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PubMed1999

Do parasites live in extreme environments? Constructing hostile niches and living in them.

We develop the hypothesis that parasites do not invade extreme environments, i.e. hostile hosts, but rather 'create' them. We argue that parasites may have driven the evolution of the constitutive and adaptive immune system. This leads to several implications. First, parasites respond to 'genes to kill' by 'genes to survive' and this triggers an indefinite selection of measures and counter-measures. Second, these coevolutionary arms races may lead to local adaptation, in which parasite populations perform better on local hosts. Third, the evolution of the immune system, whose responses are predictable, may allow parasites to specialize, to evade and even to manipulate. Finally we show that the correlations between the increase in the antibody repertoire, the expansion of MHC loci and parasite pressures support our hypothesis that both host complexity and parasite pressures can be invoked to explain the diversity of antibodies, T-receptors and MHC molecules.

Adaptation, Physiological↗
PubMed2001

The establishment, composition and severity of infection of gastro-intestinal parasites and their impact on productivity of Tswana kids in southern Botswana.

The presence of gastro-intestinal parasites in Tswana kids (n = 7) aged 1-3 weeks was studied for a period of 6 months at the Botswana College of Agriculture. The aims of this study were to find the time when they first contracted internal parasite infections, as well as to determine the severity of the infections and also its relation to production indicators (body mass and packed cell volume) of the kids as they grew older. The results indicate that they contracted coccidial and roundworm infections at approximately one month of age or immediately thereafter. The most prevalent internal parasite was coccidia, which occurred throughout the study period followed by roundworms and the least was the tapeworm, Moniezia expansa. Generally, the infection levels of all internal parasites were lower than the critical mean log (faecal oocyst/egg count + 1) of 3.3 inferred to cause reduced production in small stock. The correlation coefficients were all positive; 0.4-0.9 for individual internal parasites and production indicators, indicating that these internal parasites did not have any adverse effects on production. It was concluded that there was no need to treat kids of this age group for internal parasites.

Animals↗
PubMedDate not supplied

[The history of the formation of fish parasite fauna in lake Baikal].

The fauna of fish parasites in Lake Baikal is represented by 5 faunistic complexes, namely the boreal plain, boreal submountain, arctic freshwater, Baikal, and Sino-Indian ones. The parasites of the boreal plain complex are dominant by the number of species (43 %). Hypotheses on the origin of the recent fish and parasite faunas of Lake Baikal were advanced on the base of the data on the parasite species composition and their distribution among hosts, as well as on the base of paleontological data. It is shown that invasion of new fish species and their parasites to Baikal led to the change of the composition of natural faunistic fish complexes and parasite systems. Invading fishes play the roles of intermediate and definitive hosts in parasite systems of Baikal, that led to the change of the initial structure of these systems.

Animals↗
PubMed1994

On being a parasite in an invertebrate host: a short survival course.

Many parasites develop in invertebrate hosts that possess internal defense systems (IDS) that vigorously defined self-integrity. Invertebrates apparently do not produce a large diversity of finely tuned immunorecognition molecules but rather rely on recognition of patterns. As a consequence, requirements for immune evasion are likely to be fundamentally different in such hosts. Although parasites of invertebrates certainly employ diverse tactics to evade host IDS, this review focuses on parasite-mediated interference with the structural and functional integrity of host hemocytes and argues that this is a common strategy of immune evasion. Parasites mediating such effects on host hemocytes are termed suppressors. In some cases, interference is mediated by mutualistic symbionts carried by the suppressors. Hemocytes from infected hosts exhibit diminished adherence to substrates, impaired spreading ability, and reduced ability to participate in phagocytosis or encapsulation reactions. As a result of the action of suppressors, the host's vulnerability to opportunistic parasites is increased, a phenomenon termed acquired susceptibility. A strategy of interference is therefore risky, particularly for suppressors with relatively long development times. As a result, suppressors may provoke either a partial generalized interference or a selective interference with host IDS function, actively contribute to protection of the host to discourage growth of opportunists (termed parasite-mediated internal defense), or induce compensatory host responses that protect the host but that do not jeopardize their own development. Some parasites consistently colonize previously infected hosts and seem to be specialized opportunists.

