Blood-brain barrier disruption and angiogenesis in a rat model for neurocysticercosis.

Neurocysticercosis (NCC) is a helminth infection affecting the central nervous system caused by the larval stage (cysticercus) of Taenia solium. Since vascular alteration and blood-brain barrier (BBB) disruption contribute to NCC pathology, it is postulated that angiogenesis could contribute to the pathology of this disease. This study used a rat model for NCC and evaluated the expression of two angiogenic factors called vascular endothelial growth factor (VEGF-A) and fibroblast growth factor (FGF2). Also, two markers for BBB disruption, the endothelial barrier antigen and immunoglobulin G, were evaluated using immunohistochemical and immunofluorescence techniques. Brain vasculature changes, BBB disruption, and overexpression of angiogenesis markers surrounding viable cysts were observed. Both VEGF-A and FGF2 were overexpressed in the tissue surrounding the cysticerci, and VEGF-A was overexpressed in astrocytes. Vessels showed decreased immunoreactivity to endothelial barrier antigen marker and an extensive staining for IgG was found in the tissues surrounding the cysts. Additionally, an endothelial cell tube formation assay using human umbilical vein endothelial cells showed that excretory and secretory antigens of T. solium cysticerci induce the formation of these tubes. This in vitro model supports the hypothesis that angiogenesis in NCC might be caused by the parasite itself, as opposed to the host inflammatory responses alone. In conclusion, brain vasculature changes, BBB disruption, and overexpression of angiogenesis markers surrounding viable cysts were observed. This study also demonstrates that cysticerci excretory-secretory processes alone can stimulate angiogenesis.

The Essential Ectoenzyme SmNPP5 from the Human Intravascular Parasite Schistosoma mansoni is an ADPase and a Potent Inhibitor of Platelet Aggregation.

Schistosomes are intravascular parasitic platyhelminthes infecting > 200 million people globally and causing a debilitating disease, schistosomiasis. Despite the relatively large size of the adult worms and their disruption of blood flow, surprisingly, they do not appear to provoke thrombus formation around them in vivo. We hypothesize that proteins expressed at the host-parasite interface are key to this ability. Here, we functionally express an ectonucleotide pyrophosphatase/phosphodiesterase homologue, SmNPP5, that is expressed at the tegumental surface of intravascular Schistosoma mansoni. We report that SmNPP5, a known virulence factor for the worms, is a type one glycoprotein that cleaves the artificial substrate p-Nph-5'-TMP in a reaction that requires cations and at an optimal pH of 9. Using immunolocalization and enzyme activity measurements, we confirm that SmNPP5 is exclusively expressed at the host interactive surface of all intravascular life stages. SmNPP5 inhibits platelet aggregation in a dose-dependent manner, as measured by multiple electrode aggregometry (MEA) using whole blood. Inhibition is apparent when either collagen or adenosine diphosphate (ADP) is used as agonist but is lost following heat treatment of SmNPP5. Unlike its mammalian homologue, NPP5, the schistosome protein cleaves ADP and with a Km of 246 ± 34 µM. In sum, SmNPP5 is expressed in the intravascular environment where it can degrade ADP and act as an anticoagulant. In this manner, the protein likely helps limit blood clot formation around the worms in vivo to permit the parasites free movement within the vasculature.

Blood flukes exploit Peyer's Patch lymphoid tissue to facilitate transmission from the mammalian host.

Schistosomes are blood-dwelling parasitic helminths which produce eggs in order to facilitate transmission. Intestinal schistosomes lay eggs in the mesenteries, however, it is unclear how their eggs escape the vasculature to exit the host. Using a murine model of infection, we reveal that Schistosoma mansoni exploits Peyer's Patches (PP) gut lymphoid tissue as a preferential route of egress for their eggs. Egg deposition is favoured within PP as a result of their more abundant vasculature. Moreover, the presence of eggs causes significant vascular remodeling leading to an expanded venule network. Egg deposition results in a decrease in stromal integrity and lymphoid cellularity, including secretory IgA producing lymphocytes, and the focal recruitment of macrophages. In mice lacking PP, egg excretion is significantly impaired, leading to greater numbers of ova being entrapped in tissues and consequently, exacerbated morbidity. Thus, we demonstrate how schistosomes directly facilitate transmission from the host by targeting lymphoid tissue. For the host, PP-dependency of egg egress represents a trade-off, as limiting potentially life-threatening morbidity is balanced by loss of PP structure and perturbed PP IgA production.

