A new subgenus and species of avian haemocytozoon Fallisia (Plasmodioides) neotropicalis is described. The principal characteristics are the main host cells, thrombocytes and mononuclear leucocytes, where trophozoites, schizonts and gametocytes are found. Occasionally, granulocytes and very rarely reticulocytes are also parasitized. Phanerozoites very similar to those of Plasmodium of birds are also present. The host is the domestic pigeon, Columbalivia, an imported species but similar parasites have been identified, always mixed with species of Plasmodium, in several indigenous species of Ciconiiformes, which seem to be the natural hosts. This is the first report in birds of a representative of the genus Fallisia, parasites of neotropical lizards.

Human fibronectin isolated from citrated blood was tested for its ability to bind to Plasmodium falciparum by an indirect immunofluorescent assay using rabbit antiserum to human fibronectin. A positive reaction was observed on merozoites inside schizont-infected erythrocytes. The binding was not observed on non-parasitized red blood cells. The effect of human fibronectin on P.falciparum growth was further studied using an in vitro inhibition assay; 50% inhibition of parasite multiplication was obtained with approximately 100 μg/ml of human fibronectin. Slight inhibition was observed below 10 μg/ml. The significance of this finding is discussed.

Twenty-three years ago, the first and only report of synergism between malarial and coccidial infections in chickens was published. In view of the potential commercial importance of this possible parasitic interaction in some parts of the world, and the lack of further supporting publications, this disease complex has now been reconsidered. An experiment on Plasmodium gallinaceum and Eimeria acervulina revealed no interaction of any kind between these species and a re-examination, with statistical analysis, of the raw data on which the original publication was based shows that no evidence of synergism between malarial and coccidial infections in chickens has so far been produced.

Swiss mice with chronic Trypanosoma brucei infections become refractory to subsequent infection with Babesia microti and B. rodhaini. Infection with B. microti 7 days after T. brucei resulted in an obvious inhibition of the babesia parasitaemias and this inhibition became more profound as the time interval between the infections increased, until at 17–20 days the parasitaemias were totally abolished. Even after intravenous injection of large numbers of parasites parasitaemias were inhibited. Similar inhibition was obtained in BALB/c mice but not in C57BL/6 mice. Mice with established T. brucei infections also showed reduced susceptibility to B. rodhaini. In mice similarly infected with T. brucei and the malaria parasites Plasmodium chabaudi chabaudi and P. c. adami the pre-patent periods were noticeably prolonged but the subsequent parasitaemias were unaffected. Infections with P. yoelii were unaffected. Trypanosoma brucei infections were not affected by the intracellular parasites. Among the mechanisms investigated to explain these findings were changes in red blood cell populations, cross-reacting antigens, the release of toxic factors and the generation of activated oxygen species. None of these could account for the inhibition observed.

Relapse of infection after trypanocidal drug treatment of trypanosome infections is normally attributed to drug resistance on the part of the parasite, under-dosage of the drug, or reinfection of the host. We have demonstrated relapse infections in goats arising from none of these. Fourteen goats infected with Trypanosoma brucei suffered severe illness and 3 died within 45 days. Despite treatment with the trypanocidal drug Berenil, a 4th goat died 2 days later. Recovery of the remainder followed chemotherapy, and in 2 goats, necropsiecl 45 days after treatment, no trypanosomes or abnormalities were detected. However 2–3 months after Berenil chemotherapy, despite trypanosomes being undetectable in the blood during the intervening period, infections in 4 of the remaining 8 animals relapsed. At all stages of the primary and relapse infections, trypanosomes isolated from the blood of the goats were completely susceptible to Berenil when tested in mice, as were parasites isolated from cerebrospinal fluid and brain tissue at necropsy. At the time of treatment, only minimal cellular infiltration was found in the central nervous system (CNS), but death from the relapse infection was associated with a very severe meningoencephalitis. We conclude that the relapse infections were caused by the re-emergence of trypanosornes from the CNS, where sequestered parasites were inaccessible to the trypanocidal effects of the drug.

