In 1999, there were 818 million people living in the Region of the Americas. Of these, 299 million (36.5%) were living in areas where ecological conditions were propitious for the transmission of malaria. Of the 35 countries and territories that are members of PAHO/WHO, 21 report areas with active malaria transmission.
All these countries (Argentina, Belize, Bolivia, Brazil, Colombia, Costa Rica, Dominican Republic, Ecuador, El Salvador, French Guiana, Guatemala, Guyana, Haiti, Honduras, Mexico, Nicaragua, Panama, Paraguay, Peru, Suriname, and Venezuela) have reoriented their control programs in keeping with the Global Malaria Control Strategy (GMCS) adopted in Amsterdam in 1992.
The Global Strategy called for a shift from the traditional emphasis on vector control towards case management as its focus. GMCS is based on four principles: (1) provision of early diagnosis and prompt treatment; (2) implementation of protective and preventive measures for the individual, family and community, including vector control; (3) development of the capability to predict and promptly contain epidemics; (4) strengthening local capacity in basic and applied research to permit and promote the regular assessment of a country’s malaria situation, in particular the ecological, social, and economic determinants of the disease.
As a result, the countries of the Americas have redefined their malarious areas on the basis of different levels of exposure or the risk of transmission (Figure 1). Risk of exposure, within an ecologically propitious area, is the result of factors related to population movement, social stability, and adoption of individual and collective attitudes and behaviors that prevent malaria and protect against contact with vectors. The intensity of malaria transmission resulting from the interrelation of these factors is roughly reflected in the Annual Parasitic Index (API, see Box 1) and can be modified by access to early diagnosis and prompt treatment. This index is the basic variable used for epidemiological stratification of malaria endemic areas.
Box 1: Malariometric indices:
|Annual Parasitic Index (API)||
Number of confirmed cases_______ x 1,000
|Annual P. falciparum Index (AFI)||
Number of confirmed P. falciparum cases_ x 1,000
|Annual P. Vivax Index (AVI)||
Number of confirmed P. vivax cases_ x 1,000
|Annual Blood Examination Rate (ABER)||Number of slides examined_______________ x 100|
Total population in areas at risk of transmission
In the 21 countries presenting active malaria transmission, of 472 million people, 208 million (44.1%) live in areas with some risk of transmission. However, of these, 131 million (59.8%) are exposed to low or extremely low risk of malaria transmission. In these areas, 46,823 malaria cases were detected in 1999, a decrease from 53,778 cases in 1998. This decrease resulted from post-El Niño stabilization after epidemics in Colombia, Ecuador, and Peru in 1998. The remaining 77 million people (16.3 % of the total population of these 21 countries) live in areas with moderate and high risk of transmission. The decrease of the population at high risk, from 39 million in 1998 to 35 million in 1999, is accounted for primarily because of finer risk stratification at the department level in Peru. Severe malaria morbidity is still observed in populations of the Region at moderate and high risk of transmission, with APIs ranging from a low of 0.18/1,000 in Mexico to 309.8/1,000 in Suriname.
In the Americas, “case detection” has been used as a morbidity index (cases per 100,000 inhabitants) for easy comparison with other morbidity indices. There has been a decrease in “case detection” for the total population of the Americas, from 160.51 per 100,000 in 1998 to 147.56 per 100,000 in 1999. When considering only the population in areas ecologically propitious for transmission, the indices are higher, 418.31 and 404.37 per 100,000, respectively, for the same years. However, a decrease is again apparent in 1999. For the 21 malaria endemic countries, both the API and the Annual P. falciparum Index (AFI, see Box 1) are compared with the annual blood examination rate (ABER) (Figure 2). Since the AFI has remained relatively constant, this demonstrates a disturbing trend whereby the number of P. vivax infections reported (shown in the difference between the API and the AFI) increases with the number of blood slides examined. Such a pattern may be a reflection of incomplete treatment of the P. vivax reservoirs (i.e., incomplete case ascertainment). The same is not true of P. falciparum infections, as its transmission can be more effectively controlled by treatment administered immediately following blood slide diagnosis.
