Ingestion Of Microfilariae Research Articles

A simple isothermal DNA amplification method to screen black flies for Onchocerca volvulus infection.

Onchocerciasis is a debilitating neglected tropical disease caused by infection with the filarial parasite Onchocerca volvulus. Adult worms live in subcutaneous tissues and produce large numbers of microfilariae that migrate to the skin and eyes. The disease is spread by black flies of the genus Simulium following ingestion of microfilariae that develop into infective stage larvae in the insect. Currently, transmission is monitored by capture and dissection of black flies and microscopic examination of parasites, or using the polymerase chain reaction to determine the presence of parasite DNA in pools of black flies. In this study we identified a new DNA biomarker, encoding O. volvulus glutathione S-transferase 1a (OvGST1a), to detect O. volvulus infection in vector black flies. We developed an OvGST1a-based loop-mediated isothermal amplification (LAMP) assay where amplification of specific target DNA is detectable using turbidity or by a hydroxy naphthol blue color change. The results indicated that the assay is sensitive and rapid, capable of detecting DNA equivalent to less than one microfilaria within 60 minutes. The test is highly specific for the human parasite, as no cross-reaction was detected using DNA from the closely related and sympatric cattle parasite Onchocerca ochengi. The test has the potential to be developed further as a field tool for use in the surveillance of transmission before and after implementation of mass drug administration programs for onchocerciasis.

Experimental studies on the transmission of Onchocerca volvulus by its vector in the Sanaga valley (Cameroon): Simulium squamosum B. Intake of microfilariae and their migration to the haemocoel of the vector.

As large-scale ivermectin distribution is becoming the mainstay of onchocerciasis control in Africa, the issue of its impact on local transmission is increasing in importance. The vector competence of Simulium squamosum B in the severe focus of the Sanaga valley, Cameroon, was therefore investigated, by feeding 1320 flies on 14 carriers of Onchocerca volvulus microfilariae (mff). The results enabled the relationships between skin microfilarial load, microfilarial intake by the flies, the proportion and mean number of ingested mff that succeed in reaching the fly's haemocoel, and the frequency distribution of the ingested mff to be described, as functions of time post-engorgement (p.e.) and parasite density (while taking account of possible measurement error in the predictor variable). The proportion of flies with haemocoelic mff and the mean number of mff/fly increased up to 3 h p.e. The proportion of flies with ingested mff was non-linearly related to mean intake, via the negative-binomial distribution, with the overdispersion parameter k best described as an increasing (power) function of the mean. Approximately one in every three ingested mff escaped imprisonment by the peritrophic matrix, irrespective of the skin microfilarial load or the intake of mff. The relationship between successful and input mff is nearly linear (indicating proportionality) in S. squamosum B. These results are compared with those from O. volvulus-S. damnosum s.l. combinations in other West African foci.

Bloodmeal microfilariae density and the uptake and establishment of Wuchereria bancrofti infections in Culex quinquefasciatus and Aedes aegypti.

The relationship between ingestion of microfilariae (mf), production of infective larvae (L3) and mf density in human blood has been suggested as an important determinant in the transmission dynamics of lymphatic filariasis. Here we assess the role of these factors in determining the competence of a natural vector Culex quinquefasciatus and a non vector Aedes aegypti to transmit Wuchereria bancrofti. Mosquitoes were infected via a membrane feeding procedure. Both mosquito species ingested more than the expected number of microfilariae (concentrating factor was 1.28 and 1.81 for Cx. quinquefasciatus and Ae. aegypti, respectively) but Cx. quinquefasciatus ingested around twice as many mf as Ae. aegypti because its larger blood meal size. Ae. aegypti showed a faster mf migration capacity compared to Cx. quinquefasciatus but did not allow parasite maturation under our experimental conditions. Similar proportions of melanized parasites were observed in Ae. aegypti (2. 4%) and Cx. quinquefasciatus (2.1%). However, no relationship between rate of infection and melanization was observed. We conclude that in these conditions physiological factors governing parasite development in the thorax may be more important in limiting vectorial competence than the density of mf ingested.

Density-dependent processes in the transmission of human onchocerciasis: intensity of microfilariae in the skin and their uptake by the simuliid host.

