Vaccines against babesiosis using soluble parasite antigens

Babesiosis in cattle and dogs causes severe economical and emotional loss. Although effective chemotherapeutic treatment of infected animals is available, the prevention of babesiosis by vaccination would be preferable. Attenuated parasite lines of Babesia bovis have been used successfully to control tropical babesiosis in cattle. However, among other drawbacks associated with live vaccines, such vaccines bear the risk of variable infectivity and morbidity requiring veterinary surveillance. Soluble parasite antigens derived from different Babesia species have proven to induce immune responses that do not necessarily affect the parasite, per se, but reduce the manifestations of clinical disease upon infection. In this review, Theo Schetters and Sonia Montenegro-James present an overview of the results obtained with vaccines based on soluble parasite antigens and their characterization, and discuss the possible immune effector mechanisms of such vaccines.

Pulmonary tuberculosis in children in a developing country

OBJECTIVE

We evaluated the clinical and epidemiologic characteristics of Peruvian children presenting with pulmonary tuberculosis (PTB) to determine whether features predictive of confirmed PTB could be identified.

STUDY DESIGN

This was a cross-sectional study of 135 children (mean age: 6.8 years) presenting to the Hospital del Niño in Lima, Peru, with presumptive diagnosis of PTB. Clinical, epidemiologic, and laboratory findings were compared between 3 groups of pediatric patients with a presumptive diagnosis of PTB: those with positive Mycobacterium tuberculosis (MTB) cultures, those likely to have PTB based on clinical criteria but with negative cultures, and those who did not meet clinical diagnostic criteria or have positive cultures.

RESULTS

A total of 50 (37%) patients were diagnosed with definitive PTB based on positive sputum culture. Another 55 (47%) patients were classified as having probable PTB based on meeting at least 2 of the following criteria: cough lasting for at least 2 weeks, typical chest radiograph changes, purified protein derivative (PPD) >/=10 mm, or history of tuberculosis family contact. Patients with definitive or probable PTB were significantly older than patients without clinical PTB, and those with symptomatic disease were significantly older than those with asymptomatic disease. Patients with PTB diagnosed by culture were significantly more likely than those diagnosed using clinical criteria to have cough lasting >/=2 weeks, fever, and a PPD >/=10 mm.

CONCLUSIONS

The typical presentation of PTB in Peruvian children includes symptoms of active pulmonary disease similar to those seen in adults. This presentation differs significantly from that reported in developed countries, where many children have minimal or no symptoms at the time of presentation. The diagnostic criteria for pediatric PTB must be modified in hyperendemic developing country environments where features may differ from those described in the United States. The triad of cough lasting >/=2 weeks, fever, and a PPD >/=10 mm was highly predictive for culture-positive PTB among children in this low-income Peruvian population.

Rapid, efficient detection and drug susceptibility testing of Mycobacterium tuberculosis in sputum by microscopic observation of broth cultures. The Tuberculosis Working Group in Peru

Inexpensive, rapid, and reliable methods of detecting infection by and drug susceptibility of Mycobacterium tuberculosis (MTB) are crucial to the control of tuberculosis. The novel microscopic observation broth-drug susceptibility assay (MODS) detects early growth of MTB in liquid medium, allowing more timely diagnosis and drug susceptibility testing. Sputum samples from hospitalized patients in Peru were analyzed by using stains, culture, and PCR. Sensitivity of MODS (92%) compared favorably with the most sensitive of the other culture methods (93%). Sputum samples positive for tuberculosis were tested for susceptibility to isoniazid and rifampin with the microwell alamar blue assay (MABA) and MODS. In 89% of cases, there was concordance between MODS and MABA. Of the diagnostic and susceptibility testing methods used, MODS yielded results most rapidly (median, 9.0 and 9.5 days, respectively). MODS is a rapid, inexpensive, sensitive, and specific method for MTB detection and susceptibility testing; it is particularly appropriate for use in developing countries burdened by significant infection rates and increasing numbers of multiple-drug-resistant cases.

Local and systemic cytokine expression during experimental chronic Trypanosoma cruzi infection in a Cebus monkey model

Cebus apella is an acceptable model for chronic chagasic cardiomyopathy (CCC), since it is possible to experimentally induce cardiac lesions after 1 year of Trypanosoma cruzi infection. The T. cruzi Y strain, shown previously to produce CCC in C. apella monkeys, was used to experimentally infect 10 monkeys. Parasitological, serological and clinical parameters were monitored during a 19-month follow-up, and systemic cytokine responses were assessed sequentially in five monkeys selected according to the differential parasitemia pattern exhibited. Ten additional monkeys, infected with the same strain for 5, 10 and 12 years, were analysed cross-sectionally. Three monkeys/time point and one uninfected control animal were sacrificed for gross pathology, histology, presence of parasites, and local cytokine gene expression. Elevated expression of interleukin (IL)-4 was observed throughout the study in monkeys that had persistent, high parasitemias, whereas a high level of interferon (IFN)-gamma was seen in monkeys that controlled parasitemias soon after infection. Chronically infected monkeys expressed a nonpolarized, Th0-type response. Cardiac tissue collected from a monkey that succumbed to acute infection had elevated levels of proinflammatory cytokine [IL-1beta, IL-6, tumour necrosis factor-alpha] and interstitial cell adhesion molecule (ICAM)-1, platelet-derived growth factor (PDGF)-alpha, transforming growth factor (TGF)-beta and IL-10 transcripts. Cytokine production in cardiac tissue of chronically infected monkeys was also characterized by elevated expression of ICAM-1, PDGF-alpha and TGF-beta, which correlated with the detection of T. cruzi DNA by polymerase chain reaction.

