dhfr and dhps genotype and sulfadoxine‐pyrimethamine treatment failure in children with falciparum malaria in the Democratic Republic of Congo

Objective To determine the relationship between mutations in dhfr and dhps and SP treatment failure in Plasmodium falciparum malaria in the Democratic Republic of the Congo (DRC). Methods Therapeutic efficacy trial was conducted in Rutshuru, Eastern DRC, between June and September 2002, comparing sulfadoxine‐pyrimethamine (SP), SP plus amodiaquine (AQSP) and artesunate plus SP (ASSP) regimens for treating malaria in children under 5 years old. We genotyped 212 samples for mutations associated with SP resistance and investigated their association with treatment failure. Results In the SP arm, 61% of the subjects experienced treatment failure after 14 days. The failure rate was lower in the combination arms (AQSP: 32%, ASSP: 21%). The dhfr‐108 and dhfr‐51 mutations were nearly universal while 89% of the samples had at least one additional mutation at dhfr‐59, dhps‐437 or dhps‐540. Dhps mutations had a bigger impact on treatment failure in children with high parasite density: for children with a parasite density <45 000 parasites/μl, the risk of treatment failure was 37% for mutations at dhps‐437 and dhps‐540 mutation and 21% for neither mutation [risk difference (RD) = 17%, 95% CI: ?3%, 36%]. In children with a parasite density >45 000 parasites/μl, the treatment failure risk was 58% and 8% for children with both mutations or neither mutation, respectively (RD = 51%, 95% CI: 34%, 67%). Conclusions Dhps‐437 and dhps‐540 are strongly associated with SP treatment failure and should be evaluated further as a method for surveillance of SP‐based therapy in DRC.     

Protective and pathological activity in serum of mice developing resistance to Plasmodium berghei infection

Summary The serum from mice developing resistance against Plasmodium berghei infection using chemotherapeutic treatment has been analysed in vivo and in vitro. During the immunization period pathological as well as protective activities which could be transferred by serum were generated. The pathological activity, which was defined as destruction of erythrocytes in normal recipient mice, was generated early in the immunization procedure, peaked at day 21, and decreased to undetectable levels by day 35. After reinfection of the donor mice the pathological activity reappeared in the serum, and was maintained for at least 56 days. Analysis of the transferred serum samples showed the presence of anti-erythrocyte antibodies (ELISA), but no correlation with the in-vivo anti-erythrocyte effect could be found. The anti-erythrocyte effect of the serum samples indirectly increased the parasitaemia in the recipient mice through the induction of reticulocytosis. The protective effect of the serum samples could only be detected in samples taken from animals beyond day 61 of the immunization procedure. This net protective effect was reflected in a decreased parasitaemia at 7 days after challenge of the recipient mice with P. berghei infected erythrocytes. The protective activity of the serum was correlated with high titres of anti-erythrocyte antibodies. Anti-erythrocyte antibody titres were strongly correlated with titres against heterologous red blood cells as well as total immunoglobulin content of the serum samples, indicative of polyclonal activation of lymphocytes. Except for IgGl, all (sub-) classes were elevated during the immunization procedure, of which IgG3 was abundant. After immunity was obtained these immunoglobulin levels remained high, and the relative amount of IgGl in the serum was restored.     

联合国维和医疗分队防疟实践

疟疾是赴非洲参加联合国维和行动人员致病和致死的主要原因之一。本院参加联合国赴西非某国维和的医疗分队，通过运用预防医学理论和技术，针对具体维和任务区的情况，拟定切实可行的疟疾预防计划，因地适宜的采取综合防疫措施，控制了疟疾的流行，有力地保障了维和任务顺利完成。     

Analysis of the Anopheles gambiae genome using RAPD markers

RAPD analysis technique is used as a rapid and reliable tool for genome analysis in the malaria vector Anopheles gambiae. Using more than eighty different commercially available primers we identified more than sixty different DNA segments that were differentially amplified in different strains of An. gambiae s.s. and An. arabiensis. An estimate of the cytogenetic position of these markers is provided by their hybridization to divisional dot-blot filters. Potentially useful RAPD markers can be cytogenetically mapped with more precision by in situ hybridization and, as they segregate as dominant markers in a Mendelian fashion, they can also be genetically mapped relative to other genes or rearrangements. Finally, we identified markers for their potential use in the identification of different mosquito strains.     