Figure 3 shows the API by geographic subregion between 1995 and 1999. The apparent marked reductions in the API in Guyana, Suriname, French Guiana, Haiti and the Dominican Republic during the 1996-1997 period reflect redefinitions of the estimated at-risk populations by malarious zones. As can be seen in Figure 4, P. vivax was the main cause of malaria morbidity in the American Region, but P. falciparum is the only parasite detected among cases in the Dominican Republic and Haiti and is the predominant species in French Guiana, Guyana and Suriname.
The distribution of malaria cases by geographic area in the Region, shown in Figure 5, reflects the burden of disease. An analysis by subregion indicates that Brazil reported the greatest absolute number of malaria cases (50.5%), followed by the countries of the Andean Subregion, which accounted for 32.3% of all cases. However, the greatest risk of transmission was registered in the subregion including areas of French Guiana, Guyana, and Suriname (API = 127.5/1,000), followed by parts of Brazil (API = 118.8/1,000).
In recent years the epidemiological stratification of malaria in the Americas has guided the integration of case finding, diagnosis, and immediate treatment into the local health services. The local health services, which include the community health workers network (volunteer collaborators) had a high diagnostic efficiency, confirming 10.6% of suspected cases, whereas active surveillance continues to show a low diagnostic efficiency and high operational cost, confirming 2.2% of “recent fever” cases. Efforts continue to be made to improve microscopic diagnosis at the referral level of the general health services by training laboratory technicians in malaria diagnosis and redeploying trained microscopists. Nevertheless, routine active case detection continues to absorb about 32% of the malaria microscopic resources of the countries, in spite of its recognized low efficiency.
Table 1 displays the availability of treatment per diagnosed case, ranging from 0.57 to 241.8 first-line treatments per case reported. Up to 1999 all countries had an adequate supply of effective anti-malarial therapy. In 1999 however, all countries, with the exception of Colombia, experienced problems with drug supply to treat P. falciparum resistant strains. This reduced availability of effective drugs against P. falciparum resistant strains in Bolivia, Brazil, Ecuador, Peru, and Venezuela is among the key risk factors which may account for a potential increase in the number of resistant strains epidemics in the years to come.
From the characterization of factors leading to persistence of transmission, current and potential control measures can be identified. There is still a need to improve the selection and targeting of transmission control measures and to mobilize, guide, and support intersectoral coordination in order to ensure the sustainability of these measures. Vector control activities, almost exclusively indoor residual insecticide spraying, continue to be the main activity used by countries as a means to prevent transmission. However, 1999 country data reports were lacking insecticide usage data.
>Funds utilized by the control programs have varied greatly over the last five years. However, in recent years, expenditure per person in malarious areas has steadily decreased with the exception of a slight upturn in 1999. In 1999, average expenditure was US$ 0.45 per person for the 16 countries which reported their budget for malaria control to PAHO. This represents a 31% decrease compared to 1996 (US$ 0.65), a 4.2% decrease compared to 1997, but a 7.1% increase over funds available last year.
Table 1: Antimalarial treatment completed in 1999
|Countries and territories by geographic subregion||Treatments completed @ 1,500 mg of 4-amino quinolines||Number of reported cases||Number of first-line treatments available per case resported||
Number of treatments completed for resistant P. falciparum
|Number of P. falciparum and mixed cases reported||Number of second line treatments available per case of P. falciparum|
... no data available
Source: PAHO's Communicable Diseases Program (HCT)
Major Epidemiological Changes
Implementation of the GMCS in the Region has resulted in a significant drop in the malaria specific mortality rate. In 1994, the first year with comparable records, the P. falciparum crude mortality rate was 8.3 per 100,000 exposed population. By 1999, the mortality rate dropped to 1.7 per 100,000 exposed population, a decrease of 78%.
