RESUMO
In Colombia, Plasmodium resistance to antimalarials such as chloroquine and antifolates is a serious problem. As a result, the national Colombian health authorities are monitoring the efficacy of alternative drugs and schemes. The study of genetic polymorphisms related with drug resistance is required in the region. In vitro responses to chloroquine, quinine, mefloquine, amodiaquine, desethylamodiaquine, artesunate and dihydroartesunate were carried out by HRP ELISA. SNP analysis in Pfcrt and Pfmdr1 genes was performed by PCR-RFLP in 77 samples from the North West region of Colombia. In vitro resistance to chloroquine was high (74%), followed by mefloquine (30%) and desethylamodiaquine (30%). A positive correlation between the IC(50) of paired drugs was also detected. The allele Pfmdr1 N86 (wild) was present in 100% of the samples and 1246Y (mutant) in 92%. However, their presence did not correlate with in vitro drug resistance. Presence of the mutations K76T and N75E in Pfcrt was confirmed in all samples. Analysis of 4 codons (72, 74, 75 and 76) in pfcrt confirmed the presence of the haplotypes CMET in 91% and SMET in 9% of the samples.
Assuntos
Antimaláricos/farmacologia , Resistência a Medicamentos/genética , Proteínas de Membrana Transportadoras/genética , Proteínas Associadas à Resistência a Múltiplos Medicamentos/genética , Plasmodium falciparum/efeitos dos fármacos , Polimorfismo de Nucleotídeo Único , Proteínas de Protozoários/genética , Amodiaquina/análogos & derivados , Amodiaquina/farmacologia , Animais , Cloroquina/farmacologia , Colômbia/epidemiologia , Humanos , Malária Falciparum/epidemiologia , Malária Falciparum/parasitologia , Mefloquina/farmacologia , Testes de Sensibilidade Parasitária , Plasmodium falciparum/genética , Reação em Cadeia da Polimerase , Polimorfismo de Fragmento de RestriçãoRESUMO
Pyrimethamine resistance in cultivated laboratory isolates of Plasmodium falciparum is linked to the dihydrofolate reductase mutation Asn-108, a mutation that acts by interrupting drug binding within the active site of the enzyme. To determine the prevalence of this mutation in endemic regions harboring pyrimethamine-resistant malaria, we used a mutation-specific polymerase chain reaction assay to survey P. falciparum strains from a wide section of the Brazilian Amazon. Mutations were identified directly from blood samples without intervening steps of in vitro cultivation. Of 42 samples collected from four states in Brazil, 38 (90%) contained the Asn-108 codon AAC that confers pyrimethamine resistance, four samples contained only the wild-type Ser-108 codon AGC, and none contained the Thr-108 codon ACC found in cycloguanil-resistant pyrimethamine-sensitive strains. These findings indicate that a very high incidence of the Asn-108 DHFR mutation is responsible for pyrimethamine resistance in the Amazon, and they are consistent with recent failure rates reported for Fansidar (pyrimethamine-sulfadoxine). We suggest that limited use of proguanil be evaluated as an alternative to pyrimethamine.
Assuntos
Plasmodium falciparum/efeitos dos fármacos , Pirimetamina/farmacologia , Tetra-Hidrofolato Desidrogenase/genética , Animais , Sequência de Bases , Brasil , Códon/química , DNA de Protozoário/química , Resistência a Medicamentos/genética , Eritrócitos/parasitologia , Humanos , Dados de Sequência Molecular , Mutação , Plasmodium falciparum/enzimologia , Plasmodium falciparum/genética , Reação em Cadeia da PolimeraseRESUMO
After reviewing the use of non-human primates of the Old and New Worlds for human malaria research, we concluded that another experimental animal which is easily available to use and possible to rear indoors is needed. Thus, we studied the susceptibility of the marmoset Callithrix penicillata to Plasmodium falciparum erythrocytic infections. The marmosets received various P. falciparum human isolates, directly from a patient and from continuous cultures. The Palo Alto strain, which has been adapted to the night monkey Aotus trivirgatus and further maintained in the squirrel monkey Saimiri sciureus was also used. In a total of 20 marmosets we performed 31 inoculations, with 10(5) to 10(9) parasites, intraperitoneally, intracardiacly or intravenously. Blood samples from each animal were examined daily up to day 90 post-inoculation. None of the intact marmosets developed patent infections. Four out of 19 C. penicillata, previously splenectomized, showed circulating parasites for up to five days after intravenous inoculation with the Palo Alto strain, becoming negative thereafter. Neither the addition to the simian diet of p-aminobenzoic acid, essential for the parasite metabolism, nor drug-immunosuppression, improved the marmoset susceptibility to P. falciparum.