In vitro sensitivity of Plasmodium falciparum to amodiaquine compared with other major antimalarials in Madagascar

Chloroquine has been used in Madagascar since 1945 and remains the first-line treatment for uncomplicated cases of malaria. Low-grades of resistance type R1 and R2 have been reported. Thus, in vitro tests were performed in order to monitor the drug sensitivity of Plasmodium falciparum from different study sites, with the aim of identifying alternatives to chloroquine. Chloroquine IC50 values ranged from 0.2 nM to 283.4 nM (n = 190, mean IC50 = 52.6 nM; 95% CI = 46.1-59.1 nM). Fifteen isolates (7.9%) were chloroquine-resistant. One mefloquine-resistant isolate was detected (1/139). The test isolates were sensitive to amodiaquine (n = 118), quinine (n = 212), pyrimethamine (n = 86) and cycloguanil (n = 79). The median IC50 for amodiaquine was 12.3 nM (mean IC50 = 15.3 nM, 95% CI = 13.3-17.3 nM). Amodiaquine was 3.4 times as active as chloroquine in vitro and 7 times as active as quinine against P. falciparum. These results indicate that amodiaquine may be a potent alternative to chloroquine in Madagascar. There was positive correlation between tested quinoline-containing drugs activities, which suggests in vitro cross-susceptibility.

Validity of Lot Quality Assurance Sampling to optimize falciparum malaria surveys in low-transmission areas

To control the reappearance of malaria in the Madagascan highlands, indoor house-spraying of DDT was conducted from 1993 until 1998. Before the end of the insecticide-spraying programme, a surveillance system was set up to allow rapid identification of new malaria epidemics. When the number of suspected clinical malaria cases notified to the surveillance system exceeds a predetermined threshold, a parasitological survey is carried out in the community to confirm whether or not transmission of falciparum malaria is increasing. Owing to the low specificity of the surveillance system, this confirmation stage is essential to guide the activities of the control programme. For this purpose, Lot Quality Assurance Sampling (LQAS), which usually requires smaller sample sizes, seemed to be a valuable alternative to conventional survey methods. In parallel to a conventional study of Plasmodium falciparum prevalence carried out in 1998, we investigated the ability of LQAS to rapidly classify zones according to a predetermined prevalence level. Two prevalence thresholds (5% and 15%) were tested using various sampling plans. A plan (36, 2), meaning that at least 2 individuals found to be positive among a random sample of 36, enabled us to classify a community correctly with a sensitivity of 100% and a specificity of 94%. LQAS is an effective tool for rapid assessment of falciparum malaria prevalence when monitoring malaria transmission.

Malaria in the highlands of Madagascar after five years of indoor house spraying of DDT

The central region of Madagascar is a vast area of highlands (altitude 700-2000 m). Malaria transmission has re-established itself here since the last epidemic of 1985-90 and has caused the deaths of 40,000 persons according to the Minister of Health. To combat the main malaria vector in the region, Anopheles funestus, annual programmes of indoor house spraying of DDT were carried out between December 1993 and January 1998 in most rural areas at altitude 1000-1500 m. A parasitological and serological study was then conducted in the highland schools to evaluate the impact of the programme and set up a database on the region. Using a cluster-sampling method 2 independent selections were conducted (one of 130 sites, the other of 40 sites). During the study, 13,462 schoolchildren were examined, 71% living in sprayed villages. Parasite prevalence among schoolchildren declined as altitude increases, from 11% at 700-900 m to 0.4% at > 1500 m. Below 1500 m, the impact of the spraying on the prevalence of the parasite was very clear (an average decrease of from 20% to 2.7% below 1000 m and of from 4.5% without spraying to 0.8% at 1000-1500 m). Geographical analysis of the data showed that the marginal regions remained the most affected by malaria (especially outside spraying zones), and persistence of 'pockets of transmission' at 1000-1500 m, essentially in areas where spraying has never been used. In 9 schools, anti-Plasmodium antibodies were sought by indirect immunofluorescence on thick smears of parasitized red blood cells. The seroprevalence ranged from 22% to 63%, which suggests that the parasite is still circulating in the region. Even though our data show that vector control continues to be very successful in the Madagascan highlands, rapid reinfection could occur and must be monitored following spraying. To this end, the Minister for Health, with the support of the Italian Co-operation, has placed the region under epidemiological surveillance since 1997. An alert system for the timely detection of the sources of epidemics and the targeting of the antivectoral campaign is also in operation. Our study suggests that this strategy should be reinforced by the spraying of DDT in the marginal zones in order to consolidate the results obtained at higher altitudes.

Mefloquine-resistant strains of Plasmodium falciparum in Madagascar: impact on tourists and public health

Although the national policy for malaria control in Madagascar is to use chloroquine as the first line of treatment, mefloquine has been and is recommended to travellers to the country, both for malaria prevention and cure. The in-vitro susceptibility of Plasmodium falciparum to mefloquine was therefore assessed during a prospective surveillance study in various areas in Madagascar, including the tourist sites of Nosy-be and Sainte Marie. Of the 254 isolates of P. falciparum successfully tested, 232 (90.9%) were sensitive to mefloquine, 12 (4.7%) showed decreased susceptibility (40 nM < IC50 < 50 nM), and 10 (3.9%) were resistant (IC50 > 50 nM). Five (50%) of the resistant strains and nine (75%) of those with decreased susceptibility were from coastal areas or the two tourist sites. The drug pressure that could have induced the resistance observed could therefore be related to the donation of antimalarials, such as mefloquine, by tourists to local populations. The residents of the coastal areas take any donated drugs as self-medication, ignoring recommended doses and durations of treatment. This situation has two main consequences: (1) there is an urgent need to control the abusive and incorrect use of antimalarial drugs in Madagascar, to safeguard the effectiveness of chemotherapy in the future; and (2) these increases in resistance compromise the efficiency of the antimalarial chemoprophylaxis currently recommended to tourists. The use of mefloquine can no longer be considered as a guarantee of protection against malaria in coastal areas and other sites frequented by tourists.