Drug-Resistant Malaria - libdoc.who.int - World Health Organization

REVIEW / 31
the possible influence of prevailing inununity in the populations
tested. In this connexion, further detailed studies are apparently
required to specify the immunogenic differences, if any,
between resistant· and sensitive P.falciparum strains, and to
investigate the biological characteristics of P.falciparurn in
relation to the degree of resistance.
AMERICAN REGION
General
In the American Region falciparum malaria is a major problem
in 13 countries with a population of approximately 141 million,
where 185 .068 cases were reported in 1980. Factors like multiresistant
vectors to insecticides in Central America and serious
problems related to migration, new or shifting settlements, mining,
prospecting, pastoral or agricultural activities, construction of
darns and hydroelectric power stations, are impeding or hindering
the control of falciparurn malaria.
Presumptive treatment is widely applied, using approximately
10 mg/kg chloroquine or amodiaquine base and in some countries a
single dose of 0.75 mg/kg primaquine base is also added in order
to curb transmission.
Radical cure of P.falciparum infections is obtained with ± 25
mg/kg chloroquine or amodiaquine three days together with 0.75
mg/kg primaquine in a single dose or divided over three days.
After the advent of chloroquine resistance a combined 1.25
mg/kg pyrimethamine plus 25 mg/kg sulfadoxine treatment has been
used in South American countries since the mid-1960s when the cure
rate was close to 100%. Recently, the efficacy of this combination
has decreased by probably 30-50%.
Mass drug administration in large-scale projects has been
difficult to evaluate. In small foci different drugs have proved
to be very useful in mass drug administration.
In vivo and in vitro tests performed between 1959 and 1981
suggest that countries of North and Central America and the
Caribbean have so far only chloroquine-susceptible P. falciparum,
while chloroquine-resistant parasites are prevalent in South
American countries.
Control of Drug-Resistant P.falciparum
Since the recognition of the problem of drug resistance,
efforts have been made for the esablishment of a system to assess
it in the field. Up to the late 1970s this was mainly pursued