Pathogenesis of Babesia caballi infection in experimental horses

The present study was designed to investigate the role of cytokines in the pathogenesis of Babesia caballi in experimentally infected horses. The expression of cytokine mRNA was determined by using reverse transcription-polymerase chain reaction in two B. caballi-infected horses for 2 weeks after the infection. In one horse, there was up-regulation of interferon-gamma, tumor necrosis factor-alpha (TNF-alpha) and interleukin-2 mRNAs, while in the second horse, expression of only TNF-alpha mRNA was up-regulated. No change was observed in interleukin-4 mRNA in both of the horses. To know the relation between nitric oxide (NO) production and pathogenesis, NO production was assayed in three dexamethasone treated-B. caballi-infected horses. Production of NO in all 3 horses increased significantly before death, although the parasitemia level remained very low. Treatment with NO inhibitor resulted in the suppression of NO production and increased parasitemia level in a horse, which died of the infection. The pathological examination showed that the main cause of the death was dyspnoea and pulmonary edema. Histopathologically, diffuse global mesangial proliferative glomerulonephritis was also observed. These results suggested that NO may be a critical effector molecule of immune defense against parasite. TNF-alpha and NO might be contributing to the pathogenesis in B. caballi infection.

Development of an enzyme-linked immunosorbent assay for detection of antibodies to Babesia bigemina in cattle

Monoclonal antibodies, directed against a 58-kDa Babesia bigemina merozoite antigen that reacted strongly with immune sera from experimentally and naturally infected cattle in Western blots, were used to develop a competitive-inhibition enzyme-linked immunosorbent assay (ELISA). As based on the testing of 70 antibody-positive sera from experimentally infected cattle and 166 antibody-negative sera collected in non-endemic areas of Australia, the sensitivity and specificity of the ELISA were 95.7% and 97.0%, respectively. In sequential sera collected from six calves during the course of experimental B. bigemina infections the ELISA detected seroconversion at about 10 days post-inoculation. The specificity of the ELISA was not affected by the presence of antibodies to B. bovis, Anaplasma marginale or Theileria buffeli. In 42 sera from cattle experimentally infected with B. bovis but negative for B. bigemina the specificity of the ELISA was 95.2%. The use of a competitive-inhibition ELISA format detecting only antibody directed against a single epitope on the 58-kDa antigen appears to have overcome many of the specificity problems that have plagued serological tests for B. bigemina in the past. The test should be useful for epidemiology studies, particularly in areas where B. bovis and B. bigemina have overlapping distributions.

Babesia bovis immunity. In vitro and in vivo evidence for IL-10 regulation of IFN-gamma and iNOS

IL-10 has been shown to have profound immunoregulatory attributes and in the bovine appears to downregulate both Th1- and Th2-like responses. Using RT-PCR, we demonstrate IL-10 in vitro down-regulation of mRNA expression of iNOS, the cytokines involved in nitric oxide signal transduction initiation (IFN-gamma and TNF-alpha), and other mononuclear phagocyte associate cytokines. In addition, using RT-PCR with peripheral blood leukocytes and spleen leukocytes, the Griess reaction, and a killing assay, we provide evidence for the importance of iNOS in a successful immune response to B. bovis infection and for high and persistent IL-10 mRNA expression when the immune response is unsuccessful. We also provide evidence that antibody developed early after an initial infection appears to lack protective attributes (neutralizing and opsonic). Together, the data suggests that IL-10 and IFN-gamma are critical molecules involved in the response to this intraerythrocytic protozoan infection.

Bovine babesiosis. Seroprevalence and ticks associated with cattle from two different regions of Morocco

A total of 475 bovine sera collected in 1995-1996 from 10 areas belonging to two different bioclimatic strata were tested for antibody activity to Babesia bigemina and Babesia bovis using indirect immunofluorescence (IIF). In the Gharb, the B. bovis seroprevalence was 21.7% and for B. bigemina, 10.8%. The infection rate for either or both species as determined microscopically with Giemsa-stained blood films was 18.9%. The Tiflet area was considered an endemic focus, and the seroprevalence was 42.2% for B. bovis and 40% for B. bigemina. The infection rate by stained blood film microscopy was 66.6%. In the Haouz region, only B. bovis was found, and the seroprevalence was 10.1% with 9.4% microscopically positive blood films. More than 80% of the cattle surveyed were infested by ticks and the mean infestation rate was 36 ticks per animal and 21 ticks per animal in the Gharb and Haouz, respectively. Six species were identified. Hyalomma marginatum, Hyalomma detritum, Hyalomma anatolicum Rhipicephalus bursa, Rhipicephalus sanguineous and Boophilus annulatus. Boophilus annulatus was found in both regions with high prevalence in the Gharb (31.3%). No further correlation was made between the identified species as vectors and the presence of B. bovis and B. bigemina in these areas.

Parasite localization and dissemination in the Babesia-infected host

Babesia bovis infections in cattle and B. canis infections in dogs are characterized by non-haemolytic anaemia and low parasitaemia during the acute phase of the disease. In this phase of the disease, animals suffer from hypotension followed by disturbances of the coagulation system. This review discusses the hypothesis that may explain the process of parasite localization in the host, and the consequences of such localization. It is suggested that hypotension favours the interaction between infected erythrocytes and the endothelial lining, thus facilitating localization of the infection. In addition, activation of the coagulation system by a parasite-derived molecule (one associated with the surface of infected erythrocytes or a soluble antigen) might consolidate this situation by causing cellular plugs to form. The continued proliferation of parasites in such plugs may then result in the occurrence of capillaries that are particularly heavily parasitised. An explanation is also suggested for the protective effect of vaccines against clinical babesiosis, based on the soluble parasite antigens that are released into the medium in cultures of babesial parasites.

Immunodominant T-cell antigens and epitopes of Babesia bovis and Babesia bigemina

Despite convincing evidence that T cells are critical for both cellular and humoral immunity against haemoprotozoan parasites, the difficulty of performing meaningful experiments in cattle that would define the role of T cells in immunity to Babesia spp. has impeded research in this area. However, experiments performed ex vivo with immune T cells can reflect in-vivo events, and provide valuable insight into the nature of immunogenic proteins and the responding lymphocytes. The progress made towards identification of the immunogenic proteins and epitopes that stimulate anamnestic CD4+ type-1 (interferon-gamma-producing) T-cell responses in cattle immune to challenge with Babesia bovis or B. bigemina is the subject of the present review.

