MALARIA CONTROL, BY REGION
III. THE AMERICAS
- Parasitological species of malaria cases: P. falciparum 18%, P. vivax 72%, P. malariae
- Principal malaria vectors: A. albimanus (Central America), A. darlingi (Amazon Basin)
- Estimated proportion of population at malaria risk: 14% (21)
- Estimated contribution to the global burden of clinical malaria cases: 3% (2)
- Estimated contribution to the global burden of clinical falciparum malaria cases: 1% (2)
- Estimated contribution to the global malaria mortality burden: <1% (1)
- Main reported control strategies: prompt and effective treatment, vector control
especially IRS and space spraying, ITNs
1. Disease burden
Malaria transmission occurs in 9 countries that share the Amazon rainforest in
South America (Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Peru,
Suriname and Venezuela), 8 countries in Central America (Belize, Costa Rica, El
Salvador, Guatemala, Honduras, Nicaragua, Panama, Mexico) and in 2 countries that
share the Caribbean island of Hispaniola (Haiti and the Dominican Republic). In
addition, small numbers of cases are reported from Argentina and Paraguay in South
America. Population movement accounts for part of the malaria problem, causing
an epidemic in 2003 in Suriname in gold mining areas near the border with Brazil.
In Brazil, urban and periurban malaria associated with population movement to
the periphery of large cities is increasingly contributing to the disease burden.
The reported case rate pooled across all countries has remained fairly stable since
1990. A slight decrease in recent years mainly reflects a decrease in Mexico (Box 12)
and other countries in Central America (Fig. 35).
Across countries in South America, around 25% of reported cases are caused by
P. falciparum, the remainder are P. vivax. In Central America and the Caribbean, an
average of around 10% of reported cases are caused by falciparum malaria infection.
Between 1994 and 2003, the proportion of cases caused by falciparum infection
decreased in Bolivia, Colombia, Ecuador and Peru, increased in Nicaragua and was
stable or fluctuating in other countries.
In Colombia and Guatemala, 64% and 53% of recorded cases respectively were
male. Brazil, Colombia and Guatemala identified the age distribution of reported
cases. Adults over 15 years of age accounted for more than half of the total number
of cases in all 3 countries. The case reporting rate decreased with age in Brazil and
Guatemala, but increased with age in Colombia (Fig. 36).
Figure 35. Standardized rates of malaria reported case rate in malaria-endemic countries in Central America and the Caribbean and in South America, by calendar year,
Numerators are based on confirmed, autochthonous cases. Regional averages, given for South America and for Central America and the Carribean, are based on all countries including those not providing feedback to WHO, weighted by population size (52). Country-specific rates are shown for countries that provided feedback during the preparation of this report and for Mexico, the most populous country in Central America.
Figure 36. Age distribution of reported cases in the Americas, 2003; age distribution of cases (a) and age-specific case rates per 1000 persons per year (b)
Data are from countries that reported numbers of cases by age group in 2003, and for which the sum of age-specific numbers of cases was equal to or smaller than the reported total.
2. Control efforts
Nine countries employ ITNs as per the national malaria control strategy. Surveys
in Colombia, Nicaragua and malarious areas of Bolivia measured household
possession levels of 31%, 42% and 95% for any nets, respectively. In Colombia
and selected areas of Bolivia, 2% and 13% of households had an ITN, respectively.
The proportions of children under 5 years of age sleeping under a net according to
national surveys were 24% in Colombia, 6% in Guatemala and 77% in Suriname;
for ITNs, corresponding proportions ranged between 1% and 7%. The low coverage
levels in some of these countries probably reflect the fact that ITN promotion,
while part of the national malaria control policy, is not the highest priority
intervention. It is also important to note that by 2004, coverage is likely to have
increased compared with that measured in available surveys, which were conducted
between 1999 and 2002.
In all countries with malaria, vector control by IRS and larviciding in focal areas
form part of the national malaria control strategy. Argentina has an epidemic
preparedness strategy. Most countries are striving to integrate and/or increase
collaboration between the malaria control programme and the local health service
in order to promote community participation in malaria control.
In addition to financial support provided by national governments, Bolivia,
Guatemala, Guyana, Haiti, Honduras, Nicaragua and Suriname receive financial
support for malaria control from the GFATM. Colombia, Ecuador, Peru and Venezuela
are awaiting final approval from the GFATM for their jointly submitted grant proposal.
