Mixed infections with malarial (Plasmodium gallinaceum) and filarial (Brugia pahangi) parasites were carried out in 8 trials with filaria susceptible (REFM) and filaria refractory (REP-RR) Aedes aegypti strains. A secondary infection with B. pahangi microfilariae (mff) by intrathoracic inoculation, reduced the development rate of a pre-existing P. gallinaceum infection. The level of reduction ranged from 9·5 to 49% in REFM and from 50 to 90% in REP-RR. An immune response against oocysts was seen as melanization in mosquitoes with a double infection in the strain refractory to B. pahangi (REP-RR) and a reduction in oocyst size in both mosquito strains. Melanization was not observed in mosquitoes infected only with P. gallinaceum. This may indicate that activation of the prophenoloxidase (PPO) cascade in response to mff in the haemolymph can also be addressed against oocysts in the midgut. No significant difference in the number of filarial parasites recovered was observed when comparing groups with a single or double infection. Retardation in development of filaria larvae was observed in mosquitoes with double infection (REFM strain), together with melanization and a higher rate of abnormal development. Nutritional deficiency caused by superinfection might also be responsible for the delay in filarial development and reduced oocyst size.

The size of the infecting inoculum may influence the severity of malaria, but evidence is scarce. Malaria therapy records provide a unique source of information on induced malaria in people. The therapy was given to large numbers of neurosyphilis patients and the malaria was left untreated as long as possible. Data from patients treated at the Horton Hospital, Epsom 1923–60 with a single strain of vivax malaria were analysed to assess the influence of inoculum size on severity of disease. Malaria was induced by mosquito bite, blood inoculation or direct sporozoite inoculation. The different measures of inoculum size were inversely correlated with pre-patent period, as expected. Overall, information was available on a total of 563 non-immune patients who were not treated during the first 5 days of patent parasitaemia. No strong or consistent relationships were found between measures of inoculum size and any of the measures of severity used: neither parasitaemia levels, nor peak fevers, nor number of paroxysms of fever. In the largest data set, longer pre-patent periods were associated with tertian fever, spontaneous recovery and less use of modifying treatment. Difficulties in interpreting the results are discussed, particularly with respect to misclassification of both exposure and outcome variables. While an inoculum size-severity relationship cannot be ruled out, a strong relationship is very unlikely.

A method for phenetic analysis of karyotype data has been developed for Leishmania populations. Measurement of size difference between chromosomes recognized by a given DNA probe in different isolates led to the formulation of a Chromosome Size Difference Index (CSDI). The method was applied to phenetic analysis of 4 sets of chromosomes – each set being recognized by a different probe – in 37 L. (Viannia) peruviana isolates sampled along a North–South transect through the Peruvian Andes and, in 11 L. (V.) braziliensis isolates from the Amazonian forest (Peru, Bolivia and Brazil). Karyotype variability was better accounted for by CSDI than by a method based on disjunctive encoding of karyotype data. CSDI evidenced the nature of relationships between L. braziliensis and L. peruviana and it provided a coherent picture of geographical and genomic differentiation among parasite populations. The latter did cluster according to their geographical origin. L. braziliensis was found karyotypically more homogeneous than L. peruviana. Within L. peruviana, Northern populations were closer to L. braziliensis than to Southern L. peruviana populations. The validity of karyotypic populations, or karyodemes, was sustained.

Seroprevalence of Coxiella burnetii, the causal agent of Q fever in humans, was examined in wild brown rat populations from 4 Oxfordshire farmsteads (n = 127), 9 Somerset homesteads (n = 98), and 1 captive enclosure (n = 88) in the UK. Seroprevalence ranged between 7 and 53%, the lowest being within the captive population and the highest on dairy farmsteads with sheep present. This is the first reported investigation of C. burnetii in wild rats outside India. We suggest that the high Seroprevalence among rats (i) provides evidence that wild rats constitute an important reservoir for C. burnetii in the UK, and (ii) explains why cats, as frequent predators of rats, are so important in the epidemiology of this disease.

