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PubMed2000

Litomosoides sigmodontis: dynamics of the survival of microfilariae in resistant and susceptible strains of mice.

Litomosoides sigmodontis in the BALB/c mouse is the only model of filariasis which allows the observation of the complete development in an immunocompetent mouse. In this study, we injected microfilariae (mf) intravenously, as well as into the pleural cavity, the site of natural release of mf from adult female worms, and followed the kinetics of elimination within the host. In susceptible BALB/c mice, mf circulated at high levels in the blood. In contrast, in C57BL/6 mice, which are refractory to full development, mf were eliminated rapidly from the peripheral blood. However, 6 days after intrapleural injection, viable larvae could be found in the pleural cavity and lung capillaries of both susceptible and resistant strains. The numbers of mf in the pleural cavity and lung capillaries in individual mice were significantly correlated, but not dependent on strain or peripheral microfilaraemia. Thus, although C57BL/6 mice showed enhanced production of nitric oxide by pleural exudate cells and a faster change in the numbers of circulating leukocytes after injection, rapid killing of mf by cell or nitric oxide-mediated mechanisms were not the reason for the different outcome. Furthermore, 3 h after iv injection, only a small percentage of mf could be recovered from the peripheral circulation, indicating the presence of a reservoir for mf containment. In conclusion, injected mf showed disparate dynamics of persistence within susceptible and resistant hosts, which is similar to the disparate outcome of natural infections with L. sigmodontis. This difference became obvious within 1 day after injection. The lung capillary system plays obviously a crucial part in regulation of microfilaremia. Our model also provides a possible means to explain frequent cases of occult infections in human filariasis.

Animals↗
PubMed2002

PCR based method for identification of zoonostic Brugia malayi microfilariae in domestic cats.

The survey of 326 human blood samples in the endemic area of Surat Thani and Narathiwat, the provinces in the south of Thailand, revealed that 5 of them were infected with Brugia malayi. Similarly, 53 feline blood samples were also investigated and found that 15 of the domestic cats were also infected with B. malayi. Upon the examination of human and feline blood specimens, a pair of human and domestic cat stayed in the same house and region. The periodicities of human B. malayi and feline B. malayi were similar as well as the results of Giemsa and acid phosphatase stained blood films of microfilaria positive cases. Likewise, the PCR-RFLP profile of Hha I repeat genes and PCR amplification of Trans-Spliced Leader Exon I (SLX) demonstrated that 15 samples the feline B. malayi were the same as those of human B. malayi. The data indicated that domestic cat plays an important role as the animal reservoir for B. malayi in the endemic areas of Thailand.

Animals↗
PubMed1986

The effect of diethylcarbamazine on microfilariae of Litomosoides carinii in vitro and in vivo.

Culture-derived Litomosoides carinii microfilariae (MFF) were used in in vitro and in vivo systems to investigate the effect of diethylcarbamazine (DEC) on these MFF. In vivo: Male rats, Mastomys natalensis, all of the same age, were injected intrathoracically (12) or intraperitoneally (36) with 10(3) or 10(4) MFF. After 30 min one half of each group of rats was given DEC per os. At 30, 60, and 120 min after DEC administration, two rats from the treated and two from the untreated group were bled and killed. The pleural or peritoneal cavities were rinsed with warm saline (0.15 M NaCl) to recover MFF. In both the intrathoracic and intraperitoneal experiments, equal numbers of MFF were recovered from treated and control rats at 30 and 120 min. However, at 60 min 85.5% fewer were recovered from the treated than from the nontreated animals. MFF were not found in the blood. In vitro: MFF were added to tissue culture dish wells (Linbro Div., Flow Labs, Hamden, Conn) prepared as follows: DEC-Serum (serum from normal rats given DEC at 500 mg/kg), DEC + Serum (serum with added DEC), serum only, RPMI 1640 only, and RPMI 1640 + DEC. Furthermore, the five treatments were prepared either with or without unstimulated peritoneal exudate (PE) cells. At 30 min in the DEC-Serum wells 45% of the MFF had adherent PE cells; in the remaining wells these cells adhered to 11% or fewer MFF. We interpret the aforementioned phenomena as representing the first step in the trapping and elimination of MFF after DEC treatment of L. carinii-infected M. natalensis.

