Myxozoans are parasitic, microscopic cnidarians that have retained the phylum-characteristic stinging capsules called nematocysts. Free-living cnidarians, like jellyfish and corals, utilize nematocysts for feeding and defence, with discharge powered by osmotic energy. Myxozoans use nematocysts to anchor to their fish hosts in the first step of infection, however, the discharge mechanism is poorly understood. We used Myxobolus cerebralis, a pathogenic myxozoan parasite of salmonid fishes, and developed two assays to explore the nature of its nematocyst discharge. Using parasite actinospores, the infectious stage to fish, we stimulated discharge of the nematocysts with rainbow trout mucus in vitro, in solutions enriched with chloride salts of Na+, K+, Ca2+ and Gd3+, and quantified discharge using microscopy. We then used quantitative polymerase chain reaction to evaluate the in vivo effects of these treatments, plus Mg2+ and the common aquaculture disinfectant KMnO₄, on the ability of M. cerebralis actinospores to infect fish. We found that Mg2+ and Gd3+ reduced infection in vivo, whereas Na+ and K+ over-stimulated nematocyst discharge in vitro and reduced infection in vivo. These findings align with nematocyst discharge behaviour in free-living Cnidaria, and suggest phylum-wide commonalties, which could be exploited to develop novel approaches for controlling myxozoan diseases in aquaculture.

The clinical manifestation and course of Leishmania infections depend on factors such as species, virulence and host-immunity. Although trypanosomatids are considered to have clonal propagation, genetic hybridization has produced successful natural hybrid lineages. Hybrids displaying strong selective advantages may have an impact on pathogenesis and the eco-epidemiology of leishmaniasis. Thus, characterization of phenotypic properties of Leishmania hybrids could bring significant insight into the biology, infectivity, pathogenicity and transmission dynamics of these atypical strains. The present study focuses on phenotypic features and survival capacity of Leishmania infantum/Leishmania major hybrid isolates as compared with representative putative parental species, L. infantum and L. major. In vitro assays (growth kinetics, susceptibility to different conditions) and in vivo infection (parasite detection and histopathological alterations) showed that hybrids present higher growth capacity and decreased susceptibility to reactive oxygen species. Furthermore, evaluation of infected spleen tissue suggests that hybrids induce a stronger immune reaction than their putative parents, leading to the development of white pulp hyperplasia in B-lymphocyte compartments. Overall, these hybrids have shown high plasticity in terms of their general behaviour within the different phenotypic parameters, suggesting that they might have acquired genetic features conferring different mechanisms to evade host cells.

Material and habitat. Various Entozoa have been recorded from time to time occurring in the body cavity of their hosts, but very few records have been made of trematodes living in the coelom of fishes. Looss (1902) gives an account of Probolitrema richiardi (Lopez) occurring in the coelom of Mustelus vulgaris and Acanthias vulgaris, and this is the only form occurring in British marine fishes to which reference can be found in the literature (Nicoll, 1915).

The species of Oesophagostomum here described has been collected quite frequently from sheep and goats in certain parts of the colony, always accompanied by the commoner oesophagostome O. columbianum.

The male and female of Rhipicephalus reichenowi are re-described and the nymph and larva are described for the first time. The affinities of the species within the genus are discussed.

Its developmental periods under laboratory conditions are given and all known records of its hosts and distribution in the field are noted.

The author wishes to thank the Director of the East African Veterinary Research Organization for permission to publish this paper. She is also most grateful to everyone who submitted field collections of this species to her and to Dr Hoogstraal for permission to quote unpublished information; to Dr G. Theiler for her helpful suggestions during the preparation of the manuscript, and to Mr G. M. Kohls, Dr C. M. Clifford and Dr H. Hoogstraal, who also checked the manuscript before publication.

In 1931 a number of fleas was received from Mr Georg Stein, obtained in Dutch New Guinea. Among them were the three species described below. We are greatly indebted to Mr Stein for having made this collection.

