Review Article
Microarrays: new tools to unravel parasite transcriptomes
- G. N. GOBERT, L. P. MOERTEL, D. P. McMANUS
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- 01 June 2005, pp. 439-448
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The ability to monitor the expression levels of thousands of genes in a single microarray experiment is a huge progression from conventional Northern blot analysis or PCR-based techniques. Microarrays can play a pivotal role in the mass screening of genes in a wide range of fields including parasitology. The relatively few parasites that can be readily cultured or isolated from a host, as compared with cell lines or tissue sources, makes microarray technology ideal for maximizing experimental results from a limiting source of starting material. Khan et al. (1999a) commented in an early review of microarray technology “With this system in place, one can anticipate a time when data from thousands of gene expression experiments will be available for meta-analysis…..… leading to more robust results and subtle conclusions”. Now in 2005, microarrays represent a very powerful resource that can play an important role in the characterization and annotation of the transcriptomes of many parasites of medical and veterinary importance.
Research Article
Estimation of the sequestered parasite load in severe malaria patients using both host and parasite markers
- L. B. OCHOLA, K. MARSH, B. LOWE, S. GAL, G. PLUSCHKE, T. SMITH
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- 28 June 2005, pp. 449-458
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The virulence of the malaria parasite Plasmodium falciparum is due, in part, to its ability to cytoadhere in deep vascular beds. Our inability to quantify the load of sequestered parasites hampers our understanding of the pathophysiological mechanisms involved in disease progression and complicates diagnosis. In this study we evaluate potential biochemical markers of sequestered load by comparing them with estimates of the sequestered load from a statistical model fitted to longitudinal patterns of peripheral parasite densities in a series of 22 patients with severe Plasmodium falciparum malaria. The markers comprised the host factors: haematocrit, circulating host DNA, sTNF-R75 and parasite derived products HRP2, pLDH, pigments and circulating parasite DNA. We investigated the suitability of these markers in determining sequestered loads in patients on quinine treatment. Observed peripheral parasitaemia, plasma levels of sTNF-R75 and circulating parasite DNA were most strongly correlated with estimates of sequestered loads on admission. However the dynamics of both sTNF-R75 and circulating parasite DNA during follow-up were very different from those of the estimated sequestered mass. These analyses suggest that none of the markers gave reliable estimates of the current sequestered load, though they may reflect the history of infection. Longitudinal analyses are needed that allow for the clearance rates of the marker molecules and for variations between hosts in the history of parasitaemia.
Synergistic antimalarial activity of ketones with rufigallol and vitamin C
- S. S. MAHAJAN, V. R. KAMATH, S. S. GHATPANDE
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- 28 June 2005, pp. 459-466
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Malaria remains a major cause of human morbidity and mortality worldwide. Plasmodium falciparum, the most virulent of the 4 human Plasmodium species causing malaria, is potentially life threatening, is increasing in prevalence and is becoming even more resistant to in-use drugs. In light of the growing problem of multi-drug resistance to malarial parasites, the development of new drugs or the use of a combination therapy is of primary importance. A previous report describes a remarkable synergistic antimalarial interaction between 2 structurally similar compounds, rufigallol, an anthraquinone derivative and exifone, a benzophenone derivative, in vitro. The synergistic antimalarial activity of exifone and vitamin C was also reported. To extend the same analogy to other ketones, we carried out antimalarial testing of 20 benzophenone derivatives, individually, in combination with rufigallol, and also in combination with vitamin C, in mice infected with Plasmodium berghei. Five ketones, out of 20, showed good antimalarial activity, in vivo, when tested individually. Nine ketones, out of 20, showed good antimalarial activity, in vivo, when tested in combination with rufigallol, indicating the synergism between them. However, synergism between ketones and vitamin C was not satisfactory since only 2 ketones showed good antimalarial activity when tested in combination with vitamin C.
