Susceptibility of Plasmodium falciparum in The Gambia to pyrimethamine, Maloprim and chloroquine

A five-year malaria chemoprophylaxis study has begun with Maloprim in children aged three months to five years and pregnant women in a population of 13,000 in the area of Farafenni, The Gambia. Sensitivity of Plasmodium falciparum to pyrimethamine, Maloprim and chloroquine was assessed in vivo and in vitro in rural Gambian villages before drug intervention. 569 children aged one to seven years inclusive were sampled at the end of the wet season of 1982; 46% had positive blood films. All afebrile children were treated with a single dose of one of the antimalarials under study. Febrile children were treated with chloroquine. 109 infected children were retested 7 to 10 days after treatment and none showed asexual parasitaemia. 83 micro in vitro tests were successfully performed from fingerprick blood samples and the results confirmed the in vivo study. Pyrimethamine in combination with dapsone, in the proportion present in Maloprim, i.e., 1:8, showed a synergistic effect, the mean effective dose of pyrimethamine being reduced 13 times at the 50% inhibitory level.     

Estimates of the infectious reservoir of Plasmodium falciparum malaria in The Gambia and in Tanzania

Separate studies carried out in Farafenni, The Gambia and Ifakara, Tanzania in 1990-94 provided comparative data on population age structure, population gametocyte prevalences and gametocyte carrier infectivity. The percentage of the population estimated to be infective to mosquitoes was 5.5% and 3.8% in The Gambia and Tanzania, respectively. The age groups 1-4 years, 5-9 years, 10-19 years and 20 years or more comprised 17.5%, 21.7%, 22.2% and 37.9%, respectively, of the infectious population in The Gambia; the corresponding figures for Tanzania were 30.9%, 25.2%, 15.7% and 28.1%. These figures are in broad agreement with those from other published studies which estimated the infectious reservoir directly and suggest that adults contribute significantly to the infectious reservoir of malaria, particularly in areas of intense seasonal transmission. Control measures aimed at reduction of transmission may have only a limited effect in areas of moderate seasonal transmission if directed only at children.     

Amodiaquine fails to cure chloroquine resistant Plasmodium falciparum in the Punjab

We evaluated amodiaquine as a replacement drug for treating falciparum malaria in an area of Pakistani Punjab where chloroquine-resistant Plasmodium falciparum has recently emerged. Amodiaquine appeared to be 4 to 8 times more effective than chloroquine when P. falciparum isolates were tested in vitro. However, the recrudescence rate was greater than 50% after oral treatment with 20 mg/kg amodiaquine given over two successive days. This lack of therapeutic response from amodiaquine may have been due to selection of resistant parasites in the villages where the study was performed through extensive use of chloroquine for presumptive malaria treatment during the preceding 18 months. We conclude that amodiaquine is not a suitable replacement for chloroquine for treating falciparum malaria in our study area despite in vitro sensitivity data suggesting that it would be efficacious. Baseline in vitro sensitivity to mefloquine is also reported.     

Response of children with Plasmodium falciparum to chloroquine and development of a national malaria treatment policy in Zaire

In vivo sensitivity of Plasmodium falciparum to chloroquine was evaluated in 4 of 9 regions of Zaire in 1985 to develop a national strategy for treatment of malaria. Children less than 5 years of age were treated with either a single dose of chloroquine base, 10 mg/kg, or a dose of 25 mg/kg given over 3 d. A modified 7-day World Health Organization in vivo test was used with follow-up 2, 3 and 7 d after the start of treatment. 339 children were studied. In Bwamanda 92% of children were aparasitaemic 7 days after chloroquine, 10 mg/kg, but in Kinshasa only 44% were free of parasites after 25 mg/kg chloroquine. The mean drop in parasite density among those who did not clear parasites by day 7 was greater than 98% of the initial value. Although the parasite density decreased markedly, the failure of most subjects to become aparasitaemic indicated a marked decrease in parasite sensitivity since 1983. Only one child of 51 who were initially febrile remained febrile, although 14 (28%) of these had resistant parasites. The decrease in parasitaemia and temperature, even among children with resistant strains, led the Ministry of Health to recommend 25 mg/kg chloroquine as first line treatment for fever/malaria in their national malaria control plan. The plan includes drug sensitivity surveillance and a referral system for patients who do not respond to chloroquine treatment.     

Sensitivity of Plasmodium falciparum in The Gambia to co-trimoxazole

In The Gambia co-trimoxazole is used widely to treat children with an acute respiratory infection (ARI). Because malaria may sometimes be mistaken for ARI, some children with malaria are treated with co-trimoxazole. Therefore, we investigated the sensitivity of Gambian isolates of Plasmodium falciparum to this drug. Six days after the start of treatment with co-trimoxazole 3.3% of blood films of 65 asymptomatic subjects were positive, and 7.7% were positive after 21 d. One of 10 patients with ARI and malaria treated with co-trimoxazole had a positive blood film 3 d after the start of treatment but was negative thereafter. All 10 patients recovered satisfactorily. Thirty 'wild' isolates of P. falciparum were tested in vitro against co-trimoxazole at a ration of 5 parts sulphamethoxazole (SMZ) to 1 part trimethoprim (TMP). The mean EC50s, using a 36 h assay, were 1.2 x 10(-7) and 2.5 x 10(-8) M for SMZ and TMP respectively. When a [3H]hypoxanthine incorporation assay was employed, values of 5.7 x 10(-7) M for SMZ and 1.2 x 10(-7) M for TMP were obtained. These values are well below the peak plasma concentration. Our findings suggest that co-trimoxazole is effective against falciparum malaria in The Gambia. However, if it were to be used widely, the parasite would be likely to develop resistance to this and other dihydrofolate reductase inhibitor antimalarials.     

Malaria: radical treatment for falciparum malaria in chloroquine resistant strain areas

A trend exists in areas hyperendemic for Plasmodium falciparum (PF) malaria toward an increasing frequency and degree of resistance to chloroquine therapy. Aside from intense PF transmission in the northeastern sector of India, there is constant population movement particularly across the international border with Bangladesh. Resistance is high and widespread in those areas. Chloroquine resistance has also been observed in project areas, with some tendency toward increased resistance. The first reported confirmed case of PF resistance to chloroquine treatment was detected in Karbi-Anglong district in 1973, and then in the following year in Nowgoan. On the basis of a series of studies conducted in India, national drug policy was developed for the first time in 1982. Drug policy has since been revised in areas where significant portions of resistant cases have been detected. A list of areas with revised drug policies is presented, followed by guidelines on the radical treatment of chloroquine-resistant PF.     

Efficacy of combined chloroquine and sulfadoxine-pyrimethamine in uncomplicated Plasmodium falciparum malaria in Bangladesh

A study of the therapeutic efficacy of combined chloroquine and sulfadoxine-pyrimethamine (SP) for the treatment of uncomplicated Plasmodium falciparum malaria was carried out from June to November 2002, using the standard protocol recommended by the WHO for a low-to-moderate transmission area, in two sentinel sites in Bangladesh: Alikadam Upazilla in Bandarban district and Matiranga Upazilla in Khagrachari district. A total of 133 patients was followed-up to 28 d. Total failure rates were 25.9 and 30.7% in Alikadam and Matiranga, respectively. No severe side effects due to the drugs were encountered during the study period. Chloroquine and SP is not a suitable combination for the first-line treatment of P. falciparum in Bangladesh.     

Enzyme variation in Plasmodium falciparum in the Gambia

A study has been made of electrophoretic forms of enzymes of P. falcaparum in samples of blood from Gambian women and children. Variation was found in each of the 3 enzymes examined. 2 forms of parasite GPI, labelled GPI-1 and GPI-2, 2 forms of parasite LDH, labelled LDH-1 and LDH-2 and 3 forms of parasite 6PGD, labelled 6PGD-1, 6PGD-2 and 6PGD-3 were identified. Different combinations of enzyme forms occurred among different samples demonstrating genetic diversity of the parasite within and between blood samples. The distribution of enzyme forms among the samples suggested that the parasites belong to a single mendelian population. From statistical considerations of the distribution of enzyme forms among the samples it was estimated that the samples contained an average of about 2 parasite clones each. It was also possible to estimate the frequencies of variant forms of GPI among parasite clones as 0·62 and 0·38 for GPI-1 and GPI-2 respectively and LDH as 0·76 and 0·24 for LDH-1 and LDH-2 respectively. 6PGD-1 occurred in about 95% of blood samples showing activity of this enzyme, the remaining variants of 6PGD occurred in only 2 samples each. In many instances it was possible to identify the enzyme forms characterizing clones of parasite in individual blood samples, but rarely to estimate the actual number of clones present in a given sample. In a few samples, however, in which a single form of each enzyme occurred it could be estimated that probably only 1 parasite clone was present.     

Failure of erythromycin to improve chloroquine treatment of Plasmodium falciparum malaria in Kenya

58 children aged 1 to 10 years who had pure Plasmodium falciparum infections acquired on the coast of Kenya were treated with chloroquine 25 mg/kg given over 3 d and erythromycin 10 mg/kg 4 times a day given for 7 d. After 4 weeks follow-up, 62% had recurrent infections and 11% failed to clear their parasitaemia (1 had an RIII pattern of resistance). Of 38 children treated with chloroquine 25 mg/kg alone, 55% had recurrences and 21% failed to clear (including 1 RIII). In vitro microtests classified 74% of isolates from initial infections and 91% of isolates from recurrent infections as resistant. Erythromycin does not improve chloroquine treatment in children with infections due to P. falciparum having low to moderate levels of chloroquine resistance.     

