G. S. Nelson

Immunization of mice with gamma-irradiated intramuscularly injected schistosomula of Schistosoma mansoni.

The parameters involved in the induction of resistance against Schistosoma mansoni by injection of irradiated, artificially transformed schistosomula were studied in mice. Single intramuscular injections of 500 schistosomula exposed to radiation doses in the range 2.3 to 160 krad. resulted in significant protection (in the range 20 to 50% as assessed by reduced worm burdens) against a challenge infection administered at intervals from 3 to 24 weeks post-vaccination. However, schistosomula irradiated with 20 krad. consistently resulted in better protection than those exposed to either higher or lower radiation doses despite the persistence of stunted adults from the infections irradiated with 2.3 krad. Vaccination with 40 krad. schistosomula resulted in significant protection in terms of reduced worm and tissue egg burdens and increased survival following lethal challenge. Varying the number of irradiated schistosomula, the frequency and route of their administration, the site of challenge and the strain of host all failed to enhance the level of resistance. However, percutaneously applied, irradiated cercariae were found to be more effective in stimulating resistance (60%) than intramuscularly injected, irradiated schistosomula (40%).

Successful vaccination of cats against Brugia pahangi with larvae attenuated by irradiation with 10 krad cobalt 60

Summary Cats were vaccinated by the inoculation on 10 occasions of approximately 300 larvae of Brugia pahangi which had been irradiated with 10 krad cobalt 60. They were challenged on 3 occasions with normal larvae of either B. pahangi or B. patei. The vaccinated cats were resistant to challenge as demonstrated by either longer pre‐patent periods or failure to become microfilaraemic and by having fewer third, fourth or adult worms than normal controls. Although the vaccination procedure was unpractically heavy these results lend encouragement to the possibility of developing vaccines against filarial infections.

Immunisation of sheep against Schistosoma mattheei using either irradiated cercariae or irradiated schistosomula.

Irradiated cercariae, irradiated schistosomula, or heterologous infections were used to vaccinate sheep against Schistosoma mattheei infection. In the first experiment four doses of 10(4) S. mattheei cercariae irradiated at 6Kr were administered to sheep by percutaneous infection at 4 week intervals. This induced a 74% reduction in a challenge infection compared to control sheep while only 13% protection was achieved in a third group of sheep immunised with normal cercariae of the heterologous parasite S. mansoni. No significant differences were seen in histopathology of the liver of any of the sheep but the pathological changes were more severe in the large and small intestines of sheep vaccinated with the heterologous parasite. In the second experiment with irradiated cercariae only one or two immunising exposures were used. The degree of protection in the adult worm load (9-11%) was not significant and no significant differences were noticed in the pathology of the vaccinated and control animals. In the third experiment four doses of irradiated organisms were used to vaccinate five groups of sheep: 3Kr or 6Kr cercariae were administered by percutaneous infection; 6Kr skin-transformed schistosomula were administered by intra muscular injection; the same 6Kr skin-transformed schistosomula were given by intravenous injection and 6Kr syringe transformed schistosomula were administered by intramuscular injection. The degree of protection (determined as the reduction in worm burden) achieved by these different procedures was respectively 72%, 61%, 77%, 56% and 78%. These results indicate the possibility of making a live vaccine against ovine schistosomiasis and show that effective immunisation is not dependent on the presence of a mature worm infection or on cercarial penetration of the skin by the immunising infection.

Studies with Brugia pahangi. III: Histological changes in the affected lymph nodes of infected cats.

Cats infected with Brugia pahangi by single or repeated inoculation of infective larvae for different periods of time, were autopsied and the affected lymph nodes examined histologically, stained with methyl green and pyronin Y, haematoxylin and eosin, Lendrums eosinophil stain, Mallorys trichrome stain or the May-Grunwald Giemsa technique. In single infections, there was initially a cell-mediated type immunological response which was characterized by proliferation of mononuclear thymus-dependent cells in the paracortical region of the lymph node. The antibody-type response became more evident as the infections progressed. This response was characterized by proliferation of lymphocytes in rapidly enlarging germinal centres and the production of large numbers of plasma cells in the cortico-medullary junction and medullary cords of the nodes. In long term infections, the affected afferent lymphatic vessel and popliteal node were almost obliterated by fibrous tissue, but an inguinal lymph node complex usually developed to replace lymphatic filtration in the limb. Repeated infections produced more complicated changes. Both types of response occurred to varying degrees throughout the infection. No significant increase in mast cells or eosinophil cells was seen. Fibrous tissue increased in the lymph nodes only after long periods of infection; such nodes often became non-functional, and by-passed by new lymphatic vessels.

Studies on Onchocerca gutturosa (Neumann, 1910) and its Development in Simulium ornatum (Meigen, 1818). I. Observations on O.gutturosa in cattle in South-East England

1. O. gutturosa infections are of widespread occurrence in South-East England. 58% of 1583 cervical ligaments from milk cattle slaughtered in an abattoir at Reading, Berkshire, showed the presence of adult worms. A more detailed study of 50 cattle from a small abattoir near St. Albans in Hertfordshire showed 42 (84%) infected. 2. The adult worms were found either in the connective tissue adjoining the nuchal ligament or between the spleen and rumen. There was no evidence of an increase in the parasite density with age of the cattle suggesting a strong immunity to superinfection. 3. Irrespective of the situation of the adult worms the microfilariae of O. gutturosa appear to have a directional mechanism and were always concentrated in the skin around the umbilicus. This is an adaptation to transmission by Simulium ornatum which bites preferentially in the umbilical region. 4. There were no marked pathological changes associated with the parasites and no evidence of clinical disease attributable to infection with O. gutturosa .

