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Biomedical subjects

Abraham Aseffa

Publications and source records attributed to Abraham Aseffa.

At least 19 recordsLinked to original sources
PubMed2006

Leishmania aethiopica: identification and characterization of cathepsin L-like cysteine protease genes.

There is limited information on the biology and pathogenesis of Leishmania aethiopica, causative agent of cutaneous leishmaniasis (CL) in Ethiopia. In this study we have identified and characterized two cathepsin L-like cysteine protease genes, Laecpa and Laecpb, from L. aethiopica. The predicted amino acid sequence of Laecpa and Laecpb is more than 75% identical with homologous cathepsin L-like cysteine protease genes of other Leishmania species and less than 50% identical with human cathepsin L. Laecpa is expressed predominantly in the stationary, and to a lower level, during the amastigote stage while Laecpb is specifically expressed in the stationary stage of L. aethiopica development. Phylogenetic analysis showed that the two genes are grouped into separate clades which are the result of gene duplication. The isolation of these genes will be useful in developing Leishmania species specific diagnostics for molecular epidemiological studies and serves as a first step to study the role of cysteine proteases in L. aethiopica pathogenesis.

Amino Acid Sequence↗
PubMed2006

Identification, sequencing and expression of peroxidoxin genes from Leishmania aethiopica.

Cutaneous leishmaniasis (CL) is a painful, disfiguring and debilitating disease prevalent in Ethiopia and other countries around the world. In Ethiopia, CL is primarily caused by Leishmania aethiopica and less often by L. tropica and L. major. The intracellular survival mechanisms of Leishmania parasites are still not well understood. Recently a new family of antioxidant enzymes called peroxidoxins have been identified that play an important role in parasite survival. In this study, we have identified two distinct peroxidoxin genes (Pxn1 and Pxn2) that are part of a multi-gene family in L. aethiopica. Protein sequence analysis showed that Pxn1 and Pxn2 are highly homologous to peroxidoxins from other Leishmania species. We have found that L. aethiopica Pxn1 is predominantly expressed in amastigotes and stationary phase promastigotes, whereas Pxn2 is constitutively expressed in the different stages of the parasite. This pattern of RNA expression is consistent with patterns seen in some Leishmania species, but not all. Data from this study will be helpful in enhancing vaccine strategies and drug studies targeted towards peroxidoxins.

Amino Acid Sequence↗
PubMed2006

High diversity of group A streptococcal emm types among healthy schoolchildren in Ethiopia.

BACKGROUND: Although the prevalence of rheumatic heart disease in Ethiopia is one of the highest in the world, the epidemiology of group A streptococci (GAS) in this country is little known. GAS typing is a hallmark of both the epidemiology and understanding of diseases caused by these organisms. We have therefore conducted this study to investigate the emm (M-protein gene) type distribution of GAS carriers among Ethiopian schoolchildren. METHODS: In the present study, we performed emm typing of 82 GAS isolates collected from the throats of healthy schoolchildren (6-14 years of age) residing in 3 different urban sites in Ethiopia: Addis Ababa, Gondar, and Dire Dawa. RESULTS: We report high diversity of GAS isolates recovered from healthy schoolchildren. Eighty-two isolates represented 43 different sequence types. Thirteen newly described subtypes were detected in this study. Of the emm types prevalent in the study communities, 46% were not included in the 26-valent GAS vaccine. CONCLUSIONS: The high diversity of emm types encountered within 3 months of collection suggest that production of a vaccine candidate based on the M-protein amino termini appears to be impractical for this population. We suggest that investigations of other vaccine candidates, including the C5a peptidase, GAS carbohydrate, and fibronectin-binding proteins, as well as conserved M-protein region vaccines, should be intensified to address the needs of this population.

Adolescent↗
PubMed2006

Leishmania aethiopica: strain identification and characterization of superoxide dismutase-B genes.

