Contributions AUGUST 28 - September 1, 2000
Discussion group on UPA, Health and Environment
The following messages were exchanged during the second week of session1
(August 28 - September 1)
1. From: Karen Lock (LSHTM)
Subjects: Malaria, heavy metals, health impact assessment
In last week's e-mails there were 2 major health issues raised related to UPA to which I would like to contribute some information and comments:
* Crop contamination due to water and waste re-use. (especially heavy metals)
Water pollution and waste re-use are recurring themes in discussions on the potential health risks of UPA. There has been much less focus on malaria as a health issue for UPA.
The final point I want to coment on is how does UPA balance the conflict between individual health benefits of UPA and negative health effects in the wider community? or even balance the neagtive versus the positive health effects of UPA?
Malaria is one of the most internationally important causes of death and disease: it occurs in 90 countries and kills up to 2.7 million people each year (many in Africa).
Malaria is caused by a parasite and transmitted to humans by Anopheles mosquitoes. There are several hundred Anopheles mosquito species, and it is important to realise that different mosquito species are responsible for spreading malaria in different regions of the world. In each locality there are usually only one or two important species, each having a unique combination of breeding site preferences and other behaviours (see attached table below for detail).
Most importantly for environmental managers is that the different species breed in a variety of water types, with each species preferring characteristic sites. In general the Anopheles mosquitoes breed in water that is:
. relatively clean,
. slow flowing or still,
. surrounded by vegetation.
Examples of different mosquito breeding sites worldwide
|Regions||Environmental links||Main mosquito vectors||Typical breeding sites|
|Africa||Malaria transmission varies widely across Africa between different regions and localties||A. gambiae (main)
|An. gambiae: shallow, sunlit and temporary bodies of surface water e.g.Pits and hoofprints
ponds, swamps and lakes
|Epidemic forest fringe malaria and urban malaria||An. stephensi (urban malaria)
wells and water tanks in urban areas
An. culifacies: streams, ditches
(47% in Brazil and 17% in Central america)
|Linked to agriculture in rain forest fringes and surface mining||An. darlingi
Urban agriculture has the potential to increase malaria in an area via poor environmental management. The types of breeding sites that might be created by urban agriculture include borrow sites, poorly drained water surfaces (due to poor irrigation or interfering with natural drainage) and uncovered water tanks. Malaria mosquitoes have adapted to urban environments in India, and to a lesser extent in the Middle East and Brazil. In India, An. stephensi mosquitoes have adapted to breeding in urban areas in uncovered water containers such as wells, overhead tanks and garden ponds.
In Africa, there are some signs that mosquitoes have adapted to urban breeding sites but the main concern is with the rural pockets of land to be found in urban areas, which can result from UPA (as pointed out by J.Lines). Many surveys in Africa have indicated a gradient in malaria mosquito densities, from the urban periphery where they are high to the centre where they are low. However the real urban picture is not as simple.
In a study in Brazzaville, the Congo, the main urban sites colonised by mosquitoes were small fertile valleys, watered by streams and where vegetable crops were planted. Each new area of human settlement and cultivation initially favoured the multiplication of breeding sites and high densities of malaria vectors. Later the canalisation of surface water, domestic pollution and increased human density tended to eliminate breeding sites (Trape et al 1992).
It has been suggested that African cities have relatively more open space, abandoned land and cultivation compared with cities in other endemic malaria areas (Lines et al 1994).
Therefore, it is likely that in African towns small agricultural plots are an important source of mosquito breeding sites,and hence responsible for increasing spread of malaria. It should be noted that this is not necessarily the case elsewhere in the world as it depends on the breeding site preferences of mosquito species.
As is also indicated by Jo Lines, in his contribution to the discussion this week, the type of crops grown also has an important effect on malaria vectors. Rice and other wet crops such as sweet potato have a high risk of malaria vector breeding, whereas fields with long grass and crops such as maize and banana are not areas which would naturally favour mosquito-breeding sites. This is mainly because the cultivation of the first mentioned crops leads to the accumulation of areas of shallow surface water.
UPA and environmental management of malaria
Obviously UPA programmes should be aware of these effects, and should work with malaria control programmes to control mosquito-breeding sites through good environmental management practices.
Environmental management takes time to work but produces long lasting effects and is a very cost-effective way of reducing the impact of malaria particularly in populated areas. However it requires knowledge of local mosquitoes and their breeding sites, and skills in drainage etc. This is not often available to UPA practitioners. There are also other forms of malaria control which are often used in conjunction with environmental management. This good needs multi-sectoral planning.
