It was demonstrated that antimycotic agents are unsuitable for elimination of mycotic contamination in in vitro cultures of Leishmania spp. Ion-exchange chromatography was designed to separate the protozoan parasites from the contaminating yeast or fungal cells based on their surface net charges. The method was found to be efficient and rapid, and would also reduce bacterial contamination in cultures which have been exposed to both contaminants Viability of the cells has been shown to be unaltered by this treatment as demonstrated by their ability to multiply rapidly in culture medium, as was seen in the controls.

A considerable proportion of mice lose acquired immunity to Plasmodium berghei during the first pregnancy. Immune parous mice, however, have a better immune status than virgin mice, the risk of loss of immunity during a subsequent pregnancy is greatly reduced, the capacity to clear parasites is enhanced, and the maintenance of immunity is less dependent on certain splenic functions. The establishment of improved immunity is dependent on the presence of proliferating parasites during the second half of pregnancy when immunosup pression results in recrudescence. Immune reactivity is also improved after a (chemothera peutically controlled) recrudescent infection provoked by immunosuppressive treatment of immune mice with corticoids or anti-T cell serum. This mimics the situation encountered during pregnancy. Hence, improved immunity after pregnancy is a consequence of a reconfrontation of a suppressed and/or convalescent immune system with proliferating parasites.

In vitro formation of Plasmodium berghei ookinetes was studied. Gametocytes produced in vitro were obtained from heart and tail blood of Swiss mice and from blood removed from mosquitoes directly after feeding on these mice. In vitro produced gametocytes were obtained from short-term cultures of the erythrocytic stages of P. berghei. Reproducible ookinete production was obtained in medium RPMI 1640, pH 7°8–8°0, using in vivo and in vitro produced gametocytes. The morphology of developmental stages of ookinetes and degenerate forms at the light microscope level is described. More ookinetes were produced in medium RPMI 1640 compared to MEM and ookinete yield – defined as the ratio between the number of in vitro produced ookinetes/105 erythrocytes and the number of exflagellations/105 erythrocytes in the infected blood – increased with lower erythrocyte densities in the cultures within the range of dilutions tested. A linear relationship existed between gametocytaemia and the number of ookinetes produced. The methods for in vitro ookinete formation and for estimating ookinete yields enabled us to study aspects of functional maturity of gametocytes independent of mosquitoes. The numbers of exflagellating gametocytes and in vitro ookinete yields in tail blood corresponded with those in heart blood and blood ingested by mosquitoes, suggesting a random distribution of functionally mature gametocytes within the vertebrate host.

Medication of chicks with 70p.p.m. arprinoeid in the food, starting 2 days prior to inoculation with Eimeria tenella, resulted in decreased oocyst production and oocyst sporulation. The main morphological alteration seen during the development of the second-generation schizont was a reduction in the number of second-generation merozoites due to incomplete merogony, resulting in large masses of vacuolated residual cytoplasm. In places around the developing macrogamete the integrity of the parasitophorous vacuole was lost by either the host cell limiting membrane making contact with the parasite pellicle, or the disruption of one or both of these surfaces apparently brought about by the intervention of the host cell mitochondria. Thirty p.p.m. arprinocid reduced sporulation of the oocysts of E. brunetti and caused enlargement of the perinuclear space in the late merozoites and swelling of the endoplasmic reticulum around wall-forming bodies II.

Ten colostrum-deprived, coccidia-free lambs were reared artificially in indoor cages. At 4 weeks of age they were allocated to 5 groups of 2: Groups 1–3 received 104 105 and 106 sporulated oocysts of Eimeria erandallis/lamb respectively, each as a single inoculum. Group 4 lambs received daily doses increasing over a 4-week period. Groups 1–3 showed diarrhoea and weight loss from about day 14, followed by slow recovery from about day 30. The diarrhoea was accompanied by a wave of oocyst output and a reduction in serum albumin and plasma alkaline phosphatase activity. One lamb in group 4 died of an unrelated condition on day 15; the other showed no clinical effect of the oocyst inoculations and its oocyst output was related only to the first week or two of inoculation. Lambs in Group I showed no clinical effect or oocyst output following challenge with 106 oocysts on day 28. E. crandallis showed high pathogenicity and immunogenicity. Its pathogenicity was not closely related to infecting dose within the range 104–106.