Animals↗
PubMed1995

Zoonotic intestinal parasites of hamadryas baboons Papio hamadryas in the western and northern regions of Saudi Arabia.

Six hundred and thirty-three faecal samples were randomly collected and examined for ova and cysts of intestinal parasites from five groups of hamadryas baboons of different population densities, with different human contact and in different ecological conditions (Al-Baha, Turabah and Al-Taif in south-western and Al-Rihat and Al-Akhal in north-western Saudi Arabia). Nine parasites were recorded (Giardia lamblia, Entamoeba histolytica, Escherichia coli, Balantidium coli, Enterobius sp., Trichuris sp., Hookworm, Hymenolepis nana and Schistosoma mansoni) in 274 samples (43.28%). The prevalence of parasites was high (36.0-58.5%) in areas of mild, cool climatic conditions, where baboons were at high density and had maximum human contact. However, in an area (Al-Akhal) of hot, dry climatic conditions, low baboon density and minimum human contact, the parasites' prevalence was very low (9.5%). The concentration of parasites (ova or cysts per g of faeces) was medium. Post-mortem examination of 24, 20, 19 and 13 baboons from Al-Baha, Al-Taif, Turabah and Al-Rihat revealed most of the parasites recorded in random faecal samples at prevalence rates of 37.5, 30.0, 36.0 and 23.0% respectively. The overall prevalence rate was 32.9%. Most of the parasites recorded in baboons were also recorded in humans in the areas of study.

Adolescent↗
PubMed1997

Evaluation of environmental deterioration by analysing fish parasite biodiversity and community structure.

The degree of biological diversity is often used as an indicator of the well-being of ecological systems. This approach can also be applied to analyse biodiversity in parasite communities. In particular, studies on parasite communities can be employed to detect a decline in biodiversity which characterizes habitats affected by pollution. Beside the most widely used diversity indices, such as the Shannon, Brillouin and inverse Simpson, that have been widely applied in different host-parasite systems, new approaches have been recently developed in order to overcome problems related to high dominance. Walther et al. (1995) proposed an asymptotic equation suitable for evaluating parasite species richness as a function of sampling effort. Such an equation was earlier proposed by Miller and Weigert (1989) to describe plant species diversity and to calculate true species richness as the ratio between the increase in species richness (a) and the parameter that set the species richness asymptote (b). True species richness has been shown to decline in parasite communities of mugilids collected in polluted areas. Biodiversity calculations can also be run in parallel with other biological studies for the description of environmental conditions. The completion of parasite life cycles requires complex biocoenotic interactions and is restricted by environmental constraints. Therefore another approach for monitoring the health of an ecosystem was by analysing the ratio between monoxenous and heteroxenous parasite species infecting model hosts. By this methodology it was possible to confirm pollution effect highlighted by other quantitative methods.

Animals↗
PubMed1985

A syndromic approach to common parasitic diseases.

Standard textbooks discuss parasitic disease according to specific organisms. In contrast, patients with parasitic infections present to physicians with a variety of clinical manifestations that may involve any of several organ systems and that often mimic nonparasitic diseases. A syndromic approach to the clinical situation may help the physician in considering the most important parasitic agents. Many parasitic infections can be acquired in temperate climates. While often considered tropical or exotic, other parasitic diseases are now seen more frequently in developed countries because of immigration and increased world travel. In this review the clinical syndromes associated with common parasitic diseases in North America are discussed, with an emphasis on risk factors and diagnosis of specific infections.

Cholangitis↗
PubMed1992

Hemolymph concentrations of host ecdysteroids are strongly suppressed in precocious prepupae of Trichoplusia ni parasitized and pseudoparasitized by Chelonus near curvimaculatus.