Questions: Malaria and UPA
b. UPA, Water, Waste reuse and Health
In contrast to the limited research on Malaria and UPA, there has been an extensive literature on the potential health effects of waste reuse and polluted water used for irrigation. The emails this week have touched on a few major issues which I hope will be expanded in future weeks. I want to share some comments.
In the Ghanaian study, P.Drechsel, found acceptable levels of heavy metals. Obviously heavy metal concentrations are very variable dependent on the upstream polluters of a water source. There are several examples of water with high levels of heavy metals or non-biological contamination in urban areas that would be considered a health risk. This is a particular issue in industrial areas, or where there is groundwater contamination for various reasons, for example the arsenic pollution of groundwater in Bangladesh.
UPA caneffect heavy metals and thus human health in 2 ways:
* Bioaccumulation in crops of heavy metals and toxic chemical content e.g crops cultivated on land polluted by industrial effluent. There is limited evidence for the extent of both acute and chronic health effects.
* The effects of UPA on groundwater (e.g. the pollution by agro-chemicals, or due to the extraction of large quantities of groundwater for irrigation which effects concentrations of elements in residual groundwater)
There have actually been few studies to explore these two issues of heavy metal contamination of irrigation water.
c. Comparing health impacts of different factors (negative and positive) in UPA: Is health impact assessment useful?
There is very little research to quantify the health impact of one health issue versus another in UPA. For example, malaria mosquitoes prefer clean water and polluted sources tends to reduce mosquito breeding. Obviously heavily polluted urban water usually has high concentration of faecal coliforms. So environmental health campaigns focused on sanitaion and clean water will obviously have health benefits especially for consumers of urban agricultural products, but also potential negative effects on malaria control.
UPA can also lead to unintended man-made environmental pollution: An interesting point was raised by J.Lines about the conflicts of interest in UPA, due to unintended effects of urban agriculture on the whole community. There has been no cost-benefit analysis that I know of that compares the health benefits of UPA against the potential negative environmental and health effects. The key issue is that the costs and benefits affect different groups. The economic and nutritional benefits are usually gained by the UPA practitioner. However the health costs may effect the wider community including water contamination, and the increase of mosquito breeding in towns. One practical method, which is attempting to tackle comparing the postive versus negative health issues, is health impact assessment. It is a process, which attempts to weigh up evidence on a range of health effects to assist decision-makers in the non-health sector (Lock BMJ May 20th, 2000)
Question: How does UPA balance the conflict between individual health benefits of UPA and negative health effects in the wider community? or balance the neagtive versus the positive health effects?
Karen Lock (Dr)
Visiting Research Fellow
European Centre on the Health of Societies in Transition
London School of Hygiene and Tropical Medicine
50 Bedford Square
London WC1B 3DP
Direct phone: +44 (0) 20 7299 4738
Fax: +44 (0) 20 7299 4741
2. From: Tanya Bowyer-Bower (SOAS)
Subject: environmental impacts of UPA
Apologies for joining your discussion late but I was away last week. I am disappointed that in spite of the title of this group discussion being "UPA Health and ENVIRONMENT", so far neither in discussion, nor in the introductory paper by Zeeuw and Lock, has any mention yet been made of any environmental impacts of UPA such as land degradation, flooding, impacts on ground-water recharge, soil erosion, sedimentation of water bodies, deforestation, habitat change, biodiversity, land-use potential, alternate amenity-use, etc. Is this / should this group also be involved in these issues?
Certainly in Harare, Zimbabwe, environmental impacts such as these are given as the excuse by the authorities for banning urban agriculture activities which otherwise are essential self-help strategies of the poor, essential for improving food security, particularly in times of drought or worsening economic climate as at present.
Research I carried out for an ODA (now DfID) project 1992-95 (in collaboration with the University of Zimbabwe) determined the extent to which some of these potential environmental impacts are real, but also ascertained the ease with which many of these potentially negative impacts could easily be minimised / contained by simple management techniques which should be integral to future developments in urban agriculture planning, management or control. Should we broaden out the discussion of this group to include a discussion of these environmental impacts and their policy implications? Would anybody like to hear more about our findings of environmental impacts of UA in Harare?
