Transaminitis prevalence among HIV-infected adults eligible for tuberculosis preventive therapy

OBJECTIVE

To assess the prevalence of severe transaminitis precluding tuberculosis (TB) preventive therapy (TPT) initiation for people with HIV (PWH) in a high TB/HIV burden setting.

DESIGN/METHODS

We conducted a secondary analysis of data from a prospective cohort study of PWH with pre-antiretroviral therapy (ART) CD4 + counts 350 cells/μl or less undergoing systematic TB screening from two HIV clinics in Uganda. For this analysis, we excluded patients with culture-confirmed TB and patients without aspartate transaminase (AST) or alanine transaminase (ALT) levels measured within three months of enrollment. We compared the proportion of patients with any transaminitis (AST or ALT greater than one times the upper limit of normal ULN) and severe transaminitis (AST or ALT >3 times ULN) for patients screening negative for TB by symptoms and for those screening negative by C-reactive protein (CRP). We also assessed the proportion of patients with transaminitis by self-reported alcohol consumption.

RESULTS

Among 313 participants [158 (50%) women, median age 34 years (IQR 27-40)], 75 (24%) had any transaminitis and six (2%) had severe transaminitis. Of 32 of 313 (10%) who screened negative for TB by symptoms, none had severe transaminitis. In contrast, six-times more PWH screened negative for TB by CRP (194 of 313; 62%), of whom only four (2.1%) had severe transaminitis. Differences in the proportion with any and severe transaminitis according to alcohol consumption were not statistically significant.

CONCLUSION

Prevalence of severe transaminitis was low among PWH without culture-confirmed TB in this setting, and is therefore, unlikely to be a major barrier to scaling-up TPT.

Impact of hematocrit on point-of-care C-reactive protein-based tuberculosis screening among people living with HIV initiating antiretroviral therapy in Uganda

Point-of-care C-reactive protein (POC CRP) testing is a potential tuberculosis (TB) screening tool for people living with HIV (PLHIV). Unlike lab-based assays, POC assays do not routinely adjust CRP levels for hematocrit, potentially resulting in TB screening status misclassification. We compared the diagnostic accuracy of unadjusted and hematocrit-adjusted POC CRP for culture-confirmed TB among PLHIV with CD4 cell-count ≤350 cells/uL initiating antiretroviral therapy (ART) in Uganda. We prospectively enrolled consecutive adults, measured POC CRP (Boditech; normal <8 mg/L), collected two spot sputum specimens for comprehensive TB testing, and extracted pre-ART hematocrit from clinic records. Of the 605 PLHIV included, hematocrit-adjusted POC CRP had similar sensitivity (80% vs 81%, difference +1% [95% CI -3 to +5], P= 0.56) and specificity (71% vs 71%, difference 0% [95% CI -1 to +1], P= 0.56) for culture-confirmed TB, relative to unadjusted POC CRP. When used for TB screening, POC CRP may not require adjustment for hematocrit. However, larger studies may be required if differences close to the clinically meaningful threshold are to be detected.

A Novel, 5-Transcript, Whole-blood Gene-expression Signature for Tuberculosis Screening Among People Living With Human Immunodeficiency Virus

BACKGROUND

Gene-expression profiles have been reported to distinguish between patients with and without active tuberculosis (TB), but no prior study has been conducted in the context of TB screening.

METHODS

We included all the patients (n = 40) with culture-confirmed TB and time-matched controls (n = 80) enrolled between July 2013 and April 2015 in a TB screening study among people living with human immunodeficiency virus (PLHIV) in Kampala, Uganda. We randomly split the patients into training (n = 80) and test (n = 40) datasets. We used the training dataset to derive candidate signatures that consisted of 1 to 5 differentially-expressed transcripts (P ≤ .10) and compared the performance of our candidate signatures with 4 published TB gene-expression signatures, both on the independent test dataset and in 2 external datasets.

RESULTS

We identified a novel, 5-transcript signature that met the accuracy thresholds recommended for a TB screening test. On the independent test dataset, our signature had an area under the curve (AUC) of 0.87 (95% confidence interval [CI] 0.72-0.98), with sensitivity of 94% and specificity of 75%. None of the 4 published TB signatures achieved desired accuracy thresholds. Our novel signature performed well in external datasets from both high (AUC 0.81, 95% CI 0.74-0.88) and low (0.81, 95% CI 0.77-0.85) TB burden settings.