Regulation of ecdysteroid production in lepidopteran prepupae was studied using a parasitic wasp (C. near curvimaculatus) which specifically suppresses host prepupal ecdysteroid production after the induction of precocious host metamorphosis. At the developmental stage at which the hemolymph of the unparasitized metamorphosing host has its maximum titer of prepupal ecdysteroids, the hemolymph of 4th instar "truly parasitized" hosts (hosts with a surviving endoparasite) had a strongly reduced ecdysteroid titer. However, during the photophase about 12 h later, just prior to emergence of the parasite larva, an ecdysteroid peak was observed in the host hemolymph. Fourth instar pseudoparasitized prepupal hosts (in which the endoparasite was not present or died early in development) exhibited a sustained suppression in the hemolymph ecdysteroid titer. Small 5th instar pseudoparasitized hosts, which normally would molt to a 6th instar prior to metamorphosis, but which precociously attained the prepupal stage, also had a strongly reduced ecdysteroid titer. The late increase observed in truly parasitized hosts could be completely prevented by surgical removal of the parasite 24 h earlier, resulting in a titer similar to that in pseudoparasitized hosts. HPLC analysis of ecdysteroids in normal, truly parasitized, and 4th or 5th instar pseudoparasitized prepupae showed that both ecdysone and 20-OH ecdysone* were suppressed in truly and pseudoparasitized prepupae, with ecdysteroid levels being lowest in pseudoparasitized hosts. These data, and those of Brown and Reed-Larsen (Biol Contr 1, 136 [1992]), showing endoparasite secretion of ecdysteroids just prior to its emergence from the host, strongly indicate that: (1) the prepupal peak in truly parasitized hosts originates from the endoparasite, and (2) the low level of ecdysteroids in pseudoparasitized hosts results from the host's intrinsic inability to express a normal level of prepupal ecdysteroid titer. While precocious 4th or 5th instar prepupae of similar size had similarly suppressed ecdysteroid titers, smaller 4th instar prepupae had a lower ecdysteroid titer than larger, precocious 5th instar prepupae. Rare 5th instar pseudoparasitized prepupae that were of nearly normal size showed a prepupal ecdysteroid titer distinctly greater than those of the usual smaller, precocious 5th instar prepupae. The data suggest that the competence of the host to express a normal hemolymph titer of prepupal ecdysteroids is more closely correlated with the size of the prepupae than with the instar attained.

Animals↗
PubMed2002

The thioredoxin system of Plasmodium falciparum and other parasites.

Antioxidant defence plays a crucial role in rapidly growing and multiplying organisms, including parasites and tumor cells. Apart from reactive oxygen species (ROS) produced in endogenous reactions, parasites are usually exposed to high ROS concentrations imposed by the host immune system. The glutathione and thioredoxin systems represent the two major antioxidant defence lines in most eukaryotes and prokaryotes. Trypanosomatids, however, are characterized by their unique trypanothione system. These systems are NADPH-dependent and based on the catalytic activity of the flavoenzymes glutathione reductase, trypanothione reductase and thioredoxin reductase (TrxR), respectively. TrxR reduces the 12-kDa protein thioredoxin (Trx), which in turn provides elcctrons to ribonucleotide reductase, thioredoxin peroxidases (TPxs), certain transcription factors and other target molecules. Comparing the thioredoxin systems of different parasites and their respective host cells enhances our understanding of parasite biology and evolution, of parasite-host interactions and mechanisms of drug resistance. It furthermore opens avenues for the development of novel antiparasitic compounds. Here we review the current knowledge on the Trx systems of eukaryotic parasites, finally focusing on the malarial parasite Plasmodium falciparum.

Amino Acid Sequence↗
PubMed2006

Effects of parasitic helminths and ivermectin treatment on clinical parameters in the European wild boar (Sus scrofa).

