The treatment of mice with Lactobacillus casei induces protection against Babesia microti infection

In this study, we report that administration of Lactobacillus casei confers protection to mice against the intracellular protozoan Babesia microti. Mice treated with L. casei orally or intraperitoneally were inoculated 7 days later with an infectious dose of B. microti. Mice treated with lactobacilli showed significant reduction in the percentage of parasitized erythrocytes (PPE) compared to untreated mice. When mice were inoculated intraperitoneally with L. casei 3 or 0 days before challenge with B. microti, the PPE was significantly lower compared to untreated mice and there were no differences between treated mice and mice immune to B. microti infection. When mice treated with live or dead L. casei were compared to mice inoculated with Freund Complete Adjuvant before a B. microti infection, a significant reduction of PPE was observed. These results show the protective effect of L. casei administered to mice against a B. microti infection and suggest that it might act by stimulating the innate immune system.     

Genetic control of Propionibacterium acnes-induced protection of mice against Babesia microti.

Using various strains of inbred mice, we found that Propionibacterium acnes-induced protection against the hemoprotozoan parasite Babesia microti was controlled by a dominant gene(s) not linked to the major histocompatibility gene (H2) complex of mice. P. acnes-induced resistance to infection was not merely an amplification of the normal immune response to B. microti, since innate resistance to infection was controlled by different genes. Expression of the nonspecific protection induced by P. acnes was found to be transferable with cells of bone marrow origin, and it did not necessarily accompany the induction of hepatosplenomegaly. The implication of these results for the understanding of the mechanism of P. acnes-induced protection is discussed.     

Macrophages are critical for cross-protective immunity conferred by Babesia microti against Babesia rodhaini infection in mice

Although primary infection of mice with Babesia microti has been shown to protect mice against subsequent lethal infection by Babesia rodhaini, the mechanism behind the cross-protection is unknown. To unravel this mechanism, we investigated the influence of primary infection of mice with nonlethal B. microti using different time courses on the outcome of subsequent lethal B. rodhaini infection. Simultaneous infections of mice with these parasites resulted in rapid increases in parasitemia, with 100% mortality in BALB/c mice, as observed with control mice infected with B. rodhaini alone. In contrast, mice with acute, resolving, and chronic-phase B. microti infections were completely protected against B. rodhaini, resulting in low parasitemia and no mortalities. Mice immunized with dead B. microti were not protected from B. rodhaini infection, although high antibody responses were induced. Interestingly, the protected mice had significantly decreased levels of antibody response, cytokines (including gamma interferon [IFN-γ], interleukin-2 [IL-2], IL-8, IL-10, and IL-12), and nitric oxide levels after infection with B. rodhaini. SCID mice and IFN-γ-deficient mice with chronic B. microti infections demonstrated protective responses comparable to those of immunocompetent mice. Likewise, in vivo NK cell depletion did not significantly impair the protective responses. Conversely, macrophage depletion resulted in increased susceptibility to B. rodhaini infection associated with changes in their antibody and cytokines profiles, indicating that macrophages contribute to the protection against this challenge infection. We conclude that future development of vaccines against Babesia should include a strategy that enhances the appropriate activation of macrophages.     

Case report: spontaneous splenic rupture during acute parasitemia of Babesia microti

Babesia is a malaria-like protozoan parasite spread by Ixodes ticks primarily from the white-footed deer mouse to humans. Typically it causes subclinical disease, but occasionally causes acute febrile disease with hepatosplenomegaly. We report a case of spontaneous splenic rupture of a 56-yr-old man with acute Babesia microti infection.     

The effect of age on the infection and immunoresponsiveness of mice to Babesia microti

5he effect of age on the immunological responses to Babesia microti infection in the mouse was investigated. Aged mice experienced reduced and delayed peak parasitemias compared to younger animals; however, the old mice failed to clear the parasites from the blood and experienced fluctuating parasitemias until death. Babesiosis produced suppression of responses to nonspecific B and T cell mitogens concomitant with rising autoantibody plaque forming cells reactive with untreated and bromelain modified mouse erythrocytes. Similar observations of increased susceptibility to babesiosis with age and immunosuppression have been made in human babesiosis. Thus, the murine model for this hemoprotozoan infection is faithful to the human immunological responses.     