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.

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.

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.

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.

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.

A single dose of Ro 11–3128 was found to be 98–100% effective against Schistosoma mansoni infections at intervals of 3 h to 15 days following infection, and apparently killed the schistosomula stages soon after administration, thus allowing an assessment of the immunizing potential of progressive larval stages. Following infection with 500 unirradiated cercariae, optimum resistance was manifest by groups drug-treated at 48–96 h (60–75%). Significantly lower levels of resistance occurred with early (3 h) or later (6–15 day) treatments. Superimposition of an infection treated at 15 days on a prior infection which had been treated at 2 days did not reduce the level of resistance caused by the latter, indicating that the infection plus delayed treatment had not induced suppression. Thus the peak resistance manifest during the 48–96 h period may reflect optimum expression of protective antigens. Comparison of irradiated (20 krad.) with unirradiated infections showed that, when drug-terminated 24, 48 or 96 h post-infection, irradiated cercariae induced significantly less resistance than unirradiated cercariae, perhaps indicating a delayed appearance of protective antigens following radiation treatment.

In Medium 199 supplemented with calf serum (+ 10%), adult Schistosoma mansoni produced a mean total of 400 eggs/worm pair during maintenance for 10 days in vitro. During the period of egg deposition in vitro, the dry weight of worm pairs decreased by 35%. Biomass decreases were proportionally greater in female worms than in males. Declines in the dry weight of female worms were mainly due to decreases in protein content, while biomass decreases in males resulted from losses of both protein and glycogen. Glucose was depleted from the maintenance medium at a rate of approximately 200 μg/worm pair/day during each of the first 3 days in vitro, while concentrations of glucose in the medium of above 1 g/litre did not affect the degree of glycogen depletion observed in adult S. mansoni during culture for 24 h. The contribution of the loss of schistosome gut contents in vitro to the observed changes is discussed. The work described represents part of an attempt at logical design of in vitro culture.

The cuticle of parasitic nematodes, the main contact site with the host, plays an important role in host-parasite interaction and thus also in immunological control. We compared different surface-iodinated life-stages of the filarial worm Dipetalonema viteae (microfilariae, infective 3rd-stage larvae (L3), adult males and females) with respect to changes in their surface composition. Autoradiographs of peptide maps show that all stages present an identical set of peptide spots reflecting common surface protein(s). Spots specific for larvae L3 show that the composition of the iodinated surface differs in microfilariae and adults i.e. it changes during development. Adults show a spot typical for males or females. Identical spots are found in L3. This suggests that a surface component is also sex specific.

The abomasum of living sheep infected with 50000 larvae of Haemonchus contortus was examined before and during infection, by means of fibre optic endoscopy. Biopsy specimens were removed from the abomasum of the living sheep and were examined by means of scanning electron microscopy. Changes were noted in the surface structure of the abomasum 2 days after infection and larvae were seen on, and burrowing into, the mucosa. These changes became more pronounced as the infection proceeded, especially after day 10 of the infection when the adult worms had appeared. The behaviour of adult nematodes was observed within the abomasum and on occasions they were seen to move from surrounding areas into an area of haemorrhage, caused by removal of a biopsy specimen. Individual nematodes were removed from the abomasum by means of the biopsy forceps. Fibre optic endoscopy was shown to be a useful tool in the study of parasitic nematodes in vivo.

A limited number of metacestodes of Hymenolepis diminuta from Tenebrio molitor had host plasmatocytes and cell debris of coagulocyte origin associated with the microvillar surface. There was evidence of phagocytosis of microvilli by plasmatocytes, involving clathrin-like endocytotic vesicles. In contrast to these otherwise ‘normal’ cysticercoids, occasional batches were ‘sticky’ and, on flushing into saline, rapidly developed large bladders possibly associated with osmotic stress. In addition, numerous small surface blebs were present. These ‘surface-stressed’ cysticercoids also had host plasmatocytes and cell debris associated with the bladder bases and the blebs, and phagocytosis of microvilli was observed. In no case had precipitation of haemolymph, melanization or encapsulation (features typical of the insect immune response) occurred. The possibility that the limited host response indicates a spatially restricted impairment of the surface compatibility of the parasite, and thus insufficient to elicit the full immune response, is discussed.

