Toxocara genettae sp.nov. and Toxocara sprenti sp.nov. from viverrid hosts in Africa and S.E. Asia respectively are described. Seven Toxocara spp. from viverrid hosts are differentiated. The writer proposes that Toxocara canarisi Puylaert, 1967, from a feline host, become a species inquirendae requiring further study.

The effect of ambient temperature on the ability of Moniliformis dubius to become established in the intermediate host Periplaneta americana, and the effect of temperature on the rate of development of the parasite, has been investigated. Development is postponed at temperatures below 20 °C and infection does not normally occur at 37 °C, the parasites possibly being unable to avoid the defence mechanisms of the host. Both temperatures are tolerated by the host. A marked temperature dependence of rate of development is observed.

Trypanosomes are consistently present in the milk of lactating mice with primary phase T. cruzi infections (Peru strain). The infection is transmitted to the young, although rarely, mainly due to the difficulty of establishing infection via the oral route. Lactating females which had recovered from the primary phase of T. cruzi infection consistently transferred antibody to their young during suckling. The antibody in the serum of the young and milk of the mother was detectable by the indirect fluorescent antibody technique. In the case of the Peru strain the presence of antibody transferred to the young in this way correlated with very good protection against T. cruzi. Antibody transferred to the young was no longer detectable 6 weeks after birth. The indirect fluorescent antibody technique using bloodform antigen proved specific and highly sensitive throughout, giving prolonged and comparably high titres in mice infected with chronic and acute strains of T. cruzi.

Mice which have recovered from infections with P. atheruri are immune to challenge with the homologous parasite and are also strongly resistant to challenge with P. v. chabaudi and, to a lesser extent, B. rodhaini, B. microti and P. b. yoelii. There is little protection against P. v. vinckei and none against P. b. berghei. In the reciprocal experiments, the greatest degree of protection against P. atheruri occurs after P. v. chahaudi infections but over two-thirds of mice are protected by B. rodhaini or B. microti, half by P. v. vinckei or P. b. berghei but hardly any by P. b. yoelii. The considerable degree of cross-protection which exists between P. atheruri and P. chabaudi can be correlated with some antigenic similarities between these parasites but these are not greater than those of parasites which do not protect against one another.

Plasmodium vinckei chabaudi (which has a 24 h cycle with high synchronicity) has a peak of schizogony in the early morning at about 02.00–04.00. This cycle is orientated to the cycle of the host (mouse or thamnomys). The male gametocytes become ripe for exflagellation in a well-marked wave from 22.00 to 08.00 with peak about 00.00–04.00. This timing presumably corresponds to the hours when the vector mosquitoes are most likely to suck blood, and it is adapted to facilitate transmission. The male gametocytes remain ripe for exflagellation for a mean period of about 6 h and then apparently degenerate.

Two new species of the genus Hoplopleura are described from two closely related species of the genus Mus. H. ramgarh sp.nov. was found parasitizing Mus platythrix Bennett, 1932, in the Western Himalayan region in North India and in the Western Ghats in Peninsular India. H. sinhgarh sp.nov. was found parasitizing a species of the genus Mus, closely related to M. platythrix, and occurring sympatrically with it. The exact taxonomical status of this rodent species is still under investigation. The occurrence of two distinct species of lice on closely related sympatric populations of these mice has given an indication of their being two distinct taxa, a fact later supplemented by some consistent but not easily delineable skin and skull characters.

Mice which have recovered from infections with A. garnhami do not succumb to; challenge with the piroplasms B. rodhaini or B. microti and over half such animals are protected against the malaria parasites P. v. vinckei and P. v. chabaudi. This protection does not extend to the malaria parasites P. b. berghei or P. b. yoelii. Mice which have recovered from infections with the piroplasms are protected against A. garnhami, as are those which have recovered from infections with P. v. vinckei or P. v. chabaudi. About half the mice which have recovered from infections with P. b. berghei or P. b. yoelii are also protected against A. garnhami. This interaction between intra-erythrocytic protozoa may influence the incidence of these parasites in the wild. A. garnhami is unlikely to be of any use in the immunization of humans against malaria but could be of use in the protection of cattle against piroplasmosis.

