Acanthocheilonema viteae: octopamine and its physiological role

Octopamine acts as an important neurotransmitter and neuromodulator in arthropods, mollusks, and nematodes. In mammals, however, no definite function for this amine has yet been described. By virtue of this difference in the neurophysiological requirement of the mammalian host and nematodes, octopamine offers good opportunity for exploring this area deeply with a view to identify a unique target for filarial chemotherapy. Results of the present study indicated that Acanthocheilonema viteae, the rodent filarial parasite, utilized tyrosine as a precursor for producing octopamine and some other biogenic amines. Octopamine exhibited specific saturable binding with the membrane prepared from the anterior portion of the filariid. This amine induced concentration dependent increase in the membrane potential which possibly caused tonic paralysis of the filariid. The rate of micro filarial release by the female worms also declined in the presence of this amine. The study thus provided preliminary evidences for the presence of an octopamine neurotransmitter system and also about some of the roles it plays in A. viteae.

Expression of the filarial nematode phosphorylcholine-containing glycoprotein, ES62, is stage specific

ES62, an immunomodulatory phosphorylcholine-containing glycoprotein secreted by the rodent filarial nematode Acanthocheilonema viteae, has previously been shown to be produced by L4 larvae and adult worms only. However, homologous sequences to ES62 have recently been found in L1 and L3 cDNA libraries of certain human filarial nematodes. Therefore, the various stages of A. viteae were re-examined and it was again found that only the post-L3 stages secreted ES62. Synthesis but not secretion by earlier stages was ruled out by examination of the protein content of whole worm extracts and by immunoelectron microscopy. However, examination by PCR of the mRNA for ES62 revealed that it was found in the L1 and L3 larvae. This may explain why homologous sequences to ES62 have been found in Brugia malayi and Onchocerca volvulus larval cDNA libraries. It also suggests that filarial nematodes, in general, may secrete ES62. To obtain evidence for this, we investigated production by Brugia pahangi, a close relation of B. malayi. We found that ES62 was indeed secreted but, as with A. viteae, only by the post-L3 stages, although again the mRNA for ES62 could be detected in the earlier stages. Overall our results suggest that production of ES62 is not species specific, that it is indeed stage specific, and that this may be due to post-transcriptional control of expression.

Protective immunity induced by irradiated third-stage larvae of the filaria Acanthocheilonema viteae is directed against challenge third-stage larvae before molting

Jirds (Meriones unguiculatus) were vaccinated with irradiated L3 third-stage larvae (L3) of Acanthocheilonema viteae, and the time required for killing of the challenge L3 was determined. The number of parasites recovered from vaccinated jirds was reduced to about 10% of the control values on the second day after challenge infection and later on. Histological studies revealed an eosinophil-rich infiltrate containing macrophages, neutrophils, and mast cells in the vicinity of the L3 on day 2 after challenge and destruction of the worms by day 4 after challenge. Ultrastructural studies confirmed these data and showed that eosinophils, macrophages, and mast cells were close to the L3 on day 2 after challenge. Flattening of the eosinophils onto the surface of the worms, degranulation of electron-dense material, and rupture of the L3 surface was observed on day 4 after challenge, followed by invasion of the inner of the worms by phagocytic cells. These data show that immune attack against the challenge L3 in vaccinated jirds is initiated between the first and the second day after challenge and that killing occurs around the fourth day after challenge, before the worms undergo their first molt.

Mechanisms underlying the transfer of phosphorylcholine to filarial nematode glycoproteins--a possible role for choline kinase

Phosphorylcholine (PC) is a common constituent of proteins secreted by filarial nematodes. As this substance has been shown to interfere with immune responses, we are interested in designing strategies for blocking its attachment. Towards this end, we are investigating the mechanism of incorporation of PC into filarial molecules and in the present manuscript we describe experiments relating to elucidating the source of PC for attachment. Synthesis of phosphatidylcholine in eukaryotic organisms can occur by a mechanism involving the transfer of PC from CDP-choline to diacylglycerol (the Kennedy pathway). By (i) measuring transfer of radio-isotope labelled PC from CDP-choline to parasite molecules and (ii) employing inhibitors of CDP-choline synthesis, we have investigated whether CDP-choline can act as a source of PC for transfer to ES-62, a major secreted glycoprotein of the rodent filarial nematode Acanthocheilonema viteae. Although we can find no evidence of this, we show that attachment of PC is blocked by hemicholinium-3, an inhibitor of choline kinase, the first enzyme in the Kennedy pathway. Thus, at least the first step in this pathway--phosphorylation of choline, would appear to be necessary for attachment of PC to ES-62.

Development of in vitro screening system for assessment of antifilarial activity of compounds

Evaluation of antifilarial activity of new potential agents in vivo is extremely time consuming and uneconomic. In the present study effort has been made to develop an in vitro screening method using Acanthocheilonema viteae, a subcutaneously dwelling rodent filariid with anaerobic metabolic characteristics like human filariids, W. Bancrofti/Brugia malayi as test parasite. Motility test and tetrazolium (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide, MTT) based colorimetric assay were used as parameters in in vitro assay. Results showed that 92.3% of compounds (in vivo active) could be picked up in the in vitro assay when both adults and microfilarae (mf) were used simultaneously. Mf and adult stages separately detected, respectively, 84.6 and 69.2% of in vivo active compounds. The adults and mf separately and both the life stages together exhibited, respectively, 80.0, 50.0 and 80.0% false positive results in the in vitro test with in vivo inactive compounds. It is felt that mf stage when used in in vitro test using motility and MTT assays as parameters would be useful in primary screening of new potential filaricides.

