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PubMed1975

Factors influencing the passage of Onchocerca volvulus microfilariae into the urine.

The effect of various substances on the output of Onchocerca volvulus microfilariae in the urine was investigated in volunteers infected with the Cameroon forest and Sudan-savanna strains of the parasite. Output of microfilariae in the urine tended to be higher during periods of normal activity than during sleep. During waking hours, the rate of output remained generally steady, but in some patients occasional showers of microfilariae appeared in the urine, possibly associated with the intake of food and drink. Drinking 1.2-2.5 litres water produced a shower of microfilariae in the urine of some subjects. This began within an hour of drinking and its onset preceeded that of the diuresis. Thiazide diuretics, acting on the convoluted tubules, produced no increase in microfilaruria. In savanna subjects intravenous injection of DT TAB vaccine caused pyrexia, and simultaneously large numbers of microfilariae appeared in the urine. There was no associated diuresis, and no increase in the concentration of microfilariae in the venous blood. In forest subjects DT TAB caused no increase in microfilaruria. In all subjects 25-50 mg diethylcarbamazine (DEC) caused large numbers of microfilariae to appear in the urine on day 0, within a few hours of the first dose; and there was an increased output of urine over the first 24 hours. Microfilaruria declined sharply on day 1 of treatment, but in subjects developing a high microfilaraemia, it rose again on day 2, and declined more slowly thereafter. Betamethazone, given in conjunction with DEC, appeared to slow the rate of destruction of microfilariae in the skin and lymph glands, and to prolong the duration of microfilaraemia and microfilaruria. The findings suggest that there is a reservoir of microfilariae in the glomerular capillaries, which fills slowly by accumulating microfilariae from the circulating blood. The microfilariae probably enter the urine by penetrating the glomerular capillary.

Adult↗

PubMed1986

Longevity of microfilariae following removal of the adult worms.

The present study was undertaken to determine the longevity of a population of microfilariae in a natural host following the removal of the adult worms without drug intervention. Four squirrel monkeys previously infected with Dipetalonema gracile were allowed to develop stable microfilaremias. All adult worms were then removed surgically from the peritoneal cavity. Weekly microfilaria counts were made on each animal and the decline in microfilariae recorded. At the time of adult worm removal, microfilaremias ranged from 750 to 12,500 mf/ml. The observed decline in microfilaria densities was gradual, but steady, in all animals. Microfilariae persisted in 1-ml blood samples for 60, 62, 91, and 101 weeks following removal of adult worms. The results indicate clearly that in a naturally produced population, in a natural definitive host, microfilariae survive for 60 to 100 weeks. The gradual decrease in microfilarial densities would appear to be the result of the death of specific batches or broods of microfilariae. The microfilariae which persisted in the blood the longest undoubtedly represent those which were produced just prior to the removal of the adult worms. It is postulated that because of the long life-span of microfilariae, female worms are not called upon to produce a continual supply of microfilariae, nor is the need for mating as frequent as might be expected. Equally important, the number of microfilariae which the host is called upon to phagocytize is considerably smaller than previously suggested.

Animals↗

PubMed1979

Studies on Dipetalonema viteae (Filarioidea) 3. Antibody-dependent cell-mediated destruction of microfilariae in vivo.

Antibody-dependent cell-mediated destruction of Dipetalonema viteae microfilariae could be demonstrated in the golden hamster using a micropore chamber technique. Microfilariae were eliminated within 24 hours in chambers of 3.0 and 5.0 microm pore size when implanted into amicrofilaremic hamsters (week 30 post infection). At peak microfilaremia (week 12 post infection), only some hamsters could efficiently destroy microfilariae. In chambers with 0.3 microm pore size, microfilariae survived for more than 3 weeks in all hamsters. In uninfected hamsters, microfilariae could only be eliminated if they had been preincubated with serum or its 19S fraction containing antibodies to the cuticle of microfilariae. The opsonizing activity of the serum was abolished by 2-mercaptoethanol treatment. The composition of cells adhering to microfilariae was always significantly different from the composition of cells which migrated into a chamber. The adhesion patterns on individual microfilariae indicated that no single effector cell type was responsible for the destruction of microfilariae. The eosinophil was the predominant cell type but neutrophils, lymphocytes and monocytes also adhered to the microfilariae. Cellular adhesion led to the immobilization of microfilariae and subsequently to their disintegration within large cell clusters. During the final stages of destruction the contribution of the monocyte became more pronounced.

