Showing papers in "Parasitology in 1986"
TL;DR: Examining helminth diversity in a series of hosts concludes that there are fundamental differences between the communities of helminths in fish and bird hosts and provides explanations for the observed differences.
Abstract: Recently, some authors (Kennedy, 1981; Price & Clancy, 1983) have argued that there are fundamental differences between the communities of helminths in fish and bird hosts. Such differences are foreshadowed by the work of Dogiel (1964) and are apparent from survey data (e.g. Threlfall, 1967; Bakke, 1972; Hair & Holmes, 1975 on birds, and compare Chubb, 1963; Mishra & Chubb, 1969; Wootten, 1973; Ingham & Dronen, 1980 on fish). Questions still remain, however, as to whether the distinctions are truly justified and whether the differences are really fundamental. In this paper, we address these questions by examining helminth diversity in a series of hosts. We then discuss and provide explanations for the observed differences.
262 citations
TL;DR: It is suggested that the same mechanism which generates these lamellae forms the parasitophorous vacuole by inserting membranous elements formed by the parasite into the red cell membrane, so causing its invagination.
Abstract: In merozoites of Plasmodium knowlesi, rhoptries have a dense substructure of fine (2·5 nm diameter) granules and short rods. These are not altered by lipid extraction, and stain with ethanolic phosphotungstate indicating a proteinaceous composition. Various types of fixation also show multilamellar whorls with a periodicity of 5–7 rim in the tips of rhoptries or extruded at the merozoite apex. In merozoites fixed during invasions of red cells, membrane continuity typically occurs between the rim of the rhoptry canal and the red cell membrane, but where this contact has apparently been lost, extensive membranous whorls and blebs are often found at the apex of the parasite. Similar structures occur at the spices of merozoites within late-stage schizonts. It is suggested that the same mechanism which generates these lamellae forms the parasitophorous vacuole by inserting membranous elements formed by the parasite into the red cell membrane, so causing its invagination. A similar mechanism may be responsible for the release of merozoites from the late-stage schizont.
134 citations
TL;DR: An automated suspension culture system for the cultivation of Plasmodium falciparum is described which retains a degree of flexibility which is absent in other automated culture apparatuses and permits the development and maturation of gametocytes.
Abstract: An automated suspension culture system for the cultivation of Plasmodium falciparum is described which retains a degree of flexibility which is absent in other automated culture apparatuses. Not only does this system of cultivation promote rapid multiplication of asexual parasites but also permits the development and maturation of gametocytes. Using a combination of gelatin flotation and N-acetyl glucosamine treatment synchronous development of gametocytes was achieved. The total time for gametocyte maturation in vitro under the conditions provided was 7 days. Stages II and V required 48 h for development whilst I, III and IV needed 24 h each. Mature microgametocytes were relatively long lived in comparison with macrogametocytes. Electron microscopic study of the synchronized stages confirmed the observations of Sinden (1982) but, in addition, we noted the presence of Garnham bodies, a cytostome in all stages and dense spherules in stages I-III similar to the fenestrated buttons in sporozoites and exoerythrocytic forms. The relationship between the number of osmiophilic bodies in the mature gametocytes and their ability to escape from the red cell is reaffirmed.
129 citations
TL;DR: It is concluded that T. b.b. gambiense stands out as a real subspecies that has undergone a distinct evolution relative to the 'non-gambiense' group, and domestic animals like pig, dog and sheep constitute a potential reservoir for T.b.'s gamiense.
Abstract: The nuclear DNAs of 71 trypanosome stocks from different African countries, representative of the three Trypanosoma brucei subspecies, and one T. evansi stock, have been analysed by the combined use of restriction endonuclease digestion, gel electrophoresis and molecular hybridization with both trypanosome surface-antigen-specific and undefined genomic DNA probes. In contrast with T. brucei brucei and T. brucei rhodesiense stocks, all the T. b. gambiense stocks are characterized by a conserved, specific DNA band pattern, regardless of the probe. This allows T. b. gambiense to be non-ambiguously identified. On the contrary, T.b. brucei and T. b. rhodesiense, which could not be discriminated by the same criteria, both yield highly variable DNA band patterns. Our data confirm that domestic animals like pig, dog and sheep constitute a potential reservoir for T.b. gambiense. Using a numerical analysis of the DNA hybridization patterns we have measured the degree of similarity between the 72 trypanosome stocks. This investigation shows that all T.b. gambiense stocks are included in the same homogeneous population, while the stocks from the two other subspecies seem to be distributed in several heterogeneous groups, some of these showing correlation with the geographical origin of the trypanosomes. It is concluded that (i) T.b. gambiense stands out as a real subspecies that has undergone a distinct evolution relative to the 'non-gambiense' group, (ii) the alleged T.b. rhodesiense subspecies does not fit with any of the groups evidenced by our cladistic analysis and hence does not appear as a distinct subspecies and (iii) 'non-gambiense' trypanosomes are probably evolving much more rapidly than T.b. gambiense. Different aspects of trypanosome relationships and evolution are discussed.
