Antigenic differences between intra-lymphocytic theilerial parasites isolated from the blood of 18 African buffalo and grown in vitro were assessed with anti-schizont monoclonal antibodies (mAbs). There was marked antigenic diversity both between isolates from different buffalo and between isolates taken at different times from the same buffalo. Many of the isolates from both wild and captive buffalo appeared to consist of mixed parasite populations. Some isolates were found by limiting dilution cloning and mAb testing to contain at least 3 or 4 distinct populations of Theileria. Once cloned, Theileria-infected lymphoblastoid cell lines retained their mAb profiles during prolonged in vitro cultivation and, when recloned, the subclones had the same mAb profile as their parent clone. The implications of these results for further studies on buffalo-derived theilerial parasites are discussed.

An African buffalo (Syncerus caffer), born in captivity and demonstrated to be Theileria-free, and 2 susceptible cattle were inoculated with a Theileria parva lawrencei sporozoite stabilate. The buffalo had a very mild disease reaction, while the 2 cattle died of acute theileriosis. It was possible to isolate T. p. lawrencei from the buffalo up to 888 days after infection by the application of non-infected Rhipicephalus appendiculatus nymphs and up to 657 days after infection by the establishment of lymphoblastoid cell lines infected with T. p. lawrencei schizonts from peripheral mononuclear blood cells. The infection rate and levels of Theileria in the resultant adult ticks varied from 11 to 70% with 0·3–11 acini infected/tick. Stabilates prepared from these tick batches caused fatal T. p. lawrencei infections in cattle.

Nymphal Rhipicephalus appendiculatus (Trans-Mara) were fed on a steer infected with a Theileria parva parva (Kilae 1) stock isolated from an indigenous steer in the Trans-Mara Division, Kenya, which had a high piroplasm parasitaemia. A total of 5000 engorged nymphs which had dropped on one day were enclosed in elongated nylon bolting silk tubes in groups of 200–300 and were transported immediately to the Trans-Mara where they were suspended vertically in the grass cover with one end touching the ground. Over 98% of the nymphs moulted into adult ticks and 50% moult occurred by day 28 after exposure. The ticks showed over 80% survival up to 308 days post-exposure but thereafter showed a marked mortality so that only 22·5 % of the ticks were alive after 439 days. Theileria parasites were detected in the salivary glands by day 35 post-exposure and infection rates and levels increased markedly between 180 and 235 days post-exposure. Thereafter, the infection rates and levels generally decreased. Groups of ticks were triturated and the resultant supernatant fluid inoculated into pairs of susceptible cattle, and these proved infective from day 44 to 145 after exposure. Three subsequent attempts to induce infections with supernatant fluid were unsuccessful. From 294 days after exposure, groups of 50 ticks were applied to cattle and caused lethal T. p. parva infections up to 439 days post-exposure. Climatic observations showed a relatively even monthly rainfall as well as mean maximum and minimum monthly temperatures. Clean nymphal R. appendiculatus were applied to a steer infected by adult ticks exposed for 405 days and the resultant adults were incubated at 37 °C for 6 days. Supernatant fluid produced from these ticks caused a lethal T. parva infection in a susceptible steer.

Plasmodium chabaudi AS strain in mice is characterized by an acute primary parasitaemia, and one or more less acute recrudescences. Previous work has shown, using a passive protection assay, that the recrudescent parasites are usually antigenically different from parasites of the parent population with which the mice were first infected. In this study the effect of mosquito transmission on the antigenic expression of recrudescent populations of P. chabaudi was examined. In the first experiments the recrudescent population which was antigenically different from the parent population was uncloned. After transmission through Anopheles stephensi the recrudescent population appeared to revert to an antigenic type similar to that of the parent population. In the second experiment clones from a recrudescent population were mosquito transmitted and again the parasites of the primary patent parasitaemia in the mice, bitten by the infected mosquitoes, had reverted to the parental type. It is suggested that antigenic variants of P. chabaudi AS strain may revert to a basic type after mosquito transmission.

