Comparative histochemical studies of glycosidase activity were carried out in Clonorchis sinensis, Eurytrema pancreaticum, Fasciola hepatica, Dipylidium caninum, Hymenolepis nana, Ascaris suum, Toxocara canis, Ancylostoma caninum, Trichuris vulpis and Dirofilaria immitis. The enzymes examined were: N-Acetyl-α-Glucosaminidase (Ec 3.2.1.30), α-Glucuronidase (Ec 3.2.1.31) and α-Galactosidase (Ec 3.2.1.23). There were variations in enzyme distribution and intensity among the species and also between trematodes and nematodes; no marked positive reaction for these enzymes occurred in cestodes. In some trematodes, the caeca, especially in the brush border, and the tegument, subtegumental cells and testes, were reactive to the enzymes. In nematodes, although there was variation in reactions among species, N-acetyl-α-glucosaminidase and α-galactosidase were localized in the hypodermis and lateral cords excluding the excretory canal, and coelomocytes, intestinal epithelium and the walls of the reproductive systems.

Seasonal fluctuations in the infrapopulation size of strobilocerci of Hydatigera balaniceps (Hall, 1911), H. laticollis (Rudolphi, 1819) and H. parva (Baer, 1926) infesting liver lobes of Indian house rat populations at high altitude (1400 to 1600m) appear to be correlated with climatic oscillations in temperature. Greater susceptibility of Rattus rattus to infection was evident at lower temperatures. The distribution of strobilocerci in rodent populations could be described by the Poisson model (P<0-20-P<0001).

The influence of sex, size and weight of the Indian house rat (Rattus rattus) on concurrent liver infections with Hydatigera balankeps (Hall), H. laticollis (Rudolphi) and H. parva (Baer) has been discussed. A significant inverse relationship was recorded between cestode infection and rat size. Parasitization index and mean worm burden-host weight ratio decreased with increase in rodent weight.

Evidence has been presented showing two kinds of acidic protease activities in adult Schistosoma mansoni, Dirofilaria immitis, Angiostrongylus cantonensis and Ascaris suum. A haemoglobinolytic activity without adding any SH-containing compounds was maximal at pH 3.5, 2.5, 30 and 3.5 in S. mansoni, D. immitis, Angiostrongylus cantonensis and Ascaris suum respectively. The inhibitor studies demonstrated that this activity is ascribable to carboxyl protease(s). In the presence of dithiothreitol, activity on Azocoll (azo-dye coupled hide powder) was maximal at pH 4.6, 4.6, 3.5 and 5.6 in S. mansoni, D. immitis, Angiostrongylus cantonensis and Ascaris suum respectively. The effects of inhibitors demonstrated that this activity belongs to the thiol protease class. The intraspecific distribution of the protease activities was studied in some of the nematodes from which the organs could be anatomically separated. The distribution patterns of the haemoglobinolytic and azocollytic activities were quite different in An. cantonensis and much the same in As. suum. Based on the present results, acidic haemoglobinolytic activities reported in adult S. mansoni by other authors are thought to be due to carboxyl and thiol protease(s) respectively.

The life-cycle of Syphacia muris is described in primary infections of Wistar rats. The life-cycle of S. muris is completed within seven days and no moults were discovered inside the egg. Instead each of two moults were observed outside the egg up to 24 and 40 hours after infection, and TEM studies suggest a third moult occurs up to 64 hours. The development and maturation of the larval stages are described for the first time using both light and electron microscopy. Differences in the size and growth of female S. muris compared with previously published figures could be due to differences in the strains of rats used.

Haematological, biochemical and pathological changes were investigated in 214 sheep naturally infected with Fasciola gigantica in an endemic area in the Sudan together with 82 uninfected controls. Infected animals showed a clear decrease in erythrocyte counts, haemoglobin concentration and packed cell volume, a normochromic, normocytic anaemia, leucocytosis and eosinophilia. Serum concentrations of the enzymes glutamate dehydrogenase, sorbitol dehydrogenase and glutamate oxaloacetic acid transaminase were also elevated in the infected group, indicating hepatic damage. This was confirmed by histopathological changes, which comprised degenerative and necrotic changes in hepatocytes associated with haemorrhage, fibrosis, increased lobulation of the liver, mononuclear cell infiltration with haemosiderin deposition in fluke tracks and portal areas and the formation of granulomata around fluke eggs and fluke remnants. In the infected group there was slight hyperglobulinaemia and a marked hypoalbuminaemia, with a decrease in A/G ratio. A slight rise in the level of serum bilirubin was also observed.

Using the local strains of Schistosoma bovis and Fasciola gigantica, it was shown that Sudanese zebu calves with mature primary infections of F. gigantica were highly resistant to challenge with S. bovis cercariae, and vice versa. Liver enzyme tests showed that, in both cases, the primary infections had caused some liver damage. Primary infection with irradiated S. Bovis cercariae, which did not cause significant liver damage, did not protect significantly against challenge with F. gigantica.

Third-stage and fourth-stage Dirofilaria immitis larvae exhibited positive thermotaxis when placed in a thermal gradient. Negative thermotaxis was not observed. Positive thermotaxis may be important for the successful transmission and for directing third and fourth-stage larval migration toward predilection sites in the Host.

Various cooling (01–5.100 Cmin−1) and warming (2O–6,8OO½Cmin−1) rates, stepped cooling schedules and four cryoprotective additives (dimethyl sulphoxide, methanol, ethanediol and glycerol) were investigated in cryopreservation studies with Dictyocaulus viviparus third-stage larvae. Exsheathment with sodium hypochlorite was essential to achieve significant survival. With uninterrupted cooling, highest survival (30% normally motile) was achieved with rates of 10–70½C min−1. Survival was higher (50–75%) using 1 ½C min−1 to — 10½C followed by plunging into liquid nitrogen. The optimum warming rate was 6,8OO½C min−1. The use of cryoprotectants led to marginally lower survival while varying the suspending media had no significant effect on survival. X-irradiated, exsheathed third-stage larvae cryopreserved by the optimum protocol yielded 38–3 ±4–2% survival. Two calves each infected with 45,000 (15,000 viable) exsheathed, unirradiated, C“ryopreserved third-stage larvae harboured 494 worms (11% infectivity) and 355 worms (0-8%) at necropsy. Numbers of first-stage larvae in the faeces reached 420/G and 105/G respectively 27 days after infection.

The use of 75Selenomethionine labelled cercariae of Schistosoma mansoni for ultrastructural localization of parasites in host tissues has been evaluated. Both gamma counting of tissue, and autoradiography of resin-embedded tissue were successful. The autoradiographic technique was more sensitive and schistosomula were readily located in pulmonary tissue up to 24 days post-infection.