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PubMed1976

Seasonal variation in the concentration of Onchocerca volvulus microfilariae in the skin?

Repeated multiple skin snips in 18 persons with onchocerciasis from the Sudan-savanna of West Africa suggested the possibility of a seasonal variation in microfilarial concentrations. This variation may be an evolutionary adaptation of the parasite to the climate conditions that affect the seasonal distribution of the vector, but a migration of the microfilariae in the skin layers caused by the Simulium bites cannot be excluded.

Adolescent↗
PubMed1988

Tolerance in rats by transplacental transfer of Dipetalonema viteae microfilariae: recognition of putative tolerogen(s) by antibodies that inhibit antigen-specific lymphocyte proliferation.

We have previously reported (Nature 1982. 299:361) that the transplacental transfer of Dipetalonema viteae microfilariae (mf) can induce an antigen-specific tolerance in rats. Rats thus tolerized have serum factor(s) which block(s) antigen-specific lymphocyte proliferation. The results of experiments involving fractionation of antisera from tolerant animals indicate that the inhibitory activity for antigen-specific blastogenesis resides in IgG antibodies. Absorption of IgG (eluted from protein A) with specific filarial antigens reduced the inhibition from 58% to 9% whereas a similar immunosorption of IgG size fraction (obtained by applying to AcA 34 Ultrogel) resulted in a decrease from 72% to 35%. This suggests that IgG size fraction might include factor(s) derived from mf and was partially blocking the blastogenic response. Since the tolerant animals harbor only mf, we have used radiolabeled mf surface antigens for immunoprecipitation by antisera from tolerant animals. Antibodies from tolerant animals have a different specificity for filarial antigens compared to those from immunocompetent and mf-resistant rats.

Animals↗
PubMed1996

The sheath of the microfilaria of Brugia malayi from human infections has IgG on its surface.

Microfilariae (mf) of Brugia malayi from microfilaraemic people had human IgG on their sheath. Fluorescent antibody studies showed that the predominant IgG isotype was IgG3, with IgG4 and IgG1 being present in lower quantities. Human albumin could not be detected. The sera of patients with chronic disease contained high levels of an IgG2 antibody that reacted with the sheath of mf taken from other people.

Animals↗
PubMed1998

Immunoelectron microscopic evidence for release of eosinophil granule matrix protein onto microfilariae of Onchocerca volvulus in the skin after exposure to amocarzine.

The involvement of eosinophils in the host reaction to microfilariae (mf) of Onchocerca volvulus was studied by immunohistochemistry and immunoelectron microscopy. Skin biopsies were obtained from patients after transepidermal administration of the microfilaricide amocarzine. At 20-28 h after the application of amocarzine, mf were degenerated or dead and a marked eosinophil-parasite adherence (EPA) reaction was seen, with intense staining for intra- and extracellular eosinophil granule proteins such as eosinophil cationic protein (ECP) surrounding the mf. Immunoelectron microscopically the eosinophil granule matrix in intact and necrotic eosinophils was specifically labeled, whereas granules whose matrix had dissolved showed no specific gold particle binding. As specific labeling was seen on lowly electron-dense material adjacent to matrix-depleted granules, the material was regarded as released eosinophil granule matrix material. Intact and necrotic eosinophils, matrix-containing as well as matrix-depleted eosinophil granules, and released eosinophil granule matrix material were observed on the surface of damaged mf and between collagen fibers. The coincidence of mf degeneration, EPA reaction, and release of eosinophil granule matrix material on damaged mf and collagen fibers indicated a role of eosinophils and eosinophil granule matrix protein in the host reaction to mf after amocarzine application.

Adult↗
PubMed1991

Aedes aegypti: characterization of hemocyte polypeptide synthesis during wound healing and immune response to inoculated microfilariae.