Manipulation of vascular function by blood flukes?

Schistosomes (blood flukes) are long lived, intravascular parasites that afflict ~200 million people worldwide. Here we review the potential ability of these parasites to exert control on local vascular physiology. We examine schistosome kallikrein-like proteins that drive vasodilation. We review biogenic amine metabolism in the parasites that involve the vasodilator histamine and its receptors and the vasoconstrictor serotonin and its receptor. Schistosomes can trigger the release of histamine from host cells and can import serotonin. We consider the ability of schistosomes to generate and release the eicosanoid vasodilators PGD(2) and PGE(2) and the vasoconstrictors LTB(4) and LTC(4). The literature on nitric oxide metabolism in these blood flukes is assessed. Finally the potential impact of other schistosome metabolic processes (e.g. exogenous adenosine generation and acetylcholine degradation) on vascular function is appraised. An increased understanding of these processes could lead to novel anti-parasitics as well as new therapies to treat vascular dysfunction.

The fate of Lernaeocera branchialis (L.) (Crustacea; Copepoda) in Atlantic cod, Gadus morhua L.

Lernaeocera branchialis, a copepod crustacean parasite of gadoids, represents a potential threat to both wild and farmed cod, Gadus morhua. The pathological changes associated with the early stages of experimental infection have previously been reported in detail, and this article describes the lesions associated with later chronic stages of experimental infection. Chronic infection is characterised by extravascular granuloma formation and proliferation of fibrovascular tissue around intact and fragmented, degenerate parasites within both the gill arch and cardiac region. The majority of parasite granulomas are located within connective tissues of the gill arch or pericardium; however, low numbers are present within the wall of large vessels. The intraluminal parasites and thrombi of early stage infection are largely absent in these later lesions. We propose that organisation and incorporation of the parasite thrombus into the vessel wall with subsequent granuloma formation and extrusion into the surrounding connective tissue leads to the elimination of the parasite from the vascular system. Thus, rather than being a negative consequence of infection thrombosis is protective, allowing the host to survive the substantial initial vascular insult.

Manipulation of host hepatocytes by the malaria parasite for delivery into liver sinusoids.

The merozoite stage of the malaria parasite that infects erythrocytes and causes the symptoms of the disease is initially formed inside host hepatocytes. However, the mechanism by which hepatic merozoites reach blood vessels (sinusoids) in the liver and escape the host immune system before invading erythrocytes remains unknown. Here, we show that parasites induce the death and the detachment of their host hepatocytes, followed by the budding of parasite-filled vesicles (merosomes) into the sinusoid lumen. Parasites simultaneously inhibit the exposure of phosphatidylserine on the outer leaflet of host plasma membranes, which act as "eat me" signals to phagocytes. Thus, the hepatocyte-derived merosomes appear to ensure both the migration of parasites into the bloodstream and their protection from host immunity.

The role of blood vessels and lungs in the dissemination of Naegleria fowleri following intranasal inoculation in mice.

Primary amoebic meningoencephalitis (PAM) was induced in mice by intranasal inoculation of Naegleria fowleri (Singh et Das, 1970) to study the role of the blood vessels and lungs in the early and later stages in this disease. Upon culturing blood and lung tissue obtained at 24-, 36-, 48-, 72-, 96-, and 120-hour time periods, it was found that amoebae grew only from blood and lung tissue obtained at the 96 and 120 hour time periods. Paraffin sections of the head revealed small foci of acute inflammation and amoebae within the olfactory bulb of the central nervous system (CNS) at 24 hours. Amoebae were not observed within blood vessels of the CNS until 96 and 120 hours. Also, amoebae were observed within the connective tissue surrounding blood vessels and sutures of the skull, bone marrow, and venous sinusoids between the skull bone tables at 96 and 120 hours. No amoebae or acute inflammatory reactions were observed in the lung sections from any time period and indirect immunofluorescence microscopy was negative for N. fowleri. This study provides evidence that neither blood vessels nor lungs provide routes for N. fowleri to the CNS during the early stages of PAM and that amoebae enter veins of the CNS and bone marrow during later stages of the disease.