Expression of cytokine genes in Aotus monkeys immunized with synthetic and recombinant Plasmodium vivax and P. falciparum antigens

Cytokine responses in human host-protective immunity to malaria have yet to be completely elucidated. No data appear to exist on the cytokine patterns in non-human primate models immunized with malarial antigens. Expression of mRNA transcripts of 10 cytokines, the adhesion molecule ICAM-1 and inducible nitric oxide synthase (iNOS) in peripheral-blood mononuclear cells (PBMC) from nine Aotus monkeys was analysed by reverse-transcriptase PCR. Five of the monkeys had been immunized with multiple-antigen peptides (MAP) of the Plasmodium vivax circumsporozoite protein and two with constructs of the P. falciparum merozoite surface protein-1 (MSP-1). The other two monkeys served as non-immunized controls. PBMC were cultured for 24 h after stimulation with phytohaemagglutinin mitogen, MAP and MSP-1 antigens. Elevated expression of interleukin-6 (IL-6), IL-10, IL-12, tumour necrosis factor-alpha (TNF-alpha), TNF-beta and iNOS was seen in response to the MAP. Monkeys immunized with either P. falciparum MSP r190L or synthetic 190L peptides expressed predominantly the type-1 cytokines (IL-1 beta, IL-12, interferon-gamma, TNF-alpha, TNF-beta) characteristic of splenic, cell-mediated activity with macrophage activation and nitric oxide production.

Frequency of the Asn-108 and Thr-108 point mutations in the dihydrofolate reductase gene in Plasmodium falciparum from southwest Colombia

Several point mutations in the dihydrofolate reductase (DHFR) gene of Plasmodium falciparum have been correlated with in vitro anti-folate drug resistance of laboratory and field isolates. Furthermore, two different point mutations that generate amino acid substitutions at the same position of the enzyme have been observed in all the isolates studied to date. These point mutations change a serine (Ser-108) in the wild type to an asparagine (Asn-108 mutation) or to a threonine (Thr-108 mutation). Using the polymerase chain reaction (PCR), it is possible to identify isolates that present these mutations. We used a mutation-specific PCR to screen 71 samples from several geographic locations of Colombia for the Asn-108 mutation (pyrimethamine resistance). In this initial screening 53 of 71 yielded amplification product with the DHFR mutation-specific primers. We further analyzed the 18 samples that did not amplify using a mutation-specific nested PCR. Of those 18 samples, seven amplified with primers specific for the Thr-108 mutation (proguanil resistance), one with the wild type (Ser-108), and 10 did not amplify. Of these 10 samples, three were identified as P. falciparum using a species-specific diagnostic nested PCR base on sequences from the small ribosomal RNA subunit gene. Overall, 51.6% of the samples amplified for the Asn-108 mutation, 10.9% for the Thr-108 mutation, 35.9% with the wild type specific primer, and 4.8% did not amplify with any of the DHFR primers. We observed variability in the frequency of the mutation between the different geographic location. The frequency of the Asn-108 and Thr-108 mutations in the state of Narifio was 25% each, while in Valle del Cauca the frequencies were 59% and 11%, respectively. These results contrast with observations in Brazil in which the Asn-108 mutation was found in 90% of the blood samples screened.

Differential expression of systemic cytokine profiles in Chagas' disease is associated with endemicity of Trypanosoma cruzi infections

Chagas' disease is a serious public health problem in Paraguay, however, the immunoepidemiology of the disease has not been well documented. A preliminary cross-sectional survey was carried out in two villages of the Paraguayan Chaco region and in five villages of the Oriental region to assess the endemicity of Trypanosoma cruzi infections. Thereafter, a subset of individuals (ages ranging from 23 to 65 years) participated in a follow-up study to evaluate clinical and parasitological parameters. Physical examinations and electrocardiograms (ECG) were conducted and blood samples collected for parasite detection and serology. The most frequent ECG abnormalities which were observed among chagasic individuals were left anterior hemifascicular block and right bundle branch block. Thirty-two of these subjects, seropositive and non-parasitemic from the high endemic Chaco (n = 16) and low endemic Oriental (n = 16) regions, were randomly selected for an analysis of T. cruzi-induced expression of cytokines IL-2, IFN-gamma, IL-4 and IL-10 by RT-PCR. The individuals were grouped (n = 8) according to the presence or absence of abnormal ECG. In subjects that exhibited abnormal ECG profiles, five of eight (63%) individuals from the high endemic area showed a dominant type 2 (IL-4) response, whereas a comparable number (63%) of subjects from the low endemic area expressed a strong type 1 (IFN-gamma) response; the remainder (37%) presented a Th0-type (IFN-gamma, IL-4) response. Subjects with normal ECG showed a defined cytokine profile according to endemicity. All subjects from the high endemic region showed a Th0 response, whereas 100% of the individuals from the low endemic area demonstrated a type 1 response. In most chagasic patients regardless of ECG profile and endemicity, IL-2 expression was depressed, while IL-10 mRNA transcripts were consistently elevated. Taken together, these data indicate that chronic human chagasic disease is associated with increased systemic production of type 2 cytokines in response to T. cruzi infection and may be involved in the reciprocal down-regulation of IL-2 production.

