Molecular and serological prevalence of corridor disease (buffalo associated Theileria parva infection) in cattle populations at the livestock/game interface of KwaZulu-Natal province, South Africa

Theileria parva are intracellular protozoal parasites responsible for three disease syndromes in cattle, namely East Coast fever (ECF), Corridor disease (CD) and Zimbabwean theileriosis. The increase in reports of CD outbreaks in recent years has raised questions about the probability of adaptation of buffalo-derived T. parva strains in cattle herds adjacent to game reserves. A cross-sectional study was conducted from March 2016 to December 2018 to investigate the extent of occurrence of T. parva infections in cattle in the CD-controlled area of KwaZulu-Natal Province. Blood samples were collected from 1137 cattle from 14 herds and analysed by quantitative real-time PCR (qPCR) and indirect fluorescent antibody test (IFAT) to determine the prevalence of T. parva. A total of 484 samples from 4 of the 14 herds were further tested on qPCR for the presence of T. taurotragi infections. The data were analysed using descriptive statistics and a chi-square test was used to assess association between variables. The overall prevalence of T. parva was 1.3% (95%CI:1-2%) and 19.9% (95%CI:17-22%) on qPCR and IFAT, respectively. The qPCR positive samples were detected in March and May while IFAT positive samples were detected in all seasons sampled, with higher numbers during summer months. The Pearson Chi-squared test showed that T. parva prevalence rates based on both qPCR and IFAT were positively associated with herds with previous history of CD outbreaks (χ2 = 8.594, p = 0.003; χ2 = 69.513, p < 0.001, respectively). The overall prevalence of T. taurotragi was 39.4% (95% CI: 35-44%) with the herd-level prevalence ranging between 35.0% and 43.4%. Possible cross-reaction of T. parva IFAT to T. taurotragi was detected on few samples, however, there was no significant association between T. taurotragi infections and IFAT positivity (χ2 = 0.829, p = 0.363). Results from this study demonstrated the extent of occurrence of subclinical carriers and the level of exposure to T. parva infections in cattle populations at a livestock/game interface area of KwaZulu-Natal Province. The molecular and seroprevalence rates were low when compared with other areas where cattle-adapted T. parva infections are endemic. The adaptation of buffalo-derived T. parva in cattle population resulting in cattle-cattle transmissions seem to be unlikely under the current epidemiological state.

Anti-parasitic benzoxaboroles are ineffective against Theileria parva in vitro

East Coast Fever (ECF) is a disease affecting cattle in sub-Saharan Africa, caused by the tick-borne Apicomplexan pathogen Theileria parva. The disease is a major problem for cattle farmers in affected regions and there are few methods of control, including a complex infection and treatment vaccine, expensive chemotherapy, and the more widespread tick control through acaricides. New intervention strategies are, therefore, sorely needed. Benzoxaboroles are a versatile class of boron-heterocyclic compounds with demonstrable pharmacological activity against a diverse group of pathogens, including those related to T. parva. In this study, the in vitro efficacy of three benzoxaboroles against the intracellular schizont stage of T. parva was investigated using a flow cytometry approach. Of the benzoxaboroles tested, only one showed any potency, albeit only at high concentrations, even though there is high protein sequence similarity in the CPSF3 protein target compared to other protozoan pathogen species. This finding suggests that benzoxaboroles currently of interest for the treatment of African animal trypanosomiasis, toxoplasmosis, cryptosporidiosis and malaria may not be suitable for the treatment of ECF. We conclude that testing of further benzoxaborole compounds is needed to fully determine whether any lead compounds can be identified to target T. parva.

