Major Parasitic Groups Research Articles

A survey of ecto and endoparasites of Nile tilapia, Oreochromis niloticus (Linnaeus, 1758) fingerlings in Midmar reservoir, Adwa, northern Ethiopia

ABSTRACT Fishes are hosts to a range of taxonomically diverse parasites. This survey was intended to provide insight into the occurrence, distribution, prevalence, and intensity of parasites infesting the fingerlings of the tilapia, in Tigray. A total of 384 Oreochromis niloticus specimens were collected from Midmar consisting of 227 males and 157 females. External and internal organs were examined for parasite infection. Squash preparation of fish eyes was also examined to reveal the organisms through microscopic examination. The major groups of parasites were trematode, nematodes, protozoa and hirudinea. A total of 3762 genus Diplostomum were recorded affecting the health of 93% of fishes. Contracaecum species was the second most prevalent distributed majorly in the intestine (77.8%), pericardial cavity (19.1%), swim bladder (2.4%), gill (0.2%) and mouth (0.8%). The prevalence and mean intensity of Diplostomum spp., Contracaecum, Myxosporea, Clinostomum spp., Eustrongylides and Leeches was 93%(10.5), 62.2%(5.3), 39.3%(8.3), 2.1%(8.8),1.8%(5.7) and 1.6% (2.5), respectively. The mean temperature, dissolved oxygen, conductivity, and pH of the dam were 24.4°C, 7.55 mg/l, 849.5µs/cm, and 7.5, respectively. Therefore, responsible bodies in fisheries should perform a pre-stock assessment and provide fish farming extension services for optimum production and marketing of fish products with management and production enhancement methods.

Nanoparticles: Synthesis and Their Role as Potential Drug Candidates for the Treatment of Parasitic Diseases.

Protozoa, helminths and ectoparasites are the major groups of parasites distributed worldwide. Currently, these parasites are treated with chemotherapeutic antiprotozoal drugs, anti-helminthic and anti-ectoparasitic agents, but, with the passage of time, resistance to these drugs has developed due to overuse. In this scenario, nanoparticles are proving to be a major breakthrough in the treatment and control of parasitic diseases. In the last decade, there has been enormous development in the field of nanomedicine for parasitic control. Gold and silver nanoparticles have shown promising results in the treatments of various types of parasitic infections. These nanoparticles are synthesized through the use of various conventional and molecular technologies and have shown great efficacy. They work in different ways, that include damaging the parasite membrane, DNA (Deoxyribonucleic acid) disruption, protein synthesis inhibition and free-radical formation. These agents are effective against intracellular parasites as well. Other nanoparticles, such as iron, nickel, zinc and platinum, have also shown good results in the treatment and control of parasitic infections. It is hoped that this research subject will become the future of modern drug development. This review summarizes the methods that are used to synthesize nanoparticles and their possible mechanisms of action against parasites.

Metabarcoding options to study eukaryotic endoparasites of birds.

There is growing interest in the study of avian endoparasite communities, and metabarcoding is a promising approach to complement more conventional or targeted methods. In the case of eukaryotic endoparasites, phylogenetic diversity is extreme, with parasites from 4 kingdoms and 11 phyla documented in birds. We addressed this challenge by comparing different primer sets across 16 samples from 5 bird species. Samples consisted of blood, feces, and controlled mixes with known proportions of bird and nematode DNA. Illumina sequencing revealed that a 28S primer set used in combination with a custom blocking primer allowed detection of various plasmodiid parasites and filarioid nematodes in the blood, coccidia in the feces, as well as two potentially pathogenic fungal groups. When tested on the controlled DNA mixes, these primers also increased the proportion of nematode DNA by over an order of magnitude. An 18S primer set, originally designed to exclude metazoan sequences, was the most effective at reducing the relative number of avian DNA sequences and was the only one to detect Trypanosoma in the blood. Expectedly, however, it did not allow nematode detection and also failed to detect avian malaria parasites. This study shows that a 28S set including a blocking primer allows detection of several major and very diverse bird parasite clades, while reliable amplification of all major parasite groups may require a combination of markers. It helps clarify options for bird parasite metabarcoding, according to priorities in terms of the endoparasite clades and the ecological questions researchers wish to focus on.

