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[Distribution of entero-parasitic infections in the Peruvian Highland: study carried out in six rural communities of the department of Puno, Peru].

A prevalence study was carried out in six rural communities in the Peruvian Highlands with the purpose of achieving a better understanding of the distribution of entero-parasites. The communities were located along the banks of Lake Titicaca, in the provinces of Puno and El Collao, Department of Puno, Peru, at 3,800 m.a.s.l. To that effect, a total of 91 feces samples of adults and children from the following communities were analyzed: Conchaca, Puñutani, Capalla, Culta, Maraesqueña, and Jaillihuaya. Analysis techniques included Direct Examination, Kato Technique, Technique of Spontaneous Sedimentation in a Test Tube and the Lumbreras Rapid Sedimentation Technique. The general prelavence of intestinal parasitosis was found to be 91.2%. The pathogenic entero-parasites found were, in order of frequency, as follows: Hymenolepis nana 6.6%, Entamoeba histolytica 5.5%, Giardia lamblia 3.3%, Taenia sp. 2.2%, Ascaris lumbricoides 2.2%, Trichuris trichiura 1.1%, and Enterobius vermicularis 1.1%. The frequency of the non-pathogenic entero-parasites was as follows: Entamoeba coli 78%, Endolimax nana 39.6%, Iodamoeba butschlii 14.3%, Blastocystis hominis 9.9%, and Chilomastix mesnili 2.2%. Most of the patients had poly parasitism (58.2%), and protozoan infections prevailed over helminthic infection. From the total number of patients infected, 41.8% had one parasite, 33.0% had two parasites, 11.0% had three parasites, 4.4% had four parasites, and 1.1% had five parasites. These results show the high rates of parasitism in the rural population on the banks of Lake Titicaca, which would be associated with socioeconomic factors and the poor environmental sanitation conditions in this area.

Adolescent↗

Skin manifestations in parasite infection.

BACKGROUND: Intestinal parasites stimulate IgE synthesis by their proteinases. Because of their ability to induce IgE production and mast cell degranulation (either directly, e.g. Ascaris, or via specific IgE) it is possible that some parasites induce allergic manifestations. Some parasites may be more allergenic than others due to their allergenicity. Genetic predisposition, nutritional status, and psychosocial variables of the host and the time and degree of allergen exposure may also play an important role. THE AIM: Of our study was to investigate which parasites are more frequently related to the skin manifestations and if atopic background of the host has a role in these skin allergic hives in intestinal parasites. MATERIAL AND METHOD: 55 patients (13 men, mean age 36 years old) infested with digestive parasites were skin prick tested to inhalant allergens (house dust mites, pollens, animal dander) in order to evaluate the atopic status. All patients had allergic skin manifestations (rash and hives) and angioedema due to their intestinal parasites, which remitted after antiparasitic treatment. RESULTS: Forty (73.3%) patients presented angioedema and 15 patients (26.6%) had chronic rash. Patients who were infected with Ascaris had more severe symptoms: more than 2/3 had angioedema, and only one third had chronic rash. More than 2/3 of the patients were infested with Ascaris lumbricoides: 38 patients (69.09%), and only one third were infested with Giardia lamblia: 18 patients (32.72%). Only one third of the patients (17-30.9%) had positive skin prick tests for at least one inhalant allergen. CONCLUSIONS: The parasite most frequently implicated in skin allergic manifestations in our region is Ascaris lumbricoides. Acute angioedema or chronic rash are the major skin manifestations in parasitic infestation. The atopic trait has no importance in the appearance of allergic manifestations in parasitic infestation.

Adult↗

[Mites of the family Cheyletidae (Acari: Prostigmata): phylogeny, distribution, evolution and analysis of parasite-host relationship].