128 citations
TL;DR: It is raised the possibility that praziquantel may lower the ability of the parasite to evade host immunity by increasing the exposure of parasite antigens capable of acting as targets for host antibody, or antibody-armed cells at the worm surface.
Abstract: Praziquantel is a broad-spectrum anthelmintic active against schistosome species which are major parasites of man. Two major effects on Schistosoma mansoni have been demonstrated; (i) spastic paralysis of the parasite musculature, possibly arising as a consequence of an influx of Ca2+ into the worm (Pax, Bennett & Fetterer, 1978; Coles, 1979) and (ii) vacuolation and degeneration of the worm tegument (Becker, Mehlhorn, Andrews, Thomas & Eckert, 1980). These events may contribute to the elimination of schistosomes in vivo, but this elimination may partly be dependent on the host immune response as infected T-cell-deprived mice are less able than immunologically intact animals to reduce their worm burdens following drug treatment (Doenhoff, Harrison, Sabah, Murare, Dunne & Hassounah, 1982). This latter observation raises the possibility that praziquantel may lower the ability of the parasite to evade host immunity by increasing the exposure of parasite antigens capable of acting as targets for host antibody, or antibody-armed cells at the worm surface. Consistent with this idea is the observation that adult schistosomes in praziquantel-treated mice are invaded a few hours after treatment by host granulocytes (Mehlhorn, Becker, Andrews, Thomas & Frenkel, 1981).
127 citations
TL;DR: There was a strong positive correlation between numbers and lengths of worms in dogs with acquired and induced immunity, indicating that no 'crowding' effects were involved and in sheep populations the mean number of cysts which established was directly proportional to the number of eggs given, implying that there was no negative feedback mechanism operating at this stage of the life-cycle.
Abstract: The numerical distributions of Echinococcus granulosus in an experimental dog population are described. At all dose rates of protoscoleces from 10 to 175000 the distribution of worms was over-dispersed. Host age had no effect. There was a direct proportionality between the infective-stage density and rate of infection, and between the latter and the index of clumping. The worm burdens were significantly higher in the proximal than distal portions of the small intestine. Lengths of the 3- and 4-segmented worms increased from 4 to 10 and 4 to 8 weeks of age, respectively. Thereafter apolysis was asynchronous and could not be determined. Eggs were first detected in the faeces at 6 weeks and the mean age at oogenesis was 7.26 weeks. Retarded growth of the whole population of worms was observed in some dogs. For the first few infections, worm burdens varied widely in the same dog, but by the 6th infection 50% of the dog population had developed a relative insusceptibility to infection. Growth or oogenesis of the worms were not affected. A short-acting immune response was artificially induced in some dogs following the parenteral injection of activated embryos of E. granulosus, Taenia hydatigena, T. ovis, T. multiceps, T. pisiformis and T. serialis. The response affected either the number of worms established, growth or oogenesis or all three parameters. There was a strong positive correlation between numbers and lengths of worms in dogs with acquired and induced immunity, indicating that no 'crowding' effects were involved. In sheep populations the mean number of cysts which established was directly proportional to the number of eggs given, implying that there was no negative feedback mechanism operating at this stage of the life-cycle. The distribution of the larval population in sheep was over-dispersed and the index of clumping increased with the size of the egg dose from 25 to 2500 eggs. Protoscoleces were first observed in cysts at 2 years and the proportion producing them increased with age, with an estimate of 50% of cysts containing protoscoleces at 6.29 years. No deaths were observed in dogs or sheep even when high parasite burdens were present, implying that E. granulosus does not regulate the population of its hosts.
124 citations
TL;DR: It is suggested that resistance to reinfection in vaccinated mice has two additive components which combine to retard the migration of schistosomula within the vasculature, preventing them from reaching the hepatic protal system.