Seroprevalence of Babesia equi among horses in Israel using competitive inhibition ELISA and IFA assays

Sera from 361 horses were tested by indirect immunofluorescence antibody test (IFA) and by competitive inhibition ELISA (cELISA), to detect antibodies to Babesia equi. The concordance between the assays was 95.7%. Application of a cutoff based on a calculated percent inhibition of < 20% gave a total of 22 discrepant results, while only 8 sera negative by the cELISA were found positive by the IFA when a cutoff of > 20% inhibition was used. Approximately one-third of all the horses tested were found serologically positive to B. equi, with more horses testing positive from northern Israel. Among horses raised with access to pasture there was a significant difference in the percentage of seropositive reactors (76.6% in the north and 20.1% in the central region), compared with horses without access to pasture (14.3 and 10.3%, respectively). Nineteen percent of stallions were found to be positive, which was significantly less than the proportions of seropositive mares and geldings: 38 and 42%, respectively. No significant association was found between the mean age of horses and seroreactivity to B. equi.

Improved disease resistance after Babesia divergens vaccination

The efficacy of a new inactivated vaccine against Babesia divergens was evaluated by means of inoculation tests. The infection was initiated by i.v. injection of blood containing 2 x 10(9) living parasites into splenectomized and non-splenectomized calves. Clinical status and hematological parameters were determined. Serology examinations for antibodies against B. divergens were carried out by indirect fluorescent antibody test (IFAT). Non-vaccinated and splenectomized animals exhibited experimental infections. In vaccinated and splenectomized animals, clinical symptoms and prolonged incubation periods were observed.

Persistence of antibodies against epitopes encoded by a single gene copy of the Babesia bovis merozoite surface antigen 1 (MSA-1)

The Babesia bovis merozoite surface antigen-1 (MSA-1) is an immunodominant, neutralization-sensitive merozoite surface antigen encoded by a polymorphic gene family. MSA-1 antigenic polymorphism results in a complete lack of immunologic cross-reactivity among strains. It is unknown how rapidly this antigenic shift occurs, or whether it evolves in the mammalian host. To determine whether the dominant epitopes encoded by a single msa-1 gene copy vary during the course of a single infection, the antibody response to these epitopes was measured after infection of cattle with the Mo7 biologically cloned strain of B. bovis using an Mo7 gene copy-specific enzyme-linked immunosorbent assay. Antibodies against MSA-1 encoded by this gene copy were detected by postinoculation (PI) day 15 in each of 5 experimentally infected animals. Importantly, detectable antibody persisted in all carrier animals without a significant decrease in optical density through 12 mo PI, at which time the experiment was terminated. The results indicate that immunodominant epitopes expressed by a single gene copy of msa-1 do not undergo marked antigenic shift typical of the gene family during the course of a single infection in the mammalian host. The results are compatible with the limited MSA-1 polymorphism reported in some geographically defined endemic populations.

Partial protection of severe combined immunodeficient mice against infection with Babesia microti by in vitro-generated CD4+ T cell clones

Because CD4+ T cells were considered to be involved in protection against infection with Babesia microti, specific CD4+ T cells were generated in vitro from recovered BALB/c mice and their protective activity was tested in vivo. The cells produced varying amounts of interferon (IFN)-gamma in vitro in response to parasite antigen. In passive transfer experiments, three out of eleven T cell clones tested exerted protective activity in the early phase after infection. However, there seemed to be no correlation between this protection and in vitro IFN-gamma production by the T cell clones. Although the protection was partial and short-lived, the result provided direct evidence that CD4+ T cells play a crucial role in defense against B. microti.

The safety and efficacy of Australian tick-borne disease vaccine strains in cattle in Paraguay

Glycerol preserved, frozen tick-borne disease vaccine strains developed in Australia were imported into Paraguay to test their safety in pregnant Holando heifers and their efficacy against challenge from inoculated local field strains of Babesia bigemina, B. bovis and Anaplasma marginale in Hereford X Criolla heifers. The two Babesia strains proved to be safe and the B. bovis K strain was very effective in providing immunity to a local field strain of B. bovis. The B. bigemina efficacy trial was inconclusive, possibly due to the avirulent nature of the local field strain used in challenge. The A. centrale strain did not prove to be as safe as would be desirable in safety trials, neither did it provide as good protection as the Babesia strains in the efficacy trial. It was concluded that the Babesia strains provided good protection against field challenge in Paraguay and were safe to use in highly susceptible cattle, however an alternative to A. centrale should be sought to provide protection against local strains of A. marginale.

A case study of cytokine profiles in acute human babesiosis

The immune response in a patient with acute babesiosis was determined by measurements of lymphocyte subpopulations, serum levels of cytokines, and adhesion molecules. The ratio of CD4+:CD8+ lymphocytes was reduced early in the infection, but returned to a normal value after treatment with azithromycin and quinine. Natural killer (NK) cells markedly increased in the acute phase but progressively decreased and to the normal range in the convalescent phase. Serum levels of tumor necrosis factor-alpha, interferon-gamma, interleukin-2 (IL-2), IL-6, E-selectin, vascular cell adhesion molecule-1, and intercellular adhesion molecule-1 were highly elevated in the acute phase while normal levels of these mediators were observed one month after treatment. These results suggest that CD8+ T cells and NK cells may be involved in the host defense mechanisms against acute babesiosis.

Seroprevalence of Babesia ovis in Spanish ibex (Capra pyrenaica) in Catalonia, northeastern Spain

A serologic survey was carried out in order to detect antibodies against Babesia ovis in a large population of Spanish ibex (Capra pyrenaica) from a hunting reserve in Catalonia, northeastern Spain. For this purpose, an indirect fluorescent antibody test (IFAT) was developed using a B. ovis isolate of ovine origin as antigen. Of the total 475 sera tested, 155 (32.6%) showed titres between 1:160 and 1:1280 and were considered positive. These results reveal that exposure of Spanish ibex to B. ovis is common in the studied area. No significant differences could be detected when comparing season or year of capture and age or sex of the animals in positive and negative samples. A high proportion of low titres was found in comparison to those reported by other researchers in sheep in Spain; this could be a consequence of the existence of some minor antigenic differences between B. ovis of domestic sheep and that found in Spanish ibex.

