Analysis of nematode motion using an improved light-scatter based system

Background

The detailed assessment of nematode activity and viability still remains a relatively undeveloped area of biological and medical research. Computer-based approaches to assessing the motility of larger nematode stages have been developed, yet these lack the capability to detect and analyze the more subtle and important characteristics of the motion of nematodes. There is currently a need to improved methods of assessing the viability and health of parasitic worms.

Methods

We describe here a system that converts the motion of nematodes through a light-scattering system into an electrical waveform, and allows for reproducible, and wholly non-subjective, assessment of alterations in motion, as well as estimation of the number of nematode worms of different forms and sizes. Here we have used Brugia sp. microfilariae (L1), infective larvae (L3) and adults, together with the free-living nematode Caenorhabditis elegans.

Results

The motion of worms in a small (200ul) volume can be detected, with the presence of immotile worms not interfering with the readings at practical levels (up to at least 500 L1 /200ul). Alterations in the frequency of parasite movement following the application of the anti-parasitic drugs, (chloroquine and imatinib); the anti-filarial effect of the latter agent is the first demonstrated here for the first time. This system can also be used to estimate the number of parasites, and shortens the time required to estimate parasites numbers, and eliminates the need for microscopes and trained technicians to provide an estimate of microfilarial sample sizes up to 1000 parasites/ml. Alterations in the form of motion of the worms can also be depicted.

Conclusions

This new instrument, named a "WiggleTron", offers exciting opportunities to further study nematode biology and to aid drug discovery, as well as contributing to a rapid estimate of parasite numbers in various biological samples.

Assessment of the health and number of nematodes still relies heavily on subjective monitoring of their motion. Although less-subjective techniques exist that utilize the motility as the primary indicator, the current approaches tend to be designed for use with larger worms and not for early developmental stages. We have describe here a sensitive technique that converts the motion of nematodes into electrical waveforms, which then be used for an estimation of the number parasites present, and for detailed analysis of alterations in their movements. Using parasites of different sizes, including different stages of Brugia sp. and Caenorhabditis elegans, we have shown that the system can analyse samples containing up to 1000 microfilariae/ml, and can be used to used to detect the decrease in motility as a worm loses viability. We have also demonstrated its use in assessing the effects of chloroquine and imatinib on filariae. This sensitive technique is likely to be value to research and field laboratories where there is a need to rapidly estimate the number of parasites present in liquid samples, and can be used in drug screening programs to assess the effects of different anthelminthics.

Midgut barrier imparts selective resistance to filarial worm infection in Culex pipiens pipiens

Mosquitoes in the Culex pipiens complex thrive in temperate and tropical regions worldwide, and serve as efficient vectors of Bancroftian lymphatic filariasis (LF) caused by Wuchereria bancrofti in Asia, Africa, the West Indies, South America, and Micronesia. However, members of this mosquito complex do not act as natural vectors for Brugian LF caused by Brugia malayi, or for the cat parasite B. pahangi, despite their presence in South Asia where these parasites are endemic. Previous work with the Iowa strain of Culex pipiens pipiens demonstrates that it is equally susceptible to W. bancrofti as is the natural Cx. p. pipiens vector in the Nile Delta, however it is refractory to infection with Brugia spp. Here we report that the infectivity barrier for Brugia spp. in Cx. p. pipiens is the mosquito midgut, which inflicts internal and lethal damage to ingested microfilariae. Following per os Brugia exposures, the prevalence of infection is significantly lower in Cx. p. pipiens compared to susceptible mosquito controls, and differs between parasite species with <50% and <5% of Cx. p. pipiens becoming infected with B. pahangi and B. malayi, respectively. When Brugia spp. mf were inoculated intrathoracically to bypass the midgut, larvae developed equally well as in controls, indicating that, beyond the midgut, Cx. p. pipiens is physiologically compatible with Brugia spp. Mf isolated from Cx. p. pipiens midguts exhibited compromised motility, and unlike mf derived from blood or isolated from the midguts of Ae. aegypti, failed to develop when inoculated intrathoracically into susceptible mosquitoes. Together these data strongly support the role of the midgut as the primary infection barrier for Brugia spp. in Cx. p. pipiens. Examination of parasites recovered from the Cx. p. pipiens midgut by vital staining, and those exsheathed with papain, suggest that the damage inflicted by the midgut is subcuticular and disrupts internal tissues. Microscopic studies of these worms reveal compromised motility and sharp bends in the body; and ultrastructurally the presence of many fluid or carbohydrate-filled vacuoles in the hypodermis, body wall, and nuclear column. Incubation of Brugia mf with Cx. p. pipiens midgut extracts produces similar internal damage phenotypes; indicating that the Cx. p. pipiens midgut factor(s) that damage mf in vivo are soluble and stable in physiological buffer, and inflict damage on mf in vitro.

Culex pipiens complex mosquitoes transmit numerous diseases that affect humans and other animals. In many parts of the tropics they transmit Bancroftian lymphatic filariasis caused by the filarial nematode Wuchereria bancrofti. However, in parts of South Asia where Brugian lymphatic filariasis caused by Brugia spp. is endemic, this group of mosquitoes is present but does not play a role in transmission. The differential susceptibility of Cx. p. pipiens mosquitoes for Wuchereria but not Brugia species occurs as a result of the mosquito midgut environment. W. bancrofti larvae ingested with a bloodmeal can penetrate the Culex midgut, however Brugia larvae ingested by Cx. p. pipiens are unable to penetrate the midgut epithelium and die within the lumen. These observations suggest that toxic factor(s) exist within the lumen of the Cx. p. pipiens midgut that physically and lethally damage Brugia parasites. Understanding natural mechanisms of resistance to parasites in arthropod vectors is critical if we are to gain a complete understanding of the transmission dynamics and epidemiology of LF and other vector-borne diseases.

Role of vector control in the global program to eliminate lymphatic filariasis

Lymphatic filariasis (LF) is a major cause of acute and chronic morbidity in the tropical and subtropical parts of the world. The availability of safe, single-dose, drug treatment regimens capable of suppressing microfilaremia to very low levels, along with improvements in techniques for diagnosing infection, has resulted in the targeting of this major mosquito-borne disease for global elimination. The Global Program to Eliminate Lymphatic Filariasis (GPELF) was launched in 2000 with the principal objective of breaking the cycles of transmission of Wuchereria bancrofti and Brugia spp. through the application of annual mass drug administrations (MDAs) to entire at-risk populations. Although significant progress in initiating MDA programs in endemic countries has been made, emerging challenges to this approach have raised questions regarding the effectiveness of using MDA alone to eliminate LF without the inclusion of supplementary vector control. Here, we review advances in knowledge of vector ecology, vector-parasite relationships, and both empirical and theoretical evidence regarding vector management to assess the feasibility and strategic value of including vector control in the GPELF initiative to achieve the global elimination of LF.

The cat infected with Brugia pahangi as a model of human filariasis

The responses of cats to Brugia pahangi, which parasitizes them in nature, mimic those of humans to Brugia malayi and Wuchereria bancrofti in many important respects. It is likely that many of the features of the relationship between host and parasite that can be studied in cats infected with B. pahangi also apply to humans, but for a variety of practical reasons cannot be demonstrated in humans. Both immunologically and parasitologically there is a profound difference between B. pahangi-infected cats that have microfilariae in their blood and those that either do not become microfilaraemic or clear their blood of microfilariae and become post-microfilaraemic. Microfilaraemic cats are susceptible to reinfection and fail to recognize the surface of the sheath of microfilariae. They also do not produce antibodies against several components recognized by post-microfilaraemic cats. Cats that have destroyed their microfilariae also destroy their adult worms and are very resistant to challenge with infective larvae. Apart from the unique ability to recognize the sheath of microfilariae in fluorescent antibody tests, sera from these cats react with microfilarial antigens at 61-81 kDa, antigens of infective larvae at 22 and 18.5 kDa and adult antigens at 34, 18, 16, 13 and 11.5 kDa. None of these antigens are recognized by microfilaraemic cats.

Lymphatic filariasis: new insights into an old disease

Lymphatic filariasis has afflicted people in the tropical areas of the world for thousands of years but even up to comparatively recent times it has been poorly understood and its importance under recognised. In the last 2 decades or so there has been a flurry of activity in filariasis research, which has provided new insights into the global problem of filariasis, the pathogenesis of filarial disease, diagnosis and control.

Susceptibility of mansonia indiana (Diptera: Culicidae) to nocturnally subperiodic Brugia malayi (Spirurida: Filariodea)

Mosquitoes, Mansonia indiana Edwards, 1930, were collected from non-endemic area of human lymphatic filariasis and tested for their susceptibility of infection using nocturnally subperiodic Brugia malayai Buckley & Edeson, 1956. Three cats naturally infected with B. malayi were used in the experiment for mosquitoes feeding. The data revealed that the susceptibility of mosquito infection ranged from 30 to 70%. The results also revealed that the susceptibility rates were not linearly correlated to the microfilarial densities in the cat at the time of feeding. The microfilarial density in cats ranged from 15 to 27 per 10 microl of blood whereas the mean number of third stage larvae in the infective mosqiitoes ranged from 21.6 to 26.8. In addition, statistical analysis showed no significant difference (P > 0.05) between the mean number of third-stage larvae in mosquitoes and the density of microfilaria in cats. The study indicated that Ma. indiana, collected from non-endemic areas, is capable for transmitting the nocturnally subperiodic B. malayi.

In vitro antifilarial effects of three plant species against adult worms of subperiodic Brugia malayi

Five aqueous extracts from three plant species, i.e., dried husks (HX), dried seeds (SX) and dried leaves (LX) of Xylocarpus granatum (Meliaceae), dried stems (ST) of Tinospora crispa (Menispermaceae) and dried leaves (LA) of Andrographis paniculata (Acanthaceae) were tested in vitro against adult worms of subperiodic Brugia malayi. The relative movability (RM) value of the adult worms over the 24-h observation period was used as a measure of the antifilarial activity of the aqueous extracts. SX extract of X. granatum demonstrated the strongest activity, followed by the LA extract of A. paniculata, ST extract of T. crispa, HX extract and LX extract of X. granatum.

