Trypanosoma congolense: Natural and acquired resistance in the bovine

A total of 42 animals of various ages were infected with Trypanosoma congolense to investigate age resistance. Ten of eleven animals between 4 months and 1 year of age survived the infection without treatment. Two of eleven animals in the age range of 1 to 2 years also survived the infection whereas all 20 animals between 2 and 5 years of age died or needed treatment to survive. Young animals which needed no treatment to survive were refractive to challenge for at least 1 year after their last patent parasitemia. Older animals which required treatment to survive were also challenged at intervals after therapy. Three animals infected for 49 to 75 days before treatment were rechallenged 198 to 296 days later. Extensions in prepatent periods ranged from 5 to 13 days when compared to controls and the resulting infections were of a relapsing nature followed by self-cure. Effects of this disease on clinical parameters of previously infected animals were minimal. One animal infected for 196 days and rechallenged 501 days later had a prepatent period of 14 days as compared to 5 days for controls. This animal developed a brief relapsing infection followed by self-cure. Animals which were infected for periods of 41 to 77 days, received treatment, and were then rechallenged from 600 to 900 days later, showed some resistance to infection. Prepatent periods were extended from 1 to 3 days over those of control animals and although the resulting disease was severe, one of four animals self-cured without treatment. When animals which had self-cured primary challenges were rechallenged at periods up to 2 years later, they were completely refractory. When 12 animals which were presumed to be immune to syringe-passaged T. congolense were challenged by tsetse fly bite with the same strain of trypanosome, an appreciable immunity was evident. Five of twelve immune animals did not become patent while the other seven developed mild infections without severe clinical signs. All nine controls developed severe infections with eight requiring treatment to survive. When animals immune to the Trans-Mara I strain of T. congolense were challenged either by syringe or tsetse fly bite with a heterologous strain of T. congolense obtained from a different geographical area, no evidence of immunity was detected.     

Trypanosoma cruzi: Role of different antibody classes in protection against infection in the mouse

Immune serum obtained from mice with a chronic infection of Trypanosoma cruzi was fractionated on Sephadex G-200 or on protein ASepharose 4B. Mice were infected with a standard infective dose of T. cruzi 24 hr after injection with either IgM, IgG, IgG1, or IgG2 + IgG3 fractions. Mice were also pretreated with immune serum depleted by affinity chromatography of either IgG2a, IgG2b, or both subclasses before infection with T. cruzi. Control mice were pretreated with normal mouse serum or immune serum depleted of IgG. The parasitemia and survival of the animals were determined and used as parameters of protection. The results of these experiments demonstrated that the protective antibodies were mostly IgG2 and seem to be preferentially located in IgG2b subclass. IgM and IgG1 fractions were very little, if any, protection.     

Plasmodium berghei: Isolation and maintenance of an irradiation attenuated strain in the nude mouse

An attenuated strain of malaria causing limited parasitemia in mice was derived from a highly virulent strain of Plasmodium berghei (NK65) which produced 100% lethality in mice. A pool of mouse blood infected with the original highly virulent P. berghei was exposed to 40 Krad irradiation and parasites were inoculated into nude mice as well as into thymus competent normal littermates. Thymus competent mice showed no parasitemia, while one out of the five nude mice inoculated with the irradiated parasites developed a slow and progressive parasitemia. These parasites induced a self-limiting parasitemia in thymus competent mice, even when a large inoculum was administered. Maintenance of the low virulence strain required passage through nude mice. After 50 passages at two weekly intervals, reversion to virulence did not occur. A single vaccination with the attenuated strain induced immunity in mice against a challenge inoculation with the original virulent strain. Specific IgG persisted at high titer for more than 9 weeks in mice receiving a single inoculation of the attenuated strain.     

