Impact of ivermectin on onchocerciasis transmission: assessing the empirical evidence that repeated ivermectin mass treatments may lead to elimination/eradication in West-Africa

BACKGROUND: The Onchocerciasis Control Program (OCP) in West Africa has been closed down at the end of 2002. All subsequent control will be transferred to the participating countries and will almost entirely be based on periodic mass treatment with ivermectin. This makes the question whether elimination of infection or eradication of onchocerciasis can be achieved using this strategy of critical importance. This study was undertaken to explore this issue. METHODS: An empirical approach was adopted in which a comprehensive analysis was undertaken of available data on the impact of more than a decade of ivermectin treatment on onchocerciasis infection and transmission. Relevant entomological and epidemiological data from 14 river basins in the OCP and one basin in Cameroon were reviewed. Areas were distinguished by frequency of treatment (6-monthly or annually), endemicity level and additional control measures such as vector control. Assessment of results were in terms of epidemiological and entomological parameters, and as a measure of inputs, therapeutic and geographical coverage rates were used. RESULTS: In all of the river basins studied, ivermectin treatment sharply reduced prevalence and intensity of infection. Significant transmission, however, is still ongoing in some basins after 10–12 years of ivermectin treatment. In other basins, transmission may have been interrupted, but this needs to be confirmed by in-depth evaluations. In one mesoendemic basin, where 20 rounds of four-monthly treatment reduced prevalence of infection to levels as low as 2–3%, there was significant recrudescence of infection within a few years after interruption of treatment. CONCLUSIONS: Ivermectin treatment has been very successful in eliminating onchocerciasis as a public health problem. However, the results presented in this paper make it almost certain that repeated ivermectin mass treatment will not lead to the elimination of transmission of onchocerciasis from West Africa. Data on 6-monthly treatments are not sufficient to draw definitive conclusions

The role of 'confounding by indication' in assessing the effect of quality of care on disease outcomes in general practice: results of a case-control study.

BACKGROUND: In quality of care research, limited information is found on the relationship between quality of care and disease outcomes. This case-control study was conducted with the aim to assess the effect of guideline adherence for stroke prevention on the occurrence of stroke in general practice. We report on the problems related to a variant of confounding by indication, that may be common in quality of care studies. METHODS: Stroke patients (cases) and controls were recruited from the general practitioner's (GP) patient register, and an expert panel assessed the quality of care of cases and controls using guideline-based review criteria. RESULTS: A total of 86 patients was assessed. Compared to patients without shortcomings in preventive care, patients who received sub-optimal care appeared to have a lower risk of experiencing a stroke (OR 0.60; 95% CI 0.24 to 1.53). This result was partly explained by the presenc

Macrofilaricides and onchocerciasis control, mathematical modelling of the prospects for elimination

BACKGROUND: In most endemic parts of the world, onchocerciasis (river blindness) control relies, or will soon rely, exclusively on mass treatment with the microfilaricide ivermectin. Worldwide eradication of the parasite by means of this drug is unlikely. Macrofilaricidal drugs are currently being developed for human use. METHODS: We used ONCHOSIM, a microsimulation mathematical model of the dynamics of onchocerciasis transmission, to explore the potentials of a hypothetical macrofilaricidal drug for the elimination of onchocerciasis under different epidemiological conditions, as characterized by previous intervention strategies, vectorial capacity and levels of coverage. RESULTS: With a high vector biting rate and poor coverage, a very effective macrofilaricide would appear to have a substantially higher potential for achieving elimination of the parasite than does ivermectin. CONCLUSIONS: Macrofilaricides have a substantially higher potential for achieving onchocerciasis elimination than ivermectin, but high coverage levels are still key. When these drugs become available, onchocerciasis elimination strategies should be reconsidered. In view of the impact of control efforts preceding the introduction of macrofilaricides on the success of elimination, it is important to sustain current control efforts

Mobility and HIV in Tanzanian couples: both mobile persons and their partners show increased risk.

OBJECTIVE: To investigate how mobility is related to sexual risk behavior and HIV infection, with special reference to the partners who stay behind in mobile couples. METHODS: HIV status, sexual behavior and demographic data of 2800 couples were collected in a longitudinal study in Kisesa, rural Tanzania. People were considered short-term mobile if they had slept outside the household at least once on the night before one of the five demographic interviews, and long-term mobile if they were living elsewhere at least once at the time of a demographic round. RESULTS: Overall, whereas long-term mobile men did not report more risk behavior than resident men, short-term mobile men reported having multiple sex partners in the last year significantly more often. In contrast, long-term mobile women reported having multiple sex partners more often than resident women (6.8 versus 2.4%; P = 0.001), and also had a higher HIV prevalence (7.7 versus 2.7%; P = 0.02). In couples, men and women who were resident and had a long-term mobile partner both reported more sexual risk behavior and also showed higher HIV prevalence than people with resident/short-term mobile partners. Remarkably, risk behavior of men increased more when their wives moved than when they were mobile themselves. CONCLUSIONS: More sexual risk behavior and an increased risk of HIV infection were seen not only in mobile persons, but also in partners staying behind. Interventions aiming at reducing risk behavior due to mobility should therefore include partners staying behind