Zoonotic Transmission and Infection from Bovine Feces in Selected Ricefields of Lake Mainit, Philippines

Ricefields are suitable nidus of active parasite transmission via bovines due to often unprotected exposure by humans and livestock that utilize the habitat for farming and foraging. This study was conducted to assess infection of protozoans, trematodes and nematodes from bovine feces from ricefields of Brgy Magpayang, San Isidro and Matin-ao surrounding Lake Mainit, Philippines. Bovine fecal samples collected from these ricefields were processed using the Formalin Ethyl Acetate Sedimentation (FEA-SD) technique. A total of five species from three major parasite groups (protozoans, trematodes and nematodes) were observed. Bovines from ricefields of Brgy San Isidro harbored the highest number of fecal parasites. The liver fluke Fasciola sp. was the most predominant species observed with the highest prevalence (69%) across study areas. In contrast, multiple parasite burden of Fasciola sp., hookworms, coccidian oocysts and Ascaris sp. eggs were observed from bovines from Brgy San Isidro and Matin-ao. This study is the first report of parasites from bovine feces in selected ricefields of Lake Mainit. The high prevalence of Fasciola eggs in bovines calls for an extensive assessment of possible widespread bovine fascioliasis in the area.

Drivers of parasite community structure in fishes of the continental shelf of the Western Mediterranean: the importance of host phylogeny and autecological traits

We explored the relationships between features of host species and their environment, and the diversity, composition and structure of parasite faunas and communities using a large taxonomically consistent dataset of host-parasite associations and host-prey associations, and original environmental and host trait data (diet, trophic level, population density and habitat depth vagility) for the most abundant demersal fish species off the Catalonian coast of the Western Mediterranean. Altogether 98 species/taxa belonging to seven major parasite groups were recovered in 683 fish belonging to 10 species from seven families and four orders. Our analyses revealed that (i) the parasite fauna of the region is rich and dominated by digeneans; (ii) the host parasite faunas and communities exhibited wide variations in richness, abundance and similarity due to a strong phylogenetic component; (iii) the levels of host sharing were low and involved host generalists and larval parasites; (iv) the multivariate similarity pattern of prey samples showed significant associations with hosts and host trophic guilds; (v) prey compositional similarity was not associated with the similarity of trophically transmitted parasite assemblages; and (vi) phylogeny and fish autecological traits were the best predictors of parasite community metrics in the host-parasite system studied.

Survival Strategies of Leishmania in Hosts

In all major parasite groups, new and surprising evidence is emerging every day about the subtlety, complexity and diversity of avoidance mechanisms from host immune system. In the course of millions of years of evolutionary process, mammalian and sand fly hosts have developed defense systems against Leishmania, but Leishmania has not only escaped from their hosts’ defense systems through complex counter-strategies, but has also managed to manipulate them to support their own survival and reproduction. In this study, Leishmania’s survival strategies used in the sand fly and mammalian hosts and the mechanisms that underlie these strategies will be summarized.

Coccidian parasites of fish encompass profound phylogenetic diversity and gave rise to each of the major parasitic groups in terrestrial vertebrates

Fish are the oldest and most diverse group of vertebrates; it therefore stands to reason that fish may have been the original hosts for many types of extant vertebrate parasites. Here, we sought to determine whether coccidian parasites of fish are especially diverse. We therefore sampled such parasites from thirty-nine species of fish and tested phylogenetic hypotheses concerning their relationships, using 18S rDNA. We found compelling phylogenetic support for distinctions among at least four lineages of piscine parasites presently ascribed to the genus Goussia. Some, but not all parasites attributed to Eimeria were confirmed as such. Major taxonomic revisions are likely justified for these parasites of fish, which appear to have given rise to each of the major lineages of coccidian parasites that subsequently proliferated in terrestrial vertebrates, including those such as Toxoplasma gondii that form tissue cysts in intermediate hosts.