Abstract: The migration of the schistosomula of Schistosoma mansoni labelled with [75Se]methionine, has been followed from the skin to the hepatic portal system. Parasites were detected in all mouse tissues by compressed organ autoradiography. Two separate experiments were performed to track parasites in normal mice, and in mice previously vaccinated with irradiated cercariae. In normal mice, the profile of numbers of autoradiographic foci detected in the skin, lungs, systemic and splanchnic organs was described with time post-infection. The distribution of parasites to systemic organs, following exit from the lungs, paralleled the fractional distribution of cardiac output. Accumulation of schistosomula in the hepatic portal system was complete by day 21 post-infection. Only 2-3 passes of parasites around the vascular system would be required to produce the hepatic portal population. No significant decline in total foci was detected in the first 12 days post-infection. The majority of parasite elimination appeared to occur in the lungs as late as day 21, with lesser proportions in the systemic organs and skin infection site. The pattern of migration in vaccinated mice was similar to that in normal animals. One difference observed was the longer duration of stay in the skin; however, the majority of parasites eventually reached the lungs. The systemic phase of migration occurred on a reduced scale, as did accumulation of parasites in the hepatic portal system. The decline in total foci in vaccinated mice commenced approximately 7 days earlier than in normal mice and proceeded to a lower end-point. Again the majority of parasite elimination appeared to occur in the lungs with lesser proportions in the systemic organs and skin infection site. It is suggested that resistance to reinfection in vaccinated mice has two additive components which combine to retard the migration of schistosomula within the vasculature, preventing them from reaching the hepatic protal system.
120 citations
TL;DR: The properties of these proteins suggest they are the equivalent for natural infections of the strain-dependent antigen previously described (Leech, Barnwell, Miller & Howard, 1984) on the surface of P. falciparum- infected Aotus erythrocytes.
Abstract: We have compared the surface radio-iodinated proteins of uninfected and Plasmodium falciparum-infected erythrocytes from natural infections of human patients. Cryopreserved infected blood from Gambian children with falciparum malaria was thawed, cultured to the middle trophozoite stage, and surface radio-iodinated. Trophozoite-infected cells were enriched about 10-fold on a Percoll gradient newly designed to separate cells based on their differential permeability to sorbitol. Infected blood was radio-iodinated and erythrocyes from the fraction enriched in parasitized cells and uninfected erythrocytes from the same sample obtained from the gradient and compared by SDS–PAGE and autoradiography. In each sample, parasitized erythrocytes contained one or more polypeptides of very high molecular weight (Mr 250000–300000) that were not found on uninfected erythrocytes from the same patient. These proteins were isolate-specific in size and number, suggesting that natural isolates contain a variable number of different P. falciparum phenotypes for this surface protein. In addition, these radio-iodinated surface proteins could not be extracted from the host cell membrane by the non-ionic detergent Triton X-100, but were extracted by SDS. The properties of these proteins suggest they are the equivalent for natural infections of the strain-dependent antigen previously described (Leech, Barnwell, Miller & Howard, 1984) on the surface of P. falciparum-infected Aotus erythrocytes. In addition, we observed a second parasite-dependent modification of labelled proteins on infected erythrocytes with the appearance of a new band of Mr 30000. There were also variations in the pattern of radio-isotope labelled proteins on uninfected erythrocytes from different patients.
98 citations
TL;DR: Under the conditions that prevailed in New Zealand during the late 1950s, at the time of surveys of this parasite, the dog-sheep life-cycle was not regulated by any effective density-dependent constraint, and there was evidence for an effective acquisition of immunity to reinfection by cattle.
Abstract: A mathematical model of the life-cycle of Echinococcus granulosus in dogs and sheep in New Zealand is constructed and used to discuss previously published experimental and survey data. The model is then used to describe the dynamics of transmission of the parasite, and the means by which it may be destabilized. It is found that under the conditions that prevailed in New Zealand during the late 1950s, at the time of surveys of this parasite, the dog-sheep life-cycle was not regulated by any effective density-dependent constraint. In contrast there was evidence for an effective acquisition of immunity to reinfection by cattle. The long time to maturity of the cyst in sheep, together with the practice of feeding aged sheep to dogs, provides a time delay in the intermediate host. By comparison, the time to maturity of the adult stage in dogs is short, but it is of sufficient magnitude to be a key factor in the destabilization of the system by a regular dog-dosing programme. The model used to describe the life-cycle is a linear integrodifferential equation of the Volterra type. Such equations are intrinsically unstable in that a small perturbation in parameters can drive a previous equilibrium solution to zero. At the time of the surveys, the value of the basic reproductive rate, R0, was close to 1, and it has since been reduced below 1 by control measures.
95 citations
TL;DR: The fact that parasitized and non-parasitized snails both show increased oviposition indicates that normal development of the parasite is not necessary to trigger the response, and may be a compensatory response for expected future suppression of egg-laying.