The transmission success of Onchocerca volvulus is thought to be influenced by a variety of regulatory or density-dependent processes that act at various points in the two-host life-cycle. This paper examines one component of the life-cycle, namely, the ingestion of microfilariae by the simuliid vector, to assess the relationship between intake of larvae and the density of parasites in the skin of the human host. Analysis is based on data from three areas in which onchocerciasis is endemic and includes published information as well as new data collected in field studies. The three areas are: Guatemala (Simulium ochraceum s.l.), West and Central Africa (savanna members of the S. damnosum complex), and South Venezuela (S. guianense). The data record experimental studies of parasite uptake by flies captured in the field and fed to repletion on locally infected subjects who harboured varying intensities of dermal microfilarial infection. Regression analyses of log transformed counts of parasite burdens ingested by the flies plotted against log transformed counts of microfilariae per mg of skin revealed little evidence for saturation in parasite uptake by the flies as the intensity in the human host increased. There was a positive and highly significant rank correlation between both variables for the three blackfly species. In an alternative analysis a model was fitted to data on prevalence of flies with ingested microfilariae (mff) versus dermal mean intensities. The model assumed an overdispersed distribution of the number of mff/fly and a given functional relationship between intake and skin load. The results of both approaches were consistent. It is concluded that parasite ingestion by the vector host is not strongly density dependent in the three geographical areas and ranges of dermal loads examined. It therefore appears that this transmission process is of reduced importance as a regulatory mechanism in the dynamics of parasite population growth.

Effect of ivermectin on two filaria-vector pairsBrugia malayi-Aedes aegypti ; Litomosoides sigmodontis-Bdellonyssus bacoti1

The effect of ivermectin was studied on two filaria-vector pairs, Brugia malayi-Aedes aegypti and Litomosoides sigmodontis-Bdellonyssus bacoti. The rodent hosts, respectively Mastomys coucha and Meriones unguiculatus, were treated with ivermectin doses of 0.05 mg/kg, or 0.2 mg/kg or 2 mg/kg. Batches of vectors were fed on rodents, infected or not, treated or not, from H7 to D43 post-ivermectin. Vector survival was observed and dissections were performed to study the filarial development. It appears that ivermectin has no systemic effect on vectors, or very little. The drug acts on transmission because it affects the microfilariae. Transmission of L. sigmodontis is blocked because microfilariae are eliminated from the blood. Transmission of B. malayi is blocked although microfilaremia remains present at a low level. Two particular features are observed: microfilariae are hyper-ingested, but they do not cross the stomach wall (in contrast, they cross at a high rate in the control batch of Aedes, due to the "stomach wall limitation"). These events might be explained by a muscular passivity of the microfilariae treated with ivermectin. Transmission of the two filarioid species is restored normally about D25-40 post ivermectin because a new population of microfilariae has appeared. These ivermectin experiments emphasize the diversity and complexity of two important phases of the filarial cycle in the vector: the ingestion of microfilariae and the passage through the stomach wall.

The filariaLitomosoides galizaiin mites; microfilarial distribution in the host and regulation of the transmission

The mites, Bdellonyssus bacoti, are engorged on rodents having 800 to 60,000 microfilarie/10 mm3 blood. Quantitation of L. galizai larval development shows that an additional blood meal improves development and that high microfilaremiae do not result in a proportional increase in the number of infective larvae. The first important stage of transmission regulation occurs during ingestion of microfilariae: the numbers of ingested microfilariae are lower than expected in cases of high microfilaremia. This phenomenon cannot be ascribed to the mite vector that engorges a constant blood meal whatever the level of microfilaremia. Contrarily, one finds that microfilarial density in the small peripheral blood vessels (blood drawn from incision of the dorsal skin) increases less than in large blood vessels (retro-orbital sinus). A similar observation was reported by Dickerson et al. (1989) working with Wuchereria bancrofti. We assume that in both cases, the high microfilaremiae cause the small blood vessles accessible to the vector to become saturated with parasites. Although regulation during engorging is not the sole factor to monitor the infection in B. bacoti (another one operates during larval development of L. galizai), demonstrating its existence seems to us fundamental: it points out the concept that sub-ingestion, as well as over-ingestion, shows the inequalities of microfilarial densities in the host which seem to be dependent on mechanical factors such as the diameter of blood vessles and the size of microfilariae.

Ingestion of microfilariae from different sources by Culicoides nubeculosus (Diptera: Ceratopogonidae) through an artificial membrane

Laboratory-hatched Culicoides nubeculosus midges were membrane-fed on cattle blood containing various Onchocerca microfilariae which had been isolated from the hides of red deer ( Cervus elaphus) and from Australian and native German cattle. All microfilariae were ingested through the membrane except those of O. tarsicola, which were too large. Onchocerca gibsoni and O. lienalis reached the thoracic musculature, but no further development occurred. Microfilariae of O. flexuosa developed to the “sausage” stage. Microfilariae of O. gutturosa developed to the infective larval stage within 9 days at a temperature of 25°C.

