Toxoplasma gondii is one of the few pathogens that can cross the placenta. Frequency and severity of transmission vary with gestational age. While the control of acquired toxoplasmosis is already well explored, the control of materno-foetal transmission of the parasite remains almost unknown. This is partly due to the lack of an animal model to study this process. This review summarises the studies which have been undertaken and shows that the mouse is a valuable model despite obvious differences to the human case. The paramount role of the cellular immune response has been shown by several experiments. However, IFN-γ has a dual role in this process. While its beneficial effects in the control of toxoplasmosis are well known, it also seems to have transmission-enhancing effects and can also directly harm the developing foetus. The ultimate goal of these studies is to develop a vaccine which protects both mother and foetus. Therefore, it is useful to study the mechanisms of natural resistance against transmission during a secondary infection. In this setting, the process is more complicated, involving both cellular and also humoral components of the immune system. In summary, even if the whole process is far from being elucidated, important insights have been gained so far which will help us to undertake rational vaccine research.

The respiration rates of individual Gammarus pulex infected by larval Pomphorhynchus laevis were investigated with particular reference to the stage of development of the host and parasite and to the water temperature. At 20°C the oxygen consumption of Gammarus of all sizes was reduced by an average of 19·3 % by the presence of cystacanths of the parasite, but was unaffected by the presence of acanthellae. It is considered that the small size of this larval stage, in relation to that of its host, is responsible for the failure to detect an effect. Multiple infections did not exert any greater effect upon host respiration than single cystacanths, nor did it appear that the parasite had different effects upon hosts of different sexes. At 10°C no significant differences were observed between the respiration rates of infected and uninfected gammarids. The parasite was probably still depressing the host respiration rate at this temperature, but the oxygen uptake of G. pulex is so low that the differences between infected and uninfected individuals were too small to be detected. The parasite has a direct effect upon the physiological processes of the host, but neither the mechanism of this nor the reasons for the different effects found in different host-parasite systems are yet understood. Despite the pronounced effect of P. laevis on respiration of individual hosts, its effect upon the oxygen consumption of a natural host population is small since only a small proportion of the population carries infections and water temperatures remain below 10°C for over half the year.

Resistance to anthelmintics in gastrointestinal nematodes of livestock is a serious problem and appropriate methods are required to identify and quantify resistance. However, quantification and assessment of resistance depend on an accurate measure of treatment efficacy, and current methodologies fail to properly address the issue. The fecal egg count reduction test (FECRT) is the practical gold standard for measuring anthelmintic efficacy on farms, but these types of data are fraught with high variability that greatly impacts the accuracy of inference on efficacy. This paper develops a statistical model to measure, assess, and evaluate the efficacy of the anthelmintic treatment on horse farms as determined by FECRT. Novel robust bootstrap methods are developed to analyse the data and are compared to other suggested methods in the literature in terms of Type I error and power. The results demonstrate that the bootstrap methods have an optimal Type I error rate and high power to detect differences between the presumed and true efficacy without the need to know the true distribution of pre-treatment egg counts. Finally, data from multiple farms are studied and statistical models developed that take into account between-farm variability. Our analysis establishes that if inter-farm variability is not taken into account, misleading conclusions about resistance can be made.

We investigated changes in the behaviour of Stagnicola elodes associated with the emergence of Plagiorchis elegans cercariae. Within 15 min of the reduction in light intensity, which triggered the onset of cercarial emergence, infected snails moved to the top of the water column and remained there for 2–3 h. Seventy-nine percent of all cercariae that emerged from the snail did so during this period. Uninfected snails showed no such behavioural changes following the change in light intensity. Cercariae were released in a dense cloud around the snail at the water surface and dispersed passively. Within 3–4 h more than 80% of all cercariae had settled in the bottom 5 cm of the water column. The infectivity of cercariae increased from less than 20% upon emergence from the snail to greater than 75% 4–6 h post-emergence, and then declined steadily to below 5% by 24 h post-emergence. Cercarial longevity was greater than 30 h and exceeded the period of infectivity. This may be related to steadily falling endogenous glycogen levels. A delay in attaining maximum infectivity may represent an adaptive mechanism allowing time for cercarial dissemination, thus reducing superinfection, and subsequent parasite-associated mortality, of second intermediate hosts.

1. Heligtnosomum muris proved to be very favourable material for the study of nematode development, since it will develop perfectly normally in culture rats, infection is easily carried out and since sexual maturity is reached in 7–10 days after infection.

