14 June 1996
Intergovernmental Forum on Chemical Safety
IFCS EXPERTS MEETING ON POPs
17-19 June 1996 Manila, Philippines
Prepared by: MEXICO
MINISTRY OF HEALTH Mexico
Click to download: Experience in Reducing Use of DDT, Mexico Ministry of Health, June 1996, 21K/14K, English
Malaria in Mexico has been since tbe past a mayor public health problem that challenged the incorporation of wide areas of the territory to the national development process. In the 40's and 50's it was one of the main causes of death with an annual average of 24 thousand deaths and 2.4 millions affected individuals.
At the end of the 40's selective application of dwelling DDT sprays started in some urban and rural areas, with results that supported the international cradication proposal presented by Mexico in 1955. Even though the Malaria National eradication Campaign did not accomplished all its objectives, the transmission of P. falciparum was interrupted, deaths were eliminated and efficient technical and operative models were established allowing the introduction of others public health programs in rural localities of difficult geographical and cultural access.
The introduction of DDT in Mexico followed the pattern showed by many countries. During the early 50's DDT was introduced in Mexico and extensive agricultural use followed. Major agricultural areas used an average of 1000 tons per year. The use in the Laguna region (Central Mexico) was among the highest in the world
The evolution of malaria in relation to dwelling spray represents the intensity that has been directed to the program. The use of DDT and other newly developed organochlorine pesticides grew during the 1960's. The success of DDT spraying in the household to reduce malaria transmission became strategic. In 1968, DDT production was bought and control by the government, It was also the time in which organochlorine production peaked in Mexico with more than 80,000 tons, produccd annually. The controlled production of DDT resulted in increased availability and low cost of the product for malaria control and agricultural products. However, production was maintained in about 25,000 tons per year. During, the early 1970's the USFDA started rejecting commodities due to high residue levels especially DDT.
The growing concern on DDT persistence had a significant impact in agricultural practices in Mexico. The northern area of the country, more developed and highly dependant in exports changed to newer and more acutely toxic pesticides in order to comply with FDA/EPA regulations. The southern area of Mexico, largely devoted to local production continued the use of organochloriine pesticides. The use of DDT started to decline in agricultural practices.
In 1987 the Ministries of Agriculture, Commerce, Urban Development (currently Environment) and Health joined efforts to control the use of pesticides, fertilizers and toxic substances, This commission (CICOPLAFEST) in 1990 banned the use in Mexico of six organachlorine pesticides and DDT use was severely restricted. Organochlorine production started a steady decline and DDT was limited to sanitary campaigns needs (about 3,000 tons per year).
In the 80's, the economic crisis and changes in program activities, a significant deterioration was observed leading to the increase of malaria tranmission. In 1985, 133 700 cases were registered in 14 thousand localities. From 1985 - 1989, the annual average was 117 thousand cases.
The malaria control program was strenghten with human material and financial resources. The technical strategy was reoriented to the simultaneous elimination of the plasmodium parasites in humans and anopheline vectors. In 1989, among 21 countries of tbc American Region, with active programs against malaria, Mexico notified 9% of the Cases, second only to Brazil. In 1994, after the reinforcement of the intervention measures, the number of cases decreased, representing 1% of those reporting in the Americas.
In 1991, FERTIMEX, - the national producer of DDT - was again privatized and further restriction in organochlorine production were implemented. Changes in malaria campaigns use. has reduced DDT use and production.
In 1996, CICOPLAFEST has started a new role. Pesticide control through the life-cycle approach has been implemented and new governmental areas (Transport and Labor) have been included to intergrate every area of the life-cycle. Organochlorine pesticides have been considered priorities due to persistence and bioaccumulation.
The program is geographically orientes since 60% of the, territory from sea level to 1 800 meters of altitude present favorable conditions for malaria transmission. This include the Pacific Ocean and Gulf of Mexico slopes, the Yucatan Peninsula and interior basins of the high plateau. This area includes a population of close to 45 million.
The strategy focused on entomological and epidemiological stratification of the malarial areas. The study revealed that 70% of the cases were located in close to a thousand focal points of persistence, distributed in five states with high receptivity and vulnerability due to national and international migration.
According to these results program activities were divided in two areas:
1. For non priority states: Intensification of epidemiologic surveillance, application of selective dwelling DDT sprays, and radical treatment of diagnosed cases.
2. For priority states: Application of the Intensified Actions Plan:
2.1 Selection and training of personnel on epidemiological, therapeutical and entomological aspects, pesticides and spraying equipment, considering personnel skills and aptitudes. 2 422 workers have been trained through 90 short courses. In addition, remaining personnel is trained twice a year.
2.2 Promote active community participation and to create a health selfcare culture that includes demand of health services to public medical units, and notification centers headed by voluntary members of rural communities.
2.3 Basic sanitation aimed to reduce vector contact through: bush clearing; cleaning of water bodies; canalization of collected water and general improvement of housing conditions: promotion of bed windows and door screens.
Entomological Studies. 26 species of Anopheles mosquitos have been identified in Mexico. The main malaria vectors are: A. pseudopunctipennis and A. albimanus; the first is widely distributed in malarial areas in the country and is the first transmitter in the Pacific slopes, it is found from the coast level to 2000 meters of altitude; the second is found from sea level to 800 meters and is the main transmitter in coastal areas of the Gulf of Mexico, the Yucatan Peninsula and Chiapas forest.
