Rapid delineation of closely-related filarial parasites using genetic markers in spacer rDNA

The ebb and flow of cardiac lymphatics: a tidal wave of new discoveries

The heart is imbued with a vast lymphatic network that is responsible for fluid homeostasis and immune cell trafficking. Disturbances in the forces that regulate microvascular fluid movement can result in myocardial edema, which has profibrotic and proinflammatory consequences and contributes to cardiovascular dysfunction. This review explores the complex relationship between cardiac lymphatics, myocardial edema, and cardiac disease. It covers the revised paradigm of microvascular forces and fluid movement around the capillary as well as the arsenal of preclinical tools and animal models used to model myocardial edema and cardiac disease. Clinical studies of myocardial edema and their prognostic significance are examined in parallel to the recent elegant animal studies discerning the pathophysiological role and therapeutic potential of cardiac lymphatics in different cardiovascular disease models. This review highlights the outstanding questions of interest to both basic scientists and clinicians regarding the roles of cardiac lymphatics in health and disease.

Human gnathostomiasis: a neglected food-borne zoonosis

BACKGROUND

Human gnathostomiasis is a food-borne zoonosis. Its etiological agents are the third-stage larvae of Gnathostoma spp. Human gnathostomiasis is often reported in developing countries, but it is also an emerging disease in developed countries in non-endemic areas. The recent surge in cases of human gnathostomiasis is mainly due to the increasing consumption of raw freshwater fish, amphibians, and reptiles.

METHODS

This article reviews the literature on Gnathostoma spp. and the disease that these parasites cause in humans. We review the literature on the life cycle and pathogenesis of these parasites, the clinical features, epidemiology, diagnosis, treatment, control, and new molecular findings on human gnathostomiasis, and social-ecological factors related to the transmission of this disease.

CONCLUSIONS

The information presented provides an impetus for studying the parasite biology and host immunity. It is urgently needed to develop a quick and sensitive diagnosis and to develop an effective regimen for the management and control of human gnathostomiasis.

Dirofilaria Immitis in Bulgaria: The First Genetic Baseline Data and an Overview of the Current Status

Dirofilaria immitis, the agent of canine dirofilariosis, is a common parasite of domestic and wild carnivores with zoonotic potential and worldwide distribution, being endemic in many countries. Bulgaria is among European countries recognized as endemic for this heartworm parasite. In the present study, D. immitis adults recovered from pulmonary arteries of domestic dog and golden jackal originating from the Pazardzhik region in southern Bulgaria, and from red fox originating from the Plovdiv region in central-southern Bulgaria, were genetically analyzed in nuclear targets. The first PCR amplification of the internal transcribed region 2 (ITS2) of the ribosomal DNA with previously published D. immitis-specific primers yielded single fragments in size of 302 bp that is characteristic for these heartworms. PCR products of three isolates, resulted from the second amplification of the 5.8S-ITS2 region (235 bp) with pan-filarioid primers, were subjected to direct DNA sequencing. Identical nucleotide composition was detected across the screened target region for these Bulgarian isolates. When the 5.8S-ITS2 sequences were phylogenetically compared to the GenBank-retrieved D. immitis sequences in a worldwide context, the neighbor-joining analysis has shown three discrete clades. The first clade was composed of D. immitis isolates from Europe (including the studied Bulgarian samples), Asia and South America, in the second clade samples from Asia and South America were placed, whereas the third clade was formed by two Brazilian dog isolates originated from the north and southeast part of the country. The purpose of the present study was to verify the taxonomic characterization of D. immitis nematodes from Bulgaria based on morphology and compare their genetic structure with filariae obtained from the different world regions using molecular assays. It also summarizes previous epidemiological and ecological studies on the parasite distribution and prevalences in different hosts and regions undertaken so far in Bulgaria.

Diagnosing bovine parafilariosis: utility of the cytochrome c oxidase subunit 1 gene and internal transcribed spacer region for PCR detection of Parafilaria bovicola in skin biopsies and serohemorrhagic exudates of cattle

Background

Parafilaria bovicola (Nematoda: Filariidae) causes cutaneous bleedings in bovine species. Flies serve as intermediate hosts. In recent years, reports on bovine parafilariosis have become more frequent, corroborating the necessity of reliable diagnostic interventions especially since no molecular or serological test has been available. We aimed to establish a polymerase chain reaction assay to detect DNA of P. bovicola in flies, skin biopsies and serohemorraghic exudates of bleeding spots.

