Longitudinal muscles in adult male Schistosoma mansoni appear to remain in almost all respects functional after tegumental disruption by Triton X-100. Responses to high K+, ouabain, low temperature, praziquantel and neurotransmitters are still present. Muscle membrane potentials remain near those of control animals and lanthanum nitrate is still excluded from the muscle after the Triton treatment. Although muscle contractility remains after tegumental disruption, sodium and calcium levels, as measured by plasma emission spectroscopy, increase by 20–30% while potassium and magnesium levels decrease by 15%. 45Ca2+ accumulation is double that of control animals. Upon exposure to a bathing medium lacking Ca2+, Triton-treated animals lose responsiveness to high K+, ouabain, low temperature and praziquantel more rapidly than do control animals. D-600, which effectively blocks the high K+ response in control animals, has no measurable effect on the high K+ response in Triton-treated animals, suggesting that voltage-dependent Ca2+ channels are present in the tegument.

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.

1. The term Schizogregarinae Léger (1900) is the name now given to a sub-order of the Gregarinida, the remaining members of which are known as the Eugregarinae. The Schizogregarines were formerly known as Amoebosporidia Aimé Schneider (1884), a name given in misapprehension of the character of the cytoplasmic processes, fixative in function, present in the genus Ophryocystis. Two species of Ophryocystis (0. buetschlii and 0. francisci) were the only members of this sub-order known before 1900.

2. At present the sub-order Schizogregarinae contains five families: Ophryocystidae, Schizocystidae, Selenidiidae, Merogregarinidae, and Aggregatidae.

3. All these organisms show well-marked schizogonic stages in their life-history, and—with the possible exception of the Aggregatidae—follow after the Eugregarinae in their methods of sporogony.

4. In Ophryocystis and Schizocystis the schizogony is extracellular, that is, these forms are ectoschizous. The life-cycle of the former is shown in Fig. 1. In these parasites the number of the nuclei in the schizont increases simultaneously with its volume.

5. In Selenidium and Merogregarina the schizogony is intracellular, in other words these forms are endoschizous. The life-cycle of the former is illustrated in Fig. 3. In these forms the schizont is uninucleate during its growth, only becoming multinucleate at the end of the growing period.

6. Ophryocystis forms only one sporocyst, a fact which has been emphasised by Léger and Duboscq (1908), by the placing of the Ophryocystidae in a special section, the Monospora. However, this apparent peculiarity is easily explained by a process of reduction and degeneration having taken place, affecting with one exception all the gametes formed from each gametocyte. There is good morphological evidence in support of this explanation (see p. 382, and Fig. 4, D).

7. Figures of the interesting form Schizocystis gregarinoides (Léger, 1900) are not yet published, but a paper dealing with this organism is promised by Prof. Léger at an early date.

8. Aggregata differs from other Schizogregarines in that its schizogony takes place in one host (crab), while its sporogony occurs in another (Cephalopod mollusc). In this respect Aggregata resembles the Haemosporidia. The schizogonic phases in Crabs were formerly regarded as belonging to a gymnosporous Gregarine, Aggregata Frenzel, while the sporogonic phases were considered to belong to a Coccidian, Eucoccidium (Benedenia) in cuttlefishes and Octopus. Regarding this, Léger and Duboscq (1908, p. 102) write “…Aggregata, avec un changement de cycle coïncidant avec un changement d'hôte, c'est à dire qui soient à la fois digénétiques et hétéroïques.”

9. It is evident therefore that the Aggregatidae stand apart. On this account, I suggest a division of the Schizogregarinae into two sections, termed respectively, the Homoïica (to include the first four families discussed in this paper, wherein schizogony and sporogony take place in the same host) and the Heteroïca (for the Aggregatidae).

10. Among the Homoïca we have extracellular schizogony (ectoschizous forms) in the Ophryocystidae and Schizocystidae, and intracellular schizogony (endoschizous forms) in the Selenidiidae and Merogregarinidae. This difference is not merely superficial, it requires to be emphasised, and for this reason I would divide the section Homoïca into two sub-sections, termed respectively Ectoschiza and Endoschiza.

11. The classification of the Schizogregarines, which I would propose, is as follows:

12. Much further research is needed on the life-cycles of the Endoschiza, especially among the Selenidiidae, which occur so frequently in the Annelida. Sporogonic stages are at present unknown in Eleutheroschizon and Siedleckia.

13. In connection with the Aggregatidae, and to a less extent with the Selenidiidae, stress is laid upon the necessity of carefully distinguishing between “coelomic” and “gut” parasites. (See pp. 397 and 387.)