PCR-based amplification of total cDNA with high fidelity and high yield from minute amounts of parasite RNA

cDNA, synthesised from total RNA from Acanthocheilonema viteae, was amplified by PCR with a primer derived from the spliced leader 1 sequence of nematodes and oligo-dT. Due to the great number of side products observed in the reaction, a biotinylated oligo-dT primer was used for cDNA-synthesis and the first cycles of PCR. After binding of the PCR products to streptavidin/paramagnetic particles, the (+)strands of the cDNAs were recovered and reamplified. Analysis of the PCR products obtained revealed the presence of full-length cDNAs of at least 1.7 kbp in size in amplified total cDNA from microfilariae, postinfective L3, and adult worms. The total cDNA, from only 20 ex vivo recovered postinfective L3, was efficiently amplified.

Characterization of heterotrimeric G-proteins in adult Acanthocheilonema viteae

Heterotrimeric G-proteins have been found in eukaryotic cells, from yeast to humans, but have received little attention, to date, with respect to parasitic organisms. We now present the first report of the characterization of heterotrimeric G-proteins expressed in a filarial nematode, Acanthocheilonema viteae. Using a combination of (i) affinity labelling with [alpha-32P]GTP; (ii) ADP-ribosylation with cholera toxin and pertussis toxin; (iii) Western blotting with a panel of anti-G-protein antibodies; and (iv) reverse transcriptase-PCR with degenerate G-protein oligonucleotide primers followed by hybridization analysis using oligonucleotides specific for individual G-protein subunits, we demonstrate that adult A. viteae expresses homologues of the beta 1- and/or beta 2-like subunits and alpha-subunits of the Gs, G1, Gq and G12 subfamilies found in mammals. The role which these G-proteins may play in the biology of the organism is discussed.

Chitinase genes expressed by infective larvae of the filarial nematodes, Acanthocheilonema viteae and Onchocerca volvulus

State-specific products of 220 and 75 kDa were identified by metabolic labelling of infective larvae of the filarial nematode Acanthocheilonema viteae in ticks. Synthesis was temperature sensitive, occurring at 27 degrees C but not at 37 degrees C. These products were secreted 3-6 days after leaving the vector during post-infective development, but subsequent expression was not detected. The smaller protein with a pI of 6.2, was purified by two-dimensional electrophoresis and the N-terminal amino acid sequence was derived. This provisionally identified the protein as a chitinase, which was confirmed biochemically by glycol-chitin substrate gel electrophoresis. The polymerase chain reaction was used to amplify a product from a cDNA library of A. viteae infective larvae. The nucleotide sequence codes for a putative signal peptide of 20 amino acids and a mature protein of 504 residues (Mr 56 kDa), exhibiting 69% identity (81% similarity allowing for conservative substitutions) with the MF1 chitinase described from microfilariae of Brugia malayi. N-linked glycosylation may account for some, or all, of the discrepancy in Mr between the predicted polypeptide and the native parasite product (75 kDa). Primers based on the A. viteae sequence were used to amplify a related sequence from a cDNA library of Onchocerca volvulus infective larvae. The O. volvulus cDNA codes for a 20-amino acid signal peptide followed by 477 residues with an Mr of 54 kDa, and shares 67% identity with the A. viteae chitinase (80% similarity allowing for conservative substitutions) and 69% identity with the B. malayi MF1 molecule. It is proposed that chitinases expressed by infective stages of these filarial nematodes may play a role in ecdysis during post-infective development.

Acanthocheilonema viteae: rational design of the life cycle to increase production of parasite material using less experimental animals

The maintenance of the life cycle of Acanthocheilonema viteae is described with the aim to increase the production of parasite material using less experimental animals. The filaria was maintained in jirds (Meriones unguiculatus) and in soft ticks (Ornithodoros moubata). The optimal infection dosis for jirds was 80 infective larvae (L3). The mean worm number in groups of animals varied between 18 and 30 adult worms. A stable microfilaremia developed and only few animals developed pathological alterations as a consequence of the infection. A simple membrane feeding apparatus allowed mass feeding of ticks. Infection of ticks with microfilariae (mf) using this technique resulted in a mean no. of 594 +/- 527.2 L3/tick. L3 and mf were cryopreserved in liquid N2 with a simple technique. The described maintenance of the life cycle reduced the amount of required experimental animals to 30-40% of the originally needed numbers.

Stage-specific development of a filarial nematode (Dipetalonema dracunculoides) in vector ticks

This paper reports the development of the canid filarial worm, Dipetalonema dracunculoides, in the brown dog tick, Rhipicephalus sanguineus by determining whether development is similar within larval, nymphal and adult stages of infected ticks. This study demonstrates that only infected nymphal ticks can support the complete development of the filarial worm. Infected larval ticks are not suitable intermediate hosts, nor are infected adults. Development depends on some stage-specific property of the vector, and the maturation to the infective stage is stimulated during the course of the nymphal-adult moult.

