The cell cortex of a ciliated protozoan contains most of the structure that defines the shape and pattern of the organism. The ciliate cell cortex is composed of both cytoskeletal and membranous components. While the assembly of the cytoskeleton is believed to account for the major part of the development of shape and pattern in this cell (as in all eukaryotic cells), the contribution of membranes to the development of cellular architecture in ciliates is poorly understood. Also, how the cortical membranes are assembled and how this assembly is coordinated with cytoskeletal assembly are virtually unknown. Furthermore, membranes have several unique properties which could be useful in the storage and utilization of blueprints for cellular architecture. Freeze-fracture and freeze-etch electron microscopy provide ways to characterize the molecular architecture and assembly of membranes during development. Efforts are being made to apply these methods to an analysis of morphogenesis and ciliogenesis in Tetrahymena. The results of these studies ar summarized and their possible implications regarding the role of membranes in ciliate morphogenesis are discussed.

The prospects for vaccine development have been transformed by the advent of hybridoma technology for the production of specific monoclonal antibodies and recombinant DNA technology which permits the in vitro expression of genes coding for protective antigens of pathogenic organisms. These techniques are leading to the refinement of existing vaccines and the production of new vaccines against organisms which either cannot be cultured in vitro at all, e.g. hepatitis-B, or can be cultured only on a limited scale, e.g. plasmodial species. The techniques allow for the novel production of both live and dead vaccines. New live vaccines are produced using either site-directed mutagenesis or insertion of genes into hosts such as vaccinia virus, which is a potential carrier of polyvalent vaccines. New subunit vaccines are produced by expression of appropriate genes in E. coli, yeast cells or mammalian cell lines and some, e.g. hepatitis-B surface antigen (HBsAg) are at an advanced stage of development. Recombinant subunit vaccines are also being produced against the sporozoite and blood stages of malaria. Problems, in regard to the development of malaria vaccines, concern the antigenic plasticity of plasmodia and the need to induce both antibody and cell-mediated immunity; nevertheless, the work shows considerable promise of success.

Calmodulin is a ubiquitous endogenous calcium receptor in eukaryotic cells and is involved in many different physiological functions. The presence of calmodulins in protozoa has been reported for Tetrahymena and Paramecium. Calmodulin purified from T. pyriformis is composed of 147 amino acids and the amino-terminal is acetylated.Compared to bovine brain calmodulin, there are 11 substitutions and 1 deletion of amino acid residue(s). Besides such structural specificity, Tetrahymena calmodulin (T-CaM) is highly unique in that it has a potential ability to activate the pellicle-bound guanylate cyclase in a calcium-dependent manner. This stimulatory effect is also observed in Paramecium calmodulin (P-CaM). Bovine brain calmodulin represses the T-CaM-dependent activation of guanylate cyclase, indicating that bovine brain CaM exerts its inhibitory influence by interfering with the calmodulin-binding site of this enzyme. The 14S and 30S dyneins extracted from demembranated cilia with EDTA contai ATPase activities which are potentiated by addition of calmodulin. Taken together with its location in cilia, T-CaM appears to regulate the ciliary movement. Moreover, evidence has been provided that calmodulin may be implicated in the glycoprotein biosynthesis. The phosphorylated derivatives of the long chain polyisoprenoid alcohols (dolichol phosphates) are known to act as coenzymes, and the microsomal enzyme involving dolichol phosphorylation is calcium-requiring CTP-dependent and activated by calmodulin. A role for calmodulin in the control of cell growth is postulated by the concerted fluctuations of calmodulin contentand guanylate cyclase activity during the cell cycle in synchronized Tetrahymena cells. In addition, some other possible functions for calmodulin can be considered in protozoa.

Occurrence of protozoa in the digestive tract of herbivores is dependent upon the occurrence of an environmentally compatible section of the tract and a retention time for gut contents in that section which exceeds the protozoan generation time. In general, herbivores can be classified as pre-gastric (foregut) or post-gastric (hindgut) fermentors. Fermentation in the foregut has evolved through enlargement of the stomach in some way to slow down ingesta passage rate and provide physical separation of the ingesta from the acid-secreting regions, as well as an adequate production of buffered saliva. Hindgut fermentations occur in the caecum-proximal colon area. Most of the protozoa in the digestive tract of herbivorous mammals belong to the class Kinetofragminophorea in the orders Prostomatida, Trichostomatida and Entodiniomorphida. They are anaerobic, live in conjunction with a large bacterial population and can ferment the structural polysaccharides of plants. End products of protozoal fermentation are similar to those of the bacterial population, i.e. volatile fatty acids, lactic acid, carbon dioxide and hydrogen. Additional products of the fermentation are vitamins and microbial protein which are subsequently utilized by foregut fermentors, whereas these products are essentially lost in hindgut fermentors unless they practice coprophagy. Only limited information is available on digestive and metabolic pathways of the gut protozoa, primarily because of our inability to grow them in axenic culture. Specific faunas appear to be associated with site of fermentation, animal species and diet. Diet in turn can affect pH and contents turnover time, both of which are very important in the establishment and growth of a protozoan population in the digestive tract.

