Mono-metacercarial infections of Echinostoma revolutum in the domestic chick yielded 14- or 15-day-old worms that produced viable eggs, indicating that this species can self-fertilize under conditions which preclude cross-fertilization. In multiple infection studies, chicks were fed either 5 or 10 cysts and each infected chick contained 2–7 worms at necropsy 14 or 15 days later. Worms from multiple infections were mainly paired or clustered and they tended to locate more posteriorly in the intestine than single worms. Length measurements of single and multiple worms were similar. Both the number of eggs and the percentage of hatched eggs were considerably greater in multiple than in single infections.

The ultrastructure of the pseudohaptoral squamodiscs of the monogenean Diplectanum aequans is described. The most prominent feature of the squamodisc is the presence of epidermally-embedded spines which are covered by the outer epidermal membrane. These spines, which are ‘hollow’, are composed of a moderately electron-dense material with denser fibrils embedded within it. The squamodisc epidermis is similar in appearance to the haptor epidermis, with the exception of the epidermis ‘inside’ the spines. Here the epidermis contains free ribosomes and stacks of alternating electron-lucent/electron-dense, membrane-bound sacs. The arrangement of the musculature of the spines is described. The free, prehensile, edges of the squamodiscs contain numerous radially orientated nerves, some of which are assumed to be mechano-receptors.

The kinetoplast DNA (kDNA) of kinetoplastidae was the first mitochondrial DNA (mtDNA) to be discovered, and with its unusual network structure, consisting of more than 104 catenated DNA circles, it is without equal in nature. Analysis of networks from various genera (reviewed by Borst & Hoeijmakers (1979a) and Englund (1980)) has shown that they always consist of two components: mini-circles and maxi-circles (see Table 1). The mini-circles are the major component and deterraine the size and sliape of networks. They vary in size between 1 and 3 kilo-base pairs (kb = 1000 base pairs (bp)), they are heterogeneous in sequence, their sequence evolves rapidly and their function is not yet known. The maxi-circles, on the other hand, are homogeneous in sequence, their sequence is conserved and they probably represent the counterpart of mtDNA in other organisms.

Radio-immunoassay of plasma gastrin showed that hypergastrinaemia developed in sheep during experimental infections with Ostertagia circumcincta. Elevations of plasma gastrin occurred within 8 days of the first dose of infective larvae, with the most marked increase being after 11–20 days when adult worms would be expected to be present in the abomasum. Increases of plasma gastrin levels from 69·0 ± 7·6, 28·7 ± 5·3, 48·7 ± 5·9 and 60·6 ± 9·4 pg/ml before infection to maxima of 650, 230, 900 and 750 pg/ml respectively were recorded in 4 sheep infected for the first time. In 2 others which had been previously infected and then treated with anthelmintic, plasma gastrin rose from 16·0 ± 4·0 and 377 ± 87 pg/ml to maxima of 260 and 900 pg/ml at 24 and 29 days after re-infection, respectively. The cause of hypergastrinaemia has not been established. The elevation of abomasal pH which occurs in ostertagiasis may result in increased gastrin levels but is thought not to be the only cause since plasma gastrin increased before the abomasal pH rose and developed in sheep infected for a second time although their abomasal contents remained at pH 4·0 or lower. The presence of the parasite is critical for development of hypergastrinaemia as shown by return of the gastrin level to normal following therapy with an anthelmintic. It was shown that the parasites do not depend on the hypergastrinaemia since O. circumcincta became established in antrectomized sheep in which hypergastrinaemia did not develop.

In vector-borne diseases it is generally the vector which determines the success of disease transmission and efforts to limit the incidence of such diseases generally involve control of the vector. The very nature of their feeding habits renders haematophagous arthropods prime candidates for disease transmission and a great deal is now known of the biology of the most important vectors. Nevertheless, there are many areas in which our knowledge is incomplete or about which conflieting views exist.

