Stress, drugs and the evolution of reproductive restraint in malaria parasites.

Life-history theory predicts that sexually reproducing organisms have evolved to resolve resource-allocation trade-offs between growth/survival versus reproduction, and current versus future reproduction. Malaria parasites replicate asexually in their vertebrate hosts, but must reproduce sexually to infect vectors and be transmitted to new hosts. As different specialized stages are required for these functions, the division of resources between these life-history components is a fundamental evolutionary problem. Here, we test how drug-sensitive and drug-resistant isolates of the human malaria parasite Plasmodium falciparum resolve the trade-off between in-host replication and between-host transmission when exposed to treatment with anti-malarial drugs. Previous studies have shown that parasites increase their investment in sexual stages when exposed to stressful conditions, such as drugs. However, we demonstrate that sensitive parasites facultatively decrease their investment in sexual stages when exposed to drugs. In contrast to previous studies, we tested parasites from a region where treatment with anti-malarial drugs is common and transmission is seasonal. We hypothesize that when exposed to drugs, parasites invest in their survival and future transmission by diverting resources from reproduction to replication. Furthermore, as drug-resistant parasites did not adjust their investment when exposed to drugs, we suggest that parasites respond to changes in their proliferation (state) rather the presence of drugs.

Development and Use of Checklists for Assessment of Medical Students in Clinical Examinations on Real Patients: A Preliminary Study

Background Clinical performance examinations (CPE) are important methods for assessing medical students and postgraduate medical trainees. Unfortunately; assessment (scoring) in these exams as it is practiced in most medical schools is based mainly on the general impression and level of experience of the examiner. Hence; it has the disadvantage of being non-structured; subjective; and sometimes highly biased. The objective of this study was to develop objective structured tools (checklists); use them in the clinical examination; and to compare their scores to those given by the conventional way. Methods Case-specific checklists were developed for some common long and short clinical examination cases. These were tried in the final undergraduate surgery exam at Alazhari University; August 2008. Scores (marks) given to the same student; using the conventional and the checklist systems were compared using the chi square and correlation statistics. Questionnaires were filled by the examiners after using the checklists. Results Checklist and conventional scores were strongly correlated in the long case exams. A significant difference between the scores was; however; noted in the short case exams. Care should be taken in interpretation because of the small number of data. Evaluators felt that the checklist system was more objective and structured and hence fairer than the conventional method. Although checklist final scores took a bit longer time to calculate; that was not significant practically. examiners gave valuable feedback regarding the construction and the use of checklists. Conclusion The use of checklists in the clinical examination was more objective; more structured; and more accurate than the conventional method. The development of checklists requires hard team work and frequent updating and use to develop experience. We propose using checklists as alternative tools of assessment with many advantages over the conventional method; and to prepare the examination culture to adopt the OSCE

Increased density but not prevalence of gametocytes following drug treatment of Plasmodium falciparum.

We monitored post-treatment Plasmodium falciparum among patients treated with chloroquine (CQ) and sulfadoxine-pyrimethamine (SP; Fansidar in a village in eastern Sudan. Parasites were examined on day 0 (pre-treatment), day 7, day 14 and day 21 (post-treatment) during the transmission season. A further sample was taken 2 months later (day 80) at the start of the dry season. Asexual forms and gametocytes were detected by microscopy, and reverse transcriptase polymerase chain reaction (RT-PCR) was used to detect expression of gametocyte-specific proteins pfs 25 and pfg 377. Gametocyte carriage, as revealed by microscopy, increased significantly following CQ and SP treatment, reaching a maximum between days 7 and 14. When measured by RT-PCR, however, there was no significant difference in gametocyte rate between day 0 and days 7 or 14. RT-PCR gametocyte rates dropped dramatically by day 80 post treatment but were still 33% and 8% in the CQ- and SP-treated group at this time. Alleles associated with drug resistance of P. falciparum to chloroquine (the chloroquine resistance transporter, pfcrt, and multidrug resistance, pfmdr1) and to pyrimethamine (dihydrofolate reductase, dhfr) were seen at a high frequency at the beginning of treatment and increased further through time following both drug treatments. Infections with drug-resistant parasites tended to have higher gametocyte prevalence than drug-sensitive infections.

