Abstract. The factors contributing to anemia in falciparum malaria were characterized in 4,007 prospectively studied patients on the western border of Thailand. Of these, 727 patients (18%) presented with anemia (haematocrit Ͻ 30%), and 1% (55 of 5,253) required blood transfusion. The following were found to be independent risk factors for anemia at admission: age Ͻ 5 years, a palpable spleen, a palpable liver, recrudescent infections, being female, a prolonged history of illness (Ͼ 2 days) before admission, and pure Plasmodium falciparum infections rather than mixed P. falciparum and Plasmodium vivax infections. The mean maximum fractional fall in hematocrit after antimalarial treatment was 14.1% of the baseline value (95% confidence interval [CI], 13.6-14.6). This reduction was significantly greater in young children (aged Ͻ 5 years) and in patients with a prolonged illness, high parasitemia, or delayed parasite clearance. Loss of parasitized erythrocytes accounted for Ͻ 10% of overall red blood cell loss. Hematological recovery was usually complete within 6 weeks, but it was slower in patients who were anemic at admission (adjusted hazards ratio [AHR], 1.9, 95% CI, 1.5-2.3), and those whose infections recrudesced (AHR, 1.2, 95% CI, 1.01-1.5). Half the patients with treatment failure were anemic at 6 weeks compared with 19% of successfully treated patients (relative risk, 2.8, 95% CI, 2.0-3.8). Patients coinfected with P. vivax (16% of the total) were 1.8 (95% CI, 1.2-2.6) times less likely to become anemic and recovered 1.3 (95% CI, 1.0-1.5) times faster than those with P. falciparum only. Anemia is related to drug resistance and treatment failure in uncomplicated malaria. Children aged Ͻ 5 years of age were more likely than older children or adults to become anemic. Coinfection with P. vivax attenuates the anemia of falciparum malaria, presumably by modifying the severity of the infection.

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Abstract. The factors affecting the development of patent Plasmodium falciparum gametocytemia were assessed in 5,682 patients entered prospectively into a series of antimalarial drug trials conducted in an area of low and seasonal transmission on the western border of Thailand. Of the 4,565 patients with admission thick smear assessments, 110 (2.4%) had gametocytemia. During the follow-up period 170 (3%) of all patients developed patent gametocytemia, which in 89% had developed by day 14 following treatment. In a multiple logistic regression model five factors were found to be independent risk factors at presentation for the development or persistence of gametocytemia during follow up; patent gametocytemia on admission (adjusted odds ratio [AOR] ϭ 7.8, 95% confidence interval [CI] ϭ 3.7-16, P Ͻ 0.001), anemia (hematocrit Ͻ30%) (AOR ϭ 3.9, 95% CI ϭ 2.3-6.5, P Ͻ 0.001), no coincident P. vivax malaria (AOR ϭ 3.5, 95% CI ϭ 1.04-11.5, P Ͻ 0.04), presentation with a recrudescent infection (AOR ϭ 2.3, 95% CI ϭ 1.3-4.1, P Ͻ 0.004), and a history of illness longer than two days (AOR ϭ 3.3, 95% CI ϭ 1.7-6.6, P Ͻ 0.001). Patients whose infections responded slowly to treatment or recrudesced subsequently were also more likely to carry gametocytes than those who responded rapidly or were cured (relative risks ϭ 1.9, 95% CI ϭ 1.3-2.7 and 2.8, 95% CI ϭ 2.0-4.0, respectively; P Ͻ 0.001). These data provide further evidence of important epidemiologic interactions between P. falciparum and P. vivax, and drug resistance and transmission potential.The life cycle of Plasmodium falciparum is dependent upon the production of viable sexual stages of the parasite and their appearance in sufficient numbers in the peripheral blood of the human host. These gametocytes can then be transmitted to a feeding anopheline mosquito and on to a new human host, thus completing the life cycle of the malaria parasite. In contrast to the treatment of the three other species of human malaria, most of the antimalarial drugs used to treat the asexual stages of P. falciparum malaria have little or no effects on the viability of mature gametocytes. The rate of production of gametocytes is influenced considerably by host factors, notably immunity, 1 and this may have significant epidemiologic consequences. Integrated malaria control programs that aim to reduce malaria transmission are often based on identifying those individuals most likely to transmit malaria. We investigated the factors that influence the production of gametocytes following uncomplicated falciparum malaria in an area where there is a high prevalence of multidrug resistance, and a relatively low level of transmission and consequent background immunity. METHODSStudy site. The study took place between 1990 and 1995 in patients living in a camp for displaced person of the Karen ethnic minority situated in an area of malarious hill forest on the western border of Thailand. During the five-year period, a series of 18 antimalarial drug studies were conducted to determine the optimum treatment of ...