Abstract: Biomphalaria glabrata snails are known to be castrated by infection with the trematode parasite Schistosoma mansoni 4-6 weeks post-infection. The pattern of oviposition in the first 35 days post-exposure (p.e.) was investigated, in snails aged 14 weeks and measuring 7-10 mm diameter which had not commenced egg-laying, by counting the numbers of eggs laid in 7-day intervals. A group of exposed snails was compared with a control non-exposed group. The exposed group included both parasitized and non-parasitized snails, and showed a significant increase in the median number of eggs laid during the periods 14-21 and 22-28 days p.e. Throughout the entire 35-day period exposed non-parasitized snails laid significantly more eggs than control snails, while parasitized snails laid significantly more eggs than controls during days 22-28 p.e. and significantly fewer during days 29-35 p.e. Parasitized snails also laid significantly more eggs/egg mass in the period 16-28 days p.e. than did control snails. Growth of the snails was measured. By day 28 p.e. the mean diameter of the exposed group was significantly greater than that of the control group. The increase in oviposition by snails soon after exposure is discussed in terms of a compensatory response for expected future suppression of egg-laying. The fact that parasitized and non-parasitized snails both show increased oviposition indicates that normal development of the parasite is not necessary to trigger the response.
93 citations
TL;DR: An experimental procedure was developed to analyse the switching frequency in vitro of Trypanosoma brucei using an equation that takes the growth rates of the newly expressed antigen types into consideration as well as the proportion of switched trypanosomes and the number of generations since the population was antigenically homogeneous.
Abstract: Previously quoted figures for the frequency of antigen switching in Trypanosoma brucei are based on incorrect assumptions. In order to determine the correct switching frequency, an equation was derived that takes the growth rates of the newly expressed antigen types into consideration as well as the proportion of switched trypanosomes and the number of generations since the population was antigenically homogeneous. When this equation was applied to published in vitro data, variable values were obtained for the switching frequency in clonal populations originally expressing one antigen type. The calculated most likely switching frequencies ranged from 1.4 X 10(-7) to 3.5 X 10(-6). This variation was probably caused by differences in the growth rates of the new antigen types in the population and failure to detect slow growing variants. To overcome these problems, an experimental procedure was developed to analyse the switching frequency in vitro. Trypanosomes were cloned and grown in parallel cultures. After an appropriate number of generations, cells expressing the original antigen type were destroyed and, from the proportion of cultures that contained new antigen types, the switching frequency was calculated. The technique minimized subculturing or other procedures that could distort the results. Although the method was optimized for analysing switching frequency, the values differed between experiments, ranging from 2.2 X 10(-7) to 2.6 X 10(-6) for one variant. Possible causes for the variations in switching frequency are discussed.
TL;DR: In this article, the authors show that, in several parasite-vector systems, flight ability, fecundity or gonotrophic concordance of vectors are affected by parasites (including bacteria, rickettsia and viruses).
Abstract: Evidence from many sources indicates that, in several parasite–vector systems, flight ability, fecundity or gonotrophic concordance of vectors, are affected by parasites (including bacteria, rickettsia and viruses) and in some cases parasites cause well-documented pathogenic effects (see reviews, for example, by Lavoipierre (1958a) and Hawking & Worms (1961) on filaria; Molyneux (1977, 1983) for trypanosomatids; Killick-Kendrick (1979) for Leishmania).
TL;DR: Computer-aided reconstruction from serial sections has been used to analyse the 3-dimensional structure of entire amastigotes of Leishmania mexicana and to determine the number, arrangement and volume of each organelle.
Abstract: Computer-aided reconstruction from serial sections has been used to analyse the 3-dimensional structure of entire amastigotes of Leishmania mexicana mexicana and to determine the number, arrangement and volume of each organelle. In two reconstructions, the lysosome-like ‘megasomes’ were the most numerous organelle, there being 34 in one amastigote, and they comprised as much as 15% of the total cell volume. In contrast, as few as 9 glycosomes were present, accounting for less than 1% of the cell volume. The unitary nature of the mitochondrion was confirmed and its complex basket-like structure was revealed. The spatial arrangement of the cell organelles is here displayed in stereo-pairs.
TL;DR: An instrument for measuring the motility of larval and adult nematodes is described along with an analysis of its use as a tool to analyse drug action on these parasites.
Abstract: An instrument for measuring the motility of larval and adult nematodes is described along with an analysis of its use as a tool to analyse drug action on these parasites. Motility was detected from larval parasites of Nippostrongylus brasiliensis and Ascaris suum in the absence and presence of various anti-nematodal drugs. These agents produced, within 48 h, a significant decrease in larval parasite motility. The instrument was also capable of detecting the motility of Caenorhabditis elegans, adult female Brugia pahangi and their response to anti-nematodal drugs. The design of the instrument allows us to accurately measure motility in a single sample within 60 sec.