Methods

PCRs targeting the cytochrome c oxidase subunit 1 (cox1) gene and the internal transcribed spacer region (ITS) of the ribosomal RNA gene cluster were evaluated for their diagnostic sensitivity as well as performance and specificity on biopsy and serohemorrhagic exudate samples from P. bovicola-infected cattle.

Results

Using serohemorrhagic exudates (n = 6), biopsies (n = 2) and flies (n = 1), the PCR targeting the cox1 gene resulted in a gel band of almost 700 bp. Cloning, sequencing, and removal of primer sequences yielded a 649-bp fragment of the P. bovicola cox1 gene. The PCR targeting the ITS region showed a band of about 1100 bp. Cloning, sequencing, and removal of primer sequences resulted in a 1083 bp stretch of the P. bovicola ITS region. Testing samples from presumably affected animals, the cox1-PCR resulted in bands with the expected size and they were all confirmed as P. bovicola by sequencing. In contrast, the ITS-PCR proved to be less sensitive and less specific and additionally amplified the ITS region of Musca domestica or buttercup DNA. When analysing for sensitivity, the cox1-PCR yielded visible bands up to 2 ng of genomic DNA, whereas the ITS-PCR produced bands up to 3 ng. In a plasmid dilution series, the minimum number of target DNA copies was 10² for the cox1-PCR and 10¹ in the ITS-PCR.

Conclusions

The evaluated cox1-PCR enables reliable detection of P. bovicola DNA in skin biopsies and serohemorrhagic exudates. This PCR and, to a limited extent, the ITS-PCR, may help evaluate different therapeutic approaches. Furthermore, the cox1-PCR may be useful for epidemiological studies on the geographical distribution of P. bovicola. Further understanding of the epidemiology of this parasite will help develop and implement effective control strategies.

Differences in infection patterns of vector-borne blood-stage parasites of sympatric Malagasy primate species (Microcebus murinus, M. ravelobensis)

The dynamic relationship of vector-borne parasites, arthropod vectors and their hosts is prone to change under the influence of climate change, global integration, shifting demographics and deforestation. It is therefore essential to better understand parasitism in wildlife populations, including parasites transmitted by blood-feeding vectors, and explore host range and heterogeneity of parasitic infections. We investigated Giemsa stained blood smears of two sympatric Malagasy primate species (Microcebus murinus: 184 samples from 69 individuals and M. ravelobensis: 264 samples from 91 individuals) for blood-stage parasites and tested for a potential influence of host species, sex, body mass and sampling month on blood-stage parasite prevalence and infection intensity. No protozoan parasites were detected in either host species. A host-specific difference was observed in filarial nematode infections, with higher risk of infection in M. murinus (prevalence 30.43%), than in M. ravelobensis (prevalence 6.59%), which may be explained by differences in host behavior and/or immune competence, linked to the period of host-parasite coevolution. Neither sex nor sampling month influenced infection prevalence or intensity significantly. We did not observe a negative effect of microfilarial infections on host fitness when taking body mass as a proxy. Our results support the hypothesis of a long-term evolutionary adaptation of hosts and parasites, leading to persistent infection with low morbidity. Morphological and molecular analyses indicate the finding of a new species, “Lemurfilaria lemuris”. Genetic analysis furthermore showed >99% sequence identity with microfilariae described from a sympatric, larger-bodied lemur species of a different genus, suggesting low host-specificity of the detected filariae and pathogen transmission across genus boundaries. Findings contribute to a more comprehensive picture of vector-borne diseases of Malagasy lemurs.

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Small Malagasy primate species are hosts of the newly described Lemurfilaria lemuris.

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Risk of microfilarial infection and infection intensity differed between host species.

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This could be linked to differences in host socioecology and/or phylogeography.

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No influence of microfilarial infection on host body mass was observed.

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>99% sequence identity of filariae from lemur hosts of different genera.