Subcellular fractionation and molecular characterization of the pellicle and plasmalemma of Neospora caninum
- Y. LEI, D. BIRCH, M. DAVEY, J. T. ELLIS
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- 16 June 2005, pp. 467-475
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A characteristic structural feature of Toxoplasma gondii and Neospora caninum is the presence of a triple-membrane pellicle, on the zoite stages of their complex life-cycle. Here we report the results of electron microscopic studies which show that the pellicle is made of a typical plasmalemma covered on its cytoplasmic side by a system of flattened vesicles named the inner membrane complex. Using methods described previously for the purification of pellicle and plasmalemma fractions from T. gondii, we have evaluated the same methodology for the preparation of pellicles and plasmalemma from N. caninum. The approach used involved subcellular fractionation and sucrose gradient centrifugation to prepare fractions containing pellicles. Plasmalemma was prepared by extraction of this fraction with a high salt glycerol treatment. Fractions containing membrane structures were identified by electron microscopy, and the proteins and antigens present in them were subsequently studied by SDS-PAGE and Western blotting. Electron microscopy of the pellicle fractions of N. caninum demonstrated preservation of the triple-membrane structure which is identical to that found in T. gondii. SDS-PAGE of the pellicle fractions revealed it contained several major proteins. Analyses revealed that the plasmalemma of N. caninum contained 2 abundant proteins in addition to other much lower abundance antigens detectable by monoclonal antibodies. These studies therefore report, for the first time, a detailed molecular characterization of the pellicle and plasmalemma of N. caninum.
Germ-free mice produce high levels of interferon-gamma in response to infection with Leishmania major but fail to heal lesions
- M. R. OLIVEIRA, W. L. TAFURI, L. C. C. AFONSO, M. A. P. OLIVEIRA, J. R. NICOLI, E. C. VIEIRA, P. SCOTT, M. N. MELO, L. Q. VIEIRA
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- 28 June 2005, pp. 477-488
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In order to investigate the importance of the host microbiota on differentiation of T cell subsets in response to infection, Swiss/NIH germ-free mice and conventional (microbiota-bearing) mice were infected with Leishmania major, and lesion development, parasite loads, and cytokine production were assessed. Germ-free mice failed to heal lesions and presented a higher number of parasites at the site of infection than their conventional counterparts. In addition, histopathological analysis indicated a higher density of parasitized macrophages in lesions from germ-free mice than in conventional mice. The initial production of interleukin (IL)-12 and interferon-gamma (IFN-γ) in germ-free mice was comparable to the conventional controls. Also, germ-free mice produced elevated levels of IFN-γ and lower levels of IL-4 throughout the course of infection, suggesting the development of a Th1 response. Macrophages from germ-free mice exposed to IFN-γ and infected with amastigotes in vitro were not as efficient at killing parasites as macrophages from conventional animals. These observations indicate that the microbiota is not essential for the development of Th1 immune responses, but seems to be important for macrophage activation.
Molecular characterization of haemoparasites infecting bats (Microchiroptera) in Cornwall, UK
- R. CONCANNON, K. WYNN-OWEN, V. R. SIMPSON, R. J. BIRTLES
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- 28 June 2005, pp. 489-496
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The presence of haemoparasites from the Order Piroplasmida and the genera Bartonella and Trypanosoma was assessed in the blood of 60 bats, belonging to 7 species, inhabiting sites across Cornwall in southwest England. DNA extracted from macerated heart tissue was incorporated into taxon-specific polymerase chain reactions (PCRs) and amplification products were sequenced as a means of identifying, or assigning an identity, to detected haemoparasites. A Piroplasmida species was detected in 6 Pipistrellus spp., whereas Bartonella infections were detected in 5 bats belonging to 4 different species. Trypanosoma dionisii was detected in 1 Pipistrellus spp. Phylogenetic inference from alignment of a partial 18S rRNA-encoding gene sequence of the pipistrelle-associated Piroplasmida species with homologous sequences available for other members of the Order indicated that this organism was unique but specifically related to members of the genus Babesia, a phylogeny that would be in keeping with the organism being Babesia vesperuginis. Alignment of partial citrate synthase gene sequences from the bat-associated bartonellae revealed 5 distinct genotypes that were probably derived from 2 distinct Bartonella species. The study demonstrates the utility of molecular methods for detecting haemoparasites in dead bats and provides, for the first time, tangible identities for bat-associated Babesia and Bartonella species.
