Disease Control in Wildlife: Evaluating a Test and Cull Programme for Bovine Tuberculosis in African Buffalo.

Providing an evidence base for wildlife population management is difficult, due to limited opportunities for experimentation and study replication at the population level. We utilized an opportunity to assess the outcome of a test and cull programme aimed at limiting the spread of Mycobacterium bovis in African buffalo. Buffalo act as reservoirs of M. bovis, the causative agent of bovine tuberculosis (BTB), which can have major economic, ecological and public health impacts through the risk of infection to other wildlife species, livestock and surrounding communities. BTB prevalence data were collected in conjunction with disease control operations in Hluhluwe-iMfolozi Park, South Africa, from 1999 to 2006. A total of 4733 buffalo (250-950 per year) were tested for BTB using the single comparative intradermal tuberculin (SCIT) test, with BTB-positive animals culled, and negative animals released. BTB prevalence was spatially and temporally variable, ranging from 2.3% to 54.7%. Geographic area was a strong predictor of BTB transmission in HiP, owing to relatively stable herds and home ranges. Herds experiencing more intensive and frequent captures showed reduced per capita disease transmission risk and less increase in herd prevalence over time. Disease hot spots did not expand spatially over time, and BTB prevalence in all but the hot spot areas was maintained between 10% and 15% throughout the study period. Our data suggest that HiP's test and cull programme was effective at reducing BTB transmission in buffalo, with capture effort and interval found to be the crucial components of the programme. The programme was thus successful with respect to the original goals; however, there are additional factors that should be considered in future cost/benefit analyses and decision-making. These findings may be utilized and expanded in future collaborative work between wildlife managers, veterinarians and scientists, to optimize wildlife disease control programmes and mitigate conflict at the interface of conservation, agricultural and urban areas.

Selective breeding: the future of TB management in African buffalo?

The high prevalence of bovine tuberculosis (BTB) in African buffalo (Syncerus caffer) in regions of southern African has a negative economic impact on the trade of animals and animal products, represents an ecological threat to biodiversity, and poses a health risk to local communities through the wildlife-cattle-human interface. Test and cull methods may not be logistically feasible in many free-range wildlife systems, and with the presence of co-existing BTB hosts and the limited effectiveness of the BCG vaccine in buffalo, there is a need for alternative methods of BTB management. Selective breeding for increased resistance to BTB in buffalo may be a viable method of BTB management in the future, particularly if genetic information can be incorporated into these schemes. To explore this possibility, we discuss the different strategies that can be employed in selective breeding programmes, and consider the implementation of genetic improvement schemes. We reflect on the suitability of applying this strategy for enhanced BTB resistance in African buffalo, and address the challenges of this approach that must be taken into account. Conclusions and the implications for management are presented.

Comparative analysis of a putative tuberculosis-susceptibility gene, MC3R, and pseudogene sequences in cattle, African buffalo, hyena, rhinoceros and other African bovids and ruminants.

Studies in humans have suggested the possible involvement of melanocortin-3-receptor (MC3R) and other components of the central melanocortin system in host defense against mycobacteria. We report a genomic DNA nucleotide sequence highly homologous to human MC3R in several bovids and non-bovid African wildlife species. Nucleotide sequence analysis indicates that the orthologous genes of cattle and buffalo are highly homologous (89.4 and 90%, respectively) to the human MC3R gene. Sequence results also identified a typical non-functional, duplicated pseudogene, MC3RP, in 7 species from the family Bovidae. No pseudogene was found in animals outside Bovidae. The presence of the pseudogene in tuberculosis-susceptible species could have possible immunomodulatory effects on susceptibility to bovine tuberculosis infection, as well as a considerable influence on energy metabolism and food conversion efficiency.

Impact of age and sex on mycobacterial immunity in an area of high tuberculosis incidence.

