It is pointed out that two of the three major groups of anthelmintic act by opening membrane ion-channels. It is appropriate, therefore, to use electrophysiological methods to study the properties of the sites of action of these drugs and the changes in the properties of these receptor sites associated with resistance. This paper describes the use of the patch- clamp technique to observe the currents that flow through the levamisole-activated channels as they open and close in levamisole-sensitive and levamisole-resistant isolates. It was found that, on average, the proportion of time the channels are open, is less in the resistant isolate. The patch-clamp technique also showed that the ion-channels are heterogeneous and that one of the subtypes is lost with the appearance of resistance. The use of the current clamp technique is illustrated to record a site of action of ivermectin in the pharyngeal muscle of Ascaris.

1. Coitocaecum anaspidis sp.nov. is a Trematode which exhibits precocious genital activity whilst encysted as a metacercaria in the Tasmanian Mountain Shrimp, Anaspides tasmaniae Thomson.

2. Eggs are laid by the Trematode whilst in the encysted condition, and in some cases the eggs hatch in the cyst giving rise to miracidia which swim freely in the contained fluids.

3. Two hundred specimens of Anaspides tasmaniae were examined and one hundred and twenty-seven found to contain the encysted Trematode.

4. A systematic description of the Trematode is given.

At the beginning of 1917 Professor V. Dogiel kindly handed over to me, for scientific treatment, a series of blood-films taken from different Amphibia, Reptilia, and Mammalia by the Expedition of Professors V. Dogiel and I. Sokolov to British East Africa in 1914. The films were examined by me for blood parasites, with the result that, of 27 animals, two different species of Bufo and two snakes proved to be infected. The blood parasites were represented by haemogregarines exclusively. The blood-films had been fixed on cover-slips by the dry method, and preserved in that condition for nearly three years. Altogether, I had at my disposal only 24 slips with blood-films taken from the peripheral blood of the infected animals.

Subcutaneous injection of nursing mothers from day 16 to day 20 post partum with infective larvae of Strongyloides ratti or Nippostrongylus brasiliensis does not result in the development of worms in the litters if 1 h is allowed between injection and resumed nursing, and suckling is terminated 24 h later. Thus the low numbers of N. brasiliensis (1% of the dose) which develop in litters after 24 h, 4 day or 5 days suckling when mothers are injected and returned to their young immediately, represent skin invasion and not milk-borne infection.

Taking precautions consistent with the foregoing, S. ratti equivalent to 28%, 45%, 45% and 48% of the dose were shown to be transmitted in the milk to suckling rats of 4 mothers injected with 4000 L 3 on day 18 post partum and 72 h before weaning. One mother of the same batch failed to transmit worms (1% of the dose in the litter) and the take in all 5 mothers was insignificant (max. = 3% of the dose versus an average of 21% in controls).

Large numbers of S. ratti were subsequently found in the intestines of mothers whose litters were weaned immediately after (21%) or 6 h after (16%) injection, whereas very few (less than 1%) developed in mothers deprived of their offspring 24 h after injection. Dynamic, rather than static, determinants of larval routes inside the host present the only logical basis for an explanation of these facts.

The structure and ultrastructure of the excretory system of Panagrellus redivivus, Ditylenchus myceliophagus, D. dipsaci and the second-stage larvae of the Heterodera rostochiensis are described. Panagrellus has two lateral ducts, a median duct and a gland. The two lateral ducts are joined over the anterior part of the oesophageal bulb to form a loop. Anteriorly this loop continues as a median duct, which opens to the exterior in an excretory pit, part of the system lies free in the pseudocoelom. The lumen of the lateral excretory duct and the greater part of the median duct is surrounded by capitate tubules, which open into the lumen of the excretory duct. Capitate tubules develop by the invagination of the hypodermal membranes and lie embedded in thick cytoplasm surrounded by mitochondria. Ensheathed in cell membranes the excretory duct forms an anastomosis in the loop and at three other places along the length of each lateral excretory duct. At these regions there are nerve endings. The excretory gland opens posteriorly into the loop and is full of Golgi complexes, endoplasmic reticulum and secretory granules.