Development of a novel PCR assay capable of detecting a single Schistosoma japonicum cercaria recovered from Oncomelania hupensis
- A. J. DRISCOLL, J. L. KYLE, J. REMAIS
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- 10 June 2005, pp. 497-500
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Location and time-specific variability in Schistosoma japonicum cercarial density has been shown to be high in the mountainous regions of Sichuan Province, China. A polymerase chain reaction (PCR) assay for the detection of schistosome cercariae in these environments would aid in the determination of environmental risk, and the identification of individual-level risk factors. Here the authors present a highly sensitive and specific PCR assay for the detection of S. japonicum cercariae in laboratory samples. As few as 1 and as many as 300 cercariae, from both laboratory and field-collected S. japonicum strains, produced positive amplification results, and repeated assays showed no positive result for S. mansoni nor for non-japonicum cercariae isolated from infected snails collected in Sichuan Province. There was no difference found between the Chinese and Philippine S. japonicum strains. The results presented demonstrate the successful PCR amplification of a target sequence within the SjR2 retrotransposon from samples of S. japonicum cercariae, with the potential for application to natural water samples from endemic areas.
Altered drug influx/efflux and enhanced metabolic activity in triclabendazole-resistant liver flukes
- L. I. ALVAREZ, H. D. SOLANA, M. L. MOTTIER, G. L. VIRKEL, I. FAIRWEATHER, C. E. LANUSSE
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- 16 June 2005, pp. 501-510
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Triclabendazole (TCBZ) is a halogenated benzimidazole compound that possesses high activity against immature and adult stages of the liver fluke, Fasciola hepatica. The intensive use of TCBZ in endemic areas of fascioliasis has resulted in the development of liver flukes resistant to this compound. TCBZ sulphoxide (TCBZSO) and TCBZ sulphone (TCBZSO2) are the main molecules recovered in the bloodstream of TCBZ-treated animals. In order to gain some insight into the possible mechanisms of resistance to TCBZ, the goals of the work described here were: to compare the ex vivo transtegumental diffusion of TCBZ parent drug and its sulpho-metabolites (TCBZSO and TCBZSO2) into TCBZ-susceptible and -resistant liver flukes; and to assess the comparative pattern of TCBZ biotransformation by TCBZ-susceptible and -resistant F. hepatica. For the tegumental diffusion studies, TCBZ-susceptible (Cullompton) and -resistant (Sligo) adult flukes collected from untreated infected sheep were incubated (15–180 min) in KRT buffer containing either TCBZ, TCBZSO or TCBZSO2 (5 nmol.ml−1). For the metabolism studies, microsomal fractions obtained from TCBZ-susceptible and -resistant flukes were incubated for 60 min with TCBZ (40 μM), and the amount of the formed metabolic product (TCBZSO) was measured. Drug/metabolite concentrations were quantified by HPLC. All the assayed TCBZ-related molecules penetrated through the tegument of both TCBZ-susceptible and -resistant flukes. However, significantly lower (approximately 50%) concentrations of TCBZ and TCBZSO were recovered within the TCBZ-resistant flukes compared to the TCBZ-susceptible ones over the 180 min incubation period. The rate of TCBZ sulphoxidative metabolism into TCBZSO was significantly higher (39%) in TCBZ-resistant flukes. The flavin-monooxigenase (FMO) enzyme system appears to be the main metabolic pathway involved in the formation of TCBZSO in both TCBZ-susceptible and -resistant flukes. The altered drug influx/efflux and enhanced metabolic capacity identified in TCBZ-resistant liver flukes may account for the development of resistance to TCBZ.