TL;DR: A frequent carrier state of naturally infected cattle has been demonstrated for T. parva parva for the first time, and it is likely that this carrier state is of great importance in maintenance of T. Parva Parva infection in the field.
Abstract: The maintenance of Theileria parva parva infection in an endemic area of Kenya on the shore of Lake Victoria was studied in the field and laboratory. High prevalences of antibodies against T. parva and T. mutans and intra-erythrocytic piroplasms were detected in local zebu (Bos indicus) cattle. The mean infection rate of Theileria parasites in the tick, Rhipicephalus appendiculatus, in field collections was 1·1 %. Most of the infection was attributed to T. parva parva by application of field ticks to susceptible cattle. Five cattle, all about 1·5 years old, were purchased from local owners and transported to the laboratory. All five had oscillating antibody titres against T. parva and T. mutans and had patent theilerial infections during the subsequent 13 months. Uninfected R. appendiculatus nymphs were applied to cattle at 0, 3, 6, 9 and 13 months after transport to Muguga, and 18 out of 23 batches transmitted T. parva parva infection to cattle when 100 resultant R. appendiculatus adults were applied. Infection rates in the tick batches were usually low, with 1 salivary gland acinus infected/tick. Hence, a frequent carrier state of naturally infected cattle has been demonstrated for T. parva parva for the first time, and it is likely that this carrier state is of great importance in maintenance of T. parva parva infection in the field.
TL;DR: Eimerian oocysts were found in 98% of 422 faeces samples from goats in SE England, and it was found that kids less than 1 year old had higher oocyst counts than yearling or adult goats.
Abstract: Eimerian oocysts were found in 98% of 422 faeces samples from goats in SE England. It was found that 74% of the samples contained thousands or tens of thousands of oocysts/g. Kids less than 1 year old had higher oocyst counts than yearling or adult goats. Nine species of Eimeria were identified, and 65% of the samples contained 3-5 species. The most prevalent species were E. arloingi (94%), E. hirci (69%), E. christenseni (64%) and E. caprina (55%). E. ninakohlyakimovae (48%), E. alijevi (42%) and E. apsheronica (23%) were common, and E. jolchijevi (8%) and E. caprovina (4%) were comparatively rare. Developmental stages of E. caprina destroyed the crypt epithelium in the mucosa of the large intestine, causing severe haemorrhagic enteritis similar to that produced by E. ninakohlyakimovae. The literature on Eimeria species in sheep and goats is reviewed and, on the grounds of priority, E. bakuensis is the correct name for E. ovina in sheep.
TL;DR: Two-dimensional gel analyses of immunoprecipitated, biosynthetically labelled antigens indicate that repeated infection with P. falciparum results in the synthesis of antibodies against a large number of distinct antigENS.
Abstract: Sporozoites of P. falciparum and other Plasmodia appear to be fairly simple antigenically, in that there is a dominant antigen, the circumsporozoite (CS) protein that forms the sporozoite surface coat (Potocnjak, Yoshida, Nussenzweig & Nussensweig, 1980; Santoro et al. 1983). Consequently, the CS protein and the gene encoding it have now been studied in considerable detail (Ellis et al. 1983; Godson et al. 1983; Ozaki et al. 1983; Dame et al. 1984; Enea et al. 1984). In contrast to sporozoites, the asexual blood stages of P. falciparum are antigenically complex. Two-dimensional gel analyses of immunoprecipitated, biosynthetically labelled antigens indicate that repeated infection with P. falciparum results in the synthesis of antibodies against a large number of distinct antigens (Perrin & Dayal, 1982; Brown et al. 1981, 1983). In further contrast to the sporozoite, the asexual blood stages of different P. falciparum isolates exhibit a high degree of antigenic heterogeneity (Brown et al. 1983; Hall et al. 1983; McBride, Walliker & Morgan, 1982). Much of this antigenic diversity is no doubt due to allelic differences but clonal populations of parasites may also have the capacity to undergo antigenic variation (Hommel, David & Oligino, 1983).
TL;DR: The sequence of antigenic variation in T. vivax seems to be determined by the parasite rather than the host species, suggesting there is a spectrum, rather than discrete groupings, in the hierarchy of VAT expression.
Abstract: The sequence of appearance of specific lytic activity against more than 20 variable antigen types (VATs) of Trypanosoma vivax in the serum of 27 animals belonging to 5 species has been examined. For each host species there was a characteristic course of infection, with differences in height and duration of parasitaemia and in pathogenicity. The sequence of antigenic variation was similar in all host species, with some VATs consistently eliciting response more rapidly than others. The predominant group, comprising VATs which apparently developed within the first 3 weeks, varied in size according to the total number of trypanosomes in the bloodstream within that period, suggesting there is a spectrum, rather than discrete groupings, in the hierarchy of VAT expression. There was very little evidence for differences in appearance of VATs between host species; the only clear example was one VAT which apparently did not develop in one host species. The sequence of antigenic variation in T. vivax seems to be determined by the parasite rather than the host species.