When parasitic disease, whether of protozoan or other origin, gets out of control, it is mostly due to increasing, rarely decreasing, human population pressure and/or to changes of human behaviour. By his various activities man changes his environment; it thus appears logical to try to control disease by environmental management. The goal thereof is not to eradicate disease but rather to establish a new, tolerable equilibrium.

Environmental management has been shown to alleviate the situation. It ought not, however, be seen as a unique measure; it must rather be an integral part of a comprehensiveplan which includes various other approaches simultaneously, such as medical treatment, vector and intermediate host control, improvement of water supply and nutrition, improvement of housing and sanitary conditions.

Environmental management is thus closely interlinked with traditional occupations, customs and beliefs. In addition, environmental management, in the long run, can be undertaken only by local populations. These, therefore, need information and motivation, information through acceptable health education, motivation through long-lasting government support, from all levels and with all departments concerned co-operating, and possibly through appropriate, unobtrusive expatriate assistance.

J. O. Corliss explained that the original title given to the Workshop (namely, the phylogeny and evolution of the protozoa) seemed out of date, since today we clearly cannot persist in separating various protozoa from many of the algae and from certain zoosporic fungi by erection of formidable taxonomic barriers at the phylum (division) or kingdom level. All such forms, the species of which are being discovered to be inextricably comingled at various levels (for the latest extensive review, see Corliss, 1984), are perhaps better assigned to a single kingdom Protista or to several kingdoms predominantly containing these ‘lower’ eukaryotes (see subsequent sections of this report, below).

Eight papers were presented on topics ranging from the dissemination of drug resistance in Africa; the application of new antimalarial compounds; the basic biology of the malarial parasite; and methods for in vitro culture and its analysis, to the interaction of the malarial parasite with the infected host with particular reference to host genetic factors responsible for parasite survival.

Professor Canning opened the satellite meeting by reporting that Professor Erich Scholtyseck, who had in part organized the session had died. She expressed the feeling of the meeting that, as a distinguished scientist and gracious personality, he would be sadly missed on the international scene.

Three of the speakers dealt respectively with the systematics of Perkinsus spp. and Spiromonas spp, the eimeriine coccidia and the piroplasms. The fourth speaker concentrated on the role that some of the newer technologies could play in research on taxonomy of Protozoa.

Malaria, African trypanosomiasis, theileriosis, babesiosis and coccidiosis are of great public health and/or economic importance in eastern Africa. Leishmaniasis is an increasing problem in this area and other protozoal diseases which are found among human and/or livestock populations include toxoplasmosis, trichomoniasis, amoebiasis, giardiasis, sarcocystosis, Balantidium coli infection and histomoniasis.

Control of the vector-borne parasitic protozoan diseases has been based mainly on the use of pesticides with their attendant, adverse effects on the environment.

The paper describes the public health and economic problems posed by the main protozoan diseases in eastern Africa and discusses their control, stressing the importance of environmental considerations when planning control measures. Further, a consideration of the public health impact of these diseases when drawing up, and during implementation of, major agricultural, hydro-electric or irrigation schemes, is emphasized. The possible effects of control measures on the social and economical welfare of local communities is highlighted.

Only one paper in this Symposium dealt with what might be considered a classical zoonosis, namely that of leishmaniasis in northern Egypt. However, the closely related subject of opportunistic infections of humans by protozoa was also covered by two presentations, which noted the likely increase in the incidence of these types of protozoan diseases with the concomitant increase in the reporting of immunodeficiency diseases. A third factor in the evaluation of potential zoonotic foci is how protozoa cause disease symptoms in different host animals, and this point was addressed in the symposium by reference to the pathogenesis of some coccidia.

The activities of mankind which introduce excess nutrients and/or pollutants of various kinds into lakes, streams, estuaries, soils and the air, can, and often do, cause significant changes in aquatic and terrestrial environments world-wide. The pollution problem is critical because of the pressures of increasing populations, industrial growth and intensification of agricultural production. Conflicts of interest arise everywhere as challenges to resource use and natural state (‘beauty’) are turned into public issues.