Regional differences in the response of mice to infection with three strains of dermotropic Leishmania spp. were shown for skin covering the trunk. Lesions tended to appear earlier and to grow more rapidly on sites over the caudal half of the body than the cranial half, and caudal lesions were more likely than cranial ones to result in metastatic disease in susceptible strains of mice. Site-related variations in lesion development were observed in different strains of mice as well as in golden hamsters. The effect of these regional differences on the development of some parasite-specific, immunological reactions was examined, as were parasite thermosensitivity and location-related variations in host skin temperature as possible explanations.

Using foot-pad infection of female C57BL/6, DBA/2J and NMRI-IVIC mice as an animal model for American cutaneous leishmaniasis (ACL), we evaluated the inhibitory effect of Formycin B (FoB) on the infection produced by 7 different Leishmania isolates. When treatment was initiated some days, or even some weeks, after infection a significant leishmanistatic effect was detected on mice infected with all Leishmania isolates, which reached 30–55 weeks for some isolates. The optimal dose schedule was 1·25 mg/kg body weight/day, injected intraperitoneally for 20 consecutive days. Significant differences in the sensitivity of various Leishmania spp. to FoB were found, either in vivo, or in vitro where a high [3H]FoB incorporation rate was found only for certain Leishmania isolates. The low toxicity of this drug and the sensitivity of the 7 Leishmania isolates tested suggest that FoB could be useful in the treatment of ACL.

Laboratory studies on a group of 20 patients from the Rio Negro Valley, Colombia selected for detailed study showed that 14 gave antibody reactions on immunoassay consistent with Trypanosoma cruzi or T. rangeli infections. Four were diagnosed as having T. rangeli infection, 4 had mixed infections and 6 were infected with T. cruzi alone. Immunoprecipitation analysis showed that sera from T. crwzi-infected patients recognized a similar range of trypomastigote-derived polypeptides as sera from patients in Brazil, and all of the Colombian sera reacted with the 160 kiloDalton (kDa) polypeptide associated with active infection. Although sera from patients with T. rangeli infection alone gave a positive immunofluorescence or ELISA reaction with T. rangeli, they failed to bind to parasite polypeptides by either immunoprecipitation or Western blotting. Intriguingly, sera from patients with mixed infections consistently gave a stronger, but qualitatively similar, binding reaction in immunoprecipitation and Western blotting compared to sera from patients infected with T. cruzi alone.

Embryonic stages of various Onchocerca species have been used to stimulate resistance in CBA mice to challenge injections with the microfilariae of Onchocerca lienalis. Comparable levels of resistance to challenge (29–37% reductions) were conferred by living, freeze-killed, or sonicated organisms administered with Freunds‘ Complete Adjuvant (FCA). Antigens extracted in saline, or with the detergent sodium deoxycholate, were also protective. Adjuvants enhanced the protective effect, particularly FCA (78% reduction), Freunds‘ Incomplete Adjuvant (74% reduction), aluminium hydroxide (70% reduction) and Bordetella pertussis (70% reduction). Detergent extracts prepared from intact embryos with n-octyl glucoside also stimulated significant levels of protection against microfilarial challenge when given with FCA (37–45% reductions). Levels of resistance induced by immunizations with intact organisms were greatest following subcutaneous (s.c.) injection over the neck or by intramuscular inoculation. Soluble extracts were also particially effective given by s.c. inguinal or intraperitoneal injection. A time-interval of greater than 3 weeks between the completion of immunization and challenge was required for the expression of immunity. Cross-protection against challenge with O. lienalis microfilariae was also afforded to mice by immunization with intact embryos or detergent extracts of Onchocerca gutturosa (45 and 34% reductions), Onchocerca gibsoni (66 and 47% reductions) or Onchocerca volvulus (58 and 41% reductions). It is concluded that the embryonic stages of both human and animal parasites provide a source of cross-protective antigens of value in studies on resistance to Onchocerca microfilariae in experimental hosts.

