Radiolabeling of Brugia malayi infective larvae in mosquitoes with 75Se-methionine and detection of these larvae in tissues of the Mongolian jird by autoradiography

Through preliminary experiments, an effective method for radiolabeling Brugia malayi-infected mosquitoes in order to produce labeled infective Brugia larvae was developed. Starting on the 6th day after the infective blood meal, mosquitoes were fed a 7% sucrose solution containing 100 microCi/ml 75Se-L-methionine for 5 days. Infective larvae, retrieved 2 days after this labeling period, averaged 381 +/- 136 counts/min. Jirds were infected with these infective, labeled larvae either by allowing infected mosquitoes to feed on uninfected jirds for 30 min or by inoculating jirds subcutaneously in the groin with washed larvae recovered from mosquitoes. Jirds were killed at various times after infection and were sliced into approximately 0.5 mm thick sagittal sections, which were dried and placed on X-ray film. Autoradiograms were developed after 30-60 days at 5 degrees C. In a sample of 26 inoculated jirds, approximately 30% of the infecting larvae could subsequently be accounted for as Ag degrees foci on autoradiograms. The Ag degrees foci representing larvae were apparent up to 2.5 weeks after infection. In jirds infected by mosquito feeding, the Ag degrees associated with the feeding site persisted for more than 6 weeks after infection.

Brugia pahangi: antibodies and microfilaremias in Lewis rats

Male and female Lewis rats were inoculated subcutaneously in the left groin with 75 infective larvae of Brugia pahangi and microfilaremias were followed for as long as 420 days postinoculation. Patent infections developed in 64% of the female rats and 95% of the male rats. Mean prepatent periods were similar (65.9 and 63.9 days, respectively), but mean microfilaremias in males rose much higher, to a mean of 218 mf/0.25 ml blood at 270 days postinoculation. IgG titers, as measured by enzyme-linked immunosorbent assay (ELISA), to adult worm somatic antigen were higher than those to microfilariae in almost all rats. For both sexes, the most consistently microfilaremia rats had highest titers to these antigens. Granulomas with degenerating microfilaria were present in the spleen of male rats with high microfilaremias (greater than 100-300 mf/0.25 ml blood). Ouchterlony precipitin reactions suggested that most rats with spleen granulomas responded to microfilarial antigen components to which most rats without granulomas did not. Neither spleen granulomas nor antibody responses measured in this study appeared to have protective (microfi8laremia-lowering) value. As measured by microfilaremias, the male Lewis rat is not as susceptible as some conventional hosts of B. pahangi, but it does consistently become infected and remains microfilaremic for more than a year. Preferential male susceptibility indicates that this model may be useful for studying this aspect of human lymphatic filariasis.

Effects of serum from treated patients on antibody-dependent cell adherence to the infective larvae of Brugia malayi

Adherence assays were used to demonstrate the in vitro effect of serum-dependent cellular adherence of human buffy coat cells to infective larvae of Brugia malayi in filariasis patients treated with antifilarial drugs. In this study, microfilaraemic patients were treated with either diethylcarbamazine citrate (DEC), mebendazole or levamisole hydrochloride. It was found that DEC and mebendazole decreased the motility of infective larvae due to a direct action of the drugs. Sera of levamisole-treated patients caused increased adherence of human buffy coat cells to infective larvae, leading to a decrease in motility and cuticular damage as confirmed by scanning electron microscopic studies. However, serum of levamisole-treated patients alone could cause a similar lethal effect on infective larvae. Studies with the indirect fluorescent antibody test suggested that IgM was involved in this phenomenon. Complement did not appear to be important.

Successful cryopreservation of Brugia pahangi third-stage larvae in liquid nitrogen

Experiments are described which lead to the retention of infectivity of Brugia pahangi third-stage larvae after cooling to -196 degrees C. Methanol, a well documented cryoprotectant was used at a concentration of 20% (v/v). The schedule consisted of a 5 degrees C min-1 cool to an intermediate temperature of -21 degrees C and a subsequent rapid cool into liquid nitrogen. A rapid thaw of the parasites led to approximately 34% of motile cryopreserved larvae developing in multimammate rats (Mastomys natalensis) compared to unfrozen control larvae. Cooling rate and intermediate temperature were both found to be crucial variables affecting survival levels of the larvae.