Assessment and optimization of Theileria parva sporozoite full-length p67 antigen expression in mammalian cells

Delivery of various forms of recombinant Theileria parva sporozoite antigen (p67) has been shown to elicit antibody responses in cattle capable of providing protection against East Coast fever, the clinical disease caused by T. parva. Previous formulations of full-length and shorter recombinant versions of p67 derived from bacteria, insect, and mammalian cell systems are expressed in non-native and highly unstable forms. The stable expression of full-length recombinant p67 in mammalian cells has never been described and has remained especially elusive. In this study, p67 was expressed in human-derived cells as a full-length, membrane-linked protein and as a secreted form by omission of the putative transmembrane domain. The recombinant protein expressed in this system yielded primarily two products based on Western immunoblot analysis, including one at the expected size of 67 kDa, and one with a higher than expected molecular weight. Through treatment with PNGase F, our data indicate that the larger product of this mammalian cell-expressed recombinant p67 cannot be attributed to glycosylation. By increasing the denaturing conditions, we determined that the larger sized mammalian cell-expressed recombinant p67 product is likely a dimeric aggregate of the protein. Both forms of this recombinant p67 reacted with a monoclonal antibody to the p67 molecule, which reacts with the native sporozoite. Additionally, through this work we developed multiple mammalian cell lines, including both human and bovine-derived cell lines, transduced by a lentiviral vector, that are constitutively able to express a stable, secreted form of p67 for use in immunization, diagnostics, or in vitro assays. The recombinant p67 developed in this system is immunogenic in goats and cattle based on ELISA and flow cytometric analysis. The development of a mammalian cell system that expresses full-length p67 in a stable form as described here is expected to optimize p67-based immunization.

East Coast fever, caused by the tick-borne protozoan parasite Theileria parva, is a disease that results in significant bovine morbidity, mortality, and production losses in regions of sub-Saharan Africa. Susceptible cattle develop clinical signs within a 7–14 days of exposure, which often progress to severe pulmonary edema and death. Control of East Coast fever in affected regions of Africa is largely prohibited by the lack of an affordable and efficacious vaccine. Furthermore, pastoralist farmers in affected regions of Africa often lack resources to prevent losses due to East Coast fever, so these production losses play a significant role in food security and protein availability. Experimental immunization of cattle with a recombinant T. parva-derived antigen, p67, has shown promise in preventing East Coast fever, but this antigen is extremely difficult to produce in full-length in sufficient quantities, and results of immunization studies using truncated recombinant p67 products are highly inconsistent. In this study, p67 antigen production was optimized and produced for use in future immunization studies. Optimization of p67-based immunization strategies is an important step forward in the development of a sustainable, next-generation vaccine against T. parva, which is urgently needed to minimize losses associated with East Coast fever.

High-resolution predictive mapping for Rhipicephalus appendiculatus (Acari: Ixodidae) in the Horn of Africa

The brown ear tick Rhipicephalus appendiculatus, vector of East Coast fever (ECF) and related cattle diseases caused by Theileria parva has never been reported from the Horn of Africa. Habitat suitability for this tick species was predicted using Maxent modelling technique based on R. appendiculatus records in Sub-Saharan Africa. Two models were developed: the first is based on the tropical R. appendiculatus distribution and the one is based on the distribution records in the temperate region of Sub-Saharan Africa. The tropical model shows favourable habitat in much of the Ethiopian highlands. The whole Djibouti, the south eastern Ethiopian lowlands, majority of Somalia and Eritrea were found to be not suitable for the survival and development of this tick species. Highly suitable areas occur in areas which have moderate temperature and high precipitation. Introductions of R. appendiculatus into the Horn of Africa probably have been prevented by the natural barrier between the known R. appendiculatus distribution range in East Africa and the Horn of Africa. The effect of an introduction of R. appendiculatus and thereby ECF into the Horn of Africa could be catastrophic since the cattle in this area have no immunity against ECF, and mortality might be considerable in all age groups of cattle.