Protective immunity linked with a distinct developmental stage of a filarial parasite

Repeated low dose infections of the jird Meriones unguiculatus, with the filarial parasite Acanthocheilonema viteae cause a substantial reduction of the total worm burden, suggesting a parasite-driven immune mechanism that controls super-infections. Quantitative recovery of parasites from tissues of triple infected jirds reveals that the larvae derived from a subsequent challenge infection are inactivated or severely impaired several days after transmission, precisely during their molt from the L3 to the L4 stage. Moreover, only larvae undergoing the molt from L3 to L4 stages are capable of stimulating an immune response directed against the challenge infection, indicating that protective Ag are produced during the molting period. Consistent with this, inactivated L3 or live L4 do not produce the same effect. In contrast to susceptible animals, immune jirds elicit high serum antibody titers against molting Ag. Indirect fluorescence antibody-binding tests with sera from protected jirds reveal specific labeling of the surface of molting L3 and not other larval stages, implying a stage-specific elimination process. The identification of molting L3 as a natural target for host immune mechanisms, emphasizes the central importance of this larval stage for future efforts aimed toward the development of a filarial vaccine.

Experimental transmission of Dipetalonema dracunculoides (Cobbold 1870) by Rhipicephalus sanguineus (Latreille 1806)

A dog naturally infected with Dipetalonema dracunculoides and having a microfilaremia of 6050 microfilariae per mm3 of blood was used as source of infection. Experimentally cultivated nymphs of Rhipicephalus sanguineus were fed on the donor dog. Once engorged, ninety-three nymphs were removed and kept at 30 degrees C and RH 90% until they moulted to the adult stage. To study the development of microfilariae in the vector, ten ticks were dissected at Day 37 post-infection. Adult infected ticks were fed on two uninfected dogs. The observed pre-patent periods were 69 and 76 days. Trans-stadial transmission of Dipetalonema dracunculoides by Rhipicephalus sanguineus was demonstrated.

Changes in the surface composition after transmission of Acanthocheilonema viteae third stage larvae into the jird

This study describes the dynamics and the biochemical nature of changes in the surface of the filarial nematode Acanthocheilonema viteae after its transmission into the vertebrate host. Vector-derived third-stage larvae (mL3) were inoculated into naive Meriones unguiculatus and recovered from the tissues at different times post-infection until their moult to fourth-stage larvae (L4). Surface-specific labelling with fluoresceinated lectins revealed that the larvae are covered by a carbohydrate envelope. Although the mL3 envelope was strongly reduced one day after transmission, new surface carbohydrates appeared until the onset of moulting, some of which could also be identified on the surface of L4. In general, surface carbohydrates were partially shed by moving larvae, suggesting a loose association of these components in the epicuticle. The fate of cuticular lipids and proteins of L3 and L4 was monitored by external 125I-labelling and differential extraction of the components. Thin-layer chromatography of surface-labelled lipids revealed only minor changes 1 day after parasite transmission. Afterwards the number of lipids accessible to label decreased further until moulting was complete. Two-dimensional sodium dodecyl sulphate-polyacrylamide gel electrophoresis of surface-labelled proteins showed a consistent surface exposure of mL3 specific proteins until 1 day post-infection. Thereafter, the composition of surface-labelled proteins changed rapidly, resembling that of the L4 as early as several days before moulting. During this period individual differences in the composition of surface proteins were evident.

Dose-dependent recovery of adult Acanthocheilonema viteae (Nematoda: Filarioidea) after single and trickle inoculations in jirds

Increasing single doses of 5, 15, 30, 60 and 90 third-stage Acanthocheilonema viteae larvae per animal were inoculated into jirds. The adult worm load increased steadily, whereas the recovery rate decreased significantly, i.e. the correlation between dose and recovery was negative (rs, -0.90; n = 5; alpha, 0.05). The same inoculation doses were given as trickle inoculations of 5 L3 each (3 x 5, 6 x 5, 12 x 5, 18 x 5) at intervals of 2-6 days throughout the prepatency period. Irrespective of the number of repeated inoculations, a rather constant but low load of 7-10 worms/animal was reached. The recovery rate decreased drastically (rs, -1.0; n = 5). When trickle inoculations were carried out in animals exhibiting patient infections, the superinoculated larvae seemed to be destroyed almost completely; thus, a parasite-host equilibrium was guaranteed in all cases. The immunological background is discussed.

Recovery, distribution, and development of Acanthocheilonema viteae third- and early fourth-stage larvae in adult jirds

Living third- and fourth-stage larvae (L3 and L4) of Acanthocheilonema viteae were recovered quantitatively from adult Meriones unguiculatus within the first 10 days after subcutaneous inoculation of 60 arthropod-derived larvae (mL3). The average recovery of the inoculated larvae was about one third (28.5%), and the majority (87.7%) were found in muscular tissues. Seventy-two hours after inoculation, larvae could be isolated from all body locations, although the majority still was found near the site of inoculation. Morphological and biometrical data indicated that, at least until molting, the development of the larval population was not synchronous, with molting occurring over a period of 48 hr on days 7 and 8 postinoculation. The stomatal rings of postinvasive L3's and L4's were distinguishable structurally and could be used as stage-specific determinants. Immediately after infection, L3's showed a linear growth in diameter; rapid longitudinal growth started after the molt, leading to a doubling in the length of L4's within 4 days. The time course of shedding was reconstructed in detail using isolated L3/L4 intermediates.

