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PubMed1991

The need for live parasites for long-term immunity in malaria.

All of the results of the various experiments support a role for living, proliferating parasites in the efficient induction of anti-parasitic as well as anti-disease (CM) immunity. Non-proliferating parasites or material from disrupted parasites are poor or non-antigens in this respect. Three possibilities as to why living parasites are important in immunity could be considered: 1. circulating parasites contain insufficient antigen to induce protective immunity, but sufficient antigen can be produced during proliferation; 2. only circulating parasites arrive at critical places (e.g. parts of the white pulp of the spleen) for the presentation of the important antigen or induction of appropriate signals. 3. Architectural changes are needed (i.e. formation of barrie-cell-complexes) for the immune response to be effective. The first possibility explains why exoantigens, as well as live, proliferating parasites are efficient inducers of anti-CM immunity. Since these immunizations have no effect on parasitemia, additional/other immune reaction(s) are needed for anti-parasitic immunity. The important role of the spleen in malaria and malaria immunity is well-known. The second possibility includes the idea that live, proliferating parasites circulate through the spleen continuously where unsatisfactory or infected erythrocytes are removed rather than in the liver. Injected killed parasites or material from them when present in the circulation is to a larger extent taken up by the Kupffer cells from the liver rather than the spleen. Presence and uptake of parasites in the spleen may provide the critical confrontation and/or delivery of signals necessary for the development of immunity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Analysis of human T cell clones specific for conserved peptide sequences within malaria proteins. Paucity of clones responsive to intact parasites.

T cells are thought to be of central importance in malaria immunity. Peptides copying malaria protein sequences often stimulate human CD4+ T cells and it was thought that they represented T cell epitopes present in the parasite and may thus have particular relevance to malaria vaccine development. To verify whether synthetic peptides representing highly conserved regions of parasite Ags may contribute to a malaria vaccine, we searched the data bank for conserved regions of Plasmodium falciparum malaria proteins that were not homologous to known self (human) proteins. We synthesized 24 such peptides representing 11 of the cloned and sequenced malaria asexual stage Ags, which were predicted by algorithms to represent T cell epitopes, and 6 peptides not predicted to be T cell epitopes and used these to generate T cell clones from individuals with an extensive previous history of malaria exposure. The T cell clones responded vigorously to many peptides but only a single clone, specific for a peptide within merozoite surface protein-1, 20-39, VTHESYQELVKKLEALEDAV, and not previously defined to be a T cell epitope responded to malaria parasites by proliferation and secretion of IFN-gamma. This epitope was not revealed by studying parasite-induced T cell lines and is thus subdominant. The clone was able to significantly inhibit parasite growth in vitro. The final step in the inhibition of parasite growth appears to be nonspecific because other activated clones (not specific for malaria sequences) can inhibit parasite growth. Our data suggest that few conserved peptides within malaria parasites can be processed from the intact parasite. However, such peptides that can be processed from malaria parasites may be expected to stimulate parasite-specific T cells that could inhibit parasite growth and as such may be lead candidates for a vaccine aimed at inducing cellular immunity to malaria.

Adult↗
PubMed2002

Food webs and the transmission of parasites to marine fish.

Helminth parasites of fish in marine systems are often considered to be generalists, lacking host specificity for both intermediate and definitive hosts. In addition, many parasites in marine waters possess life cycles consisting of long-lived larval stages residing in intermediate and paratenic hosts. These properties are believed to be adaptations to the long food chains and the low densities of organisms distributed over broad spatial scales that are characteristic of open marine systems. Moreover, such properties are predicted to lead to the homogenization of parasite communities among fish species. Yet, these communities can be relatively distinct among marine fishes. For benthos, the heterogeneous horizontal distribution of invertebrates and fish with respect to sediment quality and water depth contributes to the formation of distinct parasite communities. Similarly, for the pelagic realm, vertical partitioning of animals with depth will lead to the segregation of parasites among fish hosts. Within each habitat, resource partitioning in terms of dietary preferences of fish further contributes to the establishment of distinct parasite assemblages. Parasite distributions are predicted to be superimposed on distributional patterns of free-living animals that participate as hosts in parasite life cycles. The purpose of this review is first, to summarize distribution patterns of invertebrates and fish in the marine environment and relate these patterns to helminth transmission. Second, patterns of transmission in marine systems are interpreted in the context of food web structure. Consideration of the structure and dynamics of food webs permits predictions about the distribution and abundance of parasites. Lastly, parasites that influence food web structure by regulating the abundance of dominant host species are briefly considered in addition to the effects of pollution and exploitation on food webs and parasite transmission.

