The effect of existing Brugia pahangi infections on the establishment of a subsequent population was studied using jirds which had pre-challenge infections of 4 and 8 months duration. Necropsies were performed 28 days post-challenge inoculation in order to separate challenge and initial worm populations. The results indicate that existing infections of 4 or 8 months duration increase the susceptibility to subsequent homologous infections. The location of challenge population worms in tissue sites examined did not differ significantly between previously infected and uninfected groups. Previous infections did not affect the early growth of challenge population worms as indicated by their length.

Experimental infections of white laboratory mice and wild rats (Rattus rattus) with cercariae of Schistosoma mansoni of different descent, whether murine or human, demonstrate that there is no significant difference in the probability of maturation of these cercariae into adult schistosomes.

These results enable us to hypothesise that the reverse would be true, i.e. that cercariae of murine or human descent would be capable of infecting man with the same success rate.

Circulation of the parasite from man to the rat and from the rat to man may therefore occur in natural habitats, which does not mean that rodents can maintain indefinitely and independently Schistosoma mansoni, nor does it mean that murine strains may not evolve locally.

The infective larvae of Nematospiroides dubius were exposed to various levels (0–30 krad) of gamma irradiation by means of a Cobalt 60 source. Groups of mice were infected with these larvae and autopsied 5 weeks later for worm counts. It was found that male worms were more susceptible to irradiation than female worms. In both instances, however, the survival curve on a semi logarithmic plot was characterised by a shoulder at low doses and an exponential component at the higher levels of exposure. No male worms were recovered from mice infected with larvae given more than 12 krad but some female worms were capable of surviving 20 krad. The fecundity of female worms was reduced by 61% at 4 krad and totally ablated at 8 krad.

Further experiments demonstrated that the survival of irradiated N. dubius in vivo was related to the extent of the damage caused at the time of irradiation and was not dependant on additional host parameters. Thus neither the number of irradiated worms inoculated nor the sex of the host radically altered the sex ratio or proportion of the worms lost as a result of irradiating the larvae. Furthermore, treatment with cortisone or sublethal irradiation of the host did not increase the proportion of surviving worms. It was, therefore, concluded that a host immune response was not involved.

Quantitative examinations for the distribution and density of microfilariae were carried out on male Guatemalan onchocerciasis patients by taking 6 or 13 skin biopsies each from 74 subjects. We found that microfilariae were distributed most frequently on the iliac crest and secondarily in the scapular region; higher detection rates and greater microfilarial densities were seen in these areas. From these results we recommend the taking of biopsies from both of these anatomical regions so as to avoid false negative cases. The infected patients were classified into 3 groups (light, moderate and heavy infections) on the basis of the numbers of negative skin snips out of the 13 biopsies taken. In heavy infections, a higher densities of microfilariae were detected in the head and neck regions, as compared with the densities in the lower extremities (calf). The high concentration of microfilariae in these regions is of importance in relation to the development of eye lesions and/or transmission. Of patients who had microfilariae in the anterior segment of the eye some had negative skin biopsies from the outer canthus, retroauricular region and neck.

Three groups of golden Syrian hamsters received intraperitoneally either, (1) 1 × 107 spleen cells, (2) 0.5 ml. serum or, (3) 1 × 107 spleen cells plus 0.5 ml. serum, from donors infected 6 weeks previously with 25 Opisthorchis viverrini metacercariae, one day before and at the same time as challenge with 25 metacercariae. Three groups of control animals received the same quantities of spleen cells, serum or an admixture of both from normal non-infected donors in the same manner followed by challenge with 25 metacercariae.

Animals were killed six weeks after challenge, livers and extrahepatic biliary systems carefully removed, and liver worm burdens estimated. Additionally, parasitic egg counts were performed on pooled faeces samples collected one hour prior to death.

Animals receiving spleen cells, serum, or an admixture of both, from normal non-infected donors had mean worm burdens of 11.44, 12.00 and 12.66, respectively. Animals receiving spleen cells, serum, or both, from infected donors had mean worm burdens of 9.88, 7.77 and 12.00, respectively. There were no significant differences in mean worm burdens between control and experimental groups. However, a substanial reduction in parasitic faecal egg counts and subsequently mean egg production per worm was observed in all 3 groups of animals receiving spleen cells, serum, or both, from infected donors when compared to their respective control group.

These findings are discussed in relation to adoptive transfer studies performed with other helminths and their possible relevance to naturally acquired immunity is commented on.

Thirteen bats, Tadarida mops de Blainville, collected from the Ampang district in Kuala Lumpur, Malaysia, were found positive for the trematodes Castroia kamariae sp. nov. and Limatulum kuziai sp. nov. Two distinct but morphologically similar forms of Castroia kamariae were recovered. The morphological type is apparently determined by its location in the host intestine.

The adult worms of Stilesia globipunctata, Avitellina centripunctata and Moniezia expansa with immature, mature and gravid proglottids and having almost the same length were collected simultaneously from the sheep intestine. Neutral lipid concentration is about 2.2, 1.24 and 18.4% of the dried worm tissue respectively. Cholesterol is 87.8, 85.7 and 88.0% of the unsaponifiable material respectively.

Nonspecific esterase (NSE), acetylcholinesterase (AChE) and pseudocholinesterase (ChE) have been localized by histochemical methods in various tissues of a cestode, Raillietina (Raillietina) johri obtained from the intestine of pigeon.

NSE has been found in the rostellum, suckers, hooks, tegument, subtegumental muscle, excretory canal, cirrus sac, vagina and eggs. Two types of cells have been recognized on the scolex surface—some are NSE positive and others are NSE negative. AChE, besides being localized in nerves, has also been visualized in almost all the structures as in case of NSE except in hooks, excretory canal and eggs. Additionally AChE has been observed in the vas deferens and sperm ductules. ChE has been observed only in nerves, vas deferens, cirrus sac and vagina; the intensity of enzyme activity being low when compared with AChE. Possible involvement of these enzymes in the physiology of the parasite has been discussed.

For the first 66 hours after the subcutaneous injection of rabbits with the infective larvae of Strongyloides papillosus, larvae spread gradually from the injection site to other parts of the body musculature. Their number and distribution suggests that they do so by the direct penetration of the tissues as the majority remain close to the site of injection. By 90 hours, however, the appearance of larvae in the lungs, trachea and oesophagus suggests that migration is taking place within the circulation.

Although some 90% of the total worms recovered were already established in the intestine by 8 days post-infection, significant numbers of larvae continued to be present in the muscles at 14 and 21 days. Even by 35 days the muscles of 1 of 2 rabbits still contained 43 larvae. This prolonged presence of Strongyloides papillosus in the muscle of rabbits uniformly at the early fourth stage may be analogous to the arrested development of other nematodes. While there is evidence to suggest that immunity is a major factor in the aetiology of arrested development in Strongyloides ransomi, it is an unimportant factor in the case of Strongyloides papillous in rabbits.