The worm burden distributions of a macrofilarial nematode, Ochoterenella digiticauda, and a gastroenteric digenean, Mesocoelium monas, were examined in a naturally infected population of Bufo marinus from Jamaica. Both parasite species had over-dispersed distributions which were well described by the negative binomial probability model (k = 0·35 for 0. digiticauda; and k = 0·59 for M. monas). The intensity distributions of the two parasites were uncorrelated: there was no significant association between the intensity (whether absolute or relative) of infection of either parasite in individual hosts. It is suggested that different, and parasite species-specific, factors of the host interaction are involved in generating the separate distributions of the two parasite species.

The design of mass and targetted community-based chemotherapy programmes for the control of the major helminth infections of man is discussed in relation to the population and transmission dynamics of the parasites. Rapid reinfection following a single mass or targetted anthelmintic application is shown to be a universal feature of helminth transmission, as a consequence of the regulatory or feed-back mechanisms controlling population abundance within both individuals and the community as a whole. Control of reinfection requires repeated community treatment where the intensity of application and the interval between treatments are dependent on the reproductive life-expectancy of the adult worm, the net force of transmission prior to control (the basic reproductive rate) and the factors which create aggregation in the distribution of parasite loads within the population. Selective or targetted treatment is shown to be most effective for the control of morbidity as opposed to the control of transmission. The impact of targetted treatment depends critically on the factors that generate heterogeneity in parasite burdens and on whether or not selectivity is based on a single or repeated identification of the ‘wormy’ fraction of the community. Monte Carlo simulation studies are employed to assess the likely impacts of different control strategies on average parasite abundance/person and the distributions of parasite loads within populations. Future epidemiological research needs are discussed in relation to theoretical work and recent field studies of predisposition to heavy infection.

High incidence of mycoses were found in the guts and malpighian tubes of Phlebokomus papatasi from the Jordan Valley and P. tobbi from Zakinthos, Greece. Infections with several different bacteria were also found in the guts of female P. tobbi. Fungi cultured from guts of laboratory reared P. papatasi that had similar mycoses were identified as Aspergillus scierotiorum and Saccharomyces cerevisiae. Fungi-infected laboratory reared P. papatasi were refractory to artificial infections with a Leishmania major strain specific to them. The crop contents of P. papatasi, where sugar meals are stored, demonstrated antibacterial activity against the following bacterial species in culture: Escherichia coli, Staphylococcus aureus, Shigella sonnei, Streptococcus group A and Pseudomonas aeruginosa. It is postulated that the bacteria-free gut normal to sandflies is effected by the bacterial inhibitor present in the crop.

The survival and infectivity characteristics of the cercariae of Echinostoma liei are described for 6 different water temperatures in the range 12–40 °C. Cercarial survival steadily decreased with increasing temperature, the maximum survival time falling from 75 h at 12 °C to approximately 8 h at 40 °C. Changes in environmental temperature affected the infectivity even of freshly emitted cercariae but their most noticeable effect was upon the rate at which infectivity diminished with increasing cercarial age. Infectivity rose from zero at 12 °C to a maximum at 30 °C before declining to a low level at 40 °C. The transmission efficiency of the cercariae at each temperature was calculated as the ratio of the instantaneous per capita rates of mortality and infection respectively. The efficiency of transmission was high between 19 and 30 °C, suggesting that cercariae are well adapted for transmission at water temperatures likely to be encountered in natural habitats.

The modified Kato technique has the advantages of reproducibility, simplicity and economy: the disadvantage is that it cannot be used in conjunction with traditional faecal preservatives. Sodium azide has been evaluated as a preservative for human faeces for subsequent Kato analysis. More than 400 faecal samples (from normal and malnourished children, and from mixed-age participants in a field survey of the Turks and Caicos Islands) were each mixed with 2–5 mg of sodium azide powder and stored in 2 or 4 ml autoanalyser cups at ambient tropical temperature. At intervals up to 30 weeks, aliquots were prepared for Kato analysis. Trichuris trichiura, Ascaris lumbricoides and Necator americanus eggs were well preserved without degenerative or developmental changes in morphology. Quantitative analyses of 18 samples indicated that the mean egg count/sample did not change significantly after storage for 1, 2, 4, 8, 12 and 16 weeks in preservative. The use of azide preservative extends the applications of the Kato technique to field and clinical studies in which delays may occur between specimen collection and examination. The direct costs of azide preservation are substantially lower than for traditional methods and the preserved specimens are more compact and resistant to leakage.

