Irradiation of the infective larvae of Gaigeria pachyscelis Railliet and Henry, 1910 with gamma rays upto 160 Kr had no significant effect on the in vitro survival of these larvae for a period of 49 days, maintained either at room temperature (32.2–39.4°C) or at 4°C. However, the behaviour of the irradiated larvae in the lamb host was much changed, as shown by a marked reduction in the worm establishment and the development of stunted and sterile worms from these larvae. As the level of irradiation increased, there was a corresponding decrease in the subsequent worm establishment. It was found that male larvae are more sensitive to the effects of irradiation than female ones, particularly at higher levels.

Academician K. I. Skrjabin was an outstanding Soviet scientist-helminthologist who greatly contributed to the advance of biological, veterinary and medical sciences.

Rats were infected with doses of 100, 1000, 5000 and 10 000 eggs of Taenia taeniaeformis. Haemagglutinating antibody to cysticercus antigen was detected at the 4th week of infection. The appearance and levels of antibody titre did not vary greatly with the infective dose. An IgM peak appeared at the 6th week, with IgG appearing slightly later and continuing to rise. Transfer of serum from the 1st week onwards from infections with 1000 eggs however could confer significant protection. Dilutions of hyperimmune serum (1 ml volumes) of up to 1/32 conferred significant protection on normal recipients. Hyperimmune serum transferred up to 4 days before challenge could confer 80% protection whereas serum transferred 4 days after challenge was totally non-protective. The significance of this finding is discussed in the light of current knowledge of metacestode immunity.

An attempt was made to determine if blocking antibody is involved in protecting cysticerci of Taenia taeniaeformis against a host immune response. Immunoflourescence microscopy confirmed that host antibody is present on the parasite surface within the capsule. To test if the larvae can still survive after such a coat of blocking antibody is removed, the larvae were trypsinised and then implanted into recipients. The results indicate that blocking antibody could be involved in the survival of 1 year old established larvae. Untrypsinised larvae were normal 14 days after implantation into control or immunised rats. Trypsinised larvae implanted in control rats were alive but showed on intense cell adherence on their surface. On the other hand, trypsinised larvae implanted into immunised rats were dead and completely encapsulated. However, experiments with 1 month old larvae were inconclusive.

The degree of resistance acquired by Schistosoma mansoni-infected mice against homologous challenge has been determined by perfusion of the animals within three weeks of the challenge, at which time the challenge-derived organisms were morphologically distinguishable from the primary infection which induced the resistance. The method has been compared with assays based on determination of the number of organisms migrating through the lung, and with perfusions at a later time when the challenge has matured. The results obtained with the three week perfusion method, showing that resistance was acquired by eight weeks after a primary infection, were confirmed by the longer survival of, and reduced egg excretion rates and tissue egg burdens in the experimental animals relative to respective challenge control animals. However, some discrepancy in challenge-derived worm numbers was found between animals perfused three weeks after challenge and those autopsied at later times. The possible reasons for this difference are discussed. The degree of resistance that was acquired was to some extent dependent on the size of the challenge infection.

The distribution of Ancylostoma caninum larvae in the various regions of the central nervous system of mice of previously uninfected or reinfected groups was studied. Although a dose of 4000 larvae was lethal, the distribution of larvae was not appreciable in the CNS. Many larvae were recovered from the cerebral hemispheres and cerebellum of infected mice whereas no incidence of eye involvement was observed in any mouse. In the reinfected mice groups there was a much lower recovery than in the previously uninfected groups in the latent period of study.

The results of a vaccination trial in lambs with gamma-irradiated infective larvae of Gaigeria pachyscelis are described. A single percutaneous (P/C) vaccination of lambs with 2000 infective larvae irradiated at 40 Kr induced the development of resistance. The vaccinated lambs successfully resisted a lethal challenge infection of 5000 non-irradiated larvae 3 months later. In the vaccinated lambs, the manifestations of resistance were shown by marked reduction in the worm establishment, development of retarded and functionally sterile worms and absence of clinical signs of hookworm disease after the challenge infection.

The egg shell of Dipetalonema viteae separated from the oolemma and became highly convoluted at an early stage of development. No second oolemma or trilaminate membrane was seen. Channels containing electron dense material (thought to be nutrient material from the uterine wall) were formed between adjacent embryos. Many developing embryos died.

Microvilli were formed by the uterine wall and developing embryos were closely apposed to these (again presumably to obtain nutrient).

Embryos emerged from the egg in the uterus and were born as unsheathed microfilariae.

Mice developed a partial resistance against homologous challenge with Schistosoma mansoni as early as two weeks after primary infections of 35 to 75 cercariae, and the degree of protection increased to an apparent maximum by 6 weeks. Animals given a primary infection of only 25 cercariae required a longer period to acquire maximum resistance.

A striking was difference was found in the responses of Schistosoma mansoni and S. haematobium miracidia to the intensity and direction of light and to gravity. S. mansoni miracidia were found to be positively phototactic and sensitive to small changes in light intensities. They were indifferent to gravity. S. haematobium miracidia however were negatively phototactic and unable to distinguish low light intensities from darkness. They showed a strong positive geotaxis.

