The natural infection of tench by Asymphylodora tincae in a lake was studied during one summer season. The incidence of infection was 57%, the mean intensity about 50. The distribution of the digencans along the host's intestine showed a maximum in the second half; this could be modified by the presence of other helminth species. Tench caught in early spring and kept in the laboratory retained their natural infection throughout the summer. Starvation of hosts during two months caused disappearance of the infection. Experiments showed that metaecrcariae, introduced into the intestine of tench, can excyst within one hour. In vitro, cysts in contact with tench bile opened within 15 seconds. Bile of several other cyprinid fisli species caused excystment within 60 seconds. Asymphylodora eggs appeared in tench faeces 7 to 10 days after infection. Progenetic specimens of A. tincae probably disintegrate in the intestine of the tench and their eggs arc passed out with the faeces.

Six to nine horses per month (total of 94 in a year) were examined for stomach worms in the Settat region of Morocco. All the animals were infected by at least one helminth species. Habronema muscae occurred in 95–8%, H. majits in 75.6% and Trichostrongylus axeiin 80.9% of horses. Polyparasitism was observed in 93.6% of horses. Both for Habronema spp. and T. axei the peak worm burden was observed in November and minimum in June. The infection pattern Habronema spp. was directly related to the period of activity of fly vectors.

Measurements were made of gravid worm lengths, scolex diameter, rostellum diameter, sucker diameter, and large and small rostellar hooks of adult Taenia hydatigena, T. multiceps, T. ovis and T. pisiformis obtained from dogs in North Wales. Values recorded agreed closely with published values. None of these characters could be used to differentiate reliably between the species except that, of the worms examined, those with large rostellar hooks greater than 228 μim were T. pisiformis and those with large hooks less than 168 μm were T. multiceps. The range of hook lengths of the different species overlapped considerably.

Reliable identification required examination of mature proglottis morphology of specimens which were relaxed before fixation. Relaxed mature proglottides often showed a characteristic shape.

Lengths of rostellar hooks of scolices from T. multiceps coenuri followed the same frequency distribution as adult worm hooks. A strong correlation was shown between coenurus volume and the number of scolices on the coenurus membrane, with a poor correlation between coenurus age and volume.

A controlled study was carried out to determine the effect of some known anti-filarial drugs on the pattern of emergence of Onchoccrca volvulus microfilariae from skin snips into saline. The results show that before treatment, 81·7 to 92·1% of microfilariae emerge in all the groups within 24 hours. The differences between the groups were not significant. After treatment with oral diethylcarbamazine, metrifonate and topical diethylcarbamazine (DEC) the percentage of microfilariae emerging from the snips dropped significantly to 48·4,560 and 60·1 respectively, whereas no significant change occurred following treatment with levamisole (88·1%) and yeast tablets (89·1%). A pair-wise comparison of the post-treatment microfilarial emergence in all the groups showed statistically significant differences when (i) oral DEC is compared to levamisole, topical DEC and yeast, (ii) metrifonate is compared to levamisole and yeast and (iii) topical DEC is compared to yeast. It is suggested that microfilariae which fail to emerge from snips after treatment are those that have been killed or paralysed by the action of the drugs. The study has thus established that drug action in vivo is one of the factors which affects the proportion of microfilariae which emerge from skin snips and provides an additional parameter for measuring the antimicrofilarial potential of drugs in clinical chemotherapeutic trials.

Onchocerca tarsicola is a subcutaneous filariid of the red deer living on the tendons of the radial-carpal and tibial-tarsal joints. Its micronfilariae concentrate mainly in the external ears. The extrinsic cycle of this parasite was investigated. In a hyperendemic area wild-caught Odagmia ornata were dissected, as well as samples which had fed on a tame deer and been kept in the laboratory after the infecting blood-meal. About 3 to 5% of the flies were infected with larval stages of Onchocerca tarsicola. More than 40% of Odagmia ornata induced to feed on the ears of the deer became infected and about 30% of the flies which survived more than 18 days contained third-stage larvae. The larval development in the vector is described. Prosimulium nigripes appears to be a second natural vector of Onchocerca tarsicola. Observations concerning the potential vectors of O. Jlexuosa, O. tubingensis and Cutifilaria wenki living in red deer are discussed.

All the natural hosts of Onchocerca parasites are large animals (MULLI-R, 1979) andthere is, therefore an urgent need to develop a small animal model for onchoccrciasis,preferably one that employs a strain of inbred host. Rodents have been usedsuccessfully as experimental hosts for the microfilariac of O. guiturosa (sec NELSON et al. 1966), O. cervicalis (see RAbalais, 1974), O. armilluta (see EL Bihari & Hussein, 1975) and O. ijibsoni (see Beveridge et al., 1980) but there have been few publishedattempts to infect these hosts with infective-stage larvae.

Cercariae of Schistosoma bovis, S. intercalatum and S. haematobium were radiolabelled by individual exposure of their respective host snails to 75Se-methionine in 1 ml water for a period of 20 hours. Maximum cercaria-bound radioactivity was obtained four to seven days after labelling of snails, but detectable levels of radioactivity incorporation were obtained with all three species for a period of 32 days. The radiolabelling procedure did not interfere with the production of cercariae or with the biological characteristics of the labelled larvae. The described research opens the way for the application of various radioisotope tracer systems in studies on host-parasite relationships between cercariae and schistosomula of terminal-spined species of schistosomes and the final host.