All serum transfers from donor rats or rabbits given single or multiple vaccinations of ultraviolet (u.v.)-attenuated Schistosoma japonicum cercariae conferred significant resistance against challenge to mice. Donors given 5 vaccinations, however, produced the most effective sera; rat sera giving up to 88% protection and rabbit sera up to 80%. This protective effect was species-specific and titratable. Sera from vaccinated rabbits and rats were were most effective when transferred to mice 2 h before challenge, but became progressively less effective when transferred with increasing time after challenge. These sera had no efficacy when given 6 days after challenge. Thus, sera from vaccinated rabbits and rats were effective against the early stage of migration, but did not necessarily have to act in the skin as all serum transfers were as effective against intraperitoneal as percutaneous challenge. By contrast, serum from multiply vaccinated mice had little or no protective effect when transferred to mice before challenge, but conferred 62% resistance when transferred 5 days after challenge. Further, there was an additive protective effect when vaccinated rat and mouse sera were given in combination at their optimum transfer times (days 0 and +5, respectively). Thus, there appears to be a stage-specific immune response induced by vaccination depending upon whether the vaccinated hosts are truly permissive or not. Vaccinated rats and rabbits respond to the early phase of migration and vaccinated mice make protective responses against the lung phase of migration.

The roles of different antibody isotypes in the transfer of protection with serum from rats vaccinated with irradiated cercariae were investigated by immunoadsorption of IgG, IgG2a and IgG2c, and by heating at 56°C to remove IgE. Only depletion of IgG2a reduced the levels of vaccine-induced immunity transferred, whereas immunity transferred by infection serum was reduced by both IgG2a and IgE depletion. It was also shown that exposure to irradiated parasites did not lead to either specific or non-specific induction of an IgE response. The successful passive-transfer experiments using serum from non-resistant 25 week-infected rats into recipient animals demonstrated that the waning of resistance observed in 25 week-infected rats was not due to a failure of the humoral response to protective antigens.

The influence of subcutaneous infection with protoscoleces of Echinococcus granulosus on the distribution of lymphocyte subsets in draining lymph nodes has been evaluated by immunocytochemical labelling of lymphocyte surface antigens. These studies reveal marked expansion of paracortical Thy-1 +, Lyt-1 + cells and moderate proliferation of surface immunoglobulin-bearing B-cells immediately after infection. The Lyt-1 +:Lyt-2 + ratio decreases rapidly during the first 21 days post-infection and remains below unity until at least 12 weeks post-infection due to severe depletion of Lyt-1 + cells in draining lymph nodes and a significant increase in the percentage of Lyt-2 + cells. The potential role of these Lyt-1 ∓, 2 + (putative T-suppressor) cells in regulation of the anti-parasite immune response and mediation of generalized immunosuppression is discussed in the light of evidence of inhibition of anti-parasite immunity in infected mice.

Experiments to investigate the metabolism of glycine, L-glutamic acid and L-aspartic acid by Moniliformis moniliformis were carried out by incubating adult worms aerobically for 3 h at 37°C in Tyrode's solution containing either [U-14C]glycine, L-[U-14C]glutamic acid, L-[U-14C]aspartic acid or L-[4-14C]aspartic acid. Much of the glycine and glutamic acid was absorbed by the worms, but little of either was metabolized. Aspartic acid was readily taken up and metabolized. After incubating with L[U-14C]aspartic acid, most radioactivity was found in ethanol and a volatile compound, presumed to be carbon dioxide, with smaller amounts in lactate, alanine, acetate, malate, glucose and succinate. After incubating with L-[4-14C]aspartic acid, most radioactivity was found in lactate and the presumed CO2 with small amounts in alanine, malate and succinate. No radioactivity was found associated with ethanol or acetate. Possible metabolic pathways and suggestions for a relationship between the metabolism of aspartate with that of alanine and serine in this parasite are discussed.

