Fekadu Abebe

The protective role of antibody responses during Mycobacterium tuberculosis infection

Tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) is one of the most important infectious diseases globally. Immune effector mechanisms that lead to protection or development of clinical disease are not fully known. It is generally accepted that cell‐mediated immunity (CMI) plays a pivotal role in controlling Mtb infection, whereas antibody responses are believed to have no protective role. This generalization is based mainly on early classical experiments that lacked standard protocols, and the T helper type 1 (Th1)/Th2 paradigm. According to the Th1/Th2 paradigm Th1 cells protect the host from intracellular pathogens, whereas Th2 cells protect form extracellular pathogens. During the last two decades, the Th1/Th2 paradigm has dominated not only our understanding of immunity to infectious pathogens but also our approach to vaccine design. However, the last few years have seen major discrepancies in this model. Convincing evidence for the protective role of antibodies against several intracellular pathogens has been established. Studies of B cell‐deficient mice, severe combined immunodeficiency (SCID) mice, passive immunization using monoclonal (mAb) and polyclonal antibodies and immune responses against specific mycobacterial antigens in experimental animals reveal that, in addition to a significant immunomodulatory effect on CMI, antibodies play an essential protective role against mycobacterial infections. In this review, our current understanding of the essential role of antibodies during Mtb infections, limitations of the Th1/Th2 model and the unfolding interdependence and mutual regulatory relationships between the humoral and CMI will be presented and discussed.

The emergence of Beijing family genotypes of Mycobacterium tuberculosis and low‐level protection by bacille Calmette–Guérin (BCG) vaccines: is there a link?

The world is confronted with major tuberculosis (TB) outbreaks at a time when the protection of bacillus Calmette–Guérin (BCG) vaccine has become inconsistent and controversial. Major TB outbreaks are caused by a group of genetically similar strains of Mycobacterium tuberculosis (Mtb) strains, including the Beijing family genotypes. The Beijing family genotypes exhibit important pathogenic features such high virulence, multi‐drug resistance and exogenous reinfection. These family strains have developed mechanisms that modulate/suppress immune responses by the host, such as inhibition of apoptosis of infected macrophages, diminished production of interleukin (IL)‐2, interferon (IFN)‐γ, tumour necrosis factor (TNF)‐α and elevated levels of IL‐10 and IL‐18. They demonstrate distinct expression of proteins, such as several species of α‐crystallin (a known Mtb virulence factor), but decreased expression of some antigens such as heat shock protein of 65 kDa, phosphate transport subunit S and a 47‐kDa protein. In addition, the Beijing family strains specifically produce a highly bioactive lipid (a polyketide synthase)‐derived phenolic glycolipid. This altered expression of proteins/glycolipids may be important factors underlying the success of the Beijing family strains. The Beijing family strains are speculated to have originated from South‐east Asia, where BCG vaccination has been used for more than 60 years. The hypothesis that mass BCG vaccination may have been a selective factor that favoured genotypic and phenotypic characteristic acquired by the Beijing family strains is discussed.

Diagnostic and treatment delay among Tuberculosis patients in Afar Region, Ethiopia: A cross-sectional study

BackgroundTB is a major public health problem globally and Ethiopia is 8th among the 22 high burden countries. Early detection and effective treatment are pre-requisites for a successful TB control programme. In this regard, early health seeking action from patients’ side and prompt diagnosis as well as initiation of treatment from the health system’s side are essential steps. The aim of this study was to assess delay in the diagnosis and treatment of TB in a predominantly pastoralist area in Ethiopia.MethodsOn a cross-sectional study, two hundred sixteen TB patients who visited DOTS clinics of two health facilities in Afar Region were included consecutively. Time from onset of symptoms till first consultation of formal health providers (patients’ delay) and time from first consultation till initiation of treatment (health system’s delay) were analyzed.ResultsThe median patients’ and health system’s delay were 20 and 33.5 days, respectively. The median total delay was 70.5 days with a median treatment delay of 1 day. On multivariate logistic regression, self-treatment (aOR. 3.99, CI 1.50-10.59) and first visit to non-formal health providers (aOR. 6.18, CI 1.84-20.76) were observed to be independent predictors of patients’ delay. On the other hand, having extra-pulmonary TB (aOR. 2.08, CI 1.08- 4.04), and a first visit to health posts/clinics (aOR. 19.70, CI 6.18-62.79), health centres (aOR. 4.83, CI 2.23-10.43) and private health facilities (aOR. 2.49, CI 1.07-5.84) were found to be independent predictors of health system’s delay.ConclusionsThere is a long delay in the diagnosis and initiation of treatment and this was mainly attributable to the health system. Health system strengthening towards improved diagnosis of TB could reduce the long health system’s delay in the management of TB in the study area.