Ichthyocotylurus erraticus (Digenea: Strigeidae): factors affecting infection intensity and the effects of infection on pollan (Coregonus autumnalis), a glacial relict fish
- C. HARROD, D. GRIFFITHS
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- 10 June 2005, pp. 511-519
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Lough Neagh pollan are heavily infected with the strigeid Ichthyocotylurus erraticus, with 100% prevalence and median infection intensities of 600+ metacercariae in the pericardial cavity of mature fish. Female fish were more heavily infected than males. Infection intensity, which rose in summer, varied with pollan size, year, sampling bay within the lough and water depth within bays. Heavily infected pollan were caught further offshore than lightly infected fish. Spatial variation in pollan infection intensity corresponded to variation in the abundance of the first intermediate host, Valvata snails. The data suggest that heavily infected fish had lower food intakes. Parasitism reduced condition and liver size in male fish but condition in heavily parasitized females increased. Infection intensity was greater in larger fish of a given age. These patterns are discussed in the context of risks and rewards. The data suggest that inshore waters in summer are the preferred habitat of pollan and that the greater infection intensity of offshore fish results from their reduced competitive ability as a consequence of parasitism and the increased risk of infection there.
A study of the mechanisms by which the cercariae of Microphallus primas (Jag, 1909) Stunkard, 1957 penetrate the shore crab, Carcinus maenas (L)
- D. H. SAVILLE, S. W. B. IRWIN
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- 28 June 2005, pp. 521-529
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This study established the mechanisms by which Microphallus primas cercariae penetrate the crab Carcinus maenas in which they form metacercarial cysts. Light and electron microscopy were used to investigate cercarial features and to follow the fate of cercariae released in close proximity to crabs. It was shown that cercariae were carried in respiratory currents into crabs' branchial chambers where each enveloped itself in a transparent penetration cyst on the gill lamellae. When cercariae were present the number of respiratory current reversals performed by crabs increased. Using an ‘artificial branchial chamber’ it was possible to observe how cercariae attached to crab gills during breaks in current flow that preceded each current reversal. Inside the penetration cysts the now tail-less larvae used their stylets to pierce holes through which they levered themselves into underlying haemolymph channels in the gills. Histochemical tests demonstrated that the penetration cysts were products of glands in the cercariae and that penetration of the crabs was achieved by mechanical means. The importance of crab respiratory current reversals to the success of cercarial penetration is discussed as it represents the exploitation by a parasite of a host behavioural response to an unrelated stimulus.
Effect of bioactive compounds from Sainfoin (Onobrychis viciifolia Scop.) on the in vitro larval migration of Haemonchus contortus: role of tannins and flavonol glycosides
- E. BARRAU, N. FABRE, I. FOURASTE, H. HOSTE
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- 16 June 2005, pp. 531-538
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Anthelmintic bioactivity against gastrointestinal nematodes has been associated with leguminous forages supporting the hypothesis of a role of condensed tannins. However, the possibility that other compounds might also been involved has received less consideration. Using bio-guided fractionation, the current study aimed at characterizing the biochemical nature of the active compounds present in sainfoin (Onobrychis viciifolia), previously identified as an anthelmintic leguminous forage. The effects of sainfoin extracts were evaluated on 3rd-stage larvae (L3) of Haemonchus contortus by using a larval migration inhibition (LMI) assay. Comparison of extracts obtained with several solvent systems showed that the bioactivity was associated with the 70[ratio ]30 acetone/water extract. Further fractionation of the later allowed the separation of phenolic compounds. By use of a dialysis method, compounds were separated with a molecular weight cut-off of 2000 Da. The in vitro anthelmintic effect of the fraction with condensed tannins was confirmed. In the fraction containing molecules of MW <2000 Da, 3 flavonol glycosides were identified as rutin, nicotiflorin and narcissin. At 1200 μg/ml, each inhibited significantly the migration of larvae. Addition of polyvinyl pyrrolidone (PVPP) to both fractions before incubation restored larval migration. These results confirmed the role of both tannins and flavonol glycosides in the anthelmintic properties of sainfoin.
Definition of genetic markers in nuclear ribosomal DNA for a neglected parasite of primates, Ternidens deminutus (Nematoda: Strongylida) – diagnostic and epidemiological implications
- A. R. SCHINDLER, J. M. DE GRUIJTER, A. M. POLDERMAN, R. B. GASSER
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- 23 May 2005, pp. 539-546
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Ternidens deminutus (Strongylida) is a parasitic nematode infecting non-human and human primates in parts of Africa, Asia and the Pacific islands. The present study genetically characterized T. deminutus and defined genetic markers in nuclear ribosomal DNA (rDNA) as a basis for developing molecular-diagnostic tools. The sequences of the second internal transcribed spacer (ITS-2) of rDNA were determined for adult specimens of T. deminutus (Nematoda: Strongylida: Oesophagostominae) from the Olive baboon and the Mona monkey.
