An attempt to produce Ostertagia circumcincta infections in Mongolian gerbils

Adult infections of Ostertagia circumcincta were successfully established in gerbils, although worm growth was retarded compared with infections in sheep. Chronic administration of beta-methasone to the host enhanced development of the parasite reproductive system but did not increase infection rate or prevent worm rejection. Infection rates achieved with single infections were not increased by using daily or weekly trickle infection regimes with or without prior exsheathment of larvae. Examination of stomachs from infected gerbils demonstrated pathological changes in the pyloric region which was the predilection site for O. circumcincta. This is in contrast to infections in sheep in which the fundic region of the abomasum is the preferred site.

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.

Physicochemical characteristics of non-electrolytes and their uptake by Brugia pahangi and Dipetalonema viteae

The uptake of a diverse set of 14C-labelled non-electrolytes by Brugia pahangi and Dipetalonema viteae was measured relative to the free diffusion of tritiated water. Inulin was used as a non-absorbable surface marker to account for non-electrolyte adherent to the surface of the parasite which had not crossed the cuticle. B. pahangi and D. viteae took up the non-electrolytes to a similar degree; a comparison of tissue uptake indices gave a correlation coefficient of 0.99. Worm uptake could not be described by non-electrolyte octanol/aqueous partition coefficients alone. However, greater success was achieved using further descriptors and pattern recognition techniques for data analysis. The whole molecule descriptors log P, molar refraction, melting point, dipole moment and CNDO total energy were obtained from computer chemistry and the literature. Using a linear learning machine to relate uptake to these 5 physicochemical descriptors it was possible to successfully classify non-electrolytes as high or low uptake. Multivariate regression analysis of uptake versus these 5 parameters gave a correlation coefficient of 0.77. However, this was not statistically significant and therefore could not be used for quantitative predictions of substance uptake by worms. This illustrates the value of 'pattern recognition' techniques such as the linear learning machine. Using such 'pattern recognition' methods on a chemically related set of compounds it is anticipated that predictions of uptake can be achieved and improved upon. Such predictions could then be used in drug design.

A comparison of the response of Dipetalonema viteae and Brugia pahangi adult worms to antifilarial agents in vitro

The drug response of Dipetalonema viteae and B. pahangi under various culture conditions have been evaluated. B. pahangi female worms proved to be more susceptible to CGP 6140 (4-nitro-4'-(N-methyl)piperazinyl thiocarbonylido-diphenylamine), CGP 20376 (N-(2-tert-butyl-5-methoxy-benzothiazol-6-yl)dithiocarbonic acid 5-(1-carboxyethyl)-ether) and amoscanate when glucose availability was restricted. This increased potency may be related to effects on glycogen metabolism by CGP 20376 and amoscanate. Using the parameters of parasite motility, survival, glucose consumption and microfilarial output, Eagles Minimum Essential Medium supplemented with 10% inactivated foetal calf serum plus either a 95% air:5% CO2 or a 95% N2:5% CO2 gas phase was shown to be highly suitable for short term maintenance (5 days). Examination of 12 drugs selected on their in vivo activity against B. pahangi and D. viteae demonstrated little difference between the drug susceptibilities of male and female worms. However, there were intrinsic differences between worm species. The relationship between these disparate susceptibilities and the reported in vivo efficacies of these drugs and the importance of selecting appropriate conditions for in vitro drug assays are discussed. Ivermectin at 10(-5) M caused a rapid flaccid paralysis and a complete suppression of microfilarial output by D. viteae. Despite continued paralysis of the worms they continued to utilise as much glucose as untreated worms over a 4 day period.

The efficacy of benzimidazole anthelmintics against late fourth stage larvae of Trichostrongylus colubriformis in gerbils and Nippostrongylus brasiliensis in rats

The efficacy of eight benzimidazole anthelmintics has been examined against Trichostrongylus colubriformis in gerbils and Nippostrongylus brasiliensis in rats, when the parasites were entering into the fourth and final moult. The dose--response slopes obtained from the data for both host--parasite systems did not deviate significantly from a non-parallel model, and were used for relative potency determinations. The T. colubriformis assay ranked the benzimidazoles in order of potency as follows: albendazole, oxfendazole, fenbendazole, cambendazole, mebendazole, oxibendazole, parbendazole and thiabendazole. This compares favourably with the expected relative efficacies against trichostrongyles in sheep. N. brasiliensis was found to be far less useful in this respect. All compounds tested, with the exception of thiabendazole, were highly effective against both parasites. The T. colubriformis/gerbil assay could be a very useful tool for preliminary in vivo evaluation and possibly in the early selective optimisation of chemical series.