Animals↗
PubMed1989

Scanning electron microscopic study of adults and microfilariae of Dunnifilaria meningica (Filarioidea: Onchocercidae).

Dunnifilaria meningica from naturally infected Neotoma micropus in Mexico were studied by scanning electron microscopy (SEM). The anterior end of adults is surrounded by two pairs of buccal and two pairs of cervical papillae. Two amphidial openings lie near the central mouth opening, surrounded by a thick cuticular ring. The cuticular surface of males and females shows fine transversal striations. At the posterior end of the male is a semicircular cloaca, a large preanal central papilla, two pairs of perianal and two pairs of postanal papillae. The short, strong, and almost equal spicules are rolled plates that end in a knob-shaped apex, showing a central groove. In the female, the vulva is located 550 microns from the anterior end. The inconspicuous anus is subterminally situated in the right ventrolateral portion of the posterior end. The anterior tip of the sheathed microfilariae is formed by a cap-like disk. Cuticular annulations were clearly demonstrated across the body.

Animals↗
PubMed1986

The ability of microfilariae to evade in vitro cell-mediated cytotoxicity.

When microfilariae (Mf) of Dirofilaria immitis, both uterine and systemic, were incubated in an in vitro cytotoxicity assay with neutrophils and sera from dogs with occult infections, some Mf remained free of adherent cells and consequently evaded cytotoxicity. The ability to evade cytotoxicity could not be related to the age of the Mf, and host albumin was not detected on any Mf, either uterine or systemic. However, it was shown that some Mf failed to bind IgM, IgG and C3 when incubated with occult sera. It is suggested that the ability of some Mf to evade serum-dependent, neutrophil-mediated cytotoxicity in vitro was related to differences in their antigenicity.

Age Factors↗
PubMed1991

The sheaths of Brugia microfilariae: isolation and composition.

Burgia malayi and B. pahangi microfilariae were isolated from the blood of infected Mastomys natalensis, and were exsheathed by freezing, thawing and agitation. Pure sheaths were obtained by a filtration procedure. The sheaths were found to contain about 95 mol% of amino acids, with proline, glutamic acid/glutamine, alanine, cysteine/cystine and glycine being the major components, and 5 mol% of carbohydrates, notably (N-acetyl)galactosamine, but no (N-acetyl)glucosamine.

Amino Acids↗
PubMed1991

The conditions required for the maintenance of Onchocerca lienalis microfilariae in vitro.

Microfilariae of the bovine parasite Onchocerca lienalis were maintained in vitro using a tick cell line as a feeder layer, and under the conditions provided would develop to the sausage stage. A number of media supported this achievement with CMRL 1066 producing the highest yields, particularly when used in conjunction with either medium 199, HAM's F-12, RPMI 1640 or Mark's M20. The addition of inactivated foetal calf serum (iFCS) suppressed development; on the other hand, the addition of tryptose phosphate broth (TPB) enhanced it. The pH range of the medium preferred by the developing worms was 7.35-7.85, and the most favourable osmolality lay in the range 360 to 390 mosM/kg. Insect-derived hormones did not improve yields of developed larvae nor promote moulting to the second larval stage. The culture conditions described in this work, which favour parasite survival and development, provide further insights into the physiological requirements of filariae as well as guide lines to achieving successful in vitro maintenance of Onchocerca sp. A morphological examination of the developing larvae was carried out at electron microscopical level.

Animals↗
PubMed1992

Eye lesions, blindness and visual impairment in the Taraba river valley, Nigeria and their relation to onchocercal microfilariae in skin.

