Characterization and epidemiology of influenza viruses in patients seeking treatment for influenza-like illnesses in rural Bangladesh.

CONTEXT: Infections caused by influenza viruses are a major health burden, both in developed and developing countries worldwide. Nevertheless, the overwhelming majority of influenza reports originate from industrialized countries in northern and southern temperate zones. AIMS: The aim of this study was to determine the epidemiology of influenza viruses in patients seeking treatment for acute febrile illnesses in rural Bangladesh. SETTINGS AND DESIGN: As part of our research on the causes of febrile illnesses in rural Bangladesh, nasopharyngeal swabs from patients with signs and symptoms consistent with influenza were collected from 2008 onwards. MATERIALS AND METHODS: Viral infection was established using two independent rapid diagnostic tests (RDTs) and later confirmed by RT-PCR. RESULTS: A total of 314 fever cases were enrolled in a survey of febrile illnesses carried out in Bandarban District in southeastern Bangladesh, out of whom 38 (12.1%) tested positive by RDT. Molecular subtyping showed that seasonal H3 strains (N=22; 7.0%) as well as the new H1N1v pandemic influenza subtype (N=13; 4.1%) had been circulating at the time of our investigations resulting in a PCR-adjusted positivity rate of 11.1% (95% CI 8.0 - 15.3). The positive predictive values for the RDTs used were 90.9% and 94.4%, respectively. CONCLUSIONS: This study provides a first insight into influenza epidemics in one of the most remote parts of Asia. Our findings suggest that respiratory illnesses due to influenza viruses are underreported in areas with limited access to health care and show a distinct seasonality also in rural areas of tropical countries.

Antimalarial activity of tigecycline, a novel glycylcycline antibiotic.

Tigecycline is a novel glycylcycline antibiotic with a broad antibacterial spectrum. Tigecycline was tested with 66 clinical isolates of Plasmodium falciparum from Bangladesh using the histidine-rich protein 2 in vitro drug susceptibility assay. The 50% and 90% inhibitory concentrations of tigecycline were 699 (95% confidence interval, 496 to 986) and 5,905 nM (4,344 to 8,028). Tigecycline shows no activity correlation with traditional antimalarials and has substantial antimalarial activity on its own.

In vitro activity and interaction of clindamycin combined with dihydroartemisinin against Plasmodium falciparum.

Combination regimens are considered a valuable tool for the fight against drug-resistant falciparum malaria. This study was conducted to evaluate the antimalarial potential of clindamycin in combination with dihydroartemisinin in continuously cultured and in freshly isolated Plasmodium falciparum parasites, measuring the inhibition of Plasmodium falciparum histidine-rich protein II synthesis. Interaction analysis revealed a synergistic or additive mode of interaction at various concentration ratios in all continuously cultured parasites at the 50% effective concentration (EC(50)) level. Antagonism was not found for any of the culture-adapted parasites. In fresh P. falciparum isolates, a fixed clindamycin-dihydroartemisinin combination exhibited additive activity at the EC(50) and EC(90) levels. The drug mixture showed no significant activity correlation to other commonly used antimalarials. The clindamycin-dihydroartemisinin combination appears to be a promising candidate for clinical investigation.

Paroxysm serum from a case of Plasmodium vivax malaria inhibits the maturation of P. falciparum schizonts in vitro.

In concurrent infections in vivo, the blood stages of Plasmodium vivax suppress those of Plasmodium falciparum. To see if the paroxysm (i.e. the periodic febrile episode) of P. vivax infection contributes to this suppression, sera from a P. vivax-infected volunteer were added to cultures of whole blood taken from cases of P. falciparum malaria. The crude 'rate' of schizont generation from the ring forms, measured as the percentage of all asexual parasites that were schizonts after incubation for 24 h, was similar whether the cultures contained serum samples collected during paroxysms or those collected, from the same volunteer, at other times (19.1% v. 18.9%; P=0.842). After a random-effect linear regression was used to adjust for disparities between the P. falciparum isolates, however, the degree of schizont maturation, measured as the mean number of nuclei per schizont, was significantly lower for the cultures with 'paroxysm serum' than for those with 'non-paroxysm serum' (4.8 v. 5.3; P=0.002). The proportion of schizonts considered mature was also significantly lower when 'paroxysm serum' was used (3.7% v. 6.3%: P=0.03). This appears to be the first in-vitro study in which sera collected during a paroxysm of P. vivax have been shown to inhibit the maturation of P. falciparum schizonts. The role of this mechanism in intra- and inter-specific competition is discussed.

Drug-resistant malaria in Bangladesh: an in vitro assessment.

Forty-four Plasmodium falciparum isolates from Bangladesh and 22 from western Thailand were successfully tested for their drug susceptibility. High degrees of resistance were observed against chloroquine with geometric mean IC50s of 114.25 and 120.5 nM, respectively, for Bangladesh and western Thailand. Most isolates from both sites were sensitive to quinine, and all were sensitive to artesunate. Many isolates were considered in vitro resistant to mefloquine, but the geometric mean IC50 for the Thai isolates (98.79 nM) was 1.6 times (P = 0.002) higher than that of isolates from Bangladesh (60.3 nM). The high prevalence of in vitro mefloquine resistance in Bangladesh suggests that close surveillance is necessary to delay widespread multidrug resistant problems in the area.

In vitro susceptibility of Plasmodium falciparum isolates from Myanmar to antimalarial drugs.