Sleeping site ecology, but not sex, affect ecto- and hemoparasite risk, in sympatric, arboreal primates (Avahi occidentalis and Lepilemur edwardsi)

Background

A central question in evolutionary parasitology is to what extent ecology impacts patterns of parasitism in wild host populations. In this study, we aim to disentangle factors influencing the risk of parasite exposure by exploring the impact of sleeping site ecology on infection with ectoparasites and vector-borne hemoparasites in two sympatric primates endemic to Madagascar. Both species live in the same dry deciduous forest of northwestern Madagascar and cope with the same climatic constraints, they are arboreal, nocturnal, cat-sized and pair-living but differ prominently in sleeping site ecology. The Western woolly lemur (Avahi occidentalis) sleeps on open branches and frequently changes sleeping sites, whereas the Milne-Edward’s sportive lemur (Lepilemur edwardsi) uses tree holes, displaying strong sleeping site fidelity. Sleeping in tree holes should confer protection from mosquito-borne hemoparasites, but should enhance the risk for ectoparasite infestation with mites and nest-adapted ticks. Sex may affect parasite risk in both species comparably, with males bearing a higher risk than females due to an immunosuppressive effect of higher testosterone levels in males or to sex-specific behavior. To explore these hypotheses, ectoparasites and blood samples were collected from 22 individuals of A. occidentalis and 26 individuals of L. edwardsi during the dry and rainy season.

Results

L. edwardsi, but not A. occidentalis, harbored ectoparasites, namely ticks (Haemaphysalis lemuris [Ixodidae], Ornithodoros sp. [Argasidae]) and mites (Aetholaelaps trilyssa, [Laelapidae]), suggesting that sleeping in tree holes promotes infestation with ectoparasites. Interestingly, ectoparasites were found solely in the hot, rainy season with a prevalence of 75% (N = 16 animals). Blood smears were screened for the presence and infection intensity of hemoparasites. Microfilariae were detected in both species. Morphological characteristics suggested that each lemur species harbored two different filarial species. Prevalence of microfilarial infection was significantly lower in L. edwardsi than in A. occidentalis. No significant difference in infection intensity between the two host species, and no effect of season, daytime of sampling or sex on prevalence or infection intensity was found. In neither host species, parasite infection showed an influence on body weight as an indicator for body condition.

Conclusions

Our findings support that sleeping site ecology affects ectoparasite infestation in nocturnal, arboreal mammalian hosts in the tropics, whereas there is no significant effect of host sex. The influence of sleeping site ecology to vector-borne hemoparasite risk is less pronounced. The observed parasite infections did not affect body condition and thus may be of minor importance for shaping reproductive fitness. Findings provide first evidence for the specific relevance of sleeping site ecology on parasitism in arboreal and social mammals. Further, our results increase the sparse knowledge on ecological drivers of primate host-parasite interactions and transmission pathways in natural tropical environments.

Electronic supplementary material

The online version of this article (10.1186/s12983-017-0228-7) contains supplementary material, which is available to authorized users.

Molecular characterization of Dirofilaria spp. circulating in Portugal

Background

Dirofilariosis is a potentially zoonotic parasitic disease, mainly transmitted by mosquito vectors in many parts of the world. Data concerning the canine Dirofilaria species currently circulating in Portugal is scarce. Thereby, a large-scale study was conducted to determine the Dirofilaria spp. present in Portugal, based on a molecular approach, and also to optimize a reliable and highly sensitive species-specific polymerase chain reaction (PCR) assay that could be used for the simultaneous detection and differentiation of Dirofilaria immitis, Dirofilaria repens, and other concurrent filarial species in animal reservoirs.

Methods

Blood samples were collected from three districts of Portugal (Coimbra, Santarém and Setúbal) between 2011 and 2013. Samples were tested using rapid immunomigration tests (Witness® Dirofilaria), modified Knott’s technique and acid phosphatase histochemical staining. In addition, molecular analysis was performed by amplification of the internal transcribed spacer (ITS) region using two different PCR protocols, specific for molecular screening of canine filarial species.