Apodemus sylvaticus, a new host for Acanthocheilonema viteae (Nematoda: filarioidea)

Susceptibility of Apodemus sylvaticus and A. agrarius to infection with Acanthocheilonema viteae was compared with that of hamsters and jirds. Microfilaremia in A. sylvaticus was first noted on day 52 post-infection (p.i.) and lasted during the course of the study (up to day 150 p.i.). Maximum microfilaremic levels (female worm basis) of A. sylvaticus [mean +/- S.D. (n) = 690 +/- 1288(6)] were considerably higher than those of hamsters [16 +/- 18(6)] and jirds [51 +/- 25(5)]. Adult worm recovery in A. sylvaticus ranged from 2 to 40% of the number of infective larvae inoculated. Worm development in A. sylvaticus resembled that in hamsters and jirds. In contrast, microfilaremia was not detected in, nor adult worms recovered from A. agrarius throughout the study.

Association between circulating antigen and parasite load in a model filarial system, Acanthocheilonema viteae in jirds

Jirds (Meriones libycus) were infected with various numbers of Acanthocheilonema viteae L3 stage parasites. During the course of the ensuing 16 weeks, blood samples were collected at 2 weekly intervals and the amount of the major parasite excretory-secretory product (E-S 62) and antibodies directed against it measured. After 16 weeks, animals were sacrificed and the size of the mature worm burden established. In spite of interaction between E-S 62 and host antibody, a statistically significant relationship was found to exist between the amount of E-S 62 present in the bloodstream and the size of the parasite load. It is suggested that the detectable antigen level is more influenced by the size of the worm burden than the presence of antibody and that antibody is only likely to affect adversely antigen measurement in situations where the amount released is relatively low. Examples of this are early in infection and in low-level infections. These ideas are discussed in relation to the development and assessment of serological assays which attempt to predict parasite burden in human filarial infections.

The further application of MTT-formazan colorimetry to studies on filarial worm viability

Experiments have confirmed that MTT-formazan colorimetry in its simplest form (incubation of intact worms with MTT and direct visualisation of any formazan formed) can be readily applied to several species of filariae including Onchocerca volvulus. Data is presented which will assist the development of quantitative MTT reduction viability tests for a selection of the smaller filarial species. Assays of pieces of Onchocerca gutturosa and O. volvulus females have led us to tentatively conclude that the tips of filariae, particularly the anterior ends, may well be metabolically the most active part of the worm. Selective sampling of these regions for Onchocerca might therefore be a useful indicator for the viability of the parasite. An example of how MTT-formazan colorimetry has been applied to yield additional data to support motility observations on the in vitro survival of male O. gutturosa is also given. The in vitro timecourse of worm death caused by 10 microM CGP 20376 on Acanthocheilonema viteae females has been examined by MTT reduction and compared with 6 other non-subjective parameters. The results suggests that the parameters examined could be divided into two groups according to the time taken for CGP 20376 to cause 50% inhibition (t50) of the parameter. Fast response parameters had t50's between 1 and 6 h (motility indices, 14CO2 evolution, adenine uptake and leucine uptake), they are more sensitive measures of viability and indicate possible worm damage which may or may not be reversible. Slow response parameters had t50's between 34 and 48.5 h (lactate output, MTT reduction and adenine leakage), and are probably linked with severe degenerative changes and are indicative of worm death.(ABSTRACT TRUNCATED AT 250 WORDS)

Colorimetric quantitation of filarial viability

A simple three-step colorimetric assay based on the tetrazolium salt MTT (3-(4,5 dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) has been developed for quantifying filarial viability. Living (but not dead) filariae take up MTT and rapidly reduce it to formazan, so staining themselves dark blue. This colour change which is easily seen provides a rapid qualitative test for filarial viability. Quantitative data can be obtained by solubilizing formazan out of the worm with DMSO and measuring the absorbance of the resulting solution at 510 nm. To date the technique has been demonstrated in several species of filariae including Onchocerca volvulus. MTT reduction is thought to be selective for NADH-dependent dehydrogenase activity in viable worms. The reaction occurs readily in all developmental stages of Dipetalonema viteae including fragments of filarial tissue. Enzyme activity in viable intact D. viteae appears to be primarily associated with the hypodermis/muscle cells, with minimal formazan formation in the gut and reproductive tracts. The application of this MTT assay as a parameter for quantifying in vitro drugs effects is described. Assay procedures have been developed and optimized with D. viteae and Brugia pahangi for the assessment of effects of macrofilariae and microfilarial release, and the activity of a range of antifilarial standards reported. Several potential applications of the technique to studies on filarial biology are discussed.

Homologous and crossreacting immune response of the jird and cotton rat against microfilariae of Dipetalonema viteae and Litomosoides carinii (Nematoda: Filarioidea)

Consecutive injections of microfilariae of L. carinii and D. viteae were carried out in the homologous or heterologous sequence into the corresponding natural or into the experimental hosts. Microfilariae of D. viteae are imunogenic in Sigmodon specifically and crossreacting as well. However, in the natural host, Meriones, they are doubtlessly tolerogenic. The sojourn and level of microfilaraemia are prolonged resp. higher when living D. viteae-Mf are injected s.c. followed by an i.v. injection. However, freeze-killed microfilariae of D. viteae are immunogenic in Meriones. Obviously the two filarial worms living in small mammals realize the balance with their natural hosts in quite a different manner. Which one of the two possibilities, or if one of them at all, reflects the relationship in human pathogenic filariae remains open.