Plasmodium yoelii: Antibody and the maintenance of immunity in BALB/c mice

Subpatent persistence of parasitemia was detected for up to 7 weeks after infection of BALB/c mice with Plasmodium yoelii. Serum taken from recovered mice maintained parasitemias in recipient mice at a subpatent level when transferred repeatedly at 2-day intervals. Single doses of serum from convalescent donors delayed the course of infection in recipients. Small doses of transferred hyperimmune serum had the same effect, whereas large doses (>0.5 ml) totally suppressed parasitemia. Only a single secondary challenge of recovered mice was required in order to produce a maximally protective hyperimmune serum. Mice completely protected from a primary challenge with P. yoelii by transfer of hyperimmune serum were not at all resistant to a second challenge given some weeks later. After transfer of hyperimmune serum into mice with established P. yoelii infection, parasitemia fell to subpatent levels within 48 hr. During the first 21 hr after serum transfer, a progressive reduction in the proportion of ring forms present in blood smears was observed.     

Leishmania enriettii: Immune induction of macrophage activation in an experimental model of immunoprophylaxis in the mouse

This study describes some of the parameters of the cellular immune response elicited in mice by inoculation of the nonpathogenic protozoan parasite, Leishmania enriettii. Incubation in vitro of leishmania-infected mouse peritoneal macrophages with spleen cells from syngeneic leishmania-immune animals resulted in activation of the phagocytes, leading to intracellular parasite destruction. Activation required interaction of sensitized lymphocytes with parasite antigen released or displayed by infected macrophages. The effect was dependent both on the dose of parasites used for in vivo priming and on the number of spleen cells cocultivated with parasitized macrophages. The activating capacity of lymphocytes was abrogated by anti-Thy-1 antiserum treatment and was retained in the effluent cells after nylon-wool separation. Activation was followed by lysis of part of the macrophage monolayer. Destruction of the phagocytes did not appear to result from the activation process per se and may represent a cytotoxic activity of sensitized lymphocytes for macrophages bearing parasite antigen on their surface.     

Giardia muris: Correlation between oral dosage,course of infection,and trophozoite distribution in the mouse small intestine

Oral inoculations of Giardia muris cysts to CD-1 Swiss mice resulted in a reproducible pattern of infection measured by cyst excretion and the number of trophozoites in the small intestine. Housing of animals together or individually did not alter the pattern of cyst release for the first 30 days of infection. Administration of 10 to 10⁵ cysts/mouse resulted in a similar rate of cyst excretion from Day 10 to the end of the infection period. There was a direct correlation between the size of inoculum and the length of the latent period. Mice which received larger doses (10³, 10⁴, 10⁵) had significantly higher numbers of cysts in feces during the first week of infection, compared to those which received lower doses (10 or 100). The extent of trophozoite colonization and their distribution in the small intestine was not related to the size of inoculum. The location of trophozoites in the small intestine varied during the infection. In the first 3 to 8 days of infection the trophozoites were situated in the upper 25% of the small intestine, but moved posteriorly (upper 40%) during the period of peak cyst output. The number of trophozoites in the small intestine and cyst excretion were found to be proportional at all stages of infection.     

Leishmania tropica: Association of a B-cell mitogen with hypergammaglobulinemia in mice

Infection of BALB/c mice with Leishmania tropica NIH S strain resulted in splenic enlargement, hypergammaglobulinemia, and polyclonal activation of B lymphocytes as measured by the splenic plaque-forming cell response (PFC) to trinitrophenyl (TNP) and sheep erythrocytes (SRBC). The peak anti-SRBC PFC response occurred 5 weeks after infection; both direct and indirect (facilitated) plaques were significantly increased. The in vitro primary immune response to trinitrophenyl haptenated lipopolysaccharide (TNP-LPS), as enumerated by the anti-TNP PFC response, was also increased on a per-spleen basis beginning 3 weeks after infection. The properties of a lysate of L. tropica promastigotes (LTL) was studied to determine whether polyclonal B-cell activation was related to a parasite-derived mitogen. A B-cell mitogen was identified in LTL which stimulated the proliferation of spleen cells in vitro from uninfected control and congenitally athymic (T-cell-deficient) but not from μ-suppressed (B-cell-deficient) animals. Preliminary characterization of the mitogen material indicated that it was a nonpyrogenic, heat-labile peptide or protein and was probably not bacterial lipopolysaccharide (LPS).     

Trypanosoma lewisi: Enhanced resistance in naive lactating rats and their suckling pups

Lactating rats and their suckling offspring were shown to have a naturally occurring resistance to Trypansoma lewisi which was greater than that seen in normal adult rats and was not dependent on previous exposure to the parasite. In the case of the pups maximum protection was dependent on suckling being the sole source of nutriment and also on the peak of the parasitemia falling within the nursing period. Supplementary solid food reduced survival rates in concurrent Hemobartonella muris—T. lewisi infections: pups infected at 10 days of age and totally dependent on nursing showed 82.5% survival but only 6.6% survival when solid food was allowed to supplement milk. However, supplementary food did not reduce survival in pups infected with only T. lewisi. When pups were totally dependent upon nursing until the normal time of weaning (21 days of age), infection with H. muris—T. lewisi at the following days of age allowed the indicated mean survival rates: 10 days (82.5%), 20 (32.5%), 30 (14.3%), and 40 (100%). Infection with T. lewisi alone at the following days of age allowed the indicated mean survival rates: 10 days (100%), 15 (76%), 17 (52%), 20 (100%), and 30 (100%). Lactating rat serum agglutinated “adult forms” of T. lewisi, which correlated well with the observed sudden resolution of parasitemia in lactating animals at the time of the antigenic transition from “juvenile” to “adult” type. The “adult” stage parasitemia in suckling pups was selectively reduced when compared to that of nonlactating adult rats. The lactating rat serum factor could be passively transferred with lactating rat serum to animals already weaned.     

Eimeria nieschulzi and Trichinella spiralis: Analysis of concurrent infection in the rat

The effects of concurrent primary infection of the rat with Eimeria nieschulzi and Trichinella spiralis on the number of oocysts of E. nieschulzi shed by the host and on the number, distribution, and fecundity of adult T. spiralis were analyzed. When rats were initially infected with E. nieschulzi followed 9 days later by infection with T. spiralis there occurred a significant decrease in the total numbers of adult worms in the small intestine, a significant shift in the position of these worms along the length of the small gut, a decrease in the fecundity of adult female worms, and a decrease in muscle parasitism when compared with rats infected with T. spiralis alone. When rats were initially infected with T. spiralis, followed 9 days later by infection with E. nieschulzi, there occurred a significant decrease in the numbers of oocysts shed over 24 hr on Days 7, 9, and 11 postinfection below that seen with rats infected only with Eimeria. These changes are discussed in terms of the enteropathophysiologic lesions and enteric inflammation known to occur during infections with these two parasites.     

Trypanosoma musculi and Trichinella spirails: Concomitant infections and selection for resistance genotypes in mice

Trypanosoma musculi infections were given to mice of different strains before, at the same time, and after an infection with 400 Trichinella spiralis. Examined parameters of the host response to T. spiralis were worm rejection, antifecundity responses, development of immunological memory, and muscle larvae burden. After dual infection, each mouse strain showed characteristic effects on resistance to T. spiralis. This was due to a dynamic interaction between the genes controlling rejection of T. spiralis and those influencing T. musculi growth. C3H mice develop high trypanosome parasitemias. This impairs worm expulsion and the development of memory to T. spiralis when Trypanosoma infections take place on the same day or 7 days before. The C57B1/6 mouse develops low parasitemias and T. musculi infections on the same day, or 7 days before T. spiralis, delaying worm rejection only slightly despite the overall weak capacity of B6 mice to expel worms. NFR-strain mice are strong responders to T. spiralis and also develop low parasitemias. Trypanosome infections on the same day, or after T. spiralis, produce a delay in worm rejection; the former is comparable to C3H mice. However, NFR mice alone showed enhanced rejection of worm when T. musculi infections preceded T. spiralis by 7 days. An unusual feature of C3H mice was that T. musculi infections 7 days before T. spiralis increased antifecundity responses at the same time that worm expulsion was inhibited. Trypanosome infections can therefore modulate distinct antihelminth immune responses in different directions simultaneously. The different outcomes of dual infections compared with single infections provides another selective mechanism by which genetic polymorphisms can be established and maintained in the vertebrate host.     