The amitochondriate parasitic protist Trichomonas vaginalis can utilize either glucose or maltose as carbon and energy source. The mechanisms of maltose utilization were explored with uptake experiments using radio-isotope labelled maltose in combination with the silicone-oil centrifugation technique and enzymatic assays measuring maltose hydrolysis. The uptake of maltose label became saturated after 2–3 h. The uptake of maltose as a function of the external maltose concentration was linear at low concentrations with no further increase at higher levels, kinetics characteristic of reactions obeying Michaelis–Menten kinetics preceded by a diffusion-limited step. Increased viscosity of the medium resulted in decreased maltose uptake, indicating an extracellular location of the diffusion-limited step. Most of the cellular α-glucosidase activity of T. vaginalis was detected on the cell surface, suggesting that maltose is hydrolysed to glucose outside the cell. Glucose interfered more with maltose uptake, and maltose less with glucose uptake, than would be expected if 1 mol of maltose were the equivalent of 2 mol of glucose. This pattern of interaction indicated that the interference occurs before the common metabolic pathway and even before the transport step, supporting the idea of extracellular maltose hydrolysis. We conclude that maltose is hydrolysed to glucose in the boundary layer of the cell, a process akin to membrane digestion in vertebrate enterocytes and on the teguments of helminths. The glucose formed is then transported by the glucose carrier of the organism.

Previous studies on mating behaviour of Schistosoma intercalatum and S. mansoni, two human schistosomes which may overlap in parts of Africa, have shown that in mixed infections in mice there are no physiological barriers preventing heterospecific pairings. However, when choice is possible, matings occur preferentially between partners of the same species. In this paper, further experimental studies on mating behaviour of the two species were conducted. Sequential infections showed that heterospecific pairs of worms change partners to homospecific pairs when given the opportunity. The change of mate is a progressive process requiring up to, at least 8 weeks, and this phenomenon is due to the male worm seeking the appropriate female. S. mansoni males are better at pairing with females than S. intercalcatum males, and they will change partner to pair with homologous females in preference to heterologous females whenever given the opportunity. Moreover, in the absence of S. mansoni female worms, unpaired S. mansoni male worms pull away female S. intercalatum from male S. intercalatum. It appears from this study that S. mansoni males are much more competitive than S. intercalatum males at pairing with females, and this is a disadvantage for S. intercalatum in situations of sympatry.

Codon usage and bias has been examined in 20 genes of Schistosoma mansoni. Significant heterogeneity was detected in the patterns of codon usage and bias among genes by metric multidimensional scaling and three general indictors of bias (GC3S, Nc and B). In keeping with observations on sporozoan parasites, codon usage bias was observed to be dependent on the overall base composition of the genes analysed, which in turn was reflected in the types of codons that were over or under-represented in the sequences.

During the chronic stage of Chagas disease a 160 kDa antigen appears in the blood of patients and remains detectable many years after the onset of the disease. This antigen is secreted by the trypomastigote form of the parasite while it is undetectable in the epimastigote form. We report here that the chronic 160 kDa exoantigen is encoded by a gene family (CEA 160 family). We describe the cloning and partial nucleotide sequence of a gene (CEA 160–1) belonging to the CEA160 family. Comparison of the gene sequence with other sequences present in the databases revealed homologies with several Trypanosoma cruzi surface antigens. Highest amino acid identity (59%) was with members of a family containing epitopes that mimic nervous tissues (Van Voorhis et al. 1993). Another related group (18–22% amino acid identity) comprises proteins of 85 or 160 kDa sharing an amino acid motif that is conserved among bacterial neuraminidases (Fouts et al. 1991; Pollevick et al. 1991; Kahn et al. 1991; Takle & Cross, 1991; Franco et al. 1993). The amino acid identities with the different antigens were not homogeneously distributed. Regions of higher identity (40–60%) were grouped in the central region of each protein.

NIH and C57 BL/10 (BIO) mice show genetically determined differences in their response to Trichinella spiralis infection. This study examines the influence of these on parameters of the immune response to infection after vaccination using muscle-larval excretory–secretory antigen in Freund's complete adjuvant. Serum antibody levels were greatly elevated when mice of both strains were vaccinated prior to infection; however, NIH produced significantly higher-level antibody responses than B10. Vaccination accelerated and increased the capacity of mesenteric lymph node T-cells to proliferate in vitro in response to specific antigen stimulation in both mouse strains but, in general, the stimulation indices of NIH cells were higher than those of the B10. The capacity of mesenteric lymph node cells (MLNC) and spleen cells (SC) to produce IL-5 and γIFN was measured after specific in vitro stimulation and early γIFN secretion was noted in the supernatants of NIH MLNC and SC, but not in B10 SC. Concentrations of IL-S rose steadily over the first 10–14 days after infection in cell cultures from both strains. Prior vaccination of these animals appeared to enhance cytokine levels. It is postulated that the efficacy of vaccination in NIH mice is a consequence of their genetically determined capacity to produce early and high-level responses to the antigens of T. spiralis and to express these in intestinal effector mechanisms.

