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At least 91 records · Page 5Linked to original sources

PubMed1991

Experimental ocular onchocerciasis in cynomolgus monkeys. IV. Chorioretinitis elicited by Onchocerca volvulus microfilariae.

Onchocerciasis is a major cause of blindness worldwide, and much of the blindness is caused by onchocercal chorioretinitis. In an experimental animal model for ocular onchocerciasis, intravitreal injections of 10,000 live Onchocerca volvulus microfilariae isolated from infected humans into the eyes of cynomolgus monkeys (Macaca fascicularis) resulted in patchy, progressive loss of retinal pigment with pigment clumping. Areas of pigment loss were less extensive in animals that had been sensitized with microfilariae. Intravitreal injections of dead O. volvulus microfilariae resulted in mild vitritis with relatively less clinical change noted in the retina and choroid. Histopathologic examination revealed thinning and loss of outer retinal layers with pigment migration into the retina, and inflammation was more pronounced in eyes that received live microfilariae. Clinical changes appeared in eyes receiving live microfilariae before the development of significant antibody or cell-mediated immune responses. O. volvulus microfilariae appear to be more suitable than O. lienalis microfilariae in producing lesions which resemble human onchocerciasis in the primate model.

Animals↗

PubMed1982

Diethylcarbamazine-enhanced activation of complement by intact microfilariae of Dirofilaria immitis and their in vitro products.

Microfilariae of Dirofilaria immitis and their products inhibited hemolytic complement in sera from various animal species. Inhibition of hemolytic complement activity, fluorescent antibody detection of specific complement proteins binding to microfilarial surfaces, and immunoelectrophoretic evaluation of complement protein C3 conversion demonstrated that (1) intact microfilariae depleted hemolytic complement activity maximally in the presence of diethylcarbamazine whereas the complement-fixing activity of microfilarial products was little affected by diethylcarbamazine; (2) complement proteins C3, properdin, and C5 bound to the cuticular surface of microfilariae; and (3) C3 was converted to a faster-migrating species during incubation with microfilariae or their products. The complement-depleting activity of in vitro products from viable microfilariae was soluble in 10% trichloroacetic acid, resistant to beta-elimination with 0.5 M NaOH, susceptible to treatment with 0.2 M periodate, and composed of 56% neutral sugar, 18% protein, 12% hexosamine, and 10% sulfate. The polysulfated, acidic mucopolysaccharide nature of the surfaces of microfilariae and the results presented here indicate that polyanionic components on worm surfaces or shed by microfilariae react with host complement proteins. This interaction may be enhanced by diethylcarbamazine and contribute to the pathology associated with microfilaremias.

Animals↗

PubMed1995

Brugia malayi: differential susceptibility to and metabolism of hydrogen peroxide in adults and microfilariae.

The sensitivity of microfilariae and adult Brugia malayi to hydrogen peroxide (H2O2) was determined in vitro, and parasite viability assessed by incorporation of 2-deoxy-D-[1-3H]glucose. Both stages were surprisingly resistant to peroxide stress. Microfilariae tolerated the direct addition of H2O2 to medium in which they were incubated at concentrations up to 50 microM, whereas adult worms survived the addition of 100 microM H2O2 and showed slightly impaired viability at 150 microM H2O2. Higher concentrations were lethal in both cases. This observation of differential susceptibility was reproducible when parasites were subjected to continuous generation of H2O2 via glucose/glucose oxidase. Microfilariae remained viable over a 4-hr period when challenged with concentrations which generated 20 microM H2O2 in the absence of parasites. Adults survived higher concentrations of glucose oxidase, which generated 200 microM H2O2 over the same time period. Under these conditions the parasites effectively countered the rate of peroxide generation by metabolising the product. Protein carbonyl formation was detectable at sublethal concentrations of glucose/glucose oxidase, but malonaldehyde formation was only detectable coincident with parasite death. The rate of H2O2 consumption by parasites was determined and showed that adult worms metabolised it at a rate 23x faster than microfilariae, expressed as activity per wet weight. Assessment of enzyme activities in parasite extracts demonstrated that H2O2 metabolism was effected principally by catalase activity, which was elevated in adult worms relative to microfilariae. Cytochrome c peroxidase activity was also detected and was roughly equivalent in both stages. Glutathione peroxidase and NADH/NADPH-dependent consumption of H2O2 were absent, and the rate of nonenzymic reduction of H2O2 coupled to glutathione oxidation did not contribute significantly to metabolism. Glutathione reductase activity and total glutathione content were equivalent in adults and microfilariae. This study illustrates that Brugia malayi are much more resistant to H2O2 than other filarial species examined to date and can effectively metabolise levels in excess of those potentially generated by activated leucocytes.