In the system of Ditylenchus and the second-stage larva of Heterodera the right lateral duct is absent while the left lateral excretory duct continues anteriorly past the median excretory duct; a true loop is not formed. The median excretory duct lies embedded almost throughout its length in the excretory gland. Capitate tubules are present along the length of the lateral excretory duct, but, unlike Panagrellus, are not present around the median excretory duct. Anastomosis is not formed in the excretory ducts. In other respects the system of the species studied is similar to that of Panagrellus.

The capitate tubules form a system of fine microtubules. Their ultrastructure and, particularly, their association with large numbers of mitochondria, is very reminiscent of structures thought to be concerned with an active transport role, related to ionic and osmoregulation in other phyla.

The excretory system is almost certainly hypodermal in origin. Differences between the morphology and relations of the median duct of Enoplus (Narang, 1970), on the one hand, and that of the other forms studied suggest that these ducts may have different origins: the presence of separate nuclei in the lateral duct and gland portions of the system would be consistent with this view. It is considered that the two parts may have originated separately and have become joined during evolution. It is also shown that the excretory system of Ditylenchus cannot be derived either from an H-shaped system or from a primitive gland system.

I wish to thank Professor C. Ellenby and Mr L. Smith for their helpful criticism.

1. The staining and morphology of E. parvum were characteristic of the genus Eperythrozoon. The diameter of the organism was approximately 250 mμ.

2. Visible eperythrozoa disappeared in 20 min. from infected blood incubated at 56° C., and in 12 hr. at 37° C. They persisted for several days at room temperature.

3. E. parvum was preserved for short periods at 5° C. and for longer periods at −30 and −79° C.

4. Splenectomized early-weaned piglets were experimentally infected by the parenteral and oral routes, and by means of the pig louse Haematopinus suis.

5. The mean prepatent period of 103 primary infections in splenectomized pigs was 9·7 days. Patent infections sometimes persisted for at least 36 days. One pig remained a carrier of E. parvum for 23 months.

6. A severe anaemia occurred in splenectomized piglets affected with E. parvum, but intact piglets were apparently unaffected.

7. E. parvum was susceptible in vivo to neoarsphenamine and oxytetracycline, but not to sulphadimidine, penicillin or streptomycin.

The importance of foodborne parasitic zoonoses remains high in many regions of the world. Although control efforts have been exerted for quite some time, overall progress has not been satisfactory, even in many well developed countries. An important drawback in control programmes for parasites such as Trichinella, Toxoplasma and Taenia has been the absence of rapid, accurate and sensitive diagnostic tests for these meatborne parasites. However, the rapid advances in the molecular biology of these organisms has yielded concomitant gains in precision of detection. This review highlights these advances and their impact or potential application to the control of foodborne parasites.

Weight and length profiles are presented of 3505 Ascaris worms recovered after mass anthelmintic treatment of a human community in January 1984 and, after an 11 month period of reinfection, in November 1984. Male and female worms recovered after reinfection were significantly heavier and longer than those expelled after initial treatment (P < 0·0001). Multiple regression models were employed to examine variability in parasite size. A positive influence of host body weight on the weight of parasites recovered in January, but not in November, was observed. No negative relationship was recorded at either date between worm size and the total number of worms harboured, even after controlling for host weight. Striking host age-related variability was observed in the distribution profile of weights and lengths of individual worms recovered in January. Children harboured predominantly smaller worms before initial treatment, while adults expelled mainly heavy worms. In contrast, worms expelled by both children and adults after reinfection were heavier and more homogeneous in size, particularly within the relatively heavily infected group. These patterns argue against a primary role for density- dependent or acquired resistance mechanisms in determining the size of Ascaris in humans. However, the results are consistent with a hypothesis initially suggested by Jung (1954) that established worms may inhibit the development of newly acquired Ascaris larvae, perhaps regulating their own abundance.