The major operational improvement associated with this reduction in the P. falciparum death rate is the constant increase in the coverage with second/third line treatments. The last column in Table 1 shows a remarkable reduction in the availability of P. falciparum resistant treatments, expressed as a number of second-line treatment smaller than one, which could certainly revert this important achievement.
Chloroquine resistance is highly prevalent in South America, although there is still some clinical response to chloroquine in the Andean countries. The number of reported treatment failures is increasing, having reached up to 20% in some areas of the Peruvian Amazon. Sulfadoxine/pyrimethamine resistance is also widespread and quinine and tetracycline are increasingly being used as first-line antimalarials in Colombia, the Guyanas and Suriname. In the Brazilian Amazon, mefloquine has been introduced as first-line treatment of P. falciparum infections, following diagnosis with a dipstick test. Artemisinine derivatives are still reserved for severe and complicated malaria. Isolated chloroquine treatment failures of P. vivax infections have been recently reported but not confirmed by epidemiological studies.
Major Problems and Constraints
There are three major barriers to the implementation of a successful malaria control strategy. The first is related to the need for a change in the common perception that malaria control is achieved by insecticide spraying that can only be accomplished by a major operational institution. This perception reinforces the natural institutional resistance to change, which has been targeted by all parties involved in malaria control since 1992.
The second major constraint is the drastic reduction in central budgets, concomitant with the major administrative process of decentralization of health services. Due to its focus on local health services, the implementation of the GMCS will benefit from health sector decentralization. However, the drastic reduction in human and budgetary resources generated by the process has become a major constraint for the implementation of GMCS.
Another concern is the lack of an effective vector control or vector interception measure to follow and complement the successful prevention of mortality and reduction of morbidity.
Roll Back Malaria in the Americas
Introduced by WHO in 1998, the Roll Back Malaria Initiative will complement the activities of the GMCS in the Americas. Through reinforcement of the health sector, its general objective is to significantly reduce the global burden of malaria through interventions adapted to local needs. The following five themes have been identified as important components of the initiative. Through these activities, Roll Back Malaria targets a 50% reduction in mortality rates by the year 2010.
1) Structured Interventions
The 21 malaria endemic countries of the Region all have organized malaria programs, integrated on distinct levels (national/regional/local) and with their general health services. The degree of decentralization varies among countries, but in general, municipalities (local governments) are responsible for undertaking public health activities at the local level, and a few already have control of financial resources.
Decentralization of responsibilities to the local level has not necessarily been accompanied by decentralization of technical capability. As a result, there is a significant need for technical capacity building at this level of execution as well as increasing participation of the local authorities in planning and budgeting.
2) Integration of Resources
The Community Health Worker scheme, which involves volunteers and/or paid workers, has been strongly promoted in the Region and has shown to be of great benefit in expanding coverage of the general health services. This structure is the foundation upon which intensified training efforts in malaria diagnosis, immediate treatment and transmission control have been and will continue to be undertaken.
3) Anti-Malaria Drug Policy
Assuring availability and quality control of anti-malaria drugs requires monitoring the effectiveness of anti-malaria drugs in all geographic and social settings of the Region. In addition, a definition of therapeutic regimens must be developed in accord with local situations. Protocols for drug efficacy have been developed and trials are on going in eight centers in six countries of the region, namely Brazil, Colombia, Guyana, Peru, Suriname, and Venezuela. These trials will continue to be promoted to assure continued monitoring and evaluation of drug efficacy and the constant development of alternate drug regimens, determined according to the local susceptibility.
4) Referral System
The diagnostic and treatment capabilities of the general health services have been strengthened in Brazil, Colombia, and Venezuela. Currently, the capability to manage severe and complicated malaria is being strengthened in Bolivia, Peru, and Suriname in order to provide an adequate referral system. This will expand accessibility of the population to satisfactory monitoring and diagnosis of treatment failures as well as management of severe and complicated malaria.
Continued expansion on the use of materials for the clinical level will assist in further reduction of mortality and continuous updating of both health personnel and the referral system itself will be required to adapt to changing epidemiological situations.