Lecturer, researcher and consultant,
Department of Geography,
School of Oriental and African Studies (SOAS),
University of London,
3. From: Tanya Bowyer-Bower (SOAS)
Subject: environmental impacts of UPA
Further to my introductory e-mail of yesterday, I would now like to report briefly to this group on findings of my research into the broader environmental impacts (e.g. impact on flooding, soil erosion, etc - for clarity I will refer to this here as impacts on the land-environment to distinguish it from impacts on health) of UPA in Harare, Zimbabwe.
It is my view that in some countries these are as important, and similarly important, as the health impacts - vis a vis them being used as a reason for reluctance by planners (and other residents) to fully accommodate UPA into the land-use development plans of a city (e.g. as in Harare). I would be grateful for feedback as to whether anyone else has found this so for any other part of the world as well.
First: It appears to me that much of the mention in passing on land-environmental impacts is based on little more than hear-say and presumption, rather than field research.
Secondly: there is very little mention of land-environmental impacts of UPA in the UPA literature. I would be very grateful to hear from anyone who knows of any / can correct me on this.
Why a determination of land-environmental impacts of UA was crucial to any understanding of UPA in Harare:
An outline of the findings of our research into the impact of UA on the land-environment. 75% of the land area cultivated was for maize (the main subsistence crop). A further 15% was sweet potatoes (the remainder mostly green beans, tomatoes, and a variety of others). All cultivation was using direct rainfall input (plus storm runoff) only as its water supply. A variety of techniques were used to compare land infiltration rates and land erosion rates on each soil type under each crop type in Harare by comparing measures of these factors for non-cultivated vacant city land and comparing these with the same measures for cultivated city land.
In summary, our research determined that UA decreased land infiltration by 18-50% (depending upon soil type and cultivation technique used). This meant that groundwater recharge in the vicinity of the city was being affected. It was also determined that the UA was increasing land surface runoff by as much as 7 times (depending upon soil type and cultivation technique used). This meant, for example, that there were instances of storm sewers being unable to cope with the inundation of runoff during rainfall events and thus flooding resulting in areas where UA was taking place which would not have occurred if the vacant land had been left uncultivated, etc.
It also increased the sediment load of surface runoff very significantly (by 100% - 2000% depending upon soil type and cultivation technique used). Where the runoff drained into a water course or water body (such as a stream, storm sewer, or reservoir), this water course or water body thus became more liable to siltation, than if the UA had not been taking place.
Obviously most urban planners would consider that the above actual and potential land-environmental effects need to be taken into consideration when planning for UPA in a city. With regard to this, our research determined further, however, that simple indigenous water and soil conservation measures (such as the use of ridges and furrows, contour bunding, avoiding cultivating the steepest slopes, reducing cultivation plot length, etc), if they had been implemented, could have mitigated much of even the worst of these effects. In Harare, however, with the cultivation being illegal, there was no technical support or guidance available for the cultivators, and the uncertainties of any future meant little incentive by the farmers to invest more labour than was necessary for a quick harvest. This information is crucial in suggesting what type of action the planners need to incorporate into their plans for accommodating UPA in a city - in terms of what type of land should best be targeted, what type of cultivation practices should best be targeted, the advantages of a defined tenure over the land for the cultivators, the advantages of agricultural extension services being available to support the cultivators, etc., to optimise the positive contribution UPA can make to any city.
I would be very grateful for feedback on my thoughts in this contribution.
Lecturer, researcher and consultant,
Department of Geography,
School of Oriental and African Studies (SOAS),
University of London,
4. From: Stefan Dongus (University of Freiburg)
Subject: evidence malaria?
Dear participants of the discussion on UPA, health and the urban environment,
Although I am not directly involved in the topic of malaria, I got the impression that the ongoing discussion is accepting the thesis that urban agriculture is a reason for the increase of malaria in affected regions. I agree that this is probably true for the production of wet rice. However, there seems to be a tendency to discuss this topic without having enough evidence that this might really be the case in general.
Therefore I would like to ask all participants for research results which could give a clearer picture of the situation.
MY QUESTION IS: Is there any scientific evidence that urban agriculture increases malaria in cities or is this just a fairytale brought up by former colonial powers?
University of Freiburg, Germany
Institute of Physical Geography
Section on Applied Physiography of the Tropics and Subtropics
5. From: Jo Lines (LSHTM)
Subject: reaction to Dongus malaria
Stephen Dongus thinks that participants have accepted the thesis that "urban agriculture is a reason for the increase of malaria in affected regions". He goes on to ask whether this thesis is founded on clear evidence, and suggests that it might be "just a fairytale brought up by former colonial powers?"