External stimuli and intracellular signalling in the modification of the nematode surface during transition to the mammalian host environment

Previous work has shown that the surface of infective larvae of parasitic nematodes will not bind the fluorescent lipid analogue 5-N-(octadecanoyl)aminofluorescein (AF18) until after exposure of the parasite to mammalian tissue-culture conditions. In this study, culture media which are permissive or non-permissive for the acquisition of lipophilicity for AF18 were altered in order to examine possible stimuli involved. This showed that external alkaline pH and high sodium ion concentration were highly stimulatory. The internal signalling pathways which may be involved in the surface alteration were then examined using agents which are known to affect intracellular signalling in mammalian cells. The results indicated that elevation of cGMP levels was stimulatory whereas inhibition of a putative Na+/H+ antiporter or calcium mobilization was inhibitory, and it is argued that high intracellular levels of cAMP may be inhibitory. Whilst the precise effects of the agents used on nematode cells remain to be established, these results provide a framework for the examination of the processes involved in the modification of the nematode surface which takes place immediately after the infection event.

On the infectivity of early third-stage Brugia larvae isolated from the abdomen of Aedes aegypti

Third-stage larvae (L3) of Wuchereria bancrofti, Brugia malayi and B. pahangi are known to be recovered not only from the head and thorax but also from the abdomen of dissected vector mosquitoes. For epidemiological reasons, was of interest to determine whether L3 larvae from the abdomen of the vector would be infectious for the final host. Early abdominal L3 larvae of B. pahangi isolated as early as on day 7 post-infection (p.i.) from Aedes aegypti were injected s.c. into five male Meriones unguiculatus. Four of the five jirds were microfilaria-positive after 67 days.

A proline-rich structural protein of the surface sheath of larval Brugia filarial nematode parasites

Both cDNA and genomic DNA sequences have been isolated which encode a proline-rich precursor protein of the sheath from microfilariae, the first stage larvae of the filarial nematode parasites Brugia pahangi and Brugia malayi. This 22-kDa protein is soluble only under reducing conditions and is extensively cross-linked by both disulfide and nonreducible bonds. Immunogold electron microscopy shows that the protein is localized exclusively in the sheath, a vestigial remnant of the eggshell, which is retained by and encloses the mature microfilaria. Analysis by Western blotting confirms that the protein is expressed only in microfilariae and adult female worms, although transcripts are detectable only in adult females. The deduced amino acid sequence contains a short N-terminal hydrophobic putative leader sequence, a central repetitive domain that contains 14 copies of a degenerate 5-amino acid repeat with the consensus sequence Met-Pro-Pro-Gln-Gly, and a C-terminal proline-rich domain flanked by clusters of cysteine residues. These clusters can be aligned with cysteine residues implicated in cross-linking of a family of cuticular collagens originally identified in Caenorhabditis elegans but which extends to other nematodes.

Filariasis and its control in Fujian, China

Epidemiological survey of filariasis in Fujian Province, China showed that malayan filariasis, transmitted by Anopheles lesteri anthropophagus was mainly distributed in the northwest part and bancroftian filariasis with Culex quinquefasciatus as vector, in middle and south coastal regions. Both species of filariae showed typical nocturnal periodicity. Involvement of the extremities was not uncommon in malayan filariasis. In contrast, hydrocele was often present in bancroftian filariasis, in which limb impairment did not appear so frequently as in the former. Hetrazan treatment was administered to the microfilaremia cases identified during blood examination surveys, which were integrated with indoor residual spraying of insecticides in endemic areas of malayan filariasis when the vector mosquito was discovered and with mass treatment with hetrazan medicated salt in endemic areas of bancroftian filariasis. At the same time the habitation condition was improved. These factors facilitated the decrease in incidence. As a result malayan and bancroftian filariasis were proclaimed to have reached the criterion of basic elimination in 1985 and 1987 respectively. Surveillance was pursued thereafter and no signs of resurgence appeared.

Survival and infectivity of Brugia malayi microfilariae after cryopreservation

Methods were studied for the cryopreservation of microfilariae of periodic Brugia malayi. RPMI-1640 tissue culture medium containing 6% dimethyl sulfoxide (DMSO) and 15% newborn calf serum was used as cryoprotectant. Samples were frozen slowly in the vapor phase of liquid nitrogen prior to emersion in liquid nitrogen (-196 degrees C). The freezing rate was -0.5 to -1.0 degrees C per minute, microfilariae remained viable for as long as, 212 and 375 days, survival rates were 94 to 98% and they were infective to Aedes togoi mosquitos. The infective larvae (L3) were obtained for 10-11 days after feeding at 28 degrees C room-temperature and the infection rate of L3 in test mosquitos was 22.4-30.6%. All DMSO should be removed from the freezing medium to restore microfilariae activity after freezing.

Hematological changes in subperiodic Brugia malayi infection of the leaf-monkey, Presbytis cristata

Hematological changes were monitored in the leaf-monkey, Presbytis cristata, infected experimentally with 200 subperiodic Brugia malayi infective larvae. Prepatent periods were 54-86 days and peak microfilarial geometric mean counts (GMCs) were 1324 per ml blood. Total leukocyte and differential counts were measured at pre-infection, and then at weakly intervals before and during patency. Blood eosinophil level increased to about thrice the initial level at 3 weeks post-infection and this was maintained for the next 13 weeks before it started to rise again, increasing to more than 5 times the initial level at 20 weeks post-infection. The observed pattern of eosinophilia is probably related to the level of microfilaremia and the destruction of microfilariae in the spleen. There was no significant change in the total leukocyte counts during the period of observation.