Turning sickness of cattle, a very fatal disease, long known in tropical East Africa, is characterised by circling or turning movements made by the affected animals. Recent observations prove that the malady occurs sporadically throughout Uganda and in the greater part of Kenya and Tanganyika where East Coast Fever is highly enzootic. It appears to occur mostly in hot dry periods of the year.

For the material herein dealt with, I am indebted principally to Mr G. A. H. Bedford of the Division of Veterinary Services of South Africa. Other material collected by the writer from bats in the United States National Museum some years ago and a specimen received from Dr C. R. Kellogg of Foochow, China, are also recorded.

Parmi le nombre des Diptères Pupipares de provenances diverses que j'ai eu l'occasion d'étudier récemment, certains, jugés nouveaux, seront décrits ici, d'autres, déjà connus, mais oftrant quelque intérêt aux divers points de vue systématique, éthologique ou géographique, feront l'objet d'une mention spéciale.

Life histories of the Trombidiidae, or, for that matter, other families of mites have, with few exceptions, not been studied and very little information is available as a guide. This is not entirely the fault of the acarologists, as not one of them was employed in any country of the world entirely upon the study of mites. Most of them, if official, were entomologists who could spend only a fraction of their time on mites. Their time was spent therefore on systematics, an essential branch of acarology.

An attempt to differentiate by means of the electron microscope between particles of the top and bottom components of the turnip yellow mosaic virus is described. Since the particles of the top component are thought to be hollow spheres, it might be expected that they would collapse after drying and thus throw a smaller shadow than the particles of the bottom component which are thought to have a more solid centre. No difference could be perceived between the two types of particle, so that the apparently hollow particles can withstand the effect of drying without collapsing.

Sections were cut of leaves of Chinese cabbage (Brassica chinensis) and particles were observed inside the cells which could conceivably be virus particles.

The Diptera larvae can be divided from an ethnological point of view into four categories: and the members of each, though of diverse systematic affinities, possess in common certain structural characters, which Keilin (1912) considers to be adaptations to the manner of life. The categories are as follows: (i) Saprophagous larvae: those which feed on decayed vegetable matter or the excrement of herbivorous animals; these have a buccal armature similar to that of Calliphora or Lucilia: the ventral surface of the basilar piece is feebly chitinized and has a number of longitudinal ridges projecting into the lumen of the pharynx. (ii) Phytophagous larvae, which feed on living plants, as leafminers, root-miners, etc.: these have the bucco-pharyngeal armature more concentrated, the basilar piece more chitinized, with ridges feebly developed or absent, the mandibles modified as several toothed scrapers. (iii) Parasitic larvae: their buccal armature resembles that of parasitic Tachinidae. (iv) Parasitic larvae—carnivorous larvae: It is now known from the researches of Portchinsky (1910), and later of Keilin himself, that a good number of larvae found in excrement are not really coprophagous, but live on other larvae or other small animals found with them in the excrement. These carnivorous larvae attack their prey, perforating its skin, and sucking its contents. For instance, the larvae of Graphomyia maculata, found in liquefied decomposing vegetable matter, feed on larvae of Eristalis and pupa of Tipulidae, those of Calliophris riparia, found among moss, feed on small oligochaete worms and larvae and pupae of Psychodidae. These carnivorous larvae have certain characters in common. Thus the mandibles are sharp, piercing hooks and the basilar piece of the armature is very long, narrow and strongly chitinized and entirely without the internal longitudinal ridges.” (Scott, 1915.)

Confusion exists as to whether the immunity produced by one attack of East Coast fever is absolute or whether it requires to be maintained by reinfection.

During the present experiments mild transient infections have been produced in six calves, and in five cases the immunity has been incomplete and second attacks have followed reinfestation by infected ticks.

The time interval between the attacks has varied from 1 to 16 months, and it is suggested that when the interval is prolonged the second attack will be severe and may be fatal.

It is concluded that the durability of the immunity depends on the severity of the original attack, being durable when the attack is severe, and only transient and probably never solid when the attack is mild.