Hemocytes from adult, female Aedes aegypti, intrathoracically inoculated with microfilariae (mf) of the nematode Dirofilaria immitis, were compared to saline-inoculated and uninoculated controls using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), 125I-labeling, and wheat germ agglutinin (WGA) binding techniques. Activation of wound healing and/or melanotic encapsulation responses by the inoculation of saline or mf into the host hemocoel induced alterations in the hemocyte activity of these mosquitoes. Protein assays of whole hemocyte lysates revealed that hemocytes from saline- and mf-inoculated mosquitoes had higher protein concentrations than uninoculated controls. Many polypeptides were seen within all three hemocytes preparations when stained with silver nitrate, but there was an overall increase in protein synthesis in hemocytes from inoculated mosquitoes. In addition, a 200-kDa polypeptide was uniquely expressed in hemocytes from inoculated mosquitoes. There were several prominent surface proteins labeled with 125I, and several of these increased dramatically in intensity during wound healing and/or a melanotic encapsulation response. Similar results were seen in two-dimensional separations. A set of basic polypeptides comigrated with an acidic polypeptide resulting in a surface protein of approximately 80-90 kDa that increased in inoculated mosquitoes. Hemocytes from inoculated mosquitoes exhibited a group of three acidic polypeptides, whereas hemocytes from uninoculated mosquitoes exhibited only one of these protein fragments. Three surface polypeptides bound 125I-labeled WGA, and binding of WGA to hemocyte surface polypeptides was successfully inhibited by the incubation of cells with the lectin and its competing sugar.

Acetylglucosamine↗
PubMedDate not supplied

A quantitative approach to the relationship between Wuchereria bancrofti microfilaria counts by venous blood filtration and finger-prick blood films.

Counts of nocturnally periodic Wuchereria bancrofti microfilariae (mf) in 20 mm3 finger-prick blood films were compared with membrane counts after filtration of 1 ml of venous blood for their efficacy in determining the prevalence of Bancroftian filariasis. The technique used for spreading and staining the blood films was critically important to the sensitivity of this screening procedure. There was good agreement between the 2 methods. Four statistical approaches were used to measure the correlation between the 2 sampling methods: 2 linear regression methods using untransformed and transformed data, and 2 non-parametric rank correlation methods. Based on the statistical analyses, this study strongly supports the general observation that finger-prick blood samples tend to contain more mf than equivalent volumes of venous blood, at mf densities high enough to be detectable by the finger-prick technique. It also demonstrates that finger-prick samples provide good estimates of mf densities and prevalence of infection except in areas of very low mf densities, where the membrane filtration method would provide a more accurate estimate of prevalence. Regression analyses using untransformed and transformed data, and the rank correlation tests, demonstrated a strong statistically significant correlation (P less than 0.001) between venous and finger-prick mf counts.

Adolescent↗
PubMedDate not supplied

Microfilariae recurrence in Polynesian Wuchereria bancrofti carriers treated with repeated single doses of 100 micrograms/kg of ivermectin.

Forty-six Polynesian carriers of Wuchereria bancrofti were treated with 3 successive single doses of ivermectin, 100 micrograms/kg, given every 6 months. Immediate microfilaricidal activity of ivermectin was excellent in all carriers, since residual mean microfilaraemia levels, 2 d after each of the 3 treatments, were less than 1% of pretreatment levels. Before initial treatment, geometric mean microfilaraemia was 500 microfilaria (mf)/ml for the whole group (range 21-6398 mf/ml); 6 months after each successive treatment it was 197, 108 and 87 mg/ml, respectively, 39.4, 21.6 and 17.4% of the pre-initial treatment level. By considering the mean percentage recurrent level at 6 months after the 3rd treatment (36.8%) as a threshold, it was possible to classify the carriers into 2 groups: 17 in whom the percentage recurrent level was > 36.8% and who were considered as 'fast repopulating' individuals, and the remaining 29 who were considered as 'slow repopulating' individuals. In the latter group, 6 months after each of the 3 treatments, the recurrent microfilaremia levels were 22.7%, 8.0% and 4.9% of the pre-initial treatment level, respectively, while they were 95.1%, > 100% and > 100% in the former. The constant recurrence of mf suggests that ivermectin, at a dosage of 100 micrograms/kg, had no effect on adult worms in 'fast repopulating' individuals, whereas the progressive lessening in recurrence of mf suggests some activity (sterilizing or killing) of ivermectin on W. bancrofti macrofilariae in 'slow repopulating' individuals.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMedDate not supplied

Comparison of the sensitivity of different geographical isolates of Onchocerca volvulus microfilariae to ivermectin: effects of exposure to drug on development in the blackfly Simulium ornatum.