14. The Schizogregarinae form a most interesting link between the Eugregarinae and the Coccidiidea.

Many liver-invasive parasites cause extensive liver damage which may result in an impaired ability to catabolize endotoxin. The influence of endogenous endotoxin on the progress of liver-invasive parasitic diseases has been investigated in murine Mesocestoides corti infection. Invasion of liver tissue by tetrathyridia resulted in extensive parenchymal destruction with fibrosis. In association with this, undetoxified endotoxin, in potentially biologically active concentration, was found on peritoneal macrophages, 5 months post-M. corti infection. Host susceptibility was influenced by the Lps gene for responsiveness to lipopolysaccharide (LPS). The parasite burden of LPS-responsive (C3H/HeN) mice was significantly increased in the livers of these mice when compared to LPS-resistant (C3H/HeJ) mice. LPS reduced the ability of normal peritoneal macrophages to kill tetrathyridia, when co-cultured in vitro. LPS also abrogated the ability of recombinant interferon-γ (r.IFN-γ) to enhance macrophage larvicidal activity. These in vitro findings were confirmed in vivo. Daily intraperitoneal administration of LPS, at low concentration, caused a 4-fold increase in parasite burden in the liver, while r.IFN-γ at optimal concentration reduced parasite burden by 57%. Post-infection macrophages have previously been shown to be refractory to cytokine-activation for larval killing. In this report, we conclude that (1) this refractoriness may be due to the presence of undetoxified endotoxin on post-infection macrophages and (2) endotoxin may reduce host resistance by abrogating effector macrophage response to IFN-γ.

SIV rats infected with a high dose (50000 oocysts) of Eimeria nieschulzi displayed clinical symptoms of coccidiosis such as diarrhoea (days 6 and 7 post-primary infection) and weight loss (days 6–8 post-primary infection) and were completely immune to challenge with a similar dose. The ability of rats to produce tumour necrosis factor (TNF) in vivo was enhanced during the period of oocyst excretion in the primary infection but significant production of TNF did not occur after challenge infection. Thus, TNF does not appear to be an important factor in resistance to infection with E. nieschulzi but may play some role in resistance to primary infection and in the pathology associated with E. nieschulzi infection. Parasite-specific serum IgM levels (measured by enzyme-linked immunosorbent assay) were also increased during primary infection but returned to background levels at the end of the patent period and were not affected by challenge infection. In contrast to TNF and IgM, serum concentrations of E. nieschulzi-specific IgGl, IgG2a, IgG2b, IgG2c and intestinal tissue levels of IgA did not begin to increase until after day 12 post-primary infection, reached peak levels between days 20 and 30 post-primary infection and were slightly increased by challenge infection.

Reversal of chloroquine (CQ) resistance by verapamil, a Ca2+ antagonist, has been shown in CQ-resistant human and rodent malaria parasites. Here, we report ultrastructural changes associated with this phenomenon in CQ-resistant Plasmodium chabaudi (AS strain) after infected mice were administered CQ and verapamil. At parasitaemias of 5–7%, CQ at 6 mg/kg caused little morphological effect on CQ-resistant parasites. In contrast, co-administration of CQ and verapamil at 50 mg/kg induced swelling of food vacuoles with clumped pigment at 2.5 h. Morphological changes other than food vacuole enlargement occurred at 21 and 45 h: disappearance of endoplasmic reticulum, formation of myelin structures, focal cytoplasmic vacuolization and coarse clumping of electron-dense material in nuclei. These structural changes appeared to be very similar to those observed in CQ-sensitive P. chabaudi in mice injected with CQ alone or CQ plus verapamil. On the other hand, verapamil at 50 mg/kg alone did not induce any effect on both CQ-sensitive and CQ-resistant P. chabaudi. These results suggest that swelling of the food vacuoles is an initial event associated with reversal of CQ-resistance by verapamil.

The defensive glands of beetles, Tenebrio molitor, infected with metacestodes (cysticercoids) of Hymenolepis diminuta are everted less frequently upon stimulation, and contain less toluquinone (methylbenzoquinone) and m-cresol, than glands of uninfected controls. These differences, as shown in predation trials with wild rats, increase the likelihood that both cysticercoids and beetles will be ingested by the tapeworm's definitive host. This is the first documented case of a parasite inhibiting the chemical defence of an intermediate host, and one of only a few reports of parasite-induced manipulation of host biology supported by empirical evidence implicating facilitated parasite transmission between host species.