Significant suppression in the incidence of cyclical development of Trypanosonia congolense, T. vivax and T. brucei occurred in Glossina morsitans centralis maintained on goats immunized with in vitro-propagated uncoated forms of T. congolense, T. vivax and T. brucei, respectively. This was observed when tsetse given a T. congolense-infected feed were subsequently maintained on uninfected immunized goats and also when uninfected tsetse were fed on immunized goats infected with T. congolense, T. vivax and T. brucei. Suppression of infection rates in tsetse was trypanosome species specific, but was independent of the trypanosome stock used for immunization of goats. These findings were reflected in antibody responses to uncoated trypanosomes, as measured by immunofluorescence and the solid-phase immuno radiometric binding assay. Thus, antibody from goats immunized with uncoated trypano somes of one species exhibited minimal reactivity with uncoated forms of other species of trypanosomes, but showed high levels of activity with uncoated forms of the same or unrelated stocks of the same species. However, in view of the range of hosts upon which tsetse feed, it is open to question whether the use of a vaccine which suppresses trypanosome infection rates in tsetse would have any significant effect in the field.

The intraerythrocytic multiplication of two strains of Theileria annulata was studied with parasites maintained in stationary cultures and in the blood of infected cattle. In cultures established with blood from infected cattle 20–60% of single T. annulata piroplasms divided into quadruplet forms by day 6 in vitro. Transmission electron microscopic studies of T. annulata in culture showed that piroplasms possess intracytoplasmic food vacuoles and cytostomes during a pre-division trophozoite stage. The onset of intraerythrocytic multi plication was marked by the appearance of rhoptries and electron-dense plaques beneath the parasite's plasmalemmal membrane. The plaques developed into short segments of subplasmalemmal double membranes which were closely associated with the rhoptries. It was concluded that multiplication of T. annulata in erythrocytes occurred by schizogony, as nuclear division preceded cytoplasmic division and the final separation of merozoites. The four merozoites produced by intraerythrocytic schizogony had the same ultrastructural features as the T. annulata merozoites produced by intralymphocytic schizogony. Clusters of four merozoites, identical to those observed in stationary cultures, were also seen in the erythrocytes of persistently infected cattle and appeared to represent the most significant dividing forms of T. annulata in vivo.

Antigenic proteins on the surfaces of different developmental stages of Schistosoma mansoni were radio-iodinated by the lodogen-catalysed method and identified by immunoprecipitation with a panel of antisera. The sera comprised specific immune serum from mice harbouring a chronic schistosome infection or vaccinated with γ-irradiated cercariae; serum from rabbits immunized with adult schistosome tegumental outer membranes or a partially purified Mr32K glycoprotein from adult worm membranes; and a monoclonal antibody recognizing an Mr20 K antigen on the surface of schistosomula. The Mr38–32 K glycoproteins were the major antigens identified in surface-labelled cercariae and their probable association with the glycocalyx is discussed. Schistosomula transformed from cercariae either mechanically or by penetration of host skin in vitro, expressed a similar pattern of surface antigens to that identified for cercariae, but low molecular weight antigens of Mr20, 17 and 15 K were also detected. The Mr38–32 K glycoproteins, although present on newly transformed schistoso mula, were progressively replaced with time, by a single dominant glycoprotein (Mr 32 K) expressing identical epitopes to those on the Mr 38–32 K complex. Moreover, the data confirm that the Mr 32 K glycoprotein persists on the tegument after in vivo maturation and is conserved, together with Mr 20 and 15 K antigens, through to the adult stage. New antigens (Mr 97 and 25 K) were also detected during in vivo maturation and were present in late-stage schistosomes recovered from infected hosts. In addition, the enzyme alkaline phosphatase is expressed on the surfaces of 3-week-old liver worms as a dominant antigen (Mr 65 K); this feature may be related to nutritional and/or physiological processes in the tegument of this metabolically active stage of development.