2876 persons in fourteen communities in the Taraba River Valley, Nigeria were examined for eye lesions and tested for visual acuity using the 'tumbling E'. The individuals were also examined for microfilaria of Onchocerca volvulus. More than one-tenth of the population were blind, while another 16.1% had visual impairment. The prevalence of blindness was in excess of 20% in six communities, with one community recording 71.9% blindness rate. All forms of visual involvement increased with age but were similar between sexes. Eye lesions were related to the level of vision. Both eye lesions and vision deteriorate with increase in age. Vision seems to worsen with increase in prevalence and intensity of O. volvulus. Large microfilarial loads were associated with severe eye damage and blindness. These findings indicate that the Taraba river valley could be one of West Africa's worst foci of onchocercal blindness.

Adolescent↗
PubMed1993

Risk of infection of Wuchereria bancrofti to humans by Culex quinquefasciatus in Pondicherry and its relationship with microfilaria prevalence.

The risk of infection (RI) with Wuchereria bancrofti by vector mosquitoes has been conventionally estimated from the biting population of all age classes. This estimate of RI had no correlation with microfilaria (mf) prevalence and intensity of infection in humans. A new method for estimating RI from a resting population of Culex quinquefasciatus is proposed based on a longitudinal study in seventeen sites in Pondicherry, India. Unlike previous estimates, RI calculated by the present method considering the density of parous mosquitoes collected per man-hour and the mean number of infective stage larvae per parous mosquito significantly correlated with mf prevalence in humans during both early (r = 0.559; P = 0.038) and late in the control operation (r = 0.572; P = 0.033). RI varied significantly between the early and late in the control operation and different sites. On average, RI was reduced significantly during the control operation. Further epidemiological implications are discussed.

Analysis of Variance↗
PubMed1990

Dirofilaria immitis: effect on hemolymph polypeptide synthesis in Aedes aegypti during melanotic encapsulation reactions against microfilariae.

[35S]Methionine-labeled hemolymph polypeptides from adult, female Aedes aegypti Liverpool strain mosquitoes inoculated with the microfilariae of the filarial nematode Dirofilaria immitis were compared with those from saline-inoculated and uninoculated controls by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) followed by fluorography. SDS-PAGE analysis of cell-free hemolymph collected via perfusion at 6, 12, 24, 48, 72, and 96 hr postinoculation (PI) detected the enhanced expression of an 84-kDa polypeptide. This polypeptide, expressed constitutively in the hemolymph of all three groups of mosquitoes, increased considerably in inoculated mosquitoes as time progressed as compared with uninoculated controls. Moreover, the 84-kDa polypeptide was expressed at higher levels in D. immitis-inoculated mosquitoes than in saline-inoculated controls. This stimulation of de novo biosynthesis of the 84-kDa polypeptide in inoculated mosquitoes may play a role in the immune response of mosquitoes. Since it is likely that the wound healing response in insects involves many of the same chemical processes as occur in melanotic encapsulation reactions of mosquitoes against filarial worms, the preferential expression of the 84-kDa polypeptide in saline-inoculated mosquitoes seen in this study may reflect a wound healing response. The greater increase in synthesis of this protein in D. immitis-inoculated mosquitoes may reflect production of melanotic material required for parasite destruction as well as for wound healing.

Aedes↗
PubMed1990

Effect of gamma irradiation on the hemocyte-mediated immune response of Aedes aegypti against microfilariae.

The effect of gamma irradiation on the melanotic encapsulation response of Aedes aegypti black eye Liverpool strain against inoculated Dirofilaria immitis microfilariae (mff) was assessed at 1, 2, 3, and 6 days postinoculation (PI). Mosquitoes received 6000 rad from a 137Cs source (Shepard Mark I irradiator) at 3 days postemergence and were inoculated with 15-20 mff 24 hr later. These mosquitoes were compared to nonirradiated controls that also were inoculated with 15-20 mff at 3 days postemergence. The immune response was significantly reduced in irradiated mosquitoes as compared with controls at all days PI. Although the response was significantly inhibited compared with controls, irradiated mosquitoes were still capable of eliciting a response against 69% of recovered mff at 6 days PI. External gamma irradiation did not significantly affect the proliferation of hemocytes associated with the melanotic encapsulation response of A. aegypti. The number of circulating hemocytes increased in irradiated mosquitoes in response to inoculated mff in a manner similar to nonirradiated, inoculated controls. Hemocyte monophenol oxidase activity, however, was significantly reduced in gamma-irradiated mosquitoes at 12 hr PI as compared with controls. The reduced immunological capacity of irradiated mosquitoes might be related to an interference with gene activity required for the synthesis or activation of enzymes that are directly or indirectly involved in the biochemical processes associated with the production of melanotic substances that sequester mff.