Nucleotide sequence data used in this paper are available in the EMBL, GenBank and DDJB databases under the Accession nos. AJ888729, AJ888730, AF136576, Y10789, Y10790, Y11733, Y11735, Y11736, AJ001594, AJ001599, AJ006149 and AJ006150. The former 2 sequences represent original data reported in this paper. The length and G+C content of the ITS-2 sequences was 216 bp and ~43%, respectively. While there was no sequence variation among individual T. deminutus specimens from the baboon, 6 (2·8%) nucleotide differences were detected in the ITS-2 between the parasite from baboon and that of the Mona monkey, which is similar to the difference (3·2%) between 2 other species of Oesophagostominae (Oesophagostomum bifurcum and O. stephanostomum) from non-human primates, suggesting significant population variation or the existence of cryptic (i.e. hidden) species within T. deminutus. Pairwise comparisons of the ITS-2 sequences of the 2 operational taxonomic units of T. deminutus with previously published ITS-2 sequences for selected members of the subfamilies Oesophagostominae and Chabertiinae indicated that species from primates (including those representing the subgenera Conoweberia and Ihleia) are closely related, in accordance with previous morphological studies. The sequence differences (27–48·3%) in the ITS-2 between the 2 taxonomic units of T. deminutus and hookworms (superfamily Ancylostomatoidea) enabled their identification and delineation by polymerase chain reaction (PCR)-based mutation scanning. The genetic markers in the ITS-2 provide a foundation for improved, PCR-based diagnosis of T. deminutus infections and for investigating the life-cycle, transmission patterns and ecology of this parasite.
Molecular study of Echinococcus in west-central China
- Y. R. YANG, M. C. ROSENZVIT, L. H. ZHANG, J. Z. ZHANG, D. P. MCMANUS
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- 10 June 2005, pp. 547-555
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West-central China is an important endemic focus of both alveolar and cystic echinococcosis where several species of intermediate host are commonly infected with Echinococcus granulosus and E. multilocularis. Isolates of E. granulosus were collected from humans and other animals from different geographical areas of Qinghai, Ningxia, Gansu and Sichuan, and genotyped using the mitochondrial DNA marker ATP synthase subunit 6 gene (atp6). The sheep strain (G1 genotype) of E. granulosus was shown to be the only genotype present in sheep, cattle, goats, yaks and humans in the study areas. However, some heterogeneity in the atp6 sequence was evident in a number of the isolates with the most frequent change being a silent substitution (G/A) at position 360 compared with the G1 reference sequence representing isolates collected from the majority of hosts except humans. Two E. multilocularis isolates examined also had sequences that varied from each other and from the reference E. multilocularis atp6 sequence. The genotypic variation we report may reflect phenotypic differences with important consequences in terms of increased host infectivity for hosts by local Echinococcus strains, possibly impacting on the epidemiology and control of echinococcosis. Such adaptations may also result in different sensitivity to drugs or increased virulence for hosts that will impede control efforts and even affect vaccination strategies against Echinococcus.
Covariance in species diversity and facilitation among non-interactive parasite taxa: all against the host
- B. R. KRASNOV, D. MOUILLOT, I. S. KHOKHLOVA, G. I. SHENBROT, R. POULIN
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- 23 May 2005, pp. 557-568
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Different parasite taxa exploit different host resources and are often unlikely to interact directly. It is unclear, however, whether the diversity of any given parasite taxon is indirectly influenced by that of other parasite taxa on the same host. Some components of host immune defences may operate simultaneously against all kinds of parasites, whereas investment by the host in specific defences against one type of parasite may come at the expense of defence against other parasites. We investigated the relationships between the species diversity of 4 higher taxa of ectoparasites (fleas, sucking lice, mesostigmatid mites, and ixodid ticks), and between the species richness of ectoparasites and endoparasitic helminths, across different species of rodent hosts. Our analyses used 2 measures of species diversity, species richness and taxonomic distinctness, and controlled for the potentially confounding effects of sampling effort and phylogenetic relationships among host species. We found positive pairwise correlations between the species richness of fleas, mites and ticks; however, there was no association between species richness of any of these 3 groups and that of lice. We also found a strong positive relationship between the taxonomic distinctness of ecto- and endoparasite assemblages across host species. These results suggest the existence of a process of apparent facilitation among unrelated taxa in the organization of parasite communities. We propose explanations based on host immune responses, involving acquired cross-resistance to infection and interspecific variation in immunocompetence among hosts, to account for these patterns.