Site specificity and distribution of 5 species offreshwater acanthocephalans Acanthocephalus clavula, A. lucii, A. anguillae, Pomphorhynchus laevis and Echinorhynchus trultae and I marine species, E. gadi, were studied in the intestines of several species of fish, especially Anguilla anguilla. When data are presented in the conventional manner with results from all fish and all parasites in a sample combined, each species exhibited a preference for a particular region of the intestine which altered in some species in relation to host identity and sex and abundance of parasite. Each species could nevertheless inhabit most of the length of the intestine and there was a considerable degree of overlap in most cases between the distributions of species in the same host, but the mean position of each species differed significantly from that of any other and the species appeared to exhibit site segregation and resource partitioning along the length of the intestine. In individual fish, fidelity of site location and distribution is poor and may bear little or no relationship to the position and distribution of the parasites in the population as a whole, and it is concluded that the concepts of site specificity and segregation are most applicable at the population level. Mixed species infections are very rarely encountered in Britain since most freshwater localities contain, or are almost completely dominated by, only a single species of acanthocephalan. The results are discussed in relation to current ideas on the role of interspecific competition in determining site segregation and community structure of parasites. It appears that site specificity in fish acanthocephala is not related to the probability of mating, or site segregation to interspecific competition past or present. Acanthocephalan communities do not exist as such; the normal situation is chance assemblages, with vacant niches, little organization, few or no interactions and little fidelity between habitats.

Plastic ear tags impregnated with acaricides (synthetic pyrethroids; fenvalerate, 10% (w/w); fenpropathrin, 10% (w/w); fiuvalinate, 10% (w/w); and permethrin, 8% (w/w)) were evaluated for the control of Rhipicephalus appendiculatus infesting cattle in the laboratory and field in Kenya. These controlled release devices gave excellent control of R. appendiculatus for over 20 weeks on cattle in the laboratory where they were housed mostly indoors. Fluvalinate-impregnated tags gave consistently the most rapid control of ticks, but all of the tags normally prevented feeding of the ticks on the ears of cattle. Under field conditions in the Trans-Mara Division of Kenya, excellent control of R. appendiculatus naturally infested cattle was obtained by fluvalinate-impregnated tags followed by fenpropathrin. Less impressive control was obtained by fenvalerate- and permethrin-impregnated tags, but this control was more effective than immersion of cattle in toxaphene. In contrast to the laboratory experiments, the effect of the tags on R. appendiculatus infestation waned by 58 days after application. The potential of synthetic pyrethroid-impregnated tags for the control of ticks infesting cattle in Africa was demonstrated, but a more prolonged release of the active ingredients at an effective level in the field and, in some cases, a more robust tag design will have to be achieved before tick control with impregnated tags becomes a practical proposition.

The effect of host resistance on the feeding and development of Rhipicephalus appendiculatus, the African brown ear tick, was investigated. In this 3-host species the percentages of larvae and nymphs engorging on resistant cattle, and also of those subsequently moulting, were significantly less than those of ticks feeding on susceptible rabbits (i.e. without previous tick-feeding experience). The mean weights of engorged larvae, nymphs and females were significantly reduced on resistant hosts. Fewer nymphs and females engorged, even when fed on susceptible hosts, if their previous feed had been on a resistant host, and the engorged weight was also less. If only one feed during the life-cycle was on a resistant host the final egg production was reduced by a factor of 13· 2· and l· for the larval, nymphal and adult feed respectively. The egg production of a tick population with all 3 stages feeding only on resistant hosts could be reduced by more than 98% if these effects were combined.