Haemolymph monophenol oxidase activity in Armigeres subalbatus infected with Brugia pahangi

The activity of monophenol oxidase can be elicited in the haemolymph of Armigeres subalbatus by both blood and filaria-infected blood feeding. Haemolymph collected from both blood-fed and filaria-infected mosquitoes was investigated using a quantitative radiometric assay that measured the amount of tritiated water formed during the hydroxylation of L-[3,5-3H]tyrosine to dopa. Enzyme activity in filaria-infected mosquitoes was found to be significantly lower than that found in the blood-fed mosquitoes within 3 days post-ingestion, but still remained measurable 72 h post-ingestion. The decreased enzyme activity coincided in time with the development of capsules around the microfilariae. The consumption of monophenol oxidase by the melanization of migrating microfilariae in the haemocoel of filaria-infected mosquitoes and the effects of excretory and secretory products of developing larvae on monophenol oxidase activity are suggested.

A comparison of host responses of the Mongolian jird to infections of Brugia malayi and B. pahangi

Host responses of jirds receiving a single subcutaneous inoculation of subperiodic Brugia malayi were compared with those of jirds similarly infected with B. pahangi. Parasite burdens, lymphatic lesion severity, granulomatous reactivity, antibody responses to parasite antigens, and complete blood cell counts were assessed at 60 and 150 days post-inoculation. At 60 days post-inoculation, percentages of adults recovered at necropsy and lymphatic lesion severity were greater in B. pahangi-infected jirds. At 150 days post-inoculation, lesion severity and percentages of worms recovered were similar in both infections. No significant differences were noted in either infection in reactivity to homologous or heterologous parasite antigens in any parameter measured. Similarities in the kinetics of the inflammatory reactivities of the 2 infections suggest that previous observations made in the jird-B. pahangi model could be utilized in designing studies using B. malayi. Further, the more marked lesion severity observed in B. pahangi-infected jirds and the relative ease of maintaining B. pahangi in the laboratory support the continued use of this system as a conceptual model for the study of lymphatic lesion pathogenesis.

Cultivation of sexually mature Brugia malayi in vitro

Sexually mature male and female Brugia malayi were developed from third stage larvae after 60 days in the in vitro culture system described by Franke and others in 1987 (Am J Trop Med Hyg 37: 370-375). Between 75 and 100 days in culture, many worms produced living microfilariae. Each gravid female produced 200-1,500 microfilariae/day.

Brugia pahangi adults implanted into mice: a possible screen for filaricidal activity

Brugia pahangi adults grown in the peritoneal cavities of jirds (Meriones unguiculatus) were implanted into the peritoneal cavities of six inbred mouse strains to investigate this system as a screen for detecting filaricidal activity. The mice were given 15 adult B. pahangi and autopsied 35 days later. The recoveries of adult worms were 25%, 35%, 49%, 33%, 26% and 27% of the number implanted respectively for the MF1, TO, NIH, CBA, BALB/c and C3H/HE strains. There was great variation in the number of worms recovered from each strain of mouse. It is concluded that the variation in recoveries was so high that this system is not useful in detecting low level filaricidal activity.

Experimental infection of the leaf-monkey, Presbytis cristata, with subperiodic Brugia malayi

Presbytis cristata monkeys infected through the inoculation of between 200 and 400 subperiodic Brugia malayi infective larvae (L3) in the right thigh, in both thighs or in the dorsum of the right foot were followed up for varying periods of up to about 8 months after infection. All 148 inoculated animals became patent, with mean prepatent periods being between 66 and 76 days. In animals injected in the thigh, the patterns of microfilaraemia were similar, there being a rapid rise in the geometric mean counts (GMCs) of microfilariae during the first 10-12 weeks of patency, which then plateaued at levels of greater than 1000/ml. Adult worm recovery, expressed as the percentage of the infective dose, was significantly higher in animals injected with 100 L3 in each thigh, being 9.4% as compared with 2.8%-4.8% in other groups. It is therefore recommended that animals should be injected with 100 L3 in each thigh and that the testing of potential filaricides in this model be carried out during the phase of rapid increase in microfilaraemia to ensure that any microfilaricidal effect can easily be detected.

Species variation in mosquito flight-muscle damage resulting from a single filarial infection and its repercussions on a second infection

Serial sections of females of two highly filaria-susceptible mosquitoes, Aedes togoi and Ae. aegypti, were examined by light microscopy. Following a single Brugia pahangi infection, the predominant reaction of flight muscles of Ae. aegypti was degeneration, whereas that in Ae. togoi was nuclear enlargement, a putative repair response. This also holds true following mechanical injury (Beckett 1990), suggesting an inherent species difference in flight-muscle response to injury. The filariae of a second B. pahangi infection, initiated after muscle damage had been established, usually avoided degenerate muscle fibres (which cannot support larval development) but entered similar proportions of normal fibres and those with enlarged nuclei. Filariae of a second infection, initiated whilst first-infection larvae were still within the muscle fibres, entered similar proportions of already-parasitized and non-parasitized fibres. The sole change in muscle fibres detectable by filarial larvae is therefore degeneration.