In vitro drug susceptibility profiles were assessed in 75 Plasmodium falciparum isolates from 4 sites in Myanmar. Except at Mawlamyine, the site closest to the Thai border, prevalence and degree of resistance to mefloquine were lower among the Myanmar isolates as compared with those from Thailand. Geometric mean concentration that inhibits 50% (IC50) and 90% (IC90) of Mawlamyine isolates were 51 nM (95% confidence interval [CI], 40-65) and 124 nM (95% CI, 104-149), respectively. At the nearest Thai site, Maesod, known for high-level multidrug resistance, the corresponding values for mefloquine IC50 and IC90 were 92 nM (95% CI, 71-121) and 172 nM (95% CI, 140-211). Mefloquine susceptibility of P. falciparum in Myanmar, except for Mawlamyine, was consistent with clinical-parasitological efficacy in semi-immune people. High sensitivity to artemisinin compounds was observed in this geographical region. The data suggest that highly mefloquine-resistant P. falciparum is concentrated in a part of the Thai-Myanmar border region.

Antimalarial activity of azithromycin, artemisinin and dihydroartemisinin in fresh isolates of Plasmodium falciparum in Thailand.

Antibiotics with antimalarial activity may offer an interesting alternative for the treatment of multidrug-resistant falciparum malaria. Azithromycin, a relatively recent semisynthetic derivative of erythromycin, was tested for its in vitro activity against fresh isolates of Plasmodium falciparum. As the reportedly slow onset of action of azithromycin suggests its combination with fast-acting substances, such as artemisinin-derivatives, dihydroartemisinin (DHA) was tested parallel as a possible combination partner. The effective concentrations found for azithromycin in this study (EC(50) = 29.3 micromol/l, EC(90) = 77.1 micromol/l blood medium mixture (BMM)) are comparable to those of other antimalarials in the antibiotics class and are considerably higher than those found for mefloquine or quinine. The absence of an activity correlation between azithromycin and chloroquine, quinine and artemisinin emphasises the independence of azithromycin drug response from the sensitivity to these drugs. A weak activity correlation (rho(EC90) = 0.352; p = 0.028), which could point to a potential cross-sensitivity but is probably of little clinical importance, was found with mefloquine above the EC(50) level. Provided that further clinical trials support the combination of these drugs, DHA may offer an interesting combination partner for azithromycin owing to its rapid onset of action and the comparatively low effective concentrations (EC(50) = 1.65 nmol/l, EC(90) = 7.10 nmol/l BMM). This combination may serve as an interesting alternative for tetracycline and doxycycline, which cannot be used in pregnant women and children, and exhibit phototoxicity. Nevertheless, the relatively high cost of this combination, as well as the controversial reports of the clinical efficacy, may limit the usefulness of azithromycin in malaria therapy and require an adjustment of previously used treatment regimens.

Desbutyl-benflumetol, a novel antimalarial compound: in vitro activity in fresh isolates of Plasmodium falciparum from Thailand.

Desbutyl-benflumetol (DBB) is a novel antimalarial compound closely related to benflumetol (lumefantrine), of which it is a putative metabolite. The in vitro response of Plasmodium falciparum to DBB was studied in Mae Hong Son and Mae Sot, in northwest Thailand, in 1997 and 1998. In total, 155 fresh isolates were successfully tested using the World Health Organization standard in vitro microtest system (Mark II). The mean 50% effective concentration (EC(50)) and 90% effective concentration of DBB were 6.36 and 31.09 nmol/liter, respectively. The comparison of the activity of DBB and benflumetol yielded a highly significant potency ratio of 4.52, corresponding to a more than four times higher efficacy of DBB. A considerable potency difference was found between isolates from Mae Hong Son and those from Mae Sot, reflecting lesser sensitivity in the area with marked resistance to mefloquine and quinine. This observation is also supported by a highly significant activity correlation with benflumetol (P < 0.001) and to a similar degree with mefloquine (P < 0.001), reflecting a close relationship of DBB with the class II aryl amino alcohol blood schizontocides. A less distinct association was also found with artemisinin, which was significant only at the EC(50) level, and there was no correlation at all with chloroquine. DBB is a promising antimalarial compound that merits further investigation in order to define its practical therapeutic potential.

In vivo-in vitro model for the assessment of clinically relevant antimalarial cross-resistance.

Cross-resistance may be considered one of the most important factors leading to decreased drug susceptibility of Plasmodium falciparum. The study aimed to determine whether clinically relevant cross-sensitivity of P. falciparum existed between artemisinin and mefloquine. Seventy-six patients with falciparum malaria were admitted and treated with artemisinin derivatives. Treatment response parameters were assessed and in vitro drug sensitivity tests were performed with artemisinin, mefloquine, quinine, and chloroquine. Distinct in vitro cross-sensitivity between artemisinin and mefloquine was observed (p = 0.604; P < 0.001). To assess the relevance of this finding for clinical cross-resistance, we used an analytical model based on the relation of in vivo treatment response parameters (fever, parasite and symptom clearance) to a single reference drug with in vitro drug sensitivity data of several other drugs. Artemisinin (R = 0.554; P = 0.009) and mefloquine (R = 0.615; P = 0.002) in vitro drug sensitivities were equally well reflected in the in vivo treatment response to artemisinin, thereby suggesting the clinical relevance of in vitro cross-sensitivity.