Results

Of the 878 dogs sampled, 8.8% (n = 77) were positive for D. immitis circulating antigen and 13.1% (n = 115) positive for microfilariae by the modified Knott’s technique. Of the 134 samples tested by acid phosphatase histochemical staining, 100 (74.6%) were positive for D. immitis. Overall, 13.7% (n = 120) were positive by PCR for D. immitis by ITS2, of which 9.3% (67/720) were also positive by ITS1. ITS2 PCR was the most sensitive and specific method, capable of detecting mixed D. immitis and A. reconditum infections. Heterozygosity, in the form of double peaks, was detected by sequencing of both ITS regions. No D. repens was detected by any of the diagnostic methods.

Conclusions

The present study confirmed D. immitis as the dominant species of the genus Dirofilaria infecting Portuguese dogs, based on sequencing of ITS1 and ITS2 PCR fragments. Additionally, ITS2 PCR was the most adequate method for diagnosis and prevalence estimation.

The complete mitochondrial genome of the gullet worm Gongylonema pulchrum: gene content, arrangement, composition and phylogenetic implications

Background

Gongylonema pulchrum (Nematoda: Gongylonematidae), a thread-like spirurid gullet worm, infects a range of mammalian definitive hosts, including cattle, pigs, equines, goats, primates and humans, and can cause gongylonemiasis.

Methods

In the present study, the complete mitochondrial (mt) genome of G. pulchrum was obtained using Long-range PCR and subsequent primer walking. The phylogenetic position of G. pulchrum within the Spiruromorpha was established using Bayesian analyses of the protein-coding genes at the amino acid level.

Results

The length of this AT-rich (75.94%) mt genome is 13,798 bp. It contains 12 protein-coding genes, two ribosomal RNA genes, 22 transfer RNA genes and one non-coding region. The gene arrangement is the same as those of Thelazia callipaeda (Thelaziidae) and Setaria digitata (Onchocercidae), but distinct from that of Heliconema longissimum (Physalopteridae). Phylogenetic analyses, based on the concatenated amino acid sequence data for all 12 protein-coding genes using Bayesian inference (BI) method, showed that G. pulchrum (Gongylonematidae) was more closely related to Spirocerca lupi (Spiruroidea) than other members of the infraorder Spiruromorpha.

Conclusions

The present study represents the first mt genome sequence for the family Gongylonematidae, which provides the opportunity to develop novel genetic markers for studies of epidemiology, population genetics and systematics of this nematode of human and animal health significance.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-015-0697-5) contains supplementary material, which is available to authorized users.

Mitochondrial genome of the eyeworm, Thelazia callipaeda (Nematoda: Spirurida), as the first representative from the family Thelaziidae

Human thelaziosis is an underestimated parasitic disease caused by Thelazia species (Spirurida: Thelaziidae). The oriental eyeworm, Thelazia callipaeda, infects a range of mammalian definitive hosts, including canids, felids and humans. Although this zoonotic parasite is of socio-economic significance in Asian countries, its genetics, epidemiology and biology are poorly understood. Mitochondrial (mt) DNA is known to provide useful genetic markers to underpin fundamental investigations, but no mt genome had been characterized for any members of the family Thelaziidae. In the present study, we sequenced and characterized the mt genome of T. callipaeda. This AT-rich (74.6%) mt genome (13,668 bp) is circular and contains 12 protein-coding genes, 22 transfer RNA genes and two ribosomal RNA genes, but lacks an atp8 gene. All protein-coding genes are transcribed in the same direction; the gene order is the same as those of Dirofilaria immitis and Setaria digitata (Onchocercidae), but distinct from Dracunculus medinensis (Dracunculidae) and Heliconema longissimum (Physalopteridae). Phylogenetic analyses of the concatenated amino acid sequence data for all 12 protein-coding genes by Bayesian inference (BI) showed that T. callipaeda (Thelaziidae) is related to the family Onchocercidae. This is the first mt genome of any member of the family Thelaziidae and should represent a new source of genetic markers for studying the epidemiology, ecology, population genetics and systematics of this parasite of humans and other mammals.