Cytokine responses in Trypanosoma cruzi-infected children in Paraguay

Both parasite and host immune factors may contribute to the development and progression of chronic chagasic cardiomyopathy during Trypanosoma cruzi infections. The present study targeted infected children (5-14 years of age) from an endemic area of Paraguay in an analysis of T. cruzi-specific cytokine profiles. This age group is characteristically the most affected by the early phases of infection. Trypanosoma cruzi-induced cytokine gene expression (interleukin-2 [IL-2], and interferon-gamma [IFN-gamma], IL-4, and IL-10) was studied in 25 seropositive children categorized as being either acute, symptomatic, with Romana's sign (n = 2), or early, indeterminate (postacute, n = 23). Acutely infected children showed a distinct T helper cell-1 (Th1)-type (IFN-gamma) cytokine response to infection. The cytokine pattern that was observed in the seropositive, asymptomatic (early, indeterminate) group was of the Th0 type (expression of both IFN-gamma and IL-4). We hypothesize that selective induction of a Th0-type cytokine pattern is important for development of cell-mediated and humoral immune responses that suppress parasite burden, thereby prolonging the onset or limiting the severity of chronic Chagas' disease later in life.

Comparison of the amplified Mycobacterium tuberculosis (MTB) direct test, Amplicor MTB PCR, and IS6110-PCR for detection of MTB in respiratory specimens

Several nucleic acid amplification techniques (NAAT) have been developed for rapid and direct detection of Mycobacterium tuberculosis (MTB) from clinical specimens. This study compared the performances of the Gen-Probe Amplified MTB Direct Test (AMDT), Roche Amplicor MTB PCR test, and an IS6110-PCR assay with acid-fast smear and culture in the detection of MTB from 428 respiratory specimens from 259 patients. Patients' charts were reviewed for clinical correlation. Of 98 specimens that were clinically positive for MTB, acid-fast smear was positive in 50% of cases, culture in 93%, IS6110-PCR in 83%, AMDT in 84%, and Amplicor MTB PCR in 80%. Of 337 specimens that were negative for MTB, 117 (35%) were positive for nontuberculous mycobacteria. Specificities were as follows: smear, 89%; culture, 100%; IS6110-PCR, 99%; AMDT, 98%; and Amplicor MTB PCR, 96%. The accuracies of the tests were 80%, 98%, 96%, and 92%, respectively. MTB culture-positive specimens that were smear-negative were detected by AMDT and IS6110-PCR in 77% of cases and by Amplicor MTB PCR in 70%. NAAT was less sensitive than was culture for detection of MTB, but all these techniques had acceptable accuracy and were completed within hours. NAAT may be useful for rapid screening of respiratory specimens to distinguish MTB from nontuberculous mycobacteria infection in order to isolate patients.

Development of conventional subunit vaccines for anaplasmosis and babesiosis

Tick-borne hemoparasitic diseases of cattle continue to impact the beef industry throughout a large portion of the world. A substantial amount of research is currently focused on development of improved vaccines. The two main approaches being followed are: (1) use of conventional inactivated or native protein subunit vaccines, and (2) development of recombinant DNA technology for expression of selected immunogens. Recombinant or synthetic peptide based vaccines hold promise owing to the exquisitely defined nature of the product. However, the development is long-term, and will require extensive testing and risk assessment before field trials can be considered. Until then, more conventional subunit immunogens may offer an attractive alternative, and can be defined immunologically better than before. This paper reviews progress in the development of improved vaccines for anaplasmosis and babesiosis with an emphasis on the characterization of culture-derived babesial exoantigens. Both in vitro and in vivo information is presented.

