Seroepidemiology of bovine anaplasmosis and babesiosis in Venezuela

Seroprevalence and risk factors for Trypanosoma evansi, the causative agent of surra, in the dromedary camel (Camelus dromedarius) population in Southeastern Algeria

Surra, caused by Trypanosoma evansi, is a re-emerging animal trypanosomosis, which is of special concern for camel-rearing regions of Africa and Asia. Surra decreases milk yield, lessens animal body condition score and reduces market value of exported animals resulting in substantial economic losses. A cross-sectional seroprevalence study of dromedary camels was conducted in Algeria, and major risk factors associated with infection were identified by collecting data on animal characteristics and herd management practices. The seroprevalence of T. evansi infection was determined in sera of 865 camels from 82 herds located in eastern Algeria using an antibody test (card agglutination test for Trypanosomiasis – CATT/T. evansi). Individual and herd seroprevalence were 49.5% and 73.2%, respectively, indicating substantial exposure of camels to T. evansi in the four districts studied. Five significant risk factors for T. evansi hemoparasite infection were identified: geographical area, herd size, husbandry system, accessibility to natural water sources and type of watering. There was no association between breed, sex or age with T. evansi infection. Results of this study provide baseline information that will be useful for launching control programmes in the region and potentially elsewhere.

Incidência de Anaplasma marginale, Babesia bigemina e Babesia bovis em bezerros no semiárido paraibano

RESUMO: Este estudo avaliou a incidência de infecções naturais pelos agentes da tristeza parasitária bovina (TPB), Anaplasma marginale, Babesia bovis e Babesia bigemina, em bezerros nascidos em cinco fazendas do semiárido paraibano. Em cada fazenda, foram coletadas amostras de sangue de 6 a 14 bezerros a cada 14 dias durante os primeiros 12 meses de vida de cada animal. As amostras de sangue foram processadas por microhematócrito e testadas por PCR para detecção de DNA de A. marginale, B. bovis e B. bigemina. Em paralelo, foram quantificadas as infestações por carrapatos nos bovinos nas cinco fazendas, assim como as populações de tabanídeos em três fazendas. De 41 bezerros monitorados durante o primeiro ano de vida, 25 (61,0%) apresentaram PCR positivo para A. marginale, 7 (17,1%) para B. bigemina e 3 (7,3%) para B. bovis. Os valores de incidência da infecção por A. marginale variaram de 83,3% a 100% em quatro fazendas. A infecção por B. bigemina ocorreu em bezerros de apenas duas fazendas (incidências de 12,5% e 85,7%) e a por B. bovis em apenas uma (incidência de 42,8%). Em uma fazenda os 14 bezerros permaneceram negativos para A. marginale, B. bigemina e B. bovis durante os 12 meses de acompanhamento. Os resultados de PCR foram confirmados por sequenciamento de DNA de produtos amplificados. A presença de carrapatos Rhipicephalus (Boophilus) microplus foi verificada somente em duas propriedades, nas quais houve infecção por A. marginale, B. bigemina e B. bovis (este último agente em apenas uma delas). Foram capturados 930 tabanídeos no estudo, a maioria durante os períodos de chuvas na região; 70,7% dos tabanídeos corresponderam a Tabanus claripennis. Houve associação significativa entre PCR positivo para A. marginale ou B. bigemina e menores valores de hematócrito. Este estudo demonstra que, mesmo avaliando apenas cinco propriedades rurais, a incidência dos agentes da TPB ocorreu de forma heterogênea na região, corroborando o status de área de instabilidade enzoótica para TPB previamente relatado para o semiárido paraibano.

A comparison of seroprevalence and risk factors for Theileria parva and T. mutans in smallholder dairy cattle in the Tanga and Iringa regions of Tanzania

A cross sectional serological survey was carried out in two geographical small-scale dairying areas of Tanzania to determine the distribution and prevalence and to quantify risk factors for Theileria parva and T. mutans during the period January to April 1999. The prevalence of serum antibodies to these two Theileria parasites was determined using an indirect enzyme-linked immunosorbent assay (ELISA) technique. The results suggest that the parasites are widely distributed through out the two study sites and seroprevalence of 23% and 48% for T. parva were obtained for Tanga and Iringa regions, respectively. Seroprevalence of T. mutans ranged from 17% in the Tanga region to 40% in the Iringa region. Farm and animal data were collected and analysed by multiple logistic regression models to explore the risk factors associated with seroprevalence to T. parva and T. mutans pathogens. In both regions, seroprevalence for the two Theileria spp. pathogens increased significantly with age. Pasture grazed animals were more likely to be seropositive than those that were zero-grazed. Among individual animal characteristics, seropositivity was higher in cash-bought and charity gifted animals compared to cattle obtained using a formal credit agreement. Further studies on the relative role of risk factors for theileriosis found in this study may assist in the development of an effective control package.