The temperature reaction is at the moment the best indicator as to the severity of the attack and the type of immunity evolved.

Doses from 1 to 10 sporulated oocysts of a cloned strain of Eimeria hungaryensis were used to infect laboratory-reared, coccidia-free wood mice (Apodemus sylvaticus). Total oocyst production, reproductive indices (output/dose) and daily patterns of oocyst production were compared. At doses of 10 oocysts or less, observed yields exceeded expected yields calculated using details of endogenous stages. At doses above 10 oocysts, the converse occurred. From infections initiated with 10 oocysts, total outputs were not significantly different in male and female wood mice, host age had no apparent effect and repeated infections, at 10-day intervals, of both sexes, resulted in progressive decreases in output at each successive infection, suggesting development of resistance.

1. On the assumption that the limit of significant difference is 1%, it is necessary, when concentration methods are not used, to repeat the faecal examination 3 times for the egg of Ascaris lumbricoides, 7 times for hook worm and 11 times for Trichuris trichiura in order to obtain the diagnostic results obtained by the acid-ether concentration technique using 3 g. of faeces.

2. The coefficient of the identification by a single smear examination is 83·3% for eggs of Ascaris lumbricoides, 46·5% for hook-worm eggs and 33·6% for eggs of Trichuris trichiura.

The new species herein described was found in three species of monkey at the Moscow Zoopark, the animals having been imported via Germany.

Habitat and Record. By the courtesy of G. Evelyn Hutchinson of Yale University, I have received and examined a new species of Lernaea collected by him on 7. iv. 1928 on a small Barbus, which had lost all its scales and was too young for specific identification, from an alkaline pan in the Transvaal, S. Africa. For the purpose of comparison reference will be made to L. elegans described by me, Parasitology, 1925, 17, 246.

The structure of the ovarian tissue in juvenile Corynosoma semerme and C. strumosum from a fish paratenic host and in the cystacanth stage of Echinorhynchus gadi from an amphipod intermediate host was investigated by means of transmission electron microscopy. The species were obtained from hosts living in the Baltic Sea. The observations indicate that ovarian development was more advanced in cystacanths of E. gadi than in juveniles of C. semerme and C. strumosum. Free ovaries were present in E. gadi with an obvious supporting syncytium and surface microvilli. The biological significance of the different stages of ovarian development in these species is discussed briefly in relation to either reproductive strategies and host specificity in definitive hosts or to the attainment of infectivity by cystacanths in intermediate hosts.

Antigenic variation is a powerful survival strategy adapted by certain species of parasitic protozoa to allow them to survive in the immunized host. It is exemplified by the African trypanosomes, which provide far and away the best characterized and most studied system of this kind. Why have the trypanosomes developed antigenic variation to such a sophisticated level? Because the trypanosome lives its life in the bloodstream of its mammalian host and is therefore in continuous conflict with the host's immune system. Antigenic variation represents its whole survival strategy, with some help provided by its ability to immunosuppress the host. The importance of antigenic variation to the trypanosome is underscored by the estimate that up to 10% of the trypanosome genome may be devoted to variant antigen genes (Van der Ploeg et al. 1982). Most other parasitic protozoa prefer a less confrontational existence and usually adopt an intracellular home for at least a part of their life-cycle within the mammalian host. That being the case, do other parasitic protozoa need antigenic variation within their armorarium ? The answer seems to be yes, although the reasons why are by no means clear. For example, the stages in the life-cycle which exhibit antigenic variation might be expected to be those which are released free into the bloodstream – in malaria, sporozoites and merozoites, for example. Yet there seems to be no evidence for phenotypic variation at all in these stages. Rather, it is the intracellular stages which, in both Plasmodium and Babesia, seem to elaborate molecules which are expressed at the surface of the parasitized cell, and which are capable of both eliciting an immune response and of avoiding the con- sequences of such a response by phenotypic antigenic variation. Why are such antigens expressed, and what is their functional significance?