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Q&A on resistance to main drug used to treat malaria (artemisinin)

Thursday, 12 September 2013 10:53 by General
There is a good summary here: Q&A on artemisinin resistance 

Artemisinin-based combination therapies (ACTs) are the main drugs used to treat malaria. In the majority of the world they work. In some parts of Asia resistance to ACTs has been seen because some strains of malaria are resistant to artemisinin. This is not good. There are five different ACTs and if one does not treat a particular patient, the patient is still cured as part of a longer treatment regimen, provided they are treated with an ACT containing a partner drug that is effective in that geographical area. So far, resistance is confined to four South-East Asian countries: Cambodia, Myanmar, Thailand, and Vietnam, all in the Greater Mekong subregion.

Geographic containment efforts may slow the spread of artemisinin resistance. A solution to artemisinin resistance is likely to require new malaria drugs not based on artemisinin.

Scientists have developed a simple, rapid blood test to determine the malaria parasite's resistance to artemisinin. This can help identify patients who need a second ACT to help them recover from malaria.

One implication of the reduction in efficacy of drugs to treat malaria is the need to work harder and faster to bring malaria under control so fewer people are at risk. And that’s where bednets come in.
 
 
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Status and implications of mosquitoes developing resistance to the insecticide used in LLINs and mosquitoes changing their biting time to early morning.

Thursday, 11 October 2012 09:32 by General
Mosquitoes developing resistance to the insecticide used in long-lasting insecticidal nets (LLINs) and mosquitoes changing their biting (feeding) behaviour and biting not between 10pm and 2am but towards the early morning ie 5am – or rather, in both cases, natural selection occurring favouring those mosquitoes that develop some level of resistance or having a later biting time – is starting to be seen. The extent to which either or both of these factors become a major problem for the effectiveness of LLINs is currently not clear.
 
Currently both issues – resistance to pyrethroids and changed time of biting - are not widespread. Currently LLINs remain highly effective in reducing the incidence of malaria.
 
Professor Steve Lindsay of Durham University comments: 'It is more likely we will see an increase of mosquitoes biting outdoors in the early evening, before people go to bed, although we do not have evidence for this occurring in Africa at present. Nonetheless, what is a common finding is that large-scale use of LLINs has resulted in the near extermination of Anopheles gambiae sensu stricto in houses in East Africa, with An. arabiensis remaining as the major vector, biting outdoors. In this case, the view is that there is no increase in An. arabiensis populations.'
 
On resistance to pyrethroids, Steve Lindsay comments: 'Resistance to pyrethroids is a rapidly growing phenomenon. We do not know whether this is impacting the control of malaria yet, but it is likely to be the case in the future. For the present they are probably effective in most places. New nets with different combinations of insecticides may provide better protection where pyrethroid resistance occurs, but these products are in the early stages of testing. And we shouldn't forget that an intact net is protective against malaria. For the moment, don't stop rolling out the nets.'
 
It is perfectly possible either or both – resistance to pyrethroids and changed time of biting - will remain a relatively minor problem without widespread impact.
 
It is also perfectly possible, over time, either or both - resistance to pyrethroids and changed time of biting - will become a material issue. This is the more likely scenario.
 
Resistance has been seen in other areas so it would not be a great surprise to see resistance developing to an insecticide. For example, the malaria parasite (rather than the mosquito in this case) first showed resistance to chloroquine in the 1950s and more recently, in 2004, evidence of resistance to Artemisinin Combination Therapy (ACT), the primary drug currently used to treat malaria.
 
This highlights the importance of meta-research studies that look at both these issues - resistance to pyrethroids and changed time of biting - in many more locations to both establish how prevalent the problems are and to monitor developments.
 
This is a very important time for research so we gain clearer information that can influence decisions.
 
A solution to mosquitoes developing pyrethroid resistance is the use of non-pyrethroid insecticides. Currently there aren’t any that can be used on nets. Significant research is being carried out by a variety of groups and organisations to develop such insecticides. No-one can give a clear timeframe or the chances of success although some in this research area suggest a three to ten year timeframe is likely before products are able to come to market given the strict testing of such insecticide-including products.
 
In 2010, a net incorporating a second chemical, referred to as a synergist, was introduced to the market. There is some, but not conclusive, evidence that the combination of the pyrethroid and the synergist is more effective than pyrethroid-only nets at achieving knock-down of mosquitoes developing pyrethroid resistance. Further research studies, including field studies, are currently underway. More are required. The conclusion currently therefore, is there is no clear indication that the synergist treated nets are the nets of choice for areas where resistance is indicated, or indeed for other areas to prevent resistance developing. However, they do show promise and they might prove to be better than non-synergist-including nets. The synergist treated nets are currently 30% more expensive than the pyrethroid-only treated nets.
 
A solution to mosquitoes changed time of biting is less clear, as is the extent of the problem. There is an interesting article that discusses some of the current factors that may influence how serious, or not, a problem this becomes.
 
The bottom line:
  1. Long-lasting insecticide treated nets (LLINs) remain the most effective means of malaria prevention.
  2. More research needs to be funded to understand the extent of problems such as mosquito resistance to the insecticide used on nets (pyrethroids) and change in time of day of biting of some mosquitoes.
  3. Research into both non-pyrethroid insecticides and chemical combinations (with pyrethroids) is very important.
 
 
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Mosquitoes resistance to one of the insecticides used in LLINs?

Friday, 19 August 2011 09:03 by RobMather
Research over the last decade and more shows mosquitoes can develop resistance to drugs used to combat malaria. Well-documented and extensive research conducted ten years ago showed the development of resistance in the malaria parasite to chloroquine. This emphasised the importance of drug-resistance research as this helped avoid funding millions of dollars of chloroquine to an area where there were high-levels of chloroquine resistance. Further, knowledge of this developing resistance made it imperative to find other drugs that could be used to prevent, or treat those with, malaria so the focus was not on a single drug. Indeed, another drug, artemisinin is now one of the main ones used to treat those with malaria. Unsurprisingly perhaps, malaria parasites have now been found that have developed a resistance to Artemisinin so significant work is underway to understand and limit this resistance which is currently confined to a relatively small geographic area.
 
As with malaria drugs, bednets are no different and there is the potential for mosquitoes to develop a resistance to the insecticide used in long-lasting insecticide treated nets (LLINs). 
 
A recent research study in Senegal (also covered in this BBC news article) suggests such resistance may be developing. There is debate in the scientific community as to whether the results of this research study indicate the development of widespread resistance. It is likely further research is needed to establish how much of an issue this could be and what steps may be needed, such as the use of different insecticides, to ensure LLINs remain effective. This research is very important as the consequences of us not knowing if resistance has developed could be LLINs becoming much less effective than they are currently.

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Study highlights the need for quick and accurate malaria testing

Thursday, 8 July 2010 14:11 by AndrewGarner

A recent study, looking at data from 2007, has suggested that of the 183 million African children under 5 who sought treatment for fever 43% were likely to have malaria. The common assumption is that all childhood fevers are caused by malaria and so the child is given anti-malaria treatment unnecessarily. This depletes stocks of the treatment and may also increase the chances of P.falciparum becoming resistant to current anti-malaria drugs.

This emphasises the need for accurate, rapid diagnostic tests for malaria which are simple, cheap and effective. The study, which breaks down the data geographically, may also help in prioritising where the anti-malarial spend is focused.

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