CONCLUSIONS

We identified the first gene-expression signature for TB screening. Our signature has the potential to be translated into a point-of-care test to facilitate systematic TB screening among PLHIV and other high-risk populations.

Evaluation of multi-antigen serological screening for active tuberculosis among people living with HIV

Better triage tests for screening tuberculosis (TB) disease are needed for people living with HIV (PLHIV). We performed the first evaluation of a previously-validated 8-antigen serological panel to screen PLHIV for pulmonary TB in Kampala, Uganda. We selected a random 1:1 sample with and without TB (defined by sputum culture) from a cohort of PLHIV initiating antiretroviral therapy. We used a multiplex microbead immunoassay and an ensemble machine learning classifier to determine the area under the receiver operating characteristic curve (AUC) for Ag85A, Ag85B, Ag85C, Rv0934-P38, Rv3881, Rv3841-BfrB, Rv3873, and Rv2878c. We then assessed the performance with the addition of four TB-specific antigens ESAT-6, CFP-10, Rv1980-MPT64, and Rv2031-HSPX, and every antigen combination. Of 262 participants (median CD4 cell-count 152 cells/μL [IQR 65-279]), 138 (53%) had culture-confirmed TB. The 8-antigen panel had an AUC of 0.53 (95% CI 0.40-0.66), and the additional 4 antigens did not improve performance (AUC 0.51, 95% CI 0.39-0.64). When sensitivity was restricted to ≥90% for the 8- and 12-antigen panel, specificity was 2.2% (95% CI 0-17.7%) and 8.1% (95% CI 0-23.9%), respectively. A three-antigen combination (Rv0934-P38, Ag85A, and Rv2031-HSPX) outperformed both panels, with an AUC of 0.60 (95% CI 0.48-0.73), 90% sensitivity (95% CI 78.2-96.7%) and 29.7% specificity (95% CI 15.9-47%). The multi-antigen panels did not achieve the target accuracy for a TB triage test among PLHIV. We identified a new combination that improved performance for TB screening in an HIV-positive sample compared to an existing serological panel in Uganda, and suggests an approach to identify novel antigen combinations specifically for screening TB in PLHIV.

Yield and Efficiency of Novel Intensified Tuberculosis Case-Finding Algorithms for People Living with HIV

RATIONALE

The recommended tuberculosis (TB) intensified case finding (ICF) algorithm for people living with HIV (symptom-based screening followed by Xpert MTB/RIF [Xpert] testing) is insufficiently sensitive and results in unnecessary Xpert testing.

OBJECTIVES

To evaluate whether novel ICF algorithms combining C-reactive protein (CRP)-based screening with urine Determine TB-LAM (TB-LAM), sputum Xpert, and/or sputum culture could improve ICF yield and efficiency.

METHODS

We compared the yield and efficiency of novel ICF algorithms inclusive of point-of-care CRP-based TB screening and confirmatory testing with urine TB-LAM (if CD4 count ≤100 cells/μl), sputum Xpert, and/or a single sputum culture among consecutive people living with HIV with CD4 counts less than or equal to 350 cells/μl initiating antiretroviral therapy in Uganda.

MEASUREMENTS AND MAIN RESULTS

Of 1,245 people living with HIV, 203 (16%) had culture-confirmed TB including 101 (49%) patients with CD4 counts less than or equal to 100 cells/μl. Compared with the current ICF algorithm, point-of-care CRP-based TB screening followed by Xpert testing had similar yield (56% [95% confidence interval, 49-63] vs. 59% [95% confidence interval, 51-65]) but consumed less than half as many Xpert assays per TB case detected (9 vs. 4). Addition of TB-LAM did not significantly increase diagnostic yield relative to the current ICF algorithm but provided same-day diagnosis for 26% of TB patients with advanced HIV. Addition of a single culture to TB-LAM and Xpert substantially improved ICF yield, identifying 78% of all TB cases.

CONCLUSIONS

Point-of-care CRP-based screening can improve ICF efficiency among people living with HIV. Addition of TB-LAM and a single culture to Xpert confirmatory testing could enable HIV programs to increase the speed of TB diagnosis and ICF yield.