Animals↗

PubMed1995

Lectin binding to extracellularly melanized microfilariae of Brugia malayi from the hemocoel of Anopheles quadrimaculatus.

Binding patterns of fluorescein isothiocyanate (FITC)- and gold-conjugated lectins to extracellularly melanized sheathed and exsheathed microfilariae of subperiodic Brugia malayi, isolated from and in situ in the abdominal hemocoel of Anopheles quadrimaculatus 72-hr postinfection, were examined. Five FITC-conjugated lectins [Helix pomatia agglutinin (HPA), Arachis hypogaea (peanut agglutinin-PNA), Triticum vulgaris (wheat germ agglutinin-WGA), Lens culinaris (lentil-LCH), and Concanavalin A (Con A)] with specificities for different carbohydrate moieties were tested for binding to isolated melanized microfilariae and observed with transmitted light and fluorescence microscopy. All five FITC-lectins bound strongly to the acellular material accompanying the melanin deposits on the surface of isolated melanized microfilariae. Significant inhibition of FITC-lectin binding occurred when lectins were preincubated with their complementary carbohydrates before testing. H. pomatia agglutinin binding was totally inhibited by N-acetyl-D-glucosamine and N-acetyl-D-galactosamine. Other lectins were partially inhibited, such as PNA by galactose and lactose; WGA by N-acetylneuraminic acid; LCH by N-acetyl-D-glucosamine, mannose, glucose, and methyl alpha-D-mannopyranoside; and Con A by mannose and methyl alpha-D-mannopyranoside. Three gold-conjugated lectins (HPA, PNA, and Con A), examined by using transmission electron microscopy, bound to the outer surface of the acellular material associated with the melanin deposits on isolated melanized microfilarial sheaths and melanized microfilariae and to the remnants of lysed hemocytes found in the proximity of the melanized deposits. Con A in the presence of gold-labeled horseradish peroxidase, examined by using transmission electron microscopy, showed random binding within the melanized capsule formed around the microfilarial sheath in situ. These results indicate that the acellular material accompanying melanin deposits on melanized microfilarial sheaths and sheathed and exsheathed microfilariae contain several glycoconjugates with exposed carbohydrate moieties and are possibly glycoproteins. These glycoproteins could be the by-products of the activation of the prophenoloxidase by the microfilariae.

Animals↗

PubMed1987

Isolation of pure sheaths of Litomosoides carinii microfilariae.

A method is described for the isolation of pure, chemically intact sheaths of blood microfilariae of Litomosoides carinii. Microfilariae were isolated according to standard techniques. Exsheathment was performed by freezing-thawing-shaking procedures, repeated 5-10 times, i.e., larvae were frozen in liquid nitrogen, thawed at room temperature, and shaken vigorously for 5 s. Exsheathment rates were about 50%. Sheaths were separated from ensheathed and exsheathed microfilariae and microfilariae fragments by filtration through a polycarbonate filter (2 micron pore size). The achievable yield (about 15% of the sheaths of a batch of microfilariae) was approximately 1 microgram of sheaths per 10(6) microfilariae.

Animals↗

PubMed1996

Dependence of eosinophil granulocyte infiltration into nodules on the presence of microfilariae producing Onchocerca volvulus.

Onchocercomata with a single live or dead worm were analyzed to elucidate the infiltration of eosinophils. Females were classified according to the presence or absence of microfilariae in their uteri and in the nodular tissues. Immunohistochemical staining was performed using antibodies against eosinophil cationic protein, peroxidase, and major basic protein. Very few eosinophils were detected in nodules containing females without microfilariae or male or dead worms only, whereas eosinophils were abundant in all nodules with females producing microfilariae. The occurrence of eosinophils was not related to the age of the worm. Occasionally, degenerated or dead microfilariae attacked by activated eosinophils were found. By examination of onchocercomata with or without microfilariae from the same patient, it was excluded that the occurrence of eosinophils was dependent mainly on the host's immune status. In conclusion, live adult Onchocerca volvulus do not elicit an invasion of eosinophils as long as they do not produce microfilariae. The absence of eosinophilia does not exclude onchocerciasis.

Animals↗

PubMed1984

Differences in the surface radioiodinated proteins of skin and uterine microfilariae of Onchocerca gibsoni.