Effect of octreotide on the pathology of hepatic schistosomiasis.

In clinical practice, octreotide (CAS 83150-76-9) has its greatest impact in the management of bleeding varices. The present work is the first one which was undertaken to investigate the possible use of octreotide as an antifibrotic agent and to study its effect on hepatic vasculature in Schistosoma mansoni infection. The material of this investigation consisted of two groups of albino mice (A, B), subdivided each into normal control, infected control, subgroups treated with octreotide, praziquantel (CAS 55268-74-1), and a combination of octreotide and praziquantel. Groups A and B were sacrificed at the 8th week and the 18th week post infection, respectively. By analysis of the obtained results, octreotide induced a reduction of the portal pressure, the weight of the spleen and the liver, the liver egg load (number of eggs) granuloma size and cellularity, and of the degree of hepatic fibrosis quantified by serum N-terminal peptide of type III procollagen in serum, serum laminin and tissue collagen using a Picrosirius red dye assay. Moreover, the biochemical state of hepatocytes has been improved. The subgroups treated with octreotide in association with praziquantel revealed better results than the subgroups treated with praziquantel alone. These obtained data were analysed in terms of histological extent of liver fibrosis in sections stained with Masson trichrome and sirius red, hepatocytic and sinusoidal changes at an ultrastructural level and by immunohistochemical demarcation of endothelial cells of blood vessels through the determination of factor VIII-related antigen. The promising results detected in this study may encourage to further investigate the positive findings of this drug with the intention of its possible application on a clinical level.

Histopathology of Sanguinicola inermis infection in carp, Cyprinus carpio.

The histopathological response of carp to Sanguinicola inermis was investigated by serial sectioning laboratory infected fish up to 90 days post infection (d p.i.). Juvenile flukes and adults caused mechanical damage to tissues during invasion and migration up to 28 d p.i. Adults partially occluded blood vessels and may have reduced blood circulation. In the initial phase of egg production (28-42 d p.i.), eggs and emigrating miracidia in gill tissue caused breakdown of vascular integrity, necrosis, hyperplasia, haemorrhage and eosinophilic infiltration of epithelial tissue. After 42 d p.i. the host granulomatous inflammatory response encapsulated eggs lodged in the gills, visceral sites and connective tissue displacing normal tissue. Encapsulation and subsequent degradation of eggs and miracidia within granulomata was highly developed by 90 d p.i. Laboratory infections of S. inermis can induce respiratory distress and therefore impair respiration of fish. The parasite also caused pathological changes in osmoregulatory, excretory and haemopoietic tissue and may impair function in these organ systems.

Efficacy of praziquantel in the treatment of green sea turtles with spontaneous infection of cardiovascular flukes.

OBJECTIVE: To assess the efficacy of praziquantel as a treatment for cardiovascular flukes in turtles. PROCEDURE: Six green sea turtles (Chelonia mydas) spontaneously infected with cardiovascular flukes (Digenea: Spirorchiidae) were treated orally with praziquantel, and necropsied 3 or 7 days later to look for flukes in the heart and major blood vessels. Six similar animals were maintained as untreated controls. RESULTS: Absence of flukes in treated, but not control turtles, indicated that a one day course of treatment at a dose rate of 3 x 50 mg/kg body weight is effective. CONCLUSION: This result should be of value for preventing disease in wild caught green turtles introduced into farms or aquaria.

Fatal cytauxzoonosis in a captive-reared white tiger (Panthera tigris).

Fatal (Panthera tigris) cytauxzoonosis was diagnosed in a 7-year-old female white tiger. The tiger presented with a 2-day history of anorexia and lethargy. She was mildly dehydrated, with a temperature of 105.2 F and a hematocrit of 26%. Over the next day, icterus developed, and her physical condition progressed to recumbency, coma, and death. Hematologic findings obtained shortly before death included icteric plasma, severe thrombocytopenia, mild anemia, hematuria, and parasites consistent with Cytauxzoon felis in circulating erythrocytes. Gross necropsy findings included generalized icterus, generalized petechiae and ecchymoses, splenomegaly, and peribronchial edema. Histologic changes included large numbers of intravascular macrophages containing developmental stages of Cytauxzoon felis that partially or completely occluded blood vessels in the lung, spleen, liver, and bone marrow. Except for an experimental infection of a bobcat, fatal cytauxzoonosis has not previously been diagnosed in felids other than domestic cats. These findings raise questions regarding the pathogenicity of this organism in felids and may impact husbandry and interstate transfer of captive large cats.