A modern system, phylogeny, distribution and host parasite relationships of cheyletid mites (Acari: Prostigmatal Cheyletidae) is shortly discussed. According to the phylogenetic hypothesis proposed by Bochkov and Fain (2001), the family Cheyletidae includes now 15 tribes: Acaropsellini, Bakini, Cheletogenini, Cheletosomatini, Chelonotini, Cheyletiini, Cheyletiellini, Cheyletini, Cheletomorphini, Criokerontini, Metacheyletiini, Niheliini, Ornithocheyletiini, Teinocheylini and one unnamed tribe including the genera Caudacheles and Alliea. The parasitic Cheyletidae were primarily free-living predators, frequently associated with nests of vertebrates. These mites, being predators, have numerous preadaptations to the parasitic mode of life and they possess high ecological plasticity. Therefore it was quite easy for these mites to adapt to parasitism on the vertebrates. According to our phylogenetical hypothesis, the parasitism on vertebrates has arisen independently in several phylogenetic lines of the cheyletids associated with nests of vertebrates. Such transition from nest predation to true parasitism probably occurred repeatedly and at different times. The cheyletid mites are more widely represented on birds than on mammals. Possibly, it is in relation with a more early origin of parasitism in the cheyletids associated with bird nests than in the cheyletids associated with mammal nests. An independent origin of the parasitism in many different cheyletid phyletic lines, arisen significantly later than the origin of such a parasitic group as myobiid mites, is probably the main reason, which could explain the recent mosaic distribution of the Cheyletidae among the mammalian taxa. Parasitic associations between cheyletids and vertebrates are more common than the associations between these mites and the invertebrates. In the invertebrates, these associations are generally restricted to a phoresy. The zoogeographical analysis showed that this family as whole is characterised by the extremely low endemisms. The most part of the free-living cheyletid mites are associated with Holarctic region (87%) and, therefore, this family, probably, originated there.

Acari↗

Prevalence of intestinal parasitic pathogens among HIV-positive individuals in Iran.

Parasites are important enteric pathogens among patients with human immunodeficiency virus (HIV) infection. There have been very few reports on the prevalence of intestinal parasites among such patients in Iran. To determine the prevalence of intestinal parasites among HIV-positive individuals, we collected single stool samples and analyzed them for detection of various intestinal parasites from 206 HIV-positive individuals with different immune status visited in different medical centers in Iran. The data were tested for statistical significance with chi(2) and Mann-Whitney U tests. The overall prevalence of intestinal parasites was 18.4% (95%CI: 13.7, 24.3). More specifically, the following parasites were identified: Giardia lamblia (7.3%), Blastocystis hominis (4.4%), Entamoeba coli (3.9%), and Cryptosporidium parvum (1.5%). Other parasites observed included Strongyloides stercoralis and Hymenolepis nana in two cases and Dicrocoelium dendriticum in one. Of the 38 patients who tested positive for intestinal parasites, 15 (39.2%) had diarrhea. Intestinal parasites were significantly more common among patients with diarrhea than those without (P < 0.001). Further, CD4 counts were significantly lower among individuals with diarrhea than those without (P < 0.001). This study highlights the importance of testing for intestinal parasites among Iranian HIV-positive patients, especially those with low immunity presenting with diarrhea.

Adult↗

Molecular basis of Trypanosoma cruzi and Leishmania interaction with their host(s): exploitation of immune and defense mechanisms by the parasite leading to persistence and chronicity, features reminiscent of immune system evasion strategies in cancer diseases.

A number of features occurring during host-parasite interactions in Chagas disease caused by the protozoan parasite, Trypanosoma cruzi, and Leishmaniasis, caused by a group of kinetoplastid protozoan parasites are reminiscent of those observed in cancer diseases. In fact,although the cancer is not a single disease, and that T.cruzi and Leishmania are sophisticated eukaryotic parasites presenting a high level of genotypic variability the growth of the parasites in their host and that of cancer cells share at least one common feature, that is their mutual capacity for rapid cell division. Surprisingly, the parasitic diseases and cancers share some immune evasion strategies. Consideration of these immunological alterations must be added to the evaluation of the pathogenic processes. The molecular and functional characterization of virulence factors and the study of their effect on the arms of the immune system have greatly improved understanding of the regulation of immune effectors functions. The purpose of this review is to analyze some of the current data related to the regulatory components or processes originating from the parasite that control or interfere with host cell physiology. Attempts are also made to delineate some similarities between the immune evasion strategies that parasites and tumors employ. The elucidation of the mode of action of parasite virulence factors toward the host cell allow not only provide us with a more comprehensive view of the host-parasite relationships but may also represent a step forward in efforts aimed to identify new target molecules for therapeutic intervention.

Animals↗

Specificity and specialization of congeneric monogeneans parasitizing cyprinid fish.