Effects of anti-tick cocktail vaccine against Rhipicephalus appendiculatus

Rhipicephalus appendiculatus serpin-3 (RAS-3), R. appendiculatus serpin-4 (RAS-4) and a 36-kDa immuno-dominant protein of R. appendiculatus (RIM36) were reported as candidate antigens for the anti-tick vaccine to control ixodid ticks. In the present study, we generated recombinant proteins of RAS-3 (rRAS-3), RAS-4 (rRAS-4) and RIM36 (rRIM36), and assessed their potency as an anti-tick cocktail vaccine in cattle model. RT-PCR analysis showed that RAS-3, RAS-4 and RIM36 transcripts were detected in both adult male and female ticks during feeding. Immunization of cattle with the combination of rRAS-3, rRAS-4 and rRIM36 had raised antibodies against all recombinants and anti-sera had reacted with the molecules from the tick salivary gland extract. Tick infestation challenge demonstrated protective immunity against female ticks, resulting in mortality rates of 39.5 and 12.8% for the vaccinated and control groups, respectively. Moreover, the mortality rate of Theileria parva-infected female ticks was 48.5 and 10.8% in the vaccinated and control group, respectively. In order to evaluate the levels of pathogen transmission capacity by T. parva-infected ticks fed on immunized cattle, the occurrence of T. parva in the bovine parotid lymph node and peripheral blood was also determined and quantified by real-time PCR. Although the infection with T. parva could not be protected by the vaccine, the occurrence of pathogen in peripheral blood was delayed 1 to 2 days after the infestation challenge in vaccinated group. These results suggest that this cocktail vaccine plays a role in the prevention of tick infestation.

Red blood cell volume as a predictor of fatal reactions in cattle infected with Theileria parva Katete

A comparison of mean corpuscular volume (MCV) and packed cell volume (PCV) was made between cattle undergoing lethal and non-lethal reactions following experimental infections with the apicomplexan protozoa, Theileria parva Katete. This work confirmed that anaemia occurs in infected animals. However, the fall in PCV was steeper in lethal reactions compared to non-lethal reactions. Our results show that animals with initially lower MCV values are more prone to fatal reaction, despite having normal PCV profiles. The study also found that small red blood cells are more likely to be infected with T. parva. These findings suggest that animals with a higher proportion of small red blood cells in circulation will be more likely to succumb to T. parva infections. The potential for using MCV as a predictor of the outcome of infection challenge is discussed.

Notch is constitutively active in Theileria-transformed B cells and can be further stimulated by the filarial nematode-secreted product, ES-62

Theileria parva-infected B cells express Jagged-1 and activate Notch signalling in a parasite-dependent manner. ES-62, a filarial nematode-secreted phosphorylcholine-containing glycoprotein, is able to further stimulate Notch-mediated signalling in parasitized cells. Notch is also activated to a similar extent by addition of exogenous IL-10, and this occurs prior to any increase in proliferation in T. parva-infected B cells.

Theileria parva seroprevalence in traditionally kept cattle in southern Zambia and El Niño

Sero-epidemiological surveys involving 27,526 cattle over a period of 8 years show that Theileria parva, the parasite causing East Coast fever (ECF) is found throughout southern Zambia. Higher values of T. parva sero-prevalence were observed in the plateau districts of Monze, Choma and Mazabuka than in the valley districts of Siavonga and Sinazongwe. Our results reveal a strong association between high T. parva sero-prevalence and the presence of the periodic climatic phenomenon known as the El Nino Southern Oscillation. More T. parva sero-positive samples were recorded during El Nino years (1997/98) (P<0.001) than other years in the study period. From this association, we conclude that Multiple El Nino Southern Oscillation Indices can be used to predict years with high or low ECF infection prevalence thereby contributing to the improved control of ECF in the area.

The epidemiology of Theileria parva infections on smallholder dairy farms in Kenya

The purpose of the study was to characterize the differences in epidemiology (risks of infection, morbidity, mortality) and potential control of East Coast fever (ECF) between the selected strata. Evidence of Theileria parva infection was assessed by increased antibody levels as measured in an indirect ELISA test by the percent positivity (PP) of serum samples relative to a strong positive reference serum. A prospective cohort study was conducted in five purposively sampled agroecological zone (AEZ)-grazing system strata in Murang'a District, Kenya, between March 1995 and June 1996. The study strata were selected to represent the widest range of ECF risks in the district and included, zero-grazing and open-grazing farms in the Upper Midlands (UM) one and four AEZs and zero-grazing farms in the UM2 AEZ. In total, 225 calves from 188 smallholder farms were examined from birth to age six months. Calves were recruited into the study at birth and visited within the first two weeks of life and thereafter at biweekly intervals for up to 14 visits. Important differences were observed between the different AEZ-grazing strata. Seroconversion risks of T. parva were highest in the UM4-open grazing stratum. Antibody prevalence in adult cattle and ECF morbidity and mortality risks were also highest in this stratum. In the open-grazing strata, particularly in the lower elevation AEZ, UM4, there was stronger challenge and a greater impact of ECF. There is likely to be an expansion of smallholder dairy farming into this area so that it is likely to be the most important target production system for ECF control in the central highlands of Kenya.