Nested patterns in parasite component communities of a marine fish along its latitudinal range on the Pacific coast of South America
- M. T. GONZÁLEZ, R. POULIN
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- 25 May 2005, pp. 569-577
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A major goal of community ecology is to identify and explain non-random patterns of species composition. To date, the search for nested patterns in parasite component communities of the same fish host species has not been attempted, despite the fact that this higher hierarchical level is more relevant to nestedness analyses. The aims of this study are first, to determine the structure of component communities – considering ectoparasites and endoparasites separately – of a marine fish (Sebastes capensis) with an extended geographical distribution along the southeastern Pacific and, second, to explain these patterns by taking into account the extrinsic factors associated with the distribution of this host fish. From April to September 2003 and from April to August 2004, 537 fish were captured from different latitudes along the southeastern Pacific. The component communities of both ectoparasites and endoparasites of this fish host showed significant nested subset patterns. However, the type of nestedness pattern differed between ectoparasites and endoparasites. Ectoparasite component communities of S. capensis show higher species richness between latitude 30°S and 40°S, whereas endoparasite component communities show higher species richness between 40°S and 52°S. A nested pattern in ectoparasite component communities of S. capensis result from the gradual loss of some ectoparasites species southward and northward of the central part of their latitudinal distribution, which can be explained by the interaction of S. capensis with other host fish species from the central Chilean coast. Nestedness in endoparasite component communities of S. capensis is produced by the gains and losses of species toward the south of their latitudinal distribution, caused by changes in their prey-items (intermediate hosts) along their latitudinal distributional range.
Book Review
Identification and Geographical Distribution of the Mosquitoes of North America, North of Mexico, 2nd Edition. By R. F. Darsie Jr. and R. A. Ward, pp. 416. University Press of Florida, USA, 2005. ISBN0 8130 2784 5. US$ 75.00.
- RICHARD D. WARD
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- 07 September 2005, p. 580
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This comprehensive and thorough work of scholarship is dedicated to the memory of the great American mosquito systematist and biologist, John N. Belkin. Based on an original volume by Carpenter and La Casse, the new authors have added a further 31 species and have revised the original keys. The morphological terms used for adults are substantially revised and they have adopted the chaetotaxy for immature stages developed by Belkin and his colleagues. Species names identified in the keys are followed by a plate number that refers to distribution maps, some of which cover up to 4 species. Following an introduction, a 6-page section on systematics lists new species added to the fauna since 1955, those species resurrected from synonomy and, interestingly, 9 exotic species introduced including the notorious ‘Asian Tiger Mosquito’ Aedes albopictus. This invader was first detected in 1985 and, 20 years later, is now present in 26 states of the Eastern USA. Ochlerotatus, a new genus recently raised from subgeneric status, is discussed briefly, and the authors comment on siblings now recognized through molecular evaluation, for example in the Anopheles quadrimaculatus group. An encouragement for those wrestling with elucidating such complexes is found in the final commentary on this group which notes that, although molecular markers are available, the 5 siblings are now recognized morphologically in all life-stages. The section provides a useful systematic index in tabular form to the Culicidae of the region and their zoogeographic distribution.
The main text begins with the morphology of adult female mosquitoes and is followed by illustrated keys to generic level and then detailed keys to the species of each genus. Similar treatment of the fourth instar larvae follows, again providing illustrated keys.
An extensive bibliography to the topic is provided at the end of the book, with over 800 references.
For the dedicated mosquito worshipper! This book is undoubtedly a must and with its beautifully illustrated keys sets a high standard to follow. It will also, no doubt, prove an attractive volume for more general medical entomologists and enthusiastic students of these irksome, dangerous and fascinating animals.