A 37-spined Egyptian echinostome, Echinostoma liei sp.nov., is described in adult and larval stages. The parasite develops readily in the laboratory in chicks and ducklings, hamsters and rats. Its natural final host in or near irrigation ditches of the Nile delta involves the roof rat, Egyptian giant shrew and aquatic bird hosts. Developmental forms are described from infection of the NIH strain of Biomphalaria glabrata in the laboratory. B. alexandrina, is infected in the normal habitat in Egypt and contains both developmental stages in the heart or aorta and the hepatopancreas, and metacercariae encyst in the pericardium and kidney. E. liei sp.nov. is one of six very similar species characterized by 37 collar spines with a pattern of (3 + 2) corner spines in each lappet, six laterals on each side, and 15 dorsals in alternating rows; two pairs of dorsoventral and one small pair of ventro-lateral finfolds on the cercarial tail; and rodlike cystogenous material filling the cercarial encystation glands. In addition to distinctive intermediate-host specificity, differentiating characteristics of E. liei cercariae include presence of six sets of three flame cells each per side (total 36), seven oesophageal cells, eight penetration gland outlets on the dorsal lip of the oral sucker, and an absence of paraoesophageal gland cells as determined by intravital dyes. Significance of these and other cercarial traits is emphasized to aid in defining highly similar, but none the less distinct, sibling species.

Groups of R. appendiculatus ticks infected with T. parva were irradiated at doses varying from 0 to 32 krad and then applied to rabbits; 3 and 4 days later their salivary glands were removed, processed and examined. Increasing doses of irradiation resulted both in a decreased infection rate of ticks and a decrease in the number of parasite masses observed in infected ticks. No normal parasite masses were seen after doses of 4 krad or above.

Echinostoma liei, a newly described 37-spined eehinostome from Egypt, was tested against two trematodes in paired infections in the snail host, Biomphalaria glabrata (NIH strain). E. liei, when matched with the highly predacious Brazilian echinostome Paryphostomum segregatum, was dominated by the latter's predatory rediae. Pre-existing E. liei infections were destroyed, although the P. segregatum infection was itself delayed in development by an unidentified ‘indirect antagonism’ elicited by the E. liei larvae. In concurrent exposures with the two species, or with E. liei challenge of an established P. segregatum infection, the E. liei miracidia penetrated the snail, but the infection did not become established. When E. liei and S. mansoni were paired, the former species dominated. Exposure of snails already infected with E. liei to miracidia of S. mansoni slowed growth of the latter and the schistosome sporocysts eventually disintegrated without producing cercariae. When E. liei miracidia were exposed to snails with S. mansoni infections of different ages, the echinostome became established but developed slowly. Subsequently, however, it destroyed the schistosome infection. Although E. liei is itself quickly eliminated by P. segregatum, the two species appear almost equal in anti-schistosome capacity. This can be credited in part to a deleterious or lethal effect of the E. liei-schistosome combination on the host snail, as well as to a direct anti-schistosomal effect. Greater knowledge of this host-inter-trematode balance may permit the use of trematodes to attack infected snails and their parasites in regions hyperendemic with human schistosomiasis.

Mice which have recovered from, infections with Trypanosoma musculi exhibit no immunity to challenge with the malaria parasites, Plasmodium v. vinckei, P. v. chabaudi, P. b. berghei, P. b. yoelii or P. atheruri, the piroplasms Babesia rodhaini or B. microti or the dactylosomid Anihemosoma garnhami. Recovery from infections with any one of these parasites confers no immunity against T. musculi. These results indicate that heterologous immunity between intra-erythrocytic protozoa does not extend to trypanosomes.