TL;DR: A wide variety of species or subspecies of Leishmania may be present in a small verrucose lesion developing after an infected sandfly bite or appear in lesions as the disease progresses as mentioned in this paper.
Abstract: Human leishmaniasis is a world-wide public health problem with more than 400000 new reported cases/year (Anon, 1984) in the tropics and subtropics. Were (1985) has estimated that Leishmaniases affect about 20 million people in the Third World. In hospitals where treatment is available, initially all positive cases are treated equally; it is the prognosis and follow-up that varies according to the causative organism. A wide variety of species or subspecies of Leishmania may be present in a small verrucose lesion developing after an infected sandfly bite or appear in lesions as the disease progresses. Depending on which Leishmania is present a clinial decision must be made whether to treat with drugs of varying toxicity or not.
TL;DR: Better methods of characterization are required for more precise definition of the parasites of man and domestic animals and for determining vectors and intermediate hosts as well as possible animal reservoir hosts, and a greater understanding of the genetic diversity of parasitic organisms is required.
Abstract: During the past decade, enormous technological developments have occurred in biology that have led to significant and revolutionary advances. New techniques of DNA cloning, restriction-enzyme analyses and nucleotide sequencing are providing a mass of data concerning the genomes of a wide variety of organisms. Such insights are having a great impact upon many areas of biological investigation, and would seem to be of considerable potential value for studies of taxonomy and population biology. The application of these new approaches to the characterization and identification of parasitic helminths has only recently begun, but they promise to become powerful additional tools for this purpose. Better methods of characterization are required for more precise definition of the parasites of man and domestic animals and for determining vectors and intermediate hosts as well as possible animal reservoir hosts. Moreover, a greater understanding of the genetic diversity of parasitic organisms is required since many helminths, which are morphologically similar, show marked differences in epidemiologically significant factors such as infectivity, pathogenicity, immunogenicity and drug sensitivity.
TL;DR: The distribution of parasites to systemic organs after their exit from the lungs was proportional to the fractional distribution of cardiac output and the time taken for schistosomula to pass between organs, in arterial and venous blood, was shown to be less than 30 min.
Abstract: Autoradiography of compressed mouse tissues has been used to estimate the numbers of 75Se-labelled schistosomula present in different mouse organs. Day 7 parasites extracted from the lungs of donor mice were delivered by injection to the lungs, systemic organs and liver of recipient mice as a discrete pulse. The numbers detected in various locations with time post-injection were then used to analyse the dynamics of intravascular migration. Approximately 98% of cercaria-associated label was lost during the first 14 days of parasite life, two-thirds of this in the first 7 h post-infection. Nevertheless, 99-113% of schistosomula could be detected 30 min post-injection into the locations chosen. The efficiency of the parasite delivery system was 95%. The time required for the number of foci in the lungs to decline to 50%, after injection of parasites via the femoral vein, was 55 h. Adjustment of this data to allow for parasites returning to the lungs after passage round the systemic vasculature gave a value of 30-35 h for the true mean time of lung transit. The distribution of parasites to systemic organs after their exit from the lungs was proportional to the fractional distribution of cardiac output. The probability (P) of a schistosomulum being distributed to splanchnic beds was estimated at 0.32 and its P of being trapped in the hepatic portal distributaries within the liver as 0.72-0.86. On this basis, the entire hepatic portal population of adult schistosomes would be recruited during 2-3 circuits of parasites around the pulmonary--systemic vasculature. The mean transit time of schistosomula through intestinal capillaries was 6.5 h whilst that through other systemic organs combined (muscles, kidneys, brain, etc) was 16 h, considerably more rapid than lung transit. The time taken for schistosomula to pass between organs, in arterial and venous blood, was shown to be less than 30 min in both cases (probably much less).
TL;DR: The assignation of A. physeteris and the A. simplex complex to two distinct subgenera, Skrjabinisakis and Anisakis, as proposed by Mosgovoy on a morphological basis appears to be fully justified according to genetic data.