A double clone of Trypanosoma platydactyli Catouillard, 1909, derived from a single trypomastigote from the blood of the Moorish gecko, Tarentola mauritanica, was grown in vitro. Morphogenesis of the parasites led to a stable population of promastigotes which were identical, in general morphology, ultrastructure and the electrophoretic mobility of 8 enzymes, to those cultures previously considered to be Leishmania tarentolae Wenyon, 1921. These cultures included the strain isolated from the type locality in Algeria by Parrot (1949) and later used as a laboratory model for the genus Leishmania. T. platydactyli and L. tarenlolae are synonymized and the present status of saurian Leishmania parasites is discussed.

There are comparatively few studies concerned specifically with chemotherapy of parasitic infections and its relationship with the immune status of the host being treated. In one sense this is hardly surprising. The disciplines of chemotherapy and immunology have developed independently, and the search for effective drugs has for the most part been an empirical process; when a compound showing some activity has emerged the tendency has been to look for analogues with even greater parasiticidal properties rather than to consider whether effectiveness of the parent compound could be improved if the immune status of the host were different. In many cases, test systems for drug development have actually been selected to reduce as far as possible the complications f an immune response. Thus acute, fatal infections are commonly used for the screens, and questions such as the level of specific resistance at the time of treatment, immunodepression by the parasite, and increased resistance to challenge following chemotherapy are generally irrelevant.

Larval Digenea infecting Littorina rudis, L. littorea and L. obtusata around Portavogie harbour, Co. Down, were examined. High levels of infection were found among the littorinids collected from sites on the harbour shore, though levels of infection varied somewhat with position on the shore. There was a direct relationship between size of the snail host and likelihood of infection. There was a negative association between certain pairs of helminth species in the same host, particularly where the rediae of Cryptocotyle lingua or Himasthla sp. were involved. Infection rates in gastropods declined away from the harbour and it is concluded that the high infection rate centres around the harbour were probably due to the increased concentration of definitive hosts, mainly seagulls, attracted to this area by dumping of raw fish offal. The infection of Pholis gunnellus with the metacercariae of C. lingua was also examined. Older fish were more heavily infected than younger fish but no direct relationship was found between high snail infection rates and high P. gunnellus infection rates.

The Trypanosoma brucei metacyclic population in the salivary glands of the tsetse fly displays a characteristic set of variable antigen types (VATs) which represents only a restricted part of the parasite's total VAT repertoire. After introduction into the mammalian host by fly bite, the metacyclics transform into bloodstream forms which retain expression of the metacyclic VATs. Specific antibodies, both polyvalent and monoclonal, have been used to neutralize separately 4 individual VATs from metacyclic populations. Control experiments and visual observation confirmed lysis of each VAT. On injection of the surviving trypanosomes, after washing, into mice each neutralized VAT was nevertheless expressed within a few days. Simultaneous neutralization of 2 metacyclic VATs which usually switch to one another in bloodstream infections did not prevent expression of either on subsequent injection into mice. Expression of neutralized VATs was not influenced by the antigenic composition of the population originally ingested by the tsetse fly. Metacyclic forms and their immediate successors thus appear to switch rapidly to expression of other metacyclic VATs in bloodstream populations.

Genetic differences in mice influence both the pathological and immunological responses to schistosomiasis mansoni. We have investigated the nature of the genetic factors influencing these responses by crossing two different pairs of strains of mice which vary in their response to infection, and measuring responses in the F1 hybrid and backcross offspring. The two pairs of parental strains differed with respect to faecal egg excretion, accumulation of eggs in the tissues, splenomegaly and pattern of antibody response. The numbers of adult worms which establish do not differ between strains. The inheritance of the responses measured was different in the two pairs of strains. The F1 hybrid from the C57BL/6/Ol/a /c cross resembled the low-responding parental strain (CBA/Ca) with respect to faecal egg excretion, accumulation of eggs in the tissues and splenomegaly, and was intermediate in its pattern of antibody response. The F1 hybrid mice from the NIH /Ca cross resembled the high-responding strain (CBA/Ca) with respect to faecal egg excretion, accumulation of eggs in the tissues and splenomegaly, and had an earlier and greater antibody response than either parental strain. No evidence of single gene influence on any of these responses was seen in the backcross offspring. The differing patterns of inheritance and the absence of a bimodal distribution of responses in the backcross offspring indicate that each of these responses is influenced by multiple genes. The pattern of antibody response did not correlate between strains with any of the pathological res The positive correlation of egg accumulation in the tissues and faecal egg excretion suggests that there are genetic influences on the fecundity of the worms.

Study of the mode of action of the anti-parasitic ‘hydrogenophore’, closantel, revealed that mitochondria isolated from livers of untreated rats, 13 weeks after infection with Fasciola hepatica metacercariae, were uncoupled. This uncoupling of mitochondria might be induced by a product(s) excreted by the liver fluke. The lipid extractable product(s) binds to albumin and has a molecular weight between 500 and 1000 Daltons. A second unexpected finding indicates that closantel affects the motility of Schistosoma mansoni in vitro by interferin with mitochondrial ATP synthesis. The results obtained are suggestive of a role for aerobic metabolism in the generation of energy required for motility.

The potential of antigenic differences for discriminating pathotypes of the potato cyst nematodes Globodera pallida and G. rostochiensis has been examined by the use of an antiserum raised to a homogenate of potato cyst nematode larvae. Species-specific antigens were detected among reference pathotypes but more variability was detected among field populations, and cluster analysis was used to interpret the precipitation are pattern produced by Laurell crossed-immunoelectrophoresis. A division into species was seen with this analysis but no definite pathotype groupings were detected. Cross-reaction with other cyst-nematode species was limited to general non-specific precipitation. The antigens were all proteinaceous, did not arise from micro-organisms within the cyst and were mainly hydrophilic with an acidic isoelectric point. Peptidase and acid phosphatase activity was detected in some precipitation arcs but this was not species specific.

Nine species of parasitic copepods are reported, with 3 of them being new to science. They are: (1) Chondracanthodes deflexus Wilson from Antimora rostrata Günther, Coryphaenoides (Chalinura) brevibarbis (Goode and Bean), Coryphaenoides (Nematonurus) armatus (Hector), Coryphaenoides (Chalinura) leptolepis (Günther), and Coryphaenoides (Lionurus) carapinus (Goode and Bean); (2) Chondracanthodes radiatus (Müller) from Macrourus berglax Lacepede; (3) Lernaeopodina pectinata sp.nov. from Alepocephalus agassizi (Goode and Bean); (4) Neobrachiella pinguis (Wilson) from Antimora rostrata Günther; (5) Clavella adunca (Strøm) from Macrourus berglax Lacepede; (6) Sphyrion lumpi (Krøyer) from Antimora rostrata Günther; (7) Lophoura gracilis Wilson from Synaphobranchus kaupii Johnson; (8) Lophoura pentaloba sp.nov. from Coryphaenoides (Nematonurus) armatus (Hector) and Nezumia bairdii (Goode and Bean) and (9) Lophoura tetraphylla sp.nov. from Antimora rostrata Günther. The infected fishes were collected with trawls from depths of 828 to 4815 m in the New York Bight and 403 to 1294 m near the Grand Banks (south of Newfoundland).

In spite of the continuing need for new and improved anti-protozoal drugs for use in man, a considerable contraction of industrially based research on anti-protozoal drugs has occurred in recent years. Newton (1983) reviewed the reasons for this decline and presented a compelling argument that fundamental research on the biology of the parasites is essential for the discovery of leads for the development of a new generation of drugs – a rational chemotherapy. The rapid advance in knowledge of the biochemistry of parasitic protozoa which has occurred in recent years has provided a number of potential leads to new drug development and has permitted a greater understanding of the mode of action of many current drugs. The account of these advances which follows is necessarily selective and relates to protozoan parasites of man.

A collection of stocks of Trypanosoma brucei rhodesiense isolated in Kenya have been examined for electrophoretic variation in 20 enzymes. The results obtained have been analysed in order to determine whether these trypanosomes are diploid and undergo mating and to determine the genetic distance between T. b. rhodesiense, T. b. brucei and T. b. gambiense. The enzyme electrophoretic markers were further used in experiments involving cyclically transmitted mixtures of stocks aimed at detecting genetic exchange in the laboratory. No genetic exchange was detected. Two novel features of the enzyme electro phoretic results were found. Firstly, the stocks of T. b. rhodesiense were considerably more homogeneous than equivalent collections of stocks of T. b. brucei and secondly, all the stocks examined were heterozygous for two alleles of alkaline phosphatase and showed an excess of heterozygotes at the phosphoglucomutase locus. The degree to which these features are typical of T. b. rhodesiense has been examined in relation to previously published data. The results obtained strongly support the view that T. b. rhodesiense is a set of variants of T. b. brucei rather than a subspecies and a working hypothesis as to the relationship between T. b. brucei and T. b. rhodesiense is proposed to explain the enzyme electrophoretic data obtained.