SETTING: The extent of immune reactivity measured by the tuberculin skin test (TST) and interferon-gamma (IFN-gamma) T-cell assays is usually not analysed. OBJECTIVE: To determine the impact of age and sex on assay positivity and on the extent of reactivity of both TST and T-cell assays in young persons in an area of South Africa with high TB transmission. RESULTS: Age had a strong impact on assay positivity for all seven immune phenotypes tested (P < 0.0007). Among positive responders, the extent of purified protein derivative (PPD) triggered IFN-gamma release (P < 0.003) was sensitive to age. ESAT-6 triggered IFN-gamma release (day 7, P = 0.03) and the frequency of PPD-specific IFN-gamma(+)CD4(+) (P = 0.03) and IFN-gamma(+)CD8(+) cells (P = 0.04) were weakly dependent on age. By contrast, the extent of TST induration was insensitive to age (P > 0.05), and sex had no significant impact on any phenotype measured (P > 0.05). The high proportion of positive responders in the 1-10 year age-group observed with long-term whole blood assays, but not with 3-day assays and TST, suggests that long-term whole blood assays may be confounded by bacille Calmette-Guérin vaccination in this age group. CONCLUSION: There is a significant impact of age, but not sex, on different assays of immune reactivity in this high TB transmission setting.

Evidence that the spread of Mycobacterium tuberculosis strains with the Beijing genotype is human population dependent.

This study describes a comparative analysis of the Beijing mycobacterial interspersed repetitive unit types of Mycobacterium tuberculosis isolates from Cape Town, South Africa, and East Asia. The results show a significant association between the frequency of occurrence of strains from defined Beijing sublineages and the human population from whom they were cultured (P < 0.0001).

Vitamin D receptor gene polymorphisms and sputum conversion time in pulmonary tuberculosis patients.

A cohort of pulmonary tuberculosis (TB) patients in a South African admixed population was investigated to determine if the vitamin D receptor gene (VDR) polymorphisms FokI, ApaI, and TaqI are associated with TB susceptibility or time to sputum conversion, and to investigate other clinical and demographic factors affecting the rate of response to treatment. Firstly, a case-control association study of 249 TB cases and 352 healthy controls was carried out to investigate association of VDR polymorphisms with TB susceptibility. Secondly, a cohort of pulmonary tuberculosis patients with conversion times for both sputum smear (n=220) and culture (n=222) were analysed to determine factors contributing to mycobacterial resolution in sputum. Age and gender adjusted Cox regression models were constructed. Our results indicate that the extent of disease at diagnosis was predictive of both smear and culture conversion times in the final models. Smoking status and VDR genotype contributed independently to smear conversion time, with ApaI 'AA' genotype and TaqI 'T'-containing genotypes predictive of a faster response to TB chemotherapy. We did not find an association between VDR genotype and TB in the case-control study. We conclude that the time taken for an individual to convert to sputum negativity while on antituberculosis therapy can be independently predicted by the VDR genotype.

SP110 polymorphisms are not associated with pulmonary tuberculosis in a South African population.

Susceptibility to tuberculosis (TB) in mice has recently been attributed to the Ipr1 gene. Polymorphisms in the human homologue, SP110, have been investigated in various populations with only one study finding an association with TB susceptibility. We investigated eight SP110 polymorphisms in a South African population, including two novel polymorphisms. No significant association was found with any of the polymorphisms investigated, including two polymorphisms that were previously found to be associated with TB susceptibility in West African populations.

Differentiation of Mycobacterium tuberculosis complex by PCR amplification of genomic regions of difference.

Differentiation of members of the Mycobacterium tuberculosis complex by conventional mycobacteriological methods is time consuming, making surveillance of species-specific disease difficult. A two-step, multiplex polymerase chain reaction (PCR) method based on genomic regions of difference (RD1, RD1(mic), RD2(seal), RD4, RD9 and RD12) was developed for the differentiation of M. canettii, M. tuberculosis, M. africanum, M. microti, M. pinnipedii, M. caprae, M. bovis and M. bovis BCG. The size of the respective multiplex PCR amplification products corresponded to the presence of the different M. tuberculosis complex members. This method allows for rapid differentiation, making it suitable for routine laboratories and surveillance purposes.

HLA class II disease associations in southern Africa.