Animals↗
PubMed2000

Richness patterns in the parasite communities of exotic poeciliid fishes.

Three species of poeciliids (Gambusia holbrooki, Xiphophorus helleri and X. maculatus) and 15 species of ecologically similar native freshwater fishes (mainly eleotrids, ambassids, melanotaeniids and retropinnids) were examined for parasite richness to investigate parasite flux, qualitative differences, quantitative differences and the structuring factors in parasite communities in the 2 fish types in Queensland, Australia. Theory suggests that poeciliids would harbour depauperate parasite communities. Results supported this hypothesis; poeciliids harboured more species-poor parasite infracommunities and regional faunas than natives (P < 0.0001), despite greater sampling effort for the former. Cluster analysis of presence/absence data for poeciliids and the 6 most-sampled native fishes revealed that parasite communities of the 2 fish groups are qualitatively distinct; the proportion of parasite species with complex life-cycles was lower in poeciliids than in native species, and Myxosporea, Microspora, Coccidia and parasitic Crustacea were all absent from poeciliids. Limited exchange of parasite species has occurred between natives and poeciliids. Logistic ordinal regression analysis revealed that fish origin (exotic or native), environmental disturbance and host sex were all significant determinants of parasite community richness (P < 0.05). Theoretical modelling suggests that poeciliids are at a competitive advantage over native fishes because of their lack of parasites.

Animals↗
PubMed1985

Nutritional aspects of parasitic infection.

The nutritional basis of the ecological relationship between parasites and their hosts is reviewed using examples of the parasitic infections of man whenever possible. Two important points are discussed first: the distinction between parasitic infection and parasitic disease, and the concepts of synergism or antagonism between undernutrition and parasitic disease. The effects of parasites on the nutritional status of the host are examined in four ways. First, in terms of the ways in which parasites can disturb nutritive processes by effects on physical activity to obtain food, and by effects on food consumption, digestion and absorption. Secondly, in terms of the nutritional cost of an infection to a parasitised host. Thirdly, in terms of the feeding, nutrition and metabolism of parasites. Finally, in terms of damage to the tissues of the host caused by parasites. Two other sections deal briefly with the transmission of parasites in food and the effects of food on parasites.

Animals↗
PubMed1996

Comparative analysis of the metazoan parasite communities of leatherjackets, Oligoplites palometa, O. saurus, and O. saliens (Osteichthyes:Carangidae) from Sepetiba Bay, Rio de Janeiro, Brazil.

One hundred and fifty-seven specimens of leatherjackets, 84 specimens of Oligoplites palometa (Cuvier), 37 specimens of O. saurus (Bloch & Schneider), and 36 specimens of O. saliens (Bloch) captured at the Sepetiba Bay, State of Rio de Janeiro, between March of 1991 and November of 1992, were necropsied to study their communities of metazoan parasites. All fishes studied were parasitized by one or more metazoan species. Eighteen parasite species were found in O. palometa and 13 parasite species were found in O. saurus and O. saliens, respectively. The digeneans were the majority of the parasite specimens collected, with 90.3%, 82.2%, and 87.7% in O. palometa, O. saurus, and O. saliens, respectively. The Simpson index was lower than 0.25 for the 3 host species, showing an absence of concentration for dominance. The similarity coefficients among the parasite communities of the 3 fish species was above 66%. The parasites of the 3 host species showed typical overdispersed pattern of distribution. Four cases of positive correlation between host's total length and prevalence and parasite intensity were found. The majority of the species did not show influence of host sex. The 3 host species had similar parasite diversity, which was not correlated with the host's total body length and there was no significant difference between male and female hosts. Oligoplites palometa and O. saurus each had one pair of ectoparasite species sharing a positive association and with a positive correlation between their intensities. No pairs of associated species were found in O. saliens. Parasites were found along the entire extension of the gastrointestinal tract of the 3 host species. The parasite communities of O. palometa, O. saurus, and O. saliens are defined as isolationists because there are few evidences of interspecific association or covariation. The presence of larval stages of cestodes and nematodes suggests that the three species of Oligoplites are at an intermediate level in the marine trophic web.