Abstract: The genetic structure of Anisakis physeteris from the Mediterranean Sea has been analysed electrophoretically at 22 enzyme loci. The samples studied, although differing in the life-stage (larvae and adults), and in the host (the fishes Micromesistius poutassou and Trachurus trachurus, and the sperm whale Physeter macrocephalus) were genetically homogeneous. Of these loci 11 (Ldh, Sod, Np, Adk-2, Pgm-1, Est-1, Est-2, Acph-1, Acph-2, Lap-2 and Ca) were found to be monomorphic, while the other 11 (Sdh, Mdh, Idh, 6-Pgdh, G3pdh, Got, Adk-1, Pgm-2, Lap-1, Mpi and Gpi) showed from 2 to 7 alleles. The following values of genetic variability were estimated: He = 0.11, P = 0.50, A = 1.95. Distinct alleles were found between A. physeteris and the A. simplex complex at 19 out of the 22 loci studied, and only few rare alleles were shared at the remaining 3 loci. The genetic divergence between A. physeteris and A. simplex A and B is therefore very high, the values of Nei's index D being 7.384 and 6.443 respectively (I = 0.001 and 0.002). The assignation of A. physeteris and the A. simplex complex to two distinct subgenera, Skrjabinisakis and Anisakis, as proposed by Mosgovoy on a morphological basis, appears to be fully justified according to our genetic data.
TL;DR: Evidence for the presence of 11 intestinal parasites in pre-school children from 4 rural villages in Ghana was obtained from an examination of stool samples, and evidence of associations between pairs of infections, particularly those involving hookworm and T. trichiura was revealed.
Abstract: Evidence for the presence of 11 intestinal parasites in pre-school children from 4 rural villages in Ghana was obtained from an examination of stool samples. Striking differences were detected between the prevalence of some of the 6 common infections in the 4 villages. The prevalence of Ascaris lumbricoides varied from about 76% in one village (Oshiyie, coastal savanna) to apparently 0% in another (Akuma, forest zone). No differences in prevalence for any infection were observed to be sex dependent. Investigation of the relationship between age of the children and prevalence showed that the degree of prevalence of both A. lumbricoides and Trichuris trichiura had essentially levelled off by the time the children were 4 years old. There was no evidence to suggest that the prevalence of either Entamoeba sp. or spp. or hookworm was approaching a maximum value, even in the oldest children. These trends applied across the villages regardless of the differences in prevalence values for the infections. On average, the children of Oshiyie were found to harbour twice as many infections as the children of the other villages. The investigation of the prevalence data revealed evidence of associations between pairs of infections, particularly those involving hookworm and T. trichiura.
TL;DR: The analysis suggests that both population density and host nutrition are important in determining the observed degree of inequality in reproductive success and body size.
Abstract: Two simple methods of measuring the levels of inequality in reproductive success of different individuals in parasite populations are presented. These techniques are then applied to a number of sets of data for cestodes and acanthocephalans. The analysis suggests that both population density and host nutrition are important in determining the observed degree of inequality in reproductive success and body size. Cestodes, with a more flexible growth form, are shown to exhibit higher levels of inequality than acanthocephalans. The discussion outlines the evolutionary importance of considering variation in the reproductive success of different individuals.
TL;DR: In this article, the authors examined the effect of density-dependent sex determination on parasite reproductive success and population regulation in the context of the mermithid nematode Romanomermis culicivorax, and the significance of regulatory constraints on population growth is discussed in relation to the use of mermithids as biological control agents of insect pests or disease vectors.
Abstract: Environmental sex determination in the mermithid nematode Romanomermis culicivorax is examined in the context of parasite reproductive success and population regulation. Experimental results show that the sex ratio of the nematode within its mosquito host (Culex quinquefasciatus) is dependent on parasite density. Sex ratios are biased to females at low parasite burdens and to males at high parasite burdens. Low temperature further enhances female-biased ratios. The net effect of density-dependent sex determination on parasite and host population growth is shown to be critically dependent on the frequency distribution of parasite numbers/host. Mermithid parasite distributions within natural host populations show low degrees of aggregation relative to other helminth species. The population regulation of the parasite is examined with respect to environmental sex determination and parasite-induced host mortalities by means of simple mathematical models of the dynamics of parasite transmission via its life-cycle. The significance of regulatory constraints on population growth are discussed in relation to the use of mermithids as biological control agents of insect pests or disease vectors.
TL;DR: La reponse de l'homme a ces 3 especes est quasiment similaire, mais varie considerablement dans les regions endemiques and les manifestations cliniques and parasitologiques sont probablement en relation avec the reponse immunitaire.
Abstract: Three species of filarial worms, Wuchereria bancrofti, Brugia malayi and Brugia timori, are the causative agents of lymphatic filariasis in man, defined by the characteristic tropism of adult worms of each species for the afferent lymphatics. Reproductive activity leads to the release of large numbers of microfilariae, which circulate in the vascular system, and upon ingestion by an appropriate mosquito vector, develop through to infective third-stage larvae (L3) within 10–14 days. After a subsequent bloodmeal, the infective larvae enter the definitive host via the wound and mature to the adult stage over several months, involving two moults, during which the entire nematode exoskeleton (cuticle) is replaced.