An ultrastructural study has been performed on radiation-attenuated parasites fixed in situ during their extended stay in the lungs. At day 7 post-infection all parasites were located within blood vessels. In contrast to normally migrating parasites, at days 13 and 21 post-infection the majority of radiation-attenuated parasites were lying free within alveoli. As far as could be seen, radiation-attenuated parasites had undergone the normal develop mental changes associated with the lung stage of migration. These included elongation of the body and loss of mid-body spines and the fibrous layer beneath the tegument. No ultrastructural evidence was found to suggest why schistosomula failed to migrate further and instead burst into alveoli. No parasites observed on day 7 post-infection were associated with a host inflammatory reaction. At day 13, inflammation was noticeable but could have been a response as much to pulmonary tissue damage as to the presence of parasites. At day 21 post-infection some parasites were internally disrupted but were not associated with host inflammatory reactions and had intact tegumental surfaces – all facts consistent with death by autophagy. One parasite was observed at day 21 with an adherent neutrophil infiltrate and extensive tegumental damage. The relevance of persisting lung-stage parasites to the induction of resistance to challenge is discussed.

The hamster cheek pouch has been used to investigate the skin migration of schistosomula at the ultrastructural level. Parasites have been observed up to 72 h post-infection. Despite rapidly reaching the epidermal basement membrane schistosomula remain in an epidermal location for at least 40 h post-infection, by which time the acetabular glands and their ducts have been lost and the transformation from cercaria to schistosomulum completed. Entry into the dermis and exit from the skin via the blood vessels is therefore by mechanical means or by lytic secretions emanating from a source other than the acetabular glands. The head gland which persists in the dermal schistosomula is a probable source of such secretions. The observations suggest that the apical area and musculature of the head capsule are important in gaining access to the lumen of blood vessels.

Digenean flukes can be broadly classified into three basic groups according to their location within the host: (1) the lumen of the alimentary canal or associated organ, (2) body cavity or tissue and (3) external surfaces. We selected three species of Proterometra that represent these basic groups and tested their capacities for cutaneous transport of glucose. Facilitated diffusion is the type of transport system in the tegument of P. edneyi, which lives in the gut of its host. An activetransport system is present in P. dickermani, the tissue-dwelling species. No cutaneous system for transporting glucose is present in the ectoparasitic P. macrostoma. The known capacities for tegumental sugar transport in other digeneans are correlated with similar habitats. Such associations involving unrelated as well as closely related species suggest that the niche biology of digeneans involves evolutionary specializations of the tegument for absorbing sugar.

In laboratory studies with 3 species of Calliphora more than half were shown to ingest eggs of Taenia hydatigena from the surface of clog faeces with a maximum of over 5000 eggs in 1 fly. Most eggs were voided within 48 h and between 38 and 48% of these eggs had lost their embryophores. In field studies carried out in the South Island of New Zealand, traps baited with dog faeces captured the following blowfly species in decreasing order of abundance: Hybopygia varia, Calliphora quadrimaculata, C. hortona and C. stygia. Peak numbers were trapped in January, February and March. Almost 25% of wild flies, caught after feeding for up to 3 mm on dog faeces naturally contaminated with taeniid eggs, had eggs in their intestine. When administered to lambs all 4 species of fly transferred infection. Lambs grazed in winter on plots near kennels that had housed dogs with patent infections of T. hydatigena acquired higher worm burdens than those grazed further away. The burdens were greater downwind of the prevailing wind. After removal of the dogs, blowflies caught in the vicinity contained taeniid eggs but the contents of pitfall traps did not. Blowflies, and to a much lesser degree the insects and dust caught on sticky traps during the presence of the dogs, transferred infection when administered to naive lambs.