Gastrointestinal parasites and their prevalence in the Arabian red fox (Vulpes vulpes arabica) from the Kingdom of Saudi Arabia

The gastrointestinal parasites and prevalence of infestation in the Arabian red fox Vulpes vulpes arabica Thomas, were investigated at the King Khalid Wildlife Research Centre (KKWRC) in Thumamah, Riyadh Province, Saudi Arabia. Faecal samples were collected from 58 wild caught foxes while under anaesthesia and examined for gastrointestinal parasites stages. Male and female foxes were infected with three major groups of parasites; cestodes, nematodes, protozoa as well as an acanthocephalan. Faecal analyses revealed that 22 foxes (37.9%) were infected with two different Isospora spp. and three (5.2%) with an undescribed Eimeria sp., 12 (20.7%). Nine individuals (15.5%) harboured hookworms, (Trichosomoides sp.), two (3.5%) were infected with Trichuris sp. (probably Trichuris vulpes) and one individual (1.7%) with Taenia sp. (probably Taenia hydatigena). Carcasses of five male and three female foxes were necropsied. Four of the necropsied carcasses yielded Ancylostoma caninum, two each harboured Pterygodermatitis affinis, T. vulpes and Macracanthorhynchus catalinus, in six foxes Joyeuxiella echinorynchoides was found. Five and four foxes were infected with T. hydatigena and Diplopylidium nölleri, respectively. The possible role of the Arabian red fox as an intercalary host essential for the life cycle of Trichosomoides sp., common to the Libyan jird, Meriones libycus, in particular and the importance of this species as a vector for zoonotic infections and in the spread of other parasites to wild and domestic animals in general is discussed.

Do threatened hosts have fewer parasites? A comparative study in primates

1. Parasites and infectious diseases have become a major concern in conservation biology, in part because they can trigger or accelerate species or population declines. Focusing on primates as a well-studied host clade, we tested whether the species richness and prevalence of parasites differed between threatened and non-threatened host species. 2. We collated data on 386 species of parasites (including viruses, bacteria, protozoa, helminths and arthropods) reported to infect wild populations of 36 threatened and 81 non-threatened primate species. Analyses controlled for uneven sampling effort and host phylogeny. 3. Results showed that total parasite species richness was lower among threatened primates, supporting the prediction that small, isolated host populations harbour fewer parasite species. This trend was consistent across three major parasite groups found in primates (helminths, protozoa and viruses). Counter to our predictions, patterns of parasite species richness were independent of parasite transmission mode and the degree of host specificity. 4. We also examined the prevalence of selected parasite genera among primate sister-taxa that differed in their ranked threat categories, but found no significant differences in prevalence between threatened and non-threatened hosts. 5. This study is the first to demonstrate differences in parasite richness relative to host threat status. Results indicate that human activities and host characteristics that increase the extinction risk of wild animal species may lead simultaneously to the loss of parasites. Lower average parasite richness in threatened host taxa also points to the need for a better understanding of the cascading effects of host biodiversity loss for affiliated parasite species.

Regulatory Cells and Immunosuppressive Cytokines: Parasite-Derived Factors Induce Immune Polarization

Parasitic infections are prevalent in both tropical and subtropical areas. Most of the affected and/or exposed populations are living in developing countries where control measures are lacking or inadequately applied. Although significant progress has been made in our understanding of the immune response to parasites, no definitive step has yet been successfully done in terms of operational vaccines against parasitic diseases. Evidence accumulated during the past few years suggests that the pathology observed during parasitic infections is in part due to deregulation of normal components of the immune system, mainly cytokines, antibodies, and immune effector cell populations. A large number of studies that illustrate how parasites can modify the host immune system for their own benefit have been reported in both metazoan and protozoan parasites. The first line of defense against foreign organisms is barrier tissue such as skin, humoral factors, for instance the complement system and pentraxin, which upon activation of the complement cascade facilitate pathogen recognition by cells of innate immunity such as macrophages and DC. However, all the major groups of parasites studied have been shown to contain and/or to release factors, which interfere with both arms of the host immune system. Even some astonishing observations relate to the production by some parasites of orthologues of mammalian cytokines. Furthermore, chronic parasitic infections have led to the immunosuppressive environment that correlates with increased levels of myeloid and T suppressor cells that may limit the success of immunotherapeutic strategies based on vaccination. This minireview briefly analyzes some of the current data related to the regulatory cells and molecules derived from parasites that affect cellular function and contribute to the polarization of the immune response of the host. Special attention is given to some of the data from our laboratory illustrating the role of immunomodulatory factors released by protozoan parasites, in the induction and perpetuation of chronic disease.

