Introduction
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
Population at moderate and high risk
|
| Annual P. falciparum Index (AFI) |
Number of confirmed P. falciparum cases_ x 1,000
Population at moderate and high risk
|
| Annual P. Vivax Index (AVI) |
Number of confirmed P. vivax cases_ x 1,000
Population at moderate and high risk
|
| 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 |
| Mexico |
839,733 |
6,402 |
131.17 |
0 |
16 |
0.00 |
| Belize |
8,599 |
1,850 |
4.65 |
0 |
52 |
0.00 |
| Costa Rica |
38,130 |
3,998 |
9.54 |
0 |
15 |
0.00 |
| El Salvador |
297,376 |
1,230 |
241.77 |
0 |
9 |
0.00 |
| Guatemala |
210,107 |
45,098 |
4.66 |
0 |
1,707 |
0.00 |
| Honduras |
496,732 |
46,740 |
10.63 |
0 |
1,220 |
0.00 |
| Nicaragua |
2,270,800 |
38,676 |
58.71 |
0 |
1,689 |
0.00 |
| Panama |
19,100 |
936 |
20.41 |
0 |
40 |
0.00 |
| Haiti |
.... |
1,196 |
... |
... |
1,196
|
... |
| Dominican Rep. |
130,478 |
3,589 |
36.36 |
0 |
3,584 |
0.00 |
| French Guiana |
... |
5,307 |
... |
... |
4,528 |
... |
| Guyana |
23,300 |
27,283 |
0.85 |
39,244 |
16,144 |
2.43 |
| Suriname |
12,096 |
13,939 |
0.87 |
8,301 |
11,685 |
0.71 |
| Brazil |
935,150
|
609,594 |
1.53 |
171,195 |
114,605 |
1.49 |
| Bolivia |
70,800 |
50,037 |
1.41 |
6,085 |
7,557 |
0.81 |
| Colombia |
195,230 |
66,845 |
2.92 |
112,101 |
25,389 |
4.42 |
| Ecuador |
177,842 |
87,620 |
2.03 |
110 |
49,993 |
0.00 |
| Peru |
94,259 |
166,579 |
0.57 |
57,653 |
67,169 |
0.86 |
| Venezuela |
79,497 |
19,086 |
4.17 |
1,576 |
3,531 |
0.45 |
| Argentina |
467 |
222 |
2.10 |
0 |
0 |
0.00 |
| Paraguay |
35,600 |
9,947 |
3.58 |
0 |
2 |
0.00 |
|
... 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.
Current Situation of P. falciparum Resistance
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.
Conclusions
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:
