Rat peritoneal neutrophils adhere to schistosomula of Schistosoma mansoni in vitro in the presence of antibody, complement, or both. Ultrastructural studies have demonstrated that cell adherence is not intimate, and that electron-dense secretions are not liberated onto the parasite surface in the manner described for eosinophils. Cytochemical techniques confirm that peroxidase is confined within intracellularly located neutrophil secretion granules. The metabolic burst is shown to operate during Fc-mediated interactions, but since morphological damage depends upon the presence of complement in the system, toxic oxygen products would seem not to be involved in the initiation of surface perturbation. Complement-dependent, neutrophil-mediated schistosomular damage is characterized by vesiculation of the tegumental outer membrane, an increase in density of the tegumental cytoplasm and the eventual development of focal lesions. The cells migrate laterally to push aside damaged surface tissues and then adhere intimately to the exposed musculature. Damage appears earlier when both antibody and complement are present in the system, and this correlates with higher killing efficiency. The frequently observed association of contaminant eosinophils with areas of parasite damage indicates that eosinophils and neutrophils may cooperate to effect schistosomular killing. In the presence of antibody alone, attached neutrophils exhibit intense phagocytic activity towards the antigen-antibody complex formed at the parasite surface. This phenomenon may account for the eventual detachment of cells and lack of significant parasite damage recorded in this system

O-group bib, Trisopterus luscus caught on the cooling water intake screens of Fawley Power Station in March and April 1982 were infected (prevalence = 34·8%; intensity = 1·65/infected fish) with adult females of the pennellid parasitic copepod Lernaeocera lusci. The bib sample of 293 fish was divided, for analysis, into 5 length classes. In each of these the level of parasitization with L. lusci was broadly similar and in all 5 classes the parasite population was over-dispersed. Of the living copepods on T. luscus, 93% possessed egg strings while the remaining 7% consisted of earlier developmental stages. The majority of the parasites were attached to gill arches and here they exhibited distinct microhabitat and orientation preferences. A 3–2–4–1 descending order of gill arch utilization was apparent and copepods were non-randomly distributed along the dorso-ventral axis of gill arches with medial and ventral sectors being more heavily used than dorsal ones. An analysis was carried out on the body and egg string wet weights of parasites removed from fish harbouring different parasite densities. As copepod density increased neither the mean parasite body weight nor egg string weight altered significantly. Length/weight relationships of uninfected and infected fish were remarkably similar and thus provided no evidence that L. lusci has a marked effect on the condition of O-group T. luscus. The study demonstrated a significant positive association between infection with L. lusci and heavy infections with metacercarial cysts of Cryptocotyle lingua.

Sphaerospora molnari sp.nov. is described from the gills, skin and nasal pits of yearling carp (Cyprinus carpio L.) from ponds in the South Bohemian pond region of Czechoslovakia and one infected specimen from the river Danube in Bulgaria. Small vegetative stages, often massively pervading the infected tissue, produce 1 spore each. Spores are sub-spherical, 10·3 × 10·5 μm in size, with almost spherical polar capsules of equal size. The polar filaments are wound in wide coils that are almost parallel with the longitudinal axis of the spore. There are 2 uninucleate sporoplasm cells. Developmental stages and spores are also found in circulating blood. In the gills, S. molnari invades stratified epithelium of gill filaments and secondary lamellae causing branchial lesions and must be regarded as a serious pathogen of yearling carp. A new name, Sphaerospora chinensis sp.nov. is proposed for S. branchialis Lee & Nie in Chen (1973), pre-occupied by S. branchialis Razmashkin and Skrip-chenko, 1967.

Analysis of the seasonal occurrence of Argulus coregoni on Oncorhynchus masou and Salmo gairdneri indicates that the parasites overwinter as eggs and that there are 1 or 2 generations/year. Larvae which hatch from the overwintered eggs are abundant from May through July. Individuals hatched in May and June attain maturity and lay eggs in August. Larvae of the second generation are abundant in September, and they lay eggs in October–November which overwinter. Hatched larvae from overwintered eggs may mature in July and deposit overwintering eggs in September. The sex ratio of A. coregoni is about 1:1. A. coregoni shows an age-specific site preference on O. masou. Small parasites occur on almost all parts of the skin and fins, with slightly heavier concentrations on and around the pectoral and pelvic fins. Large parasites are found mainly on the skin around these fins.

In the ideal situation, the development of new amoebicides, or more accurately anti-amoebic compounds which are compounds with activity against Entamoeba histolytica, should initially proceed with the study of parasite-specific metabolic pathways and their inhibition, followed by whole parasite in vitro studies, experimental in vivo models and finally clinical trial. However, there are considerable gaps in our knowledge which will be discussed below, and consequently many investigators consider that empirically selected compounds should be tested experimentally in addition to specifically designed compounds. Before clinical trials can begin, extensive examination of the candidate amoebicide in experimental animals is required in order to investigate possible toxicological hazards.

In addition to inhibiting the amoebic parasite, the drug has to reach the parasite in several different sites in the body, thus there is also a problem of pharmacokinetics and distribution. Prior to the discovery of the nitroimidazole class of amoebicides, the multi-site attack was solved by the use of several drugs, sometimes in sequence during the treatment of an individual case (Powell, 1972). The discovery of the nitroimidazole class of compound changed the situation dramatically and these have shown a clinical and parasitological effect against extra-intestinal and intestinal wall infections. The effect on intralumenal infection (that is mildly symptomatic or asymptomatic infections) of the large intestine is, however, less certain (Finegold, 1977; Spillman, Ayala & Sanchez, 1976).

Although the treatment of amoebiasis appears to be satisfactory at the present time, it is difficult to predict problems which might arise in the future, and therefore it is valuable to continue the pre-clinical development, especially the investigation of parasite metabolism, in order to define parasite-specific points of chemotherapeutic attack.

The chemotherapy of amoebiasis was reviewed comprehensively by Woolf (1963, 1965). The present account of the development of amoebicides therefore starts from the Woolfe reviews.