In the course of our studies on species of Rhipicephalus, we have noted the great variability in size and structure observable in the genus. This variability has been a cause of much confusion in classification, as noted by Warburton (Parasitology, 1912, v. 1). It soon occurred to me, in seeking for an explanation of this variability, that it might well be due to nutrition, it being probable that, under natural conditions, a certain number of ticks are removed from the host before they have fed to repletion. When a host is infested with ticks it will brush or rub off a certain number prematurely and the ticks which are imperfectly fed would, doubtless, give rise to adults of small size. As stated, the great variability observed in Rhipicephalus is very striking. In the genus Ixodes, on the other hand, the size of the adults is fairly constant. In the latter case, we have, as a rule, to deal with small ticks provided in the immature stages with long hypostomes, both the small size and hypostomal structure rendering it most difficult for the tick to be removed prematurely from the host. It is difficult to remove Ixodes from the host without breaking the hypostome and using considerable force. In Haemaphysalis, as in Rhipicephalus, the immature stages are provided with short hypostomes and the ticks are more readily removed. The variation in size noted in adult Haemaphysalis, whilst considerable, is not as great as in Rhipicephalus, which would appear to be attributable to the smaller size of the tick, being in a measure a protection against its being prematurely removed from the host.

Although our knowledge of Filariae parasitic in animals is continually increasing, the main source of information concerning this group remains still confined to the important monographs by Molin (1858) and Stossich (1898). Molin's descriptions of worms are, however, often so incomplete that in using them as a basis of classification Diesing failed in his attempt to subdivide the genus Filaria, whilst Stossich's descriptions are scarcely better than those of Molin. Stiles has already pointed out the absence of clear and definite characters for the subgenus Filaria of which Filaria martis Gmelin is the type-species. Before any new division of the genus Filaria is proposed the writer thinks it is advisable to re-investigate the already known species and to re-describe them more carefully, laying special stress on such characters as the structure of the female genital organs and the structure of the microfilariae. The knowledge of Filariae parasitic in animals will be of great help in identification of worms parasitic in man.

Teneral Glossina morsitans centralis were fed on the flanks of African buffalo, N'Dama or Boran cattle infected with Trypanosoma vivax IL 2337. The infected tsetse were maintained on goats and on day 25 after the infected feed, the surviving tsetse were dissected to determine the infection rates. The mean mature infection rates (% ± S.E.) in the tsetse fed on buffalo, N'Dama and Boran cattle were 34·3 ± 9·9, 33·7 ± 13·4 and 58·9 ± 7·1, respectively. Logistic regression analysis indicated that infection rates in the labrum and hypopharynx of the tsetse were significantly lower when fed on the infected buffalo or N'Dama than Boran cattle. Similarly, the risk of infection was significantly lower in male than female tsetse. When teneral G. m. centralis, G. pallidipes, G. p. gambiensis, G. brevipalpis and G. longipennis were fed simultaneously on either the buffalo cow, the N'Dama bull or the Boran steer infected with T. vivax IL 2337, the mature infection rates were higher in the two morsitans group than the two fusca group tsetse, whilst G. p. gambiensis was relatively refractory to the infection, irrespective of the host species on which they fed. Logistic regression analysis indicated that the infection rates in the labrum and hypopharynx were significantly different amongst the five tsetse species for each of the three infected host animals. Nevertheless, the trypanotolerant African buffalo and N'Dama cattle may serve as reservoirs of T. vivax infection as can trypanosusceptible Boran cattle.

The availability of genome sequence data has facilitated the development of high-throughput genetic screening approaches in microbial pathogens. In the African trypanosome, Trypanosoma brucei, genome-scale RNA interference screens have proven particularly effective in this regard. These genetic screens allow for identification of the genes that contribute to a particular pathway or mechanisms of interest. The approach has been used to assess loss-of-fitness, revealing the genes and proteins required for parasite viability and growth. The outputs from these screens predict essential and dispensable genes and facilitate drug target prioritization efforts. The approach has also been used to assess resistance to anti-trypanosomal drugs, revealing the genes and proteins that facilitate drug uptake and action. These outputs also highlight likely mechanisms underlying clinically relevant drug resistance. I first review these findings in the context of what we know about current drugs. I then describe potential contributions that these high-throughput approaches could make to the development and implementation of new drugs.