Study on the activity of antiparasitic agents against Onchocerca lienalis third stage larvae in vitro

The in vitro drug response of third stage larvae of the cattle filarial worm Onchocerca lienalis has been studied. Larvae were maintained in Minimum Essential Eagles medium supplemented with 10% inactivated foetal calf serum and exposed to the following drugs: Mel W, caparsolate sodium, suramin, ivermectin, flubendazole, levamisole and amoscanate plus 3 novel melaminylthioarsenites. Antiparasitic activity of these compounds has been assessed on their killing effects and their ability to totally inhibit the moult from the third to the fourth stage. Unfortunately, moulting occurred at a low rate in the culture system used and was not suitable as a quantitative parameter for describing drug activity. However, the results indicated that if the rate of ecdysis could be increased by improving the culture conditions, moulting could be used in this manner since exsheathment has inhibited by certain compounds at concentrations where killing effects were less than 50%. Of the compounds evaluated ivermectin demonstrated good activity, totally preventing ecdysis at 0.001 microgram/ml. The drug assay system used in this study may offer a starting point for the eventual development of a meaningful and specific in vitro screen for new anti-Onchocerca agents.

Improvement of in vitro culture conditions of Brugia pahangi four day old developing larvae for use in an antifilarial drug assay

Four day old third stage larvae of Brugia pahangi were cultured in the presence of differing concentrations of early passage dog kidney cells and inactivated foetal calf serum. After a six day culture period worm length, number of moults and worm mortality were determined. Analysis of the length data demonstrated a significant interactive relationship between cell and serum concentration. The greatest increases in length were obtained using an initial cell density of dog kidney cells of 40 x 10(4) plus a serum concentration of 10%. (The surface area of all culture vessels was 2.0 cm2). In addition moulting occurred earlier and was more prolific with higher cell and serum concentrations. The response of larvae to antiparasitic agents in the presence or absence of a confluent dog kidney feeder layer was then compared to determine whether the inclusion of cells altered drug effects. From this it was found that the killing effects of flubendazole, albendazole, furazolidone, levamisole and nifurtimox at their minimum effective concentrations were delayed under biphasic culture conditions. It is suggested that this is an advantage and will improve the selectivity of the assay over and above an assay which does not include a cell feeder layer. In addition the improved growth rates obtained in cultures containing dog kidney cells should mean an increase in test sensitivity to agents capable of disrupting biosynthesis.

A diffusion chamber technique for detecting compounds with clinical prophylactic activity against Brugia pahangi

A new technique for examining the clinical prophylactic activity of antifilarial agents against Brugia pahangi is described. Third stage larvae were confined within diffusion chambers before intraperitoneal implantation into jirds. Such larvae developed normally within the chambers for 14 days when compared with infections in which larvae were allowed to grow freely within the peritoneal cavity. After this time conditions inside the chambers deteriorated and larval growth was inhibited. Larval recoveries from diffusion chambers after 14 days were higher and more reproducible than from intraperitoneal infections. The activities of known antifilarial agents against larvae confined within chambers implanted into jirds were examined. The benzimidazoles were found to be extremely effective Flubendazole killed almost all larvae when administered at 5 x 25 mg/kg sc by day 9 after the final treatment. It is suggested that the test described has potential as a screen for detecting clinical prophylactic activity because of its reproducibility, low parasite requirement, ease of parasite recovery and relatively short result acquisition time.

Shared antigens between Litomosoides carinii and its hosts Sigmodon hispidus and Mastomys natalensis

Using a indirect immunofluorescent technique it has been shown that host or host-like antigens are present on adults and microfilariae of Litomosoides carinii from cotton rats and multimammate rats. Red blood cell components were seldom detected on any stage but serum antigens were found associated with the cuticle of adults worms. Serum components were absent from in utero and in vitro microfilariae but were found on microfilariae from pleural exudate and host blood. These components were lost from microfilariae after their ingestion by the vector, were absent from third and fourth stage larvae but reappeared as the adults matured in the pleural cavity of a new host. Countercurrent immunoelectrophoresis showed that the components had alpha 2--beta 1 and beta 1--beta 2 mobility.