Interaction of helminth parasites with the haemostatic system of their vertebrate hosts: a scoping review.

Helminth parasitoses are among the most prevalent health issues worldwide. Their control depends largely on unravelling host-parasite interactions, including parasitic exploitation of the host haemostatic system. The present study undertakes a scoping review of the research carried out in this field with the aim of unifying and updating concepts. Multiple keywords combined with Boolean operators were employed to design the literature search strategy. Two online databases were used to identify original peer-reviewed articles written in English and published before 1st January 2020 describing molecular interactions between helminth parasites and the host haemostatic system. Relevant data from the selected sources of evidence were extracted and analysed. Ninety-six publications reporting 259 interactions were selected. Fifty-three proteins belonging to 32 species of helminth parasites were involved in interactions with components of the host haemostatic system. Many of these proteins from both parasite and host were conserved among the different interactions identified. Most of these interactions were related to the inhibition of the coagulation system and the activation of fibrinolysis. This was associated mainly with a potential of parasites to reduce the formation of blood clots in the host and attributed to biological processes, such as parasite nutrition, survival, invasion, evasion and migration or the appearance of pathological mechanisms in the host. A wide range of helminth parasites have developed similar strategies to exploit the haemostatic system of their hosts, which could be regarded as an evolutionary conserved mechanism that could confer benefits to parasites in terms of survival and establishment in their vertebrate hosts.

Title: Interaction des helminthes parasites avec le système hémostatique de leurs hôtes vertébrés : un examen exploratoire. Abstract: Les parasitoses par les helminthes sont à l'origine de problèmes de santé parmi les plus répandus dans le monde. Leur contrôle dépend en grande partie du démêlage des interactions hôte-parasite, y compris l'exploitation par les parasites du système hémostatique de l'hôte. La présente étude entreprend un examen exploratoire des recherches menées dans ce domaine dans le but d'unifier et d'actualiser les concepts. Plusieurs mots-clés combinés à des opérateurs booléens ont été utilisés pour concevoir la stratégie de recherche documentaire. Deux bases de données en ligne ont été utilisées pour identifier des articles originaux évalués par des pairs rédigés en anglais et publiés avant le 1er janvier 2020, décrivant les interactions moléculaires entre les helminthes parasites et le système hémostatique de l'hôte. Les données pertinentes des sources sélectionnées ont été extraites et analysées. Quatre-vingt-seize publications rapportant 259 interactions ont été sélectionnées. Cinquante-trois protéines appartenant à 32 espèces d'helminthes parasites ont été impliquées dans des interactions avec des composants du système hémostatique de l'hôte. Beaucoup de ces protéines du parasite et de l'hôte ont été conservées parmi les différentes interactions identifiées. La plupart de ces interactions étaient liées à l'inhibition du système de coagulation et à l'activation de la fibrinolyse. Ceci était principalement associé à un potentiel des parasites à réduire la formation de caillots sanguins chez l'hôte et attribué à des processus biologiques, tels que la nutrition, la survie, l'invasion, l'évasion et la migration des parasites ou l'apparition de mécanismes pathologiques chez l'hôte. Un large éventail d'helminthes parasites ont développé des stratégies similaires pour exploiter le système hémostatique de leurs hôtes, ce qui pourrait être considéré comme un mécanisme évolutif conservé qui pourrait conférer des avantages aux parasites en termes de survie et d'établissement chez leurs hôtes vertébrés.

Human dirofilariosis in the 21st century: A scoping review of clinical cases reported in the literature.

Human dirofilariosis is a clinical entity caused by infection with nematode species of the genus Dirofilaria. The traditional picture depicts the disease as a sporadic event associated with the presence of a single immature worm causing a nodular lesion. With the aim to reassess this paradigm, establishing a more accurate picture of the disease and homogenize criteria, a scoping review was conducted by searching, screening and analysing published clinical cases of human dirofilariosis worldwide during the 21st century. After extracting data from 305 publications containing 576 case reports, results showed that human dirofilariosis is currently caused by five Dirofilaria species (mainly D. repens). Maturation was not uncommon, since 42.95% of the parasites recovered were described as mature worms, most of them females, 26.42% of which contained micofilariae in the uterus. Moreover, six microfilaremic cases have been described. The predominant clinical manifestation was the presence of a worm encapsulated within a nodule, but there is a considerable variety of accompanying symptoms depending on anatomical location and type of dirofilariosis. Parasites/nodules were found in 71 different anatomical locations, being the traditional nomenclature of human dirofilariosis unable to properly cover this complex situation. Delay in seeking medical assistance (patient perception) and the frequency of wrong clinical suspicions (doctor knowledge), strongly influenced clinical management. The initial suspicion in cases of subcutaneous and pulmonary dirofilariosis is predominantly a tumour, while in the ocular dirofilariosis a parasite (but not directly Dirofilaria) is mostly suspected. Surgery is usually applied, regardless of the use of non-invasive techniques during preoperative management and although its use is still limited, molecular approach is the most accurate technique to establish a species-level diagnosis. Accurate epidemiological, parasitological and clinical information while handling and reporting human clinical cases is a need for physicians and researchers to improve and standardize the clinical management of human dirofilariosis.