Effects of intermediary metabolites and electron transport inhibitors on action of chloroquine on Brugia pahangi and Onchocerca volvulus

We examined the possibility that chloroquine is interfering with aerobic energy-generating processes in the adult filarial parasites, Brugia pahangi and Onchocerca volvulus. Using motility of these parasites as an assay of drug effect, we found that micromolar concentrations of chloroquine caused significant paralysis, but only in alkaline medium (pH 8.4). The addition of 12 mM glutamine or 10 mM albizziin to the medium completely antagonized drug-induced paralysis. In addition, in B. pahangi, all of the tricarboxylic acid cycle intermediates (10 mM) except citrate and pyruvate antagonized the effect of chloroquine on motility; in O. volvulus, oxaloacetate as well as glutamine inhibited the effect of the drug. The effect of chloroquine on both parasites was enhanced when it was used in combination with 10 microM acivicin, a glutamine antimetabolite. Here motility of B. pahangi was reduced significantly within 24-48 hr at acidic (6.8) neutral (7.4) and alkaline (8.4) pH. This effect was partially reversible by glutamine (12 mM). Motility of O. volvulus was reduced to near zero within 4 hr with this drug combination. Antimycin A and rotenone, both electron transport inhibitors, also synergized with chloroquine at any pH to produce paralysis in B. pahangi. The effects of the rotenone and chloroquine combination were reversed in the presence of 10 mM succinate. However, glutamine (12 mM) was unable to antagonize the effects of chloroquine plus antimycin A on the motility of B. pahangi. These findings suggest that chloroquine may be inhibiting aerobic energy metabolism in the filariae, possibly at the level of electron transport. Furthermore, since chloroquine is well-tolerated but only weakly filaricidal in vivo, the data indicate that use of this drug in combination with other inhibitors of aerobic energy metabolism may be a chemotherapeutically useful approach to the treatment of filariases.

[Observation on the intake of Brugia malayi microfilariae by Anopheles sinensis and host efficiency]

The experiments were carried out under the controlled conditions with temperature at 26 +/- 1 degree C and relative humidity 75-85%. The Brugian microfilariae from the peritoneal cavity of Mongolian jirds, mixed with rabbit blood, were ingested by Anopheles mosquitoes through the artificial membrane. The experimental data show that the number of microfilariae ingested is fewer than would be expected from the microfilarial densities in the blood meal. The linear regression shows their quantitative relation, Y = 0.61X-1.37. At the same time the host efficiency of Anopheles sinensis decreases with the increase of microfilarial number ingested. In case of the relationship between Brugia malayi and Anopheles sinensis, the survival rate of vector host is the chief factor influencing the decrease of host efficiency.

Antifilarial activities of synthetic and natural retinoids in vitro

Fourteen synthetic retinoids with known and different binding affinities to retinol binding proteins of Dirofilaria immitis, retinol, and retinoic acid were tested in vitro against female Litomosoides carinii (drug levels 20, 10, 1 nM/ml) and against microfilariae of L. carinii, Brugia malayi, B. pahangi and Acanthocheilonema viteae (drug levels 100, 20, 10, 1 nM/ml). All compounds including retinol and retinoic acid had at least some effects on the filarial parasites. Except for 3 synthetic retinoids, continuous exposure of adult L. carinii to the drugs reduced the motility of the worms completely or remarkably by day 7 of incubation in a dose and time dependent fashion. Also, the release of microfilariae was completely or remarkably suppressed in a dose and time dependent manner by 20 and 10 nM/ml of all except 4 of the retinoids. Short term exposure to the drugs (up to 20 nM/ml) for 4 h followed by subsequent incubation in drug-free medium was ineffective except for one synthetic retinoid (13-cis-N-(2-hydroxyethyl)retinamide:13-cis-Her). Effects on microfilariae were also dose and time dependent. All compounds affected markedly the motility of L. carinii microfilariae within 20 h at dose levels of 1 nM/ml and above. Microfilariae of B. malayi, B. pahangi and especially of A. viteae were generally less sensitive. Eight of the synthetic retinoids, but not retinol and retinoic acid, were effective (10 nM/ml). There were generally no correlations between the various effects of individual compounds; i.e., activities varied within one species depending on the parameters used and depending on the parasite species.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro activity of some monoclonal antibodies against Brugia malayi microfiliariae and infective larvae

Two out of six monoclonals (McAbs) produced against subperiodic Brugia malayi infective larva (L3) antigens impaired B. malayi L3 motility independently of human buffy coat cells. Scanning electron microscopy studies showed damage to L3 surface and loss of regular cuticular annulations. The two McAbs (BML 1a and BM1 8b) did not affect B. malayi microfilaria (mf). They were IFAT-positive with B. malayi adult and L3 antigens; other McAbs which did not affect mf or L3 motility were IFAT-negative. All six McAbs did not promote cellular adherence of normal human buffy coat cells to mf or L3.

Egg production in Brugia pahangi (Nematoda: Filarioidea)

Oogenesis in Brugia pahangi has been studied by means of the aceto-orcein chromosomal squash technique and light-microscope autoradiography. The use of colchicine has demonstrated a 2-3 mm terminal germinative zone within the ovary, in which continuous and rapid mitotic division of germ cells occurs. In 80% of the gonads, oocytes within a 1-2 mm length of the ovary proximal to the germinative zone were at the prophase of meiosis I. Primary oocytes with markedly less condensed chromatin, apparently interphase cells, were observed in the corresponding region of the ovary in the remaining 20% of material examined. A cyclical or phased development of primary oocytes is suggested. Autoradiographic studies, concerned with the incorporation of [5-3H]uridine into germ cells of B. pahangi in vitro, further suggest that the onset of meiotic prophase is associated with the initiation of high RNA synthetic activity. Following meiotic prophase, oocytes complete meiosis I before entering a period of growth during which the chromatin material is decondensed. Recondensation of chromosomes prior to meiosis II is only observed after fertilization within the seminal receptacle. On completion of meiosis II, with the extrusion of a polar body, the haploid chromosome complement of the female unites with that of the male, re-establishing the diploid number of the zygote (2n = 10).