Patterns and likely processes connected with evolution of host specificity in congeneric monogeneans parasitizing fish species of the Cyprinidae were investigated. A total of 51 Dactylogyrus species was included. We investigated (1) the link between host specificity and parasite phylogeny; (2) the morphometric correlates of host specificity, parasite body size, and variables of attachment organs important for host specificity; (3) the evolution of morphological adaptation, that is, attachment organ; (4) the determinants of host specificity following the hypothesis of specialization on more predictable resources considering maximal body size, maximal longevity, and abundance as measures of host predictability; and (5) the potential link between host specificity and parasite diversification. Host specificity, expressed as an index of host specificity including phylogenetic and taxonomic relatedness of hosts, was partially associated with parasite phylogeny, but no significant contribution of host phylogeny was found. The mapping of host specificity into the phylogenetic tree suggests that being specialist is not a derived condition for Dactylogyrus species. The different morphometric traits of the attachment apparatus seem to be selected in connection with specialization of specialist parasites and other traits favored as adaptations in generalist parasites. Parasites widespread on several host species reach higher abundance within hosts, which supports the hypothesis of ecological specialization. When separating specialists and generalists, we confirmed the hypothesis of specialization on a predictable resource; that is, specialists with larger anchors tend to live on fish species with larger body size and greater longevity, which could be also interpreted as a mechanism for optimizing morphological adaptation. We demonstrated that ecology of host species could also be recognized as an important determinant of host specificity. The mapping of morphological characters of the attachment organ onto the parasite phylogenetic tree reveals that morphological evolution of the attachment organ is connected with host specificity in the context of fish relatedness, especially at the level of host subfamilies. Finally, we did not find that host specificity leads to parasite diversification in congeneric monogeneans.

Animals↗

Use of confidence ellipses to detect effects of parasites on the growth of yellow perch, Perca flavescens.

Determining the causes of mortality in populations of fish is inherently difficult. To simplify the determination of whether parasite-induced mortality occurs, parasitologists have relied on 3 types of subjective analyses of graphs. Peaked host age-parasite intensity curves concomitant with a decrease in the degree of dispersion (measured by variance-to-mean ratio) of parasites in older age-classes of fishes, a slope of less than 2.0 for a log-log graph of variance versus mean intensity of infection, and differences between truncated and nontruncated forms of a theoretical frequency distribution for the parasite are considered indicators of parasite-induced mortality in fishes. The nematode Raphidascaris acus causes significant parasite-induced mortality in natural populations of yellow perch (Perca flavescens) in Dauphin Lake, Manitoba, Canada. Using this fish-parasite system we present a comparison of some of the graphical techniques used by parasitologists to detect parasite-induced mortality and show how confidence ellipses based on the parameters beta 0 and beta 1 of a linear model for growth of yellow perch (weight = beta 0 + beta 1 x age) can be used to compare many growth curves simultaneously. When plotted in a bivariate fashion (beta 0 vs. beta 1), vertical displacement of confidence ellipses along the ordinate (beta 1) are due to sublethal effects on growth of fishes in response to parasites, whereas lateral shifts along the abscissa (beta 0) are suggestive of parasite-induced mortality.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

Visceral and cutaneous leishmaniasis comparative ultrastructure of host-parasite interactions.

The comparative ultrastructure of host-parasite interactions is described for the first time in patients with visceral (VL) and cutaneous (CL) leishmaniasis. In patients with VL, the parasite invades the bone marrow (BM) macrophages (Mcs) and neutrophils, while in patients with CL, the parasite invades the dermal fibroblasts in addition to Mcs. The skin Mcs seem to have more lethal effects on the parasite than the BM Mcs; this is possibly due to the presence of numerous melanosomes with acid phosphatase activity in the Mcs digestive vacuole. In patients with high level of VL parasitaemia, the parasite may induce the BM reticulocytes to phagocytose both the parasite and mature erythrocytes, i.e. lost recognition. In patients with low level of VLparasitaemia, the parasite may induce the BM Mcs to be haemophagocytic, i.e. temporarily mimick malignant histiocytosis until the course of treatment. In early stages of CL infection, the cellular infiltrate consists of the monocyte-macrophage system, plasma cells, lymphocytes and fibroblasts; while in the late stages, two types of epithelioid cells (ECs) are added to the infiltrate and are involved in the formation of tuberculous granulomas. Type I ECs thought to produce a granuloma factor, while type II ECs possibly precedes healing by fibrosis. However, the severity of host-parasite interactions seems to depend mainly on species of the parasite, the degree of parasitaemia, the type of infected tissue(s), and the variation of host tissue reaction against the parasite from one patient to another.

Adolescent↗

Parasitic causes of hepatomegaly in children.