Spatial and management factors associated with exposure of smallholder dairy cattle in Tanzania to tick-borne pathogens

A cross-sectional study of serum antibody responses of cattle to tick-borne pathogens (Theileria parva, Theileria mutans,Anaplasma marginale, Babesia bigemina and Babesia bovis) was conducted on smallholder dairy farms in Tanga and Iringa Regions of Tanzania. Seroprevalence was highest for T. parva (48% in Iringa and 23% in Tanga) and B. bigemina (43% in Iringa and 27% in Tanga) and lowest for B. bovis (12% in Iringa and 6% in Tanga). We use spatial and non-spatial models, fitted using classical and Bayesian methods, to explore risk factors associated with seroprevalence. These include both fixed effects (age, grazing history and breeding status) and random effects (farm and local spatial effects). In both regions, seroprevalence for all tick-borne pathogens increased significantly with age. Animals pasture grazed in the 3 months prior to the start of the sampling period were significantly more likely to be seropositive for Theileria spp. and Babesia spp. Pasture grazed animals were more likely to be seropositive than zero-grazed animals for A. marginale, but the relationship was weaker than that observed for the other four pathogens. This study did not detect any significant differences in seroprevalence associated with other management-related variables, including the method or frequency of acaricide application. After adjusting for age, there was weak evidence of localised (<5 km) spatial correlation in exposure to some of the tick borne diseases. However, this was small compared with the 'farm-effect', suggesting that risk factors specific to the farm were more important than those common to the local neighbourhood. Many animals were seropositive for more than one pathogen and the correlation between exposure to the different pathogens remained after adjusting for the identified risk factors. Identifying the determinants of exposure to multiple tick-borne pathogens and characterizing local variation in risk will assist in the development of more effective control strategies for smallholder dairy farms.

Seroprevalence Estimation and Risk Factors for A. marginale on Smallholder Dairy Farms in Tanzania

A cross-sectional serological survey of A. marginale was conducted on 200 randomly selected smallholder farms in each of the Tanga and Iringa Regions of Tanzania between January and April 1999. Sera, from dairy cattle of all ages, sexes and breeds were tested for antibodies against A. marginale using an indirect enzyme-linked immunosorbent assay. Antibodies to A. marginale were present in cattle throughout the study areas and the overall prevalence was 20% for Tanga and 37% for Iringa. The forces of infection based on the age seroprevalence profile were estimated at 8 for Tanga and 15 for Iringa per 100 cattle years-risk, respectively. In both regions, seroprevalence increased with age (beta = 0.01 and 0.017 per year of age, p < 0.005, in Tanga and Iringa, respectively). Older animals in Iringa were significantly and negatively associated with decreased seropositivity (beta = -0.002, p = 0.0029). Further results of logistic regression models reveal that geographic location of animals in Tanga was associated with seropositivity (odds ratio (OR) = 2.94, p = 0.005, for Tanga Rural and OR = 2.38, p = 0.066, for Muheza). Animals acquired as a gift in Iringa had higher odds for seropositivity than brought-in cattle (OR = 2.44, p = 0.005). Our study has identified and quantified some key risk factors that can guide planners devising disease control strategies.

Antigens and alternatives for control of Anaplasma marginale infection in cattle

Anaplasmosis, a tick-borne cattle disease caused by the rickettsia Anaplasma marginale, is endemic in tropical and subtropical areas of the world. The disease causes considerable economic loss to both the dairy and beef industries worldwide. Analyses of 16S rRNA, groESL, and surface proteins have resulted in the recent reclassification of the order Rickettsiales. The genus Anaplasma, of which A. marginale is the type species, now also includes A. bovis, A. platys, and A. phagocytophilum, which were previously known as Ehrlichia bovis, E. platys, and the E. phagocytophila group (which causes human granulocytic ehrlichiosis), respectively. Live and killed vaccines have been used for control of anaplasmosis, and both types of vaccines have advantages and disadvantages. These vaccines have been effective in preventing clinical anaplasmosis in cattle but have not blocked A. marginale infection. Thus, persistently infected cattle serve as a reservoir of infective blood for both mechanical transmission and infection of ticks. Advances in biochemical, immunologic, and molecular technologies during the last decade have been applied to research of A. marginale and related organisms. The recent development of a cell culture system for A. marginale provides a potential source of antigen for the development of improved killed and live vaccines, and the availability of cell culture-derived antigen would eliminate the use of cattle in vaccine production. Increased knowledge of A. marginale antigen repertoires and an improved understanding of bovine cellular and humoral immune responses to A. marginale, combined with the new technologies, should contribute to the development of more effective vaccines for control and prevention of anaplasmosis.