2. The post-embryonal development of H. muris is divided into five stages, two free and three parasitic, with three moults. There is only one moult during free life, the second and third stages being separated by change of habitat brought about by entrance into the host. Sexual maturity is attained soon after the completion of the third moult. The mature worm has two cuticular layers, the outer of which is separated by a space from the inner. This outer cuticula is probably the beginning of a fourth moult which is never completed.

3. Under favourable conditions the eggs hatch in about 20 to 24 hours after being passed with the faeces.

4. The first two stages of post-embryonal development, which are passed in free life, are separated by a relatively long moult during which the larva changes from the rhabditiform type to the filariform type. During this period there is a rapid division of the cells lining the intestine, which frees masses of these cells into the lumen and leaves the intestine of the filariform larva lined with flattened cells.

5. The infective stage is not enclosed in a sheath and tends to work its way out of the culture onto the glass or along the edges of the filter paper. At this stage it is impossible to distinguish the sexes.

6. Infection of the rat can be accomplished both by way of the mouth or through the skin although the latter method is by far the most effective. The larvae reach the lungs about 14 to 20 hours after penetration through the skin. They remain in the lungs until about 35 to 65 hours after infection. The majority of them reach the intestine 50 to 65 hours after infection, although in a few they were found as early as 45 hours.

7. In the lungs the larvae increase rapidly in size and moult just before they migrate to the intestine. Early in the development in the lungs the sexes can be distinguished by: (1) the migration toward the posterior end of the genital primordium of the female, (2) structural differences in the caudal region, and (3) differences in shape of the genital primordium.

8. After reaching the intestine the larvae grow rapidly and enter into the third moult from 96 to 108 hours after infection. In the fourth larval stage between the second and third moults growth and differentiation are most marked. It is during this stage that the differentiation of the organs of the reproductive system occurs.

9. Shortly after the completion of the third moult sexual maturity is reached and later the cuticula separates into two layers.

10. During the course of development the changes in size and shape and in the character of the cuticula were traced step by step and the differentiation of the digestive and excretory systems were followed as completely as the material would permit. However it was in following the details of the development of the reproductive organs that the investigation was most fully carried out.

11. In the male reproductive system the testes, vas deferens, seminal vesicle, cement gland and ejaculatory duct arise by differentiations of the genital primordium and are therefore called internal sex-organs, while the bursa and the spicules which are not developed from the genital primordium are known as the external sex-organs.

12. Toward the end of the third larval stage (first parasitic stage) the genital primordium of the male becomes separated into two parts by an extremely delicate strand of tissue. The anterior half of this genital primordium grows forward up to the oesophageal region and forms the testes, the narrow strand connecting the two parts develops into the vas deferens, and the posterior part grows backward to the posterior end, becomes tubular and forms the seminal vesicle, cement gland and ejaculatory duct.

13. The bursa is formed from the walls of the posterior end of the male which become very much inflated, and the spicules develop from secretions of a group of spindle-shaped cells which are early differentiated in the posterior region.

14. In the development of the female reproductive system the ovary, oviduct, seminal receptacle, uterus and the anterior part of the ovijector arise from the differentiation of the genital primordium and are therefore called internal sex-organs, while the vulva, vagina and posterior part of the ovijector arise from invagination and differentiation of subcuticular cells of the posterior end and are therefore called external reproductive organs.

15. After the genital primordium has migrated backward to a position on the ventral side just in front of the anus, it elongates very greatly and grows forward. The anterior part remains as a solid mass of cells and differentiates into the ovary. The rest of the primordium becomes tubular and differentiates into the oviduct, seminal receptacle, uterus and ovijector.

16. A group of cells just in front of the rectum and just over the posterior part of the genital primordium increases in number, invaginates, becomes differentiated into a tube which joins with the posterior part of the genital primordium. This tube differentiates into the vulva and vagina. Where it joins the posterior end of the internal reproductive organs there is an overlapping so that the posterior end of the ovijector has a double origin.