Antibody responses to Plasmodium falciparum sporozoite-, liver- and blood-stage synthetic peptides in migrant and autochthonous populations in malaria endemic areas

This study evaluates the differences in host immune responses to defined plasmodial antigens in four geographically different regions in which malaria is endemic. Sera from 527 individuals were tested for the presence of antibodies specific for three types of plasmodial antigen: liver-stage antigen (LSA-1), blood-stage antigen (SPF 70) and circumsporozoite (CS) antigen (NANP)4. The individuals taking part in the study comprised: patients with transfusional malaria due to Plasmodium falciparum or P. vivax; non-immune migrants residing in an endemic area in Rondônia; Amazonian Indians from the states of Pará (Xingu PA) and Mato Grosso (Xingu MT); people living in a hyperendemic area in Africa (Burkina-Faso); and controls that had never been to a malaria endemic area. None of the transfusional sera displayed antibodies against sporozoite or to liver stage antigen, although 80% of the P. falciparum transfusional malaria sera contained IgG antibodies against the blood-stage peptide. A low percentage of Indians from Xingu PA and of non-immune migrants displayed antibodies against liver-stage (27% and 17%) and sporozoite (11% or d 12%) peptides, although a greater frequency of antibodies against blood-stage peptide (50% and 49%) was observed in both cases. Indians from Xingu MT exhibited a greater frequency of antibodies against liver, sporozoite and blood-stage peptides (45%, 50% and 58%). Only hyperimmune African individuals exhibited higher percentages of antibodies against liver- (64%) and blood-stage antigens (87%), contrasting with a low frequency of antibodies against the CS repeat (33%). Taken together, the present data confirm that Rondonian migrants and Indians from Xingu PA constitute populations with limited exposure and immunity to P. falciparum malaria infection and conversely, Xingu MT Indians and Africans have been more exposed to malaria infection. In conclusion this study indicates that the immune response to these malaria parasite peptides can be used to assess malaria transmission in epidemiological surveys.

Malaria diagnosis: identification of an anti-40-kDa polypeptide antibody response associated with active or recent infection and study of the IgG/IgM ratio of antibodies to blood-stage Plasmodium falciparum antigens

The need for an alternative methodology to assess disease activity in the case of malaria led us to evaluate the usefulness of studying the humoral immune response to establish the diagnosis of past or recent malaria. For this purpose, we analyzed sera from 439 individuals living in endemic areas of the Amazon region (Ariquemes, Rondonia). Individuals were classified according to the number and the date of past crises. The enzyme-linked immunosorbent assay (ELISA) was performed to evaluate the IgG/IgM ratio so as to discriminate acute or recent malaria from past infections against crude and defined (SPF70) Plasmodium falciparum asexual blood-stage antigens. We also analyzed the humoral immune response against components presented in crude P. falciparum antigen by the immunoblot technique. Use of the IgG/IgM ratio values did not allow us to differentiate acute from past infections. However, when we analyzed the humoral immune response to parasite components, we were capable of identifying a polypeptide with a molecular weight ranging up to 40 kDa, which was recognized by all parasitized polyinfected individuals studied but not by individuals with negative thick blood smears. In view of these data, we conclude that the 40-kDa polypeptide may represent a powerful tool in the diagnosis of acute malaria, mainly for screening blood donors in endemic areas.

Detection of antibodies to a 70 kDa Plasmodium falciparum exoantigen in malarious subjects using synthetic peptides

Indirect fluorescent antibody (IFA) tests and enzyme-linked immunosorbent assays (ELISA) were used to measure antibodies to Plasmodium falciparum in patients with acute malaria from Bolivar State, Venezuela. Antibody titers increased significantly with repeated malarial episodes. IgG antibody responses to 4 synthetic peptides (termed C2, C3, C5, C10) derived from a 70 kDa P. falciparum (Indochina I/CDC strain) exoantigen were evaluated by a peptide-ELISA with overall positivity rates of 20%, 40%, 20% and 58%, respectively. Seropositivity to peptide C10 was consistently over 50% (range 53-75%) among patients of different ages. Overall IgM reactivity to the respective peptides was 53%, 30%, 83% and 70%. IgM reactivity was generally greater in patients with primary malarial infections. The ELISA is a useful adjunct to the IFA in measuring naturally-occurring antibodies to specific parasite proteins.

Immunogenicity and antigenic reactivity of a carrier-free synthetic peptide complex derived from a 70-kDa Plasmodium falciparum exoantigen

A 70-kDa Plasmodium falciparum exoantigen was purified from supernatant fluids of continuous in vitro P. falciparum cultures using sequential cation-exchange and high performance liquid chromatographic procedures. The purified protein was then digested with chymotrypsin and amino-acid sequences were determined for the resulting fragments. Four peptides (termed C2, C3, C5, and C10) were subsequently selected for synthesis based on their predictability for antigenic sites. The peptides were effectively used as a synthetic immunogen (SPf70) when they had been copolymerized with glutaraldehyde in the absence of a carrier. When given with Freund's adjuvant, the synthetic peptide complex was found to be highly immunogenic in rabbits. Serologic reactivity to the peptide complex and peptides C2 and C5 was uniformly high, followed by the responses to peptides C3 and C10. Peptide antigenicity was also assessed with human anti-P. falciparum sera from malaria-endemic regions of Uganda and Venezuela. Enzyme-linked immunosorbent assay (ELISA) data showed that anti-P. falciparum antibodies were specific for and reactive to the peptides. The specificity of the rabbit anti-SPf70 antibodies for P. falciparum antigen was shown by immunoprecipitation of metabolically labeled proteins and by immunoblotting. Herein we describe the peptide sequences of a 70-kDa P. falciparum exoantigen (Pf70) that, when synthesized and constructed as a copolymer (SPf70), are capable of inducing the formation of antibodies that are reactive with the native malarial protein. The high immunogenicity and antigenic reactivity of SPf70 indicate the potential use of this synthetic peptide polymer as an immunogen and a diagnostic reagent.