Four groups of scientists were invited to participate in this Symposium, including those who have systematically studied or are still studying the relatively new problems of protozoal viruses of protozoa as inactivators of viruses and on protozoa as potential reservoirs of mammalian viruses would have presented itself.

Unfortunately, not all of the invited scientists could come to Nairobi. The most recent results of the Spanish group on protozoa as inactivators of viruses were not discussed (but see Programme and Abstracts of the Congress).

In the following report no attempt has been made to render uniform the style of the reports of the four speakers. For brief summaries of the subjects which were to be discussed by the absent members of the panel, the reader is referred to the abstracts published by them in the ‘Programme and Abstracts of the Congress’.

The presence of microfilaments (MF) and microtubules (MT) in the cytoskeletal systems of unicellular eukaryotes, the differentiations of their fine structure and topography within the cells, as well as the tremendous variety of motile phenomena manifested by Protista, made it impossible to treat the subject systematically and thoroughly during one session. The Symposium concentrated therefore on a few selected topics: the organization of the MF cytoskeleton of free living amoebae, its role in producing endoplasmic flow, cell-to-substratum attachment and ectoplasmic movements, as components of the amoeboid mode of locomotion; the transition from the MF to the MT system in the case of amoeba-flagellate transformation; molecular mechanism of operation of the most specialized MT system, in cilia and flagella; and calmodulin as a likely universal sensor allowing Ca2+ to control the motility. All these subjects were covered by seven lectures.

Besides distinguishing between ‘zooplankton’ and ‘phytoplankton’, one of the more useful ways for oceanographers to classify planktonic organisms is by size (e.g. Sieburth et al., 1978). Of the free-living protozoa in the marine plankton, most fall into the ‘microplankton’ (20–200 μm, including many of the sarcodinans and ciliates as well as a number of larval metazoa and the larger phytoplankton) and ‘nanoplankton’ (2–20 μm, including the smaller ciliates and most of the heterotrophic flagellates as well as most of the phytoplankton).

The ability of the African trypanosomes to vary their surface coats of glycoprotein antigens during infections of susceptible host animals has prevented the development of vaccines employing cell surface proteins, as is being attempted with other parasitic protozoa (see Cohen, 1986). Since the phenomenon of antigenic variation in protozoa was the subject of another symposium, of the five papers presented in this symposium one dealt with the possibility of sexual phenomena occurring in trypanosomes, one with the transmission of the organisms by tsetse to vertebrate hosts and one with the characteristics of the trypanosomes isolated from man. The fourth paper described the vertebrate host response to the parasites and the fifth described the control of such infections by chemotherapy.

Endocytosis is the process by which a cell ingests material (solute, paniculate, living cells) and encloses it in a membrane-limited vacuole, the endosome. Protozoa may ingest or they may become ingested. In the latter case they may serve as food for the ingesting cell or they may, as parasites, survive and multiply at the expense of the ingesting cell. The present symposium was concerned with two topics: (1) endocytosis by free living protozoa, and (2) endocytosis of parasitic protozoa. In both cases the initial result of endocytosis is the formation of an endosome, whereas the further fate of the ingested contents differs (Fig. 1); in the first instance the contents are digested by the action of hydrolytic (lysosomal) enzymes and in the second instance the ingested parasite avoids digestion and becomes adapted to parasitism.

This report summarizes the contributions to a symposium held at the VII International Congress of Protozoology in Nairobi. Within the cell cycle of different ciliates, stages and modes controlling cell cycle length are described. In addition, cytoplasmic factors as well as genes related to meiosis are demonstrated. These factors are effective in some unrelated organisms. Several lines of evidence indicate that there is a close connection between the control of meiotic and of mitotic events.

The unique habitats of marine environments including some organically rich, but physically variable, benthic environments, and the rather uniform, regionally stable, open ocean environments have both produced species of biomineralizing protozoa of remarkable size ranging from several hundreds of microns to several millimetres (for solitary forms of foraminifera and radiolaria for example). Some colonial radiolaria are several centimetres in diameter and may reach lengths of over a metre for filiform species. These larger, free-living protozoa aften harbour algal symbionts and exhibit unusual adaptations to enhance their survival in their unique habitat and to stabilize, if not enhance, their association with their algal symbionts through structural and physiological modifications to complement the unique requirements imposed by animal–algal associations.