Antifilarial activity of CGP 20,376 in chimpanzees (Pan t. troglodytes) naturally infected with Dipetalonema vanhoofi

CGP 20,376, a benzthiazole and new antifilarial agent, was investigated at CIRMF in eight wild born chimpanzees naturally infected with Dipetalonema vanhoofi. Single oral doses (3.75, 7.5, 11 and 15 mg/kg) were administered. Drug levels during the first hour after administration were assessed in seven chimpanzees at 10 minute intervals in the blood. Levels of unchanged drug (CGP 20,376) were higher than those of its metabolite (CGP 20,308). However, there was considerable variation between individuals, although the results for each animal were consistent. Because of investigational limitations a complete drug profile could not be established. Unsheathed microfilariae of D. vanhoofi were monitored during the first hour following drug administration in seven chimpanzees. In five the microfilaraemia dropped to low counts within 10 minutes and remained below the initial values for the next 50 minutes while in two other chimpanzees it showed a more irregular reduction. Periodic microfilarial counts over the next 20 months, at roughly 30 day intervals, showed that three chimpanzees, treated with 7.5, 11 and 15 mg/kg respectively, remained free of circulating microfilariae from Day 1 to Day 600, the chimpanzee treated with 3.75 mg/kg remained microfilaremic and, in three chimpanzees low numbers of microfilariae reappeared within one year, whereas in the remaining ape they reappeared after one year. No major clinical adverse effects were observed, but liver function tests showed mild reversible changes at the 11 and 15 mg/kg doses. CGP 20,376 was therefore microfilaricidal, except for the lowest dose, and it was possibly macrofilaricidal in those chimpanzees which remained free of microfilariae for 600 days. Clinically CGP 20,376 was well tolerated.(ABSTRACT TRUNCATED AT 250 WORDS)

The potential of mice as animal models for antifilarial screening

Transplanted infections of Brugia pahangi and Dipetalonema viteae in male BALB/c and CDI mice were investigated as models for evaluating potential antifilarial compounds. The physiology and genetics of the above mouse strains are better defined than any of the rodent species currently used for primary in vivo screening, facilitating a more reproducible means for predicting the filaricidal activity of compounds. The recoveries of B. pahangi macrofilariae, implanted intraperitoneally were greater than or equal to 50% up to six weeks after implant in both CDI and BALB/c mice. The recoveries of D. viteae macrofilariae, implanted subcutaneously, were greater than 50% up to four weeks post implant but had fallen to less than 30% by six weeks. The survival of B. pahangi and D. viteae macrofilariae simultaneously implanted into mice mimicked that seen with the mono-infections, but significantly better recoveries were obtained from dual implanted CDI mice compared to the BALB/c mice when the numbers of macrofilariae implanted were varied. Standard antifilarials were evaluated against D. viteae and B. pahangi dual implanted into either CDI mice or gerbils. The mouse dual implant detected significant worm reductions against D. viteae, B. pahangi or both with all antifilarials tested except CGP 6140. Similarly under the test conditions CGP 6140 was not detected in the gerbil assay, but there were marked differences in the results obtained with the mice and gerbil models. The reasons for these differences are discussed.

Dipetalonema viteae in Mastomys natalensis: effect of pregnancy and lactation on establishment and course of infection

The susceptibility of hosts to filarial infection during pregnancy and lactation was studied using Dipetalonema viteae in Mastomys natalensis as working model. Though no difference in prepatency could be observed yet significantly higher density of microfilaraemia than controls was detected in both pregnant and lactating groups. Extended duration of patency was also found in both pregnant and lactating animals. On autopsy, animals exposed at the time of pregnancy or lactation revealed significantly higher recovery of adult worms as compared to normal controls. Thus pregnancy and/or lactation may lead to higher density and duration of microfilaraemia and enhanced establishment of adult worms in female mastomys which are otherwise less susceptible to filarial infection.

Fecundity and localization of Dipetalonema viteae (Nematoda, Filarioidea) in the jird Meriones unguiculatus

In quantitatively infected Meriones unguiculatus autopsied during prepatency, the embryonic development of fertilized eggs in the uteri of female Dipetalonema viteae commenced 29-32 days p.i., and approximately 20 days later the first microfilariae were released. In host animals examined at the onset of patency 45-59 days p.i. the average adult recovery rate was 31%. The worms were localized in the subcutaneous tissue (65.3%), fasciae of muscles (26.9%) and body cavities (7.8%). Female worms from the peritoneal and pleural cavities were significantly longer (44.3 +/- 10.4 mm) than those from the other habitats (33.7 +/- 5.5 mm). Female worms 14-20 weeks p.i. contained a total of 172,700 +/- 62,400 intrauterine stages, 21% of them pathologically altered. Based on these parameters, the expected in vivo fecundity of a female worm was calculated as about 7000 microfilariae per day.