Consumer-Resource Dynamics. By William W. Murdoch, Cheryl J. Briggs & Roger M. Nisbet, pp. 462. Monographs in Population Biology, 36. Princeton University Press, Princeton, USA and Oxford, UK, 2003. ISBN 0 691 00658 X (hbk) and 0 691 00657 1 (pbk). £55.00 (cloth) and £24.95 (paper).
- MARíA-GLORIA BASáÑEZ
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- 07 September 2005, pp. 579-580
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The issue of species persistence may be a central theme in population ecology, but it is also crucial to infectious disease control. While ecologists aim at preserving biodiversity, disease eradication seeks to drive selected pathogens to global extinction; understanding the mechanisms explaining species persistence at local and regional levels underpins both goals.
In Consumer-Resource Dynamics, Murdoch, Briggs & Nisbet attempt to provide a unifying theory of population dynamics which, starting from the most fundamental of interactions, the consumer-resource duo in a homogeneous environment, expands into multispecies interactions, collapses into single population dynamics, or ventures into unpredictability and spatial heterogeneity. The fact that disease-host systems are hardly mentioned does not detract from the relevance this book can have to parasite population biologists, field parasitologists, and those interested in pathogen and pest control. The following synopsis highlights some salient points.
Chapters 1 and 2 provide conceptual and empirical contexts for the notion of population dynamics, focusing on population regulation and persistence, and discussing the concepts of deterministic and stochastic persistence and the importance of scale. Chapters 3 and 4, on simple predator-prey models, explore the reasons behind these being inherently unstable interactions, which nonetheless embody the various manifestations of population regulation. In particular, Chapter 3 discusses Lotka-Volterra (continuous time) models, whilst Chapter 4 deals with Nicholson-Bailey (discrete time) models, and introduces discrete generation parasitoid-host systems. Chapters 5 to 7 incorporate successive layers of biological realism into the latter, with Chapter 5 introducing stage-structure, Chapter 6 exploring the dynamical effects of various parasitoid life-history strategies, and Chapter 7 bringing aspects of behavioural and evolutionary ecology in focus with population dynamics theory. Chapter 8 is dedicated to competition and multispecies interactions, leading to Chapter 9 on biological control, which ends with a discussion on the need for a resurgence of past interest in placing such control in an appropriate and rigorous ecological framework (the same can be said about disease control programmes). Chapter 10 concentrates on the dynamical consequences of making space explicit, with an insightful discussion on the origins of instability and persistence in single-species vs consumer-resource metapopulations. Chapter 11 develops a ‘phylogeny’ of models by presenting the common origin of frameworks for the description and analysis of predator-prey, parasitoid-host, pathogen-host, and herbivore-plant interactions. It is also argued that few-species models may be appropriate to describe the dynamics of populations living in many-species food-webs (by virtue of decoupling the consumer-resource interaction). The striving for a unifying and coherent population dynamics theory, present throughout the book, culminates in Chapter 12's hierarchy of models, which draws together preceding insights and points towards future theoretical and empirical research directions.
Although not presupposing a mathematical biology background, some familiarity on the part of the reader with simple population ecology models may provide a useful backdrop. The uninitiated will find the various appendices on stability analyses most helpful. The book is very well written, with interspersed tables and boxes that list the various models and their stability properties, and concluding remarks at the end of each chapter that summarize main messages and lead naturally into following chapters. On a more personal note, I found this book profoundly stimulating and found myself often discussing the various insights gained through its reading with my students and colleagues. I particularly enjoyed the sections about age- and/or stage-structured models and the advantages and pitfalls of the (often implicit) assumption of exponentially distributed waiting times. The dynamical differences between constant maturation rates and fixed maturation times are relevant to the problem of incorporating latency in parasite-host models. Ratio-dependency in models, where consumer attack rate depends on the ratio of consumers to prey, is akin to the formulation of the vector to host ratio times the biting rate in (dipteran) vector-borne disease models, most of which do not link vector abundance and biting rates to host abundance. Incorporation of overdispersion in parasitoid-host systems is effected through the widely used negative binomial distribution (May-Hassell models), with the degree of overdispersion mainly independent of host or parasitoid density. The development of stochastic models in which the distributional properties of parasitoid or parasite populations emerge from model results clearly remains a research priority. The question as to whether few-species models can appropriately describe the dynamics of many-species systems is also relevant to the topical theme of multiparasitism and the detection and importance of interspecific interactions in shaping parasite communities. If these interactions were less important than intraspecific effects in determining transmission dynamics, the traditional approach to single-species parasite-host models would be adequate. Finally, the results of the Jansen-de Roos spatial versions of the Rosenzweig-MacArthur model (with logistic growth prey and saturating predator attack rate), in which restricted movement leads to substantial decreases in local and global fluctuations, may have important implications for understanding arthropod-borne disease dynamics, as some vectors have limited mobility (ticks, mites), whilst others may connect to a greater extent pathogen-host subpopulations.
