Malaria Control Resistance

June 29, 2012, 12:35 p.m.

Nigerians have become so at home with malaria that they feel it is no longer a threat but scientists believe that it is still a very big threat to man today. Statistics show that worldwide, it kills more than 1.2 million people annually.

Prevention, they say, is better than cure so researchers at the Department of Public Health, Nigerian Institute of Medical Research (NIMR) are working hard to see that malaria is eradicated by eliminating the vehicle through which the malaria parasite is transmitted to man, the female anopheles mosquito. In this chat with Dr. Sam Awolola, head of the Department of Public Health, NIMR, he says all the efforts will come to naught if proper policies are not put in place. Excerpts:

According to Dr Awolola, the three main processes in malaria control are prevention, treatment and the possibility of having a vaccine against malaria but in NIMR, the focus is on prevention.

"When you talk of prevention, you are talking of how to prevent people from getting infected with malaria; how to prevent transmission from mosquito to human. We focus on preventing mosquitoes from infecting people with malaria through three major ways: Use of long-lasting insecticide-treated nets impregnated with insecticide. They can last up to three years; spraying the houses with WHO-approved insecticides done by trained personnel. When a house is adequately sprayed, the insecticide repels mosquitoes because it has excito-repellent effect.

It also kills those that are stubborn and land on the sprayed wall. This is done every six months or at least once a year depending on the epidemiology of malaria in that environment. The third aspect is larva source management. Mosquitoes breed in stagnant water and before they become adults, they pass through some phases and at that level, you can catch them. Larva source management has two portions - larviciding, ie applying insecticide to the larva and pupa stages.

The other aspect is environmental management. Mosquitoes breed in stagnant water and such water can be cleared or made to flow and all the larvae will be killed. If your gutters are flowing, the water will carry the larvae along and destroy them. Also, some areas of vegetation support the breeding of mosquitoes. We clear those vegetations. All these make up environmental management. So environmental management plus larviciding are put together as larva source management," he stated.

He said using protective clothing or aerosol in houses do not make much impact when it comes to reducing malaria morbidity and mortality.

Vector resistance:

Awolola noted that their research in the last 10 years has shown clearly that there is a lot of resistance to public health insecticides used for malaria vector control in Nigeria. Due to continuous use of the four classes of chemical insecticides (pyrethroids, carbamates, organophosphates and organochlorines), the mosquitoes were subjected to a lot of pressure and over the years, they adapted to the environment so well that they have now become resistant to the insecticides.

"Mosquitoes react to an insecticide in two main ways: One is by trying to metabolise (decay) it using some chemical enzymes so that it becomes non-toxic. Another way is mutation. The mosquito gets in touch with the insecticide through its integument (legs, wings), it then changes the configuration of the gene that recognises the insecticide so that the site of recognition of the mosquito changes and the insecticide becomes ineffective.

For the insecticide to be effective, the site of recognition with the mosquito must be identical. So immediately the mosquito changes the site of recognition, the whole system changes and the mosquito is able to survive. If that happens, the mosquito has mutated because genes are involved.

The gene is a heritable material which means that the next generation of mosquitoes will be resistant to the insecticide because it has passed the gene to them and that gene will continue in that population. We, therefore, have an insecticide-resistant gene in the population and the next set of mosquitoes from that line, whether they have been exposed before or not, will be resistant to insecticides.

You know that 350 mosquitoes can come out from one set of eggs. So if out of the 350, 100 survive and have a blood meal and are able to lay eggs, they will go on to produce another 350 mosquitoes each, and there will be an exponential increment in the number of mosquitoes that will be resistant in that population. That is how resistance spreads.

Way forward:

Dr. Awolola advised that all interventions must be evidence-based for them to be effective. "This means that before the intervention, you must have sufficient evidence to show that it will work. You must have collected some baseline information prior to the intervention, but unfortunately, that is not done inNigeria. But things have started changing at the national level because people have seen that you can spend millions of naira and it goes down the drain if you don't do these things.

We want to scale up our intervention, to have an ambitious coverage. So if you don't get these fundamental bases of malaria control, then you are running your programme on a faulty start and you will end up having faulty results and faulty intervention and then malaria continues to stay with us. "With insecticide resistance, we are in for it unless we put our house in order to ensure that our interventions are evidence-based."

He advocated the practice of rotational use of insecticide, saying that "when you identify that the mosquito is resistant to a particular insecticide, you use another class of insecticides becuse the classes have different target sites. But that can be done when you have a programme that is systematic, pragmatic and evidence-based where information are gathered by think-tanks and fuelled into the national bowl for use to formulate policies."

He noted that there is still a gap between research and policy which needs to be bridged. Harping on the need for surveillance systems that will be able to monitor resistance, he said: "By now, we should have in each geopolitical zone, a centre where they monitor mosquito resistance because malaria is a big issue.

People say that all the time but the will to actually do something about it is not there so we need to put that in place because if that is not in place, sooner or later, these chemicals will become useless, worthless and the issue of malaria becomes more difficult to control, the intervention will no longer be effective and it will be rejected.

"Our research has shown clearly that the resistance issue has continued to increase in Nigeria and if measures are not in place to ensure that it is curtailed, sooner or later, you will see that all these interventions will fail so government needs to put a structure in place, a structure which I refer to as a roadmap to malaria elimination.

That roadmap should be a policy statement from the Federal Government, through the Federal Ministry of Health and the National Malaria Control Programme and we will have a policy in place towards malaria elimination and this roadmap has to be well structured.

It is not something that will happen in two or five years, it might not happen in 10 years but you have timelines and milestones and indicators to show progress. Insecticide resistance is one key issue here; you cannot get malaria eliminated without focusing more on the vectors," he said.


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