I suppose he must be referring to me - at least, I was the one who originally brought up the issue in this listserv.
First, the facts.
(a) I was talking specifically about Africa (where 90% of the world's malaria occurs).
(b) In African cities, urban malaria is (and always has been) a big problem.
(c) Urban agriculture is by far the most important source of malaria vectors in African cities.
Evidence in support of these assertions is provided by following papers (among many many others).
Dossou-Yovo-J; Doannio-JM; Diarrassouba-S; Chauvancy-G. The impact of rice fields on malaria transmission in the city of Bouake, Cote d'Ivoire. Bull-Soc-Pathol-Exot. 1998; 91(4): 327-33
Trape-JF; Zoulani-A . Malaria and urbanization in central Africa: the example of Brazzaville. Part III: Relationships between urbanization and the intensity of malaria transmission. Trans-R-Soc-Trop-Med-Hyg. 1987; 81 Suppl 2: 19-25
Service MW. 1989. Urbanisation: a hot-bed of vector-borne diseases. In: Demography and vector-borne diseases (MW Service ed.) 402pp. Boca Raton Florida: CRC Press.
Robert V, Gazin P, Ouedraogo V, and Carnevale P. 1986. Le paludisme urbain à Bobo-Dioulasso. I. Étude entomologique de la transmission. Cahiers d'ORSTOM série Entomologie Médicale et Parasitologie 24: 121-128.
Onapa AW and Pape T. 1993. Breakdown of anti-mosquito measures in Kampala City, Uganda. Society of Vector Ecology Newsletter 24 (No 1.) 4-6.
Bang YH, Mrope FM, and Sabuni IB. 1977. Changes in mosquito populations with urbanisation in Tanzania. East African Medical Journal 54: 403-410
Several of these studies confirm the general importance of urban cultivation sites as Anopheles breeding sites. But my experience suggests that we can go further, and say that urban cultivation sites are BY FAR THE MOST IMPORTANT SOURCE OF MALARIA VECTORS IN MOST AFRICAN TOWNS. This is a rather strong generalisation, but it is based on quite a bit of experience gained from many happy muddy sweaty days paddling in the sunshine - mostly in Tanzania, but also in Sierra Leone, Gambia and Cote D'Ivoire. Is there anyone out there who knows what an Anopheles larva looks like who would care to comment?
London School of Hygiene & Tropical Medicine
P.S. By the way, I'd just like to ask Stephen what colonial purpose he thinks this story might serve?
6. From: Eric Thijs (ITM)
Dear participants of the discussion on UPA, health and the urban environment,
In the same order as the question brought up by Stefan Dongus on the increase of malaria in cities as a consequence of UPA, namely if there was enough scientific information available to state it, I think it is important to enlarge the discussion on other human diseases in the cities.
As veterinarian and zootechnian, I'am momently in charge of a policy supporting research project for the Belgian Co-operation (DGIC) aiming to make a review on the issues related to urban and peri-urban livestock production in African cities.
As far as the diseases transmitted by animals and the intoxications related to the consumption of animal products (likeingestion of heavy metals or pesticides through milk) are concerned and as far as I had access to literature, I fully agree with the statement on page two of the discussion paper of Henk de Zeeuw that (scientific stated) information on the actual health impact of UPA is scanty.
Moreover, I think also that loss of memory on the former situation in developed countries (for example, during second world war and even in the sixties there were still a few milk cows intra-muros in Antwerp, Belgium) and a authoritarian view on a "modern hygienic" city model implemented in developing countries brought that people believe fully that the dangers of such health problems are more important in urban than in rural environment.
It should be interesting to implement more scientific comparative surveys on diseases issues to obtain a more accurate view on the subject. Have any of the participants such information on zoonoses and intoxications brought by consumption of animal products?
Institute of Tropical Medecine
B- 2000 Antwerpen (Belgium)
tel 32 3 247 63 92
fax 32 3 247 62 68
e-mail : email@example.com
7. From: Horacio Chicata Blancas (IMAGEN Educativa)
Me llamo Horacio Chicata Blancas, trabajo en la ONG Peruana IMAGEN Educativa, uno de cuyos programas iniciado en 1992 es el referente a la "Promocion de la Agricultura Urbana y Peri-Urbana" en base a las tecnicas hidroponicas. Sobre el tema quiero aportar mi experiencia al respecto.