Attainment of endemic stability to Babesia bigemina in cattle on a South African ranch where non-intensive tick control was applied

The seroprevalence of Babesia bigemina and Babesia bovis antibodies in non-vaccinated cattle was monitored on a South African ranch. The main objective was to assess the endemic stability to bovine babesiosis in cattle maintained under relaxed tick-control measures. Cattle were bled at the age of 7, 8, 10, 17, 20 and 30-120 months and the sera tested for the presence of antibodies using the indirect fluorescent antibody (IFA) test. None of the animals were positive to B. bovis. Seroprevalence of B. bigemina antibodies was 46, 70, 90, 92, 54 and 82% in the various age classes, respectively. Endemic stability was therefore reached by the time the calves were 9 months old. The high seroprevalence of B. bigemina was probably due to the high vector tick population on the ranch, which would have encouraged frequent transmission of B. bigemina. An endemically stable situation to B. bigemina could therefore be achieved merely by adopting a tick-control method that allows a reasonable number of ticks on cattle rather than relying entirely on intensive tick control and vaccination.

Evaluation of an enzyme-linked immunosorbent assay with recombinant rhoptry-associated protein 1 antigen against Babesia bovis for the detection of specific antibodies in cattle

The gene encoding Babesia bovis rhoptry-associated protein 1 (RAP-1) was used to develop an enzyme-linked immunosorbent assay (ELISA) to measure specific antibodies against B. bovis. The B. bovis RAP-1 gene was subcloned into a baculovirus transfer vector, and the RAP-1 protein was expressed in insect cells infected with a recombinant baculovirus. The recombinant B. bovis RAP-1 of 65 kDa was detected with anti-RAP-1 mouse serum by Western blotting, and this recombinant RAP-1 was used as an antigen in the ELISA. The ELISA was able to differentiate between B. bovis-infected sera and B. bigemina-infected sera or noninfected normal bovine sera. The results demonstrate that the recombinant RAP-1 expressed in insect cells might be a useful antigen for the detection of antibodies to B. bovis.

Evaluation of an enzyme-linked immunosorbent assay using recombinant major surface protein 5 for serological diagnosis of bovine anaplasmosis in Venezuela

An indirect enzyme-linked immunosorbent assay (ELISA) was developed for the serological diagnosis of bovine anaplasmosis with purified recombinant major surface protein 5 (MSP5) of Anaplasma marginale produced in Escherichia coli. Serum antibody responses against MSP5 were detected in calves experimentally infected with A. marginale as early as 21 days postinfection and reached maximum titers at 28 days postinfection. The MSP5 ELISA performed with serum samples taken from field cattle from different regions of Venezuela showed a seroprevalence of 47%, which seems to be in accordance with the reported epidemiological status of bovine anaplasmosis in Venezuela. Positive results obtained in the MSP5 ELISA were further confirmed by immunoblotting, with the recombinant MSP5 as the antigen. Thus, these results confirmed the importance of MSP5 as a suitable antigen for the serological diagnosis of bovine anaplasmosis.

Sustainable tick and tickborne disease control in livestock improvement in developing countries

Tick and tickborne disease (TTBD) control is a major component of animal health programmes protecting livestock, thereby enhancing global food security. The present methods for TTBD control are reviewed and an integrated use of the tools is recommended with a broader view of how to link TTBD control to the control of other parasitic diseases. The work of FAO in this field is presented and it is advocated that, although there are still areas that need further investigation, a stage has been reached where robust integrated TTBD control schemes, based on ecological and epidemiological knowledge of ticks and their associated diseases, can be promoted and implemented. Major challenges are the implementation of these policies in the field through the continuation of the present on-going programme in Africa and support to Latin America and Asia. The importance of involving all parties, governments, international and private organisations and the agrochemical industry in developing sustainable, cost-efficient control programmes is stressed and a global strategy is proposed. The main thrust should now be to convince policy makers on the adoption of the strategies and veterinarians and farmers on their implementation.