Praziquantel side effects and efficacy related to Schistosoma mansoni egg loads and morbidity in primary school children in north-east Ethiopia.

A total of 611 Schistosoma mansoni infected primary school children from three schools in north-east Ethiopia were treated with praziquantel at 40 mg/kg body weight in a single dose. Pre-treatment, 40.4% had no presenting symptoms and 30-40% had nausea, abdominal cramps and/or bloody-mucoid diarrhoea. None of the pre-treatment symptoms was related to nutritional status, intensity of S. mansoni egg excretion, or to the presence of other concomitant intestinal parasitic infections. During the first 4-6 h post-treatment observation period, 90 (14.7%) children self-presented with severe gastro-intestinal symptoms. Children who self-presented with severe symptoms had a higher mean age and mean S. mansoni egg excretion compared with children who did not self-present. The following day a total of 529 (86.6%) children, including all who self-presented during the first 4-6 h post-treatment, reported for clinical check-up and were subjected to a structured questionnaire interview on symptoms they had experienced over the time lapse following treatment. Among these, 91.5% reported one or more treatment related symptoms which were at times severe. Abdominal cramps (86.9%), diarrhoea with blood and/or mucus (49.5%), dizziness (31.2%) and vomiting (24.9%) were the most common treatment related symptoms. Skin rash with oedema were observed in four cases. Among treatment related symptoms, the combination of abdominal cramps with vomiting, bloody diarrhoea, vomiting alone and general weakness were significantly higher among the malnourished. A proportion of these symptoms increased with increasing categories of S. mansoni egg excretion before and after adjusting for nutritional status and concurrent intestinal parasitic infections. Overall, the cure rate of praziquantel, among 541 children who had stool examination 5 weeks after treatment was 83.2% and this rate decreased with increasing pre-treatment egg counts. In conclusion, most of the treatment related symptoms were mild. However, some of the objective symptoms were at times severe and may reduce drug compliance in primary health care based population chemotherapy.

Prevalence of pulmonary tuberculosis and associated risk factors in Eastern Ethiopian prisons.

OBJECTIVES To determine the prevalence of pulmonary tuberculosis (PTB) and associated risk factors among inmates in three major prison settings of Eastern Ethiopia. DESIGN Between July and November, 2008, 371 prisoners with a history of cough of ≥ 2 weeks were screened for PTB using direct smear microscopy and culture. Data were analysed using descriptive statistics and multivariable logistic regression. RESULTS Of 371 PTB suspects identified by active screening, 33 (8.9%) were confirmed as smear- or culture-positive PTB. Together with the 11 PTB patients already on treatment, the point prevalence of PTB was 1913 per 100,000 (95%CI 1410-2580), about seven times higher than that of the general population. Eleven newly diagnosed PTB patients were sharing a cell with known TB patients. Factors significantly associated with PTB were young age (15-44 years of age) (OR 3.73), urban residence (OR 3.59), having a cough >4 weeks (OR 3.15), and sharing a cell with a TB patient (OR 3.39) or a prisoner with chronic cough (OR 4.5). CONCLUSIONS The study documented a high prevalence of PTB among Ethiopian prisoners. Socio-demographic and TB management factors were identified to be underlying causes of the high transmission rate and the acquisition of new cases. Active surveillance of TB and implementing prevention and control guidelines are imperative.

Is interferon-gamma the right marker for bacille Calmette–Guérin-induced immune protection? The missing link in our understanding of tuberculosis immunology

