African bush elephants inhabiting the undeveloped Kalahari Sands region of Hwange National Park, Zimbabwe are subject to episodic mortality during droughts. We monitored the drought‐related mortality ...of elephants in Hwange National Park over the course of an extended drought between 1993 and 1995. The drought‐related mortality of elephants was higher during 1994 than 1995, despite significantly higher rainfall in 1994 than 1995. We found significant differences in the age‐specific mortality of elephants during 1994 and 1995. The cumulative mortality profile from this study differed significantly from previous die‐offs at this site, with a higher mortality among adult age classes than that reported from earlier studies in Hwange National Park. The effective duration of the rainy season, not total annual precipitation, appears to be the best predictor for the potential severity of drought mortality among elephants in the Kalahari Sands habitats of Hwange National Park.
Résumé
Les éléphants de brousse qui habitent la région des Kalahari Sands du Parc National de Hwange, au Zimbabwe, sont victimes de mortalitéépisodique pendant les périodes de sécheresse. Nous avons suivi la mortalité due à la sécheresse des éléphants du Parc National de Hwange tout au long d'une sécheresse qui a duré de 1993 à 1995. La mortalité due à la sécheresse a été plus forte en 1994 qu'en 1995, malgré des chutes de pluies supérieures en 1994 qu'en 1995. Nous avons trouvé des différences significatives dans la mortalité spécifique de l'âge des éléphants en 1994 et en 1995. Le profil de la mortalité cumulée issu de cette étude était significativement différent des valeurs relevées précédemment à cet endroit, la mortalité parmi les classes d'âge adultes étant plus élevée que celle relevée dans les études antérieures menées au Parc National de Hwange. La durée effective de la saison des pluies et non les précipitations annuelles totales semble être le meilleur facteur pour prédire la sévérité potentielle de la mortalité due à la sécheresse chez les éléphants des Kalahari Sands, au Parc National de Hwange.
Enteroaggregative Escherichia coli (EAEC) is defined by a characteristic "stacked-brick" aggregative adherence (AA) pattern to cultured cells. In well-studied EAEC prototype strains (called typical ...EAEC strains), the AA phenotype requires aggregative adherence fimbriae (AAFs). However, previous studies suggest that known AAF alleles are not found in all EAEC strains. To define mechanisms contributing to adherence in an atypical strain, we studied EAEC strain C1096. An E. coli K12 derivative carrying two plasmids, designated pSERB1 and pSERB2, from C1096 adhered to cell lines and exhibited an AA pattern. Nucleotide sequence analysis of pSERB1 indicated that it is related to plasmids of the IncI1 incompatibility group. These plasmids encode genes involved in pilus-mediated conjugal transfer, as well as pilL-V, which encodes a second pilus of the type IV family. Insertional inactivation of the gene predicted to encode the major type IV pilin subunit (pilS) reduced conjugal transfer of the plasmid by 4 orders of magnitude. Adherence of the mutant strain to polystyrene and to HT29 cells was reduced by approximately 21% and 75%, respectively. In a continuous-flow microfermentor, the pilS inactivation reduced mature biofilm formation on a glass slide by approximately 50%. In addition, the simultaneous presence of both pSERB1 and pSERB2 plasmids promoted pilS-independent biofilm formation. We conclude that the IncI1 plasmid of EAEC C1096 encodes a type IV pilus that contributes to plasmid conjugation, epithelial cell adherence, and adherence to abiotic surfaces. We also observe that AA can be mediated by factors distinct from AAF adhesins.
A DNA microarray was used to analyze the distribution of plasmid and chromosomal genes among strains of enteroaggregative Escherichia coli (EAEC) isolated from a prospective diarrhoea surveillance ...study in the United Kingdom. Target genes were extracted from existing databases and from the genome sequence of prototype EAEC strain 042. We found that strains exhibiting the aggregative adherence (AA) phenotype could be broadly divided into two groups depending upon whether they harboured genes from the EAEC virulence plasmid (pAA) and a set of chromosomal genes found in EAEC strain 042. Several chromosomal loci were inherited en bloc, and were more common in strains which we designated Group 1; genes at the pheU locus were particularly conserved. Genes encoded on the pAA plasmid and those under control of the master regulator AggR were also concentrated in the Group 1 EAEC. A gene encoding a type 1 pilin allele was detected more frequently in Group 2 EAEC. Our data suggest that strains previously designated as typical EAEC harbour a large number of conserved plasmid and chromosomal loci, further illuminating a package of virulence genes common to the most important EAEC.
A single-mode waveguide and a 1 /spl times/ 3 multimode interference (MMI) power splitter are fabricated in hybrid zirconium (Zr)-doped sol-gel material by a microreplication technology with a ...polydimethylsiloxane (PDMS) replica. The power splitter, as optimized using a finite-difference beam-propagation method (FD-BPM) simulation with self-imaging effects, represents one of the first experimental demonstrations of a high-tolerance manufactured device using replication methods. The fabrication of the microreplicated power splitter demonstrates high-quality optical and geometrical properties. The local uniformity in thickness of the multimode waveguide is less than 1.0%, and the average surface roughness is about 5.35 nm. The measured splitting loss is less than 0.6 dB for both transverse polarizations at the 1550-nm wavelength. Experimental achievements indicate that the soft lithography technology allows for the performance of applications in integrated optical devices in Zr-doped sol-gel materials with high standards.