Three hundred children with hepatomegaly were selected. They were subjected to full clinical and laboratory examinations. Also serum samples were examined to detect IgG using ELISA against SEA, chromatography purified hydatid cyst antigen, commercially available Toxoplasma antigen, partially purified adult Fasciola antigen and second-stage larvae Toxocara canis antigen. IFAT was used to detect IgG against Toxoplasma and T. canis. A commercially available IHAT kit for leishmaniasis was used. Based on immunological assays, 125 cases were suffering from various parasitic infections. Thirty cases with schistosomiasis (10%), 26 cases fascioliasis (8.7%), 18 toxocariasis (6%), 35 toxoplasmosis (11.7%), 3 cases hydatidosis (1%) and 13 cases mixed parasitic infections. No parasitic causes could be found in 175 cases (58.3%). Moderate or marked hepatomegaly favours the presence of schistosomiasis. Whereas, most cases with other parasites and those with non-parasitic infections fall in the category of mild hepatic enlargement. There was no associated splenomegaly in cases with Fasciola, Toxocara, hydatid disease and/or the non-parasitic group. Most of hepatomegalic cases with non-parasitic causes were found to be associated with fever (88.5%). Fever was found in nearly 50% of cases with either Toxoplasma or Toxocara infections. Mild eosinophilia was found in all cases with parasitic causes. Only 24 cases of non-parasitic group (13.7%) had easinophilia. Moderate and high eosinophilia were found in cases with fascioliasis and toxocariasis. Cases with fascioliasis had a statistically significant increase in enzymes activities specially alkaline phosphatase. It was concluded that parasitic infections should be considered as an important cause of liver enlargement in children. Serological methods using purified antigenic fractions are an important tool for diagnosis.

Child↗

Parasite communities as indicators of ecosystem stress.

Many parasites have complex life cycles and for transmission depend on the presence of a variety of vertebrate and invertebrate intermediate hosts, including members of the benthos and zooplankton. Thus, food web dynamics and trophic interactions have a powerful influence on parasite community structure. In addition, many parasites possess free-living stages that are also susceptible to environmental conditions. Therefore, the parasite community within a single host species such as a fish is indicative of environmental stress, trophic structure, and biodiversity. We show that parasite communities of American eels (Anguilla rostrata) in Nova Scotia respond to acid conditions in rivers. Parasite species richness was greater and there were more multiple infections in eels from an experimentally limited river compared to those from an adjacent acidified river. Digeneans were absent in eels from the acidified river. The study was expanded to include 28 sites in the Southern Upland and adjacent regions of Nova Scotia, encompassing a pH gradient increasing from southwest to northeast. Survey results support those obtained by experimental manipulation. Parasite diversity in eels as measured by species richness, Shannon-Wiener Index, and Hill's Number decreased when pH < 5.4. Digeneans were absent from the southwest, where pH < 4.7. Parasite distributions among rivers in adjacent watersheds corresponded to fluctuations in pH in those rivers. These results support the hypothesis that parasite communities are good indicators of environmental stress and biodiversity, because they reflect the presence of many different types of organisms based on the variety of complex life cycles displayed by the different parasite taxa.

Anguilla↗

Life on the edge: gastrointestinal parasites from the forest edge and interior primate groups.

Humans are responsible for massive changes to primate habitats, and one unanticipated consequence of these alterations may be changes in host-parasite interactions. Edges are a ubiquitous aspect of human disturbance to forest landscapes. Here we examine how changes associated with the creation of edges in Kibale National Park, Uganda, alter the parasite community that is supported by two species of African colobines: the endangered red colobus (Piliocolobus tephrosceles) and the black-and-white colobus (Colobus guereza). An analysis of 822 fecal samples from edge and forest interior groups revealed no difference in the richness of parasite communities (i.e., the number of parasite species recovered from the host's fecal sample). However, for both species the proportion of individuals with multiple infections was greater in edge than forest interior groups. The prevalence of specific parasites also varied between edge and forest interior groups. Oesophagostomum sp., a potentially deleterious parasite, was 7.4 times more prevalent in red colobus on the edge than in those in the forest interior, and Entamoeba coli was four times more prevalent in red colobus on the edge than in animals from the forest interior. Environmental contamination with parasites (measured as parasite eggs/gm feces) by red colobus from the edge and forest interior differed in a similar fashion to prevalence for red colobus, but it did not differ for black-and-white colobus. For example, egg counts of Oesophagostomum sp. were 10 times higher in red colobus from the edge than in those from the interior. The less severe infections in the black-and-white colobus relative to the red colobus may reflect the fact that black-and-white colobus raid agricultural crops while red colobus do not. This nutritional gain may facilitate a more effective immune response to parasites by the black-and-white colobus. The fact that animals on the edge are likely not nutritionally stressed raises an intriguing question as to what facilitates the elevated infections in edge animals. We speculate that interactions with humans may be linked to the observed patterns of infections, and hence that understanding the ecology of infectious diseases in nonhuman primates is of paramount importance for conservation and potentially for human-health planning.