Significant levels of resistance against Schistosoma mansoai challenge were developed by mice exposed to highly irradiated (20 krad.) cercariae of the homologous species (53–67%), whereas vaccination with S. bovis, S. haematobiurn or S.japonicuni failed to confer significant levels of resistance (–5–12%), thus confirming the specificity ofthe immunizing procedure. Attempts to transfer resistance to naive recipients by injection of serum and of spleen or lymph node cells from donor mice vaccinated with highly irradiated cercariae were largely unsuccessful. However, significant levels of resistance could be transferred to mice by injection of serum from rabbits exposed to irradiated cercariae. Comparable levels of resistance were conferred by injection of serum at the time of challenge (34–69%) or 5–6 days later (31–56%). Tn contrast, sera from rabbits injected with solubleegg antigen or homogenized cercariae failed to confer protection upon recipient mice. Sera from vaccinated mice, vaccinated rabbits and antigen-injected rabbits all caused cell adherence to skin-transformed schistosomula hut neither the level of adherence nor the serum titre correlated with the ability to confer protection to mice.

The resistance in human malaria is mainly of practical importance in relation to Plasmodium falciparum. Strains resistant not only to chloroquine but also to dihydrofolate reductase inhibitors, and even to potentiating combinations of these with sulphonamides or sulphones, are appearing in an ever increasing geographical area which now includes tropical Africa and India. Few new drugs are available or foreseen for the near future, mefloquine and artemisinine being the leading contenders. It is vital that all measures possible should be taken to protect such new compounds, their deployment in the form of judiciously selected combinations with other antimalarials being an essential procedure that should be followed. Drugs in new chemical classes and with different modes of action are still urgently needed. Reliance should not be placed on drugs alone to control malaria on a community basis.

Non-specific immunostimulants were used in an attempt to protect baboons from infection by schistosomes. Subcutaneous vaccination with cord factor (4·50 mg) and muramyl dipeptide (4·56 mg) 6 days before percutaneous exposure to 3000 Schistosoma haematobium cercariae/baboon (c.p.b.) failed to protect naive baboons: baboons with a 7-month-old, 5000 c.p.b. S. haenzatobium primary infection had developed too strong a natural immunity to detect any protection attributable to vaccination. Subcutaneous vaccination with 0·4 ml of Bacillus Calmette-Guerin (BOG, 1–8 x 108 colony forming units7sol;ml) 4 days before exposure to 1000 c.p.b. S. mansoni gave a significant (38%) reduction in worm load compared with controls. However, vaccination with 0·8 (intramuscular) and 0·2 (intradermal) ml of BOG 11 days before exposure to S. mansoni 800 c.p.b. did not protect naive baboons, nor did it significantly reduce challenge worm recovery from baboons with a 13-week-old, 500 c.p.b. S. mansoni primary infection. Obvious pathology was seen at the site of vaccination in the first but not the second BCG experiment. These results partly support the findings in mice that non-specific macrophage and monocyte activators give partial protection against schistosome infections but they also illustrate that rodents and primates do not necessarily react identically. Hence, findings from rodent models should be extrapolated to man with some caution.

Mice can be partially protected against Schistosoma japonicum by prior exposure to ultraviolet (UV)-attenuated infections which fail to survive to the adult stage and produce no overt pathology in the host. Optimum resistance was induced by parasites exposed to 40 seconds of UV, significantly lower levels of resistance being stimulated by both shorter and longer exposures. No consistent relationship between the degree of resistance induced and the number of irradiated cercariae given could be demonstrated and equivocal results were obtained when comparing the efficacy of single and multiple vaccinations. Vaccinations with UV-attenuated cercariae given intraperitoneally (i.p.) were as efficacious as those given percutaneously but mice were as or more resistant to challenges given by the i.p. route, the possible reasons are discussed. There was no observed delay in the migration of the challenge, vaccinated mice being as resistant when perfused 6 or 3·5 weeks after challenge. Vaccination was species specific since mice exposed to either UV-attenuated S. japonicum cercariae or gamma-attenuated S. mansoni cercariae were resistant to homologous but not heterologous challenge.

Surface antigens of Schistosoma haematobium were identified by 125I-surface labelling of schistosomula followed by immunoprecipitation of the solubilized, labelled surfaces. The major antigens, after electrophoresis, formed a continuous smear corresponding to a molecular weight in the range 35–24000; in addition, a 17000 antigen was also identified. These surface antigens, in contrast to somatic antigens, were species-specific, as judged by immunoprecipitation with human anti-S. mansoni serum and serum from mice vaccinated with highly irradiated S. mansoni cercariae. S. haematobium surface antigens, however, were recognized to some extent by serum from mice chronically infected with S. mansoni. It is suggested that this cross-reactivity may reflect the heterologous immunity demonstrated experimentally between these two species, whilst the species-specificity of vaccine sera to surface antigens may mirror the highly specific immunity induced by vaccination.