Dentro de dicho programa, he dirigido varios proyectos de AUP, tanto en zonas de medio y alto desarrollo urbano como en zonas perifericas de alta pobreza critica y bajo desarrollo urbano de Lima Metropolitana. En unos casos estos proyectos han sido de "huertos familiares" (orientados al auto consumo) y en otros de "parcelas familiares" (orientados al mercado) . En ambos casos, el monitoreo y evaluacion correspondientes, no han registrado impactos negativos en la salud y medio ambiente, ni de las familias "hidrocultoras" ni mucho menos en su entorno vecinal.
Contrariamente: Primero, han contribuido a mejorar la salud fisica de sus titulares, al proporcionales en el caso de los huertos, una mejor dieta alimenticia al disponer para su consumo de productos horticolas ricos en minerales vitaminas y fibras. Tambien , en lo que respecta a la salud metal y animica, ha contribuido a experimentar un medio de distension y relajamiento e integracion familiar. Segundo, - sobre todo en el caso de las parcelas familiares- sanear los espacios disponibles que en su casi totalidad presentaban condiciones de basurales, a trasformar pendientes deslizables en terrazas estabilizadas, en oxigenar la polvorienta aridez de cerro o arenal y crear un vergel como paisaje domestico para solaz de sus moradores. Tercero, introducir en el mercado metropolitano, productos horticolas de primera calidad, libres de contaminacion patogena.
La inexistencia de un impacto negativo en la salud y el medio ambiente, ha sido posible porque las tecnologias hidroponicas, son limpias y sanas al usar agua potable o tratada, al posibilitar un significativo control natural en la eliminacion de plagas y enfermedades y una adecuada proteccion fisica frente a las condiciones medio ambientales adversas (vientos, temperatura, polvo, lluvias etc.), al monitorearse el aseo del huerto o parcela y la acepcia personal en su manejo vegetativo, de cosecha y post-cosecha, incluyendo su envasado para su distribucion en el mercado.
Finalmente, sugiero que en las zonas donde se hace AUP, las agencias de desarrollo privadas, los gobiernos locales y nacionales, como parte de su politica de saneamiento urbano y peri urbano, promuevan la descontaminacion de las aguas servidas utilizadas en regadio de cultivos, promuevan la hidroponia o semi hidroponia como alternativa tecnologica en la AUP.
Soc. Horacio Chicata Blancas
IMAGEN Educativa ONG
8. From: Hermilio Navarro Garza (Colegio de Postgraduados en Ciencias Agricolas)
Subject: Reuse of wastewater
Dear Participants, sorry for writing in Spanish, I do not manage the English language
Chers participants, dommage, mon participation dans la langue espagnol, puisque je ne parle pas anglais.
Los ultimos 4 anos, en un equipo hemos tenido la posiblidad de trabajar en el campo peri-urbano mexicano, sobre el tema de la agricultura y los sistemas de gestion de los recursos. La zona metropolitana de la ciudad de Mexico aumento sensiblemente tres veces su poblacion los ultimos 30 anos, asi como las necesidades de recursos particularmente agua y tierra. En los mismos terminos ha habido el incremento en la produccion de desechos liquidos y solidos.
Las condiciones economicas fragiles de varios tipos de productores agricolas de las zonas peri-urbanas, han conllevado sus intereses hacia las aguas negras producidas en la zona metropolitana (> 40 m3 / seg), pero tambien a nivel micro se ha observado el interes creciente (incluso clandestina) en la utilizacion de las aguas negras de cada comunidad y localidad en que se producen este tipo de aguas negras. La existencia de una ley que prohibe la utilizacion de las aguas negras sin tratamiento para la produccion de cierto tipo de productos horticolas existe, pero sobretodo las necesidades de los productores se imponen, con cierta facilidad debido a las dificultades para vigilar la aplicacion real de los reglamentos
Las aguas negras de la ciudad de Mexico se utilizan para la produccion agricola, tanto en el trayecto de un corredor que conduce por el norte del valle de Mexico y se utilizan, en un Distrito de Riego denominado comunmente Valle de Mezquital (03 y 100), situado sensiblemente a 120 kilomentros. Las aguas negras "son en su mayoria sin tratamiento", sobre 1,700 millones de m3/ano, se estiman 1,350 como desechos urbanos y 450 que tienen como origen la lluvia. En el Distrito de riego se irrigan mas de 70,000 mil ha. Los principales municipios que integran a los distritos 03 y 100 son 24, unos de ellos son contiguos geograficamente. Las aguas negras sin tratamiento son utilizadas directamente en la produccion de alfalfa, maiz forrajero e incluso hortalizas.