Phosphorylcholine (PC), an immunodominant component of the cell wall of certain bacteria, fungi and nematodes, is known to induce low anti-PC antibody levels during natural infection by Trichinella spiralis. This article reports a study in which spleen cells from BCF1 mice infected with Trichinella sp. larvae were found to produce large numbers of direct haemolytic plaques in response to PC conjugated to sheep red blood cells (SRBC) after muscle-encysted larvae had been killed by treatment with mebendazole. Inhibition of the response by PC-chloride, immunodiffusion and immunoelectrophoretic studies with the anti-PC IgA (TEPC-15) and anti-idiotype T15 serum assays showed the plaque-forming cell (PFC) response to be specific for PC. The absence of haemolytic plaques when unconjugated SRBC or TNP-SRBC were used as indicator cells ruled out involvement of a polyclonal response. Greatest anti-PC PFC response was found to be associated with a microsomal fraction designated FCpl, a particulate fraction behaving as a thymus-dependent antigen. The FCpl fractions from all four strains of Trichinella employed induced anti-PC PFC responses when injected into mice. These results suggest that FCpl is a suitable antigen for use in detailed studies of immune responses to Trichinella and related parasites.

The electrophysiological properties of the bag region of the somatic muscle cells of Ascaris suum and Ascaridia galli were studied using intracellular techniques. For Ascaris muscle cells, the mean resting membrane potentials at 20 and 37°C were −29·9 and −33·8 mV respectively, and the average input conductance was 2·12 μS. For the muscle cells of A. galli similar values were obtained. For example, the mean input conductance of these cells was 2·84 μS at 20°C. Healthy Ascaris muscle cells at near physiological temperatures show both spontaneous depolarizing and hyperpolarizing activity and, in cells close to the nerve cords, rhythmic large amplitude (approximately 30 mV) action potentials are observed. Such action potentials, which are very sensitive to temperature variations, originate in the muscle cells. In contrast the muscle cells of Ascaridia are quiescent. The rhythmic action potentials of Ascaris are resistant to tetrodotoxin (TTX) (≤ 10−6 M), verapamil (10−4 M) and cinnarizine (10−4 M), but are blocked irreversibly by 22, 23 dihydroavermectin B1a (10−7 to 5 × 10−6 M). GABA, and the GABAA receptor agonists, muscimol and isoguvacine, hyperpolarize and increase the input conductance of both Ascaris and Ascaridia muscle cells. The antagonists+bicuculline and picrotoxin were not effective in modulating the spontaneous hyper polarizations of Ascaris muscle cells, and picrotoxin (10−4 M) was not effective in altering the response to GABA (5 × 10−6 M). The significance of the results is discussed briefly.

Rats harbouring 35-day-old primary infections of Moniliformis moniliformis and Hymenolepis diminuta were inoculated with equal doses of Nippostrongylus brasiliensis and were autopsied 10 days later. Significant reductions were found in the dry weight of Moniliformis and Hymenolepis and in the numbers of Nippostrongylus recovered compared with single infections. Similarly, in infections with two parasites, the numbers of Nippostrongylus were reduced when concurrent with Moniliformis and the dry weights of Moniliformis and Hymenolepis decreased in the presence of each other. A comparison of the concurrent infections themselves revealed that Moniliformis weighed significantly less in the presence of Hymenolepis than in the three parasite infections. Parasite interactions and their possible mechanism are discussed and comparisons are made with the relevant single infection for each parasite.

Changes in the variance to mean ratio and the parameter k of the negative binomial distribution were used to study temporal changes in the degree of aggregation of the monogenean parasite, Gyrodactylus turnbulli in free-running laboratory populations of the guppy, Poecilia reticulata. The parasite undergoes recurrent epidemic cycles in the host population under conditions of regular immigration of uninfected guppies. During the early phase of the epidemic, heterogeneity among fish together with direct reproduction are thought to contribute to the increasing degree of aggregation. During the increasing phase of the epidemic cycle, parasites become increasingly aggregated in the host population, presumably because of the direct reproduction of the parasite on the surface of a single host. As the peak prevalance and abundance are approached, the parasites become less aggregated with lowest clumping occurring during the declining phase of the cycle. This is thought to be a function of density-dependent death of infected hosts, and density-dependent reduction in parasite survival and reproduction on hosts that recover from infection. This study clearly indicates that the variance to mean ratio and the parameter k of the negative binomial distribution do not quantify the same aspect of the frequency distribution. It is suggested that the variance to mean ratio is a better measure when the prevalence and−or mean burden are changing and when the tail of the distribution is of particular interest, and that k may be a preferred parameter when the zero class or the lightly infected hosts are of primary interest.