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WHO's interim position statement on larviciding for malaria control in Africa

April 30, 2012 - 16:05 -- Bart G.J. Knols

Last week, WHO published a statement regarding the potential of larviciding for malaria control in Africa. This followed the circulation of a draft version of the statement in August 2011. That draft was sent to a limited group of people (how many I don't know) for comments (including myself). I attach the official version to this editorial.

After reading this document I asked myself a number of questions. First, it is abundantly clear from this document that larval control is seen as secondary if not tertiary in importance compared to the use of LLINs or IRS. Of course, the Ross-MacDonald model explains why a focus on adult control methods should be more effective than merely reducing mosquito densities at the larval stage (due to the length of the extrinsic incubation cycle and the daily survival probability, pn). But although this may be true, we are faced with some pretty hard facts in the real world of malaria control:

1) Resistance is spreading and already rampant in many places in sub-Saharan Africa. Without a new class of insecticides for bednet impregnation, and perhaps three new active ingredients coming out of the IVCC pipeline by 2020, what will we do in the meantime?

2) With a shift in vector species composition towards Anopheles arabiensis and the disappearance of An. gambiae in many places where nets/IRS have been implemented, how will we deal with outdoor biting and shifts in biting times?

3) Considering that malaria elimination/eradication is also WHO's goal, what do they propose to add to LLINs/IRS next when it has been shown in various studies that these indoor interventions on their own will not result in elimination?

Nevertheless, the overall tenure of this document is pretty negative when it gets to larval control. There is too little evidence from Africa, it may not be cost-effective (particularly in rural areas) and it requires detailed entomological surveillance and skills to be implemented properly. It is claimed that only in places where breeding sites are few, fixed, and findable, larval control may have a role to play as a supplementary tool (with nets and/or IRS).

But what is missing here is the goal when larval control is added: is it merely control or is it elimination? Take Egypt as an example: it eliminated its malaria along the Nile from the border with Sudan all the way north to Asyut during WWII. It has not seen malaria since, and no doubt, the return on investment of that elimination campaign (largely based on larval control using Paris green) is very, very positive. Was it labour intensive? Yes. Were the breeding sites few, fixed, and findable? Not really.

Would it be possible to repeat the same elimination campaign, now starting in the border town of Wadi Halfa in Sudan and move south to its capital Khartoum -by using exactly the same strategy Egypt deployed during WWII - ? No doubt it would be, as long as the capacity and financial resources allow for sufficient number of staff to be deployed and such a campaign would be well-managed.

It is beyond any doubt that many of the drier regions in the Sahelian zone and the Horn of Africa, as well as in Southern Africa have large areas that are relatively isolated and where larval control could make a huge difference. And yes, WHO's paper states that detailed knowledge of the local vectors is required and that larval control cannot be applied everywhere. But this does not mean that larval control is not a good weapon to be added to the toolbox. The fact that a larval control trial in the Gambia faltered is highlighted, even though it is well-known why this was the case - which had very little to do with the biology of the system.

In all parts of the world where malaria was eliminated larviciding did play at least a major if not significant role (in combination with larval source management). The current position paper may push policy makers further away from adopting larviciding as an add-on tool to their ongoing control efforts. NMCP managers that are not aware of the giant contributions that larval control made to malaria control (and elimination) around the world may refrain from moving beyond nets and IRS.

I have not the smallest doubt that a decade from now we will be talking a completely different language that will include the acronym AW-IPM: Area-Wide Integrated Pest Management. So well adopted in numerous agricultural pest control endeavours, yet so distant from those in the field of malaria vector control...

What do you think? 

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Comments

Guy Reeves's picture
Submitted by Guy Reeves on

 

I read this post a few hours after a very sceptical article on larvaciding in the Financial Times (UK) that came out the same day.

http://www.ft.com/intl/cms/s/0/48c68ede-86dd-11e1-ad68-00144feab49a.html#axzz1tYapU

 It was very interesting as the FT article strongly suggests that the Ghanaians are mistaken in paying 72$ million for a 2 year larvaciding contract.  While 72$ million appears a lot to me, as I have no idea about the economics of malaria control, the FT article does not provide any reasons why the Ghanaians might think there is some value (beyond suggesting they are victims  of the  ‘high-level diplomatic connections’ of Cubans).  This is why I was so interested to read an alternative view, including historical precedents, which provides a possible answer to why the Ghanaians are showing an interest.