Animals↗

Parasites and allergies: a complex bidirectional relationship from evolutionary origins to modern therapeutics.

Parasites and allergic diseases are linked by a complex, bidirectional relationship shaped by long-term host-parasite coevolution. This review discusses how different parasites may either promote or attenuate allergic responses through immunological, epithelial, and microbiome-mediated mechanisms. IgE-mediated immunity, mast cell activation, eosinophilia, and pruritus may have evolved as protective responses against helminths and blood-feeding ectoparasites. In contrast, modern allergies may partly reflect misdirected responses to harmless environmental antigens. The effects of parasites on allergy are not uniform and depend on parasite type, infection site, exposure intensity and chronicity, host immune status, and the degree of host-parasite adaptation. Protozoa such as Giardia intestinalis may contribute to food allergy-related manifestations by disrupting the intestinal barrier, altering gut microbiota composition, and modifying mucosal immune responses, particularly in atopic individuals. In contrast, selected helminths may attenuate allergic inflammation by inducing regulatory T and B cells, anti-inflammatory cytokines, antigen-presenting cell modulation, and IgG4-associated mechanisms that can limit IgE-mediated effector responses. Molecular similarities between parasite-derived antigens and environmental allergens, including conserved protein families and carbohydrate epitopes, may contribute to cross-reactive IgE responses and complicate allergy diagnostics. Therefore, current research is shifting from live helminth therapy toward defined parasite-derived molecules and immunomodulatory pathways that may inspire safer and more controlled therapeutic strategies. A clearer understanding of parasite-allergy interactions may improve diagnostic interpretation and support the development of new approaches to the management of allergic disease.

Humans↗

Molecular mimicry between host and pathogen: examples from parasites and implication.

The studies summarized in this paper suggest that parasites may trigger activation of autoimmune mechanisms. The association between parasites and autoimmunity could by manifested by the development of pathogenic anti-parasitic antibodies and cytotoxic T cells that attack and damage self tissues as a result of molecular mimicry between host and parasites. On the other hand, the homology between self and parasitic antigens may enable parasites to protect themselves from the immune system and to induce a state of immunosuppression. Although classic autoimmune diseases have not been shown to be more common amongst patients with chronic parasitic infections than in the general population, it is clear that autoimmune activity does occur in patients with chronic parasitic infections. It is possible that infection with parasites and other microbial agents may be followed by the activation of the immune system and, in genetically predisposed individuals, by loss of functional tolerance to self, activation of autoreactive cell that leads to progression to an overt autoimmune disease.

Animals↗

The ecology of host-finding behaviour and parasite transmission: past and future perspectives.

Host location by parasites can be achieved by either active or passive mechanisms. In spite of their significance, the efficacy of these methods has been little researched. High fecundity in parasites is discussed in terms of the role it plays in dispersal and transmission. Some concepts developed by mainstream behavioural ecologists are outlined and their relevance to parasitology is indicated. 'Reproductive value' is recommended as an appropriate measure of the costs and benefits of behavioural cts. Although costs of reproduction have been rarely studied in parasites, they are likely to occur in cosexual insects, nematodes and crustaceans. Experiments using captive hosts and/or in vitro cultivation could help in the construction of realistic optimality models. We suggest that r- and K-selection theory could assist in the study of the evolution of parasite behaviour. We discuss how parasite populations are dispersed and controlled and consider the implications of overdispersion. We outline three sources of signals to which parasites may respond and suggest that understanding evolutionary mechanisms and community organisation of parasites and hosts requires evaluation of fundamental behavioural responses to environmental signals. The study of closely related groups of parasites and their hosts may advance our knowledge of the evolution of parasite life cycles and the evolutionary costs and benefits of behavioural acts.

Animals↗

Evolutionary factors influencing the nature of parasite specificity.