Babesia Microti感染鼠对Babesia Rodhaini再感染交叉免疫保护机理的研究

目的研究Babesia Microti和Babesia Rodhaini感染的交叉免疫保护作用,以探讨B.Microti和B.Rodhaini不同种属之间是否存在交叉保护及保护机制。方法首先制备Babesia Microti感染耐过鼠,再用Babesia Rodhaini进行再感染,分别于B.Rodhaini再感染后的12、24、48、72h,使用ELISA方法分别检测血清中IL-12及IL-10的浓度,并同时检测寄生虫血症、网织红细胞变化、致死率与死亡时间。结果B.Microti感染耐过鼠再感染Babesia Rodhain后24h,小鼠血液中IL-12较未感染组及B.Microti感染耐过鼠明显增高,而血液中IL-10水平在再感染后72h时与对照组比较差异显著。B.Microti感染耐过鼠再感染Babesia Rodhain后,血液中出现一过性寄生虫血症,实验鼠可完全耐过。结论B.Microti感染耐过鼠可完全保护B.Rodhain的再感染,其细胞因子的产生为IL-12早于IL-10。     

Babesia microti primarily invades mature erythrocytes in mice

Babesia microti is a tick-borne red blood cell parasite that causes babesiosis in people. Its most common vertebrate reservoir is the white-footed mouse. To determine whether B. microti invades reticulocytes, as does the canine pathogen B. gibsoni, we infected the susceptible inbred mouse strains C.B-17.scid and DBA/2 with a clinical isolate of B. microti. Staining of fixed permeabilized red blood cells with 4',6'-diamidino-2-phenylindole or YOYO-1, a sensitive nucleic acid stain, revealed parasite nuclei as large bright dots. Flow cytometric analysis indicated that parasite DNA is primarily found in mature erythrocytes that expressed Babesia antigens but not the transferrin receptor CD71. In contrast, CD71-positive reticulocytes rarely contained Babesia nuclei and failed to express Babesia antigens. Accordingly, the frequency of YOYO-1-positive, CD71-negative cells strongly correlated with parasitemia, defined as the frequency of infected red blood cells assessed on Giemsa-stained blood smears. Importantly, the absolute numbers generated by the two techniques were similar. Parasitemia was modest and transient in DBA/2 mice but intense and sustained in C.B-17.scid mice. In both strains, parasitemia preceded reticulocytosis, but reticulocytes remained refractory to B. microti. In immunocompetent C.B-17 mice, reticulocytosis developed early, despite a marginal and short-lived parasitemia. Likewise, an early reticulocytosis developed in resistant BALB/cBy and B10.D2 mice. These studies establish that B. microti has a tropism for mature erythrocytes. Although reticulocytes are rarely infected, the delayed reticulocytosis in susceptible strains may result from parasite or host activities to limit renewal of the mature erythrocyte pool, thereby preventing an overwhelming parasitemia.     

Protection of mice against haemoprotozoan Babesia microti with Brucella abortus strain 19.

When Brucella abortus strain 19 is given intraperitoneally to mice it protects them against subsequent infection with large doses of Babesia microti. The protection obtained was more effective when B. abortus was given intraperitoneally than when it was injected subcutaneously. This non-specific protection seems to be best explained by the stimulation of macrophages so as to release a mediator which limits the intracellular replication of the parasites.     

Comparison of PCR with blood smear and inoculation of small animals for diagnosis of Babesia microti parasitemia.

The specific diagnosis of babesiosis, which is caused by the piroplasm Babesia microti, is made by microscopic identification of the organism in Giemsa-stained thin blood smears, detection of babesial antibody in acute-and convalescent-phase sera, or identification of the organism following the injection of patient blood into laboratory animals. Although rapid diagnosis can be made with thin blood smears, parasites are often not visualized early in the course of infection. PCR is a new, rapid diagnostic technique for the detection of Babesia spp. that has not yet been systematically evaluated. We conducted a blinded study of the sensitivity, specificity, and reproducibility of the PCR-based test with patients with babesiosis and a group of asymptomatic subjects residing in a region in southern New England where babesiosis is enzootic. Among 19 patients with recent babesial illness, we found that PCR was as sensitive and specific as the use of Giemsa-stained blood smears and inoculation of hamsters. Among asymptomatic subjects, the PCR result was positive for 3 persons with recent babesial infection and was negative for 41 persons without previous babesial infection. We conclude that the B. microti PCR procedure is sufficiently sensitive, specific, and reproducible for use in the diagnosis of acute babesiosis.     

鼠感染Babesia microti和 Babesia rodhaini后早期 IL-12、IL-10诱生的研究

目的 研究Babesia microti 和Babesia rodhaini感染后早期IL-12和IL-10诱生情况,以探讨B. microti和 B. rodhaini不同种属感染的发病机制与免疫应答效应.方法 使用ELISA方法分别检测Babesia microti 和 Babesia rodhaini 感染鼠后的0、3、6、9、12、18、24、36、48、72、96 h血清中IL-12及IL-10的浓度.结果 B. microti感染后3 h,小鼠血液中IL-12产生达一个高峰,至感染后24 h达最高峰值,与对照组比较差异显著,同组鼠在感染的早期(96 h前)血液中IL-10水平无明显变化.而B. rodhaini感染鼠,在感染后3～72 h,血清中IL-10和IL-12水平与对照组比较均无明显差异.在感染后96 h,血清中IL-10和IL-12水平开始下降,与对照组比较差异显著.结论 B. microti 感染鼠早期诱生的细胞因子主要为IL-12,而B. rodhaini感染后早期IL-12和IL-10水平无明显变化.     