This study was performed to characterize the genes that code for superoxide dismutase (SOD) in Leishmania aethiopica. It involved three main steps: specimen collection and parasite isolation, species identification, and molecular characterization of the SOD genes. Out of 20 skin slit specimens cultured and processed from suspected cutaneous leishmaniasis patients enrolled in the study, five (25%) were found to be positive for motile promastigotes. Isoenzyme electrophoresis and PCR-RFLP results confirmed that the isolates were L. aethiopica. Superoxide dismutase-B (SODB) genes were identified from L. aethiopica for the first time. Iron superoxide dismutase-B genes amplified from promastigotes of L. aethiopica (LaeFeSODB) were similar in size to the SODB genes of other Leishmania species. Nucleotide sequences of LaeFeSODB1 showed 95.4, 93.5, and 97.3% identity with L. donovani SODB1 (LdFeSODB1) L. major SODB1 (LmFeSODB1) and L. tropica SODB1 (LtrFeSODB1), respectively. Similarly, LaeFeSODB2 showed 95.9 and 94.1 and 97.6% identity with LdFeSODB2 and LmFeSODB2 and LtrFeSODB2, respectively. On the other hand, predicted amino acid sequence comparison indicated that LaeFeSODB1 had 91.3, 89.8, and 93.9% identity with LdFeSODB1, LmFeSODB1, and LtrFeSODB1, respectively. The difference in nucleic acid sequence of LaeFeSODB from that of LmFeSODB and LtrFeSODB can be utilized to develop specific molecular methods that help differentiate these species in places where there is an overlap in the distribution of these species. In addition, the data provide information about the situation of L. aethiopica with respect to SODB genes.

Amino Acid Sequence↗
PubMed2006

LACK-reactive CD4+ T cells require autocrine IL-2 to mediate susceptibility to Leishmania major.

Mice from most inbred strains are resistant to infection with Leishmania major whereas mice from BALB strains are highly susceptible. Resistance and susceptibility result from the development of Th1 or Th2 cells, respectively. In this report, we document an IL-2 mRNA burst, preceding the reported early IL-4 response, in draining lymph nodes of susceptible mice infected with L. major. Neutralization of IL-2 during the first days of infection redirected Th1 cell maturation and resistance to L. major, through interference with the rapid IL-4 transcription in Leishmania homolog of mammalian RACK1 (LACK)-reactive CD4(+) cells. A burst of IL-2 transcripts also occurred in infected C57BL/6 mice that do not mount an early IL-4 response. However, although the LACK protein induced IL-2 transcripts in susceptible mice, it failed to trigger this response in resistant C57BL/6 mice. Reconstitution experiments using C.B.-17 SCID mice and LACK-reactive CD4(+) T cells from IL-2(-/-) BALB/c mice showed that triggering of the early IL-4 response required autocrine IL-2. Thus, in C57BL/6 mice, the inability of LACK-reactive CD4(+) T cells to express early IL-4 mRNA transcription, important for disease progression, appears due to an incapacity of these cells to produce IL-2.

Adoptive Transfer↗
PubMed2006

Effect of thalidomide on the expression of TNF-alpha m-RNA and synthesis of TNF-alpha in cells from leprosy patients with reversal reaction.

Hypersensitivity reactions called reversal reaction (RR) and erythema nodosum leprosum (ENL) occur in leprosy. They are characterized by an increase in tumor necrosis factor-alpha (TNF-alpha). Thalidomide is an effective treatment for ENL but not RR. Its effectiveness in ENL is attributed to inhibition of TNF-alpha, and this does not explain its failure to treat RR. We assessed thalidomide's effect on TNF-alpha in RR. Mononuclear cells from RR and non-RR patients and healthy individuals were treated with thalidomide and M.leprae (AFB), a cytosol fraction of M. leprae or Dharmendra lepromin. Thalidomide suppressed TNF-alpha, but when some RR patients' cells were stimulated with AFB, it enhanced TNF-alpha.

Adolescent↗
PubMed2006

Cattle husbandry in Ethiopia is a predominant factor affecting the pathology of bovine tuberculosis and gamma interferon responses to mycobacterial antigens.

