The changing pattern of Plasmodium falciparum susceptibility to chloroquine but not to mefloquine in a mesoendemic area of Somalia

Global analysis of Plasmodium falciparum Na(+)/H(+) exchanger (pfnhe-1) allele polymorphism and its usefulness as a marker of in vitro resistance to quinine

The aim of this study was to provide a comprehensive analysis of the worldwide genetic polymorphism of ms4760 alleles of the pfnhe-1 gene and to discuss their usefulness as molecular marker of quinine resistance (QNR). A new numbering of ms4760 allele, classification grouping ms4760 alleles according to the number of DNNND and DDNHNDNHNND repeat motifs in blocks II and V was also proposed. A total of 1508 ms4760 sequences from isolates, culture-adapted parasites or reference strains from various geographical regions were retrieved from GenBank (last update on 15th June 2012) or from publications and were used for genetic analyses. The association of different alleles of pfnhe-1 with resistance to quinoline antimalarial drugs showed marked geographic disparities. The validity and reliability of candidate polymorphisms in pfnhe-1 gene as molecular markers of QNR appeared restricted to endemic areas from South Asia or possibly East African countries and needs to be confirmed.

Efficacy of monotherapies and artesunate-based combination therapies in children with uncomplicated malaria in Somalia

In order to guide the antimalarial treatment policy of Somalia, we conducted therapeutic efficacy studies of routinely used antimalarial monotherapies as well as artemisinin-based combination therapies (ACTs) for uncomplicated malaria in three sentinel sites during 2003-2006. Therapeutic efficacy of chloroquine (CQ), amodiaquine (AQ) and sulfadoxine/pyrimetahmine (SP) monotherapies, and artesunate plus SP (AS+SP) or AQ (AS+AQ) were evaluated in children 6 months to 10 years old with uncomplicated malaria. For the assessment of the monotherapies, 2003 WHO protocol with 14-day follow-up was used while the 2005 WHO protocol with 28-day follow-up was used for testing the ACTs. Of the monotherapies, CQ performed very poorly with treatment failures varying from 76.5% to 88% between the sites. AQ treatment failure was low except for Janale site with treatment failure of 23.4% compared to 2.8% and 8% in Jamame and Jowhar, respectively. For SP, treatment failures from 7.8% to 12.2% were observed. A 28-day test of artemisinin-based combinations, AS+SP and AS+AQ, proved to be highly efficacious with cure rates of 98-100% supporting the choice of AS+SP combination as first line treatment for uncomplicated malaria for Somalia.

Antimalarial drug susceptibility testing of Plasmodium falciparum in Brazil using a radioisotope method

From March 1996 to August 1997, a study was carried out in a malaria endemic area of the Brazilian Amazon region. In vivo sensitivity evaluation to antimalarial drugs was performed in 129 patients. Blood samples (0.5 ml) were drawn from each patient and cryopreserved to proceed to in vitro studies. In vitro sensitivity evaluation performed using a radioisotope method was carried out with the cryopreserved samples from September to December 1997. Thirty-one samples were tested for chloroquine, mefloquine, halofantrine, quinine, arteether and atovaquone. Resistance was evidenced in 96.6% (29/30) of the samples tested for chloroquine, 3. 3% (1/30) for quinine, none (0/30) for mefloquine and none for halofantrine (0/30). Overall low sensitivity was evidenced in 10% of the samples tested for quinine, 22.5% tested for halofantrine and in 20% tested for mefloquine. Means of IC 50 values were 132.2 (SD: 46. 5) ng/ml for chloroquine, 130.6 (SD: 49.6) ng/ml for quinine, 3.4 (SD: 1.3) ng/ml for mefloquine, 0.7 (SD: 0.3) ng/ml for halofantrine, 1 (SD: 0.6) ng/ml for arteether and 0.4 (SD: 0.2) ng/ml for atovaquone. Means of chloroquine IC 50 of the tested samples were comparable to that of the chloroquine-resistant strain W2 (137.57 ng/ml) and nearly nine times higher than that of the chloroquine-sensitive strain D6 (15.09 ng/ml). Means of quinine IC 50 of the tested samples were 1.7 times higher than that of the low sensitivity strain W2 (74.84 ng/ml) and nearly five times higher than that of the quinine-sensitive strain D6 (27.53 ng/ml). These results disclose in vitro high resistance levels to chloroquine, low sensitivity to quinine and evidence of decreasing sensitivity to mefloquine and halofantrine in the area under evaluation.

Malaria among United States troops in Somalia

PURPOSE

United States military personnel deployed to Somalia were at risk for malaria, including chloroquine-resistant Plasmodium falciparum malaria. This report details laboratory, clinical, preventive, and therapeutic aspects of malaria in this cohort.

PATIENTS AND METHODS

The study took place in US military field hospitals in Somalia, with US troops deployed to Somalia between December 1992 and May 1993. Centralized clinical care and country-wide disease surveillance facilitated standardized laboratory diagnosis, clinical records, epidemiologic studies, and assessment of chemoprophylactic efficacy.

RESULTS

Forty-eight cases of malaria occurred among US troops while in Somalia; 41 of these cases were P falciparum. Risk factors associated with malaria included: noncompliance with recommended chemoprophylaxis (odds ratio [OR] 2.4); failure to use bed nets (OR 2.6); and failure to keep sleeves rolled down (OR 2.2). Some patients developed malaria in spite of mefloquine (n = 8) or doxycycline (n = 5) levels of compatible with chemoprophylactic compliance. Five mefloquine failures had both serum levels > or = 650 ng/mL and metabolite:mefloquine ratios over 2, indicating chemoprophylactic failure. All cases were successfully treated, including 1 patient who developed cerebral malaria.