Aedes↗
PubMed1982

Separation of viable and non-viable Onchocerca microfilariae using an ion exchanger.

A technique has been developed for separating viable and non-viable Onchocerca lienalis microfilariae (mff) by passing a suspension of the parasites through a column of DEAE cellulose. A proportion (between 42% and 87%) of normally motile parasites, whether unfrozen or cryopreserved, passed through the cellulose columns and retained their viability. Non-motile and sluggish mff were retained by the cellulose. The proportion of viable cryopreserved mff was greater after passage through the column as assessed by motility, migration in mice and development in the insect vector. Numbers of cryopreserved mff eluted through the columns peak quickly at a relatively high level after about 20 ml of eluate had been passed through, whereas normal unfrozen parasites rose and fell in numbers more slowly. By using sodium chloride gradients and buffers of differing conductivity it was concluded that the separation of the mff is probably due to net charge changes as well as motility. It is believed that this technique offers considerable promise as a tool to provide populations of mff of more uniform viability following freezing and thawing with existing cryopreservation techniques.

Animals↗
PubMed1983

Distribution of microfilariae in Guatemalans with onchocerciasis.

Ten Simulium ochraceum were allowed to feed at 10 different sites on 12 Guatemalans with onchocerciasis, and skin snips were taken from six of these sites. Numbers of microfilariae (mff) ingested by the flies and mff emerging from skin snips were highly correlated and showed that concentrations were greatest on the torso and decreased peripherally. S. ochraceum ingested the number of mff present in 1.0 mg or under 1.5 mm2 of skin. Numbers of mff in skin snips from the head, shoulder and upper arm correlated with over-all levels of infection but were frequently negative in subjects with light infections. Two or more skin snips were best able to detect and quantify infections.

Animals↗
PubMed1987

Distribution of vectors, transmission indices and microfilaria rates of subperiodic Wuchereria bancrofti in relation to village ecotypes in Samoa.

Aedes polynesiensis and Ae. samoanus biting densities and Wuchereria bancrofti infection and infective rates were studied in 47 villages throughout the islands of Samoa Upolu, Manono and Savaii during 1978-79, and microfilaria (mf) rates were surveyed in 28 of the villages. The mf rate was correlated with both infection and infective rates of Ae. polynesiensis in Upolu, but not of Ae. samoanus. In Upolu, Ae. polynesiensis was apparently the major vector. It was relatively more abundant in more cultivated and populated areas, along the northern coast of Upolu, except Apia town area. In Savaii, Ae. samoanus predominated over Ae. polynesiensis except in "plantation" villages. Relatively high biting densities and rates of infection and infectivity indicated that Ae. samoanus was not less important than Ae. polynesiensis as a vector in Savaii. Ae. samoanus preferred natural vegetation, in contrast to Ae. polynesiensis which was found near human habitations in cultivated land. There was no difference between the biting densities of Ae. polynesiensis in "coastal" and "inland" villages, indicating that crab holes (numerous only in some coastal villages) may not influence the density of Ae. polynesiensis. Higher mf rates were associated with villages where Ae. polynesiensis, rather than Ae. samoanus, was dominant, indicating that Ae. polynesiensis was generally a more efficient vector. In the former villages, the difference in mf rates between males and females was smaller than in the latter, probably reflecting a difference in biting habits of the vectors. Ae. polynesiensis infections were recorded in plantations over 2 km from any village, suggesting that both habitats were foci of transmission.

Adolescent↗
PubMed1988

Factors affecting transmission of Wuchereria bancrofti by anopheline mosquitoes. 1. Uptake of microfilariae.