The fate of 75Se-labelled parasites and their released pre-synthesized macromolecules has been followed in three murine infection models. Parasite numbers in specific tissues were determined by autoradiography, and released material was estimated by gamma-counting of tissues, with adjustment for the presence of parasite-associated radiolabel. Marked differences were found between the three models. The pattern of migration of normal schistosomula was similar to that previously reported. In addition we have described the transit of parasites through the lymph nodes draining the infection site. Significant quantities of released material were detected in the skin, draining lymph nodes, bloodstream and liver. The circulating material was of parasite origin, macromolecular, and hence potentially antigenic. In comparison to the normal infection, radiation-attenuated parasites (inducing a high level of resistance to challenge) persisted in the skin, draining lymph nodes and lungs, releasing a proportionally greater amount of material in the nodes. In mice exposed to attenuated parasites and treated with the compound ROl1–3128 at 24 h (inducing a low level of resistance) there was an early death and rapid clearance of the parasites whilst still in the skin. This situation resulted in the highest levels of released material in the skin, bloodstream and liver, but negligible levels in the draining lymph nodes. We suggest that the persistence of radiation-attenuated parasites in the skin and draining lymph nodes, together with the prolonged release of antigen in the latter site, compared to the normal situation, are major factors in the induction of resistance.

Bivalvulidan parasites from the gall bladder of 31 species of damselfishes (family Pomacentridae) were examined for their taxonomic identity and their relatedness to other species of myxozoans. This paper describes 11 novel ceratomyxid species and a novel Myxidium sp. Each species is characterized morphologically and small subunit (SSU) rDNA sequences were used in molecular phylogenetic analyses. Five pomacentrid species were found to harbour multiple infections of bivalvulidan species. One species of Ceratomyxa and Myxidium were found to infect more than a single species of damselfish. Phylogenetic analyses revealed there has been no radiation of ceratomyxids that can be associated with the fish host taxon and that Myxidium queenslandicus n.sp. was more closely related to Zschokkella mugilis and Ellipsomyxa gobii than other members of the genus Myxidium.

The sensory organelles and some components of the nervous system of the adult filarial worm Dipetalonema viteae have been studied by means of electron microscopy.The sensory organelles contain modified cilia innervated by nerve axons. The cilia lie within cuticle-lined channels. The amphids each contain nine such cilia, but the phasmids and the papillae contain only one cilium. The amphidial and phasmidial cilia are exposed to the external environment and it is suggested that I they function as chemoreceptors. The cilia within the cephalic and caudal papillae are modified so as to produce a greater area of sensitivity. The ciliary channels in the cephalic papillae do not open to the exterior and these papillae therefore probably function as mechanoreceptors. The caudal papillae of the male worm are structurally similar to the cephalic papillae, except that the ciliary channels are open to the external environment. It is suggested that these papillae function both as mechanoreceptors and chemoreceptors. The terminal pair of caudal papillae differ from all the other papillae. The ciliary channels of all the sensory organelles are surrounded by supporting cells, but multivesicular cells are only associated K with the amphids, phasmids and cephalic papillae.The nerve-ring encircles the muscular region of the oesophagus; it is composed entirely of nerve axons. The nerve axons contain two kinds of vesicle. The nervering is surrounded by an ensheathing cell. The major nerve bundles are carried by the hypodermal cords, but they are not embedded in the hypodermal cytoplasm. The nerve axons at the surface of the cord form synapses with the innervation processes of the somatic muscle cells.Electron cytochemical techniques have been used to investigate the distribution of cholinesterases in the structures described. Acetylcholinesterase has been identified in the amphids, phasmids, cephalic papillae and nerve-ring; it is suggested that acetylcholine functions as a chemical transmitter at these sites. Pseudocholinesterase has been identified in the amphids, phasmids and cephalic papillae, but not the nerve-ring; it is present in considerably smaller quantities than acetylcholinesterase.

Investigations on the host specificity of plerocercoids of Schistocephalus solidus were carried out using the technique of surgically transferring plerocercoids from the body cavity of Gasterosteus aculeatus to various other fish. Plerocercoids survived in all cases when transferred from G. aculeatus to other G. aculeatus; when tranferred to Pungitius pungitius the worms survived for long periods but failed to grow. Plerocercoids transferred to Coitus gobio, Nemacheilus barbatula, Phoxinus phoxinus, Salmo trutta, Coregonus clupeoides, Perca fluviatilis, Rutilus rutilus and Esox lucius always died within 2–10 days after being transferred. Electron-microscopic examinations of the tegument of plerocercoids transferred to new hosts showed: in G. aculeatus normal appearance throughout the experiment; in P. pungitius degeneration of the microtrichs after 6 days; and in S. trutta complete destruction of the tegument in 7 days.