CONCLUSIONS

P falciparum malaria attack rates were substantial in the first several weeks of Operation Restore Hope. While most cases occurred because of noncompliance with personal protective measures or chemoprophylaxis, both mefloquine and doxycycline chemoprophylactic failures occurred. Military or civilian travelers to East Africa must be scrupulous in their attention to both chemoprophylaxis and personal protection measures.

An epidemic of Plasmodium falciparum malaria in Balcad, Somalia, and its causation

The causative factors of an epidemic of falciparum malaria were investigated in Balcad, Somalia, a town with previously low malaria transmission, where malaria incidence rose more than twenty-fold between 1986 and 1988. The emergence of chloroquine resistance, accelerated by high drug pressure, low herd immunity and favourable meteorological conditions were identified as major causes of the epidemic. Chloroquine resistance of grades RII and RIII was first observed in Balcad in 1987 and rapidly increased to 72% of the Plasmodium falciparum infections in 1988. In the absence of alternative treatment, resistance resulted in the accumulation of a massive infective reservoir and therefore increased malaria transmission, associated with intensive clinical symptomatology. The advent of chloroquine resistance was less violent in the area of Malable, where malaria is stable and communal immunity higher than in Balcad.

Epidemiology of drug resistance in malaria

In the late 1950's chloroquine resistance to Plasmodium falciparum occurred in South America and on the Indochina Subcontinent. Since then it has conquered most of the areas where the parasite species is endemic. This has necessitated the use of alternative drugs such as sulphonamide-pyrimethamine combinations, quinine/tetracyclines, mefloquine, halofantrine, and recently also artemisinin-based compounds. In wide areas of South-east Asia, western Oceania and South America sulphonamide-pyrimethamine combinations have lost adequate efficacy. The situation is most serious in the Thai/Cambodia and Thai/Myanmar border areas where multiresistance necessitated the shift to the last line drug, i.e., the artemisinin derivatives. Selection of resistant parasites due to drug pressure, and their subsequent propagation by local transmission and migration of reservoirs are key factors in the dynamics of drug resistance. Selection is the result of the interplay of parasite, drug and human host, and is largely influenced by immune factors and the pharmacokinetics and pharmacodynamics of the drug. Spread of resistance is determined by eco-epidemiological factors among which migration and vectorial parameters play a major role. Rational drug use, especially adequate, monitored, therapeutic administration according to strict criteria, should curb the onset and spread of resistance, but this concept may not be readily accepted by health services whose primary goal is clinical amelioration of the disease rather than the more stringent target of epidemiologically desirable results.

Plasmodium falciparum: sensitivity to chloroquine in vivo in three ecological zones in Ghana

4690 children aged 6-15 years in 5 urban and 4 rural communities in 3 ecological zones in Ghana were screened from June 1988 to December 1990 to provide suitable candidates for the World Health Organization standard in vivo test for susceptibility of Plasmodium falciparum to chloroquine. 1880 (40.1%) had parasitaemia, mostly (83.7-98.6%) due to P. falciparum infection. Of the 626 in vivo tests performed, 570 (91.1%) showed sensitivity to chloroquine and 56 (8.9%) responses were classified as resistant to chloroquine at RI (5.1%) and RII (3.8%). The resistance responses were commonest (17.1-22.7%) in the coastal zone, followed by the savanna zone (8.6-10.0%), and lowest in the forest zone (3.1-6.3%). The RII responses occurred mainly in communities in the coastal zone. There was no RIII resistance in any zone. The pattern of RI (early) and RII responses of P. falciparum to chloroquine in this study suggested an increase in sensitivity, or a reduction in resistance, of P. falciparum to chloroquine from the coast to the forest and northern savanna zones, and from the urban to the rural communities in each zone in Ghana.

Susceptibility of Plasmodium falciparum in vitro to chloroquine, mefloquine, quinine and sulfadoxine/pyrimethamine in Somalia: relationships between the responses to the different drugs

The susceptibilities of Plasmodium falciparum to chloroquine, mefloquine, quinine and sulfadoxine/pyrimethamine were investigated in Mogadishu in 1988, after chloroquine resistance had spread widely in Somalia. Possible correlations of the responses to these drugs were also investigated. Standard World Health Organization in vitro micro-tests were performed. Of 76 isolates tested for chloroquine susceptibility, 58 (76%) were resistant to the drug with mean EC50 and EC99 values of 1.06 x 10(-6) mol/litre and 10.44 x 10(-6) mol/litre of blood, respectively, indicating a high prevalence and degree of resistance. In contrast, all isolates tested were inhibited by mefloquine 3.2 x 10(-6) mol/litre of blood, quinine at 2.56 x (-6) mol/litre of blood-medium mixture, and sulfadoxine/pyrimethamine at 6.0/0.075 x 10(-6) mol/litre of blood-medium mixture, indicating full sensitivity to these 3 drugs. However, a significant positive correlation was found between responses to quinine and chloroquine and between those to quinine and mefloquine; the responses to chloroquine and mefloquine were not correlated. The results may suggest that sites responsible for the correlation are shared between quinine and chloroquine but not essentially between chloroquine and mefloquine. Thus the evolution of chloroquine resistance together with increased use of quinine treatment of P. falciparum may increase the risks of development of quinine resistance, whereas the development of mefloquine resistance would not be triggered by chloroquine resistance.