N-acetylcysteine blocks apoptosis induced by N-alpha-tosyl-L-phenylalanine chloromethyl ketone in transformed T-cells

The serine protease inhibitor N-alpha-tosyl-L-phenylalanine chloromethyl ketone (TPCK) can interfere with cell-cycle progression and has also been shown either to protect cells from apoptosis or to induce apoptosis. We tested the effect of TPCK on two transformed T-cell lines. Both Jurkat T-cells and Theileria parva-transformed T-cells were shown to be highly sensitive to TPCK-induced growth arrest and apoptosis. Surprisingly, we found that the thiol antioxidant, N-acetylcysteine (NAC), as well as L- or D-cysteine blocked TPCK-induced growth arrest and apoptosis. TPCK inhibited constitutive NF-kappaB activation in T. parva-transformed T-cells, with phosphorylation of IkappaBalpha and IkappaBbeta being inhibited with different kinetics. TPCK-mediated inhibition of IkappaB phosphorylation, NF-kappaB DNA binding and transcriptional activity were also prevented by NAC or cysteine. Our observations indicate that apoptosis and NF-kappaB inhibition induced by TPCK result from modifications of sulphydryl groups on proteins involved in regulating cell survival and the NF-kappaB activation pathway(s).

The incidence, calf morbidity and mortality due to Theileria parva infections in smallholder dairy farms in Murang'a District, Kenya

A prospective observational study was conducted among smallholder dairy farmers in Murang'a District, Kenya, to estimate the incidence of Theileria parva infections, as well as calf morbidity and mortality caused by the infection. The study was conducted between March 1995 and August 1996, in five cohorts of female calves from birth to six months of age from different agro-ecological zones (AEZs) and grazing-system strata shown previously to have varying prevalences of T. parva infection. A total of 188 smallholder dairy farms with 225 female calves were selected purposively by five AEZ-grazing strata. All recruited calves were visited within the first two weeks of life and thereafter at biweekly intervals up to the age of six months. The mean number of cattle in these smallholder farms was 2.6. Both exotic and indigenous breeds of cattle and their crosses were present, with the former predominating. The incidence (27-54%) of sero-conversion to T. parva in an ELISA test was significantly different (p < 0.05) across the five AEZ-grazing strata and increased with lower elevation and unrestricted grazing. Calf morbidity and mortality were also variable across the AEZ-grazing strata. East Coast fever (ECF) was the highest-incidence cause calf morbidity and mortality (relative to other diseases). There are great differences in the epidemiology of ECF within a small area and this implies that there is need to carefully consider different ECF control strategies in different AEZ-grazing strata.

Vector competence of 7 rhipicephalid tick stocks in transmitting 2 Theileria parva parasite stocks from Kenya and Zimbabwe

The competence of 7 different stocks of Rhipicephalus appendiculatus and R. zambeziensis to transmit 2 different stocks of Theileria parva was compared by feeding nymphae of each tick stock simultaneously on infected cattle and assessing the infections in the salivary glands of the resultant adult ticks. There were significant differences in the patterns of infection of the 2 stocks (T. parva Muguga and T. parva Boleni) in the different stocks of ticks, and these differences were shown to be reproducible. The Muguga tick stock from Kenya and the Zambia tick stock from Eastern Province had the highest infections of T. parva Muguga and T. parva Boleni respectively. The Zambia Southern Province tick stock and the Zimbabwe Mashonaland West tick stock had the lowest infections of T. parva Muguga and T. parva Boleni respectively. The difference in mean abundance of infection between the most and least efficient vector for T. parva Muguga was 63.3 while that for T. parva Boleni was 54.4 infected acini. The implications of these results for laboratory transmission of T. parva and for the epidemiology of theileriosis are discussed.