Vascular abnormalities in experimental and human lymphatic filariasis.

Whereas clinical descriptions of grotesque lymphedema and standard light microscopy in human filariasis have elucidated the natural progression of this disease, the link between the nematode and vascular abnormalities including elephantiasis remains poorly understood. Accordingly, we examined the nature and distribution of lymphatic and blood vascular derangements in a variety of tissues and organs from 37 ferrets acutely and chronically infected with Brugia malayi and in 15 patients with Wuchereria bancrofti or Brugia malayi infestation (resected skin, subcutaneous tissue, and lymph nodes) using light and transmission electron microscopy, immunohistochemistry, and in vivo microscopy. In ferrets, eosinophilic abscesses and epithelioid and giant cell granulomas with fragmented worms in various stages of disintegration were found in multiple organs. Blood microvasculopathy consisted of endothelial hyperplasia, focal thickening and stenosis, vessel obliteration with marked perivascular infiltration of lymphocytes, plasma cells, eosinophils, and numerous large macrophages laden with a coarse golden-brown pigment. Endothelial ballooning and swelling, pavementing, denuding, scarring, and sludge formation were seen along with high endothelium in atypical locations. Dilated lymphatics were most prominent near adult worms and showed plump endothelium, thickened walls and valves, thrombus formation, and often perilymphangitis and adjacent tissue fibrosis. In vivo microscopy showed wriggling live adult worms in dilated incompetent sludge-filled groin lymphatics even when microfilaremia and peripheral edema were absent. In human tissues, in addition to "pachyderm" skin changes (keratosis, papillomatosis, acanthosis and collagen deposition), there was blood vessel and lymphatic vasculopathy similar to ferrets (angiocentric inflammation, congestion, vasculitis, thrombosis, thickened vessel walls, dilated lymphatics, lymphangitis, reactive lymph nodal hyperplasia and nodal fibrosis). These changes reflect generalized endothelial damage due to worm products, physical injury to valves and vessel walls from lymphatic-dwelling live worms, and host immune reactivity. Whereas adult worms target the lymphatic apparatus, their offspring and the host immune response primarily affects the blood microvasculature.

Proteases in the schistosome life cycle: a paradigm for tumour metastasis.

Cancers and parasites have a number of properties in common, particularly those that relate to their respective capacities to evade host defence mechanisms. This review highlights the similarities between metastatic tumours and schistosomes in particular, and describes the role that proteases may have in the migration, growth, survival and transmission of the different stages of the schistosome life-cycle in the vertebrate host. An elastase-like serine protease of schistosome larvae has been particularly well characterized, and its substrate profile and other properties are indicative of a role in facilitating migration of the parasite through skin tissue early after infection. The primary structures of a cathepsin B-like enzyme, and a putative 'haemoglobinase' found in adult worms have also recently been derived, these enzymes being responsible for degradation of haemoglobin in erythrocytes upon which the adults feed. Adult schistosome worms reside and produce eggs intravascularly, and the processes that mediate the extravasation and subsequent migration of the egg through host tissue are dependent on both blood platelets and the immune response. Fibrino(geno)lytic enzymatic activity that is present in the egg could modulate the thrombogenic potential that eggs might have as a result of their capacity to cause platelet aggregation in vitro and in vivo. The roles of other proteases and peptidases that have been found in schistosome larvae, worms and eggs are less clear. Some of these enzymes may modulate immunological and haemostatic defence mechanisms and thus prolong survival of the parasite, and the consequences of the interactions between schistosomes and host protease inhibitors could also be immune modulatory.

In vivo microscopy of schistosomiasis. IV. The dynamics of the host-parasite responses to Schistosoma mansoni in the hypodermal tissues as observed in transparent chambers in two susceptible hosts during primary and challenge infections.