Use of Video-Projected Structured Clinical Examination (ViPSCE) instead of the traditional oral (Viva) examination in the assessment of final year medical students.

CONTEXT & BACKGROUND: Assessment of medical students using the traditional oral (viva) system has been marred by being highly subjective, non-structured, and biased. The use of the objective structured clinical examination (OSCE) would circumvent these disadvantages. The OSCE is, however, costly and time-consuming particularly if used for assessment of large numbers of students. The need for another form of examination that enjoys the advantages of the OSCE while avoiding its disadvantages in the face of limited resources has been the inspiration behind this innovative approach. OBJECTIVES: (1) To identify the characteristics of the new Video-Projected Structured Clinical Examination (ViPSCE). (2) To compare the acceptability of ViPSCE and OSCE by students and tutors. (3) To compare the time-effectiveness of ViPSCE and OSCE. METHODS: We used a slide video projection to assess the surgical knowledge, problem solving and management abilities of 112 final year medical students at Alazhari University, Khartoum, Sudan. Students completed evaluation forms at the end of the examination. RESULTS: The administration of the ViPSCE was smooth and straightforward. Feedback of the students showed that they preferred the ViPSCE to both traditional oral (viva) examination and OSCE. The examination time was 2 hours using video projection compared to the 6 hours that it used to take a class of 112 students to complete a classical OSCE. CONCLUSION: The ViPSCE is a better replacement for the traditional oral exam. It is much less time- consuming than traditional OSCE.

Evolution of drug-resistance genes in Plasmodium falciparum in an area of seasonal malaria transmission in Eastern Sudan.

We investigated the evolution of drug-resistant Plasmodium falciparum in a village in eastern Sudan. The frequencies of alleles of 4 genes thought to be determinants of drug resistance were monitored from 1990 through 2001. Changes in frequencies of drug-resistance genes between wet and dry seasons were monitored from 1998 through 2000. Parasites were also typed for 3 putatively neutral microsatellite loci. No significant variation in frequencies was observed for the microsatellite loci over the whole study period or between seasons. However, genes involved in resistance to chloroquine showed consistent, significant increases in frequencies over time (rate of annual increase, 0.027/year for pfcrt and 0.018/year for pfmdr1). Genes involved in resistance to the second-line drug used in the area (Fansidar) remained at low frequencies between 1990 and 1993 but increased dramatically between 1998 and 2000, which is consistent with the advent of Fansidar usage during this period. For mutant alleles of the primary drug-resistance targets for chloroquine and pyrimethamine, higher frequencies were seen during the dry season than during the wet season. This cyclical fluctuation in drug-resistance genes most likely reflects seasonal variation in drug pressure and differences in the fitness of resistant and sensitive parasites.

Dynamics of gametocytes among Plasmodium falciparum clones in natural infections in an area of highly seasonal transmission.

The dynamics of gametocyte production in Plasmodium falciparum clones were studied in inhabitants of an area of highly seasonal malaria transmission in eastern Sudan. Reverse-transcriptase polymerase chain reaction was used to detect expression of 2 genes that encode gametocyte-specific proteins, pfs25 and pfg377, in parasites sampled from individuals throughout one year. Some patients who acquired infections during the wet season were found to harbor subpatent gametocytemia through the following dry season in the apparent absence of mosquito transmission. Genotyping of parasites in multiclonal infections showed considerable fluctuation of gametocyte production by individual clones. The gametocytes present at the end of the dry season provide the most probable source of the genetically complex cyclical malaria outbreaks following the rainy season in this region.