The immunomodulator AS101 restores T(H1) type of response suppressed by Babesia rodhaini in BALB/c mice

The immunomodulator AS101 has been previously shown to confer protection upon BALB/c mice infected with the intraerythrocytic parasite Babesia rodhaini (B. rodhaini). The present study focuses on the effect of AS101 administration on the acute phase of babesial infection where T helper cell subset patterns-TH1/TH2-were assessed in heavily infected mice. Secretion of cytokines of the TH1 subset (IL-2, IFN-gamma, IL-12) and of the TH2 subset (IL-10, IL-4) as well as TGF-beta was measured following the administration of AS101 2 weeks before parasite infection. Our results demonstrate that the parasites suppress IL-2 protein and IL-12 mRNA and that AS101 upregulates their secretion: IL-2, 8 u/ml vs 34 u/ml, respectively; IFN-gamma protein, 2370 pg/ml vs 4777 pg/ml, respectively. Conversely, babesial infection results in the upregulation of IL-10 and IL-4 proteins and TGF-beta transcripts, whereas AS101 downregulates their production: IL-10, 1800 pg/ml vs 360 pg/ml, respectively; IL-4, 58.3 pg/ml vs 24.5 pg/ml, respectively. A possible escape mechanism induced by B. rodhaini is suggested, starting with IL-10 inhibition of macrophage activities leading to a suppression of the TH1 response and of IL-2 in particular. It is therefore possible that AS101 may protect infected mice by activating cellular-mediated immunity and concurrently balancing the TH subset responses. It is suggested that AS101 may be effective as an antiparasitic drug.

Differential effects of infection with a Babesia-like piroplasm, WA1, in inbred mice

A newly identified intraerythrocytic Babesia-like organism, WA1, and its relatives were recently shown to be infectious for humans in the western United States. The purpose of the present study was to determine the susceptibilities of selected mouse genotypes to WA1 infection in an attempt to develop a murine model of the human disease. Several mouse strains were inoculated intraperitoneally with various passages of WA1-parasitized erythrocytes. Parasitemia was evaluated by blood smears and by PCR with blood samples collected at various intervals after inoculation. Hematologic parameters were monitored in blood samples at all intervals. C57BL/6 and C57BL/10 mice exhibited mortality rates of <10%. BALB/cJ, CBAJ, and 129/J mice had higher peak parasitemias than did C57BL mice, with mortality rates of 40, 50, and 50%, respectively. A/J, AKR/N, C3H, and DBA/1J mice also had higher peak parasitemia and mortality rates (>95%). An F1 cross of C57BL/6 (resistant) and C3H.RKK (susceptible) mice had a mortality rate similar to that of the resistant parental strain. Histopathology of BALB/cJ and C3H mice at 9 and 14 days after inoculation revealed erythrophagocytosis and deposition of an iron-negative pigment in multiple organs. Morbidly ill C3H mice at 14 days had severe pulmonary edema, hemoglobinuria, and glomerulonephritis.

Mapping the T cell epitopes of the Babesia bovis antigen 12D3: implications for vaccine design

The Babesia bovis antigen 12D3 was analysed to identify potential T-cell epitopes. Two predictive algorithms identified 13 possible sites but there was minimal agreement between the different predictive methods. Experimental determination of the T-cell epitopes recognized by nine cattle was achieved using a panel of overlapping peptides which identified seven different epitopes, five of which were clustered together around residues 210-320 of the molecule. No T cell epitopes were located within the tightly disulphide bonded core of 12D3. Using a series of truncated peptides, the location of two of the epitopes was mapped to residues 35-43 and 266-275. The sequences of these two epitopes was compared with a database of previously described binding motifs for MHC II alleles and each epitope was found to contain three sequence motifs recognized by HLA-DR alleles. The BoLA-DRB3 alleles occurring in these cattle were determined by a sequence specific oligonucleotide hybridization assay. Within those cattle whose T cells proliferated in response to 12D3, there was a consistent pattern of epitope recognition and presence of particular DRB3 alleles. The implications for effective vaccine design are discussed.

Vaccination of dogs against Babesia canis infection

This paper describes the clinico-pathological parameters measured in dogs that were vaccinated against Babesia canis using soluble parasite antigens (SPA) and then challenged. The packed cell volume (PCV) and the plasma creatinine value decreased immediately after challenge. Actual PCV values could be predicted in the first 5-6 days of the infection, assuming that creatinine values were modulated by increase of plasma volume. This association no longer existed after that time, and observations indicated splenic involvement in reduction of numbers of circulating erythrocytes. The anaemia due to B. canis infection appears to be the result of a multifactorial process including plasma volume increase, erythrocyte retention in the spleen and erythrocyte destruction, partly due to parasite proliferation. Vaccination limited the reduction of PCV values, and the development of splenomegaly. Differences in protection between vaccinated and control animals became apparent 6 days after infection, when a memory immune response becomes operative, and the onset of recovery of vaccinated animals correlated with the onset of antibody production against SPA.

Vaccination against Babesia bovis: T cells from protected and unprotected animals show different cytokine profiles

Vaccination of cattle against the haemoprotozoan parasite, Babesia bovis, with the recombinant antigen 11C5 resulted in 9 of 15 cattle being protected against challenge infection. The cellular immune responses of protected and unprotected cattle were compared in order to identify differences in response. No differences were observed in the pattern of change in various blood leukocyte populations throughout challenge infection. FACScan analysis revealed an increase in the proportion of cells bearing the CD2 marker in both protected and unprotected cattle over the course of infection. There were no observable differences in the frequency of various cell-surface markers between the unprotected and protected cattle. During the period of patent parasitaemia, in vitro cultures of peripheral blood mononuclear cells (PBMC) from protected cattle produced significantly more TNF-alpha (P < 0.05) than cultures from unprotected cattle. TNF-alpha concentrations remained at pre-challenge levels until day 10, when levels in the unvaccinated control and vaccinated/unprotected animals dropped. By peak parasitaemia, TNF-alpha production in vitro was significantly greater (P < 0.05) in cultures of PBMCs from protected cattle. Interferon production showed an initial peak at day 5 in all cattle, followed by a decrease and a second peak at days 10-13 in protected cattle only, which coincided with resolution of the infection.