[Use of surviving infectious larvae of Dipetalonema dessetae in study and research on filaricidal substances]

Dipetalonema dessetae in Proechimys oris, the natural final host is a rodent filariasis model used as an in vivo antifilarial screening test. The laboratory vector is Aedes aegypti. Infective larvae L3 isolated from the intermediate host develop and remain healthy for up to 30 days in a biphasic culture medium composed of a cell feeder layer (L 929) and RPMI 1640 supplemented with foetal calf serum. This culture technique has enabled us to screen antifilarial compounds on a new in vitro test. This model has been tested to several pharmacological classes of anthelmintics and effective concentrations 90% are given: diethylcarbamazine 430 mg/l, suramin 490 mg/l, Mel W 3.5 mg/l, mebendazole 78 mg/l, flubendazole 45 mg/l, levamisole 0.55 mg/l, morantel 0.62 mg/l, ivermectin 1.2 mg/l, amoscanate 2.3 mg/l. In vitro test response is remarkable for neurotoxic anthelmintics and nitro-compounds. Furthermore, all compounds considered as reference filaricides are active. For each compound, the in vitro and in vivo results have been compared to appreciate usefulness as well as limits of this in vitro test.

Protective immune responses of the jird to larval Dipetalonema viteae

In vivo and in vitro experiments were performed to study immune protective mechanisms against larval Dipetalonema viteae. Jirds infected with 30 third-stage larvae (L3) of D. viteae for 1, 3 or 5 weeks showed significant killing of challenge larvae implanted for 2 weeks in diffusion chambers. A retardation of larval growth was seen 7 days after larval implantation, and larval death was observed beginning at 10 days. When L3 were placed in vitro with peritoneal exudate cells (PEC) from normal jirds, cellular adherence was seen starting on Day 4, and larval death was seen on Day 10. It was concluded that larvae had to undergo some development in vitro, that would allow cellular adherence to larval surface. Larvae, recovered after 7 days in vivo or in vitro, were placed in culture with normal PEC; cell adherence and worm death occurred at equal rates for both groups of worms. Larvae which had been in culture for 7 days were implanted in immunized jirds for 7 days. Significant killing of these worms was observed, whereas larvae recovered from ticks prior to implantation were not killed. In vivo and in vitro results therefore show that larval development is required for generating susceptibility to specific and/or non-specific immune reactions. A hypothesis is suggested for the function of larval retardation.

Retinol deficiency and Dipetalonema viteae infection in the hamster

Following chronic retinol (vitamin A) deprivation leading to exhaustion of liver vitamin A reserves below 50 I.U. per liver hamsters were fed diets either deficient in ("Rd":250 I.U.A./kg in experiment I, 1000 I.U.A/kg in experiment II) or enriched with retinol ("Rw":10000 I.U.A/kg in experiment I and II). After 4 weeks some of the animals (36 in experiment I, 30 in II) were infected with 150 3rd-stage larvae of D. viteae, while clean animals were kept as controls. The retinol status, the immune response (indirect fluorescent antibody test: IFAT) and parasitological parameters were examined up to 8 (experiment I) and 12 weeks (experiment II) post infection (p.i.). Rd hamsters had levelling off of weight gain or weight loss, severely deficient retinol levels in serum and liver, and high mortality. Weight gain was less in infected than in uninfected hamsters, and the capacity of infected Rw animals to restore liver retinol was significantly lower than that of uninfected Rw animals. IFAT titres were similar in Rd and in Rw animals, but microfilaraemia was significantly enhanced at 8 and 10.5 weeks p.i. in Rd hamsters. While the number of worms recovered from Rd and Rw hamsters was similar, there was a significant increase in the ratio of female to male worms in Rd hamsters. Rd hamsters in experiment I produced 3.3 times the worm mass per 100 g body-weight than Rw hamsters. Also, the average mass per female worm was significantly higher in Rd than Rw in hamsters, and this parameter was negatively correlated with the liver retinol concentration in experiment I(r = -0.89). Retinol deficiency has a marked effect on growth and fertility of D. viteae in hamsters.

In vitro cultivation of Dipetalonema viteae third-stage larvae: evaluation of culture media, serum, and other supplements

Third-stage larvae of Dipetalonema viteae obtained from the tick vector developed to the fourth stage in several cell-free culture systems. Survival and development of larvae in a number of commercially available cell culture media, supplemented with serum and other defined and undefined components, were compared. All cultures were gassed with 5% carbon dioxide in nitrogen. Best survival, growth and development were obtained in stationary cultures containing 1:1 (v/v) mixtures of NCTC 135, either RPMI 1640 or Iscove's Modified Dulbecco's Medium, and a supplement of 20% non-heat-inactivated fetal bovine serum. The importance of the medium composition and physical environment of the culture system, for the survival, growth and development of D. viteae was demonstrated.

Protein kinases in different life stages of Brugia malayi and other filarial worms

The investigation of protein kinase activity in different life stages of a few filarial worms indicates the presence of different protein kinases and of dissimilarities between the distribution pattern of these enzymes during the development. Phosvitin turned out to be the preferred exogenous acceptor protein, when homogenates of adults of Brugia malayi, Dipetalonema viteae, Setaria cervi and Litomosoides carinii were used as source of enzyme. In contrast to adults the L3-larval and the microfilarial stages demonstrated much lower phosvitin phosphorylating activity and the preference for acidic and basic proteins as phosphate acceptors was about equal. The occurrence of cyclic AMP-dependent protein kinase was established for adults of B. malayi.