The number and distribution of Brugia pahangi in cats at different times after a primary infection

The number of larvae and adults of Brugia pahangi and their distribution throughout the lymphatics and extra-lymphatic tissue were studied in cats infected by subcutaneous injection of larvae into their hind feet. For the first 20 days approximately 55% of the inoculum is recovered as living worms. After 25 days the recovery falls by a half. It is suggested that this loss of worms may be due to either the developing immunological response or the moult from the 4th to the 5th stage. Larvae penetrate the lymphatics rapidly (50% within 3 h) and migrate to the popliteal lymph node after about 20 days they migrate back down into the afferent lymphatic.

Brugia malayi microfilariae from the peritoneal cavity of jirds vary in their ability to penetrate the mosquito midgut

Development in mosquitoes of Brugia malayi microfilariae obtained from the blood of jirds was compared to that of microfilariae from the peritoneal cavity. Penetration of the mosquito midgut wall as well as development into third-stage larvae was assessed. About 70% of blood-borne microfilariae penetrated the midgut wall whether ingested directly from a microfilaremic jird or from a membrane feeder containing blood from the same donor. In contrast, less than 30% of microfilariae from the peritoneal cavity penetrated the midgut wall. Microfilariae in the peritoneal cavity of jirds vary in ability to penetrate the midgut of mosquitoes; some penetrate as rapidly as do blood-borne microfilariae, others penetrate more slowly, and most fail to penetrate the midgut. Regardless of origin, microfilariae that penetrated the midgut wall developed into third-stage larvae.

Periodicity of microfilariae of human filariasis analysed by a trigonometric method (Aikat and Das)

The microfilarial periodicity of human filariae was characterized statistically by fitting the observed change of microfilaria (mf) counts to the formula of a simple harmonic wave using two parameters, the peak hour (K) and periodicity index (D) (Sasa & Tanaka, 1972, 1974). Later Aikat and Das (1976) proposed a simple calculation method using trigonometry (A-D method) to determine the peak hour (K) and periodicity index (P). All data of microfilarial periodicity analysed previously by the method of Sasa and Tanaka (S-T method) were calculated again by the A-D method in the present study to evaluate the latter method. The results of calculations showed that P was not proportional to D and the ratios of P/D were mostly smaller than expected, especially when P or D was small in less periodic forms. The peak hour calculated by the A-D method did not differ much from that calculated by the S-T method. Goodness of fit was improved slightly by the A-K method in two thirds of analysed data. The classification of human filariae in respect of the type of periodicity was, however, changed little by the results calculated by the A-D method.

On the longevity and behaviour of microfilariae of Wuchereria bancrofti, Brugia pahangi and Dirofilaria immitis transfused to laboratory rodents

Microfilariae of Wuchereria bancrofti and Brugia pahangi, which were inoculated into Meriones unguiculatus and Mastomys natalensis respectively, were found in the peripheral blood of the rodents until the ninth day after infection, but no microfilarial periodicity was observed. Microfilariae of W. bancrofti disappeared much faster from the peripheral blood of jirds after reinfection than after the first inoculation. Microfilariae of Dirofilaria immitis inoculated into M. natalensis and laboratory mice were recovered in the peripheral blood until the 17th day after infection and remained infective to mosquitoes. For the first few days the microfilarial periodicity observed in the rodents was similar to that observed in the donor dog, but then reversed.

The exsheathment and migration of Brugia pahangi microfilariae in mosquitoes of the Aedes scutellaris species complex

Studies on the Aedes scutellaris complex of mosquitoes showed that refractory and susceptible species can be distinguished by reference to the proportion of Brugia pahangi microfilariae which reach the thorax within three hours of a feed. Migration ceased approximately 1 1/2 hours after feeding in refractory species, in which only 50% of the ingested worms reached the thorax, In susceptible species over 95% of the ingested microfilariae reached the thorax, and migration lasted for three hours after a feed. Differentiation could be achieved by studying the levels of exsheathment, but it is suggested that analysis of migration levels forms a reliable, accurate and quick method of distinguishing refractory from susceptible species.