An immunisation trial with in vitro produced Babesia bigemina exoantigens

Bovine babesiosis, caused by Babesia bigemina, is an important tick-transmitted haemoprotozoan disease in the tropics. This study evaluated the immunoprotective efficacy of in vitro produced B. bigemina exoantigens in bovine calves. The calves inoculated with B. bigemina exoantigens did not show any clinical, parasitological or hypersensitivity reactions after inoculation. They withstood challenge without showing any clinical symptoms except a transient thermal reaction. In contrast, two out of four control calves exhibited clinical symptoms of babesiosis and one died. On challenge, there was a significant reduction in the haematological values of both groups. However, this was more pronounced in the control animals. Challenge resulted into a normocytic hypochromic anaemia. The vaccinated animals revealed a significant rise in antibody titres after vaccination as well as after challenge as detected by a single dilution ELISA. The rise in antibody titres of control animals was only moderate. Inoculation of B. bigemina exoantigens induced a protective immune response in the vaccinated animals which could protect them from infected blood challenge.

Clinical, anatomic, and immunopathologic characterization of Babesia gibsoni infection in the domestic dog (Canis familiaris)

The pathology associated with acute, chronic, and recrudescent Babesia gibsoni infections was characterized in a group of 6 naturally or experimentally infected, spleen-intact and splenectomized dogs. All experimentally infected dogs became acutely parasitemic, lethargic, anemic, thrombocytopenic, and hemoglobinuric. Anatomic lesions associated, with the disease included diffuse nonsuppurative periportal and centrilobular hepatitis, multifocal necrotizing arteritis, membranoproliferative glomerulonephritis, reactive lymphadenopathy, diffuse erythrophagocytosis, and extramedullary hematopoiesis. The density of CD3+ lymphocytes within the liver sinusoids was markedly increased. Aggregates of large mononuclear cells with immunohistochemical features of activated macrophages were demonstrated in the central veins of the liver. Kupffer cells throughout the hepatic sinusoids appeared hypertrophic and prominent. The density of sinusoidal T lymphocytes, macrophages in central veins, and the degree of Kupffer cell hypertrophy were greatest in the splenectomized dogs. Multifocal deposits of IgM antibody were immunohistochemically demonstrated within the walls of inflamed arteries and renal glomeruli. The results of this study suggest that intense immunostimulation resulting in activation and expansion of T and B lymphocyte populations, macrophage recruitment and activation, vasculitis, glomerulonephritis and anemia contribute to the pathology associated with B. gibsoni infections.

An enzyme-linked immunosorbent assay (ELISA) for the detection of antibodies against Babesia bovis in cattle

A method for the isolation of Babesia bovis merozoites from infected erythrocytes (Machado et al., 1994) and an enzyme-linked immunosorbent assay (ELISA) for the detection of anti-B. bovis antibodies were developed. This ELISA utilizes a soluble, alkali-digested B. bovis antigen. Sera from calves experimentally infected with B. bovis were screened by this technique from day 9 to day 233 postinfection (PI). Maximum titers were reached between days 29 and 149 PI. Sera from calves (n = 62), heifers (n = 38) and cows (n = 49), raised in tick-infested areas of São Paulo State, showed higher antibody levels in heifers and cows. A higher percentage of negative sera (19.4%) was found among calves. Sodium dodecyl sulphate-polyacrylamide electrophoresis (SDS-PAGE) and immunoblotting have identified proteins of similar molecular mass in the two species. Sera from calves experimentally infected with B. bovis reacted with homologous antigens at the level of 95, 66 and 23 kDa. The same serum reacted with the 23 kDa band of heterologous antigen. Sera from calves experimentally infected with B. bigemina recognized 82, 66, 58, 36 and the 23 kDa polypeptides of homologous and heterologous antigens. The experimental ELISA described may prove to be a practical serological test for bovine Babesia infection with the choice of specific test antigen for B. bovis and B. bigemina.

Antibodies to multiple tick-borne pathogens of babesiosis, ehrlichiosis, and Lyme borreliosis in white-footed mice

Serum samples from Peromyscus leucopus (white-footed mouse), collected in Connecticut (USA) in 1983, 1985, and during 1990 to 1993, were analyzed by an enzyme-linked immunosorbent assay (ELISA) or indirect fluorescent antibody (IFA) staining methods for antibodies to Borrelia burgdorferi (strain 2591), Babesia microti, Ehrlichia chaffeensis (Arkansas strain), and Ehrlichia equi (MRK strain). Of the 294 serum samples tested, 160 (54%) contained immunoglobulins to one or more of these pathogens. There were antibodies to two or more etiologic agents in 77 (48%) of the seropositive mice. Although it was uncommon to detect coexisting antibodies to all four pathogens (n = 5 positive mice), E. chaffeensis-reactive antibodies or immunoglobulins to E. equi were present along with those produced to B. burgdorferi and B. microti in 24 other mice. These rodents carry antibodies to several tick-borne pathogens at numerous sites in Connecticut and may play a role in the epizootiology of ehrlichiosis as well as babesiosis and Lyme borreliosis.

Prevalence of equine piroplasmosis in Central Mongolia

Antigen for the indirect fluorescent antibody test (IFAT) was routinely prepared from infected erythrocytes from horses experimentally infected with Babesia equi and Babesia caballi. With the successful establishment of in vitro cultures of B. equi and B. caballi, it is now possible to employ culture-derived antigens in this test. In this study, in vitro-propagated B. equi- and B. caballi-infected erythrocytes were used as antigen in the IFAT. Various modifications to an established protocol had to be implemented to allow repeatable results. Cultures with 3-4% parasitized erythrocytes were found to be most suitable. As cross-reactions of control sera on heterologous antigen were observed at serum dilutions of up to 1/40, a reciprocal titre of 80 was considered to be positive. In positive samples, specific fluorescence of Babesia parasites and/or erythrocyte membranes was observed. Fifteen sera from Babesia-free horses from Japan all tested negative in the IFAT. One hundred and ten field-horse sera from Central Mongolia were investigated in this study. The results indicate that both B. equi and B. caballi are endemic in horses in Central Mongolia, with 88.2% and 84.5% of horses being seropositive to B. equi and B. caballi, respectively.