Anaplasmosis in Uganda. II. Prevalence of bovine anaplasmosis

The prevalence of bovine anaplasmosis was studied in 320 Zebu cattle randomly selected from three regions of Uganda (central, south-western and north-western) using DOT-ELISA, Western immunoblotting, Rapid Card Agglutination Test (RCAT), Capillary Tube Agglutination Test (CAT), Complement Fixation Test (CFT), and parasitological techniques. Dried blood on Whatman filter paper no. 1 was eluated in PBS 0.05% Tween 20 prior to testing at an initial dilution of 1:25. The incidence of parasitaemia ranged from 25% in the central region to 35% in the north-western region and the serological prevalence was lower in the central region and highest in the north-west. Prevalence rates assayed by DOT-ELISA and Western immunoblotting were 1.5-fold greater than those tested with RCAT and 3-fold greater than in CAT. The overall prevalence rates by DOT-ELISA and Western immunoblotting compared favourably with CFT data. The present data utilizing dried blood on filter papers indicate that there is a high prevalence of anaplasmosis in those regions of Uganda surveyed and it confirms our observations and those of others that collecting blood on filter papers is a suitable technique for large-scale screening and for seroepidemiological studies.

Anaplasmosis in Uganda. I. Use of dried blood on filter paper and serum samples for serodiagnosis of anaplasmosis--a comparative study

The suitability of blood collected on filter papers in comparison with corresponding conventional serum samples in the diagnosis of bovine anaplasmosis was studied using the Complement Fixation Test (CFT), DOT-ELISA, Western immunoblot and Rapid Card Agglutination Test (RCAT). Dried blood on Whatman filter paper no. 1 was eluted in 1.8 ml of PBS 0.05% Tween 20 given an initial dilution of 1:100. The reactivity in both DOT-ELISA and Western immunoblotting was similar to that obtained with the sera diluted 1:100. Filter paper samples gave lower reactivity in all the tests as compared with corresponding serum samples. There was no significant difference in the reactivity between the eluates from filter papers stored at room temperature and those stored at 4 degrees C. Storage at room temperature did not significantly affect reactivity for up to 6 months. Eluates from filter papers stored for 6 months at room temperature continued to give similar reactivity to those from freshly prepared filter papers in both DOT-ELISA and Western blot, and in the Rapid Card Agglutination Test. It is concluded that collecting blood on filter papers is a suitable technique for large-scale screening and for seroepidemiological studies on anaplasmosis, and offers many advantages especially in developing countries where transport and cold chain facilities are a major constraint.

Anaplasmosis in Uganda. I. Use of dried blood on filter papers and serum samples for serodiagnosis of anaplasmosis--a comparative study

The suitability of blood collected on filter papers in comparison with corresponding conventional serum samples in the diagnosis of bovine anaplasmosis was studied using the complement fixation test, DOT-ELISA, Western immunoblot and rapid card agglutination test. Dried blood on Whatman filter paper no. 1 was eluted in PBS 0.05% Tween 20 giving an initial dilution of 1:10. The reactivity of the eluted samples in both DOT-ELISA and Western immunoblotting were similar to those obtained with the corresponding straight serum sample dilutions. Filter paper samples gave lower reactivity in the remaining tests when compared with corresponding serum samples. There was no significant difference in the reactivity between the eluates from filter papers stored at temperatures ranging between 15.5 and 24 degrees C and those kept refrigerated. Storage at 15.5 to 24 degrees C did not significantly affect reactivity for up to six months. Eluates from filter papers stored for six months at 15.5 to 24 degrees C continued to give similar reactivity as those from freshly prepared filter papers in both DOT-ELISA and Western blot, and in the rapid card agglutination test. It is concluded that collecting blood on filter papers is a suitable technique for large scale seroepidemiological studies on anaplasmosis and offers many advantages in developing countries where transport and cold chain facilities are a major constraint.

Prevalence and control of Babesiosis in the Americas

This review presents up-to-date information on the distribution and control measures of babesiosis in Latin America. Bovine babesiosis caused by Babesia bovis and B. bigemia will be emphasized. The disease is endemic in most countries and poses a serious economic burden on livestock production in the region (U.S. $1365 million/year, FAO, 1989). Of the estimated 250 million cattle in Central and South America, approximately 175 million (70%) are in tick-infested regions. Humid, tropical and subtropical areas favor development of the main vector, the one-host tick Boophilus microplus. In many regions bovine babesiosis is enzootically stable as a consequence of a balanced host-parasite relationship. However, Latin America offers a wide range of epidemiologic conditions that are influenced by variations from tropical to cool climates and by susceptible purebred cattle that are regularly imported to upgrade local stocks. The control measures employed in most countries for babesiosis essentially rely on chemotherapy, use of acaricides for B. microplus, and to a lesser degree, on immunization methods. In general, these measures are expensive, time consuming, and in many cases, provide limited success. Finally, the zoonotic potential of babesiosis will be addressed, with special emphasis on the situation in the United States. Even though bovine babesiosis has long been eradicated from the U.S.A., human babesiosis is endemic in the northeastern region of the country.