TL;DR: An analysis of the survival and migration rates of the infective (L3) stages of Ostertagia ostertagi and Cooperia oncophora shows as good agreement between observed and predicted larval counts as models in which these rate processes are made explicit functions of larval age and microclimate.
Abstract: We present an analysis of the survival and migration rates of the infective (L 3 ) stages of Oslertagia ostertagi and Cooperia oncophora . Although the majority of laboratory studies show that the survival of the L 3 stage depends upon temperature, moisture and the age of the larvae, a simple mathematical model of larval demography, in which their mortality and migration rates are held constant, provides as good agreement between observed and predicted larval counts as models in which these rate processes are made explicit functions of larval age and microclimate. Maximum-likelihood estimates of larval mortality rates in the faeces and on the herbage are 0·0284/day and 0·00887/day respectively. The average migration rate from faeces to herbage under temperate Northern European conditions is estimated as 0·00884/day. Finally, we discuss the probable scale of L 3 larval losses due to desiccation and lavage (active or passsive migration into the soil).
TL;DR: It was possible to ascertain that it was migration and not penetration which was inhibited at water temperatures below 10 degrees C, suggesting that it may be a possible method of controlling diplostomiasis on fish farms.
Abstract: The relationship between infection rates of rainbow trout (Salmo gairdneri) by Diplostomum spathaceum and cercarial concentration, water flow rate and temperature were investigated by means of controlled infections within a flume. A linear relationship was obtained between cercarial concentration and mean abundance of metacercariae/fish. A biphasic relationship occurred between flow rate and abundance of metacercariae. Within the confines of the flume, it was possible to control the infection rate of trout with D. spathaceum cercariae by manipulating flow rate, suggesting that it may be a possible method of controlling diplostomiasis on fish farms. No infection occurred in fish infected and maintained below 10 degrees C and the optimum infection temperature was approximately 17.5 degrees C. Infections became established in fish infected at 7.5 and 5 degrees C but maintained at 15 degrees C prior to examination. Trout were infected at 7.5 degrees C for 10-50 min and all attached cercariae were washed off and removed from the flume. Following infection, fish were either maintained at 7.5 degrees C or 15 degrees C prior to examination. Using this method, it was possible to ascertain that it was migration and not penetration which was inhibited at water temperatures below 10 degrees C.
TL;DR: Four common blood parasites belonging to the genera Babesia, Hepatozoon, Trypanosoma and Grahamella were detected in sympatric populations of Clethrionomys glareolus and Apodemus sylvaticus showed similar seasonal patterns with most transmission occurring in summer and autumn and ceasing in winter.
Abstract: Four common blood parasites belonging to the genera Babesia, Hepatozoon, Trypanosoma and Grahamella were detected in sympatric populations of Clethrionomys glareolus and Apodemus sylvaticus. Seasonal changes in the abundance of hosts and parasites were monitored in a longitudinal field survey for 18 months. All parasites in both hosts showed similar seasonal patterns with most transmission occurring in summer and autumn and ceasing in winter. Amongst aged subsets of each host population, Hepatozoon and Grahamella spp. were primarily parasites of young animals whereas Babesia and Trypanosoma spp. generally infected older hosts. Data from the aged subsets were also used to estimate values for the basic reproductive rate, R0, for each parasite. In C. glareolus, R0 = 2.0 for B. microti, 2.6 for H. erhardovae, 1.7 for T. evotomys and 2.8 for Grahamella sp. In A. sylvaticus R0 = 2.2 for Grahamella sp. These estimates are probably representative only for summer and autumn of each year.
TL;DR: The tight fit of schistosomula in the pulmonary capillaries implies that migration through them is both a strenuous and slow process.
Abstract: The migration of schistosomula through the lungs of mice has been investigated at the ultrastructural level. On Days 4 and 7 post-infection schistosomula were located only within the vasculature. Newly arrived Day 4 schistosomula were highly convoluted and completely occluded vessels measuring approximately 15–25μm in diameter. By Day 7 parasites were located in pulmonary capillaries, often causing considerable distension. The subtegumentary fibrous interstitial layer was absent in elongated lung schistosomula. The minimum diameter of such parasites was 8μm, and their tegument was usually unridged and flattened against the vascular endothelium, thus resulting in close apposition of endothelial and tegumental membranes. The tight fit of schistosomula in the pulmonary capillaries implies that migration through them is both a strenuous and slow process. The migratory delay in the lungs after arrival from the skin occurs because dimensional changes are necessary for successful capillary migration.