The prevalence of serum antibodies to tick-borne infections in cattle in smallholder dairy farms in Murang'a District, Kenya; a cross-sectional study

The most important tick-borne disease of cattle in eastern, central and southern Africa is East Coast fever (ECF) caused by Theileria parva and transmitted by the tick Rhipicephalus appendiculatus. Other less-important tick-borne diseases in cattle are benign theileriosis caused by Theileria mutans, babesiosis caused by Babesia bigemina, anaplasmosis caused by Anaplasma marginale and cowdriosis caused by Cowdria ruminatum. In Murang's District, Central Province of Kenya, five agroecological zones (AEZs) are defined according to climate, altitude and agricultural activities. A cross-sectional serological study was conducted on 750 smallholder dairy farms in Murang's District, selected in a stratified random sampling method. The farms had a total of 362 calves. One hundred and fifty farms were studied from three administrative sublocations in each of the five AEZs. Prevalence of serum antibodies to three tick-borne parasites, that is T. parva, T. mutans and B. bigemina, were determined using the enzyme-linked immunosorbent assay (ELISA) technique. Antibody prevalence values differed across the AEZs. The ranges of means for the prevalences were: T. parva (18-72%), T. mutans (1.5-28%) and B. bigemina (12-49%). The above results serve as indicators of the possible existence of endemic stability in some AEZs for some parasites.

Human babesiosis in Taiwan: asymptomatic infection with a Babesia microti-like organism in a Taiwanese woman

An asymptomatic Babesia infection was confirmed by laboratory diagnoses. The intraerythrocytic protozoan (designed TW1) isolated from a 51-year-old Taiwanese woman appeared to be morphologically consistent with small-form piroplasm, and measurements indicated that it had a body size of 1.5 to 2.5 microm in diameter. The typical features of ring, binary, and tetrad forms were observed in Giemsa-stained thin blood smears. A persistent and low-grade parasitemia was established after hamster inoculation. Indirect immunofluorescent-antibody reactivities indicate that this strain (TW1) of Babesia was serologically related to, but not identical to, the Babesia species (B. microti) that infects rodents. Antibody titers in the patient's sera combined with the clinical symptoms suggested that the present case was a chronic and subclinical babesial infection. A neighborhood human serologic survey indicated that the infection may have been acquired accidentally from an infected rodent and localized within the same family. Indeed, rodents from areas around the neighborhood were trapped, and a high prevalence (83%) of babesial infection was observed. The possible vector responsible for the transmission remains to be identified.

Monoclonal antibodies against Babesia caballi and Babesia equi and their application in serodiagnosis

The production of monoclonal antibodies to the bloodstages of the haemoprotozoan parasites Babesia caballi and Babesia equi and the characterization of their corresponding antigens are described. Species specific and immunogenic proteins of both parasites were identified using SDS-PAGE, Western blotting and ELISA. These proteins were then electroeluted from SDS-PAGE gels and used to immunize BALB/c mice for hybridoma production. One monoclonal antibody (Mab), designated BC5.37.70.27 (BC5), recognized a 70 kDa protein of B. caballi as demonstrated by Western blotting under reducing conditions. Another Mab, BE1.24/2.95 (BEI), recognized a 34 kDa protein of B. equi. Both Mabs reacted specifically in indirect ELISA when isolated whole merozoites were used as antigen. Preliminary studies using the two Mabs in a competitive ELISA (cELISA) suggest that the cELISA for the detection of B. caballi infection is more sensitive than the commonly used complement fixation test but that refinement is necessary for the B. equi system.

Duration of protective immunity in experimental canine babesiosis after homologous and heterologous challenge

Three Beagle dogs were monitored clinically and serologically for 55 weeks following an experimental primo-infection and two challenge infections with a heterologous strain of Babesia canis. There was no cross-protection when dogs were challenged with the heterologous strain after 7 months, but there was complete protection when challenged a second time with this heterologous strain 5 months later. Although the serological profile using indirect immunofluorescence showed the same trend whether homologous or heterologus antigen was used, antibody titres generally reached higher values for homologous antigen. Seropositivity in itself was no guarantee for protective immunity against heterologous challenge.

Environmental enrichment, immunocompetence, and resistance to Babesia microti in male mice

Groups of male CFLP mice housed in cages furnished with shelves and nestboxes showed increased aggression and reduced resistance to an experimental infection of Babesia microti when compared with groups in unfurnished cages. Both a bystander measure of immunocompetence (serum total IgG concentration) and resistance to B. microti decreased as the number of attacks received by mice increased, but increased with the number of times individuals were recorded on shelves or in nestboxes. Serum concentrations of testosterone and corticosterone were generally downregulated in furnished cages; the absence of hormone-related reduction in resistance may have been due partly to this, but partly also to the apparent modulation of hormone concentrations in relation to concurrent immunocompetence. Some welfare implications of the results are considered.

Experimental Babesia microti infection in golden hamsters: immunoglobulin G response and recovery from severe hemolytic anemia

We described the parasitemia, hematologic changes, and immunity developed by golden hamsters during 8 wk of infection with Babesia microti following experimental inoculation. All 8 hamsters used in this study were readily infected. Animals attained peak parasitemias asynchronously but within a 2-wk period. Most of the animals reached their peak parasitemia by 4 wk postinoculation, attaining a mean +/- SD of 21.9 +/- 9.4% infected erythrocytes (range = 20-35%). Red blood cell count, packed cell volume, and hemoglobin level were used to monitor the course of the hemolytic anemia experienced by infected hamsters. All 3 measures corresponded inversely to the parasitemia; significant hematologic changes (P = 0.0001) were observed during the 8 wk of monitoring. Although all hamsters suffered from severe hemolytic anemia, they also recovered within the same period. Golden hamsters developed a detectable anti-B. microti IgG response by 2 wk postinoculation. Individual animals typically attained peak antibody levels (> or = 1:8, 192) 1 wk after the peak parasitemia. Hamsters retained a high IgG titer (> or = 1:4,096), although parasitemias fell dramatically, fluctuating thereafter at low levels (< 5%).