Incidence and intensity of Babesia spp. sporokinetes in engorged Boophilus microplus from a dairy herd in Venezuela

The objective of this study was to determine the incidence and intensity of Babesia spp. sporokinetes in hemolymph of engorged females (EF) Boophilus microplus monthly detached from two herds of a local dairy breed of cattle named Carora breed. The experimental herds were located in 2 ranches, 45 km apart, having different management of tick control (TC). Proper methods of TC were commonly used at ranch "A," whereas ineffective methods were used at ranch "B," Babesia spp. sporokinetes were diagnosed in EF B. microplus by microscopic exam of tiny smears of hemolymph stained with Giemsa. A total of 537 smears were checked, and 108 were positive to Babesia spp. (20.1%). The incidence of Babesia spp. was higher (p < 0.01) in ranch "B," 22.3%, compared with the value detected in ranch "A," 6.5%. Incidence of Babesia spp. was greater in the dry season (Dec-Apr) compared with the values detected during the rainy season (May-Nov). The intensity of Babesia spp. was 3.43 at ranch "B" (p < 0.01), and 0.32 at ranch "A" during the rainy season. The values detected for intensity kept no correlation with those two seasons, although it is known that the incidence and seroprevalence of bovine babesiosis are greater during the dry season. The importance of these parameters in the epizootiology of bovine babesiosis in Venezuela is discussed.

Effect of management and inherent factors on birth seropositivity and seroconversion to Babesia bovis in calves in Costa Rica

The relationship between calf characteristics, farm management, seropositivity, and age at seroconversion to Babesia bovis was assessed. A total of 3624 samples obtained from 494 animals on 11 farms was analyzed by an indirect ELISA assay, and individual results classified as positive or negative. The animals were sampled from birth to weaning, beginning in April 1990 and ending in April 1992. We found 59.1% (n = 467) of seropositive neonatal calves (mean age 4.4 days). Using a logistic binomial regression model as the analytical method for predicting the likelihood of calf seropositivity, we found that the following factors were related to seroconversion at birth: time to colostrum consumption, place of birth, calving history, parity (number of lactations), and ecological life zone. To analyze the effect of management factors on time to seroconversion, we used the Proportional Hazards method. In this model the pattern of seroconversion was different for the type of production system. Calves from dual-purpose farms seroconverted earlier than calves from cow-calf farms.

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.

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.

Epidemiology of babesiosis and anaplasmosis in South and Central America

Babesiosis (Babesia bovis and Babesia bigemina) and anaplasmosis (Anaplasma marginale) affect native cattle from Uruguay and northern Argentina to Guatemala. The distribution of Babesia follows the dissemination of the tick vector. Seroepidemiological studies showed that enzootic instability exist in herds in several areas of the region. However, clinical cases occurred less frequently than expected. The babesial tick infection rate is related to the vector abundance which in turn is regulated by climate. Bos indicus cattle, because of tick resistance, are less likely to be infected by the vector. This can result in herd instability, but clinically is partly compensated by the resistance of Bos indicus and their crosses to babesiosis. Excessive use of acaricides and rotational grazing appears to be related to outbreaks of babesiosis especially in dairy cattle. Factors involved in the epidemiology and transmission of anaplasmosis are not well defined. The role of ticks, haematophagous diptera, iatrogenic and intrauterine transmissions needs to be investigated under local conditions. Therefore, the knowledge of this disease is meager. Utilization of biotechnological methods may help in obtaining information on Babesia-Boophilus-Bos relationship and on the transmission of A. marginale.

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.

Epidemiology of bovine babesiosis and anaplasmosis in Zambia

The serological prevalence of bovine babesiosis and anaplasmosis in the traditional farming sector of six provinces of Zambia was determined using the indirect fluorescent antibody test (IFAT) for babesiosis and the card agglutination test (CAT) for anaplasmosis. Antibodies to Babesia bigemina occurred throughout the country whereas the prevalence of B. bovis followed the distribution of its tick vector Boophilus microplus which is limited to the north-eastern part of the country. Low numbers of B. bovis serologically positive cattle were demonstrated in central and southern Province. Anaplasma spp. occurred throughout Zambia but the overall percentages of positive sera were low ranging between 14.7% and 38.6% using the CAT. Two hundred sera were retested for anaplasmosis using an enzyme-linked immunosorbent assay (ELISA). Sero-prevalence rates were 1.5 to 2.3-fold greater with the ELISA than with the card agglutination test.

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.