Parasite-mediated nuclear factor kappaB regulation in lymphoproliferation caused by Theileria parva infection

Infection of cattle with the protozoan Theileria parva results in uncontrolled T lymphocyte proliferation resulting in lesions resembling multicentric lymphoma. Parasitized cells exhibit autocrine growth characterized by persistent translocation of the transcriptional regulatory factor nuclear factor kappaB (NFkappaB) to the nucleus and consequent enhanced expression of interleukin 2 and the interleukin 2 receptor. How T. parva induces persistent NFkappaB activation, required for T cell activation and proliferation, is unknown. We hypothesized that the parasite induces degradation of the IkappaB molecules which normally sequester NFkappaB in the cytoplasm and that continuous degradation requires viable parasites. Using T. parva-infected T cells, we showed that the parasite mediates continuous phosphorylation and proteolysis of IkappaBalpha. However, IkappaBalpha reaccumulated to high levels in parasitized cells, which indicated that T. parva did not alter the normal NFkappaB-mediated positive feedback loop which restores cytoplasmic IkappaBalpha. In contrast, T. parva mediated continuous degradation of IkappaBbeta resulting in persistently low cytoplasmic IkappaBbeta levels. Normal IkappaBbeta levels were only restored following T. parva killing, indicating that viable parasites are required for IkappaBbeta degradation. Treatment of T. parva-infected cells with pyrrolidine dithiocarbamate, a metal chelator, blocked both IkappaB degradation and consequent enhanced expression of NFkappaB dependent genes. However treatment using the antioxidant N-acetylcysteine had no effect on either IkappaB levels or NFkappaB activation, indicating that the parasite subverts the normal IkappaB regulatory pathway downstream of the requirement for reactive oxygen intermediates. Identification of the critical points regulated by T. parva may provide new approaches for disease control as well as increase our understanding of normal T cell function.

Reducing a spatial database to its effective dimensionality for logistic-regression analysis of incidence of livestock disease

Large databases with multiple variables, selected because they are available and might provide an insight into establishing causal relationships, are often difficult to analyse and interpret because of multicollinearity. The objective of this study was to reduce the dimensionality of a multivariable spatial database of Zimbabwe, containing many environmental variables that were collected to predict the distribution of outbreaks of theileriosis (the tick-borne infection of cattle caused by Theileria parva and transmitted by the brown ear tick). Principal-component analysis and varimax rotation of the principal components were first used to select a reduced number of variables. The logistic-regression model was evaluated by appropriate goodness-of-fit tests.

Comparison of the transmission of Theileria parva between different instars of Rhipicephalus appendiculatus

The transmission of Theileria parva by nymphal and adult Rhipicephalus appendiculatus was compared by the assessment of salivary gland infections in tick batches fed on the same group of infected cattle at the same time. When larval and nymphal R. appendiculatus Muguga ticks were fed concurrently on cattle undergoing acute infection with T. parva Muguga, the resultant nymphae developed a slightly lower prevalence of infection than did the adult ticks. The abundance of infection was 5-20 times higher in the adult ticks than in the nymphae. When larval and nymphal R. appendiculatus Muguga and R. appendiculatus McIlwaine were fed to repletion on cattle infected with T. parva Boleni, a parasite causing subacute infection, resultant adult tick batches had a relatively high prevalence of infection, but infection was not detected in resultant nymphal batches. When cattle that were carriers of 2 stocks of T. parva, Marikebuni and Kiambu 5, were used as the source of infection, the infections developing in adult R. appendiculatus Muguga ticks were much higher than those developing in nymphae. The structure of salivary glands differed between nymphal ticks, adult males and adult females, and this is considered to be an important factor affecting the infection levels. The morphology of the type III acini, the target acini for sporogony, was similar, but the mean numbers of type III acini were different, with 87 in nymphae, 1346 in males and 1736 in females. This difference was correlated with the different tick instars and sexes was similar, the rate of sporogony was fastest in feeding nymphae, taking on average 2-3 days. compared to 3-4 days in females and an irregular period in the males. These results are discussed in relation to the epidemiology of T. parva.