Animals↗
PubMed2003

Interactions between parasitized and unparasitized conspecifics: parasitoids modulate competitive dynamics.

Parasitism influences many aspects of a host's behavior and physiology. Therefore, parasitism is also likely to influence the competitive ability of the host. Field populations of phytophagous insects are often a mix of parasitized and unparasitized conspecifics and the inclusion of parasitism in their competitive dynamics may alter expected outcomes. We investigated the influence of parasitism by the hymenopteran parasitoid Phanerotoma franklini Gahan on the competitive interactions among larvae of its host Acrobasis vaccinii Riley. We found that parasitized larvae were poorer competitors and required less food to complete development compared to unparasitized larvae. To examine the influence of parasitism on the competitive dynamics of this system, we constructed an individual-based model parameterized with our laboratory data. The model examined the role of resource availability and parasitism rate on larval survival. The model suggests that parasitized larvae (and, hence parasitoids) experience higher levels of mortality from competition than unparasitized larvae. Further, the model also suggests that the decreased consumption of resources by parasitized larvae results in a decline in the occurrence of competition as the parasitism rate increases. We suggest that these observations may be general to many parasitoid-host systems.

Animals↗
PubMed1999

The optimal strategy for brood-parasitism: how many eggs should be laid in the host's nest?

We consider the optimal strategy for intra-specific brood-parasitism, especially with respect to the number of eggs laid by the parasitic individual in the nest of non-parasitic individual, in particular, a host that does not reject the parasite's eggs. With a fundamental mathematical model, assuming that the survival probability of the parasite's offspring in the nest of the host is significantly smaller than that in parasite's own nest, we determine the optimal number of eggs laid in the nest of host that maximizes the expected reproductive fitness of the parasite. We show that the invasion success of brood-parasitism could significantly depend on the total number of eggs laid by the parasite in a breeding season, and that the successfully invading brood-parasitism could realize maximum fitness with a specific number of parasite's eggs laid in the nest of the host.

Animals↗
PubMed2003

Habitat overlap and gastrointestinal parasitism in sympatric African bovids.

Gastrointestinal parasite infections are widespread among wild ungulates. Because many of these parasites infect multiple host species, inter-specific interactions among hosts potentially play an important role in parasite transmission dynamics in ungulate communities. In this study, the effects of inter-specific contact on parasitism rates in 11 sympatric African bovids was examined using habitat overlap among species as a measure of cross-species contact rates. Across individual hosts, strongyle nematode abundance increased with increasing numbers of bovid species occupying a habitat. Furthermore, comparative analyses show a positive association between strongyle prevalence and level of habitat overlap across taxa. These findings suggest that among sympatric bovids, contact between species contributes significantly to the transmission of generalist nematode parasites. For a more host-specific parasite group, coccidia, parasite abundance and individual probability of infection declined in hosts living in bovid rich habitats. This pattern may reflect enhanced interspecific competition among parasites in these areas. Finally, similar to strongyle abundance, individual parasite richness also increased among hosts occupying habitats with higher numbers of bovid species. No association between habitat overlap and parasite richness was detected at higher taxonomic scales, however, which suggests that contact between host species may not contribute to parasite colonization of new host taxa.

Animals↗
PubMed1990

Effects of host age, host density and parent age on reproduction of the filth fly parasite Urolepis rufipes (Hymenoptera: Pteromalidae).

Urolepis rufipes Ashmead, a pteromalid wasp, was recently discovered parasitizing house fly and stable fly pupae in eastern Nebraska dairies. Studies have been conducted on the biology of this parasite to evaluate its potential as a biological control agent of stable flies (Stomoxys calcitrans (L.] and house flies (Musca domestica L.). House fly pupae were suitable as hosts for U.rufipes at all ages; however, significantly higher parasitism occurred on host pupae aged 96-120 h. Parasite-induced mortality (host mortality without progeny production) was higher than for other pteromalid parasites of filth flies under similar conditions. Parasitism increased with parasite--host ratio at 20 degrees C; however, the opposite was noted at 30 degrees C for parasite--host ratios ranging from 5:50 to 50:50. Fly eclosion decreased as parasite--host ratio increased at 20 degrees C, and no host eclosion occurred at the highest parasite--host ratios (20:50 and 50:50) at 30 degrees C. Females produced an average of 18.6 female and 7.6 male progeny. 88% of the progeny were produced during the first 6 days post parental eclosion. The short life span, low progeny emergence rate and high per cent host eclosion, in comparison with other parasite species, suggests that the Nebraska strain of U.rufipes may not an effective biological control agent of house flies.

Age Factors↗
PubMed2002

Modulating the modulators: parasites, neuromodulators and host behavioral change.

Neuromodulators can resculpt neural circuits, giving an animal the behavioral flexibility it needs to survive in a complex changing world. This ability, however, provides parasites with a potential mechanism for manipulating host behavior. This paper reviews three invertebrate host-parasite systems to examine whether parasites can change host behavior by secreting neuromodulators. The parasitic wasp, Cotesia congregata, suppresses host feeding partly by inducing the host (Manduca sexta) to increase the octopamine concentration in its hemolymph. The increased octopamine concentration disrupts the motor pattern produced by the frontal ganglion, preventing the ingestion of food. Polymorphus paradoxus (Acanthocephalan) alters the escape behavior of its host, Gammarus lacustris (Crustacea), possibly through an effect on the host's serotonergic system. The trematode Trichobilharzia ocellata inhibits egg-laying in its snail host (Lymnaea stagnalis), partly by inducing the host to secrete schistosomin. Schistosomin decreases electrical excitability of the caudodorsal cells. The parasite also alters gene expression for some neuromodulators within the host's central nervous system. In at least two of these three examples, it appears that the host, not the parasite, produces the neuromodulators that alter host behavior. Producing physiologically potent concentrations of neuromodulators may be energetically expensive for many parasites. Parasites may exploit indirect less energetically expensive methods of altering host behavior. For example, parasites may induce the host's immune system to produce the appropriate neuromodulators. In many parasites, the ability to manipulate host behavior may have evolved from adaptations designed to circumvent the host's immune system. Immune-neural-behavioral connections may be pre-adapted for parasitic manipulation.

Animals↗
PubMed1997

Fitness of parasites: pathology and selection.

Parasites improve their fitness as a result of the selection of traits which determine their relationships with their hosts. Some of these relationships are examined briefly. There is a cost of virulence for parasites, paralleling the cost of resistance for hosts, which implies that the good health of the host can be a component of parasite fitness; conversely, some transmission modes imply that the host be markedly weakened by the parasite. Pathogenicity can be influenced by characters such as a transmission of the parasite from parents to offspring, or the demographic characteristics of the host populations. Important components of parasite fitness are: the complexity of the life-cycle; the degree of specialization for a more or less open host range; the conspicuousness or discretion of the infective and parasitic stages. However, the best possible adaptation to a particular host is not always selected: when a parasite exploits several host species, the gene flows between parasites which have developed in different hosts may be responsible for "maladaptation". This may be important for an understanding of the pathogenicity of certain human parasitic diseases.

Animals↗
PubMed1994

The evolution of parasite manipulation of host behaviour: a theoretical analysis.

Parasite-induced modifications of host behaviour are known from a wide range of host-parasite associations. In many cases, these behavioural changes are thought to be adaptive and benefit the parasite by increasing its probability of successful transmission. However, in many cases, energy spent on host manipulation will not be available for other functions, such as growth. These trade-offs suggest that in the absence of other constraints, natural selection will optimize, and not maximize, the influence of parasites on host behaviour. This argument is developed and expanded into theoretical considerations of the evolution of host behaviour manipulation by parasites. Among populations of the same parasite species or among closely-related species, the optimal investment into manipulation, or optimal manipulative effort (ME*), of individual parasites is predicted to increase as (1) typical infrapopulation size decreases, (2) prevalence increases, (3) the longevity of the infected host, or of the parasite in its host, decreases, (4) passive transmission rates decrease, and (5) parasite fecundity decreases. This evolutionary analysis indicates that ecological and life history variables may have played an important role in the evolution of manipulation of host behaviour by parasites.