(1) Simulium ornatum larvae were regularly collected from the River Lea (Hertfordshire) and from Tilling Bourne (Surrey) during 1967–9. Preliminary surveys revealed no parasitism in pupal and adult stages of S. ornatum but several parasites, some common, occurred in the Simulium larvae. These were studied by dissection, smears and histologically. (2) Microsporida were well represented by two genera - Thelohania and Plistophora. Infection rates never exceeded 9% of larvae. Spore measurements statistically evaluated from different larval infections justified recognition of five species of Thelohania (T. minuta sp.nov., T. bertrami sp.nov., T. canningi sp.nov., T. simulii sp.nov., and T. avacuolata sp.nov.), and two species of Plistophora (P. tillingbournei sp.nov. and P. leasei sp.nov.). (3) Intra-epithelial organisms of the larval gut wall, referred to provisionally as Microsporidan-like bodies, caused light infections. (4) With the exception of the slight Microsporidan-like infections, all species of Microsporida were found parasitizing the fat body of the larva, causing its disintegration. Delay in larval growth and pupation occurred, followed by death. (5) Seasonal cycles of abundance of infection were related to summer and overwintering populations of Simulium larvae. (6) Transmission of infection was attempted by exposing apparently uninfected wild-caught Simulium larvae to spores of Thelohania but no evidence of active infection being established in the exposed larvae was obtained. (7) Although the pathogenic Microsporida taken in this study must have exerted control on natural larval densities, too little is known of their biology, mode of transmission or methods of culture to envisage their development, for biological control of simuliids, at present.

The effect of host age on the course of infection of Raillietina cesticillus in the chicken has been investigated. It was found that male hosts become resistant to the cestode with increasing age. This resistance manifests itself in an increased rate of destrobilization and consequent loss of scolices and in a decreased rate of growth of the worms. The cestodes are distributed over a greater length of intestine in old than in young birds. In female hosts age resistance develops more rapidly than in males until the birds are 84 days old and from this age onwards the manifestations of resistance decline. The possible factors responsible for age resistance to R. cesticillus are discussed.

(1) Spermophilus columbianus, S. franklinii, S. lateralis tescorum, S. richardsonii, S. tridecemlineatus and s. undulatus plesius (ground squirrels) were collected from Alberta and Yukon Territory (S. u. plesius only), Canada. Trypanosome infections were detected in all but S. l. tescorum. (2) All six species of squirrels were experimentally inoculated with trypanosomes from naturally infected S. columbianus, S. franklinii, S. richardsonii and S. tridecemlineatus. The strains from S. columbianus, S. richardsonii and S. tridecemlineatus produced infections in some or all of the other host species, whereas the strain from S. franklinii did not. (3) Natural transmission of trypanosomes has not been demonstrated, but it seems likely that fleas act as vectors. (4) Intensities and durations of experimental infections were variable and depended upon the trypanosome strain, host species and individual. Infections were non-pathogenic. (5) Previously infected ground squirrels could not be reinfected with the same or a different trypanosome strain and immunity appeared to be lifelong. (6) Size comparisons among and within trypanosome strains from naturally and experimentally infected ground squirrels revealed that the strains from S. franklinii and S. tridecemlineatus were similar to one another, but different from the other three trypanosome strains (those from S. columbianus, S. richardsonii and S. undulatus). (7) It is suggested that there is only one species of trypanosome, Trypanosoma otospermophili, in the genus Spermophilus in North America and that differences in size and types of infection are due to host-induced variations (i.e. they are plastoxenodemes). T. spermophili (present in Eurasian Spermophilus spp.) might be synonymous with T. otospermophili.

Some monocystids of British earthworms are widely distributed, occurring in hosts which were collected from different parts of the country, whereas others are localized or irregularly distributed. Only nine of the 45 monocystids identified from British earthworms have been reported from similar hosts collected from France, Germany and Sweden. Fourteen others occur in similar hosts collected from one or two of the continental countries and the remaining 22 monocystids appear to be completely absent from continental earthworms.

The course of infection of Raillietina cesticllus in the chicken has been studied and information is presented on proglottid output, the dynamics of infection and the distribution and growth of the cestode. A posterior migration of young cestodes during the first 7 days of infection was confirmed and a progressive destrobilization of the worms was observed with complete destrobilization occurring 70 days after infection. No regeneration of strobilae occurs and the scolices are eventually eliminated. A marked difference in the rate of destrobilization in the two host sexes was noted.