Babesia bovis rhoptry-associated protein 1 is immunodominant for T helper cells of immune cattle and contains T-cell epitopes conserved among geographically distant B. bovis strains

The ability of rhoptry-associated protein 1 (RAP-1) of Babesia bovis and Babesia bigemina to confer partial protective immunity in cattle has stimulated interest in characterizing both B-cell and T-cell epitopes of these proteins. It was previously shown that B. bovis RAP-1 associates with the merozoite surface as well as rhoptries and expresses B-cell epitopes conserved among otherwise antigenically different B. bovis strains. An amino-terminal 307-amino-acid domain of the molecule that is highly conserved in the B. bigemina RAP-1 homolog did not contain cross-reactive B-cell epitopes. The studies reported here demonstrate that B. bovis RAP-1 is strongly immunogenic for T helper (Th) cells from B. bovis-immune cattle and that like B-cell epitopes, Th-cell epitopes are conserved in different B. bovis strains but not in B. bigemina RAP-1. Lymphocytes from cattle immune to challenge with the Mexico strain of B. bovis proliferated against recombinant B. bovis RAP-1 protein derived from the Mexico strain. T-cell lines established by stimulating lymphocytes with recombinant RAP-1 protein responded against B. bovis, but not B. bigemina, merozoites. T-cell lines established by repeated stimulation of lymphocytes with B. bovis membrane antigen proliferated strongly against RAP-1, demonstrating the immunodominant nature of this protein. RAP-1-specific CD4+ T cell clones recognized Mexico, Texas, Australia, and Israel strains of B. bovis but neither B. bigemina merozoites nor recombinant B. bigemina RAP- 1. Analysis of cytokine mRNA in RAP-1-specific Th cell clones revealed strong expression of gamma interferon but little or no expression of interleukin-2 (IL-2), IL-4, or IL-10. Gamma interferon production was confirmed by enzyme-linked imunosorbent assay. These results indicate the potential to use selected B. bovis RAP-1 peptides as immunogens to prime for strong, anamnestic, strain-cross-reactive type 1 immune responses upon exposure to B. bovis.

Epizootiologic instability of bovine populations against Babesia bovis (Piroplasmida:Babesiidae) in the region of Poas, Costa Rica

In Poás (Costa Rica), more than 78% of the cattle population is susceptible to Babesia bovis (Babes, 1888) which indicates that care should be taken during animal movement to avoid tick exposure. Seroprevalence is less than 22%; the frequency distribution of antibody titers is presented. Significant differences (p < 0.05) were observed in the distribution of seropositive animals between ecological zones. Lower mountain rain forest and lower mountain wet forest presented higher risk for seropositivity. Based on the serological characteristics of the herds and the frequency of clinical cases, it is suggested that the cattle situation in the area is epidemiologically unstable for B. bovis.

Antibabesial effect of the immunomodulator AS101 in mice: role of increased production of nitric oxide

The immunomodulator AS101 has been shown to induce cell proliferation and to increase the secretion of a variety of cytokines. In the present study we evaluated the effect of AS101 on the pathogenicity of B. rodhaini infected mice. In order to clarify its mechanism of action we studied the ability of AS101 to activate neutrophils and macrophages, both of which inhibit parasite growth. More specifically, we studied the ability of AS101 to induce secretion of nitric oxide (NO). We found that AS101 protects mice from babesiosis in a time and dose dependent manner. At 10 and 20 micrograms/injection, two weeks prior to parasites, AS101 significantly increased the number of neutrophils and more than doubled the survival rate of infected mice. Similarly, at these concentrations when injected one month, or at 20 micrograms, injected 24 h before parasites. AS101 mitigated the course of infection and reduced by half the peak of parasitaemia. At 0.1 microgram/ml AS101 induced the secretion of significantly higher levels of NO in vitro than control. This was abrogated by adding the NO synthase inhibitor. NG-monomethyl-L-arginine. In vivo the antiparasitic protection of AS101 was abrogated by another NO synthase inhibitor, aminoguanidine. We found that AS101, partly by elevating levels of NO, can significantly mitigate the course of infection and thus increase survival, and may therefore be proven as an effective antiparasitic drug.

Erythrocyte oxidation in artificial Babesia gibsoni infection

We have already reported that anti-erythrocyte antibody induced by Babesia gibsoni infection (aEAb) showed higher reactivity against aged and/or oxidized erythrocytes than intact one in vitro (Morita et al., 1995). To clarify the meaning of such a binding character of aEAb in vivo, changes in erythrocyte oxidation were observed in artificially infected dogs. The ratio of methemoglobin concentration against total hemoglobin concentration (metHb%) as the indicator of erythrocyte oxidation was increased by the artificial infection in the intact dogs, suggesting that aEAb played a more important role in erythrocyte destruction in infected dogs. Though parasitemia approximately three times higher was observed in splenectomized dogs than that in intact dogs, metHb% did not increase in the splenectomized dogs. This suggests that the spleen plays a very important role in erythrocyte oxidation in dogs infected with B. gibsoni.

Piroplasms of domestic animals in the Macedonia region of Greece. 1. Serological cross-reactions

During a serological survey on haemoparasites in Macedonia, serum samples were collected from cattle, sheep and goats. All sera were tested by the indirect immunofluorescence test (IFAT); the cattle sera against Theileria orientalis, T. annulata, Babesia bigemina, B. bovis, B. divergens and B. major antigens; the sheep and goat sera against T. ovis, B. ovis, B. motasi and B. crassa antigens. Parallel tests of negative and positive control sera against all the antigens showed the existence of cross-reactions of different degrees between species of the same genus. In cattle, the most important cross-reactions were obtained against B. bigemina antigen, especially with the anti-B. bovis serum, in small ruminants against B. motasi with the anti-B. crassa serum. In the field sera, there was a high correlation between the antibody titres of B. bigemina and B. bovis, and also between the titres of these two Babesia spp. and B. divergens. A high correlation was also found between B. motasi and B. crassa, and lower ones between these two and B. ovis. The correlations of the sera titres were due to mixed infections or to cross-reactions. Therefore, the use of the IFAT is not always satisfactory for diagnosing infections in regions where animals are infected with different piroplasms.