In vitro cultivation of Dipetalonema viteae third-stage larvae: effect of the gas phase

The effect of the gas phase on the in vitro growth and development of Dipetalonema viteae (Nematoda: Filarioidea) third-stage larvae obtained from the tick vector and 3 day infections of jirds was examined. Measurements of the oxygen (pO2) and carbon dioxide (pCO2) tensions and the pH in the medium were made for each gas phase. In cultures gassed with 5% carbon dioxide in nitrogen the pO2 was between 32 and 50 mm Hg, the pCO2 ranged from 25 to 40 mm Hg and the pH was between 7.2 and 7.4. This gas phase resulted in the best growth and development of third-stage larvae to the fourth-stage. Survival and development of larvae were decreased in cultures with oxygen tensions less than 20 mm Hg and greater than 50 mm Hg.

Dipetalonema viteae (Nematoda: Filarioidea): culture of third-stage larvae to young adults in vitro

Infective third-stage larvae of Dipetalonema viteae (Nematoda: Filarioidea) were cultured to young adults in a cell-free culture system. Third-stage larvae from the tick vector grew, developed, and molted twice in a medium containing NCTC 135 and Iscove's modified Dulbecco's medium supplemented with fetal bovine serum under a gas phase of 95 percent nitrogen and 5 percent carbon dioxide. The availability of such a culture system for filariids should facilitate studies of their immunology, biochemistry, and sensitivity to drugs.

Identification of immunogenic proteins of Dipetalonema viteae (Filarioidea) by the "Western Blotting" technique

Sodiumdodecylsulphate (SDS)-solubilized proteins of several developmental stages of Dipetalonema viteae (adults, uterus content, microfilariae, infective larvae) were subjected to SDS-polyacrylamide gel electrophoresis and transferred onto nitrocellulose filter sheets. Their antigenicity in natural infections of Meriones unguiculatus was investigated by immuno-recognition with pooled sera of infected hosts. The antibodies were labelled by radioiodinated protein A and visualized by autoradiography. Immunorecognized protein bands were demonstrable in all stages, some of them being stage specific, others common to several or all stages. The highest number of labelled protein bands was found in extracts of adult worms, the lowest in preparations of microfilariae and infective larvae.

Comparison of surface iodination methods by electron microscopic autoradiography applied in vitro to different life-stages of Dipetalonema viteae (Filarioidea)

Different states of Dipetalonema viteae (males, females, microfilariae, and 3rd-stage larvae) have been iodinated in vitro under physiological conditions by chloroglycoluril, lactoperoxidase or chloramine T. The concentrations of the catalysts were correlated with the viability of the worms. Localization of the label with the different iodination methods had been visualized by electro microscopical autoradiography. Chloroglycoluril-mediated iodination is predominantly localized on the filarial cuticle. Lactoperoxidase-catalysed iodination is less specific and chloramine T catalyses iodination in a gradient decreasing from the cuticle to inner structures. It is necessary to visualize the labelling by electron microscopical autoradiography prior to biochemical and immunological experiments to avoid the extraction of structures iodinated by leakage of the catalyst into sub-cuticular regions.

Protein composition of various developmental stages of dipetalonema viteae (Filarioidea)

The protein composition of various developmental stages of Dipetalonema viteae was analysed on polyacrylamide slab gels in the presence of sodium-dodecylsulphate. When the total proteins of adult male and female parasites, microfilariae, eggs, and third-stage larvae were compared, apparent qualitative similarities between mature and immature filariae were observed. However, several stage specific components were also identified.

Dipetalonema viteae (Filarioidea): development of the infective larvae in vitro

The development of Dipetalonema viteae third stage larvae was attempted in vitro. A monophasic culture system consisting of BHK-21 medium supplemented with 10% tryptose-phosphate broth and 15% fresh jird serum allowed the growth of previously in vivo triggered larvae, but not of those isolated from ticks. The larvae could complete their third moult and grew on a fourth stage larvae up to 5 mm. This development was comparable to that observed in vivo. The presence of an irradiated hamster kidney cell feeder layer could replace an in vivo trigger. The development of the infective larvae took place up to the third moult. Some larvae completed the moult to the fourth stage and reached a maximum length of 3 mm after 14 days. These culture systems offer the possibility to study in vitro the complete development of the infective larvae to fourth stage larvae.

[New contribution on Dipetalonema viteae. Keeping adults alive in vitro. Scanning electron microscope study of the development of embryos and young larvae L1 and L2]

The adult stages of Litosomosoides carinii, Dirofilaria uniformis and Dirofilaria immitis have been successfully maintained in vitro though microfilaria production by the worms continued only for a period of one to 18 days. In this paper we describe the results obtained in a series of experiments in which adult L1 and L2 stages of Dipetalonema viteae were maintained in vitro.