In vitro motility of isolated adults and segments of Onchocerca volvulus, Brugia pahangi and Acanthocheilonema viteae

Observations were made on the spontaneous motility in vitro of entire adult worms and segments of Onchocerca volvulus, Brugia pahangi and Acanthocheilonema viteae. Segment motility was recorded in a mechano-transducer apparatus and responses of worm tissues to anthelmintics and other pharmacological agents were compared. Entire adult female O. volvulus showed varied patterns of motor activity, ranging from continuous low level whole body motion to periodic spasmodic contractions interspersed between intervals of quiescence lasting from a few to 30 seconds. The same range characterized movements of 1.5-4 cm segments cut from worms liberated from collagenase digested nodules. However, fresh segments dissected directly from surgical specimens were completely inactive due to the paralyzing effect of xylocaine, used as local anesthetic. This effect wore off in 2-5 hours in vitro, and recovered segments behaved in the same way as those from enzymatically liberated worms. Segments of B. pahangi and A. viteae also showed motor activity patterns which reflected those of whole adults. Segments of O. volvulus behaved reproducibly, whether examined in the field in endemic areas, or after transport of nodules or freed worms to Michigan from Guatemala or Sudan. Segments of all worms were unresponsive to most anthelmintics, but O. volvulus was susceptible to paralysis by CGP 6140, levamisole, pyrantel and carbachol at concentrations of ten to a thousand times lower than those required to produce any influence on B. pahangi. Segments of A. viteae more closely resembled O. volvulus in their dose responses to these drugs, although CGP 6140 was without effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative effects of anthelmintics on motility in vitro of Onchocerca gutturosa, Brugia pahangi and Acanthocheilonema viteae

The effects of standard anthelmintics on the motor activity in vitro of adult Onchocerca gutturosa, Brugia pahangi and Acanthocheilonema viteae were determined using a micromotility meter. Fresh adult males dissected from bovine tissues were the best source for observations on O. gutturosa. Parasites liber-ated by collagenase digestion showed poor viability and motility. Only segments of O. gutturosa females were obtainable by dissection and these were not able to sustain motility in vitro. Adult males and females of O. volvulus were active after collagenase digestion of human nodular tissue, but behaved so irregularly that satisfactory monitoring of their movements with the meter was not possible on a regular enough basis to permit quantitation of drug-induced changes. Inhibitory effects on motility of O. gutturosa, B. pahangi and A. viteae were produced by anthelmintics which showed macrofilaricidal effects in vivo in a laboratory rodent model, with the exception of the benzimidazoles. O. gutturosa was, however, much more sensitive than B. pahangi or A. viteae to the temporary paralyzing effects of levamisole and pyrantel. The utility of in vitro screening against O. gutturosa and B. pahangi was evaluated by determining the discriminatory capacity of the tests in detecting novel compounds with reproducible in vivo activity in the jird-B. pahangi/A. viteae model. The results suggested that this would be a valuable selective screening procedure. Although false positives were detected at the rate of 15-17% of the novel anthelmintic chemical series tested, no false negatives were allowed through the screen provided both O. gutturosa and B. pahangi were included.2=

Exsheathment of microfilariae of Brugia pahangi in the susceptible and refractory strains of Aedes aegypti

Exsheathment of microfilariae of Brugia pahangi was studied in susceptible (Liverpool) and refractory (Bora-Bora) strains of Aedes aegypti. It was found that the microfilariae tend to carry their sheaths into the haemocoel of both strains of Ae. aegypti within two hours after the engorgement of mosquitoes from a rat parasitized by filariae. The percentage of sheathed microfilariae in the haemocoel then progressively decreased to 0% at eight hours and to 1% at 24 hours post-ingestion in the Bora-Bora and Liverpool strains, respectively. Those microfilariae that remained in the midgut more than two hours after ingestion were most likely to cast off their sheaths there. The percentage of microfilariae exsheathed in the midgut progressively increased to about 91 and 78% at 24 hours post-ingestion in the Bora-Bora and Liverpool strains, respectively. These results suggested that the exsheathment of microfilariae occurs both in the haemocoel and in the midgut of two strains of Ae. aegypti.

Dipetalonema viteae and Brugia pahangi transplant infections in gerbils for use in antifilarial screening

Transplanted infections of Dipetalonema viteae and Brugia pahangi have been evaluated as tools for experimental chemotherapy. Attempts were made to establish these filariae in similar pharmacokinetic sites within the same host, so that direct comparisons of in vivo drug susceptibilities could be made. Unfortunately, it was not possible to establish B. pahangi in the subcutaneous tissues, the preferred site of D. viteae. Therefore, intraperitoneal B. pahangi and subcutaneously implanted D. viteae in gerbils were used for the study. D. viteae infections were significantly enhanced by concomitant infections with B. pahangi, while B. pahangi infection rates were unaffected by the presence of D. viteae. Experiments with amoscanate, CGP6140 and Mel W demonstrated the importance of employing both B. pahangi and D. viteae for antifilarial discovery work and the fundamental effect of parasite location on drug efficacy. D. viteae rapidly migrate from the peritoneal cavity of gerbils following implantation; twenty one hours after infection 73% of transplanted worms were found in the subcutaneous tissues. It was shown that the migration response could be used as a stringent parameter for demonstrating antifilarial activity. D. viteae were exposed to antifilarial drugs for 24 hours in vitro, washed and implanted into the peritoneal cavity of gerbils. At autopsy, 5 days later, 10(-8)M ivermectin and milbemycin D had prevented migration; CGP6140, amoscanate, suramin, flubendazole and furapyrimidone were also detected at less than 10(-6)M using this parameter. In all cases the migration response was more sensitive to drugs than parasite kill. Ivermectin's ability to inhibit worm migration through the tissues is discussed, with respect to the role of itinerant males in the reproductive cycle of Onchocerca volvulus.

