Anopheles gambiae Photo credit: Jim Gathany-CDC.

What can the fight against Malaria teach us about Zika?

Zika is spread by so mosquitoes, so to stop Zika, you have to stop the mosquitoes. And mosquitoes are everywhere.

Fortunately, the global health community has been fighting mosquitos for years. A look at the most recent research into effective ways to fight malaria may offer some insights into how to stop the spreading Zika outbreak in its tracks.

The problem with malaria is that it’s really difficult to eliminate.

It’s not the most fatal disease in global health, although it is very dangerous for pregnant women. It’s easily diagnosed with a blood test, and we have decent treatments for it. But it’s very difficult to stop. Ebola, for example, is actually relatively easy to stop if you can isolate people who have it. Isolating with people with malaria wouldn’t help – in fact it would make no difference since malaria isn’t contagious person-to-person except for mother to baby transmission. Malaria is spread by mosquitoes.

In other words, getting rid of malaria is about getting rid of mosquitoes. But mosquitoes don’t just spread malaria. They spread Zika virus, dengue fever, West Nile virus, and yellow fever.

The techniques for stopping mosquitoes come down to disrupting their habits by eliminating standing water and spraying pesticide, and protecting people through bednets and insecticide spraying. Programs that support these efforts are difficult to evaluate. If you spray standing water for mosquitoes and also provide bednets and medication, how do you know which activity actually led to the reduction in malaria? And also, the mosquito that spreads Zika is a different species of mosquito that spreads malaria. Both, though, are still active at night.

Something is working. We know that. We have seen substantial progress against malaria in Africa from 2000-2015. According to the World Health Organization, “Between 2000 and 2015, malaria incidence among populations at risk (the rate of new cases) fell by 37% globally. In that same period, malaria death rates among populations at risk fell by 60% globally among all age groups, and by 65% among children under 5.” Malaria case incidence declined by 40% – from 321/1,000 annually in 2000 to 192/1,000 in 2015. All but one of the 43 African mainland countries that are malaria-endemic met their MDG target of reversing incidence trends by 2015. 19 countries achieved a .50% decline, and seven countries had incidence decline by .75%.

An article in Nature, published last October, may have the answer. It used sophisticated data analysis to look at malaria in Sub-Saharan Africa and identify which activities led to reductions in the disease. The evidence comes down squarely in support of insecticide-treated bednets (ITNs). According to the article, 62–72% of the declines in the malaria parasite from 200-2015 can be attributed to the use of ITNs. Indoor spraying, by contrast, contributed 11-16% of the decline.

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This offers useful lessons for fighting other mosquito-borne diseases. ITNs clearly show the best value for money, ahead of indoor residual spraying or trying to eradicate mosquito habitats with pesticides.

What the article doesn’t say

ITNs have actually been a controversial topic. Critics of international aid frequently target the free provision of ITNs as bad aid; recipients of bednets have been seen to use them as fishnets, or as material for clothing or shelter. There is also a widespread belief that people simply do not use ITNs, even if they report they have done so on evaluation surveys. Despite these criticisms, the vast majority of ITN programs have provided them for free to make sure they are accessible to everyone.

The article demonstrates that ITNs are being used, but it does not actually differentiate between ITNs that were purchased by users and ITNs that were provided for free. Since the vast majority of ITNs are provided for free, however, I feel comfortable regarding this article as a vindication for ITN distribution programs across the boards. If only purchased ITNs had an impact, the declines in malaria would be much smaller.

Finally, this is really extraordinarily good news. We should be proclaiming these numbers from the rooftops. 3.2 billion people are at risk for malaria and we’re actually making progress against the disease. That is amazing. The article really doesn’t emphasize the value of this victory enough. I suppose, as a journal article, it can’t really show excitement.

One sentence takeaway

Insecticide treated bednets are stopping malaria and they can help stop Zika.

UPDATE: A reader suggests that bednets would not be effective against Zika because the Aedes Aegypti mosquito that carries Zika is a day-biter. To be sure, nets will not have as much of an impact on reducing bites from Aedes Aegypti as they do on Anopheles, but they will have an impact. The Aedes Aegypti bites mostly at dawn and dusk, as well as during the day. In my opinion, and that of other global health specialists, this means that bednets will have an impact. Many Ministries of Health are recommending and distributing bednets as a Zika virus response, and it is on the list of CDC-suggested measures for avoiding Zika.