Surface labeling studies using two populations of Onchocerca gibsoni microfilariae revealed important differences in major radioiodinated proteins. Small numbers of microfilariae harvested from the skin of cattle or the uteri of adult worms from skin nodules were purified, radioiodinated, solubilized and the proteins analysed by two dimensional gel electrophoresis and autoradiography. As reported previously, uterine microfilariae showed a complex profile of radioiodinated proteins, none of which appeared to be bovine albumin or immunoglobulin. In contrast, application of the same techniques to skin microfilariae demonstrated only one major labeled protein complex of approximate Mr 67 000. This protein complex was immunoprecipitated with an antiserum to bovine serum albumin. Surprisingly, fluorescence techniques failed to show bovine serum albumin on the surface of living microfilariae. Although the evidence is circumstantial at present, acquisition of host albumin (perhaps oriented in a particular way) may be a means whereby skin microfilariae evade immune effector mechanisms and, when living, generally fail to elicit inflammatory reactions in the skin of the host.

Animals↗

PubMedDate not supplied

Transglutaminase-catalyzed incorporation of host proteins in Brugia malayi microfilariae.

Recently, we have characterized and purified a novel transglutaminase (pTGase) from adults of the filarial worms Brugia malayi. pTGase-catalyzed reactions seem to play an essential role during in utero growth and development of microfilariae. The results presented here demonstrate that exudates from the peritoneal cavity of jirds, the site where adult worms of B. malayi reside and produce microfilariae, contain several host proteins that can serve as substrates in pTGase-catalyzed reactions. The peritoneal exudate proteins are avidly taken up by adult female worms in vitro and incorporated into the developing microfilariae. Among the several host proteins that were crosslinked, a 68-kDa molecular weight protein (p68) was found to be the major protein taken up by the parasites. Following uptake by the parasites, the peritoneal exudate proteins are crosslinked to form high molecular weight aggregates, that are subsequently incorporated into in utero developing embryos and microfilariae. The cross-linking of host proteins was, however, inhibited by monodansylcadaverine (MDC), a competitive inhibitor of pTGase. Antibodies raised against the jird peritoneal exudate proteins strongly immunoreacted with a 68-kDa protein in adult worms and microfilariae extracts but not with infective-stage larvae (L3) of B. malayi. These results suggest that pTGase is involved in covalent incorporation of host proteins (such as p68) into developing embryos and microfilariae of B. malayi.

Animals↗

PubMed1991

Isolation of microfilariae from blood by gravitational field-flow fractionation.

Over 100 million persons suffer from diseases caused by filariae infestation, and one billion are at risk. A simple isolation method for both analytical and preparative separation is presented. Based on the simplest field-flow fractionation technique, the gravitational one, effective isolation of microfilariae is achieved. Microfilariae are eluted in the void volume of the channel without pollution by red blood cells. The red blood cell elution peak shows a total absence of microfilariae, as demonstrated after fraction collection and microscopic investigation. The elution mode of microfilariae and red blood cells appears to be a steric one, as confirmed by a reinjection experiment. The simplicity, low cost and the relatively short time required for this separation (10 min) indicate that gravitational field-flow fractionation could become a new separation tool for screening of microfilariae. With both live and dead microfilariae, the high recovery (66-80%) allows preparative fractionation for diagnostic purposes or fundamental research.

Animals↗

PubMed1988

Exsheathment of microfilariae of Brugia pahangi in the susceptible and refractory strains of Aedes aegypti.

Exsheathment of microfilariae of Brugia pahangi was studied in susceptible (Liverpool) and refractory (Bora-Bora) strains of Aedes aegypti. It was found that the microfilariae tend to carry their sheaths into the haemocoel of both strains of Ae. aegypti within two hours after the engorgement of mosquitoes from a rat parasitized by filariae. The percentage of sheathed microfilariae in the haemocoel then progressively decreased to 0% at eight hours and to 1% at 24 hours post-ingestion in the Bora-Bora and Liverpool strains, respectively. Those microfilariae that remained in the midgut more than two hours after ingestion were most likely to cast off their sheaths there. The percentage of microfilariae exsheathed in the midgut progressively increased to about 91 and 78% at 24 hours post-ingestion in the Bora-Bora and Liverpool strains, respectively. These results suggested that the exsheathment of microfilariae occurs both in the haemocoel and in the midgut of two strains of Ae. aegypti.

Aedes↗

PubMed1985

Incorporation of arachidonic acid by microfilariae of Brugia malayi.