Plerocercoids of the genus Diphyllobothrium survived the transfer from Gasterosteus aculeatus to Salmo trutta and continued to grow in their new host.

Infection of fish with S. solidus by feeding infected copepods and by aspetic injection of procercoids into the body cavity of the fish were also tried. Gasterosteus aculeatus became infected using both these methods but it was not possible to infect Pungitius pungitius.

The mainstream forestry policy in many European countries is to convert coniferous plantations into (semi-natural) deciduous woodlands. However, woodlands are the main habitat for Ixodes ricinus ticks. Therefore, assessing to what extent tick abundance and infection with Borrelia spirochetes are affected by forest composition and structure is a prerequisite for effective prevention of Lyme borreliosis. We selected a total of 25 pine and oak stands, both with and without an abundant shrub layer, in northern Belgium and estimated tick abundance between April and October 2008–2010. Additionally, the presence of deer beds was used as an indicator of relative deer habitat use. Borrelia infections in questing nymphs were determined by polymerase chain reactions. The abundance of larvae, nymphs, and adults was higher in oak stands compared to pine stands and increased with increasing shrub cover, most likely due to differences in habitat use by the ticks' main hosts. Whereas tick abundance was markedly higher in structure-rich oak stands compared to homogeneous pine stands, the Borrelia infection rates in nymphs did not differ significantly. Our results indicate that conversion towards structure-rich deciduous forests might create more suitable tick habitats, but we were unable to detect an effect on the infection rate.

Risk factors for the transmission of Echinococcus multilocularis to humans operate at a range of spatial scales. Over a large area, such as China, regional scale risk is correlated with variation in climatic conditions because of its effect on the spatial distribution of landscapes that can support E. multilocularis transmission in wildlife hosts and the probability of egg survival. At a local scale of a few kilometres, or tens of kilometres, transmission risk is related to the spatial proximity of human populations and landscapes with active transmission. At the patch scale, when considering individual villages or households, human behavioural factors are important and for individuals genetic and immunological factors play a role. Satellite remote sensing can provide landscape information at a range of spatial scales and provide a spatial framework within which to examine transmission patterns. This paper reviews the application of remotely sensed data and spatial data analysis to develop a better understanding of disease transmission and shows how such data have been used to examine human alveolar echinocossosis infection patterns, at a range of spatial scales, in an endemic area in central China.

Low doses of the acetylcholinesterase-inhibiting carbamate nematicides disrupt chemoreception in plant-parasitic nematodes. Fluorescein isothiocyanate (FITC)/dextran conjugates up to 12 kDa are taken up from the external medium by certain chemosensory neurons in Caenorhabditis elegans. Similar chemoreceptive neurons of the non-feeding infective stage of Heterodera glycines (soybean cyst nematode) fill with FITC and the nuclei of their cell bodies selectively stain with bisbenzimide. The widely used nematicide aldicarb disrupts the chemoreceptive response of H. glycines with 50% inhibition at very low concentrations (ca 1 pM), some 10−6-fold lower than required to affect locomotion. Similarly, the anthelmintic levamisole had this effect at 1 nM. Peptides selected as mimetics of aldicarb and levamisole also disrupt chemoreception in H. glycines and Globodera pallida at 10−3-fold or lower concentration than required to inhibit locomotion. We propose an uptake pathway for aldicarb, levamisole, peptide mimetics and other soluble molecules by retrograde transport along dendrites of chemoreceptive neurons to the cell bodies and synapses where they act. This may prove to be a general mechanism for the low-dose effects of some nematicides and anthelmintics.

The tick-borne protozoan parasites Theileria parva and Theileria annulata cause economically important diseases of cattle in tropical and sub-tropical regions. Because of shortcomings in disease control measures based on therapy and tick control, there is a demand for effective vaccines against these diseases. Vaccines using live parasites have been available for over two decades, but despite their undoubted efficacy they have not been used on a large scale. Lack of infrastructure for vaccine production and distribution, as well as concerns about the introduction of vaccine parasite strains into local tick populations have curtailed the use of these vaccines. More recently, research has focused on the development of subunit vaccines. Studies of immune responses to different stages of the parasites have yielded immunological probes that have been used to identify candidate vaccine antigens. Immunisation of cattle with antigens expressed in the sporozoite, schizont or merozoite stages has resulted in varying degrees of protection against challenge. Although the levels of protection achieved have not been sufficient to allow exploitation for vaccination, there are clearly further lines of investigation, relating to both the choice of antigens and the antigen delivery systems employed, that need to be pursued to fully explore the potential of the candidate vaccines. Improved knowledge of the molecular biology and immunology of the parasites gained during the course of these studies has also opened up opportunities to refine and improve the quality of live vaccines.