Nobody who studies the parasitic amoeba of the frog (Entamoeba ranarum) and the dysentery amoeba of man (E. histolytica) can fail to be struck by the remarkable resemblance between these organisms. The development of the former I described for the first time in 1908 and 1909, since when I have had exceptional opportunities of studying the latter; and I can state, with some confidence, that there is no constant structural character which will permit of a distinction being drawn between these two species. The active amoebae can usually be readily distinguished from one another by the inclusions (food bodies) in their protoplasm, but not by their own nuclear and cytoplasmic structure; but the precystic amoebae, devoid of all food bodies, and the cysts, at every stage in their development, are so closely alike that preparations of the one could be used as demonstration specimens of the other.

Cross-species infection among humans, chimpanzees (Pan troglodytes) and baboons (Papio spp.) is potentially a significant public health issue in Africa, and of concern in the conservation of P. troglodytes. However, to date, no statistical comparisons have been made between the prevalence, richness and composition of parasite communities in sympatric populations of baboons and P. troglodytes. We compared parasite communities in sympatric P. troglodytes and Papio papio living in a wilderness site, in the Republic of Senegal, West Africa. We asked whether, in the absence of humans, there are significant differences between these hosts in their interactions with gastrointestinal parasites. We tested whether host, location, or time of collection accounted for variation in prevalence, richness and community composition, and compared prevalence across six studies. We concluded that, despite being closely related, there are significant differences between these two hosts with respect to their parasite communities. At our study site, prevalence of Balantidium, Trichuris and Watsonius was higher in P. papio. Papio papio harboured more parasites per host, and we found evidence of a positive association between Trichuris and Balantidium in P. troglodytes but not P. papio.

Parasite-host systems often include an obligatory environmental stage in the parasite life-cycle, which can be transmitted between successive populations. Complexity even increases if immunity only gradually develops upon re-infection. For a better understanding of such systems we study Eimeria spp. in chickens, a protozoan parasite transmitted through oocysts on the floor. This paper deals with dynamics within and between successive cohorts of chickens by coupling a within-host description of the parasite life-cycle (with immunity) to re-uptake of oocysts from the environment. First the initial environmental oocyst level is related to the maximum infection load within a cohort, as a measure of production damage, from which we conclude that minimum damage levels can be observed with intermediate oocyst levels. Then we relate the initial to the final oocyst level of a cohort, and study the dynamics between cohorts in relation to an oocyst cleaning efficiency after each cohort. The resulting unstable dynamics lead to the conclusion that it will often be impossible to minimize damage by repeatedly cleaning with the same effort: it may be necessary to artificially increase oocyst levels in the shed before each chicken cohort.

This study investigated the genetic and antigenic diversity of Theileria parva in cattle from the Eastern and Southern zones of Tanzania. Thirty-nine (62%) positive samples were genotyped using 14 mini- and microsatellite markers with coverage of all four T. parva chromosomes. Wright's F index (F ST = 0 × 094) indicated a high level of panmixis. Linkage equilibrium was observed in the two zones studied, suggesting existence of a panmyctic population. In addition, sequence analysis of CD8+ T-cell target antigen genes Tp1 revealed a single protein sequence in all samples analysed, which is also present in the T. parva Muguga strain, which is a component of the FAO1 vaccine. All Tp2 epitope sequences were identical to those in the T. parva Muguga strain, except for one variant of a Tp2 epitope, which is found in T. parva Kiambu 5 strain, also a component the FAO1 vaccine. Neighbour joining tree of the nucleotide sequences of Tp2 showed clustering according to geographical origin. Our results show low genetic and antigenic diversity of T. parva within the populations analysed. This has very important implications for the development of sustainable control measures for T. parva in Eastern and Southern zones of Tanzania, where East Coast fever is endemic.

Thirty-five lambs (14 weeks old), the progeny of Border Leicester rams mated with Border Leicester × Merino ewes, were divided at random into two groups. Seventeen lambs in Group A received 3500 Haemonchus contortus larvae weekly and 18 lambs in Group B received 500 larvae each day: the dosage was decreased to 1400 larvae weekly and 200 larvae per day after 8 weeks.