The effect of repeated dehydration and hydration on the salt content of 2nd-stage larvae of Anguina tritici was studied. The sodium, potassium, magnesium and calcium contents of the larvae after subjection to varying periods of desiccation and rehydration were determined with atomic absorption spectrophotometry and flame photometry. External cation concentrations on the cuticle of the head, middle body and tail regions were determined semi-quantitatively with scanning electron microscopy in conjunction with X-ray analysis (EDAX). Salt concentrations decreased with each dehydration/rehydration cycle. The greatest loss occurred on revival from the first desiccation period. The results indicated that A. tritici was incapable of regulating it's internal sodium content during revival, but suggested a limited ability to control potassium, magnesium and calcium loss. Salt loss through the nematode cuticle was restricted to potassium and calcium during desiccation. The salt losses encountered are discussed in relation to nematode osmoregulation and to the survival of the nematode in the anhydrobiotic state.

Cholinesterase activity has been demonstrated histochemically in the nervous system, tegumental and sub-tegumental musculature of the haptor and in the pharyngeal bulb of the oncomiracidium of Pricea multae. The presence of cholinesterase in the nervous system is attributed to neurotransmission and its presence in the tegumental and sub-tegumental musculature of the haptor and pharyngeal bulb is discussed. The nervous system of the oncomiracidium with respect to cholinesterase activity is described and is compared with the nervous system of the oncomiracidium of Protopolystoma xenopodis.

The in vitro interaction between rat peritoneal macrophages and Dipetalonema viteae microfilariae in the presence of amicrofilaraemic rat immune serum was studied by transmission electron microscopy. The probable sequence of events leading to the killing of D. viteae microfilaria by macrophages is as follows. (a) Rat peritoneal macrophages in the presence of amicrofilaraemic rat immune serum adhere to the parasite surface, (b) the macrophages extend their pseudopodia around the parasite, (c) the ‘lysosome-like’ granules discharge their contents on to the parasite surface, (d) the lytic activity of these products begins at the parasite surface and (e) subsequent breaking of the microfilarial cuticle occurs, exposing the parasite intracellular material.

Infective 3rd-stage larvae of Dictyocaulus viviparus were filmed whilst climbing sporangiophores of the coprophilous fungus, Pilobolus and invading sporangia in numbers up to about 50, shortly before the sporangia were explosively discharged. Like the sporangiophores of Pilobolus the nematodes reacted positively towards light. Robinson (1962) demonstrated the spectacular way in which D. viviparus can be dispersed by Pilobolus, although he saw the nematodes accumulating only on top of the sporangia. Hazards including desiccation would offset the advantage of dispersal unless protection is somehow provided. Free D. viviparus larvae are susceptible to desiccation and discharged sporangia appear to dry quickly, so what protection, if any, operates? Several other nematodes that are susceptible to desiccation survive because structures surrounding them dry quickly (for example, an ensheathing cuticle, egg-shell, gelatinous ‘egg-sac’ matrix) and in doing so form barriers which limit the rate of water loss from the nematode within. Such dried sporangia of Pilobolus could aid survival of the ensheathed D. viviparus larvae inside them by retarding desiccation of the nematodes, in much the same way that within cysts of Globodera and Heterodera spp. the cyst wall, egg matrix and outer eggs protect the inner eggs by reducing the rate, if not the extent, of water loss. The sporangium wall may also protect the nematodes from harmful ultraviolet irradiation and from being washed by rain into less advantageous situations.

The introduction, establishment and subsequent history of a population of the eye-fluke Tylodelphys podicipina in perch in a small lake was studied over a period of 2 years. The introduction was a natural, chance colonization, and within 2 years of its first appearance the parasite was infecting 100% of the 0 + perch. Its dispersion within the perch population was initially random and fitted a Poisson model, but subsequently it became over-dispersed. Infection of fish took place only in or about June and only young of the year fish were susceptible. Fish were infected on one occasion only, shortly after birth, and there was no subsequent re-infection or mortality within the eye. The parasites lived for at least 2 years and there was no evidence of parasite-induced host mortality. Infection levels are thus an indication of the recruitment level in the year in which the fish were born. T. podicipina therefore differs from all other species of eye-flukes, which accumulate in fish throughout their life, but this infection strategy facilitates transmission of the parasites to their definitive host. Lower infection levels in older fish here and in other localities are considered to be due to the parasite being a recent introduction to the British fauna, and to its still being in the expansion phase of colonization in all localities.