Bovine tuberculosis is a major economic problem and a potential public health risk. Improved diagnostics like the gamma interferon (IFN-gamma) test with ESAT6 and/or CFP10 could contribute to the control program. We assessed IFN-gamma responses in zebu (Ethiopian Arsi breed) and Holstein cattle kept indoors or in a pasture to tuberculin purified protein derivative (PPD) and an ESAT6-CFP10 protein cocktail. Furthermore, the intensity and distribution of pathology of bovine tuberculosis were compared between the two breeds. Our data demonstrated significantly (all P < 0.02) higher IFN-gamma responses to avian PPD, bovine PPD, and the ESAT6-CFP10 protein cocktail in Holstein than in zebu cattle, while lesion severities in infected animals and tuberculin skin test responses did not differ significantly (P > 0.05) between the two breeds. Holstein cattle that were kept indoors produced significantly (all P < 0.01) higher IFN-gamma levels in response to avian PPD, bovine PPD, and the ESAT6-CFP10 protein cocktail than did Holstein cattle kept in a pasture. Moreover, lesion severity was significantly higher in Holstein cattle kept indoors (P = 0.001) than in those kept in the pasture. Lesions were localized predominantly in the digestive tract in cattle kept in a pasture, while they were localized in the respiratory tract in cattle kept indoors. In conclusion, in Holstein cattle, husbandry was a dominant factor influencing the severity of tuberculosis lesions and IFN-gamma responses to mycobacterial antigens compared to breed. A difference in the cellular immune response between zebu and Holstein cattle was observed, while tuberculosis lesion severities were identical in the two breeds, when both were kept in a pasture.

Animal Husbandry↗
PubMed2006

Recognition of stage-specific mycobacterial antigens differentiates between acute and latent infections with Mycobacterium tuberculosis.

Mycobacterium tuberculosis is estimated to infect 80 to 100 million people annually, the majority of whom do not develop clinical tuberculosis (TB) but instead maintain the infection in a latent state. These individuals generally become positive in response to a tuberculin skin test and may develop clinical TB at a later date, particularly if their immune systems are compromised. Latently infected individuals are interesting for two reasons. First, they are an important reservoir of M. tuberculosis, which needs to be considered for TB control. Second, if detected prior to recrudescence of the disease, they represent a human population that is making a protective immune response to M. tuberculosis, which is very important for defining correlates of protective immunity. In this study, we show that while responsiveness to early secretory antigenic target 6 is a good marker for M. tuberculosis infection, a strong response to the 16-kDa Rv2031c antigen (HspX or alpha-crystallin) is largely restricted to latently infected individuals, offering the possibility of differential immunodiagnosis of, or therapeutic vaccination against, TB.

Acute Disease↗
PubMed2006

The 6-kilodalton early secreted antigenic target-responsive, asymptomatic contacts of tuberculosis patients express elevated levels of interleukin-4 and reduced levels of gamma interferon.

It is well known that the majority of healthy individuals exposed to Mycobacterium tuberculosis do not become clinically ill. We have previously shown that in recently exposed healthy contacts of tuberculosis (TB) patients, a strong immune response to the M. tuberculosis 6-kDa early secreted antigenic target (ESAT-6) virulence factor correlated with a higher risk of subsequent disease, although the mechanism was unclear at that time. Inspired by recent reports that elevated expression of interleukin-4 (IL-4) in health care workers exposed to M. tuberculosis also correlated with a higher risk of their subsequently developing disease, we examined expression of IL-4, its competitive antagonist IL-4delta2, and gamma interferon (IFN-gamma) in healthy household contacts of TB patients from Ethiopia. We then compared cytokine expression to their recognition of ESAT-6 (which is largely restricted to members of the tuberculosis complex and which serves as a reliable marker of infection) or to Ag85A (an antigen that is conserved among the mycobacteria and serves as a nonspecific control). Our study shows that in these recently exposed individuals, there is a correlation between a strong response to ESAT-6 and elevated expression of IL-4. Further, elevated expression of IL-4 is associated with lower expression of its antagonistic splice variant IL-4delta2 and with the Th1 cytokine IFN-gamma, suggesting that in these at-risk individuals, immunity is skewed away from a protective Th1 response, even before the development of clinical symptoms.

Antigens, Bacterial↗
PubMed2006

Characterization of Neisseria meningitidis isolates from recent outbreaks in Ethiopia and comparison with those recovered during the epidemic of 1988 to 1989.