Hybridization between Brugia patei, B. pahangi and sub-periodic B. malayi

Virgin females of Brugia malayi, B. pahangi and B. patei were mated with males of species other than their own to determine whether they would hybridize. Microfilariae were produced in all but one cross (that between B. pahangi males and B. malayi females). Hybrid infective larvae, produced in mosquitoes and inoculated intraperitoneally into jirds, grew to adults but these were unable to produce microfilariae because hybrid males did not produce spermatozoa. Hybrid females were fertile and produced microfilariae when crossed with males of their parental species.

The periodicity of Brugia malayi in South Thailand

The periodicity of Brugia malayi microfilariae were studied in the two endemic areas of the South Thailand i.e. in Pattani and Narathiwat provinces. It was found that in Pattani province the microfilariae had a markedly nocturnal periodicity character while in Narathiwat province they were of a nocturnal sub-periodic type. Moreover, the microfilariae of periodic form in Giemsa stained blood films usually had "unsheathed" appearance (71.5%), while those of sub-periodic type were mostly of "sheathed" form (93.4%).

Rapid morphological transformations of spermatozoa in the uterus of Brugia pahangi (Nematoda, Filarioidea)

Mature, umated male and female Brugia pahangi worms were implanted into the peritoneal cavity of gerbils, allowed to mate, and then recovered and examined by means of electron microscopy. The proximal portion of the uterus of female worms recovered in copula contained a morphologically heterogenous population of sperm ranging from a rigid, nonmotile form to the mature ameboid sperm. The immotile sperm are identical in morphology to sperm found within the seminal vesicle of the male. The in utero transformations occur in less than 1 hr, and probably represent a final maturation event preceding competency to fertilize eggs. First in the sequence of events leading to the mature spermatozoon is a decrease in the density of the cytoplasmic matrix concomitant with the elaboration of an abundant tubular smooth endoplasmic reticulum. The position and appearance of the sperm in the uterus suggest that the formation of this membranous system occurs within minutes and involves de novo assembly from cytoplasmic precursors. Following the appearance of the tubular membranous system, certain other membranous organelles become spherical, fuse with the plasmalemma, and release their electron-dense contents into the lumen of the uterus. Filamentous rodlike elements, previously extending the length of the peripheral cytoplasm, begin to disintegrate and cytoplasmic projections form at the margins of the cell. Polarization of the sperm results from the aggregation of mitochondria, nuclear material, endoplasmic reticulum, and membranous organelles at one pole of the cell leaving an organelle-free filamentous pseudopod at the other.

Studies on Brugia pahangi 9. The longevity of microfilariae transfused from cat to cat

Microfilariae in whole uncentrifuged cat blood were transfused from infected to normal cats. The recipient cats were bled frequently and the life-span of the microfilariae in the peripheral circulation was determined; The life-span on microfilariae in different cats was ver variable. Microfilariae were detected fro 2-136 days after inoculation. In immunized cats microfilariae could not be detected 18 hours after inoculation. Any attempt to concentrate or clean the microfilariae caused them to disappear from the circulation more quickly.

Studies on filariasis. IV. The rate of escape of the third-stage larvae of Brugia pahangi from the mouthpart of Aedes togoi during the blood meal

The rate of escape of the third-stage larvae of Brugia pahangi from Aedes togoi which were allowed to probe on a cat and a mouse at time intervals of 5, 10, 20, 30 and 60 seconds was studied. The rate of escape of third-stage larvae at all time intervals was greater during probing on the cat than on the mouse, and was in a logarithmic linear relation to the length of probing time by the mosquito host. The greatest loss (91.35%) of third-stage larvae was in mosquitoes which fed on a cat until fully gorged. There was a remarkable rate of escape (57.41%) within 5 seconds. This striking rate of escape of third-stage larvae may have important implications on filariasis transmission. Most larvae migrated towards the proboscis and head of mosquitoes during these feeding periods. Nearly equal numbers of third-stage larvae escaped from mosquitoes which fed to repletion for more than 60 seconds on a mouse and from those which probed fro more than 60 seconds on the same mouse but did not engorge. This confirmed our view that filling up of the stomach with blood does not constitute the single factor in causing the release of third-stage larvae from the mosquito host.