I wondered if anybody would be able to answer if 72$ million is likely to be a high price?  Could a robust evaluation be made for less?

MPI, Plön (Germany)

William Jobin's picture
Submitted by William Jobin on

Dear colleagues,

In this discussion of larval source management (LSM) relative to other control methods such as IRS and bednets, it is important to:

1.  See the economic development which is triggered thru LSM by land reclamation, and

2.  Recognize that LSM includes several other techniques besides repeated application of Bacillus to larval habitats.

In fact, I would argue that we should realize the very large importance for agricultural and economic development in Africa from the impact of malaria suppression through LSM by land reclamation - 

MALARIA SUPPRESSION THROUGH LARVAL SOURCE MANAGEMENT CAN BE A FIRST STEP IN ECONOMIC DEVELOPMENT FOR AFRICA

There is abundant historical evidence that an important first step in economic development in many tropical and semi-tropical areas was land reclamation, which led to suppression of malaria and then to agricultural development.  Malaria transmission was suppressed by draining and filling of the swampy habitats of the mosquito larvae,  a process called larval source management.  Perhaps the most famous example of larval source management was the drainage of the feverish Pontine Marshes near Rome by Mussolini in the 1930s.  Reclamation of this ancient focus of malaria was successful, and the land was settled by thousands of farmers and their families.  They have made the area the most productive agricultural zone in Italy.  Similar successes have occurred across the globe in Malaysia, Puerto Rico and the Holy Land. 

Larval source management is more than the popular practice of larviciding with biological agents, but should be seen in its broader sense which includes drainage and filling of flooded depressions, flushing of streams, and salinity control in coastal areas.  These are simple methods, accomplished with local labor and resources.  

In contrast, tropical areas where malaria has been suppressed by the current chemically dependent strategy of WHO using mass drug administration, widespread spraying of houses with biocides and lavish distribution of treated bednets, have not led to economic development.  In a larger sense these ephemeral methods for malaria control increasingly drain the local and national economies, and also stress international donors.  Attempts by WHO to control malaria in Africa with these ephemeral methods exceed their own budgetary capacities, and have led to recent donor fatigue in the Global Fund.  This current situation is a repeat of the donor fatigue which caused the failure of the first WHO Global Eradication Program in the 1970s, also based on drugs and biocides.  Current global needs for malaria suppression are over $6 billion annually, while available resources are only a few billion.  This disparity is getting worse, not better.

It is fairly easy to see the positive agricultural and economic effects of mosquito suppression, after simple ditching and drainage convert the land from pestilential marshes into productive farms.  Farmers can then afford to improve their housing, including screening of doors and windows.  They can also afford the necessary health care and medicines needed to diagnose and treat the increasingly rare malaria infections.  Eventually these improvements in human ecology make permanent the suppression of malaria transmission in the agricultural communities.

Conversely, the economic drain increases from expensive drugs, bednets and biocides used in the WHO strategy, as new drugs and new biocides are needed to counter the inevitable chemical resistance in the mosquitoes and the malaria parasite.  This growing economic drain negatively affects individuals, ministries of health, WHO, and international donors alike. 

Not only is the WHO approach to malaria control expensive, it is dangerous because of its ephemeral nature, dependent on fickle cycles of donor support. The costly WHO strategy for ephemeral suppression of malaria is unsustainable by African governments and by the people who have the most at stake - the feverish farmers.  Intermittent failure of programs to suppress malaria due to donor fatigue can lead to fatal epidemics in populations which have lost their immunity during temporary suppression of malaria transmission.

