Fifty-six sheep, worm-free birth, were each given a sigle infection of 50 000 Haemonchus contortus larvae at varying at varying times over a 2 year period. They were killed from 13 to 89 days infection and the lengths of both male and female parasites measured. Using a computer, growth curves for each sex were constructed and the relative lengths of the worms in each infection were calculated by dividing their measured lengths by the lenghts predicted by the appropriate curve. Since there was no significant difference between the relation length of male and female worms in an infection, the mean value was used in further analyses. Differences in sex of host and duration of infection had no significant effect on the relative length of parasites. There was a close relation between relative length and the time of year of infection. The relation was cyclical and closely followed a sine curve with a maximum at day 90 and a minimum at day 275 of the year. Arrested development at the 4th larval stage occurred at the time of year risen again. It is suggested that this cyclic change in growth pattern and arrested development is controlled by the seasonal variation in concentration of a substances present in the host’s blood. Parasite relative length was also related to sheep age, but the relationship observed was largely an artifact of the close birth dates of many of the sheep.

Parkin (1975) considered that the water content of the unhatched 3rd-stage larva of Nematodirus battus increased as it approached hatching, and then fell immediately after the larva escaped from the egg-shell, to the very low value for estimated water content for hydrated individuals of 43·7%. A repetition of this work suggests that these results are in error. Prior to hatching, the water content of larvae remained constant; after hatching there was a marked increase in water content to an estimated value for fully hydrated individuals of 74·5%, a value more in keeping with other findings.

The effect of different relative humidities on the survival of individual larvae and adults of Ditylenchus dispasci and D. myceliophagus has been examined; experiments were carried out at 5 and 18°C with D. myceliophagusand at 18°C with D. dipsaci. Survival of both species was enhanced when they were dried at high humidities and, for D. myceliophagus, by the lower temperature. The survival of all stages of D. myceliophagus was poor. Generally it was expressed in minutes only; 4th-and 3rd-stage larvae, however, were marginally better at surviving drying than adults and much better than 2nd-stage larvae.

Although the 4th-stage larva of D. dipsaci was overwhelmingly superior to all other stages, the 3rd stage, and to a lesser extent, the adult of this species also showed remarkable powers of survival to desiccation. In general, survival of 4th-, 3rd- and 2nd-stage larvae could be expressed in weeks, days and minutes respectively; for adults, survival was expressed in hours at relative humidites under 50% but in days at higher relative humidites.

The results are discussed in relation to the survival value of the aggregations formed by these species; the validity of the term ‘resistantstage’ as applied to the 4th-stage larva of D. dipsaci is assessed.

At a temperature of 27°C the external cuticular membrane of the first larval stage (L1) of Meloidogyne javanica is formed within a day of the start of elongation of the embryo within the egg. The first and only moult within the egg starts to occur 50 h after the commencement of elongation. Thus the cuticle of the L1 is shed approximately a day after its formation. It is much thinner than the cuticle of the L2, is not covered during its formation by a closely adherent cuticle in the process of being moulted and its outermost membrane may be formed differently.

Vaccination with whole male worm extract (AMA), stichoseome extract (SA) and a short-term inculbation fluid (EXA) of adult Trichuris muris induced a high degree of protective immunity in mice as assessed by reduction in larval worm burden.

Immunodiffusion of AMA against rabbit anti-AMA serum revealed five precipitin lines, one of which was common to both EXA and SA with which only single lines were obtained.

Physico-chemical tests suggested that the antigen is a protein and that carbohydrate, lipid and DNA do not contribute to its antigenicity. Partial fractionation was obtained with ammonium sulphate. All preparations with immunogenic activity showed the common line of EXA on immunodiffusion.

It is concluded that one of the protective immunogens is a protein which can be associated with the precipitin line and originates in the stichosome.

In outbred (CFLP) and inbred (NIH) mice, the inflammatory response which is thought to be party responsible for the expulsion of Trichinella spiralis from the mid-region of the small intestine, also seemed to be largely responsible fo rthe simulataneous (i.e. early) expulsion of Trichuris muris from the caecum and large intestine during concurrent primary infections. The intractive explusion operated only when the concurrent infections were timed to produce T. Spiralis expulsion before T. muris expulsion would normally occur and the effect persisted for several days after T. Spiralis has been expelled.