Both S. mansoni and S. haematobium miracidia could successfully find and infect snails to a depth of 2 metres of water: the significance of these findings in relation to transmission of schistosomiasis in the field is discussed.

The offspring from hybridization experiments between Schistosoma intercalatum, Cameroun (intermediate host Bulinus forskalii) and S. intercalatum, Zaïre (intermediate host B. globosus) was investigated. Reciprocal crosses between the two forms were performed.

F1–and F2– miracidia developed in both parental intermediate hosts. The minimum prepatent period was 24 days at 26°C, an average of the prepatent periods for the two parental strains.

The total cercariae production per 100 exposed snails decreased sharply from 121 000 for the parental strain from Cameroun in B. forskalii to 21 000 and 5000 from the F1–and F2–generations, respectively. The figures for S. intercalatum, Zaïre in B. globosus were 270 000, 134 000 and 3000, respectively. F1–and F2–generations were from the cross between males from Cameroun and females from Zaïre.

The viability of the four cross-breeding experimentas carried out (two with each combinations of the parental strains) were low. It was only possible to obtain F2–cercariae. No miracidia were hatched from eggs produced by the F2–generation.

A new species of polystomatid monogenean, Eupolystoma anterorchis sp. n. is described from the urinary bladder and kidneys of Bufo pardalis from the Cape Peninsula, Republic of South Africa. It is distinguished from other Eupolystoma species, and from all other species except one within the Polystomatidae, by the anterior pre-ovarian extension of a large proportion of the testis follicles. This and other morphological characteristics are incorporated into an amended generic diagnosis.

The morphology of E. alluaudi from Bufo regularis in West Africa is also described. The known range of this species is enlarged with new geographical records in the Cameroun and Ethiopia, and a new host record from Nectophrynoides malcolmi.

Material from each area shows that the eggs of Eupolystoma spp. complete development in utero and that all developmental stages of the parasite occur side by side within the same host individual. This represents a significant evolutionary departure from the pattern of transmission typical of Polystoma in most of the other anuran hosts.

Diplozoon homoion gracile from the southern barbel (Barbus meridionalis) displays an egg-laying and an egg hatching rhythm, the latter being more clearly defined. Egg laying continues both day and night but significantly more eggs are laid at night. The oncomiracidia hatch at dusk. If parasite eggs are eaten by the host they pass through the gut undamaged and hatch normally.

Different groups of mice were infected with various single or repeated doses of larvae of Ancylostoma caninum. Considerable loss of larvae occurred in the immunised groups when compared with their counterpart unimmunised groups. Larval migration and distribution in the different tissues was less in immunised mice, as most larvae were expelled from the gastrointestinal tract. This resulted in a poor onward larval migration to liver, lungs, brain and muscle regions in immunised groups. The heavily immunised group infected five times was most affected and a significant lesser larval distribution in various organs and muscle region observed.

Infective larvae of Brugia pahangi were irradiated at 10, 25 or 45 krads by means of a Cobalt 60 source. In cats, 10 krads caused the worms to be stunted and sterile but allowed them to become 5th stage, migrate posterioly into the afferent lymphatic, and produce pathology.

25 krads prevented the worms from developing beyond the early fourth stage and from migrating away from the popliteal lymph node. No gross pathological reactions were evident. 45 krads produced the same effects as 25 krads but the longevity of the worms was much reduced.

Allometric growth of body proportions and organs is determined for three species of digenetic trematodes of marine fishes from Belize: Apocreadium mexicanum Manter, 1937 (Apocreadiidae), Pseudocreadium lamelliforme (Linton. 1907) Manter, 1946 (Lepocreadiidae), Paracryptogonimus americanus Manter, 1940 (Cryptogonimidae). These are compared with three other species in which allometric growth has been studied. In all species only the hindbody shows positive growth, whereas the forebody, suckers, and pharynx are consistently negative. The body width, posttesticular body, testes, and ovary are positive in some species and negative in others. In some instances the body proportion or organ is growing at the same rate as the body length.

Balanotaenia newguinensis sp. n. is described from Tandanus brevidorsalis from Papua New Guinea. It differs from B. bancrofti from Australia primarily in being much smaller, having the testes and vitellaria beginning at the same level, and in having the gonopore posterior to the ovarian commissure. On the basis of this new species and B. bancrofti a new family of the order Caryophyllidea is described. Unlike any of the other three families the vitellaria and testes are in the cortical parenchyma. Drawings of the new species, comparative muscle distribution within all families of the Caryophyllidea, and photographs of the inner longitudinal muscles of B. bancrofti complement the description.

In cats infected with normal, or irradiated, infective (L3) larvae of Brugia pahangi counterimmunoelectro-phoresis revealed the presence of antibody to soluble antigens derived from microfilariae, adults and infective larvae of the same parasite. Infected cats with a persistently high to moderate microfilaraemia gave positive precipitin reactions to L3, microfilarial and adult worm antigens. Cats which had become amicrofilaraemic had antibody to L3 and microfilarial antigens but not to adult worm antigen. Serum from cats inoculated with irradiated L3 larvae produced a precipitin reaction only to the L3 antigen.