Point-of-care C-reactive protein-based tuberculosis screening for people living with HIV: a diagnostic accuracy study

Background

Symptom-based screening for tuberculosis (TB) is recommended for all people living with HIV (PLHIV) resulting in unnecessary Xpert MTB/RIF testing for the vast majority of individuals living in TB endemic areas and thus, poor implementation of intensified case finding (ICF) and TB preventive therapy. Novel approaches to TB screening are therefore critical in achieving global targets for TB elimination.

Methods

In a prospective study of PLHIV with CD4+ T-cell count ≤350 cells/uL initiating antiretroviral therapy (ART) from two HIV/AIDS clinics in Uganda, we evaluated the performance of C-reactive protein (CRP) measured using a rapid and inexpensive point-of-care (POC) assay as a screening tool for active pulmonary TB.

Findings

Of 1177 HIV-infected adults (median CD4+ T-cell count 168 cells/µL) enrolled, 163 (14%) had culture-confirmed TB. POC CRP had 89% (145/163) sensitivity and 72% (731/1014) specificity for culture-confirmed TB. Compared to the WHO symptom screen, POC CRP had lower sensitivity (difference −7% [95% CI: −12 to −2], p=0.002) but substantially higher specificity (difference +58% [95% CI: +61 to +55], p<0.0001). When Xpert MTB/RIF results were used as the reference standard, sensitivity of POC CRP and the WHO symptom screen were similar (94% [79/84] vs. 99% [83/84]; difference −5% [95% CI: −12 to +2], p=0.10).

Interpretation

The performance characteristics of CRP support its use as a TB screening test for PLHIV with CD4+ T-cell count ≤350 cells/µL initiating ART. HIV/AIDS programs should consider POC CRP-based TB screening to improve the efficiency of ICF and increase uptake of TB preventive therapy.

FUNDING

National Institutes of Health; Presidential Emergency Plan for AIDS Relief; University of California, San Francisco, Nina Ireland Program for Lung Health

Impact of mycobacterial culture among HIV-infected adults with presumed TB in Uganda: a prospective cohort study

BACKGROUND

Implementation of new tuberculosis (TB) diagnostic strategies in resource-constrained settings is challenging. We measured the impact of solid and liquid mycobacterial cultures on treatment practices for patients undergoing TB evaluation in Kampala, Uganda.

METHODS

We enrolled consecutive smear-negative, human immunodeficiency virus positive adults with cough of ⩾2 weeks from September 2009 to April 2010. Laboratory technicians performed mycobacterial cultures on solid and liquid media. We compared empiric treatment decisions with solid and liquid culture in terms of diagnostic yield and time to results, and assessed impact on patient management.

RESULTS

Of 200 patients enrolled, 26 (13%) had culture-confirmed TB: 22 (85%) on solid culture alone, 2 (8%) on liquid culture alone, and 2 (8%) on both solid and liquid culture. Thirty-four patients received empiric anti-tuberculosis treatment, but only 10 (29%) were culture-positive. Median time to a positive result on solid culture was 92 days (interquartile range [IQR] 69-148) compared to 106 days (IQR 66-157) for liquid culture. No patients initiated treatment following a positive result on liquid culture.

CONCLUSION

The introduction of mycobacterial culture did not influence care for patients undergoing evaluation for TB in Kampala, Uganda. Attention to contextual factors surrounding implementation is needed to ensure the effective introduction of new testing strategies in low-income countries.

Prevalence of occupational exposure to HIV among health workers in Northern Uganda

BACKGROUND

The prevalence of HIV in Gulu district is 10.3%. This poses a high risk of occupational exposure and transmission to health workers in hospitals attending to these patients. The risk of HIV transmission from a patient to a health worker has been shown to be between 0.3% and 0.09% following percutaneous and mucocutaneous exposure respectively.

OBJECTIVES

This research aimed at determining the prevalence of occupational exposure to HIV.

METHOD

A cross sectional study of health workers in Gulu Regional Referral Hospital and St. Mary's Hospital Lacor, in northern Uganda was conducted to establish the frequency of occupational exposures to human immunodeficiency virus (HIV)-infected body fluids.