Field evaluation of an exoantigen-containing Babesia vaccine in Venezuela

Bovine babesiosis is endemic in Venezuela, causing significant losses in highly susceptible imported cattle. Current immunoprophylactic methods include the less desirable use of live parasites. Inactivated vaccines derived from exoantigen-containing supernatant fluids of in vitro Babesia bovis and B. bigemina cultures have been developed and constitute a major improvement in vaccine safety, stability and ease of handling. Vaccination trials conducted under field conditions provide the final evaluation of a culture-derived B. bovis-B. bigemina vaccine. During a 5-year period, approximately 8,000 cattle were vaccinated and 16 clinical trials carried out in 7 states of Venezuela. Clinical, serologic and parasitologic data were collected monthly from 10% of the animals over a 2-year period. Data were also collected from a similar number of nonvaccinated control cattle. Analysis of results from these trials demonstrated a reduction in the incidence of clinical disease among vaccinated animals and complete protection against mortality caused by babesiosis. Vaccine efficacy was measured calculating the incidence rates of disease and mortality among vaccinated and nonvaccinated cattle. Use of this inactivated vaccine offers the best combination of safety, potency and efficacy for the effective immunoprophylactic control of bovine babesiosis.

Molecular approaches to malaria and Babesisosis diagnosis

The development of additional methods for detecting and identifying Babesia and Plasmodium infections may be useful in disease monitoring, management and control efforts. The preliminary evaluate synthetic peptide-based serodiagnosis, a hydrophilic sequence (DDESEFDKEK) was selected from the published BabR gene of B. bovis. Immunization of rabbits and cattle with the hemocyanin-conjugated peptide elicited antibody responses that specifically detected both P. falciparum and B. bovis antigens by immunofluorescence and Western blots. Using a dot-ELISA with this peptide, antisera from immunized and naturally-infected cattle, and immunized rodents, were specifically detected. Reactivity was weak and correlated with peptide immunization or infection. DNA-based detection using repetitive DNA was species-specific in dot-blot formats for B. bovis DNA, and in both dot-blot and in situ formats for P. falciparum; a streamlined enzyme-linked synthetic DNA assay for P. falciparum detected 30 parasites/mm3 from patient blood using either colorimetric (2-15 h color development) or chemiluminescent detection (0.5-6-min exposures). Serodiagnostic and DNA hybridization methods may be complementary in the respective detection of both chronic and acute infections. However, recent improvements in the polymerase chain reaction (PCR) make feasible a more sensitive and uniform approach to the diagnosis of these and other infectious disease complexes, with appropriate primers and processing methods. An analysis of ribosomal DNA genes of Plasmodium and Toxoplasma identified Apicomplexa-conserved sequence regions. Specific and distinctive PCR profiles were obtained for primers spanning the internal transcribed spacer locus for each of several Plasmodium and Babesia species.

Anaplasmosis in Uganda. II. Prevalence of bovine anaplasmosis in Uganda

The prevalence of bovine anaplasmosis was studied in 320 Zebu cattle randomly selected from three regions of Uganda: (Central, Southwestern and Northwestern) using dot-ELISA, Western immunoblotting, rapid card agglutination test (RCAT), capillary tube agglutination test (CAT), complement fixation test (CFT), and parasitological techniques. Dried blood on Whatman filter paper No. 1 was eluted in PBS 0.05% Tween 20 prior to testing at an initial dilution of 1:25. The prevalences of parasitaemia were 25% in the central region, 28% in the southwestern region, and 35% in the northwestern region, and the serological prevalence was lowest in the central region and highest in the northwest. Overall, prevalence rates obtained by dot-ELISA (61.9%) and Western immunoblotting (62.5%) were 1.5 times those obtained by RCAT (41%) and three times those obtained by CAT (22.5%). The overall prevalence rates obtained by dot-ELISA and Western immunoblotting compared favourably with the CFT data. The present data utilizing dried blood on filter papers indicate that there is a high prevalence of anaplasmosis in those regions of Uganda surveyed, and confirm our observations and those of others that collecting blood on filter papers is a suitable technique for large scale screening and for seroepidemiological studies.