Piroplasms of domestic animals in the Macedonia region of Greece. 3. Piroplasms of small ruminants

A study was carried out on piroplasms of small ruminants in the Macedonia region of Greece. During 1984-1985, 721 serum samples were collected from sheep in 49 localities and 487 from goats in 43 localities. Blood smears were also prepared from 26 sheep and eight goats in 16 localities. The prevalence of positive IFA titres for sheep and goat sera, respectively, was: 24.6% and 0.6% for Theileria ovis, 52.1% and 36.4% for Babesia ovis, 10.5% and 4.2% for Babesia motasi, 12.6% and 6.6% for Babesia crassa. Many of the positive reactions, specially for the large Babesia species, B. motasi and B. crassa, probably resulted from cross-reactions and the presence of these two species is doubtful. Antibodies against B. ovis were found in animals from more than 90% of the localities. T. ovis was also common, but it was confined essentially to sheep. The examination of Giemsa stained blood smears revealed the presence of T. ovis and B. ovis in sheep, and Anaplasma ovis in a goat.

Piroplasms of domestic animals in the Macedonia region of Greece. 2. Piroplasms of cattle

A study was carried out on piroplasms of cattle in the Macedonia region of Greece. During 1984-1986, 602 serum samples were collected from cattle in 33 localities. Blood smears were also prepared from 50 of the animals in 13 localities. The indirect fluorescent antibody (IFA) test revealed that 41.4% of cattle sera were positive to Theileria orientalis, 2.0% to Theileria annulata, 21.6% to Babesia bovis, 15.2% to Babesia bigemina, 5.1% to Babesia major and 2.7% to Babesia divergens. Some of the positive titres were probably due to cross reactions. T. orientalis was widely distributed. T. annulata was limited to a small number of foci. B. bigemina and B. bovis, often present together, were widespread, whereas B. major was only present in a small number of localities. No convincing evidence of B. divergens infection was found. By examination of Giemsa stained blood smears T. orientalis, T. annulata and a Babesia sp. were detected.

Effect of Mycobacterium phlei on the development of immunity to Babesia bigemina

The immunomodulatory role of Mycobacterium phlei against intracellular blood protozoan Babesia bigemina was demonstrated following experimental immunisation and challenge in bovine calves. A lysate of erythrocytes infected (6 x 10(9)) with B. bigemina was used as a source of dead antigen either with Freund's complete adjuvant (FCA) or with a trypsinised culture of M. phlei as a non-specific immunomodulation (NSI) agent with appropriate controls. Following virulent challenge with B. bigemina infected erythrocytes (1 x 10(7)), the NSI printed calves showed 100% protection, while the dead antigen alone with FCA afforded 75% protection. The protective status of the immunising regimes was studied by clinicopathological parameters and assessment of humoral and cell-mediated immune responses. The role of babesial dead antigen and the effects of M. phlei on the development of immunity to B. bigemina is discussed.

Acquisition of resistance to the tick Amblyomma variegatum in Boran cattle, Bos indicus and the effects of Trypanosoma congolense and Babesia bigemina on host resistance

Resistance was induced in cattle to the tick Amblyomma variegatum by five consecutive infestations with nymphs and adults. Using the principal component analysis (PCA), it was found that percentage of adults engorged, percentage of adults which died, percentage of nymphs which engorged, percentage of nymphs which moulted and percentage of nymphs which died, were the main indicators of resistance against A. variegatum. The percentages of nymphs which engorged or moulted after the third infestation were significantly (P < 0.01) reduced while the percentage of nymphs which died increased significantly (P < 0.01) after the third infestation. Percentages of adults which engorged or died started to decrease significantly (P < 0.01) from the fourth infestation after an initial increase during this period. The acquisition of resistance by cattle to the adult ticks was slower than to the nymphs. Infection of cattle with Trypanosoma congolense and Babesia bigemina after the fifth infestation enhanced the acquired immunity as revealed by the significantly (P < 0.01) increased feeding period of the adult ticks and changes in other parameters.

Effects of depletion of T cell subpopulations on the course of infection and anti-parasite delayed type hypersensitivity response in mice infected with Babesia microti and Babesia rodhaini

To elucidate the role of T cell subpopulations in the protective cell-mediated immune response at the initial phase of infection with Babesia microti (BM) and B. rodhaini (BR), the changes in the course of infection and anti-parasite delayed type hypersensitivity (DTH) response after BM or BR inoculation were investigated in Lyt-2+ T cell or L3T4+ T cell-depleted mice. Depletion of Lyt-2+ T cells strongly enhanced the resistance to BM infection, whereas it increased the susceptibility to BR infection. In contrast, depletion of L3T4+ T cells increased susceptibility to BM infection, while it enhanced resistance to BR infection. The anti-parasite DTH response in BM-infected mice was significantly enhanced by depletion of Lyt-2+ T cells, while significantly reduced by depletion of L3T4+ T cells. No effects of depletion of either Lyt-2+ or L3T4+ cells on DTH response was observed in BR-infected mice. From these results, it was suggested that the roles of Lyt-2+ and L3T4+ T cells in the protective cell-mediated immune response at the initial phase of infection were different between BM- and BR-infected mice, resulting in the difference in their course of infection.