Dipetalonema viteae infective larvae reach reproductive maturity in rats immunodepressed by prior exposure to Schistosoma mansoni or its products and in congenitally athymic rats

Infective larvae of Dipetalonema viteae did not reach maturity in inbred Fischer rats. However, female adults of D. viteae when transplanted surgically into Fischer rats established and the resulting microfilaraemia from the transplanted worms persisted for about 120 days after infection. Sequential dissections showed that some of the female worms transplanted remained viable in rats for about 35 days after infection. After inoculation of infective larvae into rats a varying number transformed into stage-4 larvae but they did not develop into adult worms and were killed. However, when the rats were immunodepressed non-specifically by a pre-existing Schistosoma mansoni infection or by treatment with S. mansoni-derived substance(s), a number of stage-4 larvae renewed their development and reached sexual maturity. These worms produced microfilariae which were observed in the peripheral blood for about 40 days. The effect of previous infection with S. mansoni on the survival and growth of D. viteae in Fischer rats depends greatly on the relative timing of infection because infective larvae of D. viteae reached maturity only when rats were inoculated with infective larvae after 15 days of S. mansoni infection but not after 21 or 28 days of S. mansoni infection. D. viteae will also develop to maturity in congenitally athymic rats. In congenitally athymic rats (Nu/Nu) each given 75 infective larvae, both the microfilaraemia and adult worm recovery at post-mortem were higher than those which resulted in Nu/Nu rats given an infection of 200 larvae. These experiments show that in rats innate immunity to this filarial nematode reflects a very rapidly induced acquired immunity which kills the parasite before it reaches maturity.

[The larval development of Dipetalonema rugosicauda (syn. Wehrdikmansia rugosicauda) in the tick Ixodes ricinus. II. The development of Dipetalonema rugosicauda in Ixodes ricinus and investigations about the occurrence of the microfilariae in the roe deer (C. capreolus) (author's transl)]

Microfilariae of D. rugosicauda, which were taken up by nymphs of I. ricinus during their attachment on roe deers, developed in those ticks to infective larvae after two moults. The larval development lasted 56-67 days at 20-22 degrees C and occurred similar to other species of Dipetalonema inclusive a sausage stage. During this time the nymphs moulted to adult ticks. Adult females and males of I. ricinus collected in the area of Biberach/Riss, Southern-Germany, contained up to 12 infective larvae of D. rugosicauda per tick. The occurrence of those infective larvae and of microfilariae in roe deers depended on the season. The highest rate of infected ticks was 4.3% in spring, whereas the maximum rate of infected roe deers was 46.8% in autumn. Based on investigations of fawns of roe deers the prepatent period of D. rugosicauda can be estimated as approximately 6 months. Compared with microfilariae of Onchocerca tarsicola from red deers the microfilariae of D. rugosicauda prefered deeper layers of the ear skin of their hosts. Besides D. rugosicauda microfilariae of a further hitherto unknown species were detected in the ear skin of roe deers additionally. They resembled microfilariae of O. tarsicola.

[Simultaneous infection of Mastomys natalensis with Dipetalonema witei and Litomosoides carinii (author's transl)]

Mastomys natalensis that has been described by Lämmler et al. (1968) as suitable host for Litomosoides carinii can also serve as final host for Dipetalonema witei. At the end of the prepatency period the microfilaraemia increased as rapidly in Mastomys as in the original final host Meriones persicus. Maximal microfilaraemia was observed earlier in Mastomys (120 days p.inf.) than in Meriones (250 days p.inf.). Accordingly microfilariae counts decreased more rapidly in Mastomys. The maximal counts found in Mastomys was 78000 microfilariae/ml blood, which is 3.2 times less than in M. persicus. Furthermore it could be demonstrated that a simultaneous experimental infection of Mastomys with D. witei and L. carinii in possible. The course of microfilaraemia and the number of macrofilariae were comparable in mono- and simultaneous infections for both species of filariae. The macrofilariae of D. witei began to die earlier than those of L. carinii both in mono- and in simultaneous infections. The percentage of dead macrofilariae was 3.8% 110 days p.inf., and 13.1% 130 days p.inf. respectively. Therefore, chemotherapeutic experiments should be terminated and evaluated about 110 days p.inf.

[New aspects of the part of the vector played by Ixodes ricinus L. in Switzerland. Preliminary note (author's transl)]

The authors, after having recalled their recent work on Ixodes ricinus ecology, give the new results about the part played by this species in the transmission of different infectious agents in Switzerland. I. ricinus was already known to be the most important vector of the tick borne encephalitis virus, and of protozoans of the Babesia genus. In this article, we describe the existence in the hemolymphe of different I. ricinus populations, of a rickettsia species related to the RMST group (Rocky-Mountain Spotted Fever), of a trypanosome, which is close to T. theileri, and of an infectious larval form (L3) of Dipetalonema rugosicauda. An outline is suggested with the object of illustrating the functioning of a natural foci of tick encephalitis. The biological significance of the unusual presence of trypanosomes and of larval filariae in ticks is also discussed. The authors underline the fact that rickettsia, trypanosomes and filarial forms are observed for the first time in Swiss I. ricinus.

[Experimental infection of soft ticks with Dipetalonema witei (author's transl)]

The intermediate host of Dipetalonema witei, the soft tick Ornithodoros moubata, can be infected experimentally with microfilariae. Microfilariae isolated from the blood of infected donor animals were injected into the dorsal haemocoel of the ticks where they developed to infectious filariae within approx. 50 days. The rate of infection of ticks was 100% when more than 100 microfilariae were injected. An average of 23% was recovered as infectious filariae. Up to 450 ticks can be infected with 1000 microfilariae each from a single donor animal within one year, whereas donor animals can only be used for about 1 month if ticks are naturally infected. The method described has advantages compared to natural tick infections with respect to the rate of infection of ticks, the development of microfilariae, and the amount of infectious material produced.