Limited information exists on serum biochemistry and haematology of the European wild boar, and few correlations have been found between parasitic burden and clinical parameters in this species. Naturally infected wild boars were experimentally treated to study the effect of nematode parasites and ivermectin treatment on phytohaemagglutinin (PHA) skin reaction and haematological and serum biochemical parameters. White blood cells decreased in untreated wild boars, whereas triglyceride, lactate and creatinine concentrations increased in ivermectin-treated wild boars, and total protein and aspartate aminotransferase activity increased in both groups. Band neutrophils variation was positively correlated with the number of total adult parasites. Band neutrophils, creatinine and total protein variations were negatively correlated with both total egg counts and Metastrongylus eggs per gram variations. Alkaline phosphatase activity showed a negative correlation with Ascaris sp. eggs. The PHA skin reaction was positively correlated with the number of total adult parasites in untreated wild boars and with Metastrongylus sp. eggs of all wild boars at time 0. Two models including leukocytic and serum biochemical parameters were also highly correlated with the variation of Metastrongylus sp. eggs. Clinical parameters were thus in our study affected by helminth parasitism in the European wild boar, particularly those related to nutrients uptake, physical condition and immune response. Therefore, they could be useful in studies on subclinical effects of parasites, and parasitic burden must be considered when assessing the physical condition of European wild boars through haematological and serum biochemical parameters.

Alkaline Phosphatase↗
PubMed1996

The effects of parasitism by Glyptapanteles liparidis (Braconidae: Hymenoptera) on the hemolymph and total body composition of gypsy moth larvae (Lymantria dispar, Lymantriidae: Lepldoptera).

The hemolymph and total body tissue composition (carbohydrates, lipids, proteins, and free amino acids) of gypsy moth larvae (Lymantria dispar, Lymantriidae:Lepidoptera) were analyzed and compared with the composition of larvae infected by their main parasitoid, Glyptapanteles liparidis (Braconidae:Hymenoptera). In the body tissue the concentrations of total lipids and total proteins decreased, whereas the glycogen concentration in the total body tissue was significantly elevated and exceeded the concentration of the nonparasitized larvae by a factor of approximately 3. Trehalose, glucose, and sorbitol were found in the hemolymph of both parasitized and nonparasitized larvae, but levels of all three carbohydrates were significantly reduced in parasitized individuals. The total lipid concentration was not altered due to parasitism. In the hemolymph the concentrations of total proteins nearly doubled in parasitized larvae, whereas the total free amino acid concentration was reduced; however, the levels of some single amino acids were reduced and those of others were elevated in the parasitized larvae. The polypeptide profile of the host hemolymph provided one parasitism-specific polypeptide at approximately 80 kDa. The results demonstrate that parasitization of gypsy moths by G. liparidis leads to significant alterations in levels of nearly all substance classes within the host's hemolymph and tissue.

Animals↗
PubMed2004

Parasite biodiversity and host defenses: chewing lice and immune response of their avian hosts.

Antagonistic host-parasite interactions lead to coevolution of host defenses and parasite virulence. Such adaptation by parasites to host defenses may occur to the detriment of the ability of parasites to exploit alternative hosts, causing parasite specialization and speciation. We investigated the relationship between level of anti-parasite defense in hosts and taxonomic richness of two chewing louse suborders (Phthiraptera: Amblycera, Ischnocera) on birds. While Amblyceran lice tend to occur in contact with host skin, feed on host skin and chew emerging tips of developing feathers to obtain blood, Ischnoceran lice live on feathers and feed on the non-living keratin of feather barbules. We hypothesized that Amblyceran abundance and richness would have evolved in response to interaction with the immune system of the host, while Ischnoceran taxonomic richness would have evolved independently of immunological constraints. In an interspecific comparison, the abundance of Ischnocerans was positively related to host body size, while host body mass and Ischnoceran taxonomic richness accounted for the abundance of Amblycerans. Amblyceran taxonomic richness was predicted by the intensity of T-cell mediated immune response of nestling hosts, while the T-cell response of adults had no significant effect. In contrast, Ischnoceran taxonomic richness was not predicted by host T-cell responses. These results suggest that the taxonomic richness of different parasite taxa is influenced by different host defenses, and they are consistent with the hypothesis that increasing host allocation to immune defense increases Amblyceran biodiversity.

