The diversity of the genes encoding 2 merozoite surface proteins (MSP-1 and MSP-2) of Plasmodium falciparum has been examined in parasites infecting members of 4 households in a village in Tanzania. The polymerase chain reaction (PCR) was used to characterize allelic variants of these genes by the sizes and sequences of regions of tandemly repeated bases in each gene. In each household extensive polymorphism was detected among parasites in the inhabitants and in infected mosquitoes caught in their houses. Similar frequencies of the alleles of these genes were observed in all households. Capture-recapture data indicated that both Anopheles gambiae and A.funestus freely dispersed among households in the hamlet. The results confirm that cross-mating and gene flow occur extensively among the parasites, and are discussed within the context of spatial clustering of natural populations of P. falciparum.

Cortisone acetate, given to mice on two days during a primary infection with the nematode Trichuris muris, suppressed the development of acquired immunity to the parasite. The proportion of mice in which suppression occurred was greatest when the drug was given (at 2.5 mg per mouse) on days 14 and 15 of the infection. Suppression of the response prevented the elimination of larvae, which otherwise occurs during the third week, and allowed the parasite population to mature and survive for at least a further 3 weeks. Similar treatment given during a challenge infection in resistant mice prevented the elimination of the challenge larvae for 2 or 3 days only. Mice in which cortisone treatment had prevented the elimination of a primary infection were not only found to be fully susceptible to subsequent challenge, but showed no development of immunity to the challenge infection itself. This long-lasting suppression of the immune response to T. muris is discussed and the possibility of the induction of a specific immunological unresponsiveness to the parasite is considered.

Lymphatic filariasis (LF), a common parasitic infection in tropical countries, causes lymphoedema of limbs, hydrocele and acute attacks of dermato-lymphangio-adenitis. Recent advances in diagnosis have helped to recognize that LF infection is often acquired in childhood. Newly available diagnostic techniques like sensitive antigen and antibody assays, Doppler ultrasonography and lymphoscintigraphy have helped to understand the subclinical pathology caused by this infection, which was hitherto generally believed to be irreversible. Recent studies indicate that drugs used in the mass drug administration (MDA) programme under GPELF are capable of reversing the sub-clinical lymphatic damage in children and provide benefits other than interruption of transmission. Albendazole and ivermectin used in MDA are effective against soil-transmitted helminthic infections common in children in LF endemic areas. Thus MDA had other ‘beyond LF’ benefits in treated children including increased appetite, weight gain, greater learning ability and concentration, better school attendance and prevention of anaemia. MDA should no longer be viewed as a measure for interrupting transmission alone. Recent findings of reversibility of early lymphatic pathology in treated children indicate that both MDA and ‘foot-hygiene’ measures are effective strategies in preventing and managing morbidity. Programme managers should effectively utilize this information to strengthen their advocacy efforts to achieve high and sustainable coverage in MDA.

Schistosoma mansoni eggs, miracidia and primary sporocysts were labelled with phalloidin-rhodamine to visualize filamentous actin structures. Analysis of these forms by confocal fluorescence microscopy revealed the presence of previously well-defined circular and longitudinal muscle layers. Besides these muscular layers that sustain and provide motility to these parasite forms, we found in these 3 consecutive developmental stages of the parasite previously unidentified actin-rich tubular structures. In the 3 forms, 4 actin-rich tubules could be observed by optical sectioning underneath the well-developed muscle layers. The tubules appear in pairs, transversal to the length of the parasite, and located towards the extremities. By using an anti-flame cell specific antibody we confirmed that the tubules co-localize with flame cells and also determined that the tubule core is filled with microtubules. The additional presence of myosin in these tubules strongly suggests that they are contractile structures.

1. Suspensions made from infected caecal material, derived from chickens which had been artificially infected with Histomonas meleagridis by the administration of embryonated Heterakis ova, can be used to transmit the organisms to other chickens when administered per os.

2. Infections with histomonad suspensions can only be obtained in chickens that have been starved, or in chickens that are feeding but have received an alkali mixture immediately before the suspension is administered. The highest incidence of infections is obtained by administering suspensions to starved chickens that have received 1 g. alkali mixture beforehand.