Un estudio de la Universidad Nal. Autonoma de Mexico estima un porcentaje mas importante de enfermedades gastro-intestinales entre los habitantes de la region, en comparacion con habitantes de zonas contiguas. El Instituto Mexicano de Tecnologia del Agua publico una referencia del contenido de parasitos: 160.8 huevos de helminthos, asi como de coliformes fecales 3*10 a la 8/100 ml, valores arriba de los permisibles. La participacion pretende relacionar la ciudad y el campo a traves de dicha utilizacion y los efectos de la relacion. Cabe precisar que los productores son fuertemente interesados en el uso de tales aguas.
Una caracterizacion agronomica que realizamos durante 1996, la evaluacion de los impactos, Navarro, Flores y Perez (1997) de un proyecto en colaboracion con la Comision Nal. del Agua, nos muestra como promedio para un analisis de 11 muestras durante un periodo de 4 meses de intervalo, lo siguiente, solo senalaremos algunos parametros, en su caso podriamos enviar el estudio completo: Fosforo total: 10. 4 en mg/l Potasio total: 49.2 en mg/l pH: 7.8 Conductividad electrica: 2.19 Salinidad total: 16.7 Plomo: 0.065 en mg/l Cadmio: 0.011 en mg/l Cromo: 0.014 en mg/l Estos analisis fueron realizados en el canal de salida hacia el norte de la ciudad de Mexico.
Los efectos sobre el medio ambiente son implicitos en los contenidos que se muestran sobre algunos parametros, tanto por la acumulacion en el suelo, su incorporacion en los ciclos a traves de la produccion agricola, de la cual una parte sustantiva se orienta a los centros de abasto de la ciudad de Mexico, por lo cual hemos denominado que existe una "interaccion tipo boumerang". Algunos estudios apuntan a identificar contaminacion en pozos que abastecen de agua potable a numerosos poblados.
En resumen, la agricultura peri-urbana es una practica socio-economica muy importante para varios sectores de la poblacion urbana, en jugar la funcion-vector de una amplificacion de los riesgos contra la salud, en los paises donde las dificultades economicas para el tratamiento de las aguas negras es limitado, asi como la vigilancia y control de la inocuidad de los productos alimentarios que son producidos con la misma.
Atentos saludos participantes de la conferencia.
Dr. Hermilio Navarro Garza
Colegio de Postgraduados en Ciencias Agricolas. Mexico
Estudios del Desarrollo Rural
Area Campesinos, Politica e Innovacion
Tel. (52-5)95.202.00 ext. 1853
9. From: Pay Drechsel
Subject: malaria economic impact
Although little evidence is reported so far we found the malaria discussion very interesting. Currently we are working on a FAO supported study on the economic assessment of the environmental impact of UPA in our area (Kumasi). Hard data on an increased malaria risk could be an important contribution (you might know that some data on the adaptation of Anopheles to urban conditions comes from Ghana; reference below). So we contacted the Kumasi Centre for Collaborative Research in Tropical Medicine and agreed on a related study, probably carried out through students of the local university. We are looking forward to the results and will share them with you!
Best regards and thanks for this stimulation.
International Board for Soil Research and Management (IBSRAM)
Africa Office c/o KN-UST, Kumasi, Ghana
Tel / Fax: +233-(0)51-60206,
CHINERY, W.A. 1984. Effects of ecological changes on malaria vectors Anopheles funestus and the Anopheles gambiae complex of mosquitoes in Accra, Ghana. Journal of Tropical Medicine and Hygiene 87:75-81
10. From: Leo van den Berg (ALTERRA)
Subject: malaria fish - rice
Dear fellow participants,
Going through the arguments on malaria and UPA so far I feel a few things ought to be said:
1. urban rice cultivation seems quite convincingly a factor in Africa, but it it isn't in S.E.Asian cities. A possible reason is, that down there paddy cultivation is combined with fish and ducks. So why not do the same in Africa?
2. 'musquito breeding' has often been put forward as a major reason for slashing maize and banana in cities in Central Africa (next to illigality and maizefields acting as hiding place for criminals), but I have been assured by specialists and feel supported by Jo Lines (22/8) and Karen Lock (29/8), that maize, banana and tall grass themselves don't provide breeding niches for the Anopheles mosquito. In other words, it is the farming method rather than the crop that affects the incidence of malaria.