Absence of malaria mortality in villagers with chloroquine-resistant Plasmodium falciparum treated with chloroquine

We carried out a series of malaria studies in Robek , Flores, Indonesia, a coastal village of 900 farmers and fishermen where malaria is hyperendemic by parasite rate and holoendemic by spleen rate. The studies showed that: (i) 28 of 31 isolates (90%) of Plasmodium falciparum were resistant to chloroquine in vitro, (ii) 3 of 12 isolates (25%) were resistant at the R-11 level in vivo, (iii) 376 P. falciparum infections occurred in 301 individuals during one year, (iv) no villagers who were treated with chloroquine for P. falciparum infections during the year died, and (v) increasing the dosage of chloroquine base from 15 to 25 to 37.5 mg/kg led to improved clearing of parasitaemia. We conclude that chloroquine can still be used as the primary antimalarial in Robek , but the dosage may have to be increased to clear parasitaemia.     

A randomized comparison of oral chloroquine and sulfadoxine-pyrimethamine for the treatment of uncomplicated Plasmodium falciparum malaria in Laos

Between June and October 2000 we conducted the first randomized trial in Laos comparing chloroquine (CQ) with sulfadoxine-pyrimethamine (SP) in the treatment of uncomplicated Plasmodium falciparum malaria (n = 29, 42-d follow-up, age > 5 years). The proportion of patients with treatment failure was high (CQ = 78%, RIII 46%; SP = 36%, RIII 15%). The treatment policy for uncomplicated P. falciparum malaria in Laos needs to be reviewed urgently.     

Genetic backgrounds of the Plasmodium falciparum chloroquine resistant transporter (pfcrt) alleles in Pakistan

Chloroquine (CQ) resistance in Plasmodium falciparum has been associated with point mutations in the P. falciparum CQ resistance transporter gene (pfcrt). Previous studies have shown 4-5 independent origins for CQ resistant pfcrt alleles globally, two in South America, one each in Southeast Asia, Papua New Guinea (PNG) and Philippines. In Asia, at least two different alleles corresponding to amino acids 72-76 (CVIET and SVMNT) have been found. The CVIET allele originated in Southeast Asia and then spread to Asia and Africa as well. The SVMNT allele, originating from PNG, has been found in India. This study was undertaken to investigate the genetic background of the CQ resistant pfcrt haplotypes in Pakistan. We genotyped microsatellite markers surrounding the pfcrt gene (six different markers at -12.3, -4.8, -1, 1.5, 3.9, 18.8 kb) in 114 clinical isolates of P. falciparum collected from different regions in Pakistan. Microsatellite analysis showed a significant reduction in genetic variation among the mutant SVMNT pfcrt alleles when compared to wild type alleles. The predominant SVMNT haplotype found in this study shared the same microsatellite haplotype found in both PNG and India. Two isolates with CVIET haplotypes showed similar microsatellite background to those found in Africa and Asia. In conclusion, this study suggests that CQ resistant SVMNT haplotypes in India and Pakistan have a common ancestral origin similar to that of Papua New Guinean isolates.     

Multiple drug resistant Plasmodium falciparum malaria in a pregnant indigenous Zambian woman

A 24 year old Zambian female presented with falciparum malaria when 27 weeks pregnant. She had recently travelled to the copperbelt from Solwezi in the North-West Province of Zambia. Oral chloroquine in a dose of 29 mg/kg failed to clear the parasitaemia. Chloroquine resistance was confirmed by testing in vitro and in vivo. In addition, Fansidar (2 courses), amodiaquine, quinine and quinine plus erythromycin failed to achieve radical cure. Quinine resistance was confirmed in vitro and in vivo. She was eventually cured by 10 d of quinine plus clindamycin, which was greatly assisted by the spontaneous delivery of a live normal infant at 37 weeks gestation. The baby's birth weight was 2.68 kg and its blood slide was negative for malaria.     

In vitro sensitivity of Plasmodium falciparum to chlorcycloguanil in The Gambia

Chlorcycloguanil (10732), the active metabolite of the antifolate chlorproguanil, has been tested in vitro against 17 isolates of Plasmodium falciparum in The Gambia. Minimum inhibitory concentrations were 10(-9) molar or less. 11 isolates simultaneously tested with pyrimethamine were sensitive to 10(-8) molar concentrations of that drug.