3. Successful infection appears to depend upon the pH of the gizzard and, possibly, of the upper intestine. The incidence of lesions produced by feeding suspension is increased as the contents of the gizzard become alkaline. It is also suggested that the consistency of the food may play a part, as coarse food, along with the infective material, is retained in the gizzard until it is completely ground up and mixed with the gastric juice.

4. In one series of passages the suspension became attenuated after fourteen passages through chickens. In other cases suspensions became attenuated after only six passages through chickens.

5. The courses of infections produced by histomonad suspensions and Heterakis ova are compared.

6. The advantages of the method of using histomonad suspensions are discussed in their relation to the screening of chemotherapeutical agents.

The larvae of Brugia pahangi recovered from the jird have been shown to grow continuously between moults, their length increasing at least 5-fold during the 4th instar. This intermoult growth is achieved without an increase in the surface area of larvae. The cuticle of very early 4th and 5th-stage worms is highly folded and intermoult growth is accommodated by an expansion of surface annular folds. The major increases in the surface area of larvae occur only through ecdysis, with an 8-fold increase in the surface area being achieved at the 3rd moult. The growth curve of these worms is therefore sigmoidal but the surface area curve is stepped. The relationship between the cuticles of nematodes and insects is discussed

The circadian migration of Hymenolepis diminuta in the small intestine of the rat may be correlated with a circadian variation in 5-hydroxytryptamine levels present in worm tissue, in the intestinal lumen, in the intestinal mucosa, with the amount of food present in the small intestine and in arterial blood. The 5-HT and food levels in uninfected animals were also determined. The 16.00 h stage in the circadian cycle marks both the commencement of host feeding, followed by rising 5-HT levels in both worm and host tissues, and initiation of an anteriad migration of worm biomass. It was found that 5-HT levels in the intestine of parasitized animals were significantly higher than in the intestine of uninfected controls. This is the first report of circadian variation in mucosal and luminal 5-HT levels. The similarity in the circadian patterns of worm migration and worm luminal, mucosal and blood 5-HT levels were striking. Fasting eliminated the circadian rise in intestinal 5-HT levels and the worms did not migrate. Luminal 5-HT levels were significantly lower in fasted animals than in the comparable rats fed ad libitum. When the intestine was ligatured at the pyloric sphincter, worm anteriad migration still occurred after feeding, indicating that the presence of exogenous food in the intestine is not a factor in the initial migration of the worms.

The base compositions of DNA from some species of malarial parasite have been estimated by measurement of density in CsCl gradients and of thermal denaturation temperatures. Species from avian (Plasmodium gallinaceum) and rodent (P. berghei and P. vinckei) hosts – often used as model systems in malarial studies – contain single DNA components with base compositions of about 20% G + C. By contrast, species from primate hosts (P. knowlesi and P. falciparum) contain major DNA components of about 40% G + C and minor ones of about 20% G + C. These differences could be reflexions of markedly different genomes within these two groups of the genus Plasmodium.

Apart from differences in base composition, the physico-chemical properties of the main components of DNA from primate and rodent malarial parasites are very similar to those of DNA from mammalian cells. DNA from avian malarial parasites appears to have some unusual properties.

One of us (P.I.T.) received financial assistance from the World Health Organization. We thank Dr F. Hawking and Dr J. Williamson for many helpful discussions, Dr W. H. G. Richards, Dr A. Voller and Dr D. C. Warhurst for the provision of some of the strains and Miss Jane Dunnett, Mrs A. C. Gutteridge and Mr T. Scott-Finnigan for technical assistance.

Acquired immunity influences the severity of parasitic disease, but modelling the effects of acquired immunity in helminth infections has proved challenging. This may be due to a lack of suitable immunological data, or to the perceived complexity of modelling the immune response. We have developed a model of T. circumcincta infection in domestic sheep that incorporates the effects of acquired immunity on parasite establishment and fecundity. A large data set from commercially managed populations of Scottish Blackface sheep was used, which included relationships between IgA activity and worm length, and between worm length and fecundity. Use was also made of a recently published meta-analysis of parasite establishment rates. This realistic but simple model of nematode infection emulates observed patterns of faecal egg counts. The end-of-season faecal egg counts are remarkably robust to perturbations in the majority of the parameters, possibly because of priming of the immune system early in the season, reducing parasite establishment and growth and, therefore, faecal egg counts. Lowering the amount of early infection leads to higher end-of-season egg counts. The periparturient rise in egg counts in ewes appears to have an important role in supplying infection for the priming of the immune response. This feedback in the immune priming suggests that nematode infections may be difficult to eliminate.