The hydrolytic, reductive and oxidative enzyme systems involved in the phase I biotrans formation of xenobiotic compounds have been investigated in Hymenolepis diminuta. Adult H. diminuta are able to carry out a range of hydrolytic and reductive reactions, but in common with other helminths oxidative detoxification reactions were absent (oxidative demethylation, aniline hydroxylation, nitrobenzene hydroxylation, biphenyl hydroxylation). These oxidative reactions were readily demonstrated in rat liver. Extracts of H. diminuta hydrolysed nitrophenylphosphates and inorganic pyrophosphate, but not arylsulphates, nor could epoxide hydratase activity be detected. N-Deacetylase activity was present. However, O-deacetylase activity could not be demonstrated, although butyrate and palmitate, but not benzoate, esters were hydrolysed. H. diminuta was capable of hydrolysing a range of a-and β-glycosides, but not β-glucuronides. Extracts of H. diminuta reduced azo-compounds, aldehydes and disulphides, but ketones and aromatic nitro-compounds were not reduced. The phase I detoxification systems of H. diminuta differ considerably from those of its rat host; the results also suggest that, within the cestodes, there may be considerable species variation in detoxification reactions.

The pattern of daily food intake of well-nourished rats infected with Nippostrongylus brasiliensis included 2 distinct phases when food intake was much less than that of uninfected controls (days 0–4 and days 6–10 p.1.). These phases were separated by a period (days 4–6) of still reduced but relatively constant food intake. From day 10 p.i. food intake increased so that between days 12 and 17 infected rats ate more than uninfected controls. In each of the phases of reduced food intake there was a threshold dose above which food intake was further decreased as dose increased. In contrast to the obvious relationship between food intake and dose, food intake could not easily be related to the size of the adult Nipposirongylus population, as judged by egg and worm counts. The relationship appears to be complicated by host variability in susceptibility to infection and to the pathological effects of infection. Effects of N. brasiliensis on the daily pattern of food intake can be explained with respect to stages in the development of the parasite and host responses directed against the adult worms.

Corynetoxins, the toxic glycolipids produced by Corynebacterium rathayi colonizing bacterial galls induced by the seed gall nematode Anguina agrostis in annual ryegrass (Loliurn rigidum), did not affect embryogenesis or larval development of A. agrostis although they did inhibit the rate of egg hatching. Corynetoxins were not toxic to several species of nematode which are parasites of roots nor to various stages of the free-living nematode Caenorhabditis elegana and they did not appear to influence the numbers of C. rathayi that became attached to the surface of the cuticle of infective larvae of A. agrostis.

The effect of mouse population density on the establishment, survival and fecundity of single cohorts of Heligmosomoides polygyrus was investigated. No significant relationship was found between host population density and the worm burden at post mortem. But, lower host population densities were associated with higher parasite fecundities and with higher overall mean daily faecal output. The results might be explained by a decrease in male hormone secretion or digestive disturbances associated with lower ingesta in the higher host population densities. Effects resulting from changes in immunological responses might also exist.

Rotylenchulus reniformis, Anguina agrostis and Meloidogyne javanica respond differently to gradients of chemical attractants. In chemotaxis assays performed on agarose plates, R. reniformis L2 larvae oriented their movement to several common inorganic salts, cyclic AMP and AMP, as well as to germinated host plant seeds. M. javanica L2 larvae were attracted to germinated seeds, but not to the salts tested, and A. agrostis dauer larvae were not strongly attracted to any of 12 different tested agents, including host root or shoot tips. Attraction of R. reniformis to salts was measured by comparing different pairwise combinations of ions at equivalent concentrations. The indicated order of attractiveness was: Cl− > Na+ > C2H3O2− > Mg2+, NH4+, SO42−. The least attractive salts, (NH4)2 SO4 and MgSO4, were weakly attractive at an orientation threshold of 1 mm, whereas the most attractive salt, MgCl2, was strongly attractive at a threshold of 0·2 mM Cl−. 3′, 5′ cyclic AMP was strongly attractive at a threshold of 0·05 mM, whereas 5′-AMP was a weak attractant. Some of these responses may affect the distribution of R. reniformis in its natural environment.