Filaricidal effect of mefloquine on adults and microfilariae of Brugia patei and Brugia malayi.

Mefloquine, DL-erythro-2,8-bis(trifluoromethyl)-alpha-(2-piperidyl)-4-quinoline methanolhydrochloride, a recently developed antimalarial drug shows filaricidal activity against larval and adult stages of Brugia patei and B. malayi maintained "in vitro". In the concentration range of 10 to 2 microM mefloquine paralysed and killed the filarial worms within 10 h and 3 d, respectively. The lethal effect of mefloquine treatment on larval and adult worms was shown by loss of motility as well as by decrease of lactate excretion by adults. Chloroquine at a concentration of 10 microM did not affect motility and survival of microfilariae and adults of B. patei. Addition of serum to the cultivation medium abolished the filaricidal effect, possibly due to the tight binding of mefloquine to serum proteins, thereby affecting the uptake of the drug into the parasite.

Parasite-specific interaction of N-[4-(4'nitroanilino)-phenyl]-S-(beta-carboxyethyl)-dithiocar bamic acid-ester with arginyl-tRNA-synthetase from Dirofilaria immitis.

A potent inhibition of arginyl-tRNA-synthetase from Dirofilaria immitis by N-[4-(4'nitroanilino)-phenyl]-S-(beta-carboxylethyl)-dith iocarbamic acid-ester (CGP 8065) is demonstrated, which indicates the charging of amino acids to tRNA as a possible target for the chemotherapeutic attack by this filaricidal compound. CGP 8065 competes with ATP; the inhibition constant was determined to be 13 micrograms ml-1 (34 microM). The Michaelis constants for arginine and ATP were found to be 5 microM and 0.4 mM, respectively. The inhibition of arginyl-tRNA-synthetase by CGP 8065 was shown to be specific for D. immitis; the isofunctional enzymes from Ascaris suum and rat liver were not affected.

The susceptibility of Liberian Culex quinquefasciatus to Wuchereria bancrofti in Sri Lanka.

Strains of Culex quinquefasciatus collected in Liberia showed low susceptibility to Wuchereria bancrofti from Liberian donors. However, when the same mosquito strains were fed on W. bancrofti donors from Sri Lanka they showed equally high susceptibility as Sri Lankan C. quinquefasciatus simultaneously fed on the same donors. A Liberian strain did not respond to selection for refractoriness. Thus the strains of W. bancrofti from Liberia and Sri Lanka differ in their ability to infect specific mosquito strains and it is concluded that Liberian C. quinquefasciatus could not provide genes for use in the construction of a refractory strain intended for the replacement of Sri Lankan vector populations.

[Scanning microscopical observations on the foregut structures o mosquitoes and their role for the ingestion of microfilariae (author's transl)]. / Rasterelektronenoptische Studien zur Morphologie und Bedeutung der Vorderdarmbewehrung verschiedener Stechmückenarten für die Aufnahme von Mikrofilarien.

Experiments on the transmission of Brugia malayi by various mosquitoes had shown that microfilariae ingested by some species were badly damaged when they reached the stomach, but were much less hurt in others. The structures of the foregut likely to cause these injuries, were investigated and documented by scanning microscope techniques. In Anopheles albimanus, A. arabiensis, A. stephensi and A. pharoensis which have well developed armatures the microfilariae showed a high rate of destruction. In A. stroparvus as well as in Aedes aegypti, Ae. togoi and Culex fatigans in which these structures are missing or poorly developed the larvae were much less affected. From the size, shape and position of the different papillae, spines, rods and cones observed it can be concluded and confirmed that the pharyngeal armature (buccopharyngeal bar) will be by far the most important structure responsible for the injuries of the microfilariae. However, it appears that the characteristics of different filaria species can play an important role in preventing such damages.

[Daily and seasonal changes in the oviposition activities of Culex pipiens pipiens L. (author's transl)]. / Tages- und jahreszeitliche Veränderungen der Eiablageaktivität von Culex pipiens pipiens L.

The oviposition activity of C. p. pipiens during summer and autumn has been investigated at two breeding sites in West and North Germany. The egg rafts were collected and counted daily or hourly. Soon after its begin oviposition reached a high peak and then decreased sharply and faded out towards sunrise. There was an obvious correlation between the hourly maximum number of egg rafts deposited and nightfall. The peak of oviposition regularly followed the sunset with one hour delay. It shifted with the changing daylight period according to the season and geographic latitude. The decrease and ending of the oviposition in September is considered not to be related to the decreasing temperatures, but to be due to the disappearance of the gonoactive summer generation and the predominance of the diapausing females of the over-wintering population.

Dynamics and intensity of Wuchereria bancrofti transmission in the savannah and forest regions of Liberia.

