The nature of complement binding to the surface to infective larvae of Trichinella spiralis and Nippostronaylus brasiliensis differs. When worms were incubated in serum from uninfected hosts, washed and incubated in fluorescent reagent the whole surface of T. spiralis fluoresced but in N. Brasiliensis fluorescence was confined to the anterior end and some internal organs. The outer structure of the cuticle of the T. spiralis larvae was shown not to contain ATP-ase, thus differing from many cell membranes.

The possibility of cryopreserving the eggs of Angiostrongylus cantonensis collected from the uterus of female worms was investigated. Eggs were cultured in NCTC 109 medium containing 50% rat serum, and various growth stages, from one-cell eggs to embryonated eggs, were used in this study.

As a cryoprotective agent, dimethylsulphoxide (Me2SO) was added to the medium at a final concentration of 1 M. Eggs suspended in 0·2 ml of the medium at 37°C were cooled to 0°C at a rate of l°C min−1, then an equal volume of 2M-Me2SO solution was added. After equilibration for 15min, the freezing procedures were started. In the freezing procedures, the effectiveness of (i) a seeding process, (ii) different cooling and warming rates and (iii) the relationship between the growth stages of the eggs and their tolerance to freezing at −20°C were investigated.

It was found the highest level of survival could be obtained with 32-cell eggs cooled at a rate of 0·3° C min−1 or more slowly with seeding at −4°C and warming at a rate of 5°C min−1. Survival was influenced more by cooling rate than by warming rate.

Using these optimum conditions, the survival of eggs was then investigated following cooling to various temperatures. While more than 50% of eggs were found to survive cooling to −30–C, extremely low survival was noted from lower temperatures.

Lyophilized eggs of Schistosoma mansoni, when incubated briefly with serum from infected mice, bind antibodies, as made evident by subsequent binding of flurorescein labelled anti-IgG or 125 I-labelled protein A. On the basis of these findings, a radioimmunoassay was devised which employs whole lyophilized eggs (500 or 250 eggs/serum sample) as antigenic particles and 125 I-labelled protein A as a probe for antibody binding. Only 10 μl of serum are required to obtain 90% of the maximal binding. Kinetic studies indicated that 70% of the maximal seropositivity develops in mice between five and six weeks after a light infection, reaches a maximum at eight weeks and fluctuates around a high plateau thereafter. Pre-incubation of the test serum with soluble egg antigen (sea) considerably inhibits antibody binding to the eggs, suggesting that SEA-like antigens participate in the reaction.

Monoamine oxidase (MAO), catalysing oxidative deamination of biogenic monoamines, has been detected in adult Ascaridia galli. MAO was present in mitochondria and deaminated noradrenaline at the maximal rate, although serotonin, adrenaline, tyramine and dopamine were also degraded but more slowly. Of the organs studied, the body wall, female reproductive organ and intestine, the body wall (containing neuronal structures) showed highest MAO activity. Km value for chick ascarid mitochondrial MAO using tyramine as substrate was 1·66 x 10−3 M and it was most active at 2·5 mm tyramine concentration, pH 7·5 and 40°C. MAO of A. galli appeared to be thermolabile as nearly 80% of its activity was lost when the incubation temperature was increased 5° above optimum.

Microfilariae of Dirofilaria immitis retained their infectivity for susceptible mosquitoes after cooling to −196°C in the presence of 5% dimethylsulphoxide (Me2SO) using a two-step cooling sequence. Motility and in vitro development of cryopreserved microfilariae also compared favourably with unfrozen controls. Third-stage larvae frozen by the same cooling sequence in the presence of either 5% Me2SO or 16% hydroxyethyl starch were motile upon thawing. Thawed larvae completed the third- to fourth-stage moult in vitro at a frequency approximately 5 to 10% of that seen in unfrozen controls.

40-kR /-irradiated third-stage larvae of Oesophagostomum columbianum were used for the immunization of Kashmir Merino lambs. Male lambs (aged from 8 to 12 weeks) were immunized in two separate experiments by two doses of irradiated larvae, given 21 days apart, and subsequently challenged with normal larvae. Judging by the establishment of worms resulting from the challenge infections in the immunized and control groups of lambs in the two experiments, a high degree of immunity was shown to develop in young lambs vaccinated with 500, followed 21 days later with 2000, 40-kR irradiated larvae. Lambs from the immunized groups showed more nodules in the intestine, a high percentage of which were positive for histotrophic stages of O. columbianum, than did controls. The importance of this finding in relation to the possible use of a vaccine for the immuno-prophylaxis of oesophagostomiasis in sheep and other animals is discussed.

The filarial parasites Litomosoides carinii and Dipetalonema viteae both show transcuticular uptake of adenosine 3′, 5′-cyclic monophosphate but isoproterenol is taken up by D. viteae only. The importance of this difference is discussed from the point of view of metabolic regulation. Inhibition of uptake by lectins indicates the involvement of surface sugar moieties in the transport processes.

Mice infected with Nematospiroides dubius were incapable of responding normally to i.p. or i.v. challenge with SRBC. The HA and PFC response to SRBC in infected animals was characterized by a severe depression of antibody to SRBC on day 4 and a reduced HA peak titre during the following week. The greatest depression of the response to SRBC was associated with an interval of 14 days between infection and the administration of antigen, suggesting that a particular stage of the parasite contributed significantly to immunodepression during this critical period. It was proposed that a combination of parasite induced damage to the intestine, release of parasite secretory/excretory products and loss of appetite by the host produced trauma during which the host was incapable of responding normally.

However, mice given low-level and long-standing infections also showed reduced responses to SRBC, although these animals were not severely depressed. It is possible that this generalized weakening of host immunocompetence is the inevitable consequence of a parasite mechanism which operates more specifically to suppress the expression of homologous immunity at the intestinal level.

Onchocerca raillieti is the only Onchocerca species infecting Sudanese donkeys; it occurs only in the ligamentum nuchae, especially in the lamellar part of the ligament. The morphological features of both uterine and skin microfilariae were determined. Skin microrilariae are shorter than uterine ones and tend to accumulate in the regions of Linea alba and withers of infected donkeys. The possible identity of the vector of this worm in the Sudan is discussed.