Entomological surveillance include: a) hydroentomological monitoring of water bodies in the anophelinic areas; b) capture of adult mosquitos around dwellings during the period of hematophagous activity, includes animal lodgings and natural shelters; c) determination of parity; and d) insecticide resistance testing for each insecticide used in the program following WHO recommended methodologies and equipment.
International trade and partners.- DDT international commerce has been limited in Mexico. For the period 1990 to 1996. DDT imports amounts 27 tons, all of them coming from the U.S. On the other hand, exports have had significant amounts and partners, from 1990 to 1996 exports have focused in four countries (U.S.A., Colombia, Guatemala and Panama). Two other countries have expressed interest in Mexican DDT (Venezuela and Brazil).
Registered exports range from a high of more than 500 tons in 1990 to a low in 1993 when only one ton was exported. However, since 1993, DDT exports have increased (3 tons in 1994 and 21 in 1995).
DDT - current legal status.- The organochlorine pesticide DDT use is severely restricted and has been registered in Mexico only for antimalaria control programs. Two registries are available, technical grade (100% pure) for formulation and 75% for household application. Commercial product is labelled "only for public health campaigns use" and it is not available for pest control management or rural use.
This pesticide is classified as a persitent compound with low acute toxicity for humans and high for animals. Chronic effects are a serious consideration due to its possible association with breast canccr and reproductive considerations.
Production is legally limited to public health needs and for international trade. Imports are banned due to high levels of contaminants in DDT available from other countries (China and India). Exports are regulated by the CICOPLAFEST and every shipment is registered.
Promotion of Notification.- It's considered a crucial aspect in the epidemiological surveillance of malaria; in Mexico around 30 thousand notification centers have been established and headed by voluntiers, they produce each year 11% of the two million blood samples that are examined and notify around 43% of the total cases.
Study of Feverish Persons at Home.- An active domiciliary surveillance of feverish persons is developed by specific personnel involved in the program and voluntary notifiers, with a monthly periodicity and giving priority to localities considered as persistent transmission foci.
Microscopic Examinations of Blood Samples and Antimalarial Treatment of the Cases.- In 140 local laboratories located through the malarial areas, each year an average of two million blood samples are examined in order to maintain the epidemiological surveillance. The cases are controlled by name in order to follow its treatment efficacy, which include Cloroquine-Primaqine in schemes of five consecutive days.
Actions Against Parasites in Human Massive Medical Treatment in Foci of Persistence.- Focuses in the elimination of plasmodium parasites in blood and in liver.
Actions Against Parasites in Mosquito Vectors.- Entomological surveillance defines persistent foci, those sites and hours of the day and night where vectors concentrate to feed and rest after feeding, in order to apply selectively ULV imagocide fogging with Malathion.
Antilarval Activities.- As a relevant activity of sanitary improvement, breeding sites are eliminated through drainage or replenishment, promoting community participation; when not feasible, the larvicide Temophos is selectively applied simultaneous to the fogging in breeding sites located in areas with active transmission of the disease.
Statistics.- The program gathers information by colecting weekly epidemiological data by locality, country and state and monthly operative data of each operative units and levels of structure.
Supervision.- It's performed to correct deviations and omissions by training on service, improving skills and attitude of the personnel.
Evaluation.- It's preformed monthly on each one of the levels, (brigade, sector, sanitary, jurisdiction, state and national) comparing proposed goals with those obtained mainly in each one of the field activities.
Operative Applied Assays.- Field and laboratory Research has been conducted aiming to eliminate the plasmodium parasites including house spraying with Bendiocarb and Fenitrothion which were tested for four years.
DDT spraying.- Household spraying continues to be a successful part of the program. The number of households sprayed has diminished as persistant focci has been eliminated. Currently less than 600,000 sprays are required nationwide.
Malaria was a major public health consideration in Mexico from 1950 to 1989. More than 60% of the territory is endemic for this disease, that was reflected in high prevalence and mortality. The use of pesticides has diminished the number of cases from more than 120,000 to less than 5,000. Malaria mortality has decline sharply, it was one of the top ten causes of death in Mexico during then 1950's and since 1982 there have been no deaths. These results show that an integrated approach is highly effective to control malaria and dengue vectors.
Public health programs involves a large number of workers, with more than 10% of the Health Ministry workforce is currently involved in malaria control. More than 7,000 workers have been trained and equiped for household DDT spraying. The investment is considerable, with the exception of the pesticide, substitutes are 7 to 8 times more expensive. Low acute toxicity for humans have also promote the use of DDT.
DDT substitutes are available; however, the approach taken has been innefective. It has been stated that DDT should be substituted with another pesticide, currently a more intergrated approach is requires.
In 1995, Mexico decided that an integrated pest management for malaria could substitute the heavy dependance on pesticides. Improved sanitation, surveillance and minimum use of pesticides to control mosquitos and larvas are being considered as key elements. When the Commission for Environmental Cooperation of North America (CEC) decide on limiting human exposure to toxic and persistant substances, DDT became one of the four initial targets.
The initial target on DDT is the reduction of human and environmental exposure through a gradual and organized approach that will focus on: