The host—parasite relationships of two geographical isolates of Schistosoma haematobium in CBA mice are described and compared to previous reports on this parasite in other experimental hosts and in man. The mean percentage establishment of worms in mice was 17% and was not affected by the age or sex of the host. Adult worm burdens remained constant over 20 weeks, but were reduced after 18 months of infection. Male and female worms reached mean maximum lengths of 4·78 and 5·9 mm respectively. Egg laying commenced 9·5 weeks after infection and eggs accumulated in the tissues throughout the period of infection. A large increase in the rate of egg accumulation occurred coincidental with the appearance of eggs in the bladder of some mice. Faecal eggs were first observed in some mice at 12·5 weeks and most mice excreted a few eggs by 17 weeks p.i. (post-infection). Eggs were not found in the urine of infected mice. Excreted eggs and eggs isolated from the livers of infected mice hatched, but the resulting miracidia were unable to infect appropriate snail hosts. The development of hepatic granulomas and egg-induced pathology in the bladder of mice is described.

The disease “Heart-water” of sheep, cattle and goats has been recognised in South Africa for upwards of 70 years, and as long ago as 1902 Lounsbury demonstrated the part played by the common bont-tick, Amblyomma hebraeum Koch 1844, in its transmission. The virus of the disease does not pass through the egg of the tick, but a tick infected in the larval or the nymphal stages is capable of transmitting the infection when feeding as a nymph or adult respectively. Further, according to Lounsbury, a tick infected as a larva may feed upon an insusceptible host during the nymphal stage, and still remain infective until the final feed as an adult.

From the results of our experiments we may conclude that the development of T. lewisi outside the invertebrate host is not confined to one species or genus, but may take place at least in the rat louse and the rat flea and also (though perhaps more incompletely) in the bed-bug. We see further that development needs not always to be combined with longevity in the invertebrate host, but that sometimes life without development may be longer than with it (behaviour in the tick compared to that in the louse).

When we compare the behaviour of T. lewisi in the four invertebrate hosts studied here, we see that the most complete cycle takes place in the flea, where forms are produced which are never found in cultures. In the louse the development may be truly described as a natural culture; in the bug, the development (as far as we could judge by our incomplete experiment) does not even produce all the cultural forms (only the crithidiae) and at last in the tick the trypanosomes do not develop at all but are only preserved for some time.

We finish this paper by thanking Professor Nuttall for the liberal way in which he enabled us to carry out these experiments, and for the keen interest he always took in our work.

Experiments were designed to dissociate the effect of Eperyfhrozoon coccoides on the blood of mice from the effect of splenectomy. Both agents caused a decrease in number of red blood cells which was followed by an increased production of reticulocytes. The anaemic condition caused by the eperythrozoa persisted for more than 230 days after splenectomy, and parasites were seen in fluctuating numbers at intervals throughout this period.

At the height of infection, red blood cells were more fragile than normal in hypotonic saline and the blood clotted more rapidly than normal. No breakdown products of haemoglobin were detected in the urine or serum, and no haemolysins or haemagglutinins were detected in the serum. The white cell count was usually increased after heavy infections, the chief increase being in the number of myelocytes and other immature cells.

The structure of the head and mouth parts of the Streblidae has been very briefly described by Speiser (1900) and subsequently by Muir (1912) in the genera Ascodipteron and Nycteribosca. The description given by the latter author is, however, still incomplete. Having, therefore, collected the necessary material I have re-investigated their structure and compared it with that of the Hippoboscidae and the Nycteribiidae, already described by me elsewhere (1926 and 1928).

In three separate experiments the behaviour of Dermacentor andersoni larvae on normal and tick-resistant guinea-pigs was studied at intervals throughout 5-day infestation periods. Fewer larvae survived on resistant hosts and their mean sizes were less than those of larvae on normal hosts, the differences becoming more obvious as time progressed. When measured at 32°C, the peristaltic rates of midgut diverticula of the larvae surviving on resistant hosts were consistently lower than those of larvae from normal hosts. Mean surface temperatures of infested ears were higher on resistant than on normal hosts. This was assumed to be a result of cutaneous hypersensitivity reactions in the resistant animals. Larvae detached, or changed attachment sites, more often on resistant than on normal hosts. This was consistently evident after 26 h post-infestation and correlated with the known timing of basophil cell infiltration and degranulation in the skin of infested, resistant guinea pigs. It appeared that most larvae, after detaching from the resistant host, died off the host. However, some died in situ while still attached. Such deaths occurred on resistant but not on normal animals between 8 and 26 h post-infestation.

Nematode surface coat (SC) proteins and excreted–secreted products (E–S) are likely to play important roles in the host–parasite interaction and considerable similarities can be found in SC proteins and E–S products from certain plant and animal parasitic nematodes. Monoclonal antibodies raised to E–S products of plant-parasitic nematodes were shown to cross-react with E–S products and the surface coats of the animal parasites Trichinella spiralis and Haemonchus contortus. Most of the antibodies recognized carbohydrate epitopes but the activity of 2 MAbs (IACR–CCNj.2a.15 and IACR-Misec.8D.3) which recognized proteic epitopes in these nematodes were further characterized. Antibody 2a.15 recognized the SC and oral exudate of Meloidogyne incognita, T. spiralis and H. contortus. This antigen was also immunolocalized in the lining of the oesophagus and gut and in the exudate present during ecdysis of H. contortus L3. Antibody 8D.3 reacted with the SC of these nematodes on cryosections but on live nematodes the immunofluorescence was very patchy and was shed from the nematode SC.

Mice immunized by single pyrimethamine terminated infections of Plasmodium berghei berghei, strain NK65 or the Nigerian P. berghei-like parasite, N67, were immune to challenge by P.b. berghei, P.b. yoelii strain 17X, P.b. killicki strain 194ZZ and N67. Mice similarly immunized against P.b. yoelii were only immune or N67 resulted in infections comparable to those found in normal mice. Mice immunized against P.b. killicki were similar except that they also possessed some protection against challenge by N67. Evidence was obtained which indicated that the difference between P.b. yoelii and N67 was not associated with the virulence of the parasites. Prolonged exposure to P.b. yoelii infection slightly increased homologous and heterologous immunity. Two lines of parasites were crossed; one of these was derived from P.b. yoelii and the other from N67. They differed in pyrimethamine sensitivity, glucose phosphate isomerase type and the ability to survive in mice immunized against P.b. yoelii. Ten lines of parasites showing the P.b. yoelii characters of pyrimethamine resistance and GPI-1 were isolated in drug treated mice immune to P.b. yoelii challenge. Twenty-one clones were isolated without drug or antibody selection from the parasites resulting from the cross between P.b. yoelii and N67. Sixteen of these clones were classified according to the markers which they possessed and six were found to be recombinant in character. The experiments showed that genetic recombination occurred as a frequent event in P. berghei and involved factors which control the cross-immunity produced following infection with these parasites.

Off-host stages of temperate parasites must cope with low temperatures. Cold tolerance is often highest in winter, as a result of diapause and cold acclimation, and low during the active summer stages. In some blood-feeding ectoparasites, offspring provisioning determines cold tolerance through all the non-feeding, off-host stages. Large size increases survival in the cold, but so far seasonal variation in within-female offspring size has not been associated with offspring cold tolerance. The deer ked (Lipoptena cervi) reproduces on cervids from autumn to spring. Newborn pupae drop off the host, facing frosts without any acclimation. We examined cold tolerance through 4 seasons and from birth to adulthood by means of short- and long-term frost exposure. We expected females to produce more tolerant offspring in winter than in spring. Large spring pupae survived prolonged frosts better than did small winter pupae. Thus more tolerant offspring were not produced when the temperature outside the host is at its lowest. Unexpectedly, the freezing points were −20°C or below all year round. We showed that high cold tolerance is possible without acclimation regardless of life stage, which presumably correlates with other survival characteristics, such as the starvation resistance of free-living ectoparasites.

Epidemiological models are used to analyse 8 published data sets reporting age–prevalence curves for trypanosome infections of the tsetse fly Glossina pallidipes. A model assuming a fixed maturation period and a rate of infection which is independent of fly age is adequate for Trypanosoma vivax-type infections, explaining 98% of observed variance in prevalence by site and age, allowing that the rate of infection may be site dependent. This model is not adequate for T. congolense-type infections and the fit can be improved by allowing (i) the rates of infection to decline with age (although non-teneral flies remain susceptible), (ii) a fraction of resistant flies, which may vary between sites, (iii) increased mortality of infected flies and (iv) variation in the maturation period. Models with these features can explain up to 97% of observed variance. Parameter estimates from published experimental data suggest that all may contribute in practice but that (i) and/or (ii) are likely to be the most important.

Since 1906 trypanosomes have been found in ten species of mammals by officers of the Health of Animals Branch.

The southern fiddler ray, Trygonorrhina fasciata (Rhinobatidae), is parasitized by 3 monogenean (platyhelminth) species from 3 families on 3 different sites of the host: Calicotyle australis (Monocotylidae) from the cloaca, Pseudoleptobothrium aptychotremae (Microbothriidae) from the skin and Branchotenthes octohamatus (Hexabothriidae) from the gills. Cues that promote egg hatching were investigated for each species and the behaviour of their larvae was also documented. Eggs were laid by parasites in vivo and maintained at 22 °C. Three different egg hatching and host finding strategies were discovered. Calicotyle australis eggs hatched spontaneously with a strong diurnal rhythm that is likely to be under circadian control. The larva is ciliated, photo-responsive and can survive for up to 24 h at 22 °C after hatching. Pseudoleptobothrium aptychotremae may have a ‘bet-hedging’ strategy. Some eggs hatched spontaneously and rhythmically. However, since the hatching success was low, it is possible that other eggs require a different cue provided by the host. The larva is also ciliated but shows no photo-response and was observed to remain active for <4 h at 22 °C after hatching. Branchotenthes octohamatus has a ‘sit-and-wait’ strategy that depends on mechanical disturbance to stimulate hatching. The larva is unciliated, shows no photo-response but may survive for more than 2 days at 22 °C after hatching. The implications of hatching strategy, larval behaviour and morphology in the goal to find a host are discussed for each species.