Host-Parasite Relationships in Porcine Ascariosis: Anticoagulant Potential of the Third Larval Stage of Ascaris suum as a Possible Survival Mechanism.

In order to evade the response of their hosts, helminth parasites have evolved precise and highly regulated mechanisms, including migration strategies of the larval stages. In regard to porcine ascariosis caused by Ascaris suum, its infective third-stage larvae (AsL3) undergo a complex migratory route through the bloodstream of their host before establishing in the small intestine to reach maturation. Despite the benefits attributed to this migration, blood clots formation could compromise larvae survival. The aim of this work was to study the interaction between the cuticle and excretory/secretory antigens of AsL3 and the host coagulation cascade. Larvae were obtained after incubating and hatching A. suum eggs, after which the antigenic extracts were produced. Their ability to disrupt the coagulation cascade was studied using anticoagulation and chromogenic assays, and techniques based on electrophoresis. The obtained results showed that both antigenic extracts possessed anticoagulant potential, being able to inhibit the intrinsic, extrinsic and/or common pathways of the blood coagulation cascade as well as the activated factor X. Moreover, three A. suum serpin proteins were identified as candidates to inhibit this host coagulation factor. To the best of our knowledge, this study shows, for the first time, the anticoagulant potential of the infective larvae of A. suum, which could be used by the parasite as a mechanism to facilitate its invasion and survival in the host.

Pro-fibrinolytic potential of the third larval stage of Ascaris suum as a possible mechanism facilitating its migration through the host tissues.

BACKGROUND: Ascaris roundworms are the parasitic nematodes responsible for causing human and porcine ascariasis. Whereas A. lumbricoides is the most common soil-transmitted helminth infecting humans in the world, A. suum causes important economic losses in the porcine industry. The latter has been proposed as a model for the study of A. lumbricoides since both species are closely related. The third larval stage of these parasites carries out an intriguing and complex hepatopulmonary route through the bloodstream of its hosts. This allows the interaction between larvae and the physiological mechanisms of the hosts circulatory system, such as the fibrinolytic system. Parasite migration has been widely linked to the activation of this system by pathogens that are able to bind plasminogen and enhance plasmin generation. Therefore, the aim of this study was to examine the interaction between the infective third larval stage of A. suum and the host fibrinolytic system as a model of the host-Ascaris spp. relationships. METHODS: Infective larvae were obtained after incubating and hatching fertile eggs of A. suum in order to extract their cuticle and excretory/secretory antigens. The ability of both extracts to bind and activate plasminogen, as well as promote plasmin generation were assayed by ELISA and western blot. The location of plasminogen binding on the larval surface was revealed by immunofluorescence. The plasminogen-binding proteins from both antigenic extracts were revealed by two-dimensional electrophoresis and plasminogen-ligand blotting, and identified by mass spectrometry. RESULTS: Cuticle and excretory/secretory antigens from infective larvae of A. suum were able to bind plasminogen and promote plasmin generation in the presence of plasminogen activators. Plasminogen binding was located on the larval surface. Twelve plasminogen-binding proteins were identified in both antigenic extracts. CONCLUSIONS: To the best of our knowledge, the present results showed for the first time, the pro-fibrinolytic potential of infective larvae of Ascaris spp., which suggests a novel parasite survival mechanism by facilitating the migration through host tissues.

Dirofilaria immitis possesses molecules with anticoagulant properties in its excretory/secretory antigens.

Dirofilaria immitis is a parasitic nematode that survives in the circulatory system of suitable hosts for many years, causing the most severe thromboembolisms when simultaneous death of adult worms occurs. The two main mechanisms responsible for thrombus formation in mammals are the activation and aggregation of platelets and the generation of fibrin through the coagulation cascade. The aim of this work was to study the anticoagulant potential of excretory/secretory antigens from D. immitis adult worms (DiES) on the coagulation cascade of the host. Anticoagulant and inhibition assays respectively showed that DiES partially alter the coagulation cascade of the host and reduce the activity of the coagulation factor Xa, a key enzyme in the coagulation process. In addition, a D. immitis protein was identified by its similarity to the homologous serpin 6 from Brugia malayi as a possible candidate to form an inhibitory complex with FXa by sodium dodecyl sulfate polyacrylamide gel electrophoresis and mass spectrometry. These results indicate that D. immitis could use the anticoagulant properties of its excretory/secretory antigens to control the formation of blood clots in its immediate intravascular habitat as a survival mechanism.