Efficacy of purified Anaplasma marginale initial bodies as a vaccine against anaplasmosis

Anaplasma marginale initial bodies of the Florida strain were purified from infected erythrocytes using a combination of ultrasonic disruption, nonionic detergent and differential centrifugation. Immunochemical analysis revealed at least 12 A. marginale proteins in the molecular mass (m) range 81-15 kDa with a prominent band at 38 kDa. Several of these proteins remained insoluble in the presence of nonionic detergent. Preparations of purified Anaplasma initial bodies contained negligible erythrocytic contamination, as confirmed by the minimal induction of isoantibodies against bovine blood group antigens and the absence of delayed-type hypersensitivity to erythrocytic antigens in immunized animals. A total of 33 crossbred and purebred Holstein cattle were vaccinated with either 1.5, 1.0, or 0.1 mg protein of intact initial bodies, or with 1.0 mg of solubilized Anaplasma protein. The immunogens were supplemented with 3.0 mg Quil-A saponin adjuvant and administered in 2 subcutaneous injections given at a 4-week interval. A similar number of nonvaccinated cattle served as controls. Three months after vaccination, all cattle were challenged by inoculation of 10(9) virulent A. marginale of either the homologous (Florida) or heterologous (Venezuelan) strains. Vaccinated cattle showed solid protection after homologous and heterologous challenge, characterized by parasite clearance and minimal hematocrit reductions. Initial data from four field vaccine trials revealed a reduced incidence of clinical anaplasmosis among immunized animals. Use of immunogens consisting of purified A. marginale initial bodies offers a potential immunoprophylactic approach to control of bovine anaplasmosis.

Use of the dot enzyme-linked immunosorbent assay with isolated Anaplasma marginale initial bodies for serodiagnosis of anaplasmosis in cattle

Isolated Anaplasma marginale initial bodies were successfully used in a dot ELISA for rapid detection of antibodies to Anaplasma organisms. The enzyme immunoassay used only 25 ng of antigen dotted onto nitrocellulose disks. Antigen-antibody complexes were detected by use of alkaline phosphatase-conjugated protein A, and reactions were read visually after addition of a precipitable, chromogenic substrate. The test allowed the processing of multiple sera, either for screening or for titer determination, in less than 3 hours and was found to be as sensitive as the indirect fluorescent antibody test. The overall performance of the dot ELISA, using isolated A marginale initial bodies, for 580 bovine serum samples was as follows: sensitivity, 93%; specificity, 96%; and predictive value, 95%. Cross-reactivity was not observed with sera positive to Babesia bovis and B bigemina, Trypanosoma vivax, or common bacteria or viruses infecting cattle. The antigen dotted onto nitrocellulose disks was stable when stored at -20, 4, or 25 C. Compared with the indirect fluorescent antibody test, the dot ELISA allowed easier, faster, and more objective interpretation of results. Its simplicity and low cost combined with high sensitivity and specificity indicate that this assay could effectively replace serologic assays currently used for diagnosis of anaplasmosis in cattle.

Immunoprophylactic control of bovine babesiosis: role of exoantigens of Babesia

A major breakthrough in babesiosis vaccine research was achieved with the development of methods for continuous propagation in vitro of Babesia parasites. The development of a soluble, exoantigen-containing immunogen, free of erythrocytic antigens, has been proposed as a practical and realistic means of immunoprophylactic control of babesiosis. Such immunogens have been tested for immunogenicity of different strains, minimal protective dose, and protective efficacy of a combined B. bovis-B. bigemina immunogen. During the last 7 years, most of these aspects have been studied in a co-operative research programme between the University of Illinois and the Veterinary Research Institute of Venezuela. The Babesia exoantigen vaccine prevents clinical disease, is effective against different parasite strains, induces protective immunity for at least 13 months, does not immunize against host blood groups, is antigenically stable for at least 3 years at 4 degrees C, and is available in large quantities. Continued improvement of currently available culture-derived immunogens will best guarantee the successful production of food-producing animals in the tropics. Since July 1984, 16 field vaccination trials have been conducted in 7 states of Venezuela in areas where large-scale dairy and beef production is crucial for the livestock industry. These ranches encompassed a cattle production of 14,000, of which 3000 have been vaccinated with a combined B. bovis-B. bigemina immunogen in 2 subcutaneous inoculations with a 4-week interval. In the first 5 trials, a 1-year monitoring period following vaccination and natural tick exposure indicated that the culture-derived vaccine has effectively controlled the clinical manifestation of infection. Studies on antigen characterization are shifting the emphasis from crude antigenic preparations to purified polypeptides, isolated and identified using new biochemical techniques. Current research efforts are directed toward isolation of protective antigens and the production of synthetic vaccines. Until optimal molecular vaccines are developed, a polyvalent inactivated B. bovis-B. bigemina immunogen may offer the best combination of potency, efficacy and safety available for effective immunoprophylaxis against bovine babesiosis.