The migration of Schistosoma mansoni cercariae and schistosomules, and the cellular responses of the hosts to these parasites, in primary and challenge infections, were examined and cine-recorded in vivo in the hypodermal tissues in Algire chambers which had been inserted in dorsal skins of C3H/HeJ mice and cheek pouches of Syrian hamsters, and checked in serial sections. In hamsters, many cercariae penetrated blood vessels within minutes after being injected into their chambers, in contrast to mice, in which penetration into vessels was scanty during the first hour. Schistosomule penetration into blood vessels was slow in both species. To ascertain whether or not the cercariae that had rapidly penetrated blood vessels in hamsters were capable of producing the disease, the chambers were removed a few hours after infection had been induced. Eight to 10 weeks later it was found that the parasites had produced the disease, since egg granulomas were found in the liver of hamsters. The cellular reactions of the hosts to the parasites revealed that granulocytes adhered first and most extensively to the tails of cercariae in essentially equal amounts in primary and challenge infections, but the adherence of such cells to the body of cercariae was greater in challenge infections. Nevertheless, an appreciable number of cercariae in both naive and challenge-infected animals were free of granulocytes or had less than five cells adhering to them. Furthermore, granulocyte adherence to cercariae or schistosomules was not necessarily permanent; the latter were usually free of cells a few hours after infection had been induced. Another difference between naive and challenge infections was that cercarial motility was more rapidly depressed in the latter infections.

Role of mosquito saliva in blood vessel location.

In order to ascribe a blood feeding function to the saliva of mosquitoes, we determined whether this secretion may limit the initial probing phase of biting behaviour. The probing of hosts was indeed prolonged when the salivary ducts were severed, but this prolongation was absent when mosquitoes were fed on an artificial meal contained beneath a membrane. In vitro, turbidometric assays demonstrated that saliva inhibits the ADP- and collagen-mediated aggregation of platelets. ATP and ADP were hydrolysed by saliva, and this apyrase activity explains, in part, the observed effect upon platelets. We conclude that the saliva of mosquitoes functions by facilitating location of blood vessels.

Sarcocystis singaporensis Zaman and Colley, (1975) 1976, Sarcocystis villivilliso sp. n., and Sarcocystis zamani sp. n.: development, morphology, and persistence in the laboratory rat, Rattus norvegicus.

Sporocysts obtained in Singapore in the feces of the boid snake, Python reticulatus, were given by mouth to laboratory rats, mice, and a monkey (Macaca mulatta). Infections developed in rats only. Schizonts were observed in vascular endothelium of various tissues of rats examined at 7 to 15 days of infection; and in each of 20 rats examined at 1 mo to 2 yr, cysts of three species of Sarcocystis were observed. Based on observations made by light and electron microscopy, one species was identified as S. singaporensis and redescribed; two species, S. villivillosi and S. zamani, were described as new. The cyst wall of S. singaporensis is thick with tall, stalked, digitiform villi. That of S. villivillosi is moderately thin and bears short, stout villi that are covered with microvilli; and that of S. zamani is thin and bears delicate, branched villi. The cyst of S. zamani is macroscopic with rounded ends; it induces multiplication of host-cell nuclei and causes resorption of the myofibrils. Cysts of the other species are microscopic with fusiform shape that changes markedly with contraction of the host cell. Refrigerated sporocysts of S. singaporensis, S. zamani, and S. villivillosi remained viable for at least 24, 14, and 6 mo, respectively. Sarcocystis singaporensis and S. zamani apparently have been reported previously from several species of Malaysian wild rodents; S. villivillosi represents a unique type in rodents.

Sarcocystosis: a clinical outbreak in dairy calves.

Death and illness in a pen of eight yearling dairy heifers was caused by the protozoan parasite Sarcocystis. All animals had weight loss, weakness, marginal anemia, and elevated serum enzymes. Affected animals had high hemagglutinating antibody titers to Sarcocystis antigen. Affected tissues of the two animals that died demonstrated schizonits and young cysts during pathologic examination. The resident farm dog was shedding Sarcocystis sporocysts and was incriminated as the source of infection.

Disseminated parasitosis in an immunosuppressed patient. Possibly a mutated sparganum.

The autopsy of a man who died of Hodgkin disease revealed that a peculiar metazoan parasite had proliferated and disseminated throughout his body. The parasite could not be identified; however, electron microscopical studies revealed that it had the structure of a flatworm. This, together with its shape and structure, convinced us that the parasite was an aberrant sparganum manifesting uncontrolled proliferation and dissemination.