Groups of rats, infected 7 weeks previously with Fasciola hepatica, together with appropriate control groups, were challenged either orally or intraperitoneally with 30 metacercariae. The mean worm recovery from the previously infected, orally challenged rats was significantly lower than from their respective controls (2.2 ± 1.1 worms as opposed to 9.0 ± 2.6). There was no significant difference in mean worm recovery from the previously infected, intraperitoneally challenged rats and their respective controls (5.3 ± 3.2 worms as opposed to 6.2 ± 1.9). Livers of the orally challenged group appeared to be largely free from secondary damage but considerable damage was evident in rats which received an intraperitioneal challenge. This evidence supports the view that the gut acts as an important barrier to metacercariae of a challenge infection. In a further experiment, young flukes were recovered from the gut, abdominal cavity and liver of immune and control rats 9, 18, 27, 36 and 45 h after oral challenge. It was found that fewer flukes successfuly penetrated the guts of immune rats (3%) than those of uninfected controls (13%), again pointing to the gut as a barrier to metacercariae of a challenge infection. Protective mechanisms that may oprate at the level of the gut are discussed.

Examination of naturally infected felids and viverrids in Malaysia confirmed previously published records which indicated that P. westermani occured only in felid cats. Felis planiceps and F. temnickii were reported as new host records. Analysis of stomach contents revealed no crab remains in either family of cats, but confirmed that felids were strictly carnivorous while viverrids were often omnivorous. In feeding experiments, only viverrids ate the host crabs Potamiscus johorensis and Parathelphusa maculata. The probable transmission of P. westermani to felids via paratenic hosts was discussed.

Adult Strongyloides ratti were expelled from the small intestine of rats starting 14—18 days after a primary infection. In a secondary infection very few adult worms developed and most of these were expelled before day 14. At the time of expulsion the worms migrated posteriorly in the intestine and their size decreased.

Paraoligorchis taterae gen. et sp.n. is described from the Indian gerbil Tatera indica. It is characterised by unarmed suckers; rudimentary and unarmed rostellum; 4–7 testes of which 1–2 are aporal and anterior to others which are in a transverse row; cirrus pouch extending beyond excretory stems; unilateral genital pores; genital ducts dorsal to excretory stems; prominent external and internal seminal vesicles; large rosette-like ovary; saccular uterus; vaginal opening posterior to that of the cirrus pouch; three-layered eggs devoid of both a pyriform apparatus and polar filaments. It has been compared with related genera of Hymenolepidinae and Anoplocephalinae and found to differ from all of these in some character or other.

Episthmium everardi sp.n. is described from a bird, Pitangus sulfuratus, from Trinidad, W.I. It differs from all other species in the genus in having 20 circumoral spines, each 20 to 22 long, and in the shape of the body, which is attenuated at its anterior end.

Monanema nilotica n.sp. (Nematoda: Onchocercidae) is described from the right auricle and pulmonary artery of the Nile rat, Arvicanthis niloticus testicularis (Sundevall, 1842), trapped in Khartoum-North, Sudan. It differs from other species principally in length of adults and microfilariae, in the shape of the buccal capsule and in the structure of the spicules of the males.

Dietary feeding of drugs for 5 days to mice infected with Nematospiroides dubius and Hymenolepis nana detected all modern anthelmintics examined except stilbazium. A simple test using eggs of Nematodirus spathiger and adult Nippostrongylus brasiliensis to detect anthelmintics in vitro is reported.

A further survey in East Caprivi, Chobe National Park, Okavango swamps and Kavango was undertaken in June 1976. No evidence of lechwe schistosomes was found in droppings of African buffalo (Syncerus caffer) nor baboons (Papio ursinus) living in lechwe habitats. It was thought that they were not capable of spreading or maintaining these parasites outside the confines of the known distribution of Kobus sp. The role of goats was equivocal but probably they too are poor hosts.

Kavango, an endemic area of S. haematobium and S. mansoni, was thought to be free of all animal schistosomes, thus confirming the hypotheses that (1) cattle and goats are poor hosts of the lechwe schistosomes and (2)S. mattheei was blocked from entering the territory by the presence of lechwe schistosomes in the surrounding areas. Evidence of schistosomes was not found in cattle and goats at Maun for the same reasons. The prevalence of S. mansoni at Maun has increased alarmingly over the past 20 years with a simultaneous disappearance of lechwe from the area. S. margrebowiei and S. leiperi eggs were found in lechwe and tsessebe droppings some 80 km north of Maun.

A high proportion of children with negative excreta from “non-endemic” areas in East Caprivi had positive CFT and/or skin tests, suggestive of exposure to lechwe schistosomes resulting in a possible immunity to S. mansoni and S. haematobium.

Border Leicester X Suffolk sheep infected with a strain of S. mattheei maintained in hamsters do not develop the same pathological changes as Romney Marsh sheep infected with the same strain of parasite before hamster passage. To determine the cause of this reduced pathogenicity, five Romney Marsh sheep were each infected with 10 000 cercariae of the hamster-passaged parasite and five with 10 000 cercariae of a S. mattheei strain from Onderstepoort, South Africa, passaged exclusively through sheep.

