Homologues of the mammalian multidrug resistance gene have been identified in isolates and clones of Plasmodium falciparum and designated pfmdr1 and pfmdr2. Mutations in pfmdr1 have been associated with chloroquine resistance but confirmation could not be obtained in a genetic cross. We have examined the copy number and expression of pfmdr1 and pfmdr2 in chloroquine-sensitive and -resistant P. falciparum and have found no relationship between the copy number of either gene and chloroquine resistance. However, a marked correlation was seen between levels of mRNA transcribed for each gene and chloroquine resistance. Two transcripts of pfmdr1 were detected, and in the asexual blood cycle an 8 kb transcript appeared first, followed by the appearance of a 7 kb species.

Ultra-violet irradiated larvae of Schistosoma mansoni stimulate high levels of resistance to challenge infection in experimental animals. In the experiments presented here, the binding patterns of antisera specific for the cercarial glycocalyx, and of various lectins, demonstrate that u.v. irradiation causes a pronounced modification of the carbohydrate antigens expressed at the surface of cercariae and newly transformed schistosomula.These alterations were dependent on the irradiation dose, and on the batch of cercariae used in each experiment. Our results strongly suggest that the changes in carbohydrate antigens consequent upon u.v. irradiation may be important in generating the enhanced immunogenicity of irradiated cercariae.

The snail Bulinus nasutus 1214 possesses a potent haemagglutinin (end-point titre with human erythrocytes, 2−18) in its cell-free haemolymph which also binds to the miracidia (but not other larvae) of the incompatible parasite Schistosoma margrebowiei. We have purified a protein possessing this haemagglutinating property from the plasma of this snail. The native Mr of this protein was estimated by SDS polyacrylamide gel electrophoresis to be 210 kDa; under denaturing conditions in a 7.5% PAGE gel it ran as a major band of 135 kDa. Proteins of similar Mr were also found in the haemolymph of 16 other Bulinus spp. (the major intermediate hosts of human and veterinary schistosomiasis in Africa) although the plasma of none of these agglutinated human erythrocytes. Nonetheless, Cleveland mapping of the Mr 135 kDa bands from these different Bulinus spp. revealed 4 identical major peptide fragments (30, 28, 19 and 16 kDa) in each, thus demonstrating a similarity in the primary structure of these plasma proteins. Antisera from Balb/C mice immunized with the 135 kDa polypeptide from Bulinus truncatus 1521 cross-reacted in Western blots with the 135 kDa band of other members of the same truncatus/tropicus species complex but not with species from the africanus or forskalii species groups.

In order to estimate the value of population genetics for both the taxonomy of trypanosomes belonging to the species Trypanosoma brucei and a better understanding of Human African Trypanosomiasis (HAT), we undertook a cellulose acetate electrophoresis isoenzyme study involving 55 stocks isolated from man and animals in Congo, Zaire and Cameroun. Out of the 24 loci surveyed, 15 exhibited variability, which made it possible to delimit 23 zymodemes, divided into 2 groups. The first group equated to the classical subspecies Trypanosoma brucei gambiense, while the second corresponded to the classical subspecies Trypanosoma brucei brucei. These results broadly agree with the current taxonomy, and are corroborated by RFLP analysis of kDNA. Statistical analysis indicates a basically clonal reproduction system of the trypanosomes in the area studied; the zymodemes are equivalent to natural clones (or a family of closely related clones), stable in space and time. Epidemiological hypotheses are proposed according to the geographic distribution of the clones in this area.

Trypanosoma (Nannomonas) congolense comprises morphologically identical but genetically heterogeneous parasites infective to livestock and other mammalian hosts; three different genotypes of this parasite have been described previously. Restriction enzyme fragment length polymorphisms (RFLPs) in both kinetoplast DNA minicircle and nuclear DNA sequences, and randomly amplified polymorphic deoxyribonucleic acid (RAPD) patterns have been used here to demonstrate the existence of another type of T. (N.) congolense that is genotypically distinct from those that have so far been characterized at the molecular level. A highly repetitive, tandemly arranged DNA sequence and oligonucleotide primers, for use in polymerase chain reaction (PCR) amplification are described, which can be used for specific identification of the trypanosome and its distinction from others within the Nannomonas subgenus.