Animals↗

PubMed1979

The exsheathment of Brugia pahangi microfilariae under controlled conditions in vitro.

Two reproducible techniques for the exsheathment in vitro of microfilariae of Brugia pahangi, and other sheathed microfilariae, are described. Microfilariae were isolated from infected cat blood by filtration and suspended in Hank's Balanced Salt Solution. The first technique involved the incubation of isolated microfilariae for one hour in 20 mM CaCl2 in a phosphate-free Balanced Salt Solution, during which time approximately 90% of the microfilariae lost their sheaths. The second method of exsheathing microfilariae of B. pahangi involved exposure of microfilariae to solutions of endopeptidase (5.8 units/ml) or papaya extract protease (3.0 units/ml) in Ca2+-free HBSS. Exsheathment rates of 95--100% occurred within 30 minutes in both enzyme solutions. Both the Ca2+ ion and the endopeptidase technique have proven equally effective in stimulating exsheathment of microfilariae of Brugia malayi, Wuchereria bancrofti and Litomosoides carinii. Such artificially exsheathed microfilariae are used for in vitro cultivation studies. The viability of Ca2+- and endopeptidase-exsheathed microfilariae of B. pahangi has been confirmed by inoculation of exsheathed larvae into susceptible female mosquitoes.

Aedes↗

PubMed1988

Comparative densities of Wuchereria bancrofti microfilaria in paired samples of capillary and venous blood.

Concurrent finger-prick and venous blood samples were obtained from 43 patients infected with Wuchereria bancrofti. Microfilariae were counted in blood smears and on nuclepore filters. Based on the numbers of microfilariae in 20-microliters finger-prick samples, an expected (theoretical) number of microfilariae in venous samples was calculated. This expected value was compared to the actual number of microfilariae present in venous blood. The actual number of microfilariae present ranged from 0.7 to 30 times (median 3) less than expected. The exponential function y = 16.74e.17x, r2 = .69, where y = venous counts and x = capillary counts was found to accurately reflect the relationship between venous and capillary counts. Each unit (microfilaria) change in capillary blood would result in an expected 19% unit increase/decrease in venous blood. The results support strongly the theory that microfilariae are unevenly distributed in the blood system. The epidemiological implication is that persons with low or ultralow microfilaremia levels in venous blood may have a much greater pool of microfilaria available in capillaries. We believe that the present study explains, at least partially, why mosquitoes feeding on these kinds of microfilaria carriers (frequently) have a greater uptake fo microfilariae than expected.

Adolescent↗

PubMed1986

Loa loa: output of microfilariae in single pair infections.

The intent of the present study was to assess the production and release of microfilariae by a single female filaria, in an in vivo system. Experimental infections of Loa loa were established in baboons by implantation of juvenile worms, typically, one female and two or three males. Infected animals were bled weekly and the number of microfilariae counted. Microfilarial counts were converted to number of microfilariae per milliliter and then the total number of microfilariae present calculated for the total volume of blood. Weekly increases in microfilarial counts were calculated for each animal. During the primary wave of microfilariae, the average weekly increase ranged from 16,000 to 194,000 (ave. 74,000). This figure gave an average daily output of 10,000 microfilariae per female. During the secondary wave of microfilariae following splenectomy, the average weekly increase ranged from 83,000 to 270,000 (ave. 157,000), giving an average daily output of 22,000 microfilariae per female. It is postulated that this level of production occurs only during the early phase of infection and is markedly reduced after the microfilaremia plateaus. The results indicate that the shedding of microfilariae by the female worm does not occur necessarily on a daily or weekly basis, and that female worms do not shed uniform numbers of microfilariae over a given period of time.

Animals↗

PubMed1982

Experimental infection of mice with the microfilariae of Onchocerca lienalis.