3. It is my contention that in cities without paddyfields (eg in Central Africa) it is more likely to find breeding facilities for malaria mosquitoes in abandoned, unmanaged sites than in small, agricultural plots. Therefore, the best way to get rid of them is either by developing the land (building) or by encouraging farmers and gardeners to use them intensively while ensuring there are NO bits of clean, shallow, stagnant water. If you need such waterbodies as part of your farming system, make sure they are full of fish and ducks!
Leo van den Berg
11. From: Jo Lines (LSHTM)
Subject: Malaria (reaction to Van den Berg)
My comments on Leo van den Berg's points....
Van den Berg: "urban rice cultivation seems quite convincingly a factor in Africa, but it it isn't in S.E.Asian cities. A possible reason is, that down there paddy cultivation is combined with fish and ducks. So why not do the same in Africa?"
Well, the fish might indeed help (but probably not the ducks). But the main reason why urban rice cultivation is an issue for malaria in cities in Africa but not SE ASia is that the two continents have different malaria vector Anopheles species. In Africa, the main vector is An. gambiae, which breeds in all kinds of small temporary pools - typically sunlit, shallow, muddy, and ephemeral. So the "architypal" breeding site for Anopheles gambiae is a muddy hoofprint. It does not have or need any special adaptation to urban conditions, but is an extremely efficient vector, so just a few small breeding sites are enough to maintain transmission. Whereas in mainland SE Asia, the most important vectors are An minimus and An dirus, and neither of these is a ricefield breeder. There are OTHER Anopheles species that ARE abundant in SE- Asian ricefields, but these species are not good vectors, mainly because they are short-lived as adults, and becuase they don't bite man very much.
Incidentally, and while we are on the topic, there are only two Anopheles species that have made major adaptations to life in urban conditions, and they are An claviger in Syria, and An stephensi in India/Pakistan. In both cases they have adapted to breeding in man-made containers (You do occasionally find other species in containers, including sometimes An gambiae, but this is very much the exception rather than the rule). This adaptation is no longer important in the case of claviger in Syria, as malaria is no longer a problem there. But it is of crucial importance in India. India is the only place on the planet where malaria transmission is often more intense in town than in the surrounding countryside, and this is entirely attributable to this adaptation of An stephensi.
And finally - again as far as I know - the other place where urban malaria is a big problem (apart from Africa and India) is Brazil, where malaria transmitted by An darlingi is a problem in several of the new and rapidly growing cities in the Amazon basin. I believe that the reason for this problem is precisely this newness - that these cities are growing so fast that the urban periphery is a constant (but shifting) mosaic of new buildings amidst land that is essentially still rural. In other words, the streams and other water bodies have yet had time to be enclosed in concrete or to become full of human organic rubbish. When eventually this concreting and pollution occurs, the malaria will disappear, or rather it will move on to the new and still expanding edge of the city. Anyway, if I'm right about all this, then I would also expect urban wet agriculture to be associated with malaria in THESE cities. Does anyone know if that's correct?
Van den Berg: " 'Musquito breeding' has often been put forward as a major reason for slashing maize and banana in cities in Central Africa (next to illigality and maizefields acting as hiding place for criminals), but I have been assured by specialists and feel supported by Jo Lines (22/8) and Karen Lock (29/8), that maize, banana and tall grass themselves don't provide breeding niches for the Anopheles mosquito. In other words, it is the farming method rather than the crop that affects the incidence of malaria."
Van den Berg: " It is my contention that in cities without paddyfields (eg in Central Africa) it is more likely to find breeding facilities for malaria mosquitoes in abandoned, unmanaged sites than in small, agricultural plots. Therefore, the best way to get rid of them is either by developing the land (building) or by encouraging farmers and gardeners to use them intensively while ensuring there are NO bits of clean, shallow, stagnant water. If you need such waterbodies as part of your farming system, make sure they are full of fish and ducks!"
Weeeelll... yes & no. You are right about abandoned unmanaged sites being potential breeding sites, but as I hinted before, it is NOT only rice that is important. Sweet-potato and yams are also very important. Sweet potato, in my experience, is normally grown in wet soil piled into ridges, or in shallow-flooded plots. Yam is grown in small footprint-sized depressions. Both crops like to have their roots constantly flooded, or at least to live in wet and sometimes waterlogged soil. Cassava, on the other hand, is only occasionally a problem. This is when it is grown in cultivation ridges in wet clay soil. But such plots are not often used for cassava, which will tolerate drier conditions and sandier poorer soil than these other crops. Obviously when cassava is grown in dry sandy soil, there is usually no standing water and no mosquitoes. Maize-growing is hardly ever a problem. For maize you don't ridge the soil, and you try to till the plot so that even if it rains for a week, the maize will not have sit for days with its feet in water.