Animals↗
PubMed2004

Mixed inoculations of a microsporidian parasite with horizontal and vertical infections.

Mixed infections, where more than one parasite genotype is present in a single host, have been suggested to be an important factor in host-parasite interactions. As the host represents a limited resource, co-infecting parasite genotypes are expected to be under resource competition. Competition will not only modify the survival of the co-infecting genotypes, but is also likely to affect total within-host parasite growth as well as host survival and reproduction. We measured parasite infectivity and spore production of seven isolates of Octosporea bayeri (Microsporidia) and their effect on the reproduction and longevity of its host Daphnia magna (Cladocera), after single- or double-isolate inoculations through vertical and horizontal transmission. Double-isolate inoculations increased parasite infectivity and total spore production in horizontal infections, but had no significant effect on host reproduction or longevity. The increase in spore production in double-isolate inoculations was not found when infections occurred vertically. Our results suggest that, depending on the way the infection was acquired, within-host reproduction can increase as a result of parasite genetic diversity, without necessarily affecting the host's fitness. Whether this challenges the current views of virulence evolution depends on the definitions used.

Animals↗
PubMed1995

The population dynamics of communities of parasitic helminths.

This paper considers the dynamics of a host (animal) species that would grow exponentially in the absence of parasitism, and a community of parasite species that may regulate this growth. The model consists of a single differential equation for the host and one for each of the parasite species. This level of simplicity is achieved by assuming that each parasite species has a negative binomial distribution within the host population, with either zero covariance between the species (exploitation competition), or a specified covariance structure (interference competition). Conditions on the model parameters that determine the abundance of the different species are formulated, as are conditions that determine when a parasite species can invade a community and when a species is likely to be squeezed out. The results show that highly aggregated parasite species are more likely to coexist, but are less able to regulate their host population. A negative correlation between the distributions of the parasite species enhances both their ability to coexist and their ability to regulate the host population. The results of this analysis apply more generally to other systems where communities of exploiter species coexist on discretely distributed hosts, for example, insects on plants.

Animals↗
PubMed2004

Living on the edge: parasite taxonomy in Australia.

The way in which the huge Australian parasite fauna is described (discovery and naming) is the subject of this address. The approach to the task has never been well-organised so that a few groups of parasites are now relatively well-known because of the efforts of small groups of workers who have made sustained efforts in these groups, but equally some host-parasite systems have been almost completely ignored in that no worker has ever given them sustained attention. A high proportion of Australian parasites have been described by international workers. The sustaining of interest in a group of parasites over a long period is the key to real progress being made. The nature of the organisation of Australian science presently means that few positions are available for parasite taxonomists and funding for taxonomic research is scarce. Thus, parasite taxonomy (like the taxonomy of many groups of Australian plants and animals) can only be considered to be in crisis.

Animals↗
PubMed2004

Epizootiology of blood parasites in an Australian lizard: a mark-recapture study of a natural population.

The dynamics of a naturally endemic blood parasite (Hepatozoon hinuliae) were studied in a lizard (Eulamprus quoyii) host population, using 2 years of longitudinal data. We investigated how parasite abundance in the population varied over time, examined whether certain host sub-populations were more prone to infection, and compared parasite loads in relation to host reproductive behaviour. We recorded blood parasite infections of 331 individuals, obtained in 593 captures. Prevalence (the proportion of the host population infected) of blood parasites was high; approximately 66% of the lizard population was infected. Probability of infection increased with host age and size, but did not differ between the sexes. Within individuals, parasite load (the intensity of infection within individuals) did not vary over time, and was independent of host reproductive behaviour. Parasite load was significantly higher in males compared to females.

Age Factors↗
PubMed2005

Human behaviour and the epidemiology of parasitic zoonoses.