The effect of sera from cats infected with Brugia pahangi and subsequently treated with levamisole on the infectivity of third-stage larvae of B. pahangi

Cats were treated with levamisole and the infective (L3) stage of Brugia pahangi. Serum from infected cats was subsequently tested for its ability to infect jirds. Jirds autopsied at 33 days postmortem showed significant levels of parasitemia. This is contrary to reports of a previous study wherein serum from humans infected with B. malayi was found to induce cell adherence and death of the L3.

Cryopreservation of infective-stage larvae of Brugia malayi

Third-stage larvae of Brugia malayi (Guizhou, China strain), in RPMI-1640, 6% DMSO and 15% calf serum, frozen slowly in the vapor phase of liquid nitrogen prior to emersion in liquid nitrogen, remained viable for as long as as 321 days and were infective to Mongolian jirds. All DMSO should be removed from the freezing medium to restore larval activity after freezing.

Exsheathment of microfilariae of Brugia pahangi in Anopheles quadrimaculatus and Culex quinquefasciatus

In order to determine whether the exsheathment patterns described in our previous study occurred in other microfilaria-mosquito systems, exsheathment of microfilariae of Brugia pahangi was studied in two species of mosquitoes. The results of the quantitative observation revealed that the microfilariae of Brugia pahangi tend to carry their sheaths into the haemocoel of Anopheles quadrimaculatus and Culex quinquefasciatus within 4 hr after infected blood meals. The percentage of the sheathed microfilariae in the haemocoel progressively decreased to 0% at 24 hr post-ingestion. Microfilariae remaining in the midgut of both species of mosquitoes were recorded most frequently casting off their sheaths in the midgut 2 hr post-ingestion. The percentage of microfilariae exsheathed in the midgut progressively increased to about 100% and 40% 24 hr post-ingestion in Anopheles quadrimaculatus and Culex quinquefasciatus respectively. These results confirm that exsheathment of microfilariae of Brugia pahangi occurs both in the haemocoel and in the midgut of two species of mosquitoes.

Increased dissemination of dengue 2 virus in Aedes aegypti associated with concurrent ingestion of microfilariae of Brugia malayi

We investigated whether concurrent ingestion of dengue 2 virus and microfilariae of Brugia malayi would increase viral infection and dissemination rates in Aedes aegypti. Infection rates were similar in mosquitoes that ingested virus alone or both virus and microfilariae concurrently. However, viral dissemination rates, as determined by recovery of dengue virus from both legs and bodies separately, were significantly greater in mosquitoes that ingested both agents concurrently than in those that ingested virus alone. This study confirms that vectorial capacity of a natural vector of an arbovirus may be enhanced by the concurrent ingestion of microfilariae.

Human in vitro immune reactions to animal filariids

Infective third stage larvae of animal filariids Brugia pahangi and Breinlia booliati incubated in vitro in the presence of normal human peripheral leucocytes and sera from human filariasis subjects resulted in decrease in motility, cell adherence, and formation of precipitates around the larvae. Strongest immune reactions were seen with sera from amicrofilaraemic symptomatic subjects, normal exposed individuals, and patients with tropical pulmonary eosinophilia syndrome (TPE). Weaker reactions were observed with sera from patients with elephantiasis. In all cases, reactivity to B. pahangi larvae was considerably higher than against B. booliati. Sera from microfilaraemic patients and unexposed control subjects were nonreactive. The implication of these human in vitro immune reactions against filarial parasites of animal origin is discussed in the context of the hypothesis of "zooprophylaxis" previously suggested by other workers.

The Wellcome Trust lecture. Inflammatory responses to filarial connective tissue parasites

The inflammatory responses to lymphatic filariae and to Onchocerca volvulus are reviewed with particular attention to evolutionary biology; inflammatory host spectrum; non-specific components; immunoregulation; immune evasion versus immunomodulation; chronic tissue damage and scarring and disease models. Basic principles of pathogenesis are emphasized, comparisons drawn with schistosome infection, and critical items of missing information are highlighted.

Formation by the uterus of a peripheral layer of the sheath in microfilariae of Litomosoides carinii and Brugia malayi

The eggshells of young developmental stages in the uterus are rather thin and homogenous. In the brezel stage of Brugia malayi they are 35 nm thick and 20 nm in Litomosoides carinii. In young developmental stages up to brezel stages the eggshells bind the lectins WGA, DBA and PNA labelled with colloidal gold. This shows that GlcNAc, GalNAc and Gal residues are present at the surface of the sheath. In intrauterine microfilariae of B. malayi the original sheath is reduced to a thickness of 7 nm. It is reinforced by secretions from a specialized area of the epithelium of the uterus which do not appear as a homogeneous layer but look like a string of pearls. This layer may be called the "uterine layer". It has a thickness of 40-80 nm. In the microfilaria of L. carinii, the thickness of the original sheath is reduced to 2-3 nm and the uterine layer has a thickness of 7 nm. The uterine layer does not react with any of the lectins, which shows that the surface lacks N-acetylglucosamine, N-acetylgalactosamine and galactose residues. The uterine layer appears to be an ancestral (plesiomorphic) feature which is present in free-living nematodes and the highly specialized bloodforms of filariae. The uterine layer seems to protect and disguise the original sheath against the immune reactions of the host.