Human thelaziosis is an underestimated parasitic disease caused by the eyeworm Thelazia callipaeda (Spirurida: Thelaziidae). Although this parasite is of significance in humans in many Asian countries, its genetics, epidemiology and biology are poorly understood. Mitochondrial (mt) DNA can provide useful genetic markers for fundamental investigations, but no mt genome had been characterized for any members of the family Thelaziidae. In this study, we sequenced and characterized the mt genome of T. callipaeda. This circular mt genome is 13,668 bp long and contains 12 protein-coding genes, 22 transfer RNA genes and two ribosomal RNA genes, but lacks an atp8 gene. Phylogenetic analyses of the concatenated amino acid sequence data for all 12 protein-coding genes by Bayesian inference showed that T. callipaeda is closely related to the family Onchocercidae, consistent with previous study. This is the first mt genome of any member of the family Thelaziidae, and represents a new source of genetic markers for studies of the epidemiology, ecology, population genetics and systematics of this parasite of human and animal health significance.

Molecular diagnosis of infections and resistance in veterinary and human parasites

Since 1977, >2000 research papers described attempts to detect, identify and/or quantify parasites, or disease organisms carried by ecto-parasites, using DNA-based tests and 148 reviews of the topic were published. Despite this, only a few DNA-based tests for parasitic diseases are routinely available, and most of these are optional tests used occasionally in disease diagnosis. Malaria, trypanosomiasis, toxoplasmosis, leishmaniasis and cryptosporidiosis diagnosis may be assisted by DNA-based testing in some countries, but there are very few cases where the detection of veterinary parasites is assisted by DNA-based tests. The diagnoses of some bacterial (e.g. lyme disease) and viral diseases (e.g. tick borne encephalitis) which are transmitted by ecto-parasites more commonly use DNA-based tests, and research developing tests for these species makes up almost 20% of the literature. Other important uses of DNA-based tests are for epidemiological and risk assessment, quality control for food and water, forensic diagnosis and in parasite biology research. Some DNA-based tests for water-borne parasites, including Cryptosporidium and Giardia, are used in routine checks of water treatment, but forensic and food-testing applications have not been adopted in routine practice. Biological research, including epidemiological research, makes the widest use of DNA-based diagnostics, delivering enhanced understanding of parasites and guidelines for managing parasitic diseases. Despite the limited uptake of DNA-based tests to date, there is little doubt that they offer great potential to not only detect, identify and quantify parasites, but also to provide further information important for the implementation of parasite control strategies. For example, variant sequences within species of parasites and other organisms can be differentiated by tests in a manner similar to genetic testing in medicine or livestock breeding. If an association between DNA sequence and phenotype has been demonstrated, then qualities such as drug resistance, strain divergence, virulence, and origin of isolates could be inferred by DNA-based tests. No such tests are in clinical or commercial use in parasitology and few tests are available for other organisms. Why have DNA-based tests not had a bigger impact in veterinary and human medicine? To explore this question, technological, biological, economic and sociological factors must be considered. Additionally, a realistic expectation of research progress is needed. DNA-based tests could enhance parasite management in many ways, but patience, persistence and dedication will be needed to achieve this goal.

Aedes vexans and Culex pipiens as the potential vectors of Dirofilaria immitis in Central Turkey

This study was carried out to investigate the potential vectors and relative mosquito infection rates of Dirofilaria immitis throughout two mosquito seasons (2008-2009) in Kayseri province where is located in Central Anatolian part of Turkey. For this aim, totally 1198 genomic DNA pools, extracted and grouped according to the species and collection site (1-17 specimens/pool) from 6153 mosquito specimens, were examined by PCR using species-specific primers for D. immitis. The captured mosquitoes from 46 focuses were survived under in vitro conditions for 7 days to allow the development of larval stages of D. immitis. DNA extraction was performed individually to both thorax-head and abdomens in order to determine infective and infected mosquito specimens, respectively. The most abundant mosquito species in the study area was determined as Ae. vexans (51.7%) and this was followed by Cx. pipiens (42.1%), Cx. theileri (3.1%), Cs. annulata (1.5%), An. maculipennis (1.0%) and Cx. hortensis (0.6%). The PCR results indicated that 9/312 and 12/312 pools from Ae. vexans abdomens and thorax-heads were positive for filarial DNAs, respectively where as 3/241 pools of each abdomens and thorax-heads from Cx. pipiens were positive for D. immitis DNAs. The minimum infection rates (MIRs) for Ae. vexans and Cx. pipiens were calculated as 0.41 and 0.12, respectively. Although D. immitis DNA's were found in both pools from Ae. vexans and Cx. pipiens, the calculated MIRs provide evidence that Ae. vexans could be the main potential vector of D. immitis in Kayseri.