The behaviour of Homo sapiens has a pivotal role to play in the macro and microepidemiology of emerging or re-emerging parasitic zoonoses. Changing demographics and the concomitant alterations to the environment, climate, technology, land use and changes in human behavior, converge to favour the emergence and spread of parasitic zoonoses. The recent unprecedented movements of people, their animals and their parasites around the world, introduce and mix genes, cultural preferences, customs, and behavioral patterns. The increasing proclivity for eating meat, fish, crabs, shrimp, molluscs raw, undercooked, smoked, pickled or dried facilitates a number of protozoan (Toxoplasma), trematode (Fasciola sp., Paragonimus spp., Clonorchis sp., Opisthorchis spp., Heterophyes sp., Metagonimus sp., Echinostoma spp., Nanophyetus sp.) cestode (Taenia spp, Diphyllobothrum sp.) and nematode (Trichinella spp., Capillaria spp., Gnathostoma spp., Anisakis sp., Parastrongylus spp.) caused zoonoses. The increasing world population and the inability to keep pace with the provision of adequate sanitation and clean, safe drinking water, has led to an increased importance of waterborne zoonoses, such as those caused by Giardia, Cryptosporidium and Toxoplasma. Our close relationship with and the numerous uses to which we put companion animals and their ubiquitous distribution has resulted in dogs and cats unwitting participation in sharing over 60 parasite species including: Giardia, Cryptosporidium, Toxoplasma, most foodborne trematode species, Diphyllobothrum, Echinococcus spp., Ancylostoma and Toxocara. Changing human behaviour through education, to encourage the proper cooking of food, which may have cultural and social significance, will remain as challenging as controlling stray and feral pet populations, improving hygiene levels and the provision of safe drinking water and the proper use of sanctuary facilities. Long pre-patent periods and the normally insidious sub-clinical nature of most zoonoses makes advice requiring behavioural change for their control a difficult task. Our clearer understanding of the heterogeneity of susceptibility to infection, the complex genetic variations of people and parasite species and the development of molecular epidemiological tools is shedding more light on transmission routes and the spectrum of disease that is observed. Improved and new serological, molecular and imaging diagnostic tests and the development of broad spectrum chemotherapeutic agents has led to the attenuation of morbidity and mortality due to parasitic zoonoses in economically advantaged regions. Such advancements, in partnership with supportive behavioural change, has the potential for a sustainable global reduction in the burden of ill health due to parasitic zoonoses. Whether this will materialise is a challenge for us all.

Animals↗
PubMed2005

Mediterranean Diplodus annularis (Teleostei: Sparidae) and its brain parasite: unforeseen outcome.

Patterns of parasite load and aggregation of the bird trematode Cardiocephaloides longicollis in its main intermediate host in the Mediterranean, the annular sea bream, Diplodus annularis, were studied in a large sample collected off Valencia (Spain) and are discussed within the context of the parasite induced host mortality hypothesis. The metacercariae were located within large composite cysts of host origin in the ventricles of the optic lobes of the cerebrum. A weak immunological response was detected in older fish, which was significantly associated with the total parasite load. Although the mean abundance of C. longicollis showed a tendency to increase with host size, the infection levels were generally homogeneous with a noticeable plateauing in the intermediate size classes. The distribution of the metacercariae was aggregated and agreed with the negative binomial distribution. There was a marked decline in parasite aggregation in the largest size-class, suggesting parasite-induced host mortality in the oldest fish possibly due to predation by large non-host fish predators. On the other hand, levelling off of abundance and decrease in heterogeneity of parasite distribution within the intermediate age cohort could indicate that these sizes are being rapidly and/or constantly removed from the host population due to by-catch fishing. The overall high infection levels and the continuous recruitment across age cohorts provides evidence that an enhanced parasite transmission is taking place in the Gulf of Valencia due to increased spatial overlap of the hosts involved in the life cycle. We suggest a human-induced facilitation of the digenean life cycle due to the fact that gulls in the area feed extensively on discards, thus indicating the possibility of an unforeseen effect of fishing practices in a marine littoral system.

Animals↗