RESULTS

108 (46%) respondents were found to have been exposed to potentially infectious body fluids. Needle stick injuries was the commonest route of exposure, with a prevalence of 27.7%, followed by mucosal exposure 19.1%, contact with broken skin (5.5%) and lastly by a cut with sharp objects (5.1%). There is therefore need for more sensitization of health workers on infection control and post exposure prophylaxis for health workers.

Community engagement in health research: two decades of experience from a research project on HIV in rural Uganda

OBJECTIVES

To describe how a research project on HIV epidemiology in rural Uganda has engaged the community over the past two decades, describing activities, opportunities and challenges that have arisen.

METHOD

The review draws on the experience of the authors as investigators involved in the project at various times since its inception in 1989, and on project documents and peer-reviewed publications.

RESULTS

The project attracts community interest, participation and support mostly through community groups. The three main areas of activity are: health care and promotion, HIV/AIDS prevention and care, and community development aimed at poverty reduction. Key opportunities arise from the long-term joint commitment of the project and the community over nearly 20 years, and the potential to accommodate research beyond HIV. Challenges arise from participation fatigue, countered by innovations for the community and investment in capacity development for staff, and from the need to balance community development expectations and the project focus on HIV research.

CONCLUSIONS

Judged by criteria of longevity, acceptance, and scientific output, community engagement in this HIV research project in rural Uganda has been successful. The experience from this project contributes to the collective documentation and analysis of case studies from various research projects in developing countries which identify good practices from multiple stakeholder perspectives.

Cloning, characterization, and expression of a 200-kilodalton diagnostic antigen of Babesia bigemina

Current serological tests for Babesia bigemina use semipurified merozoite antigens derived from infected erythrocytes. One of the major drawbacks of these tests is that antigen quality can vary from batch to batch. Since the quality of the antigen contributes to the sensitivity and specificity of serological tests, the use of standardized recombinant antigens should ensure consistency in assay quality. Previously, a 200-kDa merozoite antigen (p200) was identified as a candidate diagnostic antigen for use in a serological assay for the detection of B. bigemina antibodies in infected cattle. In this study, we have cloned, characterized, and expressed p200. A 3.5-kbp cDNA clone encoding p200 was isolated and shown to be almost full length, lacking approximately 300 bp at the 5' end. The predicted amino acid sequence shows that p200 consists of a long, highly charged central repeat region of an uninterrupted alpha helix, indicative of a fibrous protein. Immunoelectron microscopy localized p200 to the merozoite cytoplasm, suggesting that the antigen may be a structural protein involved in forming filament structures within the cytoskeleton. The 3.5-kbp cDNA was expressed in bacteria as a fusion protein with glutathione S-transferase (GST), but the yield was poor. To improve the yield, cDNA fragments encoding antigenic domains of p200 were expressed as fusions with GST. One of these fusion proteins, C1A-GST, is composed of a 7-kDa fragment of the p200 repeat region and contains epitopes that react strongly with sera from cattle experimentally infected with B. bigemina. Recombinant C1A-GST should permit the development of an improved enzyme-linked immunosorbent assay for the detection of antibodies against B. bigemina.

Development of sero-diagnostic and molecular tools for the control of important tick-borne pathogens of cattle in Africa

Tick-borne diseases (TBDs) are a major economic constraint to livestock production in sub-Saharan Africa. ILRI is focussing on developing a range of products, such as vaccines, diagnostics and decision support services to underpin improved control programmes against these diseases. We have developed three highly sensitive and specific enzyme linked immuno-assays (ELISAs), which allow precise diagnosis of Theileria parva, Babesia bigemina and Anaplasma marginale. These tests have been standardised and validated using defined experimental and field infection sera. Parasite specific recombinant antigens and monoclonal antibodies against bovine immunoglobulins as secondary antibodies have played an important role in in enhancing the sensitivity and specificity of the assays. They have been further evaluated in on-farm longitudinal sero-epidemiological studies to define infection dynamics and disease risks in various farming systems in Kenya and Uganda. In addition, DNA-based tests for differentiation of Theileria species and characterisation of Theileria parva stocks have been developed. These tests have been derived through physical mapping and sequencing of key elements of the T. parva genome, which include repetitive and telomeric regions, minisatellite sequences, antigen genes and a number of random DNA sequences. These tools are currently being deployed in conjunction with field immunisation programmes to determine the biological impact of introducing live vaccines of T. parva on population dynamics.