Trypanosoma vivax: Courses of infection with three stabilates in inbred mouse strains

The courses of infection in inbred mouse strains were compared following infection with three Stabilates of high, intermediate, and low virulence of Trypanosoma vivax stock Zaria Y486. Mouse strains could only be shown to differ in their resistance to T. vivax infections as judged by the height of the initial parasitemia and survival times when a trypanosome population of low or intermediate virulence was used. A T. vivax population of high virulence was uniformly lethal. Comparison of lytic antibody titers between groups of resistant ($\text{C}\text{57}\text{B}\text{1}\text{6}$) and susceptible ($\text{Balb}\text{c}$) mice did not show any significant differences in titers of the surviving mice but the mice in either group which did not control the initial parasitemia had lower lytic antibody titers than those which did. A significantly larger number of $\text{Balb}\text{c}$ mice failed to control the initial infection as compared to the $\text{C}\text{57}\text{B}\text{1}\text{6}$. Treatment with cyclophosphamide did not ablate differences in susceptibility between the two strains. The use of congenic mice showed that these differences in susceptibility were not related to differences in the major histocompatibility complex between these strains.     

Plasmodium chabaudi: Adoptive transfer of immunity with different spleen cell populations and development of protective activity in the serum of lethally irradiated recipient mice

Groups of lethally X-irradiated NIH mice were injected with either glass wool-filtered (g.w.) immune spleen cells or nylon wool enriched immune T cells from syngeneic mice immune to Plasmodium chabaudi, or g.w. normal spleen cells. After cell recipients were infected with P. chabaudi the three groups reached similar mean peak parasitaemias on Day 11. In passive transfer tests serum obtained from mice sacrificed at this time gave little protection compared to normal serum. On Day 14 g.w. immune spleen cell recipients had subpatent infections and enriched immune T-cell recipients had a lower mean parasitaemia than g.w. normal spleen cell recipients. Serum obtained on Day 14 from g.w. immune spleen cell recipients gave better protection after passive transfer than sera from enriched immune T-cell or g.w. normal spleen cell recipients. Day 14 serum from enriched immune T-cell recipients, but not from g.w. normal spleen cell recipients, produced some initial protection after passive transfer. These results suggest that the transferred immune spleen cells contributed to the observed humoral immunity in lethally irradiated recipient mice.     

Theileria parva: Kinetics of infection in the lymphoid system of cattle

The kinetics of infection with Theileria parva in cattle were studied by examining the total cellularity and numbers of parasites in a range of lymphoid organs from animals killed at intervals during the course of the infection. With the dose of T. parva stabilate used, macroschizonts were initially detected in the drainage lymph node about 7 days after inoculation and death of the host resulted on Day 18–19. Associated with the initial detection of parasites, there was a marked increase in cellularity of the drainage lymph node and a more gradual and less pronounced increase in cellularity of the other lymphoid organs. From about Day 12 onward, there was a gradual decrease in the cellularity in all of the lymphoid organs, so that in animals examined in the terminal stages of the infection there was often cellular depletion. The pattern of these cellular changes was similar in groups of Boran and Friesian cattle, although both the increase in cellularity and the terminal depletion were more marked in the Friesians. Blood leukocyte counts in infected Boran started to drop as early as Day 7 of infection and by Day 14 had reached values less than 25% of normal. Quantitation of parasitic schizonts indicated that the numbers of parasites in the lymphoid organs do not increase in a simple exponential manner. Rather, there appears to be an early rapid increase in parasite numbers followed by a phase of less rapid multiplication. Because of the marked changes which occured in total cellularity of the lymphoid organs during the course of the infection, a significant discrepancy was found between the replication rate of the parasite as calculated using total numbers of parasites and that obtained using schizont index (SI). These results indicated that the use of SI, as described in previous studies, is not a reliable method of determining the replication rate of the parasite.     