The feeding behaviour of parasitic 3rd-stage larvae (L3) of the hookworms Ancylostoma caninum, A. ceylanicum and Necator americanus was examined. Less than 11% of A. caninum L3 recovered from the small intestines of dogs infected orally were feeding at 4–48 h post-infection (p.i.). and none of the A. ceylanicum L3 recovered from the intestines of orally infected hamsters had resumed feeding. All L4 of both species recovered at 36 and 48 h p.i. had resumed feeding. On the other hand, approximately 16% of the A. ceylanicum L3 recovered from the skin of percutaneously infected hamsters at 18 h were feeding, and the percentage feeding increased to nearly 58% at 44 h p.i. Necator americanus L3 recovered from the skin of percutaneously infected neonatal hamsters resumed feeding at 6–12 h p.i. and reached 90–94% by 18 h. Feeding began to decline at 66 h, and reached 29% at 120 h p.i. This decrease was associated with the migration of larvae from the skin to the lungs. By 192 h p.i. over 95% of the larvae had reached the small intestine, and all had moulted to the L4. The results indicate that parasitic L3 resume feeding in the skin during percutaneous infections, and suggest that feeding by hookworm L3 correlates with the resumption of development.

Specific antisera, directed against the highly conserved C-terminal hexapeptide amide of mammalian pancreatic poly-peptide (PP) and the invertebrate peptide FMRFamide, have been used in conjunction with post-embedding, IgG-conjugated colloidal gold immunostaining to demonstrate peptide immunoreactivity at subcellular level in the nervous system of adult Diclidophora merlangi. Gold labelling revealed that immunoreactivity for PP and FMRFamide was localized exclusively in dense-cored vesicles occupying the majority of axons in the central nervous system. Double-labelling demonstrated an apparent co-localization of PP and FMRFamide in the same dense-cored vesicles. Antigen pre-absorption experiments indicated cross-reactivity of the two antisera as unlikely, and that some if not all of the PP/FMRFamide immunostaining in the parasite was due to a neuropeptide F-like peptide.

Fifty tetrathyridia of Mesocestoides corti showing various degrees of scolex fission during asexual multiplication were subjected to estimation of the total number of neurons in the central ganglia, using a ‘fractionator’ designed sampling scheme on every 10th Historesin section through the specimen. Neurons were stained with Cresyl fast violet and viewed by transmission light microscopy. Cells were only counted if a nucleolus was present. The animals were divided into groups according to their stage in the asexual reproduction process indicated by head shape and sucker number. Animals which had a narrow head with 4 suckers contained about 250 neurons. As their heads became wider, in preparation for fission, neurons were overproduced by up to 5-fold. As additional suckers were developed (8 in total), neurons were reduced to about 500. Finally, when the animals had 2 clearly discernible heads, with 4 suckers on each, the total number of neurons (per head) was again approximately 250. As the heads became wider again, neuron over-production recommenced. Exceptionally shaped animals with an X- or T-shaped single head were observed. These results suggest that there is a preparatory stage for neuronal regeneration, during which the basic population of neurons is about 250. This is followed by neuron over-production followed by a selective cell death of neurons which occurred during asexual multiplication. Another cycle for neuronal regeneration can occur before an animal completes its fission process.