Microfilariae of Onchocerca lienalis were obtained from the umbilical skin of naturally infected cattle and were injected into mice. Maximum numbers of microfilariae were recovered from the skin and ears of mice when using the subcutaneous route of inoculation. Microfilariae were distributed throughout the pinna of the ear but were concentrated towards the tip where histological sections showed them to be in the dermis and adipose tissue. Using the number of parasites recovered from the ears as an index of the intensity of infection it was found that inbred CBA/H T6T6 mice were one of the most susceptible of 11 strains of mice examined. No difference in susceptibility was found between male and female CBA mice of the same age, but marked differences were demonstrated between male CBA mice of different ages. After infection with 5 000 microfilariae the recovery of parasites from the ears increased rapidly to a peak at day 35 when 10% of the inoculum was recovered, and thereafter declined up to day 242. Over a range of inoculation doses examined it was found that there was a direct, linear relationship between the number of microfilariae recovered from the ears and the number in the inoculated dose. CBA mice showed marked resistance to reinfection with microfilariae. Six days after challenge with a secondary infection recoveries of microfilariae from the ears were only 26% of the level in challenge controls and fell to 3% of the level of controls by day 35. It is concluded that the model of O. lienalis microfilariae in CBA mice shows considerable promise as a tool for research into immunological responses to skin-dwelling microfilariae, which are the principal cause of pathology in onchocerciasis.

Aging↗

PubMedDate not supplied

Microfilariae in cytologic smears: a report of six cases.

BACKGROUND: Filariasis is a major public health problem in tropical countries, including India. Despite this high incidence, it is unusual to find microfilariae in fine needle aspiration cytology. (FNAC) smears and body fluids. Six cases of filariasis diagnosed by FNAC are reported. CASES: In case 1, a thyroid aspirate from a 23-year-old female showed a microfilaria with colloid and thyroid follicular cells. In case 2, pericardial fluid from a 50-year-old male with breathlessness and chest pain showed clusters of malignant cells and many microfilariae. In case 3, a bronchial aspirate from a 55-year-old male with fever and chest pain showed aggregates of acute inflammatory cells and a microfilaria. Cases 4 and 5 were lymph node aspirates from a 29-year-old male and 3-year-old female. Both smears showed microfilariae in a background of reactive lymphoid cells. In case 6, FNAC from a 21-year-old female with a cystic swelling in the breast showed clusters of microfilariae, lymphocytes and granular debris. CONCLUSION: In three of the six cases microfilariae were the cause of symptoms, whereas in the other three cases, microfilariae were associated with other diseases, including malignancy. Thus, careful screening of FNAC smears might be helpful in detecting microfilariae, even in asymptomatic patients.

Adult↗

PubMed1976

Onchocercal dermatitis: ultrastructural studies of microfilariae and host tissues, before and after treatment with diethylcarbamazine (Hetrazan).

Specimens of skin from four Cameroon patients with severe onchocercal dermatitis, before and after treatment with diethylcarbamazine (DEC), were studied by light and electron microscopy. Microfilariae of Onchocerca volvulus have ultrastructural features resembling those of microfilariae of other genera. Between the surface layer of the cuticle and the trilaminate membrane, there is an electrolucent zone which is much wider in degenerating microfilariae than in intact microfilariae. Widening of the zone may result from DEC-induced release of component(s) of the cuticle, possibly collagen or mucopolysaccharide. Between the cuticle and dermal collagen there are granular deposits which might be immune complexes involving the collagenous component of cuticle. Others have shown that DEC does not kill microfilariae in vitro. Treatment with DEC presumably "unmasks" microfilariae in the skin so that they are recognized as foreign bodies and are destroyed by the host's defenses. Histiocytes and eosinophils are seen in close proximity to degenerating microfilariae. Enzymes from histiocytes and eosinophils might readily penetrate the cuticle altered by DEC treatment, and digest various components within the microfilariae. Alternatively, the widening of the electrolucent zone might result directly from the action of leucocytic or histiocytic enzymes, after the microfilaria has been killed by other mechanisms.

Adult↗

PubMed1987

Lectin-binding characteristics of Wuchereria bancrofti microfilariae.