This article considers how specificity patterns are shaped during the course of parasite evolution. Parasites are first and foremost specific to site, or microhabitat; host ranges are far more subject to change than is microhabitat. Specificity results from a number of convergent phenomena starting with habits (microhabitat and feeding styles) of free-living progenitors and the way in which the parasitic association arises (e.g., passive oral contamination as opposed to intrusive entry). These bias the types of interaction parasites have with the host, and, through this, the way specificity develops. Host ecology acts as an external factor affecting specificity and predominates in parasites that interact minimally with the hosts physiological and immune systems. Coevolutionary factors are more important in parasites that feed on host tissues or occur in extraintestinal sites. Here, parasites must present the right cues, and respond appropriately to the host defense system. The ability to generalize these cues and responses across host boundaries may act as a constraint on host range. The functional role of the host in the parasite life history also affects the degree of specificity; thus, parasites may act as host generalists in hosts that act as trophic channels to the final host. The role of competition in determining specificity is difficult to assess. However, competition has been reported to influence microhabitat and host distribution through interactive site selection and/or competitive seclusion.

Animals↗

Within-lake dynamics in the similarity of parasite assemblages of perch (Perca fluviatilis).

Although parasite communities have been studied extensively in recent years, spatial and temporal variation in factors affecting the communities has received less attention. This paper examined the similarity of parasite assemblages of perch (Perca fluviatilis) in 18 locations within a single lake in relation to geographical distance and temporal dynamics in the host and parasite populations. We expected that in the present study-scale where distinct but potentially interacting host subpopulations could occur, similarity of the assemblages could be affected by seasonal dynamics in host movements particularly during the spawning period. Parasite species showed differences in infection levels between the sampling locations and similarity of the assemblages of autogenic parasite species in winter, measured inversely as difference in parasite numbers, was negatively affected by geographical distance between the locations. However, no such relationship was observed in the allogenic species Ichthyocotylurus variegata. Furthermore, no relationship was found either in autogenic parasites when the locations were re-sampled in summer, after the spawning period of perch. We concluded that the effect of geographical distance on the similarity of parasite assemblages is a dynamic process, which is affected by seasonal dynamics in host and parasite populations.

Animals↗

Models of parasite virulence.

Several evolutionary processes influence virulence, the amount of damage a parasite causes to its host. For example, parasites are favored to exploit their hosts prudently to prolong infection and avoid killing the host. Parasites also need to use some host resources to reproduce and transmit infections to new hosts. Thus parasites face a tradeoff between prudent exploitation and rapid reproduction-a life history tradeoff between longevity and fecundity. Other tradeoffs among components of parasite fitness also influence virulence. For example, competition among parasite genotypes favors rapid growth to achieve greater relative success within the host. Rapid growth may, however, lower the total productivity of the local group by overexploiting the host, which is a potentially renewable food supply. This is a problem of kin selection and group selection. I summarize models of parasite virulence with the theoretical tools of life history analysis, kin selection, and epidemiology. I then apply the theory to recent empirical studies and models of virulence. These applications, to nematodes, to the extreme virulence of hospital epidemics, and to bacterial meningitis, show the power of simple life history theory to highlight interesting questions and to provide a rich array of hypotheses. These examples also show the kinds of conceptual mistakes that commonly arise when only a few components of parasite fitness are analysed in isolation. The last part of the article connects standard models of parasite virulence to diverse topics, such as the virulence of bacterial plasmids, the evolution of genomes, and the processes that influenced conflict and cooperation among the earliest replicators near the origin of life.

Animals↗

Parasitism, the diversity of life, and paleoparasitology.

The parasite-host-environment system is dynamic, with several points of equilibrium. This makes it difficult to trace the thresholds between benefit and damage, and therefore, the definitions of commensalism, mutualism, and symbiosis become worthless. Therefore, the same concept of parasitism may encompass commensalism, mutualism, and symbiosis. Parasitism is essential for life. Life emerged as a consequence of parasitism at the molecular level, and intracellular parasitism created evolutive events that allowed species to diversify. An ecological and evolutive approach to the study of parasitism is presented here. Studies of the origin and evolution of parasitism have new perspectives with the development of molecular paleoparasitology, by which ancient parasite and host genomes can be recovered from disappeared populations. Molecular paleoparasitology points to host-parasite co-evolutive mechanisms of evolution traceable through genome retrospective studies.

Animals↗