Recent studies on parasite communities have considered the factors which contribute to variability in parasite infections among populations of one host species. This paper examined parasite assemblages of crucian carp (Carassius carassius) in a natural set-up of two distinctive environments inhabited by the same host species and differing in respect to composition of other fish species: ponds, where extreme conditions prevent other fish species from occurring and lakes, where crucian carp coexist with other fish species. Our aim was to evaluate the significance of parasite exchange, environmental conditions and host suitability for the depauperate parasite assemblages observed in pond crucian carp. As predicted, crucian carp had more diverse parasite species composition in lakes, which supports the hypotheses of increased opportunities for parasite exchange with other fish species and better environmental conditions for the parasites. However, for instance, diplostomids were found only from few fish individuals in very low numbers. Experimental exposure trials with the eye fluke Diplostomum spathaceum in the laboratory indicated that crucian carp were totally resistant to infection, which is exceptional and suggests that the low number of these parasites in crucian carp was due to physiological unsuitability of the host. To obtain a better understanding on the mechanisms underlying the formation of parasite assemblages in these fish, further studies on the relationships between the unique physiology of crucian carp and infection success by other parasite species are needed.

The metacestode of Echinococcus multilocularis is the etiological agent of alveolar echinococcosis. The metacestode stage used for research is maintained in rodents by serial passages. In order to determine whether cryopreservation of E. multilocularis metacestodes would be suitable for long-term maintenance and replace serial passages, isolates of different geographic origin were cryopreserved in 1984–1986. The aim of the current study was to test the viability of cryopreserved isolates following long-term cryopreservation (up to 35 years) and to determine the phylogenetic clades these isolates belonged to. Cryopreserved isolates were tested for viability in vitro and in vivo in gerbils. In vitro results of 5 isolates indicated protoscolex survival in 13 of 17 experiments (76%) and metacestode survival in 5 of 12 (42%) in vivo experiments. In vivo results showed ‘abortive lesions’ in 13 of the 36 animals, 15 were negative and 8 harboured proliferating metacestode tissue containing protoscoleces. Genetic analysis confirmed the isolates belonged to European, Asian and North-American clades. In conclusion, the results of the current study indicate that metacestodes of E. multilocularis are able to survive long-term cryopreservation. Therefore, cryopreservation is a suitable method for long-term storage of E. multilocularis metacestode isolates and reduces the number of experimental animals.

FhCaBP2 is a Fasciola hepatica protein which belongs to a family of helminth calcium-binding proteins which combine an N-terminal domain containing two EF-hand motifs and a C-terminal dynein light chain-like (DLC-like) domain. Its predicted structure showed two globular domains joined by a flexible linker. Recombinant FhCaBP2 interacted reversibly with calcium and manganese ions, but not with magnesium, barium, strontium, copper (II), colbalt (II), iron (II), nickel, lead or potassium ions. Cadmium (II) ions appeared to bind non-site-specifically and destabilize the protein. Interaction with either calcium or magnesium ions results in a conformational change in which the protein's surface becomes more hydrophobic. The EF-hand domain alone was able to interact with calcium and manganese ions; the DLC-like domain was not. Alteration of a residue (Asp-58 to Ala) in the second EF-hand motif in this domain abolished ion-binding activity. This suggests that the second EF-hand is the one responsible for ion-binding. FhCaBP2 homodimerizes and the extent of dimerization was not affected by calcium ions or by the aspartate to alanine substitution in the second EF-hand. The isolated EF-hand and DLC-like domains are both capable of homodimerization. FhCaBP2 interacted with the calmodulin antagonists trifluoperazine, chlorpromazine, thiamylal and W7. Interestingly, while chlorpromazine and thiamylal interacted with the EF-hand domain (as expected), trifluoperazine and W7 bound to the DLC-like domain. Overall, FhCaBP2 has distinct biochemical properties compared with other members of this protein family from Fasciola hepatica, a fact which supports the hypothesis that these proteins have different physiological roles.

The extent of sequence diversity among the genes encoding 10 antigens (Tp1–10) known to be recognized by CD8+ T lymphocytes from cattle immune to Theileria parva was analysed. The sequences were derived from parasites in 23 buffalo-derived cell lines, three cattle-derived isolates and one cloned cell line obtained from a buffalo-derived stabilate. The results revealed substantial variation among the antigens through sequence diversity. The greatest nucleotide and amino acid diversity were observed in Tp1, Tp2 and Tp9. Tp5 and Tp7 showed the least amount of allelic diversity, and Tp5, Tp6 and Tp7 had the lowest levels of protein diversity. Tp6 was the most conserved protein; only a single non-synonymous substitution was found in all obtained sequences. The ratio of non-synonymous: synonymous substitutions varied from 0.84 (Tp1) to 0.04 (Tp6). Apart from Tp2 and Tp9, we observed no variation in the other defined CD8+ T cell epitopes (Tp4, 5, 7 and 8), indicating that epitope variation is not a universal feature of T. parva antigens. In addition to providing markers that can be used to examine the diversity in T. parva populations, the results highlight the potential for using conserved antigens to develop vaccines that provide broad protection against T. parva.