Saponin treatment of cercariae and schistosomula alters the surface membrane so that it may be sheared from the organism and isolated as fragments by centrifugation. Saponin-calcium chloride treatment or freezing and thawing of adult worms removes the surface membrane, which can be washed from the bodies and collected by centrifugation. The small quantities of material available necessitated the development of a sensitive technique for detecting the proteins in the membranes. The surface membranes were radioiodinated after butan-1-ol extraction and electrophoresed in polyacrylamide gel. Adult surfaces prepared by the saponin-calcium chloride and by the freezing and thawing technique had identical protein components, detected as gel-cut profiles or in autoradiographs. The quantity of a rapidly migrating PAS-positive amido black negative component was greater in the surfaces prepared by saponincalcium chloride than in the frozen and thawed surfaces. This component contains lipid, some of which may be glycolipid. It was largely absent from the surface membranes of cercariae and schistosomula. Cercarial surface membranes contained a major protein component which was absent from the surface membranes of schistosomula. Otherwise the surface membranes of the cercariae were identical to those of the schistosomula in their protein components. The rate of incorporation of freshly synthesized protein per unit area of surface membrane of schistosomula was very low in the first 5 days in culture, after which there was a very rapid increase to a maximum rate on the 15th day. After this time, the rate of protein synthesis decreased to a low level at 26 days. In these studies the activity per unit area was measured and this would not be expected to vary greatly during growth. The biological significance of the observed variation in protein incorporation into the membrane is unclear.

During the summers of 1969–71, 554 ground squirrels belonging to six species (115 Spermophilus columbianus, 46 S. franklinii, 13 S. lateralis, 327 S. richardsonii, 20 S. tridecemlineatus and 33 S. undulatus) were sampled for trypanosomes. Natural infections were recorded in all but S. lateralis. In 1969 and 1970 the prevalences of infection were approximately equal within, but varied between each species of ground squirrel. In 1971 the prevalences of infection increased for all host species sampled. Trypanosomiasis was detected in twice as many ground squirrels when the haematocrit centrifuge technique was used for diagnosis instead of stained thin blood films. In S. richardsonii the prevalences of infection varied from month to month but showed the same trends in both 1969 and 1970. Prevalence was lowest in May and highest in June. It is suggested that susceptible juveniles accounted for the high prevalence in June.

A trypanosome identified as Trypanosoma (Schizotrypanum) dionisii Bettencourt & França, 1905, has been isolated from Pipistrellus pipistrellus (Chiroptera) in England. At least five out of eight P. pipistrelhis were infected. 2. In the blood of P. pipistrelhis, the parasite closely resembled T. (S.) cruzi. When grown in vitro in monophasic or diphasic media at 28°C, epimastigotes and trypomastigotes developed. The latter were of two types — very long, thin forms and less numerous shorter individuals. 3. The trypanosomes multiplied as amastigotes within HeLa and mouse L cells in vitro. After 6–9 days in HeLa cells at 37°C, they transformed into small trypomastigotes and emerged from the cells. Higher infection rates (up to about 4%) were obtained in cell cultures inoculated with flagellates from older monophasic cultures, which contained more of the long, slender trypomastigotes. 4. Trypanosomes also entered (or were phagocytosed by) up to 60% or more of mouse peritoneal macrophages in vitro. Multiplication occurred by binary and multiple fission of amastigotes in at least some of the parasitized macrophages and transformation into trypomastigotes was seen after 7 or more days at 37°C. Development in macrophages was less synchronous than in HeLa cells.

The ultrastructure of the normal caecum of chickens and of chickens infected with Trichomonas gallinarum has been investigated. In infected caeca some villi and crypts of LieberkÜhn appear normal whereas others show marked changes in structure of the epithelial cells. The most obvious changes are loss of microvilli and glycocalyx and an increase in number of vesicles which stain metachromatically with Azur II. T. gallinarum has been detected between epithelial cells and in the lamina propria. Bacteria often, but not always, accompanied the protozoa in the tissues.