Elaphostrongylus rangiferi: Influence of temperature,substrate, and larval age on the infection rate in the intermediate snail host, Aarianta arbustorum

The infection rate of the first stage larval nematodes, Elaphostrongylus rangiferi, was studied experimentally, using the juvenile snail Arianta arbustorum as intermediate host. The nematode showed a linear, fivefold increase in infection rate within the temperature range of 4 to 28 C. The snails were exposed to the larval nematodes on three different substrates. The highest infection rate was recorded when snails were exposed in tap water and significantly slower infection rates were obtained when either lettuce or soil was used as the substrate. First stage larvae of E. rangiferi were infective for at least 2 months when stored at 12 C. Throughout this period, the infection rate showed a significant decline, while the motility of the larvae remained unchanged.     

Plasmodium berghei: Uptake and distribution of chloroquine in infected mouse erythrocytes

The capacity of mouse erythrocytes infected with Plasmodium berghei to accumulate chloroquine is developed with maturation of the parasites. This is shown by direct comparison of the early and mature stages, which are separated by density difference. After drug accumulation, infected cells were fractionated by saponin lysis or nitrogen decompression to study the drug distribution. Effectiveness of isolating intact parasites and host components was checked by SDS-polyacrylamide gel electrophoresis and by low leakage of parasite-specific lactate dehydrogenase used as a marker enzyme. At low external drug concentration (~10^?7M), chloroquine is principally accumulated in the parasites. However, at higher drug concentrations (~10^?5and ~10^?3M), the proportion of the drug found in the host cytosol fraction is increased. A small but significant proportion of the drug (<20%) is associated with the host cell membrane. The pellet fraction of the freed parasites, further fractionated by freeze-thaw lysis, contains a major proportion of the drug at low external concentrations. However, the pellet fraction obtained from prolonged sonication of the parasites, which contains the bulk of hemozoin pigment, carries only a small proportion of the drug. This indicates that parasite membrane components may bind most of the drug. As external chloroquine concentration is increased, the proportion of drug in the parasite supernatant increases, some or most of which is probably bound by soluble hemecontaining compounds. However, the presence of chloroquine in the parasite does not affect the partition of heme in particulate and soluble forms.     

Dipetalonema viteae: Microfilariae production in various mouse strains and in nude mice

Adult female Dipetalonema viteae worms obtained from hamsters were introduced beneath the dorsal skin of $\text{Balb}\text{c}$, $\text{C}{}_{57}\text{Bl}\text{6}$, and $\text{C}{}_3\text{H}\text{He}$ mice. The microfilaraemia from the transplanted worms in $\text{Balb}\text{c}$ mice was higher and persisted longer than in $\text{C}{}_{57}\text{Bl}\text{6}$, and in $\text{C}{}_3\text{H}\text{He}$ mice was intermediate between these two strains. The transplanted adult worms were killed earlier in $\text{C}{}_{57}\text{Bl}\text{6}$ compared to $\text{Balb}\text{c}$ mice; adult worms were killed before the microfilariae were cleared from the circulation. D. viteae infective larvae did not reach maturity in mice but when female worms were implanted into mice which had been infected with third-stage infective larvae 6 or 19 days previously, microfilarial production was inhibited. Outbred as well as inbred nude mice infected with 10 or 20 infective larvae died by Day 15, whereas the normal littermate control mice that received the same number of infective larvae remained alive and healthy. There was no difference in the duration and level of microfilaraemia from implanted female worms in outbred nudes and their heterozygous littermate control mice. In contrast, microfilaraemia in inbred $\text{Balb}\text{c}$ Nu+ was similar to that of inbred $\text{Balb}\text{c}\text{Nu}\text{Nu}$ only until Day 45; thereafter the microfilaraemia declined to zero around Day 160 in the Nu+, at which time it was still high and persisted longer in the $\text{Balb}\text{c}\text{Nu}\text{Nu}$. Transplanted adults were viable in inbred $\text{Balb}\text{c}\text{Nu}\text{Nu}$ for a longer time than in $\text{Balb}\text{c}$ Nu+. When infected, amicrofilaraemic nudes, littermate controls, and three strains of mice were challenged, a very low level short-lasting microfilaraemia resulted.     