The expression of the Schistosoma mansoni 28 kDa glutathione S-transferase (Sm28) was studied using molecular (PCR, in situ hybridization), and immunocytochemical techniques. The presence of Sm28 was demonstrated in all developmental stages of the parasite except the intra-uterine immature egg. In the parenchyma of male and female adult worms the distribution of Sm28 was limited to a subpopulation of parenchymal cells and to the dorsal tubercles of the male. The tegument, the muscles, the digestive tract, the neural mass, the vitelline glands, and mature gametes were not immunoreactive. Immature germinal cells in both sexes, and the ootype in the female genital system, were found to express Sm28. Deposits of immunoreactive material on host skin following cercarial penetration, exfoliation from the male tubercles, and especially emission of Sm28 from eggs in hepatic granulomas are suspected to be a source of antigen during the parasite infection. The reduction in worm fecundity previously observed in immunization experiments may result from an antibody response directed against Sm28 present in the ootype. There was no cross-reactivity observed, under the experimental conditions used, between the anti-Sm28 sera and either vertebrate or invertebrate host tissue.

Risk factors related to herd and farmer status, farm and pasture management, and environmental factors derived by satellite data were examined for their association with the prevalence of F. hepatica in sheep and goat farms in Thessaly, Greece. Twelve farms (16·2%) and 58 farms (78·4%) of 74 had evidence of infection using coproantigen and serology respectively. The average normalized difference vegetation index (NDVI) of farm location for 12 months before sampling was the most significant environmental risk factor for F. hepatica infection based on high seropositivity. The risk of infection increased by 1% when the value of NDVI increased by 0·01 degree. A geospatial map was constructed to show the relative risk (RR) of Fasciola infection in sheep and goat farms in Thessaly. In addition, geospatial maps of the model-based predicted RR for the presence of Fasciola infection in farms in Thessaly and the entire area of Greece were constructed from the developed model based on NDVI. In conclusion, this study demonstrated that Thessaly should be regarded as an endemic region for Fasciola infection and it represents the first prediction model of Fasciola infection in small ruminants in the Mediterranean basin.

Malaria remains one of the most significant global public health burdens, with nearly half of the world's population at risk of infection. Malaria is not however a monolithic disease – it can be caused by multiple different parasite species of the Plasmodium genus, each of which can induce different symptoms and pathology, and which pose quite different challenges for control. Furthermore, malaria is in no way restricted to humans. There are Plasmodium species that have adapted to infect most warm-blooded vertebrate species, and the genus as a whole is both highly successful and highly diverse. How, where and when human malaria parasites originated from within this diversity has long been a subject of fascination and sometimes also controversy. The past decade has seen the publication of a number of important discoveries about malaria parasite origins, all based on the application of molecular diagnostic tools to new sources of samples. This review summarizes some of those recent discoveries and discusses their implication for our current understanding of the origin and evolution of the Plasmodium genus. The nature of these discoveries and the manner in which they are made are then used to lay out a series of opportunities and challenges for the next wave of parasite hunters.

It will be convenient at this point, before proceeding to a more general discussion of the findings, to summarize all the experiments recorded in the eight preceding subsections. Briefly the results are as follows:

(i) An attempt to infect a Macacus rhesus by feeding it with Trichomonas isolated from a monkey of the same species failed completely.

(ii) Four similar attempts to infect a Macacus sinicus with the same Trichomonas (from M. rhesus) were equally unsuccessful.

(iii) Two attempts to infect another M. sinicus by intra-intestinal inoculation with the same flagellate were likewise wholly negative.

(iv) One attempt to infect a man per os with the same strain of Trichomonas (from M. rhesus) did not succeed.

(v) A strain of Trichomonas from Man, when fed to a Macacus rhesus, produced no infection.

(vi) The same strain (T. hominis) fed to a Macacus sinicus likewise failed to infect.

(vii) A strain of Trichomonas from Macacus nemestrinus, however, when fed to M. rhesus, gave rise to a temporary infection lasting about a month.

(viii) This Trichomonas (from M. nemestrinus, after passage through M. rhesus) produced, nevertheless, a permanent infection—lasting 4½ years to date—when fed to a man.