Parasites are increasingly recognized for their profound influences on individual, population and ecosystem health. We provide the first report of gastrointestinal parasites in gray wolves from the central and north coasts of British Columbia, Canada. Across 60 000 km2, wolf feces were collected from 34 packs in 2005–2008. At a smaller spatial scale (3300 km2), 8 packs were sampled in spring and autumn. Parasite eggs, larvae, and cysts were identified using standard flotation techniques and morphology. A subset of samples was analysed by PCR and sequencing to identify tapeworm eggs (n=9) and Giardia cysts (n=14). We detected ⩾14 parasite taxa in 1558 fecal samples. Sarcocystis sporocysts occurred most frequently in feces (43·7%), followed by taeniid eggs (23·9%), Diphyllobothrium eggs (9·1%), Giardia cysts (6·8%), Toxocara canis eggs (2·1%), and Cryptosporidium oocysts (1·7%). Other parasites occurred in ⩽1% of feces. Genetic analyses revealed Echinococcus canadensis strains G8 and G10, Taenia ovis krabbei, Diphyllobothrium nehonkaiense, and Giardia duodenalis assemblages A and B. Parasite prevalence differed between seasons and island/mainland sites. Patterns in parasite prevalence reflect seasonal and spatial resource use by wolves and wolf-salmon associations. These data provide a unique, extensive and solid baseline for monitoring parasite community structure in relation to environmental change.

Paramphistomoids are ubiquitous and widespread digeneans that infect a diverse range of definitive hosts, being particularly speciose in ruminants. We collected adult worms from cattle, goats and sheep from slaughterhouses, and cercariae from freshwater snails from ten localities in Central and West Kenya. We sequenced cox1 (690 bp) and internal transcribed region 2 (ITS2) (385 bp) genes from a small piece of 79 different adult worms and stained and mounted the remaining worm bodies for comparisons with available descriptions. We also sequenced cox1 and ITS2 from 41 cercariae/rediae samples collected from four different genera of planorbid snails. Combining morphological observations, host use information, genetic distance values and phylogenetic methods, we delineated 16 distinct clades of paramphistomoids. For four of the 16 clades, sequences from adult worms and cercariae/rediae matched, providing an independent assessment for their life cycles. Much work is yet to be done to resolve fully the relationships among paramphistomoids, but some correspondence between sequence- and anatomically based classifications were noted. Paramphistomoids of domestic ruminants provide one of the most abundant sources of parasitic flatworm biomass, and because of the predilection of several species use Bulinus and Biomphalaria snail hosts, have interesting linkages with the biology of animal and human schistosomes to in Africa.

Schistosomiasis is a health problem in Brazil and the role of rodents in maintaining the schistosome life-cycle requires further clarification. The influence of Schistosoma mansoni on a population of Nectomys squamipes was studied by capture-recapture (1st phase, from June 1991 to November 1995) and removal (2nd phase, from April 1997 to March 1999) studies at Sumidouro, Rio de Janeiro, Brazil. During both phases coproscopic examinations were performed. At the 2nd phase the rodents were perfused and worms were counted. The population dynamics of parasites was studied. During the 1st phase, female reproductive parameters, longevity, recruitment and survivorship rates and migration patterns were studied in relation to schistosome prevalence. Water contamination (source of miracidia), abundance intermediate host and rodent migration were related to prevalence. The N. squamipes population was not obviously influenced by the infection, as shown by the high number of reproductive infected females, high longevity of infected individuals and the absence of a relationship between recruitment or survivorship rates and the intensity of schistosome infection. The data indicate that N. squamipes can increase transmission of S. mansoni in endemic areas and carry it to non-infected areas. Furthermore, this rodent can be used as an indicator of a transmission focus.