Zoonoses and Communicable Diseases Common to Man and Animals. By P. N. Acha and B. Szyfres. Vol. 1. Bacterioses and Mycoses, pp. 378; Vol. 2. Chlamydioses, Rickettsioses and Viroses, pp. 408; Vol. 3. Parasitoses, pp. 395. 3rd Edition. Pan American Health Organisation, Washington, DC, 2003. ISBN 92 75 11991 0. US$ 36.00 for each volume (Orders may be placed at http://publications.paho.org/english/index.cfm).
- PAVOL DUBINSKÝ
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- 07 September 2005, pp. 580-581
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This highly topical book offers information on two groups of communicable diseases: the first being zoonoses, with animals playing an essential role in maintaining the infection in nature and man is only an accidental host. The second group comprises the diseases common to man and animals, where they generally contract the infection from the same source, and the animals may contribute in particular to the distribution and actual transmission of infections.
Ecological and social changes, along with the migration of large numbers of people between continents, have caused the spread of once endemic diseases, which can now pose a threat in distant communities. The risk of bio-terrorism has highlighted the need for detailed knowledge of those diseases in terms of their epidemiology, mechanisms of transmission to humans, diagnosis and control.
In each volume, the groups of communicable diseases are listed in alphabetical order, which makes it easy to use. The great asset of this publication is that a number of pages devoted to each disease follows its incidence rate and pathogenicity for humans and animals. Less serious infections are listed briefly while those possessing serious threat are described in great detail. Each chapter is followed by the list of most important references, though some of them are not the most up-to date.
What also makes it easy to use for a reader is the listing of the synonyms for each disease, and chapters divided into paragraphs with headings such as etiology, geographic distribution, occurrence in man and animals, symptoms, sources of infections and mode of transmission, and the role of animals in its epidemiology, diagnosis and control. However, the tables, figures and photographs are included unevenly in the volumes. The transmission cycles are mostly presented in the second volume, while in the third one regarding Parasitoses they are completely missing. And it is in particular in Parasitoses, where the life-cycles are often quite complicated and for a better understanding of the mode of transmission, such illustrations would be very suitable.
What might be rather confusing are a few listed synonyms, which in several cases are somewhat contradictory in terms of their suffixes – osis (-iosis) and -iasis, even if the agents have the same generic suffix – e.g. Balantidiasis versus Balantidiosis (Balantidium coli,) and Cryptosporidiosis (Cryptosporidium spp.).
In conclusion, the publication, primarily targeted at academics and students in schools of public health, medicine and veterinary medicine, researchers as well as the staff of public health and veterinary health institutions, provides an attractive read – not just for everyone who must or wants to be familiar with the subject, but also for all seeking a broad overview in the world of known and emerging zoonoses.
Correction
Evaluation of the standard membrane feeding assay (SMFA) for the determination of malaria transmission-reducing activity using empirical data
- M. VAN DER KOLK, S. J. DE VLAS, A. SAUL, M. VAN DE VEGTE-BOLMER, W. M. ELING, R. W. SAUERWEIN
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- 07 September 2005, p. 582
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We regret that in the article by M. van der Kolk et al. in Parasitology (2005) Vol. 130 (1), 13–22, W. Sauerwein should have been given as R. W. Sauerwein.
We apologise to the author and readers for this error.