and whole population levels monitored. Biocontrol insects were more effective at Mt Panorama (central Queensland) than at Plain Creek (north Queensland). At Mt Panorama, the leaf-feeding beetle Zygogramma bicolorata Pallister caused 96% defoliation and the stem-galling moth Epiblema strenuana Walker affected 100% of the plants, resulting in reductions of 90% in weed density, 40% in plant height, and 82% in flower production. Exclusion of biocontrol insects resulted in a 52% increase in seedling emergence and a seven-fold increase in the soil seed bank in the following season. At Plain Creek, E. strenuana was the only prominent agent. It affected 92% of the plants and prevented 32% of plants from producing any flowers, reduced plant height by 40% and flower production by 49%, but did not reduce the plant biomass, weed density or soil seed bank. However, exclusion of biocontrol insects resulted in an eight-fold increase in the soil seed bank in the following season.

Hemoglobin-degrading, aspartic proteases of blood-feeding parasites - Substrate specificity revealed by homology models

Blood-feeding parasites, including schistosomes, hookworms, and malaria parasites, employ aspartic proteases to make initial or early cleavages in ingested host hemoglobin. To better understand the substrate affinity of these aspartic proteases, sequences were aligned with and/or three-dimensional, molecular models were constructed of the cathepsin D-like aspartic proteases of schistosomes and hookworms and of plasmepsins of Plasmodium falciparum and Plasmodium vivax, using the structure of human cathepsin D bound to the inhibitor pepstatin as the template. The catalytic subsites S5 through S4' were determined for the modeled parasite proteases. Subsequently, the crystal structure of mouse renin complexed with the nonapeptidyl inhibitor t-butyl-CO-His-Pro-Phe-His-Leu [CHOHCH2]Leu-Tyr-Tyr-Ser-NH2 (CH-66) was used to build homology models of the hemoglobin-degrading peptidases docked with a series of octapeptide substrates. The modeled octapeptides included representative sites in hemoglobin known to be cleaved by both Schistosoma japonicum cathepsin D and human cathepsin D, as well as sites cleaved by one but not the other of these enzymes. The peptidase-octapeptide substrate models revealed that differences in cleavage sites were generally attributable to the influence of a single amino acid change among the P5 to P4' residues that would either enhance or diminish the enzymatic affinity. The difference in cleavage sites appeared to be more profound than might be expected from sequence differences in the enzymes and hemoglobins. The findings support the notion that selective inhibitors of the hemoglobin-degrading peptidases of blood-feeding parasites at large could be developed as novel anti-parasitic agents.

Immune responses in hookworm infections

Hookworms infect perhaps one-fifth of the entire human population, yet little is known about their interaction with our immune system. The two major species are Necator americanus, which is adapted to tropical conditions, and Ancylostoma duodenale, which predominates in more temperate zones. While having many common features, they also differ in several key aspects of their biology. Host immune responses are triggered by larval invasion of the skin, larval migration through the circulation and lungs, and worm establishment in the intestine, where adult worms feed on blood and mucosa while injecting various molecules that facilitate feeding and modulate host protective responses. Despite repeated exposure, protective immunity does not seem to develop in humans, so that infections occur in all age groups (depending on exposure patterns) and tend to be prolonged. Responses to both larval and adult worms have a characteristic T-helper type 2 profile, with activated mast cells in the gut mucosa, elevated levels of circulating immunoglobulin E, and eosinoophilia in the peripheral blood and local tissues, features also characteristic of type I hypersensitivity reactions. The longevity of adult hookworms is determined probably more by parasite genetics than by host immunity. However, many of the proteins released by the parasites seem to have immunomodulatory activity, presumably for self-protection. Advances in molecular biotechnology enable the identification and characterization of increasing numbers of these parasite molecules and should enhance our detailed understanding of the protective and pathogenetic mechanisms in hookworm infections.

Antibody levels to the class I and II epitopes of the M protein and myosin are related to group A streptococcal exposure in endemic populations

Rheumatic fever (RF)/rheumatic heart disease (RHD) and post-streptococcal glomerulonephritis are thought to be autoimmune diseases, and follow group A streptococcal (GAS) infection. Different GAS M types have been associated with rheumatogenicity or nephritogenicity and categorized into either of two distinct classes (I or II) based on amino acid sequences present within the repeat region ('C' repeats) of the M protein. Sera from ARF patients have previously been shown to contain elevated levels of antibodies to the class I-specific epitope and myosin with the class I-specific antibodies also being cross-reactive to myosin, suggesting a disease association. This study shows that immunoreactivity of the class I-specific peptide and myosin does not differ between controls and acute RF (ARF)/RHD in populations that are highly endemic for GAS, raising the possibility that the association is related to GAS exposure, not the presence of ARF/RHD. Peptide inhibition studies suggest that the class I epitope may be conformational and residue 10 of the peptide is critical for antibody binding. We demonstrate that correlation of antibody levels between the class I and II epitope is due to class II-specific antibodies recognizing a common epitope with class I which is contained within the sequence RDL-ASRE. Our results suggest that antibody prevalence to class I and II epitopes and myosin is associated with GAS exposure, and that antibodies to these epitopes are not an indicator of disease nor a pathogenic factor in endemic populations.