Latitudinal gradients of parasite species richness in primates

ABSTRACTInfectious disease risk is thought to increase in the tropics, but little is known about latitudinal gradients of parasite diversity. We used a comparative data set encompassing 330 parasite species reported from 119 primate hosts to examine latitudinal gradients in the diversity of micro and macroparasites per primate host species. Analyses conducted with and without controlling for host phylogeny showed that parasite species richness increased closer to the equator for protozoan parasites, but not for viruses or helminths. Relative to other major parasite groups, protozoa reported from wild primates were transmitted disproportionately by arthropod vectors. Within the protozoa, our results revealed that vector‐borne parasites showed a highly significant latitudinal gradient in species richness. This higher diversity of vector‐borne protozoa near the tropics could be influenced by a greater abundance or diversity of biting arthropods in the tropics, or by climatic effects on vector behaviour and parasite development. Many vector‐borne diseases, such as leishmaniasis, trypanosomiasis, and malaria pose risks to both humans and wildlife, and nearly one‐third of the protozoan parasites from free‐living primates in our data set have been reported to infect humans. Because the geographical distribution and prevalence of many vector‐borne parasites are expected to increase because of global warming, these results are important for predicting future parasite‐mediated threats to biodiversity and human health.

Relative infection levels and taxonomic distances among the host species used by a parasite: insights into parasite specialization

Parasites often exploit more than one host species at any stage in their life-cycle, but the extent to which these host species are used varies greatly. Parasites typically achieve their highest prevalence, intensity and/or abundance in one host species (the principal host), whereas infection levels in auxiliary hosts range from relatively high to very low. The present study examines what influences the distribution of parasite individuals among their different host species, using metazoan parasites that use freshwater fish as their definitive or only host. Specifically, I test the hypothesis that differences in relative infection levels by a parasite among its auxiliary hosts are proportional to the taxonomic distance between the respective auxiliary hosts and the parasite's principal host. Taxonomic distance among hosts is a surrogate measure of their similarity in terms of ecology, physiology and immunology. Using data on 29 parasite species and 6 fish communities, for a total of 47 parasite-locality combinations, it was found that taxonomic distance between the auxiliary hosts and the principal host had no real influence on infection levels in auxiliary hosts, measured as either prevalence, intensity or abundance. The analysis revealed differences in the degree of specialization among major groups of parasites: in terms of abundance or intensity, auxiliary hosts were less important for cestodes than for nematodes and copepods. The lack of an effect of taxonomic distance may indicate that ecological similarity among host species, arising from convergence and not from relatedness, is more important than host phylogeny or taxonomy. Although the results are based on a limited number of parasite taxa, they suggest that parasites may be opportunistic in their colonization of new hosts, and not severely constrained by evolutionary baggage.

Comparative morphology of the body wall in flatworms (Platyhelminthes)

The soft-bodied nature of the platyhelminths is due largely to the structure of the body wall and its lack of sclerotic elements such as cuticle. Free-living members, i.e., most turbellarians, show considerable variety, but the basic form of the body wall comprises a simple ciliated epithelium overlying a network of muscles. We illustrate this body wall structure in a representative typhloplanoid rhabditophoran and discuss variations in representatives of the Acoela, Catenulida, and other free-living rhabditophorans. The major parasitic groups of platyhelminths, the rhabditophoran Neodermata, follow a developmental pattern that replaces a similar ciliated epidermis in a larval stage with a specialized epidermis called a neodermis, which is assumed to be key to their success as parasites. This neodermis consists of a syncytium that covers the body in a continuous sheet connected to perikarya that lie below the body wall musculature. The neodermis can be seen as a special adaptation of a developmental mechanism common to all platyhelminths, in which epidermal growth and renewal are accomplished by replacement cells originating beneath the body wall. The cell type responsible for all cell renewal, including body wall renewal, in platyhelminths is the neoblast, and its presence may be the one autapomorphic character that unites all taxonomic groups of platyhelminths.

The unique voice of parasitologists

edited by Albert O. Bush, Jacqueline C. Fernández, Gerald W. Esch and J. Richard Seed, Cambridge University Press, 2001.

A molecular evolutionary framework for the phylum Nematoda.