Acquired resistance to Schistosoma haematobium in the baboon (Papio anubis) after cercarial exposure and adult worm transplantation

: Observations were made on the development of acquired resistance to Schistosoma haematobium in the baboon following immunization with cercariae by the percutaneous route and by the transplantation of adult worms into the mesenteric veins. In the first experiment six baboons were immunized with 1000 S. haematobium cercariae given percutaneously. They were challenged with 10 000 cercariae given 73 weeks later and the results were compared with a similar infection in non-immunized animals. The results showed that the baboon can develop a strong resistance to reinfection with S. haematobium. The manifestations of the immunity were (i) the absence of any increase in egg output after challenge (ii) the substantially lower level of adult worms and eggs in the tissues of the immunized baboons compared with the challenge control animals (iii) a reduction in the egg laying capacity of the residual worms and (iv) the virtual absence of gross pathology and the mild lesions seen in the tissue sections of all the immunized animals. The depression in egg laying of the worms was confirmed by transplanting them into non-immune baboons. This experiment indicated that the non-egg-laying worms in the immune baboons were not irreversibly damaged since they survived, some even migrating to the vesical and ureteric vessels, and egg-laying was rapidly resumed after transplantation. A further experiment was designed to see if a similar degree of immunity could be produced by an adult worm infection without previous exposure to cercariae or schistosomula. The immunization dose consisted of 50-100 S. haematobium worm pairs which were transplanted into the mesenteric veins of each of six baboons and the animals were challenged percutaneously with 7000 cercariae 35-55 weeks later. There was little difference in the worm burdens of the immunized and control animals but the worms in the immunized baboons produced fewer eggs and the pathology seen in these animals was much milder than in the challenge control animals suggesting that some degree of resistance to reinfection was produced by the transplanted worms.

Further observations on immunization of sheep against Schistosoma mansoni and S. bovis using irradiation-attenuated schistosomula of homologous and heterologous species.

This paper describes further characteristics of the immunization of sheep against schistosomes using live, irradiation schistosomula. Sheep immunized with a non-virulent strain of Schistosoma mattheei were protected against a more virulent strain of the same species for over a year. As there was no evidence that the irradiated parasites were able to persist this long, it was concluded that the vaccine had induced a sterile resistance. Heterologous vaccination, using irradiated S. mattheei schistosomula to immunize against S. bovis or irradiated S. mansoni schistosomula to immunize against S. mattheei, failed to induce any protection.

Immunisation of baboons against Schistosoma mansoni using irradiated S. mansoni cercariae and schistosomula and non-irradiated S. rodhaini cercariae.

In an attempt to develop a non-pathogenic procedure for immunising baboons against S. mansoni, groups of five baboons were exposed to three doses of 5000 6 Kr-irradiated S. mansoni cercariae or to similar numbers of normal S. rodhaini cercariae and challenged at week 15 with 500 normal S. mansoni cercariae. Faecal egg counts, worm and tissue egg counts, and histopathological examination, showed that neither of the immunising schedules had produced significant protection. In the second experiment baboons were injected by the intramuscular route with 31000 schistosomula of S. mansoni in three doses and the irradiation dose was reduced to near the minimum required for worm sterilisation (2-1--2-4 Kr). Challenge with 3500 normal cercariae of S. mansoni 21 weeks after the first immunising dose again showed no significant protection, although reductions of 20--30% were found in egg and worm counts resulting from the challenge. These results indicate that it may be difficult to develop an effective live vaccine for S. mansoni unless the antigenicity of the immunising larvae can be greatly increased.

Cross resistance between Schistosoma haematobium and S. mansoni in the baboon

Abstract Experiments were carried out to determine whether infection of the baboon with Schistosoma haematobium could stimulate significant acquired immunity to S. mansoni. Baboons immunized with S. haematobium were first shown to have developed a strong immunity to the homologous infection before challenge with the heterologous parasite. The baboons immunized with S. haematobium developed resistance to the S. mansoni challenge infections, as reflected in a reduction of mature worms and of S. mansoni egg excretion, compared with those of the challenge control animals. None of the immunized baboons lost weight or appeared to be sick, their PCV values did not decrease and they produced very little haemorrhagic diarrhoea. The observed pathology of the large intestine was much more severe in the challenge control baboons than in the immunized animals, very little host reaction being provoked by many of the eggs retained in the tissues of these animals. The antibodies being measured by the ELISA test are different to those being estimated by the antibody-mediated cellular cytotoxicity test. It is concluded that a baboon infected with S. haematobium can develop a marked degree of acquired immunity to S. mansoni and that, although the challenge infection may become established, the worm level is markedly reduced and the pathogenicity of the infection ameliorated. It is considered that these findings may have profound immunological and epidemiological implications in endemic areas where man is exposed to the transmission of both parasites.

Studies with Brugia pahangi. 5. Structure of the cuticle.

The structure of the cuticle of third and fourth stage larvae and of adult Brugia pahangi (Nematoda: Filarioidea) was studied by light microscopy and by transmission and scanning electron microscopy. The cuticle of these worms was basically typical of the class Nematoda and consisted of cortical, matrix, and basal layers. Finely spaced annulation grooves were present and their function is discussed. Descriptions of the cuticular ultrastructure of filarial nematodes are meagre. Studies on the cuticle of adult worms are limited to those of Kagei (1960, 1963) on Setaria cervi and Litomosoides carinii and of McLaren and Hockley (personal communication) who examined L. carinii and Dipetalonema vitea