To initiate studies on the significance of filarial arachidonic acid metabolism in the immunopathogenesis of human filariasis, we evaluated the ability of microfilariae of the human filarial parasite Brugia malayi to take up and incorporate exogenous arachidonate. When 4 X 10(5) microfilariae were incubated in vitro with 3 nM [3H]arachidonic acid for 0.2, 24, and 48 hr, 23%, 70%, and 75% of tritium activity were associated with microfilariae, respectively. [3H]arachidonic acid was taken up by viable but not by killed microfilariae. Electron microscopic autoradiographic examination of living microfilariae incubated with [3H]arachidonic acid demonstrated numerous tritium-induced silver grains over sectioned parasites. Chromatographic resolution and quantitation of classes of neutral lipids and phospholipids of parasites established that incorporated [3H]arachidonic acid was rapidly and almost completely esterified into these lipids, predominantly into phosphatidylinositol and phosphatidylcholine. Microfilariae, the blood-borne stage of B. malayi, possess the requisite biochemical pathways to rapidly take up and incorporate exogenous arachidonate.

Animals↗

PubMed1975

Onchocerciasis in Guatemala. II. Microfilariae in urine, blood, and sputum after diethylcarbamazine.

Guatermalan volunteers with onchocerciasis were given a dose of diethylcarbamazine to learn if this caused migration of microfilariae of Onchocerca volvulus into urine, blood, and sputum. In 5 of the 10 volunteers, the num0ers of microfilariae in the urine increased considerably following the drug. In the same 5, relatively large numbers of microfilariae were observed in the blood and sputum specimens. Response in the remaining 5 was negligible. Four controls given a placebo did not respond. Interestingly, however, 2 control subjects had onchocercal microfilariae in their concentrated blood specimens and 3 control subjects had microfilariae in the sputum. Therefore, we believe that microfilariae, if searched for, may be found in other parts of the patient not normally associated with the infection.

Administration, Oral↗

PubMed1975

Reactions to subconjunctival inoculation of Onchocerca volvulus microfilariae in pre-immunized rabbits.

Rabbits, pre-immunized by intravenous inoculations of live, or of freeze-killed microfilariae of Onchocerca volvulus, were later challenged by subconjunctival inoculation of live microfilariae. Those pre-immunized with live microfilariae showed a marked chemotic conjunctivitis and reactions in the cornea (stromal keratitis and limbal abscesses), starting within one day of challenge. They were classed as sensitized. Those pre-immunized with dead microfilariae produced minimal reactions also starting on day 1, and were classed as tolerant. Histologically the reactions were distinctly greater in sensitized than in tolerant animals. The predominant cells in the inflammatory exudate were polymorphonuclear leucocytes and lymphocytes. The immunological basis for the differences between sensitized and tolerant rabbits is discussed, together with its possible bearing on human onchocerciasis. The effects of long-term subconjunctival and sclerocorneal inoculation of microfilariae were compared in one sensitized, one tolerant, one previously exposed, and one sensitized control rabbit. The sensitized test animal showed lesions resembling the sclerosing keratitis of human onchocerciasis. Immature microfilariae taken from intra-nodular fluid showed little ability to penetrate the cornea of the rabbit, and were minimally pathogenic.

Animals↗

PubMed1991

Immunohistological and electron microscopic studies of microfilariae in skin and lymph nodes from onchocerciasis patients after ivermectin treatment.

Microfilariae were studied in skin and lymph node biopsies from Liberian patients with generalised onchocerciasis 12-78 hours after administration of a single dose of 150 micrograms/kg body weight using histology, transmission electron microscopy and immunocytological staining with antibodies against an immunodominant antigen of Onchocerca volvulus. Most microfilariae in the skin appeared morphologically intact and beginning signs of degeneration were seen only on the ultrastructural level. The densities of microfilariae in the lymph nodes were about thousandfold higher in ivermectin treated patients. More than 90% of the microfilariae in the lymph nodes showed distinct signs of degeneration. Early changes were seen in the muscle cells. The disintegrating microfilariae in the lymph nodes were always encircled by eosinophils or macrophages or both cells. Immunohistological staining with antifilarial antibodies increased the detection of small and disintegrating pieces of microfilariae considerably.

Animals↗

PubMed1991

[Observation on the behavior of microfilariae in human filariasis].