中米グァテマラにおけるオンコセルカ症伝搬ブユ その研究のあゆみと最近の知見

The present paper was read as a special presentation at the 31st annual meeting of Southern Region of the Japan Society for Sanitary Zoology held at Kumamoto on November 7, 1981. It reviews chiefly the recent advances of knowledge on the biology and ecology of the adult blackflies in relation to the transmission of onchocerciasis in Guatemala and also outlines the history of the research work carried out during the period from 1915 when Dr. R. Robles discovered onchocerciasis in his country, to the present time. The contents are summarized as follows : 1) Simulium ochraceum, S. metallicum and S. callidum were incriminated as the vectors of onchocerciasis in Guatemala on the basis that they were naturally infected with the third-stage larvae of Onchocerca calculus, whereas S. gonzalezi, S. haematopotum, S. veracruzanum and S. horacioi were regarded as potential vectors due to their capability of supporting the larval development to the third stage experimentally. 2) With regard to the fate and migration of microfilariae of O. calculus larvae, it was reported that the numbers of microfilariae taken up by the three vector species mentioned above were usually larger than might be expected considering the microfilarial density in the skin. The percentage of the microfilariae developing to the third stage per individual females was very low, ranging from 0.2 to 4.3%. The decrease in the number of the larvae was caused by various factors differing between the blackfly species. In S. ochraceum most microfilariae ingested were damaged and killed by the toothed buccopharyngeal armature when they passed through, and only a few larvae could reach the thorax where most of them developed to the third stage. Whereas, in S. metallicum which had no such armature as a barrier, about 70% of the microfilariae ingested could penetrate through the wall of the midgut, but in the thoracic muscles inefficient development occurred with many undeveloped and/or abnormally formed larvae still remaining even after the normal period required for the completion of the larval development. The proportion of S. ochraceum fed on an O. volvulus-microfilariae carrier becoming infected with the third-stage larvae was three times higher than that of S. metallicum. This difference was mainly due to the latter vector's high mortality within 24 hours after ingestion of microfilariae usually observed when large numbers of microfilariae were ingested. 3) Concerning biological and ecological aspects of the vectors, it was shown that S. ochraceum was highly anthropophilic but S. metallicum and S. callidum were more zoophilic. The most predominant anthropophilic species were S. ochraceum and S. metallicum, although their relative proportion differed between localities, by months and even within a day. The proportions of the parous females of these two vectors caught on man also varied greatly depending on the situation. The duration of the gonotrophic cycle of S. ochraceum was estimated as two to four days in nature. 4) Among the factors influencing the transmission, various degrees of microfilarial densities in the skin were assessed in terms of the infection rate of the blackflies by the third-stage larvae, and it was shown that even a person with very low microfilarial density such as 0.5 mf/mg in the skin could become a source of infection, yielding a low percentage of S. ochraceum females harbouring the infective larvae. It was reported that the temperature greatly influenced the development of O. volvulus larvae in S. ochraceum and also the latter's longevity. The development of larvae to the third stage took place between 18 and 30°C, and its duration ranged from four to 13 days increasing with the decrease in temperature.

The contributions of different age groups to the transmission of onchocerciasis in a cameroon forest village

The population of 3 rain-forest villages, heavily infected with O. volvulus, were divided into age and sex groups. Samples from each group were studied with regard to total numbers of nodules; concentrations of mf. per mg. in calf skin snips; intake of microfilariae by, and numbers of infective larvae developing in, groups of S. damnosum fed on their lower legs. The theoretical contribution of each age and sex group to the over-all transmission of O. volvulus in the village is calculated, and the value predicted by experiment for the whole village is compared with the value recorded under natural conditions from dissections of wild flies.

Experimental studies on the transmission of Guatemalan and West African strains of Onchocerca volvulus by Simulium ochraceum, S. metallicum and S. callidum

The distribution of O. volvulus microfilariae in the skin of Guatemalan patients is described, and compared with the distribution of the bites of S. ochraceum, S. metallicum and S. callidum. Full development of the microfilariae of the Guatemalan strain of O. volvulus was recorded on a quantitative basis in large numbers of S. ochraceum, S. metallicum and S. callidum from the Finca El Amparo in an endemic onchocerciasis zone; and similar development in the same species was observed at the Finca El Faro in a zone where no endemic onchocerciasis has been reported. S. ochraceum, S. metallicum and S. callidum are compared in regard to (a) the ingestion of microfilariae, (b) survival after infected blood meals, (c) development of infective larvae, and (d) probable potentialities as vectors in the field. A 10–25-fold concentration of microfilariae of the Guatemalan strain of O. volvulus was observed in feeding S. ochraceum, S. metallicum and S. callidum, and it is suggested that this phenomenon might make possible the use of a xenodiagnostic test. Quantitative observations were made on the intake and development of West African forest and sudan savanna strains of O. volvulus in Guatemalan simuliids, and comparison is made with those seen in S. damnosum. Central American onchocerciasis is considered to be an indigenous infection differing in many respects from the African disease.