Detection of culture-derived Babesia bovis exoantigen using a two-site enzyme immunoassay

Soluble exoantigens in the supernatants of Babesia bovis cultures have been shown to be efficient immunogens against bovine babesiosis. We used a two-site enzyme immunoassay to monitor the release of these antigens during in vitro cultivation. Bovine immunoglobulin G was isolated from serum of an adult cow previously immunized with culture-derived B. bovis exoantigens and challenged via needle with virulent parasites. The specific immunoglobulin G was used as a capture antibody and as an enzyme-conjugated recognizing antibody. The optimal protein concentration of capture antibody was 10 micrograms/ml. The 24-h cultures showed the greatest antigen concentration. The test was sensitive for detection of differences in species-specific antigenic activity among B. bovis isolates, for determining loss of antigenicity during storage and formalinization, and for monitoring the kinetics of exoantigen release during in vitro cultivation. Antigens cross-reactive with the other major Babesia species of cattle, Babesia bigemina, were also detected with this assay. The high specificity, sensitivity, and reproducibility of this technique should facilitate detection and quantitation of Babesia antigens during purification and in standardization of candidate immunogens.

Antigenic relationship between Plasmodium falciparum and Babesia bovis: reactivity with antibodies to culture-derived soluble exoantigens

Antigenic similarities between Plasmodium and Babesia parasites of the phylum Apicomplexa have been previously demonstrated primarily by the serological cross reactivity observed in the indirect fluorescent antibody (IFA) test. We have now studied the antigenic relationship between the human malaria parasite, Plasmodium falciparum, and the hemoparasitic agent of cattle, Babesia bovis, using rabbit monospecific antibodies produced against individual culture-derived P. falciparum polypeptides and bovine polyspecific antibodies to B. bovis exoantigens. These respective antibodies were found to be distinctly cross reactive in the IFA test using infected erythrocytes (squirrel monkey--P. falciparum; bovine--B. bovis) as antigen substrates. Immunofluorescence was shown to be highly specific for parasite surfaces. Additionally, the degree of reactivity with soluble exoantigens contained in Plasmodium and Babesia culture supernatants was monitored by a two-site enzyme immunoassay employing the cross-reactive antibodies. Further evidence for antigenic cross reactivity between P. falciparum and B. bovis parasites was shown with the in vitro inhibition assay. Antibodies to P. falciparum and B. bovis were found to be highly inhibitory for the in vitro growth of P. falciparum in human erythrocytes.

Bovine babesiosis: induction of protective immunity with culture-derived Babesia bovis and Babesia bigemina immunogens

The comparative protective efficacy of culture-derived Babesia bovis and B. bigemina immunogens against challenge exposure of susceptible crossbred cattle to heterologous strains was examined and correlated with the antigenic threshold requirements for induction of protective immunity. Strong protection was observed in animals vaccinated with 10 ml-equivalent doses of soluble, B. bovis exoantigen-containing supernatant fluids. Similar protective responses to B. bigemina exoantigens were evident even at 1 ml-equivalent dosages. In addition, the efficacy of a combined B. bovis-B. bigemina immunogen was assessed with a dose-response analysis in highly susceptible, purebred cattle. Vaccinated animals were protected against clinical babesiosis, and significant weight gains were recorded after challenge infection with virulent parasites.

Heterologous strain immunity in bovine babesiosis using a culture-derived soluble Babesia bovis immunogen

The cross-protective capacity of culture-derived soluble immunogens against heterologous Babesia bovis strains from different geographical locations of Latin America was examined. Susceptible yearling cattle were either immunized with immunogens derived from Venezuelan or Mexican strains, or were administered a multi-component immunogen containing antigens of the Australian, Mexican and Venezuelan strains. Cattle were challenged with virulent B. bovis organisms of the Argentinian, Colombian, Ecuadorean, Mexican and Venezuelan strains. The major parameters used to evaluate cross-protection were the following: presence, level and duration of parasitemia; maximal PCV reduction; level and duration of fever; determination of fibrinogen and cryofibrinogen; homologous and heterologous antibody levels; and net gains in body weight. Results showed good protection with a Venezuelan B. bovis immunogen after homologous and heterologous challenge exposures. A low degree of cross-immunity was observed when cattle vaccinated with the Mexican immunogen were challenged with each of the heterologous strains.

Modified indirect fluorescent antibody test for the serodiagnosis of Anaplasma marginale infections in cattle

A modified indirect fluorescence antibody technique was used for the serodiagnosis of Anaplasma marginale infections in cattle. Nonspecific antibodies adherent to infected erythrocytes were removed, using acidic glycine buffer. Evans blue was used as a counterstain.

Localization of culture-derived soluble Babesia bovis antigens in the infected erythrocyte

Immunoprecipitates derived from crossed immunoelectrophoresis of Babesia bovis culture supernatant fluid against a polyspecific anti-B. bovis serum were used to produce monospecific rabbit antibodies to individual B. bovis antigens. These antibodies were utilized in an immunofluorescence test to identify the location of the respective antigens within the infected erythrocyte. Two antigens were found on or near the erythrocyte membrane, while a third antigen was directly associated with the parasite itself.

Isolation of an in vitro-produced soluble Anaplasma-albumin complex

A soluble Anaplasma-albumin complex was isolated from supernatants of A marginale cultures by affinity chromatography. Holstein calves inoculated with this fraction produced anti-A marginale antibodies detected in the indirect fluorescent antibody test at titers similar to those found in cattle immunized with unfractionated culture supernatant. Titers of both groups peaked slightly above 1:2,000 on postinoculation day 46.