Cystic echinococcosis is a zoonotic disease of difficult diagnosis and treatment. The use of protoscolicidal agents in procedures is of utmost importance for treatment success. This study was aimed at analysing the in vitro and ex vivo activity of Melaleuca alternifolia oil (tea tree oil – TTO), its nanoemulsion formulation (NE-TTO) and its major component (terpinen-4-ol) against Echinococcus ortleppi protoscoleces obtained from cattle. Concentrations of 2·5, 5 and 10 mg mL−1 of TTO, 10 mg mL−1 of NE-TTO and 1, 1·5 and 2 mg mL−1 of terpinen-4-ol were evaluated in vitro against protoscoleces at 5, 10, 15 and 30 min. TTO was also injected directly into hydatid cysts (ex vivo analysis, n = 20) and the viability of protoscoleces was evaluated at 5, 15 and 30 min. The results indicated protoscolicidal effect at all tested formulations and concentrations. Terpinen-4-ol (2 mg mL−1) activity was superior when compared with the highest concentration of TTO. NE-TTO reached a gradual protoscolicidal effect. TTO at 20 mg mL−1 showed 90% protoscolicidal action in hydatid cysts at 5 min. The results showed that TTO affects the viability of E. ortleppi protoscoleces, suggesting a new protoscolicidal option to the treatment of cystic equinococcosis.

The effect of the parasitic water mite Hydrachna virella on its host Buenoa scimitra was investigated using laboratory experiments. The mite parasitizes all but the first instar of the host. Survival rates were found to be greater among unparasitized than parasitized individuals of these instars. Instantaneous death rates were observed to be linear functions of the number of mites supported/host. The mite's effect on the host's death rate appeared to be directly related to the size of the engorged mite compared to the size of the host; greater relative sizes were associated with greater impacts. Unparasitized females oviposited significantly more eggs than parasitized females, and the instantaneous birth rate of the host was observed to be a non-linear function of mite load.

A mermithid nematode emerging from a male ant, Prenolepis henschei Mayr, in Baltic amber is the first fossil record demonstrating nematode parasitism of ants. This parasite, described as Heydenius formicinus sp. n., is compared to extant mermithid parasites of ants, especially Allomermis myrmecophila Baylis 1921. The present fossil, together with earlier reports of braconid and mite parasitism of ants in Baltic amber, indicates that several diverse groups had already evolved parasitic associations with ants by the Eocene.

Ultrastructural observations on the intestine of Metastrongylus sp. have shown that it is composed of a single layer of epithelial cells each with a basally placed nucleus and resting on a basement layer. The basal plasma membrane of each cell is highly infolded and at the cell apex the lateral plasma membranes of adjacent cells are thickened to form a terminal bar.

The brush border consists of numerous microvilli which possess dilated tips. The tips contain a granular material and the evidence obtained suggests that they are released into the lumen indicating a form of micro-apocrine secretion. Golgi complexes, glycogen, lipid droplets and granular endoplasmic reticulum are present in the intestinal cells. The Golgi complexes are associated with the production of an electron dense body. Other inclusions are cytolysome-like in their structure. The discharge of lamellar bodies into the intestinal lumen is described and the role of the intestine in secretion, absorption, and excretion is discussed.

The authors wish to acknowledge the co-operation and facilities provided by Professor J. Brough in the Department of Zoology and Mr J. H. M. Hughes (Veterinary Officer) for allowing unrestricted access to infected material at the Roath abattoir, Cardiff. Grateful acknowledgement is also expressed for the financial support given to one of us (T. J.) by the Pig Industry Development Authority. Any views expressed in this paper are not necessarily those of the Authority.

The authors also wish to express their appreciation of the excellent technical assistance provided by Mr T. W. Davies.

On a coastal farm in New South Wales where beef and dairy cattle production was carried on side-by-side, separate pasture plots were contaminated with eggs of Ostertagia ostertagi by calves from each production system in autumn, winter or spring. Successive groups of parasite-free tracer calves grazed on the plots for 14 days at 4-week intervals and were then killed for worm counts 14 days after removal from pasture. On all plots, the proportion of inhibited early 4th-stage larvae in tracer calves reached a maximum in spring, and was consistently and very significantly higher in calves which grazed plots contaminated with O. ostertagi of beef cattle origin. Factors which may be responsible for this difference between beef and dairy cattle populations of O. ostertagi are discussed.

1. The musculature and excretory and nervous systems of Cysticercus taeniae-taeniaeformis are described.

2. The nervous system consists often longitudinal nerve cords in the strobila and of a brain and complicated system of nerves in the scolex. The nervous system of the scolex shows several variations on the earlier description by Bartels (1902).

3. Minor abnormalities have been found in the form of multiplication of the lateral margins and duplication of the ventral excretory vessels.

4. Three specimens showed spiral torsion of the internal organs involving the musculature and excretory and nervous systems of the strobila. The number of turns of the spiral and the positions of the chiasmata are variable. It is suggested that the spiral twisting occurs before growth and strobilation in the neck region has begun, the chiasmata being carried back as new segments are formed.