Adaptation, Physiological↗
PubMed2002

Cleaning symbioses from the parasites' perspective.

Cleaning behaviour has generally been viewed from the cleaner or client's point of view. Few studies, however, have examined cleaning behaviour from the parasites' perspective, yet they are the equally-important third players in such associations. All three players are likely to have had their evolution affected by the association. As cleaner organisms are important predators of parasites, cleaners are likely to have an important effect on their prey. Little, however, is known of how parasites are affected by cleaning associations and the strategies that parasites use in response to cleaners. I examine here what parasites are involved in cleaning interactions, the effect cleaners have on parasites, the potential counteradaptations that parasites have evolved against the predatory activities of cleaner organisms, the potential influence of cleaners on the life history traits of parasites, and other factors affected by cleaners. I have found that a wide range of ectoparasites from diverse habitats have been reported to interact with a wide range of cleaner organisms. Some of the life history traits of parasites are consistent with the idea that they are in response to cleaner predation. It is clear, however, that although many cleaning systems exist their ecological role is largely unexplored. This has likely been hindered by our lack of information on the parasites involved in cleaning interactions.

Adaptation, Physiological↗
PubMed1992

Lipid peroxidation in Plasmodium falciparum-parasitized human erythrocytes.

cis-Parinaric acid (PnA) was used as a fluorescent probe to study lipid peroxidation in nonparasitized and Plasmodium falciparum-parasitized erythrocytes, upon challenge by cumene hydroperoxide and tert-butyl hydroperoxide. Parasitized erythrocytes were less susceptible toward lipid peroxidation than nonparasitized erythrocytes with which they had been cultured. Furthermore, nonparasitized erythrocytes cultured together with parasitized cells, and thereafter isolated on a Percoll gradient, were less susceptible toward lipid peroxidation than erythrocytes kept under the same experimental conditions but in the absence of parasitized cells. We concluded, therefore, that the intracellular development of the parasite leads to an increase in the resistance against oxidative stress, not only of the host cell membrane of the parasitized erythrocyte, but also in the plasma membrane of the neighboring cells. The erythrocyte cytosol of parasitized cells and/or the intraerythrocytic parasite was required for the increased protection of the host cell membrane, since ghosts prepared from parasitized erythrocytes were more susceptible to lipid peroxidation than those prepared from nonparasitized ones. Vitamin E content of parasitized erythrocytes was lower than that of nonparasitized cells. However, parasitized erythrocytes promoted extracellular reduction of ferricyanide at higher rates, which might be indicative of a larger cytosolic reductive capacity. It is suggested that the improved response of intact erythrocytes is due to an increased reduction potential of the host-erythrocyte cytosol. The role of vitamin C as a mediator of this process is discussed.

Animals↗
PubMed1992

Plasmodium chabaudi: association of reversal of chloroquine resistance with increased accumulation of chloroquine in resistant parasites.

The effects of tricyclic antidepressants, desipramine and imipramine, and phenothiazines, chlorpromazine and trifluoperazine, on chloroquine (CQ)-resistant and CQ-sensitive lines of P. chabaudi were examined in vivo. In mice that received daily injections of these drugs the growth of CQ-resistant and CQ-sensitive parasites was unaffected or affected very slightly, if at all. A combination of CQ and each drug suppressed the growth of CQ-resistant parasites in a dose-dependent manner. In addition, in CQ-sensitive parasites each drug also increased the susceptibility to CQ. Measurements of CQ levels by high-performance liquid chromatography showed that CQ accumulated in sensitive parasites to more than twice the level in resistant parasites at 2 to 4 hr after an injection of CQ. Verapamil and desipramine substantially increased CQ levels in both CQ-resistant and CQ-sensitive parasites. These results suggest that not only Ca2+ antagonists but tricyclic antidepressants reverse CQ resistance in CQ-resistant parasites and enhance the inhibitory effect in sensitive parasites by increasing CQ levels in those parasites. The effects of Ca2+ antagonists, tricyclic antidepressants, and phenothiazines on a pyrimethamine-resistant line of P. chabaudi were also studied. None of the Ca2+ antagonists (verapamil, nicardipine, and diltiazem) affected the growth of the parasite in combination with 20 mg/kg pyrimethamine. Tricyclic antidepressants and phenothiazines suppressed pyrimethamine-resistant parasites to some extent. However, the extent of this suppression was less pronounced as compared with that of suppression of CQ resistance by the same drugs.

