Forage plants as an alternative feed resource for sustainable pig production in the tropics: a review.

Globally, pressure on concentrate feed resources is increasing, especially in the tropics where many countries are net importers of food. Forage plants are a possible alternative, but their use as feed ingredients for pigs raises several issues related to their higher fibre and plant secondary metabolites contents as well as their lower nutritive value. In this paper, the nutritive value of several forage species and the parameters that influence this nutritive value in relationship to the plant family, the physiological stage, the plant part and the preservation method (fresh, hay and silage) are reviewed. The influence of the breed and the physiological status of the animal on animal voluntary intake of fibre-rich ingredients, digestibility as related to gastrointestinal volume and transit time and growth performances are also discussed. The final section highlights the advantages and drawbacks of forage plants in pig diets and stresses the need for proper economic evaluation to conclude on the benefits of the use of forage plants in pig feed.

Comparison of two bacteriophage tests and nucleic acid amplification for the diagnosis of pulmonary tuberculosis in sub-Saharan Africa.

SETTING: National reference laboratory in Zambia, a high-incidence setting with a high prevalence of HIV infection. OBJECTIVE: To compare the performance of a commercial bacteriophage kit with a nucleic acid amplification kit and an 'in-house' bacteriophage method for rapid diagnosis of pulmonary tuberculosis (TB). METHODS: Sputum specimens from suspected pulmonary TB cases were examined by direct fluorescence microscopy and culture on Löwenstein Jensen (LJ). In a blinded study, remaining samples were tested by AMTD and FASTPlaqueTB or an in-house bacteriophage assay. Two specimen decontamination protocols were investigated. RESULTS: Microbial contamination of 40.4% was observed when using the FASTPlaqueTB kit specimen preparation protocol. When compared to culture on LJ, the sensitivity of the FASTPlaqueTB test was 20.7%. Implementation of a modified Petroff's decontamination protocol reduced contamination to 5.8% and the FASTPlaqueTB test detected 8/25 (32%) of culture-positive specimens. The sensitivity of AMTD and smear microscopy for these specimens were 64% and 48%, respectively. In a separate experiment the sensitivity of an in-house bacteriophage assay was 45.3% compared to 64.2% for AMTD and 45.3% for direct smear microscopy. CONCLUSIONS: Additional analysis of sputum specimens by bacteriophage assay provided no advantage in this setting. For the rapid diagnosis of TB, AMTD offered improved sensitivity over direct smear microscopy.

HIV-1 and recurrence, relapse, and reinfection of tuberculosis after cure: a cohort study in South African mineworkers.

BACKGROUND: The proportion of recurrent tuberculosis cases attributable to relapse or reinfection and the risk factors associated with these different mechanisms are poorly understood. We followed up a cohort of 326 South African mineworkers, who had successfully completed treatment for pulmonary tuberculosis in 1995, to determine the rate and mechanisms of recurrence. METHODS: Patients were examined 3 and 6 months after cure, and then were monitored by the routine tuberculosis surveillance system until December, 1998. IS6110 DNA fingerprints from initial and subsequent episodes of tuberculosis were compared to determine whether recurrence was due to relapse or reinfection All patients gave consent for HIV-1 testing. FINDINGS: During follow-up (median 25.1 months, IQR 13.2-33.4), 65 patients (20%) had a recurrent episode of tuberculosis, a recurrence rate of 10.3 episodes per 100 person-years at risk (PYAR)-16.0 per 100 pyar in HIV-1-positive patients and 6.4 per 100 pyar in HIV-1-negative patients. Paired DNA fingerprints were available in 39 of 65 recurrences: 25 pairs were identical (relapse) and 14 were different (reinfection). 93% (13/14) of recurrences within the first 6 months were attributable to relapse compared with 48% (12/25) of later recurrences. HIV-1 infection was a risk factor for recurrence (hazard ratio 2.4, 95% CI 1.5-4.0), due to its strong association with disease caused by reinfection (18.7 2.4-143), but not relapse (0.58; 0.24-1.4). Residual cavitation and increasing years of employment at the mine were risk factors for relapse. INTERPRETATION: In a setting with a high risk of tuberculous infection, HIV-1 increases the risk of recurrent tuberculosis because of an increased risk of reinfection. Interventions to prevent recurrent disease, such as lifelong chemoprophylaxis in HIV-1-positive tuberculosis patients, should be further assessed.

Utility of nucleic acid amplification techniques for the diagnosis of pulmonary tuberculosis in sub-Saharan Africa.

SETTING: Lusaka, Zambia. OBJECTIVES: To investigate the utility of nucleic amplification tests for the diagnosis of pulmonary tuberculosis in a resource-poor setting with a high incidence of human immunodeficiency virus (HIV). DESIGN: Sputum specimens from suspects attending a referral chest clinic were examined by low-cost 'in-house' one-tube nested polymerase chain reaction (PCR), the enhanced Gen-Probe Amplified Mycobacterium Direct Test (AMTD), auramine smear and Lowenstein-Jensen culture. RESULTS: PCR and AMTD detected respectively 80% and 92% of smear-positive specimens and 40% and 60% of smear-negative, culture-positive specimens. AMTD was positive for 18 culture-negative suspects; subsequent investigation indicated these to be six confirmed tuberculosis patients, nine judged from radiological data and clinical follow-up studies to have pulmonary tuberculosis, and three non-tuberculosis patients. Sensitivity for smear, culture, PCR and AMTD, when compared to a gold standard incorporating both microbiological and clinical data, was respectively 29%, 69%, 55% and 81%. CONCLUSION: In this setting, the sensitivity of the low-cost PCR proved insufficient for its effective use as a tool for diagnosing pulmonary tuberculosis, while AMTD performed considerably better than the current laboratory methods for diagnosis of pulmonary tuberculosis. However, the high cost of this technology may limit its application in the public sector of low-income countries.

Tuberculosis treatment failure and drug resistance--same strain or reinfection?

Tuberculosis patients may have Mycobacterium tuberculosis in their sputum at the end of treatment, and may show new drug resistance, due to either inadequate treatment of the original episode or reinfection with a new strain during therapy. In a cohort study of mineworkers with tuberculosis in South Africa, 57 of 438 patients had positive sputum cultures 6 months after recruitment in 1995. Of the 31 patients who initially had fully sensitive strains, 3 developed multidrug resistance (MDR) and 3 single-drug resistance (SDR). Of the 6 who started with SDR, 3 became MDR. HIV infection was not associated with drug resistance at enrollment or 6 months later. We compared pairs of DNA fingerprints from isolates of M. tuberculosis at recruitment and 6 months later in the 48 patients for whom we had both available. In 45, the pairs were identical. In 1 patient, although both isolates were fully sensitive, the later fingerprint had 1 less band (transposition). In 2 pairs, the fingerprint patterns were completely different: one seemed to be the result of laboratory error and the other was a true reinfection with an MDR strain. Despite a high risk of infection, with a moderate proportion of background drug-resistant strains (11% SDR, 6% MDR), reinfection is not a common cause of treatment failure or drug resistance at 6 months.