The sensitivity of eggs of Echinococcus multilocularis to environmental and controlled laboratory conditions was tested. Egg material was exposed and the infectivity was subsequently monitored by in vitro activation and by oral infection of the natural host, Microtus arvalis. To study the impact of environmental conditions in an endemic area of south-western Germany, eggs were sealed into bags of nylon mesh and exposed to the natural climate during various seasons. The maximal survival time of eggs was 240 days in an experiment performed in autumn and winter and 78 days in summer. A study of the tenacity of eggs under laboratory conditions revealed a high sensitivity to elevated temperatures and to desiccation. At 45 °C and 85–95% relative humidity the infectivity was lost after 3 h as well as after 4 h exposure to 43 °C suspended in water. Exposure to 27% relative humidity at 25 °C as well as exposure to 15% relative humidity at 43 °C resulted in a total loss of infectivity within 48 and 2 h, respectively. Temperatures of 4 °C and of –18 °C were well tolerated (478 days and 240 days survival, respectively), whereas exposure to –83 °C and to –196 °C quickly killed off the eggs (within 48 h and 20 h, respectively). Eggs of E. multilocularis were not killed off by exposure to various commercially available disinfectants applied according to the manufacturers' instructions and by exposure for 24 h to low concentrations of ethanol. Irradiation with 40 krad. from a 137Caesium source prevented the development of metacestodes but allowed seroconversion of infected rodents.

The nervous systems of helminths are predominantly peptidergic in nature, although it is likely that the full range of regulatory peptides used by these organisms has yet to be elucidated. Attempts to identify novel helminth neuropeptides are being made using immunocytochemistry with antisera raised against peptides isolated originally from insects. One of these antisera was raised against allatostatin III, a peptide isolated originally from the cockroach, Diploptera punctata, and a member of a family of related peptides found in insects. Allatostatin immunoreactivity was found throughout the nervous systems of Mesocestoides corti tetrathyridia, and adult Moniezia expansa, Diclidophora merlangi, Fasciola hepatica, Schistosoma mansoni, Ascaris suum and Panagrellus redivivus. Immunostaining was observed in the nerve cords and anterior ganglia of all the helminths. It was also apparent in the subtegumental nerves and around the reproductive apparatus of the flatworms, in neurones in the pharynx of D. merlangi, F. hepatica, A. suum and P. redivivus, and in fibres innervating the anterior sense organs in the nematodes. Immunostaining in all species was both reproducible and specific in that it could be abolished by pre-absorption of the antiserum with allatostatins I–IV. These results suggest that molecules related to the D. punctata allatostatins are important components in the nervous systems of a number of helminth parasites, and a free-living nematode. Their distribution within the nervous system suggests they function as neurotransmitters/neuromodulators with roles in locomotion, feeding, reproduction and sensory perception.

The epidemiology of Strongyloides stercoralis was studied in families of clinical (reference) cases and their neighbours at endemic foci in Jamaica. Thirteen foci were studied based on the place of residence of a reference case. For each household of a reference case, the 4 most proximal neighbourhood households (spatial controls) were included in the study. Out of 312 persons contacted 244 were followed up using questionnaires, stool examination and serology. Prevalence of infection based on stool examination was 3·5% and on ELISA 24·2%. Prevalence increased with age but was not related to gender. Reference cases were significantly older than the general study population. The prevalence of infection based on both serology and stool examination was significantly higher in reference than in neighbouring households (the reference cases, themselves, were not included in the analysis). Furthermore, prevalence of infection was highest among persons who shared a bedroom with a reference case and decreased significantly with increasing spatial separation. This is indicative of close contact transmission which has not been previously shown for a geohelminth, but which is common among microparasites.

This paper describes a study of 194 children (aged 9–13) from a mountain village in Ecuador who were infected with one or more species of intestinal helminth or protozoan parasite. In addition to parasite load, the assessment consisted of a battery of psychological and neuropsychological tests, an EEG examination, measures of iodine level, presence of goitre and level of nutrition. We found that, in general, parasite infection, as measured at the baseline level, was not associated with cognitive impairment. The intensity of infection with A. lumbricoides, however, was correlated with the level of verbal ability and with inhibition-control aspects of cognitive behaviour. Multivariate analysis with level of nutrition, EEG status and parasite burden showed a consistent main effect of the degree of nutrition on neuropsychological performance, particularly the language, problem solving and inhibition-control dimensions.

Trypanosoma (Nannomonas) godfreyi sp. nov. from tsetse flies in The Gambia: biological and biochemical characterization

Parasitology109, 497–511

p. 499, para. 2, 104/ml to replace 104/μl

p. 501, para. 1, chromsomes to replace chromosome

p. 501, para. 2, 1/148 to replace 1/48

p. 504, para. 3, BAN 9 or KEN 7 to replace BAN 9 & KEN 7