Studies on the intake of microfilariae by their insect vectors, their survival, and their effect on the survival of their vectors. X. The survival of the tropical rat mite, the vector of filariasis in the cotton rat.

Studies on the intake of microfilariae by their insect vectors, their survival, and their effect on the survival of their vectors. X. The survival of the tropical rat mite, the vector of filariasis in the cotton rat.

Studies on the Intake of Microfilariae by their Insect Vectors, their Survival, and their Effect on the Survival of their Vectors

(1955). Studies on the Intake of Microfilariae by their Insect Vectors, their Survival, and their Effect on the Survival of their Vectors. Annals of Tropical Medicine & Parasitology: Vol. 49, No. 1, pp. 114-120.

Studies on the Intake of Microfilariae by their Insect Vectors, their Survival, and their Effect on the Survival of their Vectors

Studies on the Intake of Microfilariae by their Insect Vectors, their Survival, and their Effect on the Survival of their Vectors

Studies on the intake of microfilariae by their insect vectors, their survival, and their effect on the survival of their vectors. VII. Further observations on the intake of the microfilariae of Dirofilaria immitis by Aedes aegypti in laboratory conditions: the pattern of the intake of a group of flies.

Studies on the intake of microfilariae by their insect vectors, their survival, and their effect on the survival of their vectors. VII. Further observations on the intake of the microfilariae of Dirofilaria immitis by Aedes aegypti in laboratory conditions: the pattern of the intake of a group of flies.

Studies on the intake of microfilariae by their insect vectors, their survival, and their effect on the survival of their vectors. VI. Further observations on the intake of the microfilariae of Loa loa and Acanthocheilonema perstans by Chrysops silacea in laboratory conditions: the pattern of the intake of a group of flies.

(1955). Studies on the Intake of Microfilariae by their Insect Vectors, their Survival, and their Effect on the Survival of their Vectors. Annals of Tropical Medicine & Parasitology: Vol. 49, No. 1, pp. 114-120.

Studies on the intake of microfilariae by their insect vectors, their survival, and their effect on the survival of their vectors. V. The survival of Loa loa in chrysops silacea under laboratory conditions.

(1954). Studies on the Intake of Microfilariae by their Insect Vectors, their Survival, and their Effect on the Survival of their Vectors. Annals of Tropical Medicine & Parasitology: Vol. 48, No. 3, pp. 340-344.

Studies on the intake of microfilariae by their insect vectors, their survival, and their effect on the survival of their vectors. IV. The survival-rate of Chrysops under laboratory conditions, and the effect upon it of Loa loa.

Studies on the intake of microfilariae by their insect vectors, their survival, and their effect on the survival of their vectors. IV. The survival-rate of Chrysops under laboratory conditions, and the effect upon it of Loa loa.

Studies on the intake of microfilariae by their insect vectors, their survival, and their effect on the survival of their vectors. III. The intake of the microfilariae of Acanthocheilonema perstans by Culicoides austeni and C. grahamii.

Studies on the intake of microfilariae by their insect vectors, their survival, and their effect on the survival of their vectors. III. The intake of the microfilariae of Acanthocheilonema perstans by Culicoides austeni and C. grahamii.

Studies on the intake of microfilariae by their insect vectors, their survival, and their effect on the survival of their vectors. II. The intake of the microfilariae of Loa loa and Acanthocheilonema perstans by Chrysops spp.

(1954). Studies on the Intake of Microfilariae by their Insect Vectors, their Survival, and their Effect on the Survival of Their Vectors. Annals of Tropical Medicine & Parasitology: Vol. 48, No. 1, pp. 102-109.

Studies on the intake of microfilariae by their insect vectors, their survival, and their effect on the survival of their vectors. I. Dirofilaria immitis and Aëdes aegypti.

Studies on the intake of microfilariae by their insect vectors, their survival, and their effect on the survival of their vectors. I. Dirofilaria immitis and Aëdes aegypti.