(ix) The same strain of Trichomonas (from M. nemestrinus), after passage through M. rhesus and Man, when fed to a Macacus sinicus gave rise to an infection which endured for approximately 1½ months and then died out. But

(x) The very same Trichomonas (which was derived from M. nemestrinus, and which produced a temporary intestinal infection in M. rhesus and M. sinicus, and a permanent intestinal infection in Man) when introduced into the vagina of M. sinicus established itself enduringly as a typical “T. vaginalis.” The infection has now persisted for ome 3⅓ years.

(xi) The monkey (M. sinicus) in which a permanent vaginal infection with an intestinal Trichtomonas was established, has probably since reacquired no permanent intestinal infection—despite every natural opportunity for such reinfection.

(xii) No macaque suffered any harm whatsoever as a result of inoculation with any strain of Trichomonas–whether successful or unsuccessful.

(xiii) The one man successfully infected with Trichomonas (from M. nemestrinus) has likewise remained normal ever since.

Endoperoxides kill malaria parasites via cleavage of their endoperoxide bridge by haem or iron, leading to generation of cytotoxic oxygen-centred radicals. In view of the Leishmania parasites having a relatively compromised anti-oxidant defense and high iron content, this study aims to establish the underlying mechanism(s) accounting for the apoptotic-like death of Leishmania promastigotes by artemisinin, an endoperoxide. The formation of reactive oxygen species was confirmed by flow cytometry and was accompanied by inhibition of mitochondrial complexes I–III and II–III. However, this did not translate into a generation of mitochondrial superoxide or decrease in oxygen consumption, indicating minimal impairment of the electron transport chain. Artemisinin caused depolarization of the mitochondrial membrane along with a substantial depletion of adenosine triphosphatase (ATP), but it was not accompanied by enhancement of ATP hydrolysis. Collectively, the endoperoxide-mediated radical formation by artemisinin in Leishmania promastigotes was the key step for triggering its antileishmanial activity, leading secondarily to mitochondrial dysfunction indicating that endoperoxides represent a promising therapeutic strategy against Leishmania worthy of pharmacological consideration.

The development of strains of Eimeria maxima resistant to buquinolate, methyl benzoquate, clopidol, sulphaquinoxaline and robenidine is described. It was not possible to standardize a schedule of inoculations and drug administration, which would enable the development of resistance to the different drugs to be compared directly. Resistance developed most readily to the quinolones. One robenidine-resistant strain proved to be drug-dependent. Dinitolmide showed unusual effects upon sporogony and three attempts to develop resistance against this activity failed. Chicks previously immunized with the parent strain were completely protected against infection with the drug-resistant strains.

1. It has previously been shown [by Dobell] that, in cultures of strain K 28c, Entamoeba histolytica could be maintained indefinitely and made to pass through all the stages of its life history.

2. It was also demonstrated that all non-encysting strains of E. histolytica could be induced to encyst in vitro by substituting their concomitant bacterial flora by that of strain K 28c.

3. In order to ascertain what part each constituent of the bacterial flora of K 28c played in the life of E. histolytica, a detailed analysis of this flora was carried out. It was found to comprise eight aerobic organisms (mostly of the B. coli group) and six anaerobes.

4. The properties of individual species and varieties of bacteria were studied by adding them to cultures of the amoebae or by hatching the cysts of E. histolytica in media previously seeded with the bacteria to be tested.

5. With the same end in view two methods were devised for producing simplified strains of E. histolytica associated with from one to four species of bacteria only. By treating the cysts with acriflavine, the mixed flora could be freed of the aerobic organisms, leaving only the spores of the anaerobes. The spore-bearing anaerobes, in their turn, could be eliminated by treatment of the mixture with gentian violet. By using these methods it was possible to produce cultures of ‘synthetic’ strains of E. histolytica accompanied by any desired combination of bacteria, whose properties it was desired to investigate.

6. The results of the earlier experiments suggested that the essential constituent of the flora of K 28c was B. coli, all varieties of which appeared to promote growth, induce encystation and excystation, and generally favoured the completion of the life-cycle of the amoebae in vitro, whereas the anaerobic bacteria present in the strain appeared to be inactive as regards encystation.