And disturbing the soil.... well again, yes, but remember that marshy reedy patches (waterlogged in the rainy season, possibily dry and brown in the dry), don't breed too many Anopheles until they are disturbed. In undisturbed marshes with tall reeds (including papyrus), the water is black with tannins. Cows and dogs will not drink this water. You will see it trickling slowly through the reeds full of floculated black or dark brown particles of organic matter, which I suppose is undergoing anaerobic degradation. But when people dig up or burn the reeds, and turn over the soil for cultivation, then the water starts to be open to the sun, becomes more aerated, loses the black particles and the smell of undrinkability, and becomes suitable for An gambiae. It may become completely opaque with mineral silt - as brown and thick as beef&tomato soup - but the cows and dogs will now be happy to drink it, and it will also be fine for the mosquitoes.
I once saw this happen in Zanzibar town. The main river / stream through the city drained into the sea via a large flat area beside a big old tourist hotel. This hotel had been constructed with the aim of making a boating lake for the tourists, but the stream was very silty, and the area was never dredged, so it rapidly filled up with mud. When I arrived there in the early 1980s, the entire several-hectares of surface was completely covered with very tall reeds 1.5 - 2 metres tall. We looked for Anopheles larvae and found none - in fact very little insect life at all. Several years later, there was a very dry period, and some of the reeds dried out. Someone took the opportunity and burned off a patch of reeds, cleared away the stubble and planted some rice. It did very well, and the next year a large proportion of the whole area had been put to rice. And yes, sure enough, this was swiftly followed by a sudden mini-epidemic of malaria in the neighbouring part of the old town, which was especially conspicuous because it was an area that had for many years been more or less free of transmission.
Jo Lines, LHSTM
12. From: Oleg Moldakov (St-Petersburg Downtown Gardening Club)
Subject: re-use of urban wastes; physical problems of older farmers
The text of the following contribution was slightly edited by me to make it more easy to read and to prevent misunderstandings. Henk de Zeeuw, moderator
My name is Oleg Moldakov. I am a Researcher on Urban Agriculture (soil science and agro chemistry are my background). My contribution is based on research I have been implementing in Russia in the context of the project Soil and Water management in agricultural Production in Urban Areas in CEE and NIS countries (SWAPUA).
1. Which are the health risks associated with UPA that in your experience - cause major negative impacts on the urban population?
The application of waste water for irrigation and the use of municipal sludge as fertilizer has a limited effect on the agricultural area or even not at all. The composts prepared on the plots is stored a long time (12 months) which is enough to destroy disease borne bacteria. Townspeople, engaged in an agriculture, and especially the many middle-aged and pensioners among them, frequently complain of a pain in hands and back. On Saturday and Sunday they work very hard with very simple agricultural tools or by hands and almost do not apply pesticides and equipment.
During harvest and big sale of production (August - September) the sanitary inspectors have no time to check up the quality of the products sold by all salesmen and consumer don't know whether these products was grown in a safe place or close to a highway or industry. Therefore there is a danger of occurrence of contamination of milk products, mushrooms, vegetables, etcetera in the food market during these periods.
2. What positive impacts of UPA on health and environment did you observe? In your opinion, do the positive health impacts outweigh the negative impacts? How could we measure or evaluate this?
The positive impact is a supply of fresh and guanranteed uncontaminated production from the own plot or from a plot of the relatives. A positive environmental impact is the re-use of kitchen wastes in the compost heaps on suburban plots. In St Petersburg the health risks associated with UPA are hardly discussed and controlled nowadays. Of course, there are some sanitary problems and activities like the composting of household wastes (vermiculture) in cellars of multi-storey houses with roof top gardens, is only permited by the veterinary service up to the first complaint from the neighbours.Consumers have a traditional mistrust to the vegetables which have been grown in the urban environment due to massive attention of the mass media to the potential risk of heavy metal contamnitaion. The positive results of tests of the quality of urban-grown products do not effect consumers mistrust.
St-Petersburg Downtown Gardening Club