The binding of 10 different lectins to the surface of microfilariae of Wuchereria bancrofti has been investigated. Wheat germ agglutinin (WGA) and Helix pomatia lectin (HPA) bound specifically to the sheathed microfilariae indicating the presence of N-acetyl-D-glucosamine and N-acetyl-D-galactosamine respectively on the surface. Exsheathed microfilariae did not react with any of the lectins. Treatment of sheathed microfilariae with proteases resulted in increased binding of WGA and HPA. Such treated microfilariae showed a weak binding of Concanavalin A (Con A), and lectins of lentil (LCH) and of Limulus polyphemus (LPA). Sheathed microfilariae incubated with sera of people living in endemic zones of filariasis but with no apparent evidence of infection (endemic normals), or with sera of chronic elephantiasis patients, or with their respective gamma globulin fractions, bound Con A and LCH. These lectins bound weakly to exsheathed microfilariae under the same conditions. Binding was due to the mannose components of the specific immunoglobulins of the sera which coated the microfilariae. However, microfilariae when incubated with sera or their globulin fractions from non-endemic normals (NEN), or from microfilarial carriers, did not bind Con A and LCH, suggesting that specific immunoglobulins were neither present in NEN sera nor in significant amounts in sera of microfilarial carriers.

Acetylgalactosamine↗

PubMed1984

Deposition of eosinophil granule major basic protein onto microfilariae of Onchocerca volvulus in the skin of patients treated with diethylcarbamazine.

We investigated the association between eosinophil degranulation, as evidenced by the deposition of granule major basic protein (MBP), and the killing of microfilariae of Onchocerca volvulus in vivo following treatment with diethylcarbamazine (DEC). Utilizing an immunofluorescence procedure for the cellular and extracellular localization of eosinophil MBP in formalin-fixed, paraffin-embedded tissues, we studied skin biopsies from onchocerciasis patients before and during treatment with topically or orally administered DEC. Before DEC, there was little or no inflammatory response in either dermis or epidermis and microfilariae were essentially intact. Immunofluorescent staining for MBP revealed some filamentous fluorescence associated with dermal collagen fibers, very few eosinophils, and no fluorescence in association with intact microfilariae. In contrast, during treatment with DEC, immunofluorescent staining for MBP revealed extensive eosinophil infiltrates in both dermis and epidermis with numerous intraepidermal eosinophil abscesses containing degenerating microfilariae. An intense extracellular immunofluorescence for MBP surrounded degenerating microfilariae in the dermis and epidermis in both the presence and absence of eosinophil infiltrates as early as 4.5 hours after starting therapy. Many intact nondegenerating microfilariae were also present, but they did not show immunofluorescent staining for MBP nor a surrounding inflammatory infiltrate. The results show that immediately following administration of DEC, eosinophils localize and degranulate around microfilariae in the skin and release granule MBP onto or in close proximity to the parasite's surface. Because of the striking association between eosinophil localization, degranulation, and deposition of MBP onto microfilarial surfaces, and the degeneration of microfilariae in the skin, these observations support the hypothesis that the eosinophil, through helminthotoxic granule proteins such as MBP, damages the microfilariae of O. volvulus.

Adult↗

PubMed1983

Macro- and microfilariae in nodules from onchocerciasis patients in the Yemen Arab Republic.

Fourteen subcutaneous nodules from five patients with severe localized onchocerciasis, from one person with a mild dermatitis and from two men with the generalized form of the disease were studied. Ten nodules contained adult parasites with an average sex ratio of 1.6 for female to male worms. The median worm burden was two filariae per person. The onchocercomata of two patients with severe localized onchocerciasis comprised one or two pairs of microfilariae producing worms whereas the microfilaria load in the skin of these patients was estimated to have been less than 100 000 microfilariae. One nodule contained no intact microfilariae but more than 10 000 small granulomas with all stages of degenerating microfilariae whereas the density of 0.08 live microfilariae per milligram in the skin near to the nodule was very low. None of the patients had received antifilarial drugs before nodulectomy. It is concluded, therefore, that these patients with severe localized onchocerciasis possessed the capacity naturally to kill microfilariae. In the nodules of these patients many degenerating microfilariae were observed which were surrounded by eosinophils or macrophages or which lay in small abscesses with neutrophil leucocytes or in small granulomas. The adherence of eosinophil leucocytes to only slightly altered microfilariae could be observed as a first stage.

Adolescent↗

PubMed1980

Experimental infection of laboratory rodents and calves with microfilariae of Onchocerca gibsoni.

Uterine microfilariae of Onchocerca gibsoni migrated to skin of all parts of the body when inoculated into rats and mice. Higher microfilarial densities were obtained in the skin of mice compared with rats. In guinea pigs very few microfilariae migrated to the skin and densities of microfilariae were very low. Densities of skin microfilariae were lower in rats when inoculated intraperitoneally compared with inoculation by 2 subcutaneous routes. In the latter case, higher densities of microfilariae were obtained in areas of skin closer to the injection sites. Persistence of microfilariae in the skin of rats was variable but only low numbers were recovered between 21 and 70 days after infection. Microfilariae also migrated to the skin in calves experimentally infected by subcutaneous injection into the dewlap. Microfilaria were recovered consistently and in high numbers from skin snips along the ventral midline. Small numbers of microfilariae were occasionally found in skin snips from the dorsal midline.

Animals↗

PubMed1990

Distribution of microfilariae of Onchocerca lienalis and Onchocerca gutturosa in the skin of cattle in Germany and their development in Simulium ornatum and Culicoides nubeculosus following artificial infestation.

Onchocerca microfilariae were isolated form the umbilicus and neck of 438 cow hides at the abattoir in Tübingen, F.R.G. The overall Onchocerca infection rate was 40.4%. The presence of Onchocerca lienalis and O. gutturosa microfilariae, which are difficult to distinguish by morphological criteria, was retrospectively demonstrated after artifically infesting Simulium ornatum and Culicoides nubeculosus and identifying the infective larvae recovered. Nine of 16 samples of umbilical microfilariae fed to C. nubeculosus through a latex membrane developed to O. gutturosa third stage larvae (L3). Six of seven umbilical samples injected into the thorax of S. ornatum yielded O. lienalis L3. In six infestation trials in which microfilariae were introduced both into S. ornatum and C. nubeculosus, O. lienalis L3 were recovered exclusively from simuliids, while O. gutturosa L3 developed only in midges. Of six umbilical skins tested by cross-infestation, one contained exclusively O. gutturosa microfilariae, four only O. lienalis microfilariae and one was infected with both species. Developmental success of O. lienalis microfilariae to L3 in S. ornatum following intrathoracic injection was 22% of the mean inoculum. O. gutturosa microfilariae, ingested by C. nubeculosus through a latex membrane, developed to L3 at a rate of 2.3% of the mean microfilarial uptake.

Animals↗

PubMed1981

Serum-mediated adherence of feline granulocytes to microfilariae of Brugia pahangi in vitro: variations with parasite maturation.

Feline eosinophils and neutrophils readily adhered in vitro to the sheaths of microfilariae of Brugia pahangi in the presence of suitable serum. Both cell types flattened along the surface of the parasite undergoing cytoplasmic changes which included degranulation. Adherence was dependent on properties of both the serum and the history of the microfilaria used. Two types of serum factor were found to mediate adherence. Heat labile factors were present in sera from infected and uninfected cats as well as in sera from other species. They were removed by preincubation of sera with zymosan suggesting that complement components were involved. This suggestion was supported by the demonstration of C3 on the surface of microfilariae participating in adherence reactions. A heat stable factor, present in the serum of less than 10% of infected cats, also mediated adherence. This factor was demonstrated to be IgG by immunoadsorption and immunofluorescence. The ability of the microfilariae to participate in the adherence reaction mediated by complement factor varied with maturation of the parasite. Microfilariae obtained directly from the uteri of adult worms, or produced in vitro, did not possess the ability to participate in adherence. Young blood microfilariae (i.e. taken from the blood of cats recently patent) were similar to the in vitro produced parasites; however, the majority of blood microfilariae from infections of greater than three weeks patency participated in this form of adherence. No difference between blood and uterine/in vitro microfilariae was seen in adherence reactions mediated by heat stable antibody.

Animals↗

PubMed1992

Brugia malayi: ivermectin inhibits the exsheathment of microfilariae.

Brugia malayi-infected microfilaremic jirds (Meriones unguiculatus) were treated with ivermectin at a single dose of 200 micrograms/kg of body weight injected subcutaneously. Susceptible Aedes aegypti mosquitoes were fed on treated jirds 24 hours later. Mosquitoes fed on untreated jirds served as controls. Infected mosquitoes were dissected at 1, 3, 24, 48, 72, and 96 hr after the blood meal, and differential counts of sheathed microfilariae, exsheathed microfilariae, and cast sheaths were performed using fluoresceinated wheat germ agglutinin. Microfilariae failed to exsheath in mosquitoes fed on ivermectin-treated jirds. Microfilariae from ivermectin-treated jirds also did not exsheath in vitro in the presence of 10 mM CaCl2, whereas 85-90% of sheathed microfilariae from untreated jirds exsheathed in vitro. In addition, sheathed microfilariae from untreated jirds, when pretreated in vitro with ivermectin at 0.25, 0.5, or 1 microgram/ml, lost their ability to exsheath in vitro in the presence of 10 mM CaCl2. However, ivermectin treatment had no effect on exsheathing of microfilariae when incubated with papaya protease. Thus, ivermectin appears to inhibit the intrinsic exsheathing process of microfilariae in the mosquito host, thereby blocking their development and further transmission of infection.

Aedes↗

PubMed1987

Ivermectin effect on microfilariae of Onchocerca volvulus after a single oral dose in humans.

Ivermectin is a broad spectrum anti-helminthic agent which is currently being tested for use in human onchocerciasis. Its activity is believed to result from its effect on GABA-mediated neurotransmission. We examined the effects of ivermectin on motility of microfilariae of O. volvulus following administration to humans. When ivermectin was given in dosages of 100, 150 and 200 mcg/kg on day 1 there was a clear reduction in motility of microfilariae obtained on day 3 when compared to microfilariae from the placebo group. The mean motility scores in microfilariae from ivermectin recipients were 3.1, 2.3, and 2.2 at 0, 12, and 24 hours of incubation compared to 3.3, 2.9, and 2.5, respectively, in microfilariae from placebo recipients (p less than 0.003, p less than 0.005, and p less than 0.012, respectively). Examination of the effect according to dose suggested a dose-response relationship. Microfilariae in the anterior chamber of the eye 2 days after a single oral dose of ivermectin showed abnormal and reduced winding and coiling. Microfilariae in 50% of ivermectin recipients showed abnormal motility compared to no such effects in subjects examined concurrently who received oral DEC, DEC lotion or placebo. These observations indicate that ivermectin has an effect on motility of microfilariae of O. volvulus following administration to humans.

Animals↗

PubMed1984

Immunity to onchocerca lienalis microfilariae in mice. I. Resistance induced by the homologous parasite.

The model of Onchocerca lienalis microfilariae injected into inbred CBA/HT6T6 mice has been examined for its value to study immunity to the skin-dwelling microfilariae in onchocerciasis. Mice injected with living microfilariae during primary or secondary infections exhibited a high level of resistance to challenge relative to normal controls (91-98% reduction in recoveries). The survival of microfilariae during a primary infection was significantly prolonged in T-cell deprived animals compared with immunologically intact mice. Serum and spleen cells transferred from donors 90 days after infection conferred significant protection in syngeneic recipients to challenge with microfilariae (59% reduction in recoveries compared with controls). Boostered injections with freeze-killed or fragmented microfilariae reduced parasite recoveries after challenge by 39-78%: none of 5 adjuvant preparations enhanced the protective effect. Mice exposed to living infective larvae or adult males of O. lienalis also exhibited lowered recoveries of microfilariae following a challenge infection. It is concluded that the mouse model offers potential for immunological studies on the microfilariae in onchocerciasis, which have hitherto been limited because of the lack of suitable laboratory hosts.

Adjuvants, Immunologic↗