Bacille Calmette–Guérin (BCG), developed a century ago, is the only licensed tuberculosis (TB) vaccine in use to date. The protective efficacy of BCG against TB varies with no apparent protection in some population, and mechanisms of its immune protection is poorly known, and yet BCG is the most widely used vaccine, with more than 4 billion BCG‐vaccinated children globally. BCG is probably the only licensed vaccine currently in use believed to mediate immune protection through the production of interferon (IFN)‐γ by CD4 T cells, which in turn activates macrophages to kill Mycobacterium tuberculosis (Mtb). Currently, a number of new TB candidate vaccines are in different phases of clinical trial. The majority of these new vaccines are either recombinant forms of BCG or prime boosters of BCG (rBCG) and their immunogenicity is tested using BCG as a benchmark by measuring specific IFN‐γ produced by CD4+ T cells as a protective immune marker. However, some recent studies that examined mechanisms of immune protection of BCG in animals and humans have reported a lack of correlation between IFN‐γ production by CD4 cells and BCG‐induced immune protection. These studies point to the fact that there is a missing link in our understanding of TB immunology. Conversely, there is emerging evidence that other T cell subsets (gammadelta, γδ), CD8+ T cells and natural killer (NK) cells may play a vital role in immune protection against Mtb infection and BCG‐induced immune protection. γδ T cells and NK cells, which were considered to be part of the innate immunity in the past, have been shown to develop immunological memory upon re‐encounter with the same pathogen. In this paper, the controversy over the role of IFN‐γ as a marker for protective immunity against TB, and emerging data on the role of γδ T cells, CD8+ and NK cells in TB immunology, will be presented.

Cytokine profile during latent and slowly progressive primary tuberculosis: a possible role for interleukin- 15 in mediating clinical disease

Recently, mouse models for latent (LTB) and slowly progressive primary tuberculosis (SPTB) have been established. However, cytokine profiles during the two models are not well established. Using quantitative reverse transcription‐polymerase chain reaction (qRT‐PCR) we studied the expression levels of interleukin (IL)‐2, IL‐4, IL‐10, IL‐12, IL‐15, interferon (IFN)‐γ and tumour necrosis factor (TNF)‐α during the course of LTB and SPTB in the lungs and spleens of B6D2F1Bom mice infected with the H37Rv strain of Mycobacterium tuberculosis (Mtb). The results show that, except for IL‐4, cytokine expression levels were significantly higher during SPTB than LTB in both the lungs and spleens. During LTB, all the cytokines (except IL‐2 in the lungs) had higher expression levels during the initial period of infection both in the lungs and spleens. During SPTB, the expression levels of IL‐15 increased significantly from phases 1 to 3 in the lungs. The expression levels of IL‐10, IL‐12 and IFN‐γ increased significantly from 2 to 3 in the lungs. IL‐10 and IL‐15 increased significantly from phases 2 to 3, whereas that of TNF‐α decreased significantly and progressively from phases 1 to 3 in the spleens. Over‐expression of proinflammatory cytokines during active disease has been well documented, but factor(s) underlying such over‐expression is not known. In the present study, there was a progressive and significant increase in the expression levels of IL‐15, together with Th1 cytokines (IL‐12 and IFN‐γ) during SPTB but a significant decrease during LTB. IL‐15 is known to up‐regulate the production of proinflammatory cytokines, IL‐1β, IL‐8, IL‐12, IL‐17, IFN‐γ and TNF‐α and has an inhibitory effect on activation‐induced cell death. IL‐15 is known to be involved in many proinflammatory disease states such as rheumatoid arthritis, sarcoidosis, inflammatory bowel diseases, autoimmune diabetes, etc. Our results, together with the above observations, suggest that IL‐15 may play an important role in mediating active disease during Mtb infection.

Pathology of Camel Tuberculosis and Molecular Characterization of Its Causative Agents in Pastoral Regions of Ethiopia

A cross sectional study was conducted on 906 apparently healthy camels slaughtered at Akaki and Metehara abattoirs to investigate the pathology of camel tuberculosis (TB) and characterize its causative agents using postmortem examination, mycobacteriological culturing, and multiplex polymerase chain reaction (PCR), region of difference-4 (RD4)-based PCR and spoligotyping. The prevalence of camel TB was 10.04% (91/906) on the basis of pathology and it was significantly higher in females (χ2 = 4.789; P = 0.029). The tropism of TB lesions was significantly different among the lymph nodes (χ2 = 22.697; P = 0.002) and lung lobes (χ2 = 17.901; P = 0.006). Mycobacterial growth was observed in 34% (31/91) of camels with grossly suspicious TB lesions. Upon further molecular characterization using multiplex PCR, 68% (21/31) of the colonies showed a positive signal for the genus Mycobacterium, of which two were confirmed Mycobacterium bovis (M. bovis) by RD4 deletion typing. Further characterization of the two M. bovis at strains level revealed that one of the strains was SB0133 while the other strain was new and had not been reported to the M. bovis database prior to this study. Hence, it has now been reported to the database, and designated as SB1953. In conclusion, the results of the present study have shown that the majority of camel TB lesions are caused by mycobacteria other than Mycobacterium tuberculosis complex. And hence further identification and characterization of these species would be useful towards the efforts made to control TB in camels.