An enzyme-linked immunosorbent assay for detection of Theileria parva antibodies in cattle using a recombinant polymorphic immunodominant molecule

Field and experimental bovine infection sera were used in immunoblots of sporozoite and schizont lysates of Theileria parva to identify candidate diagnostic antigens. Four parasite antigens of Mr 67,000 (p67), 85,000 (the polymorphic immunodominant molecule, PIM), 104,000 (p104), and 150,000 (p150) were selected for a more detailed analysis. The p67 and p104 antigens were present only in the sporozoite lysates, whereas PIM and p150 were found in both sporozoite and schizont lysates. The four antigens were expressed as recombinant fusion proteins and were compared with each other in an enzyme-linked immunosorbent assay (ELISA) and in the whole-schizont-based indirect fluorescent antibody test (IFAT) in terms of their ability to detect antibodies in sera of experimentally infected cattle. The PIM-based ELISA provided a higher degree of sensitivity and specificity than did the ELISA using the other three recombinant antigens or the IFAT. Further evaluation of the PIM-ELISA using experimental sera derived from cattle infected with different hemoparasites and field sera from endemic and nonendemic T. parva areas showed that the assay had a sensitivity of > 99% and a specificity of between 94% and 98%.

Generation of monoclonal antibodies to the anti-trypanosomal drug isometamidium

Mice were immunized with either an isometamidium-human serum albumin (HSA) conjugate or an isometamidium-porcine thyroglobulin conjugate (PTG). Thereafter, monoclonal antibodies (MAbs) IL-A 1001, IL-A 1002, IL-A 1003, 5F7.B7, and 5F7.C9 were generated and selected on the basis that they recognized conjugated and unconjugated isometamidium, but lacked cross-reactivity with the carrier molecules. All five MAbs were of the IgG1 isotype. Each of the five MAbs was assessed in a competitive ELISA for isometamidium; in each case, the minimum level of detection was approximately 10 ng/ml. Each MAb exhibited approximately 0.1% cross-reactivity with the anti-trypanosomal compound diminazene. However, based on their cross-reactivity with the anti-trypanosomal compound homidium, the MAbs could be divided into two groups; IL-A 1001, IL-A 1002, and IL-A 1003, produced using an isometamidium-HSA conjugate as an immunogen, exhibited low levels of cross-reactivity (approximately 0.1%). In contrast, 5F7.B7 and 5F7.C9, produced using an isometamidium-PTG conjugate as an immunogen, exhibited high levels of cross-reactivity.

Identification of Babesia bigemina infected erythrocyte surface antigens containing epitopes conserved among strains

The presence of previously uncharacterized antigens (new antigens) on the surface of intact erythrocytes infected with three strains of Babesia bigemina from Kenya and one each from Puerto Rico, Mexico, St. Croix, and Texcoco-Mexico was demonstrated by indirect immunofluorescent antibody (IFA) reactions. These antigens were not strain specific because antibodies in bovine immune serum to either the Mexico or Kenya isolates reacted with all seven strains tested. Homologous and heterologous immune serum antibodies bound a maximum of 83% and 55%, respectively, of intact erythrocytes infected with the Kenya-Ngong strain but not uninfected erythrocytes. Both sera caused agglutination of only infected erythrocytes. Antibodies eluted from the surface of glutaraldehyde (0.25%) fixed infected erythrocytes had IFA reaction patterns among strains similar to those of immune sera before elution. Eluted antibodies were used to determine if these antigens were protein and encoded by B. bigemina. Eluted antibodies bound seven parasite-encoded proteins of 240, 220, 66, 62, 58, 52 and 38 kDa in an erythrocyte surface-specific immunoprecipitation reaction of 35S-methionine labelled proteins. It was concluded that the surface of B. bigemina infected erythrocytes had parasite-encoded proteins and that these proteins had surface exposed epitopes that were conserved among the seven strains examined which were from two continents.