Striking pathological and parasitological differences were found between the two strains. Infection with the “sheep” strain was lethal, whereas infection with the “hamster” strain produced little evidence of clinical disease. By 13 weeks post-infection the mean body weight of the sheep infected with the sheep strain had declined by 15% compared with both the uninfected controls and the sheep infected with the hamster strain, and the mean PCV was lowered to 20% in the sheep strain infected animals. Egg production began at seven weeks with the sheep strain, faecal counts rising to more than 300 e.p.g., whereas only two of the sheep infected with the hamster strain passed eggs in the faeces (at nine weeks) and the maximum egg count was 50 e.p.g. Twice as many adult worms of the sheep strain were recovered, and, although the number of eggs found in the tissues “per worm pair” was not significantly different, overall egg production was higher for the sheep strain; also more of the sheep strain eggs were deposited in the intestines. Similar parasite differences were seen in a supplementary study in mice and it seemed that “attenuation” of the parasite had occurred, presumably due to its maintenance in hamsters. Histopathological observations and faecal egg counts both indicated an inability of hamster strain eggs to penetrate the intestinal lumen; this was probably important in reducing the pathogenicity of the hamster strain.

We have previously described the characteristics of a relatively non-pathogenic laboratory strain of S. mattheei, attenuation of which was apparently caused by passage in hamsters. We now show that chronic infection with this avirulent strain largely protects sheep from the manifestations of acute schistosomiasis when challenged with a virulent strain of S. mattheei.

Four sheep were each infected with 10 000 cercariae of the avirulent strain and, together with four worm-free sheep, challenged 63 weeks later with 10 000 S. mattheei cercariae of a pathogenic strain. Four more sheep acted as uninfected controls. Following challenge, the animals were weighed and bled weekly for PCV and serum protein determinations, and egg counts were carried out fortnightly on faeces taken from the rectum. Red cell and albumin turnover were monitored for two weeks immediately before challenge and for a similar period before necropsy, when the adult worms were recovered by perfusion and tissues sampled for histopathology and egg counting.

The unvaccinated sheep developed severe disease 6—12 weeks after exposure characterised by marked anaemia, hypoalbuminaemia and hyper-gamma globulinaemia coinciding with the passage of blood-stained faeces and progressive inappetence. In the vaccinated sheep, there was and even earlier rise in gamma globulins, but the other clinico-pathological changes were generally slower to develop and much milder in severity. The parasitological data showed that although this was partly due to a reduction in the establishment of the challenge worm population the main factor was probably a reduction in the fecundity of these worms.

Cyst wall, brood capsules and evaginated protoscoleces of E. granulosus (ovine and equine) and E. multilocularis were fixed in 10% formol-saline embedded in paraffin and cut at 8 μm. Specific rabbit antisera to antigen 5 and antigen B of hydatid cyst fluid were used with immunoperoxidase methods to localise the antigens in the histological sections.

Antigen 5 was found in all parasites and was associated with cells of the subtegumental area of the protoscolex, the brood capsule wall and the germinal membrane. The labelled antigen appeared as distinct granules in all areas. It is suggested that antigen 5 may be synthesised in all of these sites and that a source of the antigen in cyst fluid may be the germinal and brood capsule membranes. The laminated membranes of E. granulosus (ovine and equine) were, except for the superficial layers, free from antigen 5.

Antigen B was present in all parasites. It was distributed diffusely throughout the laminated membrane, germinal membrane and brood capsule wall. There were areas of densely labelled antigen B on the surface of the distal cytoplasm of the protoscolex tegument and the surface of calcareous corpuscles. The distribution of antigen B in relation to PAS positive meterial and possible complement activating substances is discussed.

The laminated membrane of E. granulosus was apparently more permeable to antigen B than to antigen 5. It is suggested that differences in the diffusion of these antigens through the laminated membranes of hydatid cysts in the same or different host species may account for variable serological responses during infection.

Notocotylus tadornae n.sp. is described from the New Zealand paradise shelduck Tadorna variegata (Gmelin), and Notocotylus gippyensis (Beverley-Burton, 1958), is recorded from three waterfowl species in New Zealand. The life histories of both species are shown to involve an hydrobiid snail Potamopyrgus antipodarum, as intermediate host. The taxonomic affiliations of N. tadornae and N. gippyensis are discussed.

Oxyhaemoglobins of six digenetic trematodes,—Srivastavaia indica, Gastrothylax crumenifer, Gigantocotyle explanatum, Fasciolopsis buski, Gastrodiscoides hominis, Isoparorchis hypselobagri, and of their 3 vertebrate hosts, Bubalus, bubalis, Sus scrofa, Wallago attu, were subjected to alkali denaturation at a pH of 12·4. All oxyhaemoglobins from trematodes and their hosts differ from each other in the rate and extent of alkali denaturation which may be explained due to variations in the amino acid sequences of a particular haem protein in addition to other factors.

The genus Sulcascaris is upheld and redefined. Sulcascaris sulcata from Chelonia mydas and Caretta caretta is redescribed, from Rudolphi's type material and material from the Mediterranean and Western Pacific, demonstrating that the excretory pore opens between the subventral lips and that the excretory cell is bilateral, comprising a short filamentar right component and a more capacious ribbon-like left component containing the nucleus. The phylogenetic significance of this form of excretory system occurring in an ascaridoid of a marine reptile is discussed. It is concluded from comparative studies, based on measurements, sections and electron scanning micrographs, that fourth stage larvae of S. sulcata collected from the stomach of turtles are identical with fourth stage ascaridoid larvae found in the adductor muscle of scallops (Amusium balloti and Chlamys sp.) and that turtles become infected with this species by eating bivalves. Adult S. sulcata were obtained from tank-reared C. caretta fed with encapsulated larvae from scallops.