Factors influencing infections in Rhipicephalus appendiculatus ticks fed on cattle infected with Theileria parva

A large database on the transmission of a stabilate of the Theileria parva Muguga stock from one breed of cattle using two stocks of Rhipicephalus appendiculatus, Muguga and Ol Pejeta was developed and analysed. Factors associated with the ticks and cattle, and the infections developing in cattle were studied in relation to the infection variables in the tick batches harvested daily from cattle. Generalized Linear Interactive Modelling (GLIM) was used to determine the importance of factors and interactions in influencing the levels of tick infection variables using Type I and Type III sums of squares analyses. Analysis of the 6 variables, prevalence (percentage of ticks infected), abundance (mean number of infected salivary gland acini per tick examined) and intensity (mean number of infected salivary gland acini per infected tick) in batches of 30 male and 30 female ticks showed that 24 covariates, factors or interactions had a significant effect (P < 0.05). Certain covariates and factors were particularly important for all 6 tick infection variables; parasitaemia of animal on the day of tick harvest, stabilate dilution administered to animal, month in which tick batch was harvested, minimum packed cell volume of animal over the sampling period, age of animal, and the minimum leukocyte count of the animal over the sampling period. The GLIM analyses were found to be a useful tool in identifying factors that influence infection levels and in devising methods of producing tick batches with more predictable infections.

Optimization of the in vitro feeding of Rhipicephalus appendiculatus nymphae for the transmission of Theileria parva

An apparatus for artificial feeding of Rhipicephalus appendiculatus nymphae was modified to improve feeding performance. Heparinized blood was supplied above a treated artificial membrane while the ticks attached below on its undersurface. The feeding apparatus was incubated at 37 degrees C in an atmosphere of 3% CO2 concentration and a relative humidity of 75-80%. Under these conditions, 91% of the engorged nymphae attained a mean weight of 6-11 mg, and an average of 93% of those nymphae moulted into adults. When this system was used to feed nymphal ticks on blood infected with Theileria parva piroplasms, the mean prevalence of infection in the resultant female and male ticks was 86% and 54%, respectively. The feeding performance and T. parva infection levels were comparable to those of nymphal ticks fed on the blood donor cattle. The apparatus used in this study has potential for modification to suit the artificial feeding needs of other species of ixodid ticks and for use in investigations to examine other tick/pathogen relationships.

The naming game: the changing fortunes of East Coast fever and Theileria parva

Since first being recognised at the turn of the century, East Coast fever of cattle and its causal parasite Theileria parva have undergone numerous name changes as scientists have observed differences in the distribution, severity, characteristics and host associations of the disease within Africa. These changes have caused considerable confusion to scientists and affected the control of infections caused by T parva in the field. The justification for the decisions affecting the nomenclature of T parva and the diseases it causes are documented and reviewed, and their validity is considered in the light of current knowledge. Areas of research required to clarify the remaining confusion are identified.

Progress in research on tick-borne diseases: theileriosis and heartwater

The rapid population growth in subsaharan Africa necessitates a great increase in animal production in the more humid zones. Vector-borne diseases occurring in these zones will assume more importance, but are difficult to control. They include theileriosis and heartwater. Recent developments in research on these diseases are presented. Indigenous animal populations in endemic areas, subjected to natural selection, are far less susceptible than exotic stock. Heartwater, caused by the rickettsia Cowdria ruminantium, transmitted by Amblyomma ticks, causes high mortality in exotic ruminants. It has received much attention in recent years, partly because the disease has been introduced from Africa into the Caribbean and threatens the American mainland. Since the recent success of in vitro culture, much progress in research has been made, but so far prevention still relies mainly on acaricidal tick control; an infection and treatment method is used on a limited scale. Antigenic diversity is a complication for immunization procedures. Theileria parva (East Coast fever, Corridor disease and January disease) and T.annulata (Mediterranean or tropical theileriosis) are the most pathogenic of the 6 species of this protozoan genus that infect cattle. Great progress has been made in recent years in knowledge on the immunology, the epidemiology, the taxonomy and the chemotherapy of theileriosis. Intensive acaricidal tick control can now be supplemented by an attenuated schizont vaccine against T.annulata, while immunization against East Coast fever is carried out on a limited scale using virulent sporozoite infection and treatment. Research on recombinant vaccines is promising. Antigenic diversity in T.parva is a serious complication.