Fortunately the positive and generally beneficial aspects of these links between land reclamation, malaria suppression and agricultural productivity can form a rational basis for economic development in many parts of Africa.  International agencies and donors should recognize the economic value in this positively reinforcing process, based on larval source management. 

William Jobin Director of Blue Nile Associates

Submitted by Guest (not verified) on

MPI, We knew about the presence of the Cuban company when I launched our larvicide on the 20th April in Accra - with careful statements that we used a complex solution of mineral products but excluded the use of our Preventine MLC over water intended for human consumption as we simply did not have proof of long term medical effects and offered a product liability insurance of $10Mill - only underwritten by Loyds  Underwriters if you can proof in both scientific and field trial terms that it does what it says on the tin. 

Let's put it this way : I would be able to deliver within 74$Million not only spray teams but also the aircraft that they intend to use. Oh, do they have long term clinical tests on the effects on the retina, respiratory system, melanona ? None that we can trace. 

Is Ghana buying Malaria health today for other ill health tomorrow and do they need to spend 74$Mill every 2 years as mosquitoes from Togo and the Ivory coast migrate back to Ghana ? This is a slap in the face of donors who provided other tools, nets, indoor sprays, paints - specially from the USA for a product from Cuba. 

An MOU is not a contract and general elections take place in December. 

You will note in the media that we invite the 'opposition' to a head to head trial over 20 known breeding sites, applying the protocol of the WHO scoop tests and measuring effects and results on Anopheles, Aides Aegypti and Culex at all 4 larvae development stages. 

Lets see where we get to. It is a pity that neither the WHO or buying foundations put producers through a due diligence procedure where ethics are tested, batch samples are drawn at random to check for quality in accordance with a Classification Society (without their certificate,no payment is made) to ISO standards and with a product liablity insurance that every product should have which can enter the food chain. 

MPI, I emigrated from Germany in 1968 to set up my first company in the UK but have always retained an office in Ascheberg, right next to Ploen - so, Gruesse an die alte Heimat. 

Peter

 

 

 

Prabhjot Singh's picture
Submitted by Prabhjot Singh on

Larval control using biological, physical and/or chemical methods was promoted in Central American countries in 2004-2008 by the DDT-GEF-PAHO project that focussed on vector control without the use of insecticides and especially DDT. That has left a lasting legacy in these countries where larval control is a part of the integrated vector control operations in the field, although a national strategy may be lacking in many areas.

One of the observations that can be made from these experiences is that it is costly to maintain a larval control program vis a vis IRS or bednet campaigns, offers indirect impact which is hard to measure and demonstrate but technically not challenging. The use of larval control for elimination argument might not hold as use of larval control in low and no endemic areas has led to decrease in the adult density but not translated into decrease in malaria. An investigation done for the same purpose (not published) revealed that at the start of a study in a couple of villages, 9 cases were positive for malaria in a blood survey but 2 years after using continuous and exclusive larval control the final prevalence was 5 cases in a population of over 3000 people. In the control area where no larval control was used, malaria prevalence decline was higher.

In all we have to be guarded in our approach of promoting a method where we are not sure about all the details.

Submitted by Christine Chundusu (not verified) on

WHO recently released a larval source management manual. Has anyone got a soft copy or has a link to the material online?

Andy Graham's picture
Submitted by Andy Graham on

I am here in Kara, Togo, and have lived a year in Ghana. The bio-larvicide project is something, and much better than nothing. One traveling or living in Ghana has to see that open drains are full of plastic bags. In many ways, I believe malaria infested countries are looking for the silver bullet that kills all, and it does not exist. As best I can understand from living in West Africa, the locals do not even see malaria or mosquitoes as a problem. We give them bed nets, because they refuse to buy them. Did you know, one aluminum water wash basin, they use to carry water cost more than a mosquito net in the market? I can buy a baby bed net for 1500 CFA, 3 dollars U.S. and this is the same a large bag of toilet paper.

Thank you, Andy Graham working on eradication of malaria in Kara, Togo West Africa. Togo Cell: +228 9294 0714 Benin Cell: +229 9559 6685 USA Skype: hobotraveler.com