Southern Africa harbors several population groups representing a diversity of gene pool origins. This provides a unique opportunity to study genetic disease predisposition in these populations against a common environmental background. Human leukocyte antigen (HLA) association studies of these populations could improve knowledge on inter-population variation and HLA-related disease susceptibility. The aim of this paper is to review HLA class II disease associations reported for southern African population groups, compare them with findings in other populations and identify those unique to southern Africa. A number of HLA class II disease associations appear to be unique to southern African populations. These include DRB1*14011 association with insulin-dependent diabetes mellitus susceptibility in the Xhosa and DRB1*10 and DQB1*0302 with rheumatoid arthritis susceptibility in the South African (SA) Indian and SA Coloreds, respectively. A noteworthy similarity in class II disease association was observed among southern African Caucasoid and their European parental populations. Unique HLA class II disease associations observed in southern Africa are consistent with the notion that unique environmental and natural selective factors have resulted in certain ethnic-specific HLA class II disease associations, while common HLA class II disease associations found across different populations support the notion that common diseases are caused by common, ancient alleles present in indigenous African populations.

Total antioxidant levels are low during active TB and rise with anti-tuberculosis therapy.

In tuberculosis, oxidative stress is a result of tissue inflammation, poor dietary intake of micronutrients due to illness, free radical burst from activated macrophages, and anti-tuberculosis drugs. These free radicals may in turn contribute towards pulmonary inflammation if not neutralized by antioxidants. The total antioxidant status (TAS) of individuals is a function of dietary, enzymatic, and other systemic antioxidants and is therefore an indicator of the free radical load. Our aim was to evaluate the TAS of healthy and M. tuberculosis-infected persons from a high TB incidence community, as well as tuberculosis patients at various stages of antituberculosis drug treatment and to correlate results with plasma micronutrient levels. Blood plasma samples from TB infected patients and following antituberculosis drug treatment were assayed for TAS, vitamins A, E and Zinc. Statistical analysis of results was by one-way ANOVA and the Tukey multiple comparison post test. Active TB patients showed a significantly lower TAS (P < 0.001) compared to the community controls. We also show that TAS values increase during therapy. Results correlated with micronutrients vitamin A and zinc but vitamin E remained unaffected. We suggest that total antioxidant status of TB patients should be considered for more effective disease control and that diets low in antioxidants may render individuals susceptible to tuberculosis.

SLC11A1 (NRAMP1) but not SLC11A2 (NRAMP2) polymorphisms are associated with susceptibility to tuberculosis in a high-incidence community in South Africa.

SETTING: Stellenbosch University Faculty of Health Sciences, and metropolitan Cape Town, Western Cape, South Africa. OBJECTIVE: To investigate whether the reported association between SLC11A1 (also NRAMP1) polymorphisms and susceptibility to tuberculosis (TB) can be confirmed in a different population, and whether polymorphisms in SLC11A2 (also NRAMP2, DCT1, DMT1) are associated with TB. DESIGN: A case-control study design was used to compare the frequencies of five polymorphisms in SLC11A1 and three in SLC11A2 between a group of bacteriologically confirmed TB patients and healthy community controls. RESULTS: The 5' (GT)9 allele in the promoter of SLC1A1 was found at significantly higher frequencies among 265 controls than in 224 pulmonary TB (PTB) patients (P = 0.002; OR 0.6; 95% CI 0.43-0.83). Homozygotes for the TGTG deletion (1729+55del4) in the 3'UTR of SLC11A1 were over-represented among PTB patients (P = 0.013; OR 5.19; 95% CI 1.42-18.94). Stepwise logistic regression analysis indicated that the 5' and 3' polymorphisms contribute separate main effects. Tuberculous meningitis patients (n = 22) showed the same allele and genotype frequency as PTB patients. No SLC11A2 polymorphisms tested were associated with TB. CONCLUSION: The 5' (GT)n allele driving the highest rate of transcription of SLC11A1 appears to be associated with protection against TB in the majority of the populations studied.

Plasmid preparation on sephacryl s1000.