Four geographical isolates (Ghana forest, Ghana savannah, Cameroon forest, Guatemala) of Onchocerca volvulus microfilariae (mf) and O. lienalis mf (UK) were examined for their sensitivity to ivermectin by incubation in vitro in drug followed by assessing their ability to develop in the blackfly Simulium ornatum after intrathoracic injection. Parasites were incubated for 30 min in ivermectin (10(-6) to 10(-9) M), which resulted in a concentration dependent decrease in the numbers of parasites surviving and developing in the insect; there were significant reductions in parasite recoveries from all isolates in the 10(-6) M to 5 x 10(-8) M ivermectin groups, but no significant effect was seen following incubation in concentrations of 10(-8) M and below. Experiments consistently demonstrated that the 4 isolates of O. volvulus were similarly sensitive to ivermectin (in the 10(-7) M ivermectin groups there was a reduction of 76.3% to 85.1% in numbers of infective larvae, and 60.9% to 85.5% in numbers of all larval stages, compared to controls); O. lienalis mf were significantly more sensitive (100% reduction in infective larvae, 98.7% reduction in all larval stages). This baseline information on drug sensitivity and techniques should prove useful for examining populations of O. volvulus for possible development of drug resistance in the future.

Animals↗
PubMed2006

Isolation of Wuchereria bancrofti microfilariae from archived stained blood slides for use in genetic studies and amplification of parasite and endosymbiont genes.

Information on change in genetic diversity of Wuchereria bancrofti is important in view of the launching of the Global Lymphatic Filariasis Elimination Programme, as it may have important consequences on the control operations and on the potential resurgence after their withdrawal. Since attention was not paid to generate such information when the programme was launched, use of archived parasite material will provide an opportunity to derive this information in a prospective manner. In this paper a simple and effective technique is reported for isolation of microfilariae of W. bancrofti from dried and stained slides archived for several years and their utility in analysis of genetic structure and amplification of certain genes of the parasite is tested. The method was found to be efficient in purifying mf from the dried smears and the DNA of the parasite found to be useful in studying the genetic structure of Wuchereria bancrofti populations using random amplified polymorphic DNA (RAPD)-PCR and for amplifying genes of the parasite and its endosymbiont, Wolbachia sp.

Animals↗
PubMed2006

Penetration of the mosquito midgut is not required for Brugia pahangi microfilariae to avoid the melanotic encapsulation response of Armigeres subalbatus.

Insect vectors of disease have the capacity to respond to, and prevent further development of, parasites and pathogens using a response known as melanotic encapsulation. The naturally-occurring Armigeres subalbatus-Brugia spp. system provides an excellent way to investigate melanotic encapsulation and immune recognition in a mosquito host, because Brugia malayi microfilariae (mf) acquired via a blood meal are rapidly melanized in the body cavity of Ar. subalbatus, but Brugia pahangi mf evade or suppress the immune response and develop normally into infective stage larvae. Previous studies have suggested that B. pahangi mf are changed in some manner in the process of exiting the mosquito gut, thereby facilitating escape from, or suppression of, the melanotic encapsulation response. By inoculating mosquitoes with parasites, thus circumventing the midgut, we show that approximately 88% of B. pahangi mf escape the melanotic encapsulation response while approximately 90% of inoculated B. malayi mf are melanized. Methods to isolate parasites for this procedure are described. These results mimic those observed in Ar. subalbatus against Brugia spp. mf that are ingested following blood feeding, and demonstrate that midgut penetration is not required for B. pahangi mf to avoid the melanotic encapsulation response of Ar. subalbatus.

Animals↗
PubMedDate not supplied

Long-lasting reduction of Brugia timori microfilariae following a single dose of diethylcarbamazine combined with albendazole.

The long-term effect of a single oral dose of 6 mg/kg bodyweight of diethylcarbamazine (DEC) combined with 400 mg albendazole (ALB) on the microfilariae (mf) of the lymphatic filarial parasite Brugia timori was studied on Alor island, Indonesia from April 2001 to April 2002. Before treatment the geometric mean of the mf density in 96 infected study subjects was 150 mf/mL night blood (range 1-5696 mf/mL). One year after treatment 69 subjects (72%) were mf-negative and the overall geometric mean mf density reduced to 3 mf/mL (0-2456 mf/mL). The reduction of mf was more pronounced 1 year after treatment compared with 6 months after treatment. It can be concluded that a single dose of DEC + ALB leads to a long-term and progressive suppression of B. timori mf for at least 1 year. Therefore, DEC+ ALB can be recommended as an effective strategy to control B. timori infection in the framework of the Global Programme to Eliminate Lymphatic Filariasis.

Adolescent↗
PubMed2001

Relationship between microfilaria count and sensitivity of the direct smear for diagnosis of canine dirofilariosis.

Direct blood smear examination (using 0.05 ml of whole blood) detected 168 (80.9%) of 204 microfilaremic canine blood samples as determined by the modified Knott test for microfilariae (mff) of Dirofilaria immitis (using 1 ml of whole blood). Direct smear examination detected all of 134 microfilaremias greater than 50 mff ml(-1), but only 31 of 70 (44.3%) microfilaremias having less than 50 mff ml(-1). In a separate retrospective query of a database of 963 dogs with necropsy-confirmed heartworm infections, 834 (86.6%) were positive by the DiroCHEK heartworm antigen test, and 504 (52.3%) were microfilaremic by the modified Knott test. Only 2 (0.4%) of the microfilaremic dogs were DiroCHEK negative and another 18 (3.6%) were very weak positives. Although these microfilaremic dogs were not tested by direct smear, only one of the two DiroCHEK-negative and six of 18 weakly DiroCHEK-positive dogs had microfilaremias so low that a direct smear may have given a false negative result. Significant adverse reactions to either diethylcarbamazine or the macrolide endectocides have not been reported for microfilaremias less than 500 mff ml(-1), thus substitution of the direct smear for a concentration test for mff, such as the modified Knott test or membrane filtration, does not appear to increase the risk of an unexpected adverse reaction to heartworm prophylactic drugs. Such a substitution results in only a very slight decrease (on the order of 0.1%) in the overall sensitivity of heartworm screening, provided a test for mff is run concurrently with an antigen test. If a test for mff is the only screening test used, then substitution of a direct smear for a concentration test may decrease the sensitivity of heartworm screening by nearly 20%, depending on the prevalence of low level microfilaremias in the population of dogs tested.

Animals↗
PubMed1994

Determination of the earliest appearance and peak count of microfilariae of Wuchereria bancrofti and Brugia malayi after taking a single dose of diethylcarbamazine at noon.

Six nocturnal microfilarial carriers (three with Wuchereria bancrofti and three with Brugia malayi) from mainland China were selected to determine the earliest appearance and peak count of microfilariae (mf) administration of DEC at noon. Before diethylcarbamazine (DEC) administration, blood samples of 60 microliters were obtained by finger-prick at 2 h intervals for 24 h. A blood sample was then taken just before each carrier intaking 100 mg, 150 mg or 200 mg of DEC orally at noon. After drug administration, blood samples were obtained at 45 and 60 sec and at 2, 3, 4, 5, 10, 15, 20, 25, 30, 40, 50, 60, 90 and 120 min. Samples were then taken at 2 h intervals for the next 2 h and at 6 h intervals for the next 7 days. Both W. bancrofti and B. malayi showed typical nocturnal periodicity. One mf was first detected in the peripheral blood 45 sec in a mf. carrier. The mf peak counts were found 1-40 min after DEC administration at noon. The nocturnal cycle was distributed during the first two days after DEC administration. It became regular with a much lower peak count by the third day after administration. The results of the present study indicate that the provocative effect of DEC on the mf is very fast; the first appearance in the peripheral blood vessels could be under 45 sec.