Interaction between Wolbachia and the fibrinolytic system as a possible pathological mechanism in cardiopulmonary dirofilariosis.

Dirofilaria immitis is a mosquito-borne parasite that produces an inflammatory process in the wall of the blood vessels of its definitive host during cardiopulmonary dirofilariosis, known as proliferative endarteritis. Parasite antigens participate in the appearance of this inflammatory event, among other mechanisms through the over-activation of the host fibrinolytic system. Since Wolbachia, endosymbiont bacteria of filarial nematodes, is released into the vertebrate host when worms die, the aim of this work was to analyse the interaction between this bacteria and the host fibrinolytic system to complete the study of this part of the host-parasite relationships. For that purpose, the recombinant form of the major Wolbachia surface protein (rWSP) was cloned, sequenced and expressed and then, its ability to bind plasminogen and enhance the generation of plasmin was assessed. We demonstrated that rWSP is a conserved antigen within the family Onchocercidae with ability to bind plasminogen and stimulate plasmin generation in a tissue-plasminogen activator (t-PA) and lysine residues of the rWSP-dependent manner. These results indicate that the recruitment of plasminogen by Wolbachia and the possible excess of plasmin generated could contribute to exacerbate the pathological events occurred at the vascular level during cardiopulmonary dirofilariosis, as well as in other diseases caused by filarial nematodes that harbour Wolbachia, when the bacteria is released after the death of the worms.

The Complexity of Zoonotic Filariasis Episystem and Its Consequences: A Multidisciplinary View.

Vector-borne transmitted helminthic zoonosis affects the health and economy of both developing and developed countries. The concept of episystem includes the set of biological, environmental, and epidemiological elements of these diseases in defined geographic and temporal scales. Dirofilariasis caused by different species of the genus Dirofilaria is a disease affecting domestic and wild canines and felines and man, transmitted by different species of culicid mosquitoes. This complexity is increased because Dirofilaria species harbor intracellular symbiont Wolbachia bacteriae, which play a key role in the embryogenesis and development of dirofilariae and in the inflammatory pathology of the disease. In addition, the vector transmission makes the dirofilariasis susceptible to the influence of the climate and its variations. The present review addresses the analysis of dirofilariasis from the point of view of the episystem, analyzing the complex network of interactions established between biological components, climate, and factors related to human activity, as well as the different problems they pose. The progress of knowledge on human and animal dirofilariasis is largely due to the multidisciplinary approach. Nevertheless, different aspects of the disease need to continue being investigated and cooperation between countries and specialists involved should be intensified.

Dirofilaria immitis and D. repens in sylvatic reservoirs of Krasnodar Krai (Russian Federation).

Dirofilariosis is a cosmopolitan vector-borne transmitted disease whose causal agents in Europe are D. immitis and D. repens. Hosts are mainly domestic and wild canines and felines. While there is a great amount of data on dirofilariosis in pets (dogs and cats), information on the extension of this parasitosis in wild reservoirs is scarce. In the present study, we analyzed the carcasses of 451 carnivores that were legally shot during the hunting periods of 2006-2011 in 4 different geo-climatic areas of Krasnodar Krai, Southwestern Russian Federation. Two hundred and thirty-five foxes, 60 jackals, 90 raccoon dogs and 66 badgers were examined for the presence of D. immitis and D. repens. Worms were identified by morphological and morphometric characteristics, anatomical location and their identities being confirmed by PCR. One hundred and seven animals were parasitized by Dirofilaria spp. (23.7%). D. immitis was found in foxes, jackals and raccoon dogs with a global prevalence of 23.4%. D. repens was observed in jackals and badgers with a global prevalence of 10.3%. Mixed infections were observed only in 4 jackals. The highest prevalence was observed in raccoon dogs (31.1%), but no significant differences exist among the 4 species. Comparing the results obtained in each geo-climatic area, there is a higher prevalence in animals from the bay marshes (35.4%). These prevalences are, in general, higher than those reported in other countries from Central Europe and Balkans. Two new wild hosts in Europe, raccoon dog for D. immitis and badger for D. repens, were reported in Krasnodar Krai. Future research can contribute to establish the real risk of dirofilariosis in wild reservoirs for man and their pets in this region.