Modern chemical insecticides revolutionized the fight against vector-borne diseases during the period following the Second World War. They are extensively used at present for that purpose and will very likely continue to play an important role in the foreseeable future. However, these insecticides have their limitations.

Variant antigenic types (VATs) represented in a total of 47 first relapse populations of 6 clones of Trypanosoma brucei LUMP 227 were identified by immunofluorescent staining of living trypanosomes, using antiserum raised against purified surface antigens. The relative growth rates of these 6 clones were measured both individually and when grown together in a mixed population, and were found to be different under these two sets of conditions. A pattern emerged in the VATs represented in relapses of each clone, with some types being expressed more frequently than others and certain VATs being only very rarely expressed. It is suggested that new VATs are expressed according to a statistically definable order of priority which is different for each parent VAT, and that some VATs may be able to change to certain others only after passing through an intermediate VAT. The order of priority of appearance of VATs does not appear to correlate with growth rate measured either in individual clones or when clones are grown in a mixed population.

During the early period of the study of microsporidia (now phylum Microspora) simple morphological features, in particular the number of spores produced by each sporoblast, were used to define genera. This led to the assemblage in genera of parasites, which when their developmental characters and host/parasite relationships were examined, could not be considered to be closely related. The Workshop was convened in Order to discuss the relative value of characters used for defining genera and to investigate selected problems of generic segregation and aggregation in representative classes. It was hoped to expose some of the inadequacies in the present methods and make recommendations for generic definitions which would form the basis of a taxonomic System, itself reflecting the phylogeny of the group.

Two stocks of Trypanosoma congolense were established in culture at 28 °C using trypanosomes from the proboscides of infective Glossina morsitans. Successful primary cultures were initiated by placing an infected tsetse proboscis beside a bovine dermal collagen explant in Eagle's minimum essential medium supplemented with foetal calf serum. The trypanosomes multiplied rapidly in the medium and also gradually formed an adherent layer on the plastic surface of the culture vessel. Three primary cultures produced organisms infective for mice from 14, 20 and 35 days after initiation and thereafter continuously until days 76, 76 and 52 when they were discarded. Four attempts to initiate infective cultures using infected tsetse proboscides in medium without dermal explants were unsuccessful. When trypanosomes from primary cultures were placed in culture medium with proboscides from uninfected tsetse flies, the parasites multiplied, formed an adherent layer in the culture flasks and were seen in the proboscides within 24 h. A line of 1 stock was serially sub-passaged in this way 4 times during a period of 215 days. Infectivity titrations in mice indicated that primary and sub-passaged cultures each contained similar numbers of infective organisms. Another line of the same stock was also sub-passaged 4 times in medium alone over a period of 186 days. These sub-cultures again retained infectivity for mice, but titrations showed a decrease in infective organism production in the 4th sub-culture. Primary and sub-passaged cultures all included a variety of morphologically different developmental forms of T. congolense, closely resembling those described in the labrum and hypopharynx of Glossina by previous workers. Short metacyclic-like trypanosomes and organisms with proteinaceous surface coats were present in infective cultures. Cultures were successfully re-established after cryopreservation at −196 °C and retained the ability to produce infective organisms.

Clun Forest sheep, aged between 3 and 18 months and worm-free from birth, were given a single dose of 25000 infective larvae of the nematode Haemonchus contortus. The host animals were killed between 4 and 100 days after infection and the nematode populations were examined to determine size and composition. The relation between worm body length, dry weight and age was studied and growth curves were constructed. Variations in the sex ratio for infections of different ages were noted. No evidence was found for a relation between rate of growth and population density. The rate of expulsion was determined and its variability discussed.