5) Resource Networks
In the Roll Back Malaria initiative, resource networks will be created to provide direct support to control operations and address critical issues for malaria control policy.
Of the resource networks established by Roll Back Malaria, those of particular relevance for the Region of the Americas are: prevention and control of epidemics (which will collaborate with the disaster preparedness and mitigation programs at the international, national and local levels); quality and provision of anti-malaria drugs at the local level; and monitoring of resistance to anti-malarial drugs and insecticides. In addition, it will be necessary to establish a network for validation and improvement of alternative methods for selective transmission control. There is also the need for increased financing to permit a continuation of ongoing activities and initiation of others in efforts to Roll Back Malaria in the Region of the Americas.
A sixth element is deemed necessary for successful implementation of the initiative in the Americas:
6) Control of Malaria Transmission
While continuing their efforts to reduce malaria mortality, the countries of the Region are pursuing the additional objective of reducing malaria incidence through transmission control. Efforts have been and will continue to be undertaken in testing the use of insecticide impregnated materials in the Region. However, this and other transmission control activities continue to offer a great challenge to the decentralized health services of the Region.
Since the 1950’s and the advent of malaria eradication programs, the countries in the Region of the Americas have developed extensive expertise in indoor spraying of insecticides for the control of malaria transmission. The efforts were effective in large areas of the Region, especially those experiencing a stable social and economic development. Nevertheless, the indoor residual spraying of insecticides was not helpful in interrupting malaria transmission in areas with unstable social/demographic and political situations. In such areas, alternative methods to intramural residual spraying of insecticides are being actively sought to further reduce morbidity through alternative efforts aimed at controlling transmission.
Plan of Intensive and Simultaneous Actions
In endemic areas where the population at risk is demographically stable and in areas of newly formed rural and peripheral urban settlements, reduction of transmission can be accomplished by means of antiparasitic measures applied simultaneously to human and vector reservoirs. This technique, developed by Mexican authorities, requires an organization with national, state/province/department, municipality/district/canton, district/locality/sector, infrastructure in order to be efficiently and systematically applied in each endemic community of the country. The costs of such a program (US$ 40 million/year for 6 continuous years, or US$ 1/person living at risk of acquiring malaria, as estimated by Mexican authorities) may be considered high for some countries, but can be feasibly financed by most countries of the Americas.
Selective Vector Control
In areas of “economic frontier” expansion, such as forested regions under human settlement pressure and areas with low technological exploitation of natural resources, the intramural spraying of insecticides has had very limited effect in controlling malaria. In these epidemiological situations, alternative methods for transmission control have been proposed by a Regional Expert Committee on Selective Vector Control. They include: source reduction of breeding sites, personal family and community protective measures, biological control of vectors, and space spraying of insecticides in epidemic situations.
Utilization of stratification techniques based on epidemiological and entomological parameters allows for the prioritization and selection of the combination of transmission control methods appropriate to each transmission focus.
GMCS implementation in the Americas is far from complete and requires an intensified effort to overcome the detected barriers to its full implementation. The implementation of the GMCS is very complex and calls for a political commitment, which can be provided by the Roll Back Malaria initiative in the following ways:
- Changing from a traditional approach, characterized by vertical organizations and programs;
- Organizing health services in areas of difficult access;
- Preparing human resources capacity for the effective implementation of a decentralized health services;
- Providing adequate financial and material resources in time and quantity.
The challenge is even greater in the context of health sector reform. Only a joint commitment by all interested partners can achieve this goal. The Roll Back Malaria initiative provides the mechanism to do this and is essential for the success of malaria control in the Region of the Americas.
Source: PAHO. Division of Disease Prevention and Control, Communicable Diseases Program (HCP/HCT)
The case definition of malaria is available in Vol. 20, No, 2 of the Epidemiological Bulletin. Previous articles on malaria include: "Malaria in the Americas" (Vol. 17, No. 4 - December 1996) and "Malaria in the Americas, 1996" (Vol, 18, No. 3 - September 1997).