Variation in sensitivity of Trypanosoma congolense to diminazene during the early phase of tsetse-transmitted infection in goats

Twenty-five goats were randomly allocated to five groups of five animals each and infected with Trypanosoma congolense IL 3274 via the bites of infected Glossina morsitans centralis. At intervals of 1, 4, 8, 12 or 19 days following infection, each group of five animals was treated intramuscularly with diminazene aceturate at a dose of 7.0 mg kg-1 body weight (b.w.). While treatment on Day 1 eliminated infections in all five goats, treatment on Day 19 did not cure any of the animals; in groups treated 4, 8 or 12 days following infection, two of five goats in each group were cured. Since the alteration in apparent resistance of T. congolense IL 3274 between Day 1 and Day 19 could have been due to alteration in expression of drug resistance by trypanosomes as the population expanded, the experiment was repeated using trypanosomes that reappeared in the animals that had been treated with diminazene aceturate on Day 19. On Day 36, when all five animals were parasitaemic, five groups of teneral G. m. centralis, each containing 160 flies, were fed on one occasion on each of the five goats (one group of testse flies per goat). Thereafter, each group of tsetse flies was maintained on clean rabbits. When infective, five flies from each group were allowed to feed on two naive goats each (i.e. two goats per group of tsetse flies). One animal in each pair was treated 24 h after infection with diminazene aceturate at a dose of 7.0 mg kg-1 b.w., the other was treated on Day 19, when parasitaemic, with the same drug dosage. As before, treatment 24 h following infection eliminated infections in all animals, but when treatment was delayed until Day 19, trypanosomes in all animals were refractory to treatment. Thus, although tsetse flies were infected with trypanosomes that had arisen in infected goats following treatment with diminazene aceturate at a dose of 7.0 mg kg-1 b.w., when the same flies were allowed to feed on clean goats, the resultant infections were sensitive to treatment with the same drug dosage when administered 24 h following infection. These data therefore indicate that there is a significant alteration in diminazene sensitivity of IL 3274 between Day 1 and Day 19 and that this is associated with an alteration in the resistance phenotype of the trypanosomes.

New methods for the diagnosis of Babesia bigemina infection

Accurate diagnosis of Babesia bigemina infection, an economically important tick-transmitted protozoan parasite of cattle, is essential in the management of disease control and in epidemiological studies. The currently used methods of diagnosis are blood smear examination and serological tests which include agglutination and immunofluorescence tests. These tests have been used in the fild but because they lack sensitivity and specificity, newer and improved methods of diagnosis are being developed. The quantitative buffy coat (QBC) method, using microhaematocrit tubes and acridine orange staining allows rapid and quicker diagnosis of B. bigemina and other blood parasites compared to light microscopic examination of stained smears. Parasite specific monoclonal antibodies have been used in antigen/antibody capture enzymelinked immunosorbent assays with greater sensitivity and specificity than previously described serological tests. Similarly, DNA probes, derived from a repetitive sequence of the B. bigemina genome, offer a method of detecting very small numbers of parasites which are undetectable by conventional microscopy. An extrachromosomal DNA element, present in all the tick-borne protozoan parasites so far tested, provides an accurate means of differentiating mixed parasite populations in infected animals. These improved methods will greatly facilitate epidemiological studies.

Long-acting oxytetracycline prophylaxis to protect susceptible cattle introduced into an area of Kenya with endemic East Coast fever

Two field trials were carried out in successive years at the Ngong Veterinary Farm, Kenya, in which young cattle, previously unexposed to tick-borne diseases, were introduced into an area with endemic East Coast fever while protected by a series of injections of a long-acting oxytetracycline. In 1984, 12 animals which received injections of 20 mg/kg of the drug on days 0, 7, 14 and 21 after introduction, together with 12 untreated controls, were exposed without tick control until clinical disease occurred. All 12 control animals contracted East Coast fever by day 24 and 10 of them died. Five of the 12 injected animals had detectable parasites, and one of them required antitheilerial treatment. In 1985, four groups of 10 calves were introduced. One group received injections of 20 mg/kg of oxytetracycline on days 7 and 14, one group received injections on days 7, 14 and 21, and a third group received injections on days 7, 12 and 17; the fourth group (controls) had no treatment until clinical disease occurred. By day 35 all the control animals had contracted the disease and one had died despite antitheilerial treatment. Three injections of oxytetracycline suppressed the disease so that mild reactions occurred in only four animals in each group, but two injections failed to prevent severe reactions in two animals and mild reactions in four others.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of East Coast fever immunisation and different acaricidal treatments on the productivity of beef cattle