Pathogenicity was found to be higher when the lambs were infected with a small number of larvae daily (daily group) than when the same number of larvae were given in one dose at weekly intervals (weekly group). The period of survival was consistently shorter in the former group.

No significant difference in faecal egg counts was observed between the two groups.

Reduction in food intake per head per day and in live weight were more pronounced in the ‘daily group’ than in group dosed weekly. The discrepancy in food consumption and live weight between these two treatments was more apparent at the end of the experiment.

Some resistance was observed in both groups but the level of resistance was not high.

Accumulation of inhibited larvae was apparent after 104 days in the ‘weekly group’ and after 78 days in the ‘daily group’. An infection arising from a large number of larvae given at weekly intervals induced a mild form of resistance leading to an accumulation of inhibited larvae at the end of the experiment. This was less apparent in lambs infected with the same number of larvae given each day.

Interference with ovulation in adult females was recorded in both treatments. Sex discrimination against the female population both in the extent of elimination of adults and in the retardation of development of fourth-stage larvae was recorded and the intensity of discrimination was more pronounced with the weekly regime of larger doses than with the same number of larvae but given in daily doses. The worms were eliminated sporadically and not continuously. A challenge infection of 10000 larvae given to two lambs in the ‘weekly’ regime treatment on the 107th day initiated a partial selfcure reaction demonstrated by an immediate fall in faecal eggs per gram (i.e. Epg) but the egg count returned to the original value in 28 days.

As part of studies on the nature of the endemic virus infections in natural rodent hosts, the possible association of cyst forms of Pneumocystis spp. with the presence of hanta-, cowpox-, and arenavirus antibodies in wild mice (Apodemus flavicollis, N=105; Apodemus agrarius, N=63; Micromys minutus, N=50) and the common shrew (Sorex araneus, N=101) was studied in south-central Finland. One hantavirus (Saaremaa virus, SAAV) seropositive A. agrarius, and 2 cowpoxvirus (CPXV) seropositive S. araneus were detected, and antibodies against an arenavirus (Lymphocytic choriomeningitis virus, LCMV) were found in all 3 mouse species but not in shrews. Cyst forms of Pneumocystis spp. were detected in all species except A. agrarius. There was no significant association between virus antibodies (LCMV in mice, and CPXV in shrews) and cyst forms of Pneumocystis in any of the species. Concurrent presence of virus antibodies (LCMV) and cyst forms of Pneumocystis were detected only in 1 M. minutus. In conclusion, we found no evidence of any association between Pneumocystis and antibodies to any of the viruses tested.

Susceptibility/resistance to larval Echinococcus multilocularis infection varies greatly depending on host species and strains. Whereas several mice strains and non-human primates are highly susceptible to alveolar echinococcosis, rats and most of humans are considered as more resistant. In this study, we aimed to elucidate factors responsible for host resistance in rats (Experiments A–D). (A) The parasite establishment was not observed in immunocompetent Wistar rats orally inoculated with sodium hypochlorite resistant eggs with/without pig bile, or activated/non-activated oncospheres (NAO). Peritoneal inoculation with NAO or metacestode tissue allowed the parasite establishment in rats. (B) T-cell-deficient athymic nude rats showed complete resistance against the metacestode establishment after oral inoculation with parasite eggs. This finding suggests that T-cell-independent parasite clearance occurred in the animals during early phase of the parasite invasion. Finally, Wistar rats that received pharmacological immunosuppression using either dexamethasone (DMS) alone or methotrexate (MTX) i.p. alone or a combination of these compounds were orally inoculated with the parasite's eggs. As a result (D), successful establishment of metacestode with protoscoleces was observed in all 3 rats treated with DMS (s.c.) alone or in all 6 rats treated with DMS (s.c.) plus MTX but not in 8 rats with MTX alone, suggesting that factors affected by DMS treatment are responsible to regulate the parasite invasion and establishment.