Using postoperative cardiac troponin-I (cTi) levels to detect myocardial ischaemia in patients undergoing vascular surgery

Background, Cardiac complications occur commonly in vascular surgery patients. Diagnosis of cardiac complications is difficult because of the inaccuracies associated with traditional cardiac enzyme measurements. CTi, a highly sensitive and specific marker of myocardial injury, may be able to detect cardiac complications with greater ease and accuracy. Methods. The study prospectively examined 100 consecutive patients who underwent major vascular surgery between 6/7/98 and 31/12/98 at the Royal Brisbane Hospital. Daily measurements of cTi, creatine kinase (CK), creatine kinase MB (CKMB), CKMB index, renal function and haemoglobin were taken for three postoperative days. One postoperative electrocardiograph (ECC) was taken. An extensive cardiac history was taken. Intraoperative and postoperative events were recorded. Findings. There were 100 patients, 18 patients (18%) had a cTi elevation. On the basis of classical diagnostic criteria, 15 patients (15%) suffered one or more cardiac complication (either myocardial infarction, congestive cardiac failure, unstable angina or atrial fibrillation), One patient (1%) who had a cTi elevation died. CTI elevation occurred in five patients (5%) who were not diagnosed with cardiac complications based on traditional criteria. Despite not meeting specific diagnostic criteria for cardiac complications, all patients showed signs and symptoms that could be attributed to myocardial ischaemia, Every patient who developed congestive cardiac failure or atrial fibrillation had a cTi elevation. A Chi-square analysis revealed a significant association between cTi elevation and postoperative cardiac complications. Four variables contributed small but significant amounts of unique variance to the prediction of peak cTi on linear regression analysis. These were peak CKMB index, postoperative congestive cardiac failure, postoperative chest pain and postoperative cardiac complications. Conclusions. Routine cTi monitoring of postoperative vascular patients would be an effective and inexpensive way to detect patients with cardiac complications. The relationship between postoperative cTi elevation and significant coronary artery disease remains to be shown, (C) 2001 The international Society for Cardiovascular Surgery. Published by Elsevier Science Ltd. All rights reserved.

Transient mesenteric ischaemic episodes tracked by continuous jejunal PCO2 monitoring during liquid feeding

Objective: To test the effect of liquid feeds on the responses to splanchnic ischaemia of a continuous rapid response PCO2 sensor inserted in the jejunum. Design: Prospective experimental animal study in a university research laboratory. Subjects: Adult male Wistar rats. Interventions: Adult male Wistar rats (285-425 g) were anaethetised with sodium pentobarbitone 60 mg/ kg i.p. and ventilated with 100 % oxygen and isoflurane via tracheostomy to a PaCO2 of 30-40 mmHg. A sensor was inserted into the mid-jejunum to record PCO2 every second. Distal aortic pressure was transduced. Four control rats received no feeds whilst in another four rats liquid feed was infused into the proximal jejunum at 3 ml/h. In each rat five episodes of splanchnic ischaemia were induced by 2-min elevations of an aortic sling to a mean distal aortic pressure of 30 mmHg. Measurements and main results: PCO2 elevations were always detectable, usually less than a minute from the onset of splanchnic ischaemia in both fed and unfed rats, with no difference in mean times to detectable response. In the fed rats there was a small but significant increase in the time to peak sensor response (196 +/- 16 vs. 180 +/- 12 s) and a trend towards an elevated mean baseline luminal PCO2 (67 +/- 9 vs. 55 +/- 4 mmHg). Conclusions: Brief episodes of splanchnic ischaemia were tracked successfully by a rapid response jejunal continuous PCO2 sensor during the infusion of a proprietary liquid feed preparation despite minor changes in PCO2 response characteristics and a possible elevation in baseline luminal PCO2.

Patterns and levels of endemism in the Australian Wet Tropics rainforest: evidence from flightless insects

This study examines the level and pattern of endemism among 274 flightless rainforest insects found in the Wet Tropics region of Australia. Endemism is measured at two nested scales: (1) those confined to the Wet Tropics, termed 'regional endemics'; and (2) the subset of those species confined to a single subregion of the Wet Tropics, termed 'subregional endemics'. Fifty per cent of the regional endemic flightless insects are also subregional endemics compared with 15% of the known regional endemic vertebrates. The four subregions with the most endemic flightless insect species are the uplands of Mt Finnigan, Carbine, Bellenden-Ker/Bartle Frere and Atherton. Multiple regression suggests that the combination of rainforest area and shape explain the most variance (R-2 = 0.603) in the numbers of species of regional endemic insects. However, subregional endemism is not closely correlated with the size or shape of the subregions in which they occur, or a combination of these factors. Candidate refugial and recolonised subregions are identified, and are consistent with data from palaeoclimatic models and refugia identified using other taxa. We group upland subregions into larger areas of endemism using parsimony analysis of endemism. These groupings are consistent with our understanding of the history of the Wet Tropics rainforests.