The objectives of this study were to collect and characterize epidemic meningococcal isolates from Ethiopia from 2002 to 2003 and to compare them to 21 strains recovered during the previous large epidemic of 1988 to 1989. Ninety-five patients in all age groups with clinical signs of meningitis and a turbid cerebrospinal fluid (CSF) sample were included in the study of isolates from 2002 to 2003. Seventy-one patients (74.7%) were confirmed as having Neisseria meningitidis either by culture (n = 40) or by porA PCR (n = 31) of their CSF. The overall case fatality rate (CFR) was 11.6%; the N. meningitidis-specific CFR was 4.2%. All 40 strains were fully susceptible to all antibiotics tested except sulfonamide, were serotyped as A:4/21:P1.20,9, and belonged to sequence type 7 (ST-7). The strains from 1988 to 1989 were also equally susceptible and were characterized as A:4/21:P1.20,9, but they belonged to ST-5. Antigenic characterization of the strains revealed differences in the repertoire of lipooligosaccharides and Opa proteins between the old and the recent strains. PCR analysis of the nine lgt genes revealed the presence of the lgtAHFG genes in both old and recent strains; lgtB was present in only some of the strains, but no correlation with sequence type was observed. Further analysis showed that in addition to their pgm alleles, the Ethiopian ST-5 and ST-7 strains also differed in their tbpB, opa, fetA, and lgtA genes. The occurrence of new antigenic structures in strains sharing the same serogroup, PorA, and PorB may help explain the replacement of ST-5 by ST-7 in the African meningitis belt.

Adolescent↗
PubMed2006

Seroprevalence of human immunodeficiency virus among blood donors in Northwest Ethiopia, 1995-2002.

Data on age, sex, occupation, HIV serostatus and year of donation were collected from the blood donors log book of Gondar College of Medical Sciences Hospital, Northwest Ethiopia, for the period between January 1995 and December 2002 and analysed. The crude HIV seroprevalence was 9.9% (1109/11,204). A declining trend in the prevalence was observed from as high as 15.7% (207/1321) in 1995 to 9.3% (123/1327) in 1999 and down to 4.3% (68/1576) in 2002. The declining trend observed in recent years is encouraging and should further be strengthened by making use of the blood bank as an entry point for HIV testing and counselling services.

Adolescent↗
PubMed2005

Challenges presented by nerve damage in leprosy.

The basis of nerve damage in leprosy is the unique tendency of Mycobacterium leprae to invade Schwann cells. alphaBeta-Dystroglycan on the basement membrane of Schwann cells binds to laminin alpha2, in turn binding to receptors on the M. leprae surface, comprising a histone-like protein and phenoglycolipid-1. When nerve damage during reversal reactions was found to be associated with an abrupt increase in delayed type hypersensitivity against M. leprae antigenic determinants released from Schwann cells, it suggested that the nerve is damaged as an innocent bystander during the immune response. This strongly influenced the introduction of therapy based on immunosuppression combined with continued anti-mycobacterial medication. Lysis of Schwann cells presenting M. leprae antigenic determinants by activated CD4+ T cells and interaction of M. leprae with Toll-like receptors on Schwann cells are additional mechanisms implicated in nerve damage. Persistence of M. leprae antigen in local lesions after regular multiple drug therapy (MDT) is an important risk factor for late reactions. In spite of significant advances in the provision of MDT globally, early diagnosis, together with effective treatment of the disease and associated nerve damage at initial presentation remains a major challenge for the health services. Reduced prevalence as a result of MDT should not be taken to indicate that the challenges of leprosy control are diminished as long as nerve damage is not controlled and new case detection rates are not declining.

Drug Therapy, Combination↗
PubMed2004

Healthy individuals that control a latent infection with Mycobacterium tuberculosis express high levels of Th1 cytokines and the IL-4 antagonist IL-4delta2.

The majority of healthy individuals exposed to Mycobacterium tuberculosis will not develop disease and identifying what constitutes "protective immunity" is one of the holy grails of M. tuberculosis immunology. It is known that IFN-gamma is essential for protection, but it is also apparent that IFN-gamma levels alone do not explain the immunity/susceptibility dichotomy. The controversy regarding correlates of immunity persists because identifying infected but healthy individuals (those who are immune) has been problematic. We have therefore used recognition of the M. tuberculosis virulence factor early secretory antigenic target 6 to identify healthy, but infected individuals from tuberculosis (TB)-endemic and nonendemic regions (Ethiopia and Denmark) and have compared signals for cytokines expressed directly ex vivo with the pattern found in TB patients. We find that TB patients are characterized by decreased levels of Th1 cytokines and increased levels of IL-10 compared with the healthy infected and noninfected community controls. Interestingly, the healthy infected subjects exhibited a selective increase of message for the IL-4 antagonist, IL-4delta2, compared with both TB patients or noninfected individuals. These data suggest that long-term control of M. tuberculosis infection is associated not just with elevated Th1 responses but also with inhibition of the Th2 response.