Production of pure plasmid DNA is a prerequisite for most laboratories engaged in recombinant DNA research. There are a number of procedures available for plasmid purification, all of which have common features; namely, (1) growth of plasmid-containing bacteria, (2) lysis of bacteria, (3) low-speed centrifugation to remove the majority of bacterial DNA and protein, (4) an ultracentrifugation step in cesium chloride and ethidium bromide to separate plasmid DNA from RNA and chromosomal DNA, and (5) recovery of plasmid DNA band (extraction of ethidium bromide and cesium chloride). Steps (4) and (5) of this procedure are expensive, time-consuming, and require expensive machinery [ultracentrifuge, rotor(s)]. In addition, incomplete extraction of ethidium bromide can result in plasmid DNA that is not manipulable by many enzymes commonly used in DNA research.

The regulation of tissue plasminogen activator activity by human fibroblasts.

We have found that live and ethanol-fixed fibroblasts, when covered with conditioned medium containing tissue plasminogen activator, associate with the enzyme and remove it from the medium. Binding of tissue plasminogen activator to fixed cells showed equilibrium kinetics with maximal uptake corresponding to 2.4 units of enzyme per 10(6) fixed cells. Enzyme bound to fixed cells could activate plasminogen and produce plaques of caseinolysis in casein-plasminogen-agar overlays. Electrophoretic analysis showed it covalently attached to a fibroblast component with a molecular weight of 40,000-50,000. Sequestration of tissue plasminogen activator by live fibroblasts showed nonsaturable first order kinetics with a rate constant of 0.465/hr. We conclude that active enzyme is bound to a surface receptor, then internalized and degraded. Fibroblasts did not release the binding molecule into the medium; binding of tissue plasminogen activator from the medium was unaffected by heparin or thrombin. This phenomenon differs from that described by Baker et al. and ascribed to "proteasenexin."

Specific molecular activities of recombinant and hybrid leukocyte interferons.

Hybrid interferon DNA recombinants were constructed from the IFLrA and IFLrD leukocyte interferon-coding sequences. Each of the hybrid interferons was purified with the use of a monoclonal antibody to human leukocyte interferon. Three amino acid residues were identified, one or all of which function to potentiate antiviral activity on feline cells and reduce activity on human cells. Because at sufficiently high concentrations human interferons can interact with mouse and rat receptors, it is apparent that the species barrier is only relative and that interferons can be forced into heterologous receptors by mass action. In addition, the specific molecular antiviral and antiproliferative activities (molecules of interferon/cell required for a specific effect) for each of these interferons were determined. The specific molecular activities permit an accurate comparison of the efficacy of different interferons for a specific effect. Because the ratios of antiproliferative/antiviral activity of these interferons vary over a 12-fold range, it appears that the antiviral and antiproliferative activities are promulgated through different mechanisms. To account for these results, it is proposed that there are at least two distinct interferon receptors on cells.

Molecular species of plasminogen activators secreted by normal and neoplastic human cells.

A survey of 56 normal and neoplastic tissues has shown that plasminogen activators were released by cultured human cells in several molecular weights and their susceptibility to inhibition by antibodies to the normal urinary enzyme, urokinase. Melanoma cells characteristically secreted plasminogen activators which were immunochemically distinct from urokinase and which migrated on sodium dodecyl sulfate-polyacrylamide gel electrophoresis as a prominent, closely spaced doublet with an apparent molecular weight of approximately 70,000 and a minor molecular weight component of approximately 60,000. Enzymes with similar characteristics have been observed in serum-free harvest fluids collected from other neoplastic tissue (a breast carcinoma, a glioblastoma, a malignant teratoma, a uterine sarcoma, and a carcinoma of the renal pelvis) and from normal tissue (8-week embryo fibroblasts, normal esophageal fibroblasts, and one culture of normal adult bladder epithelium). Plasminogen activators released by cells derived from most normal adult tissues, or from a 26-week-old embryo, and from other tumors of ectodermal or mesenchymal origin were inhibited by anti-urokinase antibody and showed a closely spaced doublet with a molecular weight of 60,000 as the most abundant molecular species with no evidence of the enzyme with a molecular weight of 70,000.