Discrimination between six species of canine microfilariae by a single polymerase chain reaction

Canine dirofilariasis caused by Dirofilaria immitis is usually diagnosed by specific antigen testing and/or identification of microfilariae. However, D. immitis and at least six other filariae can produce canine microfilaremias with negative heartworm antigen tests. Discriminating these can be of clinical importance. To resolve discordant diagnoses by two diagnostic laboratories in an antigen-negative, microfilaremic dog recently imported into the US from Europe we developed a simple molecular method of identifying different microfilariae, and subsequently validated our method against six different filariae known to infect dogs by amplifying ribosomal DNA spacer sequences by polymerase chain reaction using common and species-specific primers, and sequencing the products to confirm the genotype of the filariae. We identified the filaria in this dog as D. repens. This is the first case of D. repens infection in the United States. Additionally, we examined microfilariae from five additional antigen-negative, microfilaremic dogs and successfully identified the infecting parasite in each case. Our diagnoses differed from the initial morphological diagnosis in three of these cases, demonstrating the inaccuracy of morphological diagnosis. In each case, microfilariae identified morphologically as A. reconditum were identified as D. immitis by molecular methods. Finally, we demonstrated that our PCR method should amplify DNA from at least two additional filariae (Onchocerca and Mansonella), suggesting that this method may be suitable for genotyping all members of the family Onchocercidae.

Characterisation of nuclear ribosomal DNA sequences from Onchocerca volvulus and Mansonella ozzardi (Nematoda: Filarioidea) and development of a PCR-based method for their detection in skin biopsies

The internal transcribed spacer region (ITS1, 5.8S gene and ITS2) of the two filarial nematodes Onchocerca volvulus and Mansonella ozzardi was sequenced, and two species-specific primers designed in the ITS2 to develop a PCR-based method for their specific detection and differentiation. When used with a universal reverse primer, the two species-specific primers gave amplification products of different size, which were readily separated in an agarose gel. The PCR was tested on skin biopsies from 51 people from three localities in Brazil where M. ozzardi is present, and results have been compared with those of parasitological examination of blood. The species-specific PCR gave a higher percentage of detection of infection by M. ozzardi than the parasitological examination of blood. No infection with O. volvulus was detected by PCR. This PCR-based assay may assist in determining the nature of infection in areas where both filarial species exist in sympatry.

PCR-based technology in veterinary parasitology

DNA technology is having a major impact in many areas of veterinary parasitology. In particular, the polymerase chain reaction (PCR) has found broad applicability because its sensitivity permits enzymatic amplification of gene fragments from minute quantities of nucleic acids derived from limited amounts of parasite material. This paper discusses some recent applications of PCR-based methods to parasites and highlights their usefulness or potential for those of veterinary importance. The focus is on PCR tools for the accurate identification of parasites and their genetic characterisation, the diagnosis of infections, the isolation and characterisation of expressed genes, the detection of anthelmintic resistance, and mutation scanning approaches for the high resolution analysis of PCR products.

What's in that band?

The analysis of molecular variation in parasites has important implications for studying gene function and organisation, taxonomy, phylogeny and population genetics. Polymerase chain reaction-based mutation scanning methods can have significant advantages over some currently used DNA approaches for the analysis of allelic and mutational sequence variation in parasites. The present report describes briefly the principles of some of these methods, examines some of their advantages and disadvantages, and indicates their potential for applications in parasitology.

Mutation scanning methods for the analysis of parasite genes

Molecular variation is widespread in parasite populations, and its analysis has important implications for studying aspects relating to the function and organisation of genes, and the taxonomy, phylogeny and population genetics of parasites. This article reviews some PCR-based mutation scanning techniques that have advantages over currently used DNA methods for the analysis of genetic variation in parasites. The review is technical and describes briefly the principles of relevant techniques, examines some of their advantages and disadvantages and gives several examples for possible applications.