Ingestion of Wuchereria bancrofti microfilariae (mf) from humans by 639 Anopheles gambiae, 557 An. arabiensis, 117 An. melas and 9 An. funestus was investigated. The mf densities in blood fell into 3 groups; 0-32mf/ml, 107-122 mf/ml and 421-1140 mf/ml. In An. gambiae and An. arabiensis percentage of mosquitoes ingesting mf was strongly associated with mf density in host blood; in An. melas the association was much weaker. Mean number of mf ingested per mosquito was also strongly correlated to mf density in An. gambiae and An. arabiensis but not in An. melas. At low mf densities both An. gambiae and An. arabiensis concentrated mf, with concentration decreasing as density increased. From regression analysis, observed and expected uptake of mf would be equal at 622.9 mf/ml in An. gambiae and 391.6 mf/ml in An. arabiensis.

Adult↗
PubMed1988

Factors affecting transmission of Wuchereria bancrofti by anopheline mosquitoes. 2. Damage to ingested microfilariae by mosquito foregut armatures and development of filarial larvae in mosquitoes.

Microfilariae (mf) of Wuchereria bancrofti from the midgut of 639 Anopheles gambiae, 557 An. arabiensis, 117 An. melas and 9 An. funestus were examined immediately after the mosquitoes had fed on carriers with different densities of mf. The percentages of mf damaged during ingestion were 57.1-60.0 in An. gambiae, 33.3-50.6 in An. arabiensis and 38.7-55.7 in An. melas. In each species the percentage of mf damaged was independent of mf density in the human host. A further 3657 An. gambiae, 2875 An. arabiensis, 347 An. melas and 32 An. funestus were examined 7 d or more after feeding on mf carriers. In An. gambiae and An. arabiensis, mean numbers of larvae per mosquito were strongly correlated to mf blood density, with similar regression slopes to those obtained from the regression of mf blood density on mean uptake of mf/mosquito. The ratio of mean numbers of larvae per mosquito to mean numbers of intact mf ingested per mosquito increased as the density of mf in the human host increased in An. gambiae and An. arabiensis, but decreased in An. melas as host mf density increased.

Animals↗
PubMedDate not supplied

Factors affecting transmission of Wuchereria bancrofti by anopheline mosquitoes. 3. Uptake and damage to ingested microfilariae by Anopheles gambiae, An. arabiensis, An. merus and An. funestus in east Africa.

Laboratory observations were made on the uptake of microfilariae (mf) of Wuchereria bancrofti by Anopheles gambiae, An. arabiensis, An. merus and An. funestus. Over host mf densities ranging from 450/ml to 1735 mf/ml neither the percentage of mosquitoes ingesting mf nor the mean number of mf per mosquito was correlated to host mf density. All mosquito species damaged mf during ingestion but the proportion harmed was independent of host mf density. The mean proportion damaged was 0.67 in An. gambiae, 0.51 in An. merus, 0.47 in An. Arabiensis and 0.26 in An. funestus. A comparison of the mean number of undamaged mf ingested and the number of larvae in the thoracic muscles revealed that not all undamaged mf were able to reach the thoracic muscles.

Africa, Eastern↗
PubMedDate not supplied

Ecdysteroid-like compounds in the serum and urine of African patients infected with Loa loa and Mansonella perstans microfilariae.

Ecdysteroids are compounds related to 20-hydroxyecdysone, the insect moulting hormone. Surprisingly, they have been found in serum and urine of patients infected with helminths. In these cases, the substances are assumed to be produced by the parasites and, therefore, might be used as a marker of parasitic infection. Thus, we need to know exactly which species, at which developmental stage, can release ecdysteroids in such large quantities that they could be detected in the biological fluids of the host. Large-scale investigations must, accordingly, be devoted to the major species of helminths. In the present study, we examined 100 African patients with Loa loa and/or Mansonella perstans microfilaraemia. About 70 of them had high levels of ecdysteroid-like materials in serum or urine. In contrast, uninfected patients and European controls had much lower concentrations. However, the ecdysteroid titres did not reflect the concentration of microfilariae actually present in the blood, and some heavily infected patients were even negative. Nevertheless, the most important point was that high ecdysteroid levels in man were always associated with a pathological condition. The precise significance of the phenomenon should be determined.

Adult↗