In four villages in the savannah and in the rain forest of Liberia, regular assessment of the biting activity and infection rates of anthropophilic mosquitoes have been carried out through full annual cycles. The microfilaremia rates in the localities in the savannah were 18.3% and 20.0% and in those of the forest 10.3% and 12.5%. The all-night catches were performed inside ordinary inhibited houses at monthly or fortnightly intervals. Presence of infective larvae of Wuchereria bancrofti proved Anopheles gambiae, A. funestus and A. nili to be the local vectors. Biting densities were high in the savannah, and low in the forest. From the mosquito catches and the results of their dissections for filarial larvae it could be estimated, that during the observation year a person in the savannah villages would be bitten annually by 18,165 and 36,450 vector mosquitoes respectively, and would receive 236 and 536 infective bites with 570 and 1211 infective larvae. In the two forest villages the number of vector bites per person per year was calculated to be in the order of 6120 and 1102 of which 64 and 8 would be infective bites transmitting 101 and 8 larvae. The findings of considerable differences in transmission intensities between villages of the same bioclimatic zone and of comparable microfilaremia rates indicates instable epidemiological conditions in at least some of the localities investigated.

Localization of acid phosphatase in microfilariae of Loa loa and Dipetalonema perstans from Cameroun.

The histochemical pattern of acid phosphatase activity in the microfilaria of L. loa showed a diffuse red staining all over the body, with conspicuous staining of the excretory and anal vesicles, Innenkörper, amphids and phasmids. In D. perstans, the enzymatic activity was localized chiefly in four regions corresponding to the excretory and anal vesicles, amphids and phasmids of the microfilariae. A considerable loss of enzyme activity was observed in microfilariae that had been stored in a refrigerator for somedays prior to their fixation.

Cholinesterase activity in the microfilaria of Wuchereria bancrofti Cobbold.

The distribution of cholinesterase activity in the microfilaria of the nocturnally periodic Wuchereria bancrofti has been described. Using histochemical methods, cholinesterase activity has been demonstrated in the amphids (Mundgebilde), phasmids (Schwanzgebilde), nerve-ring, excretory and anal vesicles of the microfilaria. It has been found that the enzyme activity disappeared completely after treatment with the specific cholinesterase inhibitor eserine. Evidence is presented that the greater amount of the cholinesterase activity detected is related to acetylcholinesterase and the functional significance of the enzyme in the enzyme reactive structures is discussed.

On the inheritance of susceptibility for infection with Wuchereria bancrofti in Culex pipiens fatigans.

From a colony of C.p.fatigans from Monrovia showing 21.6% susceptibility of W. bancrofti a refractory strain could be selected but not a highly susceptible one. Experiments to select a refractory strain out of the highly susceptible colony from Delhi failed. From these results and those of the crossing experiments between the selected refractory strain from Monrovia and the Delhi colony it appears that in the mosquito population from Monrovia susceptibility for W. bancrofti is not dominating refractoriness while this is the case in the population from Delhi. Therefore, it is concluded that there will be at least two genetic factors controlling susceptibility for W. bancrofti in C.p.fatigans.

Distribution and prevalence of Wuchereria bancrofti in various parts of Liberia.

A nightblood survey has been carried out in 82 localities situated in various parts of Liberia. A total of 8072 people have been examined for the presence of microfilariae of Wuchereria bancrofti and 403 (5.0%) have been found positive. However, the distribution of the disease was quite uneven. The infection was common in the coastal zone showing an average microfilaria prevalence of 9%, while in the forest belt among 5383 people living in rural areas only 109 (2.0%) were found to harbour microfilariae. In the savannah area out of 2198 people examined 209 (11.4%) persons were carriers of microvilariae.

[Gonotrophic dissociation in Culex pipiens pipiens L. (author's transl)]. / Gonotrophische Dissoziation bei Culex pipiens pipiens L

Under certain conditions gonotrophic dissociation has been observed in Culex pipiens pipiens. To contribute to a better understanding of the factors which govern the appearance of this phenomenon and of its ecological importance a population in Northern Germany has been investigated. Follicular development, feeding activity and occurrence of gonotrophic dissociation were examined in females obtained from wild-caught larval stages and kept under outdoor conditions after emergence in July and August. In addition overwintering females collected in cellars in September and October were investigated after reactivation by exposure to 16 hours illumination periods and 28 degrees C. In females emerging in August the follicles were generally small, the feeding activity was very low but the rate of gonotrophic dissociation appeared to be higher than that in mosquitoes which had emerged in July. Overwintering females had small follicles and did not take a blood meal during the first days under reactivation conditions. Only after five days a development of follicles and an increase in feeding activity became apparent. Through the effect of long illumination and high temperature the state of diapause was gradually overcome and the females were fully reactivated. At the same time the rate of gonotrophic dissociation in fed females which was high in the early time of exposure to reactivation conditions became low. This suggests that gonotrophic dissociation occurs commonly in females with low feeding activity, i.e. those which are not reactivated completely. In Northern Germany the overwintering females are unfed and nulliparous and gonotrophic dissociation does not seem to play an important role for the overwintering of the mosquito in this area.