Animals↗
PubMed1978

Intrauterine development of the microfilariae of Dipetalonema viteae.

The egg shell of Dipetalonema viteae separated from the oolemma and became highly convoluted at an early stage of development. No second oolemma or trilaminate membrane was seen. Channels containing electron dense material (thought to be nutrient material from the uterine wall) were formed between adjacent embryos. Many developing embryos died. Microvilli were formed by the uterine wall and developing embryos were closely apposed to these (again presumably to obtain nutrient). Embryos emerged from the egg in the uterus and were born as unsheathed microfilariae.

Animals↗
PubMed1995

Analysis of migration success of Onchocera lienalis microfilariae in the haemocoel of Simulium vittatum.

Migration success (i.e. the proportion of worms that reach the thorax) of Onchocerca lienalis microfilariae (mf) in the haemocoel of Simulium vittatum was studied by inoculating mf into the posterior abdomen, and recording their distribution in the blackfly body at predetermined time points. Mf arrive into the thorax by active locomotion rather than by drifting in haemolymph currents. Migration into the thorax was completed by 12 h post inoculation (pi) but was not continuous throughout this period. Migration proceeded in two phases; the first occurred 0-2 h pi and the second at 6-12 h pi. Overall, migration success 12-24 h pi was only 36%, indicating that a substantial number of mf failed to reach the thorax, either because they were eliminated by the fly's defensive response or because they remained in the abdomen. Migration success was density independent. Mf that arrive into the thorax within 2 h pi did not differ in their migration potential from mf that remained in the abdomen at this time. In flies where more mf migrated successfully there was lower mf loss, indicating that migration success was linked to mf loss. Moreover, the proportion of mf in the thorax was not correlated with mf loss, suggesting that mf loss affected the number of mf that migrated successfully, rather than the reverse causal relationship.

Abdomen↗
PubMed1989

Human host selection by anophelines: no evidence for preferential selection of malaria or microfilariae-infected individuals in a hyperendemic area.

Host selection among humans by Anopheles punctulatus was studied in an area of Papua New Guinea endemic for malaria and filariasis. Blood films were made from the stomach contents of freshly engorged mosquitoes found resting on the walls of houses in which the parasite status of the occupants was known. Engorgement rates on humans were non-random but could not be consistently related to the parasite status of individuals in the houses for either malaria or filaria. In some households, anophelines preferentially fed on parasitaemic individuals while in other households aparasitaemic individuals were significantly more often selected. This finding is believed to reflect the fact that malaria and filarial infections in this endemic area are predominantly asymptomatic. There were no significant differences in axillary temperatures between malaria or microfilariae positive or negative individuals.

Adolescent↗
PubMed1995

Chemical guidance of Onchocerca lienalis microfilariae to the thorax of Simulium vittatum.

The behavioural responses of Onchocerca lienalis microfilariae (mf) to tissue factors of the surrogate black fly host, Simulium vittatum, were studied using a novel in vitro bioassay. Mf accumulated towards thoracic tissues to a density 4 times higher than towards abdominal tissues, despite the larger surface area and volume of abdominal tissues. Mf migrated toward thoracic tissues regardless of whether or not contact with thoracic tissues was possible. Therefore, mf directed themselves toward the thorax rather than arresting their movement after they make contact with thoracic tissues. Chemical cue(s) provided a principal guidance for mf to locate thoracic tissues. Mf lost their ability to differentiate thoracic and abdominal tissues following addition of thoracic attractant(s) to excised abdomens and reversed their differential response when excised thoraces were depleted of chemical cue(s). Mf did not respond to salivary gland product, but to other thoracic factor(s). Intact thorax that was connected to 1-2 abdominal segments attracted considerably less mf than excised thorax. However, intact thorax attracted more mf than excised abdomen. Abdominal tissue size did not affect thorax attractiveness. Involvement of a large molecular weight protein(s) was suggested by the high attractiveness of the 100 kDa Centricon concentrator retentate and complete precipitation of attractant(s) by ethanol.

Animals↗