Mexico and the Central American countries receive support from the Global
3. Drug efficacy
Recent drug efficacy studies in South America documented over 80% resistance of
P. falciparum to chloroquine (Fig. 37), and close to 20% resistance to sulfadoxine–
pyrimethamine (Fig. 38). Confirmed and/or suspected resistance of P. falciparum
was also reported for primaquine, mefloquine and quinine. Based on these data,
8 of the 9 endemic Amazon countries (Bolivia, Colombia, Ecuador, French Guiana,
Guyana, Peru, Suriname and Venezuela) have changed national drug policies and
now use ACTs for the treatment of falciparum malaria. However, in several of these
countries various other antimalarial drugs remain readily accessible through private
pharmacies and/or informal suppliers.
In Central America north of the Panama Canal, the only case of chloroquine failure
against falciparum malaria that has been documented so far was in Guatemala.
Chloroquine continues to be used for prophylaxis for international travellers to the
Dominican Republic and Haiti, (57) and for treatment during recent falciparum
malaria epidemics in the Dominican Republic. The drug has generally retained its efficacy
for the treatment of vivax malaria in the Americas, although chloroquineresistant
P. vivax has been reported in Brazil, Colombia, Guatemala, Guyana and Peru.
BOX 12. IMPACT OF "FOCALIZED TREATMENT" STRATEGY IN MEXICO
Climatic conditions such as temperature and humidity would seem to permit malaria
transmission in much of Mexico, except for the mountainous and desert areas. The vast
majority of cases (99% in 2003) are caused by P. vivax,which explains the absence of reported
malaria-related deaths since 1982. Effective control measures have now restricted malaria
transmission to foci that are in dispersed rural areas, in 15 of the country’s 32 states. Thus,
99.8% of Mexico’s population now live in areas where malaria is not a threat.
The unsuccessful eradication campaign, centred on IRS with DDT from 1956 to 1982, was
followed by a transition phase during which malaria cases dramatically increased (Fig. 39).
In 1989, a Plan of Intensive and Simultaneous Actions was instituted, consisting of massive
drug administration and insecticide spraying in high-transmission areas. While this plan
initially yielded good results, its activities were costly and malaria transmission resumed
when the activities were interrupted or limited by budgetary constraints. This occurred in
1998, generating an epidemic affecting mainly Oaxaca State.
Since then, a new strategy, "focalized treatment", was adopted consisting of:
- epidemiological surveillance and identification of "malaria reservoirs" for malaria patients
and their families;
- repeated drug treatments—chloroquine and primaquine—for patients and their families
over a 3-year period;
- focal, selective spraying with pyrethroid insecticides.
Intensive surveillance is a key activity because:
- climatically, many areas remain suitable to malaria transmission and epidemics could
occur if cases are not treated promptly before the parasites spread further.
- population movements from countries south of Mexico with higher malaria endemicity
represent a continuous risk of introduction of malaria parasites, including of
chloroquine-resistant P. falciparum.
The rational use of insecticides has decreased the number of houses sprayed from 500 000
in 1997 to 100 000 in 2003. IRS is now only used in the southern border areas, which
reduced the costs of the control programme.
These activities have prevented epidemics and successfully interrupted transmission in
99% of the localities. Between 1985 and 2003, the numbers of reported cases decreased
by 97%—3819 cases (Fig. 40). Most remaining cases occur in foci near the country’s
southern borders, and in four north-west states where difficult access hinders control
activities. To date, no drug resistance has been reported. Eventual elimination of the
disease does not appear to be an unrealistic goal; such an achievement would yield
important health benefits for the country and its neighbours, as well as substantial economic
dividends, particularly for Mexico’s tourism industry.
Figure 37. Treatment failure of chloroquine against falciparum malaria in South America, 1997–2003
||Drug efficacy expressed as total treatment failure with 28-day follow up ( 9). Boxes indicate the 25th and 75th percentile of failure rates observed across available studies, error bars indicate the upper and lower adjacent values and the grey line in each box indicates the median.
Figure 38. Treatment failure of sulfadoxine–pyrimethamine against falciparum malaria in South America, 1997–2003
||Drug efficacy expressed as total treatment failure with 28-day follow up (9). Boxes indicate the 25th and 75th percentile of failure rates observed across available studies, error bars indicate the upper and lower adjacent values and the grey line in each box indicates the median.
Figure 39. Malaria cases and insecticide sprayings in Mexico, 1959–2003
PAIS = Plan of Intensive and Simultaneous Actions – Source: Mexico Ministry of Health (Secretaría de Salud)