A Besnoitia species of the teiid lizard Ameiva ameiva (L.), from north Brazil was established in laboratory mice and hamster by the intraperitoneal inoculation of bradyzoites in the tissue cysts. In the lizards all the cyst wall layers were closely apposed. In the mice the layers of the wall were distinguishable, and ultrastructurally the inner cytoplasmic layer contained either a tight network of endoplasmic reticulum or packed mitochondria or both. These components were less frequent or sparse in the inner cytoplasmic layer of cysts in the lizard. The only animals available for experiments in attempts to indicate the definitive host of the parasite were 3 kittens of the domestic cat and a juvenile specimen of the snake Boa constrictor raised in captivity. No evidence of infection could be detected in these animals after feeding them with the tissues of mice harbouring cysts with very large number of bradyzoites.

1. Entamoeba aulastomi and Hexamita sp. from Haemopis sanguisuga have been cultivated in inactivated horse-serum diluted 1 : 10 in 0·5 NaCl solution + solid sterile rice-starch, and upon an inspissated horse-serum slope covered with the liquid medium + sterile rice-starch. Cysts of E. aulastomi appeared on or after the 9th day from subcultivation, but cysts of Hexamita have not appeared in the cultures.

2. The amoeboid phase of E. aulastomi divides by a simple direct method, without the formation of a spindle. There is no equatorial plate. It was not possible to count the number of chromatin granules.

3. The mature cyst is quadrinucleate, though occasional octonucleate cysts are found. Chromatoids are present but are absorbed before hatching. A. large glycogen vacuole is present in the uninucleate cyst. The nucleus divides by the formation of a delicate spindle but no chromosomes were found.

4. E. aulastomi are not harmed by being kept at 2° C. but they die out in the 2nd subculture if kept at 30° C. and within 24 hours if kept at 37° C. The cysts also are killed at 37° C.

5. If treated with N/20 HCl all amoebae are killed in less than 10 min. but the cysts are unharmed.

The infection biology of Branchotenthes octohamatus (Monogenea: Hexabothriidae) from the gills of the southern fiddler ray, Trygonorrhina fasciata (Rhinobatidae), was studied using the fluorescent dye, 5(6)-carboxyfluorescein diacetate N-succinimidyl ester (CFSE). This is the first use of this technique on a monogenean species with unciliated larvae and the first for any monogenean larva infecting an elasmobranch host. CFSE-labelled post-larvae were recovered from gills of T. fasciata within 30 min of exposure to the host, providing strong evidence that larvae invade host gills directly and do not migrate after initial attachment elsewhere. The rapidity with which larvae settled suggests that the mode of infection may deliver larvae directly to the gills via the host's inhalant respiratory current. The specificity of B. octohamatus was investigated by exposing a sympatric rhinobatid host species, the western shovelnose ray, Aptychotrema vincentiana, to B. octohamatus larvae newly emerged from eggs laid by adult parasites from gills of T. fasciata. Experimental exposure of A. vincentiana to freshly hatched B. octohamatus larvae resulted in a persistent infection, indicating that B. octohamatus may not be strictly host specific. Post-larval development charted on these experimentally infected A. vincentiana specimens was slow. Parasites appeared to be sexually mature at 91 days at 21–25°C. Branchotenthes octohamatus larvae bear only 4 pairs of hooklets on the haptor whereas all other hexabothriid larvae described so far have 5 hooklet pairs. Ontogenetic changes to the haptor revealed that it is probably hooklet pair III that is lost from B. octohamatus prior to larval development.

Although some of the earliest work on the Strongylid parasites of horses was done by Giles in India in 1892, the subject has been almost completely neglected in this country since that date; even the comparatively recent list of Indian parasites compiled by Gaiger (1910) makes no attempt to differentiate the numerous Nematodes which had been confused under the names Sclerostomum equinum and S. tetracanthum until the appearance of Looss' famous monograph in 1902.