A trial was performed on a farm in the Coast Province of Kenya to study the effects of East Coast fever immunisation and different acaricidal treatments on the productivity of immunised and unimmunised beef cattle. Eighty cattle were immunised against Theileria parva parva (Marikebuni) by the infection and treatment method and a similar group was left as an unimmunised control. Immunisation had no deleterious effect on the cattle. After immunisation, the immunised and control groups were each subdivided into four groups of 20 and each subgroup was managed under a different tick control regimen. The tick control regimen were, acaricidal spraying twice a week or once every three weeks, the application of acaricide-impregnated ear-tags, and no tick control. During a nine-month exposure period there were 18 cases of East Coast fever among the 80 immunised cattle, three which were severe and the others mild. Among the 80 unimmunised cattle there were 57 cases of East Coast fever, 50 of which were severe. The highest morbidity and mortality occurred in the groups under limited tick control or without tick control. Overall weight gain in the immunised cattle, irrespective of the tick control regimen, was better than the weight gain in the unimmunised groups. Within the immunised groups, the weight gain of the cattle sprayed twice weekly was comparable to the weight gain of the animals with acaricidal ear-tags and was significantly higher than the weight gains in the groups sprayed once every three weeks or with tick control. Preliminary cost/benefit analysis showed that it was uneconomical to maintain unimmunised cattle under limited or no tick control.(ABSTRACT TRUNCATED AT 250 WORDS)

Epidemiology of animal trypanosomiasis on a cattle ranch in Kilifi, Kenya

A study of the epidemiology of animal trypanosomiasis was carried out on a 2500 ha cattle ranch, with a history of trypanosomiasis, in the Coast Province of Kenya in 1982. The tsetse survey on the ranch revealed one breeding focus of Glossina austeni in a thicket of approximately 50 ha. Trypanosomes were detected in 20% of the 46 dissected tsetse. During the study period of 9 months, 0.8% of the 3315 samples collected from 2300 Ayrshire X Sahiwal crossbred cattle were found infected with trypanosomes; 32% of 5909 samples collected from the same cattle had a packed cell volume (PCV) of 30% or less. Animals with a PCV of 30% or less were treated with a trypanocide (Berenil, Ethidium or Novidium). Antibody to trypanosomes was detected in 22.1% of the 343 sera collected from the cattle. A sentinel herd of 20 cattle was exposed for 182 days inside the tsetse infested thicket. All animals became infected with Trypanosoma congolense, on average after 53 days; they were subsequently treated with Berenil (6 mg/kg). A second, third and fourth T. congolense infection was diagnosed in 17, 11 and 1 animals, respectively. The cattle were treated similarly with Berenil after each of these infections. T. vivax and T. brucei were not diagnosed in the sentinel cattle. The results suggest that acquired immunity to T. congolense infection did not play a significant role in the sentinel cattle.

Immunization against East Coast fever: the use of selected stocks of Theileria parva for immunization of cattle exposed to field challenge

Two antigenically different stocks of Theileria parva parva (Kilifi and Marikebuni), previously characterized as belonging to groups A and C respectively on monoclonal antibody (MAb) profiles, were selected for immunization of different breeds of cattle against East Coast fever (ECF) by the infection and treatment method. A total of 52 immunized cattle and 33 susceptible controls of different group sizes were exposed to field challenge by ticks for periods of 42-90 days at three field sites where ECF is endemic on the Kenyan coast. All immunized cattle survived ECF challenge, but 87% of the controls died of the disease. The cattle exposed at one site had been immunized 1 year earlier and maintained tick-free in the intervening period. The level of immunity in these cattle was similar to that of cattle which had been immunized 1 or 2 months prior to exposure. Thus, immunity had not waned over the 1-year period. A study at another site showed that acaricidal treatment of immunized cattle could be safely extended from twice a week to once every three weeks, whereas in susceptible cattle even twice weekly spraying did not control ECF. The isolates made from infected controls during the trials indicated the presence of three T. p. parva stocks as defined by MAb profiles. Of the two stocks used for immunization, T. p. parva Marikebuni induced broader protection. In view of the apparent limited antigenic diversity of T. p. parva strains within the Coast Province it is suggested that the Marikebuni stock might represent a key stock for vaccination in this area.