7. However, later experiments have demonstrated conclusively that, although the aerobic bacteria individually induced the cysts of E. histolytica to hatch and supported the growth of the amoebae indefinitely, only one species—the anaerobe N5—was capable of promoting encystation. As regards the aerobic bacteria, their chief role is to provide the anaerobic conditions necessary for the growth of the amoebae with N5 in culture.

Mating was observed in populations of Gyrodactylus turnbulli from guppies. Copulation took place between older (post-1st birth) flukes and resulted in the insemination of spermatozoa into the seminal receptacle. New-born flukes, and flukes which had only recently given birth for the first time (in which the penis was absent or developing), were never inseminated. Flukes were promiscuous, copulating with several partners in succession. The occurrence of mating was related to the size, age and crowding of the G. turnbulli population, taking place most frequently when the parasites were most densely crowded upon the peduncle of the fish on days 5 and 6 of the infection. Maximum population size was positively correlated with the number of flukes initiating an infection. As a result, mating began earlier, and continued for longer in populations founded by several parasites rather than those begun by single flukes. These observations are discussed with respect to the population biology of G. turnbulli: it is likely that sexual and asexual reproduction alternate, with sex being important only during phases of epidemic population growth. The significance of sex in gyrodactylids is discussed, and the potential importance of continuous sexual reproduction in G. turnbulli infections on cultivated guppies is noted.

Glycoproteins of Trypanosoma congolense have been detected on SDS-polyacrylamide gels using the Concanavalin A peroxidase technique. Using [35S]diazoniobenzenesulphonate as a marker for cell surface proteins it was possible to distinguish between internal glycoproteins and the surface coat proteins. On SDS-polyacrylamide gels Con A reacted with the surface coat proteins. Results obtained from Con A-induced agglutination of living trypanosomes indicated that sugars of the surface coat proteins were accessible to Con A. This was reinforced by the cytochemical visualization of Con A binding to the trypanosome surface. The results suggested that the surface coat protein contained α-linked d-mannosyl, d-glucosyl, or N-acetyl-d-glucosaminoyl residues, which are exposed exteriorly on the surface coat.

A variety of morphological forms developed during monophasic culture of ruptured brood capsules of equine Echinococcus granulosus. Attached to some protoscoleces were small posterior bladders, with a surface ultrastructure of truncated microtriches, and these never developed a laminated layer. In contrast, small free vesicles of similar size and ultrastructure, but devoid of an attached protoscolex, produced a layer by 20–30 days. The surface ultrastructure of both these forms is similar to that of the protoscolex attachment stalk and the brood capsule lining, and posterior bladders and small free vesicles are considered to be derived from portions of the stalk±part of the brood capsule lining retained at protoscolex release. Also present were large vesicles interpreted from their size and surface anatomy as ruptured, everted brood capsules. When devoid of attached protosoleces these formed cysts each with a laminated layer, whereas similar vesicles with several attached protoscoleces did not develop a layer, or only very occasionally after 70 or more days. In contrast, a few large vesicles with a single attached protoscolex produced a laminated layer. The possibility that protoscolex attachment to stalk remnants or brood capsules inhibits the cystic development of these structures is discussed.

The aims of the study were (1) to describe the Dactylogyrus communities living on selected South European Barbus species, (2) to analyse morphometric variability of their attachment and reproductive organs, and (3) to perform molecular phylogenetic analyses, in order to investigate the mode of speciation in Dactylogyrus species parasitizing congeneric hosts. In Bulgaria, Dactylogyrus crivellius, D. dyki and D. petenyi were found on B. balcanicus, and D. dyki on B. cyclolepis. In Spain, Dactylogyrus carpathicus and D. dyki were detected on B. meridionalis. Morphometric analyses of D. dyki revealed significant differences in the attachment and reproductive organs when individuals from different Barbus species were compared. Two monophyletic groups were recognized from the molecular phylogenetic analyses: the first included D. carpathicus and D. crivellius which have large body size and anchors, with a weakly supported basal position of D. malleus from B. barbus; the second included D. dyki and D. petenyi which have small body and anchor sizes. The comparison of host and parasite phylogenies did not indicate the intrahost speciation. Intraspecific molecular variability was found between individuals of D. dyki and D. carpathicus from different Barbus species, suggesting the need for a taxonomic revision for these species.