SECTION II:

I. AFRICA

I. ASIA

II. THE AMERICAS

  1. Disease burden
  2. Control efforts
  3. Drug efficacy

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, 1990–2003

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 Environmental Facility.

 

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)