Concurrent Borrelia burgdorferi and Babesia microti infection in nymphal Ixodes dammini.

Ixodes dammini nymphs were examined for evidence of concurrent infection with Borrelia burgdorferi and Babesia microti. A total of 19 nymphs (18.6%) from Nantucket Island were simultaneously infected, as were 24 nymphs (8.2%) from Naushon Island. These observations are consistent with a common reservoir host for both I. dammini-transmitted pathogens.     

Roles of CD4+ T Cells and Gamma Interferon in Protective Immunity against Babesia microti Infection in Mice

Babesia microti produces a self-limiting infection in mice, and recovered mice are resistant to reinfection. In the present study, the role of T cells in protective immunity against challenge infection was examined. BALB/c mice which recovered from primary infection showed strong protective immunity against challenge infection. In contrast, nude mice which failed to control the primary infection and were cured with an antibabesial drug did not show protection against challenge infection. Treatment of immune mice with anti-CD4 monoclonal antibody (MAb) diminished the protective immunity against challenge infection, but treatment with anti-CD8 MAb had no effect on the protection. Transfer of CD4(+) T-cell-depleted spleen cells resulted in higher parasitemia than transfer of CD8(+) T-cell-depleted spleen cells. A high level of gamma interferon (IFN-gamma), which was produced by CD4(+) T cells, was observed for the culture supernatant of spleen cells from immune mice, and treatment of immune mice with anti-IFN-gamma MAb partially reduced the protection. Moreover, no protection against challenge infection was found in IFN-gamma-deficient mice. On the other hand, treatment of immune mice with MAbs against interleukin-2 (IL-2), IL-4, or tumor necrosis factor alpha did not affect protective immunity. These results suggest essential requirements for CD4(+) T cells and IFN-gamma in protective immunity against challenge infection with B. microti.     

Specific immune responses are required to control parasitemia in Babesia equi infection.

Horses possessing a normal immune system and spleen often control infection caused by Babesia equi. However, splenectomized horses are unable to control B. equi infection and usually succumb to the infection. To investigate the role of the spleen in the control of B. equi infection in the absence of specific immune responses, two 1-month-old foals with severe combined immunodeficiency (SCID) and two age-matched normal foals were inoculated with B. equi. The SCID foals became febrile seven days postinoculation and developed terminal parasitemias of 41 and 29%. The SCID foals had greater than 50% decreases in indices of total erythrocytes, packed-cell volumes, and hemoglobin concentrations. Both SCID foals were euthanized in extremis at 10 days postinoculation. As expected, the serum of the SCID foals lacked detectable antibodies to B. equi antigens. In contrast, the normal foals inoculated with B. equi produced detectable anti-erythrocyte-stage parasite antibodies by 7 days and controlled clinical disease by 12 days postinoculation. Although SCID foals lack functional T and B lymphocytes, they do possess complement, macrophages, granulocytes, and natural killer cells, as well as a spleen. Therefore, the data indicate that specific immune responses are required to control B. equi parasitemia but are not required for erythrocyte lysis in infected horses. Furthermore, the spleen is not able to control B. equi parasitemia in the absence of specific immune responses to parasite antigens.     

Genotypic status of Babesia microti within the piroplasms

For resolution of the controversial taxonomic status of Babesia microti in relation to other Babesia and Theileria spp. a phylogenetic analysis of an American and a German B. microti strain was performed on the basis of sequences of the small-subunit rRNA gene (rDNA) using distance-matrix, maximum-parsimony, and maximum-likelihood algorithms. Both B. microti isolates clearly separated from a group containing other Babesia spp. as well as from a second group consisting of Theileria spp. Interestingly, the B. microti isolates clustered in a monophyletic group together with other piroplasm species of unclear taxonomic status, B. rodhaini, and a recently described small canine piroplasm species. These results support the existence of a third taxonomic entity of equal rank besides the Babesiidae and Theileriidae. Received: 11 February 2000 / Accepted: 24 February 2000     

Antigen-induced protection against infection withToxocara vitulorum larvae in mice

Larvae ofToxocara vitulorum hatched and migrated in the tissues of normal mice. Larvae survived in reasonable numbers, particularly in the liver and, to a lesser extent, in the lungs and kidneys, for at least 4–7 days and in muscles, albeit only in low numbers, for at least 3 weeks. Oral infection of mice on three or more occasions withT. vitulorum eggs induced protection against a challenge infection with eggs ofT. vitulorum. Prior parenteral immunization of mice with a variety ofT. vitulorum soluble antigens (extracts, excretions/secretions, or perienteric fluid and their fractions) from adult parasites and/or infective larvae induced statistically significant protection against infection. The most effective protective immunogens were three or more injections with perienteric fluid from adults (100% protection) and excretions/secretions from infective larvae ofT. vitulorum (>92% protection).