Microbial parasites adapted to thrive at mammalian mucosal surfaces have evolved multiple times from phylogenetically distant lineages into various extracellular and intracellular life styles. Their symbiotic relationships can range from commensalism to parasitism and more recently some host–parasites interactions are thought to have evolved into mutualistic associations too. It is increasingly appreciated that this diversity of symbiotic outcomes is the product of a complex network of parasites–microbiota–host interactions. Refinement and broader use of DNA based detection techniques are providing increasing evidence of how common some mucosal microbial parasites are and their host range, with some species being able to swap hosts, including from farm and pet animals to humans. A selection of examples will illustrate the zoonotic potential for a number of microbial parasites and how some species can be either disruptive or beneficial nodes in the complex networks of host–microbe interactions disrupting or maintaining mucosal homoeostasis. It will be argued that mucosal microbial parasitic diversity will represent an important resource to help us dissect through comparative studies the role of host–microbe interactions in both human health and disease.

Evolutionary pressures exerted by parasites on the immune system, and vice versa, are surveyed from a speculative viewpoint. New information is presented about the possible channelling of suppression by MHC Class II genes in the mouse, where a novel pattern of dominant unresponsiveness mediated by H-2Ab is described. In addition, the hypothesis is advanced that phosphatidyl–inositol anchorage on the surface of parasites may represent a novel evasion mechanism, in which the spread of the immune response by epitope linkage is inhibited by host phospholipase.

This study investigated why the susceptible or resistance phenotype to the nematode Heligmosomoides polygyrus was lost when susceptible (C57BL/6) and resistant (Balb/c) strains of mice were housed together in indoor arenas with continuous transmission of the parasite larvae present in peat trays (Scott, 1991). First, both strains expressed their normal phenotype when given a controlled challenge while living in arenas, and when experimentally infected with only 5 parasite larvae. To test whether chronic exposure to peat altered the resistance phenotype, mice were given a challenge infection while living on peat. C57BL/6 mice living on peat had higher egg production and higher worm numbers than Balb/c mice, except at 2 months post-challenge. Finally, natural transmission rates were increased in arena experiments through either regular replacement of arena mice with naïve mice or direct introduction of additional larvae. A transient difference in infection levels between strains was detected in response to a modest increase in transmission whereas a 10-fold increase in transmission allowed C57BL/6 mice to exhibit the typical profile of high egg production and elevated worm numbers. These data indicate that C57BL/6 mice are less able to regulate parasite numbers at high transmission rates compared with lower transmission rates.

Cysteine peptidases of protozoa have been implicated in a variety of biological events, and the expression of these enzymes is modulated in response to distinct stimuli, including environmental changes and differentiation. In the present work, we have examined the expression of cysteine peptidases from Herpetomonas samuelpessoai grown at distinct temperatures and during dimethylsulfoxide (DMSO)-elicited differentiation. We demonstrated that a 45 kDa cysteine peptidase had its activity reduced during the parasite growth at 37°C in comparison to 26°C, and when cultured up to 72 h in the presence of DMSO. The modulation in the 45 kDa cysteine peptidase expression is connected to the differentiation process, since both temperature and DMSO are able to trigger the promastigote to paramastigote transformation in H. samuelpessoai. The possible immunological similarity of H. samuelpessoai proteins with well-known cysteine peptidases produced by trypanosomatid pathogens, including cruzipain (Trypanosoma cruzi) and cysteine peptidase b (cpb) from Leishmania mexicana, was also investigated, as well as with calpain molecules. The protein cellular lysate of H. samuelpessoai reacted with antibodies raised against cpb of L. mexicana and calpain of Drosophila melanogaster; however, no reaction was observed against cruzipain. The 35 kDa cpb-like protein had its expression diminished in DMSO-treated parasites, while the 80 kDa calpain-like molecule was enhanced and an additional 30 kDa calpain-related polypeptide was exclusively observed in these cells. Fluorescence microscopy and flow cytometry analyses corroborated these data. The results described above add H. samuelpessoai to the list of parasites whose differentiation seems to be correlated with cysteine peptidase expression.