Nematodes are important: parasitic nematodes threaten the health of plants, animals and humans on a global scale; interstitial nematodes pervade sediment and soil ecosystems in overwhelming numbers; and Caenorhabditis elegans is a favourite experimental model system. A lack of clearly homologous characters and the absence of an informative fossil record have prevented us from deriving a consistent evolutionary framework for the phylum. Here we present a phylogenetic analysis, using 53 small subunit ribosomal DNA sequences from a wide range of nematodes. With this analysis, we can compare animal-parasitic, plant-parasitic and free-living taxa using a common measurement. Our results indicate that convergent morphological evolution may be extensive and that present higher-level classification of the Nematoda will need revision. We identify five major clades within the phylum, all of which include parasitic species. We suggest that animal parasitism arose independently at least four times, and plant parasitism three times. We clarify the relationship of C. elegans to major parasitic groups; this will allow more effective exploitation of our genetic and biological knowledge of this model species.

Ultrastructure of Epidermis and Sperm of the Turbellarian Syndisyrinx-Punicea (Hickman, 1956) (Rhabdocoela, Umagillidae)

Syndisyrinx punicea has an epidermis with intraepidermal nuclei, a thick basal lamina, and microvilli containing an array of densely packed filaments and, in the widened tips, an electron-dense cap. The epidermal cilia posess a widened cytoplasmic portion close to the base and vertical and horizontal cross-striated rootlets; the latter are anchored in the adjacent matrix by means of transverse bars. Basal bodies have a distinct spike opposite the horizontal rootlet. In the tips of epidermal cilia, one of the microtubules disappears first in doublets 7-9 and 1, and gradually all peripheral doublets disappear; there is no electron-dense rod along the central microtubules, but cilia have a terminal electron-dense cap. Spermatozoa have two flagella, much shorter than the sperm (and not incorporated in it); axonemes are of the 9+'1' type; an elongate nucleus, numerous small mitochondria and electron-dense bodies are surrounded by a single peripheral row of microtubules in the thicker parts of the sperm, in the thinner parts (apparently close to the ends) microtubules are also found in the interior; some electron- dense bodies were also seen free between sperm, indicating their secretory function. Ultrastructural evidence does not support the view that Umagillidae (as well as Temnocephalida) are particularly closely related to the Neodermata, the major parasitic groups of Platyhelminthes.

Endoparasites of birds of paradise in Papua New Guinea

General endoparasitiasis in 16 species of captive birds of paradise (BOP) in Papua New Guinea ranged from 60.0 to 79.6% during 1977, 1978, 1981, 1983 and 1984. Percent prevalence of the three major groups of parasites during thefive survey years was as follows: haematozoa, 36.7–53.0%; coccidia, 42.2–63.3% and helminths, 35.6–67.3%. Percent prevalence of blood parasites in the years 1977 and 1984 was: Haemoproteus 14.3, 20.0; Plasmodium 10.2, 4.5; Haemoproteus or Plasmodium 18.4, 8.9; Leucocytozoon 6.1, 6.7; Trypanosoma 8.2, 6.7; microfilaria 10.2, 4.5. Oocysts of Eimeria paradisaeai, Isospora raggianai and I. volki were common, as were oocysts morphologically distinct from these three species. The most frequently observed cestode eggs belonged to Raillietina and Biuterina species. Eggs of Strongyloides, Capillaria, Syngamus and Trichuris species of nematodes were also recovered. The Magnifident Bird of Paradise ( Diphyllodes magnificus) had the highest mean eggs per gram (EPG) during the five survey years, except in 1978 when the highest mean was recorded from the Lesser Bird of Paradise ( Paradisaea minor). Highest mean oocysts per gram (OPG) for the first 3 years were also recorded from D. magnificus, but Paradisaea raggiana had the highest mean OPG in 1983 and 1984. Possible causes for the greatest prevalence of endoparasites in the birds during 1977 and 1984, despite their having been regularly treated prophylactically, are considered.

Discussion of Dr. Paul C. Beaver's Paper

Dr. Beaver is to be congratulated for calling attention to the frequency and importance of visceral larva migrans, for demonstrating the most important etiological agent and the consequent epidemiology of the disease, and for subsequent work in his laboratory which has made it possible, for the first time, correctly to identify larval nematodes found in tissues. When parasites invade so-called “foreign” hosts to which they are not fully adapted, they frequently lose their way; the guide posts, whatever they may be, that enable a parasite to migrate to its proper destination in a “normal” host are absent, causing the parasites to become stranded along the way, or to end up in abnormal situations. Such misplaced parasites frequently cause more disturbance and embarrassment than they do in their normal hosts. There are examples of this phenomenon in all the major groups of parasites.