Community-based cross-sectional survey of latent tuberculosis infection in Afar pastoralists, Ethiopia, using QuantiFERON-TB Gold In-Tube and tuberculin skin test

BackgroundThere is little information concerning community-based prevalence of latent tuberculosis infection (LTBI) using T-cell based interferon-γ (IFN-γ) release assays (IGRAs), particularly in TB endemic settings. In this study, the prevalence of LTBI in the Afar pastoral community was assessed using QuantiFERON-TB Gold In-Tube (QFTGIT) and tuberculin skin tests (TST).MethodsA community-based cross-sectional survey of LTBI involving 652 apparently healthy adult pastoralists was undertaken in the pastoral community of Amibara District of the Afar Region between April and June 2010.ResultsThe prevalence of LTBI was estimated as 63.7% (363/570) using QFTGIT at the cut-off point recommended by the manufacturer (≥ 0.35 IU/ml IFN-γ), while it was 74.9% (427/570) using a cut-off point ≥ 0.1 IU/ml IFN-γ. The QFTGIT-based prevalence of LTBI was not significantly associated with the gender or age of the study participants. However, the prevalence of LTBI was 31.2% (183/587) using TST at a cut-off point ≥ 10 mm of skin indurations, and it was higher in males than females (36.8% vs. 23.5%, X2 = 11.76; p < 0.001). There was poor agreement between the results of the tests (k = 0.098, 95% CI, 0.08 - 0.13). However, there was a positive trend between QFTGIT and TST positivity (X2 = 96.76, P < 0.001). Furthermore, individuals with skin indurations ≥ 10 mm were 13.6 times more likely to have positive results using QFTGIT than individuals with skin indurations of 0 mm (adjusted OR = 13.6; 95%CI, 7.5 to 24.7, p < 0.001).ConclusionsThere is currently no agreed gold standard for diagnosis of LTBI. However, the higher prevalence of LTBI detected using QFTGIT rather than TST suggests that QFTGIT could be used for epidemiological studies concerning LTBI at the community level, even in a population unreactive to TST. Further studies of adults and children will be required to assess the effects of factors such as malnutrition, non-tuberculosis mycobacterial infections, HIV and parasitic infections on the performance of QFTGIT.

Molecular characterization of Mycobacterium bovis isolates from Ethiopian cattle

BackgroundBovine Tuberculosis (BTB) is a widespread and endemic disease of cattle in Ethiopia. Information relating to genotypic characteristics of Mycobacterium bovis strains affecting the cattle population in Ethiopia is limited. We carried out molecular characterization of M. bovis strains isolated from BTB infected cattle using the spoligotyping technique. The relationship between distribution of spoligotypes and recorded variables was also investigated. A new approach that can numerically reflect the degree of genetic polymorphism in a M. bovis population was also developed. The study was conducted from July 2006 to January 2007 in cattle slaughtered at five representative abattoirs in Ethiopia.ResultsForty-five M. bovis isolates were obtained from 406 pathologic tissue specimens collected from 337 carcasses with lesions compatible with BTB. Twelve spoligotypes were identified from 34 distinct strains; with SB1176 as a dominant spoligotype (41.2% of the isolates) followed by SB0133 (14.7%). Comparison of spoligotypes with an M. bovis global database http://www.mbovis.org revealed six new spoligotypes which were subsequently registered in the database with international identification codes of SB1517, SB1518, SB1519, SB1520, SB1521 and SB1522. The majority of strains were obtained from cattle slaughtered at Addis Ababa abattoir. On the basis of the Spoligotype Evolutionary Index, SEI (a numeric expression approach to make standardized comparison of spoligotype evolution), M. bovis isolates from Ethiopia were relatively more heterogeneous (SEI = 3.2) compared to isolates from other countries. This might be attributed to extensive livestock movement linked to trading or seasonal migration, high degree of livestock mingling, and also diversities of the countrys agricultural and livestock ecosystems, in addition to lack of disease control measures that led to high infection prevalence. Multiple spoligotype infection was recorded in nine (50%) of infected carcasses and this may indicate the prevailing high degree of super infection.ConclusionsThis study provided molecular evidence for the widespread distribution of M. bovis in the cattle population in Ethiopia. It also demonstrated a relatively high degree of genetic polymorphism of the isolates. Further molecular investigation of M. bovis strains in humans and other domestic animals is recommended in order to elucidate the zoonotic importance as well as reservoirs and pattern of transmission among various hosts.