Endogenous mouse mammary tumor virus (MMTV) proviruses have recently been shown to cosegregate genetically with the minor lymphocyte-stimulating loci, also termed self-superantigens. The antigenic ...activity has been localized to the open reading frame (ORF) protein encoded in the long terminal repeat of MMTV. We show here that unlike their nontransgenic littermates, transgenic mice expressing high levels of an ORF protein derived from the C3H exogenous MMTV specifically delete their V beta 14+ T cells and do not become infected with this virus when it is present in their mother's milk. Thus, it appears that MMTV utilizes cells of the immune system in its infection pathway, and mice that retain endogenous MMTVs should be immune to infection by exogenous virus. These results offer possible new approaches to anti-viral therapy or immunization.
Avian influenza viruses are now widely recognized as important threats to agricultural biosecurity and public health, and as the potential source for pandemic human influenza viruses. Human ...infections with avian influenza viruses have been reported from Asia (H5N1, H5N2, H9N2), Africa (H5N1, H10N7), Europe (H7N7, H7N3, H7N2), and North America (H7N3, H7N2, H11N9). Direct and indirect public health risks from avian influenzas are not restricted to the highly pathogenic H5N1 “bird flu” virus, and include low pathogenic as well as high pathogenic strains of other avian influenza virus subtypes, e. g., H1N1, H7N2, H7N3, H7N7, and H9N2. Research has shown that the 1918 Spanish Flu pandemic was caused by an H1N1 influenza virus of avian origins, and during the past decade, fatal human disease and human-to-human transmission has been confirmed among persons infected with H5N1 and H7N7 avian influenza viruses. Our ability to accurately assess and map the potential economic and public health risks associated with avian influenza outbreaks is currently constrained by uncertainties regarding key aspects of the ecology and epidemiology of avian influenza viruses in birds and humans, and the mechanisms by which highly pathogenic avian influenza viruses are transmitted between and among wild birds, domestic poultry, mammals, and humans. Key factors needing further investigation from a risk management perspective include identification of the driving forces behind the emergence and persistence of highly pathogenic avian influenza viruses within poultry populations, and a comprehensive understanding of the mechanisms regulating transmission of highly pathogenic avian influenza viruses between industrial poultry farms and backyard poultry flocks. More information is needed regarding the extent to which migratory bird populations to contribute to the transnational and transcontinental spread of highly pathogenic avian influenza viruses, and the potential for wild bird populations to serve as reservoirs for highly pathogenic avian influenza viruses. There are still uncertainties regarding the epidemiological and ecological mechanisms that regulate “spill-over” and “spill-back” transmission of highly pathogenic avian influenza viruses between poultry and wild bird populations, and the interspecies transmission of avian influenza from infected birds to humans and other species of mammals. Further investigations are needed to evaluate the effectiveness of poultry vaccination programs for the control and eradication of avian influenza in poultry populations at the national and regional level, and the effect of long term poultry vaccination programs on human public health risks from avian influenza viruses. There is a need to determine risk factors associated with the extent of direct human involvement in the spread and proliferation of avian influenza viruses through commercial supply chain and transportation networks, and specific risk factors associated with domestic and international trade in live poultry, captive wild birds, poultry food products, (meat, eggs), poultry by-products (feathers, poultry meal), poultry manure, and poultry litter. Addressing these issues will greatly enhance our ability to implement economically and ecologically sustainable programs for the control of avian influenza outbreaks in wild and domesticated birds, increase our capability for promoting the protection of wild bird populations from disease and disruption, and help improve food security and public health in countries worldwide.
We examined the relationship among biventricular hemodynamics, pulmonary regurgitant fraction (PRF), right ventricular outflow tract (RVOT) aneurysm or akinesia, and baseline and surgical ...characteristics in adults with repaired tetralogy of Fallot (rTOF).
The precise relationship of pulmonary regurgitation with biventricular hemodynamics has been hampered by limitations of right ventricular (RV) imaging.
We assessed 85 consecutive adults with rTOF and 26 matched healthy controls using cardiovascular magnetic resonance imaging.
Patients had higher right ventricular end-diastolic volume index (RVEDVi) (p < 0.001), right ventricular end-systolic volume index (RVESVi) (p < 0.001), right ventricular mass index (RVMi) (p < 0.001), and lower right ventricular ejection fraction (RVEF) (p < 0.001) and left ventricular ejection fraction (LVEF) (p = 0.002) compared to controls. The PRF (range 0% to 55%) independently predicted RVEDVi (p < 0.01) and the latter predicted RVESVi (p < 0.01) and RVMi (p < 0.01). The RVOT aneurysm/akinesia was present in 48/85 (56.9%) of patients and predicted RV volumes (RVEDVi, p = 0.01, and RVESVi, p = 0.03). There was a negative effect of RVOT aneurysm/akinesia and RVMi on RVEF (p < 0.01 and p = 0.02, respectively). There was only a tendency among patients with transannular or RVOT patching toward RVOT aneurysm/akinesia (p = 0.09). The LVEF correlated with RVEF (r = 0.67, p < 0.001).
Pulmonary regurgitation and RVOT aneurysm/akinesia were independently associated with RV dilation and the latter with RV hypertrophy late after rTOF. The RVOT aneurysm/akinesia was common but related only in part to RVOT or transannular patching. Both RV hypertrophy and RVOT aneurysm/akinesia were associated with lower RVEF. Left ventricular systolic dysfunction correlated with RV dysfunction, suggesting an unfavorable ventricular-ventricular interaction. Measures to maintain or restore pulmonary valve function and avoid RVOT aneurysm/akinesia are mandatory for preserving biventricular function late after rTOF.
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