A total of 19 female adult filariae containing microfilariae in uteri collected from 25 filariasis patients were examined. Light transmission microscopic observations showed: (1) some of the adult worms entered the lumen of blood vessels by penetrating the venous wall and discharged immature and mature microfilariae and embryos into the blood stream; (2) microfilariae developed into maturation in the uterus of adult female worms, but when the adult worm began to degenerate, the microfilariae did not degenerate concurrently; (3) some microfilariae could form thrombus, inducing the infiltration of segmented neutrophils and eosinophils followed by the formation of granuloma; (4) embryos 8 female adults parasitizing lymphatics were seen to discharge immature microfilariae and ova, which might form emboli after entering the blood stream.

Adolescent↗

PubMedDate not supplied

[The correlation between onchocercomas and positivity for microfilaria in onchocerciasis].

The objective of this work is to evaluate the palpation sensitivity of onchocercomata for the diagnosis of onchocerciasis in individuals residents of the locality of Nueva Costa Rica, Mapastepec, in the south endemic area of the state of Chiapas, Mexico. Every one of the 243 individuals who voluntarily participate in this study was interrogated and physical examined for the detection of nodules. The positivity and the worm burden to the Onchocerca volvulus infections was estimated by the presence of one or more microfilariae in any of the for skin snips taken from both suprascapular and gluteal regions, and by the mean of the Dmf/mg of each skin snip. From the total number of individual studied, 131 (53.9%) were positives to microfilariae and 37 (15.2%) to onchocercomata. Only 23 (17.6%) of the microfilariae positive individuals carried nodules. The distribution of positive individuals to nodules in relation to age, was similar in all the age groups. In relation to the intensity of the infection was found that, the mean of the Dmf/mg of all individuals was 6.67, there was not significant differences (p greater than 0.001) between males and females; being the Dmf/mg of 6.35 and 6.99, respectively. The age group between 21 and 30 years old showed the higher mean of Dmf/mg than the rest of the groups (p greater than 0.001). However, there was a high microfilariae positivity in the oldest groups than in the young. The prevalence for onchocerciasis in this locality, estimated by the positivity to either microfilariae or nodules, was 59.9 per cent. It is concluded that, the onchocercomata detection sensitivity for the diagnosis of onchocerciasis was very low, probably due to the nodulectomy activity of the onchocerciasis control program, which has been operating since 1930 and therefore, there are an important number of individuals positive to microfilariae without detectable nodules.

Age Factors↗

PubMed1988

Antibody response against Litomosoides carinii and the distribution of bound antibodies on microfilariae from the different internal organs of cotton rats.

The courses of IgG and IgM antibody levels against adult worm and microfilarial antigen were determined in isogenetic cotton rats infected quantitatively with Litomosoides carinii. Against both antigens, IgG as well as IgM, antibody levels exceeded significantly those of noninfected animals, and the IgG levels were generally higher than the IgM levels. The total antibody production was depressed transiently 8 weeks p.i. by the appearance of microfilariae in the peripheral blood. A second transient depression occurred two weeks earlier against microfilarial antigen than it occurred against adult worm antigen. At 3 different times after the infection, the amount of adsorbed antibodies was assessed on adult worms and on microfilariae, which were isolated from blood and by a specially developed method from the internal organs. The percentual distribution of microfilariae in the different organs and blood changed during patency. In spleen, kidney, and lung a continuous increase was observed, whereas in heart and liver the percentage initially increased, and then decreased. The opposite course was seen in blood. Most antibodies adsorbed on the surface of microfilariae and adult worms belonged to the IgM class. Predominantly, the antibodies were detected on organ microfilariae, particularly on those in spleen and kidney, while blood microfilariae had lower amounts of bound antibodies. Furthermore, by complement fixation, no common antigens could be detected on the surface of host cells and the different L. carinii stages.

Animals↗

PubMed1987

Seasonal changes in density and tissue distribution of Onchocerca cervicalis microfilariae in ponies and related changes in Culicoides variipennis populations in Louisiana.

Seasonal changes in density and spatial distribution of Onchocerca cervicalis microfilariae were studied in ventral-midline skin of 15 infected pony mares in southern Louisiana. Triple running mean analysis of data over a 13-mo period indicated that a distinct pattern exists in total microfilariae population density and in microfilariae occurrence in different levels of the dermis. Microfilariae density reaches peak levels in the spring followed by a 58% decrease in the summer, a 19% increase in the fall, and a decrease to the lowest numbers in the winter. Microfilariae were found in all levels of the skin during the spring, summer, and fall but were not found in the superficial layers of the dermis during the winter months. The population density of Culicoides variipennis, a demonstrated vector of O. cervicalis, appeared to have seasonal fluctuations similar to the changes in microfilarial density. Harmonic wave analysis of microfilariae density data in individual ponies showed that all individuals did not follow the population trend.

Animals↗