Babesia microti: Infectivity of parasites from ticks for hamsters and white-footed mice

To compare the infectivity of tick-transmitted Babesia microti for natural and experimental hosts, we permitted parasitized nymphal Ixodes dammini to feed on white-footed mice (Peromyscus leucopus) and hamsters. About nine-tenths of infested mice developed patent infection, but only about one-half of the hamsters become parasitemic. Tick-bitten mice become parasitemic more rapidly, but parasites became more abundant in hamsters than in mice. More than 100,000 B. microti were present in the salivary glands of nymphal ticks that remained attached to rodents for 60 hr. These parasites were collected, diluted, and inoculated into mice and hamsters. The mean infectious dose for both experimental hosts was in the range of 10,000 to 25,000 salivarian parasites. Compared to experimental hosts, natural hosts were more susceptible to tick-transmitted infection, became parasitemic more rapidly, but developed less intense parasitemias. Paradoxically, natural and experimental hosts were similarly susceptible to measured inocula of salivarian parasites.     

Trypanosoma vivax: Absence of host protein on the surface coat

The possible presence of host serum proteins on the surface of Trypanosoma vivax stock Zaria Y486 was studied. Intact washed bloodstream forms from mice were not lysed or neutralized by antisera against mouse serum proteins. Serum against T. vivax prepared in rabbits against an antigen which was a water-soluble trypanosome extract, failed to cross-react with mouse serum when tested by immunoelectrophoresis and immunodiffusion. The T. vivax antigen failed to cross-react with three different anti-mouse sera when tested by the same techniques.Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analyses of ¹²⁵I-surface-labeled parasites showed the presence of a cluster of proteins ranging in molecular weights between 57,000 and 45,000 daltons. None of these proteins was precipitated by anti-mouse serum protein sera. The serum against T. vivax precipitated a protein of 50,000 daltons molecular weight.     

Plasmodium berghei: Premunition,sterile immunity,and loss of immunity in mice

Loss of immunity to Plasmodium berghei in mice was found to be correlated with the gradual clearance of parasites from circulating blood and from tissues; complete clearance apparently is followed by a period of residual sterile immunity. Starting with the day of challenge, the pattern of the time-dependent loss of immunity was the same in young adult and old mice, and was not influenced by previous challenges. Since the clearance of parasites from the peripheral blood occurred much faster in old mice, and in view of the observed similarity of clearance rates in different tissues, the period of residual sterile immunity in old mice is different from that in young adults.     

Trypanosoma cruzi: In vivo and in vitro correlation between T-cell activation and susceptibility in inbred strains of mice

The in vivo susceptibility of several inbred strains of mice to the Y and CL strains of Trypanosoma cruzi was compared to the in vitro ability of spleen cells from infected mice to generate factor(s) able to activate macrophages to a trypanocidal state. Spleen cells from resistant immune mice generate higher levels of the factor(s) and do so at earlier times during infection than those of susceptible mice. The spleen cells capable of generating the in vitro factor(s) are also capable of conferring resistance upon passive transfer. Removal of immunoglobulin-bearing cells from the immune spleen cell population did not affect either transfer of protection in vivo or generation of the factor(s) in vitro. The cellular basis underlying the differences between susceptible and resistant mouse strains has not yet been determined.