Analysis of egg and worm counts of Ascaris recorded at various intervals following a mass anthelmintic treatment programme in a South Indian fishing community is presented. Three indices of infection in the community are compared, namely the prevalence and intensity of egg output (at 2, 6 and 11 months following treatment) and the number of worms expelled following an 11 month period of reinfection. Detailed examination of these measurements revealed significant associations with patient sex and age. The age-prevalence profile of Ascaris infection changed little over time (except immediately following treatment) with the peak prevalence found in the 5–9 year age group. Although 85% of both males and females harboured Ascaris initially, the prevalence following 11 months reinfection was decreased, due to a significantly lower proportion of males being reinfected. By the 11th month of reinfection, the age-intensity profiles of egg output were similar to those observed at initial treatment in the older age groups (10 years and above) and in male children (< 10 years). However, a dramatic increase in the egg output of female children, greatly exceeding the initial mean, was observed within a 6 month period of reinfection. The intensity of egg output did not accurately reflect the abundance of Ascaris recovered via drug-induced expulsion following an 11 month period of reinfection. Although the egg output attained preintervention levels, the average worm intensity reached only half the initial value. The trends in the sex- and age-intensity profiles were consistent at the two sampling dates and showed similar patterns to the egg output curves. The relevance of the results to helminth control and the monitoring of reinfection is discussed.

Programmes to control Ascaris lumbricoides, Trichuris trichiura and hookworm infections have often been targeted at each infection separately, but the advent of benign and broad-spectrum anthelmintics suggests that combined control ma be feasible. The extent to which the infections co-occur in communities will determine the need for, and potential benefits of, such a combined approach. This paper examines the comparative distribution of the three geohelminths in different geographical areas and shows that A. lumbricoides and T. trichiura have closely related distributions, while hookworm infection is largely independent of the other two. These results indicate that many communities are at risk of disease from infection by more than one species of helminth. The similar distributions and epidemiological characteristics of A. lumbricoides and T. trichiura suggest that simultaneous control of these two parasites by the same strategy would be feasible and highly beneficial to communities. Multiple species control strategies which aim to control hookworm infection may require a more complicated protocol with more precise locality targeting.

Cysteine proteinases from the fruit and latex of plants, including papaya, pineapple and fig, were previously shown to have a rapid detrimental effect, in vitro, against the rodent gastrointestinal nematodes, Heligmosomoides polygyrus (which is found in the anterior small intestine) and Trichuris muris (which resides in the caecum). Proteinases in the crude latex of papaya also showed anthelmintic efficacy against both nematodes in vivo. In this paper, we describe the in vitro and in vivo effects of these plant extracts against the rodent nematode, Protospirura muricola, which is found in the stomach. As in earlier work, all the plant cysteine proteinases examined, with the exception of actinidain from the juice of kiwi fruit, caused rapid loss of motility and digestion of the cuticle, leading to death of the nematode in vitro. In vivo, in contrast to the efficacy against H. polygyrus and T. muris, papaya latex only showed efficacy against P. muricola adult female worms when the stomach acidity had been neutralized prior to administration of papaya latex. Therefore, collectively, our studies have demonstrated that, with the appropriate formulation, plant cysteine proteinases have efficacy against nematodes residing throughout the rodent gastrointestinal tract.

A 3-step procedure for cloning Theileria parva parasites was developed. The first step involved the in vitro infection of a fixed number of bovine lymphocytes with titrated sporozoites. The cell lines obtained from infections initiated using sporozoite/lymphocyte ratios below 1:100 were then selected for cloning as these contained schizont-infected cells, each of which was derived from infection with a single sporozoite. In the second step, these cell lines were cloned by limiting dilution. As sporozoites infect lymphocytes and transform to induce clonal multiplication, this step produced infected cell lines containing both cloned parasites and cloned lymphocytes. In the third step, the cloned cell lines were used to infect cattle and isolation of the parasite in ticks was made during piroplasm parasitaemia. Finally, sporozoites were harvested from infected ticks and used for further characterization. Sporozoites derived from cloned cell lines of T. parva Muguga, Marikebuni, Boleni, Uganda and buffalo-derived 7014 were characterized using monoclonal antibody profiles, DNA restriction fragment length polymorphism detected using repetitive and telomeric probes, in vivo infectivity and, in one case, cross-immunity studies. Additionally, several distinct schizont-infected lymphocyte clones were isolated from the Muguga, Mariakani and buffalo-derived 7014 stocks. The combined results of the characterization revealed that the cloning procedure selected clones of T. parva from the parental stocks which were known to contain a mixture of genetically different parasite populations. The cloning method and the clones generated will be of value in studies of the biology of the parasite and in elucidating the strain specificity of immune responses in cattle.