A survey revealed that Onchocerca tarsicola Bain & Schulz-Key, 1974 is a widespread parasite among reindeer in northern Finland. Of 407 animals studied from 12 reindeer herds, 124 (30·5%) were infected. There was a marked difference in infection levels between different reindeer herds and the frequency as well as the intensity of infection was highest in old animals whereas the parasites were rare in yearlings.

The biochemical composition of the metacercariae of Clinostomum complanatum is: free glucose 0·516% of wet wt (2·14% of dry wt), glycogen 4·39% of wet wt (18·30% of dry wt), protein 8·7% of wet wt (36·23% of dry wt), lipids 8·64% of wet wt (35·96% of dry wt), RNA 0·08% of wet wt (0·335% of dry wt) and DNA 0·035% of wet wt (0·145% of dry wt). The pattern of glucose uptake, glucose leakage and effect of starvation on the glycogen content is similar to that reported for adult digeneans. Lactic and pyruvic acids (1·478 and 0·019μimol/g wet wt/h respectively) were found in the incubates, suggesting the presence of an active carbohydrate metabolism. Protein and lipid metabolism are also discussed briefly.

1. Investigations were made of the effect of various procedures in raising or lowering the microfilaria count of Pacific type Wuchereria bancrofti in the peripheral blood.

2. Raising the body temperature in the early morning was followed by a moderate fall in the counts. Breathing increased oxygen, or reduced oxygen (hypoxia) or increased carbon dioxide, or the ingestion of sodium bicarbonate produced no consistent and significant changes in the count. Ingestion of glucose (in one volunteer) was followed by a small rise in the count. Muscular exercise was followed by a fall in the count, which is interpreted as probably being a response to a lower concentration of oxygen in the venous blood returning to the lung.

3. It has not been possible to identify the physiological components of the circadian rhythm of the human body which entrain the cycle of these microfilariae. Attempts to obtain evidence incriminating the stimuli described above have been unsuccessful.

Experimental infections were established with Diphyllobothrium sp. plerocercoids obtained from Salmo gairdneri. a fish introduced at the beginning of the 1900s in the lake region of Chile. These permitted us to obtain adult parasites in Larus dominicanus and Canis familiaris.

The histological features of the plerocercoids, their relation to the host, adult pattern and susceptibility of hosts allowed us to determine the presence of Diphyllobothrium dendriticum (Nitzch) for the first time in South America in the lacustrine region of southern Chile.

It is believed that this cestode was introduced to this ecosystem by infected persons travelling from North America or Europe or, alternatively, brought by migratory birds, e.g., Sterna hirundo, S. paradisea or Larus pipixcan on their winter visits to South America.

Echinococcosis in man and animals has been reported to be endemic in the Middle East(MAIOSMAN et al., 1977). As a result of this report and recent interest by the WorldHealth Organization to define more clearly the problem of hydatid disease in theMiddle East, the incidence of hydatid cysts found at surgery and at autopsy in theNcgcv region of Israel was retrospectively examined for the years 1970–1979.

A comparative biochemical study was performed on adult and cystic stages of Echinococcus granulosus. Basic quantitative differences in metabolism were apparent between the cystic forms of sheep origin from the UK and Kenya which suggest that each may represent a different geographical strain or sub-strain.

The biochemistry of the human and sheep forms from Kenya was very similar, which probably reflects a certain close affinity between the two. The fact that the cattle, goat and camel forms of E. granulosus, from that country, were distinct biochemically, both from each other and from the sheep and human types, suggests the existence of an unusually complex strain picture there, and that these organisms are either noninfective or only poorly infective to man.

The differences in biochemical composition and metabolism observed between adults produced experimentally and those obtained from naturally infected dogs, may have been as a result of their original hydatid source and/or their differing stage of development.

The life span and the pathogenicity of amphistomes developing from Cercariae indicae XXVI (Paramphistomum epiclitum) were considerably reduced when the metacercariae were gamma-irradiated at 2krad or 3krad. The higher irradiation dose resulted in the complete absence of the flukes in infected animals. Single vaccination of lambs and kids with 3000 metacercariae irradiated at 2 krad or 3 krad stimulated a significant degree of resistance against challenge with 5000 non-irradiated metacercariae. The resistance was more pronounced in the group vaccinated with metacercariae irradiated at 3krad.

Fly load of Onchocerca volvulus microfilariae and their early development in Simulium ochraceum were examined at intervals of 10, 30 and 60 min after ingestion and then hourly up to 72 hours. Many microfilariae ingested were damaged by the cibarial armature of the vector, limiting the fly load, but some of these damaged microfilariae were able to penetrate the gut before they died. Thus, the mean number of the living parasites per fly in the head and thorax decreased gradually with elapse of time after ingestion. The parasites ingested by S. ochraceum did not develop beyond the microfilarial stages during the first 24 hours; thereafter only thoracic forms (lst-stage larvae) were found to be alive. The high mortality of the infected fly might be caused by the high intakes of microfilariae and also by normal and/or partly wounded microfilariae invading various organs. The numbers of microfilaria ingested from different biting sites were usually high in comparison with the densities observed in each site; this indicates that the microfilariae might be attracted by the biting females.

The susceptibility of rats to Hymenolepis nana (Cestoda) and the chemotherapeutic response of anti-cestode drugs was studied during egg-induced and cysticercoid-induced infections. In cysticercoid-induced infection, the percentage of infected animals and the number of mature worms were significantly more than in egg-induced infection. The former mode of transmission required more drug to clear the parasites. These differences have been discussed on the basis of immunity engendered in the definitive host by the developing larvae.