Observations on the use of ELISA for detection of Babesia bigemina specific antibodies

An indirect enzyme-linked immunosorbent assay (ELISA) was evaluated to study the cause of the high level of background reactions which hinders the application of ELISA as a field diagnostic test for Babesia bigemina. Different blockers to improve the specificity of the ELISA were compared. THe use of soya milk (25%), gelatin (2.5%) and chicken serum (2%) did not significantly improve the specificity of the test. It was noted that the presence of fibrinogen contributed to the positive ELISA results more than the presence of B. bigemina specific antigen. This conclusion was confirmed by testing bovine fibrinogen as a host protein antigen in ELISA which strongly responded against B. bigemina positive control sera. It is suggested that application of ELISA for B. bigemina is still unreliable until a more purified Babesia-specific antigen or specific monoclonal antibodies are available.

Field observations on the duration of immunity in cattle after vaccination against Anaplasma and Babesia species

In an outbreak of Babesia bovis in a large herd of Friesian x Malawi Zebu cattle, which occurred after an interruption of intensive dipping, clinical or fatal babesiosis occurred in 54/299 (18.1%) animals which had never been vaccinated, as compared to 9/153 (5.9%) vaccinated animals. Eight of the nine affected vaccinates had been vaccinated more than 27 months previously. Sera were collected every 3-4 months from 33 Friesian x Malawi Zebu heifers maintained with intensive dipping and vaccinated with trivalent B. bovis, Babesia bigemina and Anaplasma centrale vaccine. After 2 years, 25% had become seronegative for B. bovis by indirect immunofluorescence, as compared to 97% for B. bigemina and 46% for A. centrale. Because of the evidence that immunity following vaccination against B. bovis declines after 2 years in the absence of tick challenge, it is recommended that tick control should be relaxed after immunity has been established, in order to save acaricide, reinforce immunity and avoid any need for revaccination.

Viability after thawing and dilution of simultaneously cryopreserved vaccinal Babesia bovis and Babesia bigemina strains cultured in vitro

A live, frozen experimental vaccine containing Babesia bovis and Babesia bigemina multiplied in vitro was stored in liquid nitrogen after simultaneous cryopreservation using glycerol as cryoprotectant. The viability of the vaccine was tested by inoculating (subcutaneously) three groups of seven steers each, 2, 12 and 24 h after thawing at 40 degrees C and dilution to obtain a dose of 2 x 10(7) of each organism. All vaccinated cattle developed detectable parasitaemia in thin and/or thick blood smears. No statistically significant differences in the prepatent period were detected amongst the cattle groups (analysis of variance). This prepatent period was 12.3 days for B. bovis and 8.4 days for B. bigemina. Vaccinal organisms derived from in vitro culture systems may replace antigens obtained from in vivo culture to produce vaccine against cattle babesiosis.

Effect of silica treatment on resistance to Babesia rodhaini infection in immunized mice

The effect of silica treatment on the course of Babesia rodhaini infection was investigated in ICR mice pretreated with either a mixture of B. rodhaini parasitized red blood cell hemolysation-sonication (S) antigen and Propionibacterium acnes bacterin or P. acnes bacterin alone and not subjected to immunization. In the normal mice (non-immunized), the mean survival time was decreased by approximately 1 day when 5 mg per mouse of silica were intraperitoneally inoculated at 5 h before infection. In immunization with S antigen and P. acnes bacterin, all mice survived regardless of the dose of silica (15-25 mg per mouse) treatment. In contrast, in immunization with P. acnes bacterin alone, 3/10, 4/10 and 1/10 mice died of B. rodhaini, when inoculated with 15 mg per mouse, 20 mg per mouse and 25 mg per mouse of silica treatment 5 h before infection, respectively. These results suggest that peritoneal macrophages (M luminal diameter of), especially when activated non-specifically by P. acnes bacterin, play an important role in inhibiting multiplication of organisms at the early stage of infection and the mice immunized with S antigen were ready to quickly acquire an enhanced solid specific protection even if the function of M luminal diameter of was damaged by a high dose of silica treatment.

Not peripheral parasitaemia but the level of soluble parasite antigen in plasma correlates with vaccine efficacy against Babesia canis

Groups of five dogs were vaccinated against Babesia canis using soluble parasite (SPA) antigens from in vitro cultures. Although vaccination did not significantly alter peripheral parasitaemia upon challenge, protected animals had lower levels of SPA in the plasma after a challenge infection. The severity of anaemia correlated with the SPA-load during the post-challenge period in that high levels of SPA were associated with low haematocrit values. In addition, it was found that recovery was associated with the production of antibodies against SPA. The results suggest that SPA induce anaemia during B. canis infection, and that vaccination with SPA results in antibody production that can neutralize the effects of SPA after a challenge infection.

Clinical and serological observations on experimental infections with Babesia canis and its diagnosis using the IFAT

Naive Beagle dogs (n = 5) were experimentally inoculated with two stocks of Babesia canis. Dogs were examined regularly for parasitaemia and for antibodies, using the indirect immunofluorescent antibody test (IFAT). This test proved to be useful for the diagnosis of babesiosis. After primo-infection dogs seem to develop a certain degree of immunity, although this immunity is neither absolute nor of long duration. Treatment of infected dogs with imidocarb (6 mg/kg) cleared the infection, but did not prevent the production of IFAT-antibodies. An infected dog treated with long acting oxytetracycline (20 mg/kg) became a subclinical, chronic carrier of the disease.

Babesiosis: new insights from phylogenetic analysis

Piroplasms of the genus Babesia, along with their relatives to the Theileridae, comprise a genetically and antigenically diverse group of tick-transmitted intraerythrocytic pathogens that together have considerable veterinary, medical, and economic importance. Since the first description of a human case of babesiosis in 1957, this zoonotic infection has now attained a worldwide distribution. In the northeastern and upper midwestern United States, the transmission cycle of Babesia microti overlaps that of another well-known zoonotic agent, Borrelia burgdorferi, the causative agent of Lyme disease. Phylogenetic analysis of Babesia and Babesia-like piroplasms from human and animal sources has shown that many of the small Babesia spp., including B. microti, B. equi, B. gibsoni, and a recently described piroplasm infectious for humans known as WA1, may be phylogenetically related to Theileria. Implications of this observation may include the possible existence of an exoerythrocytic stage of parasite development and attendant features of chronicity, immune suppression, and perhaps lymphoproliferation. In this review, we provide a brief summary of recent developments in the study of Babesia and related piroplasms and speculate on the ramifications of chronic babesial infection in humans.