Interactive expulsion wasss depressed during application of the nonsteroid, anti-inflammatory drug indomethacin and by T-cell expulsion of T. spiralis. These results indicate that a T-cell mediated inflammatory response was probably the basis of the interaction.

When the timing of the infections was altered such that the expulsion of T. spiralis there was no reciprocal ecpulsion of the latter. Mice immunized againest one or the other species did not show cross-immunity on heterologus challenge, confirming that the interaction did not involve similar antigens in the two species. The interactive expulsive response is considered as an example of an indirect cross-immunity.

Hymenolepis microstoma was found to live for at least 728 days in a mouse, but an initial infection of 10 worms per mosue decreased exponentially for approximately the first 110 days to a level of 3–5 worms, after which little further loss occurred.

A primary infection of six H. microstoma, expelled with anthelmintic on day 21, strongly protected against a single worm H. diminuta challenge; worms in 80 ‘immunized’ mice weighed less than 5% of the weight of worms from 80 control mice. However, a primary (5-worm) H. diminuta infection led only to a small, though statistically significant, decrease in weight of the 3-worm H. microstoma challenge.

The results are interpreted as indicating that H. microstoma evokes a strong immunological response which cross-reacts with H. diminuta. The failure of H. diminutato protect strongly against a 3-worm challenge by H. microstoma suggests, as does the long survival of a primary infection when it is reduced to approximately 4 worms, that H. microstoma survives in low infection because it is able to avoid the immune response. This could be due to antigen camounflage, ability to repair immune damage or to the low permeability of the bile duct wall to components of the immune response. The worm loss which occurs from heavy infection until only 3–5 worms remain may be physiologically rather than immunologiacally mediated.

The nature of antigens present on the surface coat of Trypanosoma brucei brucei (serotype AnTat–1) trypanosomes has been investigated by light and electron microscopy using indirect immunofluorescence and immunoenzymatic labelling techniques. The use of a monospecific anticomponent V serum has shown that the variant-specific antigen, component V, is the major constituent of the surface coat. Antigens of heterologous serotype, of culture form trypanosomes, of host serum proteins or host red blood cells were not demonstrated on the surface coat.

Five normal rhesus monkeys were infected with Plasmodium knowlesi sporozoites (A-strain); two developed rapidly fatal malaria and three chrinic relapsing infections. Vaccination with P. knowlesi (W-strain) merozoites (unmodified or formol-treated and freeze-dried) in Freund's complete adjuvant (FCA) did not inhibit pre-erythrocytic parasite development after challenge with A-strain sporozoites. However, the subsequent blood-stage infection was terminated in nine out of ten vaccinated monkeys even though the challenge strain was different form that used for vaccination. The degree of parasitaemia (0·01–0·70 %) and brevity of infection (1–12 days) in six animals vaccinated with untreated merzoites was similar to that observed after direct challenge with blood-stage parasites. Monkeys were equally resistant to sporozoite challenge given as the post-vaccination infection or administered 6 months after blood challenge. These results are discussed in relation to the development of a human malaria vaccine.

The response of intestinal host-cell nuclei of calves infected with Eimeria zuernii 6 and 8 days post-infection was examined using Feulgen-DNA microspectrophotometry. The results show that nuclear hypertrophy is dissociated from DNA replication. In the light of previous work (Fernando, Pasternak, Barrell & Stockdale, 1974) it is surmised that the specificity of infection of cells by E. zuernii is not stringent, with the major target being non-proliferative cells. At most, 20% of the first-generation schizonts develop within cells that would have had proliferative potential and as a result some non-scheduled DNA synthesis occurs.

Experiments are described which support the view that, in Eimeria maxima, drug resistance factors are transferred at zygote formation. The phenomenon occurred between infections which were initiated by the inoculation of merozoites. It also took place between variants of the same, but not between different species. Transference of drug resistance wsa not affected by the treatment of the chicks with acriflavine.