To understand the mechanism for the expulsion of Nippostrongylus brasiliensis from rats, age-dependent variations in the metabolism of reactive oxygen species in the parasite and the host intestines were examined. N. brasiliensis showed an age-dependent increase in its susceptibility to xanthine-xanthine oxidase and t−butyl hydroperoxide generated oxidants as well as to H2O2. Protection obtained with several scavengers suggested that the worms were damaged by the combined action of oxidants generated by the in vitro systems employed. The level of superoxide dismutase in the nematode and its release into the surroundings exhibited a marked depression with advancement of age. No such alteration was, however, recorded for catalase and glutathione peroxidase. An appreciable decrease in the level of reduced glutathione in older N. brasiliensis appears to render them prone to oxidant attack. The rat intestines, on the other hand, exhibited an appreciable depression in catalase and a reduced glutathione content with progress of the infection. Vitamin E levels were elevated. The release of O27 and H2O2 by the intestines was also found to be greater during later stages of the infection. The combined effect of the changes observed in N. brasiliensis and in the rat intestines may be at least partly responsible for expulsion of the nematode from the rats after day 10.

In order to identify Echinococcus multilocularis DNA in fox faeces for epidemiological purposes, we have developed a new method to prepare DNA suitable for PCR amplification. DNA isolation from fox excrement was performed according to a novel procedure involving lysis in KOH, phenol–chloroform extraction and a purification step on a matrix (Prep-A-Gene®). The target sequence for amplification was the E. multilocularis U1 snRNA gene. PCR products were indistinguishable for 32 different E. multilocularis isolates and no signal was observed after ethidium bromide staining with DNAs from other tapeworm species, including E. granulosus. The sensitivity of amplification was monitored by the addition of E. multilocularis DNA or eggs to faeces free of E. multilocularis and was estimated to be 1 egg per 4 g of faeces. PCR products were blotted onto nylon membranes and hybridized with an internal oligonucleotide probe in order to confirm the results. Twenty nine faecal samples from foxes shot in Franche-Comté (East France) were tested. Out of 10 samples from foxes in which no E. multilocularis adult worms could be observed after necropsy, 7 were PCR positive, showing that the PCR test is more sensitive than microscopical examination. Out of 19 samples from foxes harbouring E. multilocularis adult worms, 18 were PCR positive. The remaining PCR-negative sample could be due either to the misidentification of the species of adult worm (E. granulosus and E. multilocularis), or to DNA variation between different isolates of E. multilocularis. Further work in the field should be initiated in order to confirm these results.

When incubated in vitro for 24 h, intact eggs, chemically shelled eggs (obtained by treating intact eggs with NaOCl), activated larvae (eggs in which the outer shell and inner envelope were removed), and oncospheres (activated larvae treated with papain to remove the embryophore) absorb and metabolize radioactive glucose. Intact eggs, which are covered by the impermeable shell, absorb only small amounts of exogenous radioactive glucose, while chemically shelled eggs, activated larvae, and oncospheres absorb much larger amounts. Only very small amounts of the exogenous glucose are incorporated into the ethanol-precipitable carbohydrate fraction (which would include glycogen) by any of the preparations of eggs/larvae. However, the glucose is incorporated into higher molecular weight end-products that are liberated into the incubation medium. There is a temporal shift in the ability of activated larvae and oncospheres to metabolize exogenous glucose. Activated larvae and oncospheres absorb but do not metabolize glucose during the first 8 h post-activation. Between 8 and 16 h post-activation, however, virtually all of the absorbed glucose is metabolized into higher molecular weight end-products that are liberated into the incubation media. This temporal shift suggests that activation of oncospheres and cysticercoid morphogenesis are accompanied by distinct changes in carbohydrate metabolism.

There is growing emphasis on the use of community treatment to reduce the level of morbidity caused by helminth infection. The design of chemotherapy programmes, in terms of frequency of treatment and proportion of the community treated, would be assisted by a quantitative framework which enabled the morbidity reduction achieved by different approaches to be compared. The present study describes a model developed for this purpose which embodies two innovative features. First, a quantitative score of morbidity (the proportion of individuals harbouring an intense infection) is used to rate the success of a programme and, second, the distribution of helminths in the host population is generated by a mechanism that allows the distribution to change dynamically as a function of both treatment and reinfection. The model behaviour, using values typical of Ascaris lumbricoides, indicates that the benefit derived from community chemo- therapy increases non-linearly with the coverage and efficacy of treatment.