The fine structure of the envelopes surrounding hatched and unhatched oncospheres of Hymenolepis nana has been investigated by transmission and scanning electron microscopy (SEM), together with light microscope histochemical observations of JB-4 embedded material. The oncosphere is surrounded by 3 layers – the capsule, the outer envelope and the inner envelope, the latter giving rise to the embryophore and the ‘oncospheral membrane’. An additional layer – the polar filament layer – lies between the ‘oncospheral membrane’ and the oncosphere. Shell material is deposited on the capsule as a thin layer. It is secreted by the outer envelope, which degenerates once shell formation is complete. The uterus may also contribute to shell formation. The embryophore forms a thin, incomplete and peripheral layer within the inner envelope. In the basal region of this envelope, partial development of an ‘oncospheral membrane’ takes place, but it does not become detached as a separate layer. The polar filaments, which are characteristic of the oncosphere of H. nana, are derived from the epithelial covering of the oncosphere itself, which delaminates to form a separate polar filament layer. The filaments arise from knob-like projections at opposite poles of this layer. The design of the embryonic envelopes in H. nana show a number of modifications from the basic cyclophyllidean pattern, and these can be related to the demands of its ‘direct’ life-cycle.

Details are given of a method for the separation of the eggs of the nematode Nematodirus battus from sheep faeces. Faecal pellets obtained from worm-free lambs experimentally infected with N. battus were homogenized and passed through a graded series of metal sieves. The material retained in a 53, µm aperture sieve was transferred to a cylindrical column and the eggs were cleaned and separated from other suspended material by controlled differential flotation using tap water. A model experiment indicated that, within limits, the principle held for any size of tower. The density distribution for eggs at the morula stage of development was determined. Suggested flow rates for a specified tower are given.

The ecology of Leishmania of man is concerned with the circulation of the parasite in nature from one mammal to another by the bite of phlebotomine sandflies. The natural vertebrate hosts are anthropocentrieally referred to as reservoir hosts although in sorac foci of human leishmaniasis (anthroponotic cutaneous leishmaniasis and Indian kala-azar) man himself is thought to be the reservoir.

Ouabain applied to adult male Schistosoma mansoni causes a large, non-reversible tension increase of the parasite's musculature and elimination of spontaneous contractions. The tension increase and the time-course of tension development caused by ouabain are dose dependent with significant effects obtained at 3 × 10−6m. Digoxin and digoxigenin act in a similar manner with a relative potency of ouabain ≃ digoxin > digoxigenin. Lowered temperature as well as substitution of Li+ for Na+ increases muscle tension. The membrane potential recorded from the ventral tegument is also affected by treatments which interact with Na+–K+ transport systems. Ouabain (0·1 mm) causes a rapid depolarization without a significant effect on membrane resistance. The tegument is depolarized by temperatures below 30 °C. The effect of temperature is readily reversible and the temperature sensitivity is eliminated by pretreatment with ouabain. Substitution of Li+ for Na+ also causes a depolarization of the tegument. Tracer experiments show both an increase in Na+ and a decrease in K+ in the parasite within 10 min after treatment with ouabain (1 × 10−5m). Decreasing temperature of the bathing medium also causes an accumulation of Na+ as well as a decrease in the animals. The above results indicate a significant role for active Na+–K+ transport in muscle contraction and in maintenance of the tegumental membrane potential. The data also suggest that the Na+–K+ transport in S. mansoni may be electrogenic.

The fine structure of the oncosphere of Hymenolepis nana has been investigated by transmission and scanning electron microscopy, together with light microscope observations of JB–4 embedded material. The outer surface of the oncosphere is covered by an epithelial layer, termed the embryonic epithelium. Cell types present within the oncosphere include the penetration gland cell, oncoblast, or hook-forming cells, nerve cells, muscle cells (both somatic and hook), and undifferentiated ‘stem’ cells. The penetration gland is a large, U-shaped structure, situated in the anterior region of the oncosphere, and filled with secretory granules of 2 distinct morphological types. Histochemically, the secretory material yields reactions characteristic of an acid mucopolysaccharide. A proteinaceous-substance and small amounts of glycogen are also present. Up to 4 pairs of ducts from the penetration gland have been observed. They pass through the basal lamina and the epithelial layer to open against the polar filament layer at the anterior end of the oncosphere. Nerve cells are described in a cestode oncosphere for the first time. The cells are paraldehyde-fuchsin-positive and show a high level of secretory activity, as evidenced by the large numbers of dense-cored vesicles produced by the Golgi apparatus in the perikarya; consequently, they are tentatively regarded as possible neurosecretory cells. The vesicles are transported down the axon to be stored in specialized swollen axon terminals, which form definite junctions with the muscle cells.