Red cell morphology and malaria anaemia in children with Southeast-Asian ovalocytosis band 3 in Papua New Guinea

Southeast-Asian ovalocytosis (SAO) was diagnosed in children from Madang, Papua New Guinea, by detection of the SAO band 3 gene variant using the polymerase chain reaction. SAO band 3 was present in 16/241 (6.6%) children living in the community and 32/389 (8.2%) children with acute Plasmodium falciparum malaria ( P  = 0.42). SAO band 3 was detected in 8.2% (23/281) of α⁺-thalassaemia homozygotes, 9.4% (20/214) of heterozygotes and 2.4% (2/85) of children with a normal α-globin genotype ( P  = 0.12). The most consistent feature of SAO band 3 on microscopy of thin blood films was red cells with two or more linear or irregularly-shaped pale regions. In children living in the community, these were present in 15 with SAO band 3 (sensitivity 93.8%) and only two normals (specificity 99.1%). The presence of 20% ovalocytosis was a poorer indicator of SAO band 3 (sensitivity 68.8% and specificity 100%). Haematological data were similar in SAO band 3 and normal children. However, in children with acute malaria, haemoglobin levels and red cell counts were significantly lower in SAO band 3 than normal children. The degree of ovalocytosis was lower in children with SAO band 3 during acute malaria, suggesting that a selective loss of ovalocytes may contribute to malaria anaemia in Southeast-Asian ovalocytosis.     

A theoretical framework for the immunoepidemiology of Plasmodium falciparum malaria

Molecular genetic analyses of P. falciparum have led to the cloning and sequencing of a number of antigens that are potential candidates for vaccination against malaria. Seroepidemiological studies in endemic areas have attempted to assess the relative importance of these antigens in protection against malaria. In this paper, we attempt to evaluate the relative contributions of conserved and strain-specific immune responses by modelling their influence of age-specific patterns of infection and disease. The modelling exercises in this paper clearly demonstrate that the observed patterns of age-prevalence are best explained by proposing that the accumulation to a threshold of an immune response against a conserved determinant is required for protection against infection, while ‘anti-disease’ immunity develops more linearly with exposure. This is compatible with the conjecture that the parasite population is structured into several independently transmitted strains, that each confers some degree of ‘anti-disease’ immunity, but does not protect against further infection by the same strain. Within this framework, the average duration of parasitaemia increases with age, as previously encountered strains endure for longer periods at a subclinical level. Indirect evidence for the increase in duration of parasitaemia with age may be obtained from a comparison of age-prevalence curves between dry and rainy seasons. By using mathematical methods to structure epidemiological and immunological information, we provide a coherent theoretical framework for the dissection of the important components of naturally acquired immunity to malaria.     

Nitric oxide synthase activity in malaria-infected mice

Nitric oxide ( NO ) is implicated in a variety of major cellular functions including defence from invasion by microbical pathogens. Evidence has been presented suggesting that it is an important mediator of protection in the early non-specific responses to malaria in mice infected with Plasmodium chabaudi ( Taylor-Robinson et al . 1993 ) . Other data from in vitro studies on the asexual stages of human parasite Plasmodium falciparum indicated that while nitric oxide itself may not be inhibitory to parasite development, its downstream products do have some anti-plasmodial activity ( Rockett et al . 1991 ) and these could be generated by macrophages ( Gyan et al . 1994  ) . Similarly, the sexual phases of both rodent ( Motard et al . 1993 ) and human malaria ( Naotunne et al . 1993 ) are reportedly susceptible to the toxic effects mediated by nitric oxide generated by blood leucocytes in the course of transmission to the mosquito vector.     

间日疟间接荧光抗体试验观察者变异与正常值上限研究

将间日疟阳性血清作系列倍比稀释进行间接荧光抗体试验,不同观察者平行读数或同一观察者先后读数的终点滴度之变异在一个倍比稀释度之内。对无疟疾感染史的正常人群522份血清作间日疟间接荧光抗体试验,其荧光抗体滴度正常值上限按99%位点估计为<1:10。     

Is malaria control a priority? Evidence from Nepal

The research reported here assessed the value of malaria control through a cost-effectiveness study of the vertically-organized malaria control programme in Nepal. It presents a methodological framework for analysing cost-effectiveness which includes resource-saving consequences as well as health consequences. The methods used to collect data on control costs, cases and deaths prevented, treatment costs averted and production gains are described and the assumptions required by the analysis are made explicit. A variety of cost-effectiveness ratios are calculated, sensitivity analysis applied and the policy implications of the results considered. The results from Nepal are compared to estimates for parasitic disease and other health programmes in other countries: it is concluded that the Nepalese programme appears no less cost-effective than many other health interventions. It can also be justified by reference to the population groups benefiting from malaria control.