Preliminary analysis of the transmission dynamics of Theileria parva in eastern Africa

Two mathematical models are developed that investigate the transmission dynamics of Theileria parva by the ixodid tick Rhipicephalus appendiculatus to cattle in endemically stable areas. A method of estimating the rate of infection to cattle of T. parva at the endemically stable state is given. Empirical estimates of all the parameters in the model are available. The degree to which animals that have recovered from theileriosis (the 'carrier' state) are able to transmit the infection to tick nymphs or larvae is a crucial determinant of the dynamics of infection in a herd. Two control methods influencing the transmission of infection are considered--infection and treatment immunization and the reduction in tick feeding by acaricide application. The impact of each method on the transmission of infection is evaluated. Future developments and the data required to predict the dynamics of T. parva infections in cattle and ticks are discussed.

A clinical trial of buparvaquone in the treatment of East Coast fever

A clinical trial was conducted to test buparvaquone (Butalex; Coopers Pitman-Moore) in the treatment of East Coast fever under field conditions in Kenya. Data from 229 cases were analysed following treatment with one (69), two (142) or three (18) doses at 2.5 mg/kg. The majority of cattle (95.2 per cent) were exotic (Bos taurus) or improved (Bos taurus cross Bos indicus) and 39.3 per cent were infected with Anaplasma marginale. There was an overall recovery rate of 85.6 per cent, with 90.1 per cent recovering following one treatment and 75.4 per cent recovering following two treatments. At a follow-up visit three to six months after completion of the trial data was obtained on 224 cases. Thirty had died, 13 of which were reported to have been from East Coast fever, nine had been sold and six slaughtered. Of the remaining 146, 86.3 per cent were in good condition, 13.7 per cent fair and 2.0 per cent in poor condition. A two dose regimen was most effective and should be recommended except in very early cases or those under direct veterinary supervision.

Effects of gamma interferon, tumor necrosis factor alpha, and interleukin-2 on infection and proliferation of Theileria parva-infected bovine lymphoblasts and production of interferon by parasitized cells

Theileria parva is a protozoan parasite that infects bovine B cells and alpha beta and gamma delta T cells and transforms them into continually proliferating cells. CD4+ T. parva-antigen-specific immune T cells have been shown to produce cytokines in response to stimulation with parasitized cells, and T. parva-infected lymphocytes produce and consume T-cell growth factors and interleukin-2 (IL-2). To ascertain the role of T-cell cytokines on T. parva infections, we evaluated recombinant gamma interferon (rIFN-gamma), rIL-2, and tumor necrosis factor alpha (rTNF-alpha) for their effects on establishment, proliferation, and survival of parasitized cells. The results indicate that neither rIFN-gamma nor rTNF-alpha had an enhancing or inhibitory effect on the growth of established T. parva-infected T-cell clones, whereas bovine rIL-2 increased the proliferation of infected B-cell and alpha beta T-cell clones but not that of gamma delta T-cell clones. To evaluate the effects of the cytokines on establishment of parasitized cell lines, peripheral blood mononuclear cells were cultured in their presence immediately following infection with T. parva sporozoites. Neither rIFN-gamma nor rIL-2 altered the proportion of cells initially developing schizonts, but both enhanced establishment of infected cell lines by about twofold. In contrast, rTNF-alpha resulted in about a 33% decrease in the proportion of schizont-infected cells. Inhibitory effects on establishment of parasitized cell lines by rTNF-alpha were no longer apparent by 12 days following infection. Tests conducted during this study indicated that T. parva-infected lymphocytes also spontaneously produce IFN that is neutralized by acidic pH treatment. In conclusion, we speculate that none of these T-cell cytokines are likely to have a profound inhibitory effect in vivo on T. parva infections. Instead, IFN-gamma and IL-2 may facilitate the establishment of infection by T. parva.