Adult↗
PubMed2004

Direct colorimetric assay for rapid detection of rifampin-resistant Mycobacterium tuberculosis.

The colorimetric 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay was standardized for direct detection of rifampin-resistant Mycobacterium tuberculosis in sputum samples. The sensitivity and specificity of the direct MTT assay matched those of the standard indirect susceptibility assay on 7H10 medium, and interpretable results were obtained for 98.5% of the samples within 2 weeks. Traditional methods of in vitro drug susceptibility testing are time consuming and laborious. Susceptibility tests on clinical isolates require 6 to 9 weeks, and tests conducted directly on smear-positive samples take about 3 weeks (International Union Against Tuberculosis and Lung Disease, The public health service national tuberculosis reference laboratory and the national laboratory network. Minimum requirements, role and operation in a low-income country, Paris, France, 1998, and P. T. Kent and G. P. Kubica, Public health mycobacteriology. A guide for the level III laboratory, Centers for Disease Control and Prevention, Atlanta, Ga., 1985). More-rapid methods are available but are very expensive for routine use under program conditions in countries with high levels of tuberculosis endemicity.

Colorimetry↗
PubMed2003

Diagnosis of tuberculous lymphadenitis in Butajira, rural Ethiopia.

Tuberculous lymphadenitis (TBLN) is a diagnostic challenge in sub-Saharan Africa, where there is a high rate of human immunodeficiency virus (HIV) infection. This study aimed to find ways to improve the diagnosis in Butajira, rural Ethiopia, where TBLN constitutes 40% of the total tuberculosis (TB) diagnosis. Among 147 clinically suspected cases, 107 (72.8%) were confirmed as TBLN by fine-needle aspiration (FNA) cytology and acid-fast bacillus (AFB) smear examination. Of the remaining 40 cases, denoted non-tuberculous lymphadenitis (NTBLN) after this smear examination, 37 (92.5%) showed a cytological pattern with neutrophil aggregates. The clinical manifestations were similar and cervical lymph nodes were the most affected in these 2 groups. 24 of the 107 TBLN cases (22.4%) and 9 (22.5%) of the other cases were seropositive for HIV infection (p > 0.5). FNA cytology combined with AFB smear examination is a good alternative to histology in rural Ethiopia where the expertise in taking biopsies is very limited. Polymerase chain reaction for Mycobacterium tuberculosis complex DNA was positive in 15 of 23 cases tested with NTBLN cytology, showing that an additional independent criterion for the presence of M. tuberculosis is needed for diagnosis in lymphadenitis cases of this kind. These findings could help to strengthen the diagnostic algorithm suggested by the National TB Control Program.

Adolescent↗
PubMed2002

The early IL-4 response to Leishmania major and the resulting Th2 cell maturation steering progressive disease in BALB/c mice are subject to the control of regulatory CD4+CD25+ T cells.

Susceptibility and development of Th2 cells in BALB/c mice infected with Leishmania major result from early IL-4 production by Vbeta4Valpha8 CD4+ T cells in response to the Leishmania homolog of mammalian RACK1 Ag. A role for CD4+CD25+ regulatory T cells in the control of this early IL-4 production was investigated by depleting in vivo this regulatory T cell population. Depletion induced an increase in the early burst of IL-4 mRNA in the draining lymph nodes of BALB/c mice, and exacerbated the course of disease with higher levels of IL-4 mRNA and protein in their lymph nodes. We further showed that transfer of 10(7) BALB/c spleen cells that were depleted of CD4+CD25+ regulatory T cells rendered SCID mice susceptible to infection and allowed Th2 differentiation while SCID mice reconstituted with 10(7) control BALB/c spleen cells were resistant to infection with L. major and developed a Th1 response. Treatment with a mAb against IL-4 upon infection with L. major in SCID mice reconstituted with CD25-depleted spleen cells prevented the development of Th2 polarization and rendered them resistant to infection. These results demonstrate that CD4+CD25+ regulatory T cells play a role in regulating the early IL-4 mRNA and the subsequent development of a Th2 response in this model of infection.

Adoptive Transfer↗