Microfilarial perforation of the midgut of a mosquito

To determine whether the midgut envelope of mosquitoes is disrupted by the passage of microfilariae, ultrastructural changes induced by microfilariae of Brugia malayi were observed in midguts of Aedes aegypti mosquitoes. Basal and apical plasma membranes were destroyed, disrupting the full depth of the midgut wall. Ingested ferritin lay against the gut wall, suggesting absence of the peritrophic membrane during penetration. Exsheathment of microfilariae appears to be enhanced by movement against the constricting midgut wall. It was concluded that particles present in the lumen of the gut may be disseminated passively to the hemocoel.

Micromotility meter: an instrument designed to evaluate the action of drugs on motility of larval and adult nematodes

An instrument for measuring the motility of larval and adult nematodes is described along with an analysis of its use as a tool to analyse drug action on these parasites. Motility was detected from larval parasites of Nippostrongylus brasiliensis and Ascaris suum in the absence and presence of various anti-nematodal drugs. These agents produced, within 48 h, a significant decrease in larval parasite motility. The instrument was also capable of detecting the motility of Caenorhabditis elegans, adult female Brugia pahangi and their response to anti-nematodal drugs. The design of the instrument allows us to accurately measure motility in a single sample within 60 sec.

The ability of Aedes aegypti mosquitoes to survive and transmit infective larvae of Brugia pahangi over successive blood meals

The mortality of Aedes aegypti mosquitoes increased; immediately following a blood meal containing microfilariae of Brugia pahangi, when infective larvae began to migrate out of the flight muscles and when infective larvae were lost from the mosquitoes during a blood meal. When infective mosquitoes took a second blood meal 86.2% of the infective larvae escaped from their bodies. However, only 50.3% escaped when mosquitoes fed through a thin layer of cotton. Infective larvae in the abdomen of the mosquitoes stood the least chance of escaping from the insects. When infective mosquitoes were offered a third blood meal four days later, the proportion of infective larvae in the head and labium had risen from 56.6% in the control group to 66.0% and 69.4% in the two test groups. At this third feed 54.7% and 75.7% of the infective larvae were lost from mosquitoes with a low and medium pre-feeding worm burden respectively. This suggests that the escape of infective larvae from mosquitoes with only a few worms is less efficient than from mosquitoes with a medium worm burden.

Clearance of inoculated microfilariae of Brugia malayi by monoclonal antibodies in BALB/c mice

A stable and long-lasting microfilaremia was developed by intravenous injection with 2 X 10(5) microfilariae (mf) of Brugia malayi into BALB/c mice. Mf density in mice was maintained at least at 30 to 40 mf/20 microliter blood for 4 weeks, then gradually decreased as the same as in the jird. However, mf inoculated were cleared from the blood within 3 weeks in the mice which was immunized with repeated intravenous injections with live mf. The effect of mf clearance was passively transferred into the mice with inoculated microfilaremia by intravenous injection of 0.2 ml serum from the immunized mice. For the analysis of the role of anti-mf antibodies, monoclonal antibodies (MABs) against mf of B. malayi were produced. An IgG1 MAB gave a significant mf reduction in mice and it promoted in vitro adherence of normal mouse spleen cells to mf.

The migration of infective larvae of Brugia pahangi within the mosquito, Aedes aegypti

The course of the migration of infective larvae of Brugia pahangi within the mosquito, Aedes aegypti, is described. The presence of blood or eggs in the abdomens of mosquitoes at a time when the infective larvae are beginning their migration out of the thorax leads to a significant increase in the proportion of larvae accumulating in the abdomen. The evidence supports the hypothesis that infective larvae may accumulate in the labium as a direct consequence of the insect's internal anatomy i.e. infective larvae on moving into a confined space tend to remain there. In addition, the rate at which infective larvae migrate into the labium is shown to be density dependent.

The domestic cat as a host for Brugian filariasis in South Kalimantan (Borneo), Indonesia

Three hundred and twenty-five domestic cats (Felis catus) from six villages of the Hulu Sungai Tengah and Banjar Regency of South Kalimantan (Borneo), Indonesia, were examined for filarial nematodes. Parasites were found in 66 cats, of which 61 (92.4%) had Brugia pahangi, four (6.1%) has B. malayi and one (1.5%) had Dirofilaria repens. Infection rates ranged from 11% to 22% in cats from secondary forest/rice-field habitats, from 15% to 30% in open village/rice-field habitats, to 50% in an open coastal village. In all cases the infection rate of B. malayi in man was greater than in cats from the same collecting area. The number of B. pahangi microfilariae per 20 microliter cat blood ranged from 34 at 1000 hours to 571 at 2200 hours. The results of this study suggest that in this region of Indonesia the domestic cat is not an important host for maintaining B. malayi.