Animals↗
PubMed1998

Effects of parasitization by Cotesia congregata on the brain-prothoracic gland axis of its host, Manduca sexta.

The ability of prothoracic glands (PTGs) from parasitized and unparasitized Manduca sexta 5th-instars to respond to ecdysiotropic extracts prepared from day-5 5th instar brains was compared. An in vitro bioassay revealed that PTGs from parasitized animals were much less responsive to brain PTTH than glands from unparasitized larvae. However, when incubated in Grace's medium in the absence of brain extract, glands from day-3 and -4 hosts remained active for a much longer period of time than did those dissected from their unparasitized counterparts. Rather than exhibiting reduced (basal) levels of synthesis after the 3rd hour of incubation, glands from these parasitized larvae continued to synthesize/release ecdysteroid into the medium at relatively high rates. The timing of this enhanced secretory activity is coincident with the ecdysteroid peak that occurs just prior to and during wasp emergence. Following parasite emergence, gland activity decreased, and by the third day after emergence, was reduced to low levels. Results suggest that the requirement for PTTH to stimulate ecdysteroid production has been bypassed, i.e. that the parasite has uncoupled the normal mechanisms that permit brain regulation of PTG activity. The ability of brains from parasitized M. sexta to stimulate PTGs from unparasitized day-2 5th instars was also examined. Dose-response analyses performed for the first 7 days of the 5th instar showed that on a per brain basis ecdysiotropic activity in brains from parasitized and unparasitized animals was similar. However, when differences in brain size were considered, ecdysiotropic activity appeared to be more concentrated in brains from day-7 parasitized larvae than in brains from similarly aged unparasitized larvae. Analysis of the size distribution of the ecdysiotropic activity in brains from parasitized larvae revealed a unique form that was larger than the 29kDa standard. This suggests that parasitization may inhibit neuropeptide processing, particularly during the final stages preceding emergence of the wasps from the host. Thus, both an inhibition of prothoracicotropic hormone processing and the inability to respond to this neurohormone may contribute to the developmental arrest characteristic of parasitized 5th instars.

Journal Article↗
PubMed1997

Vector-parasite transmission complexes for onchocerciasis in West Africa.

BACKGROUND: In West Africa, there are two strains of the filarial parasite Onchocerca volvulus, which differ in their ability to induce ocular disease. Transmission studies have suggested that six sibling species of the parasite vector, the black fly Simulium damnosum sensu lato, allow development of the two strains of O volvulus with varying efficiency. We aimed to test the hypothesis of parasite-vector complexes, whereby the two parasite strains, known as forest and savanna, are preferentially transmitted by distinct groups of the species of S damnosum S l. METHODS: During 1993 and 1994, wild black flies were collected from 11 river basins within the area covered by the Onchocerciasis Control Programme (OCP). The flies were dissected and filarial larvae, ovaries, and malpighian tubules removed. Genomic DNA was extracted from larvae, and PCR amplification was used to classify O volvulus parasites as forest or savanna strains. PCR-amplified DNA from ovaries and malpighian tubules was used to distinguish sibling species of S damnosum s l. S yahense and S squamosum were distinguished by body colour. FINDINGS: 214 of 105105 flies dissected were infected with filarial larvae; 84 of these were infected with mature O volvulus parasites. Of the 35 savanna-dwelling infected flies. 17 carried forest-strain parasites and 18 savanna-strain parasites. Of the 45 infected flies identified as the forest dwelling sibling species. 20 carried savanna-strain parasites and 25 forest-strain parasites. No significant differences were found in the numbers of mature larvae of each strain carried by the forest-dwelling species of fly or in the number of forest and savanna larvae in savanna-dwelling vector species. INTERPRETATION: Vector-parasite transmission complexes do not currently play a part in the biology of O volvulus transmission in the area of the OCP in West Africa. This finding has important strategic implications for the future of efforts to control onchocerciasis in West Africa.

Africa, Western↗