The predisposing factors, clinical presentation, and outcome of severe malaria in a Karen community living on the western border of Thailand were studied over a period of 2 years. This was an area of low malaria transmission (approximately one infection per person per year), where asymptomatic malaria is unusual. In a population of 4728 persons, who had good access to facilities for malaria diagnosis and treatment, there were 2573 cases of vivax malaria, none of whom died, and there were 5776 cases of falciparum malaria, 303 (5%) of whom had severe malaria and 11 (0.2%) of whom died-a case fatality rate of 1.9 per 1000 (95% confidence interval [CI] 1.0-3.3). The risks of developing severe malaria and dying declined steadily with age. The clinical features of severe malaria differed between children and adults. Anaemia was more common in children under 5 years old than in older children and adults, whereas the incidence of cerebral involvement increased with age. Severe malaria was 3 times (95% CI 1.4-6.2) more common in pregnant than in non-pregnant women, but was 4.2 times (95% CI 2.3-7.9) less common in patients with mixed Plasmodium falciparum and P. vivax infections than in those with P. falciparum alone, suggesting that P. vivax may attenuate the severity of P. falciparum malaria.

Antimicrobial resistance poses a growing threat to public health and the provision of health care. Its surveillance should provide up-to-date and relevant information to monitor the appropriateness of therapy guidelines, antibiotic formulary, antibiotic stewardship programmes, public health interventions, infection control policies, and antimicrobial development. In Europe, although the European Antimicrobial Resistance Surveillance Network provides annual reports on monitored resistant bacteria, national surveillance efforts are still fragmented and heterogeneous, and have substantial structural problems and issues with laboratory data. Most incidence and prevalence data cannot be linked with relevant epidemiological, clinical, or outcome data. Genetic typing, to establish whether trends of antimicrobial resistance are caused by spread of resistant strains or by transfer of resistance determinants among different strains and species, is not routinely done. Furthermore, laboratory-based surveillance using only clinical samples is not likely to be useful as an early warning system for emerging pathogens and resistance mechanisms. Insufficient coordination of surveillance systems of human antimicrobial resistance with animal surveillance systems is even more concerning. Because results from food surveillance are considered commercially sensitive, they are rarely released publicly by regulators. Inaccurate or incomplete surveillance data delay a translational approach to the threat of antimicrobial resistance and inhibit the identification of relevant target microorganisms and populations for research and the revitalisation of dormant drug-discovery programmes. High-quality, comprehensive, and real-time surveillance data are essential to reduce the burden of antimicrobial resistance. Improvement of national antimicrobial resistance surveillance systems and better alignment between human and veterinary surveillance systems in Europe must become a scientific and political priority, coordinated with international stakeholders within a global approach to reduce the burden of antimicrobial resistance.

From November 1991 to November 1992 a prospective, descriptive study of malaria epidemiology was conducted in a Karen population on the western border of Thailand. Two study groups were selected at random and more than 80% of the subjects were followed for one year. In Group 1, comprising 249 schoolchildren (aged 4-15 years), daily surveillance for illness was combined with fortnightly malaria surveys. These children experienced 1.5 parasitaemic infections per child-year (95% confidence interval [CI] 1.3-1.7), of which 68% (193/285) were symptomatic (Plasmodium falciparum 84%, P. vivax 57%). The estimated pyrogenic densities were 1460/microL for P. falciparum and 181/microL for P. vivax. In Group 2, comprising subjects of all age from 428 households, malaria was diagnosed during two-monthly surveys, at weekly home visits, and otherwise by passive case detection. Malaria and splenomegaly prevalence rates were low in all age groups (spleen index 2-9%; P. falciparum prevalence rate 1-4%; P. vivax 1-6%). Group 2 subjects had 1.0 infections per person-year (95% CI 0.9-1.1), most of which were symptomatic (312/357; 87%). Malaria infections clustered in households. Overall, P. vivax caused 53% and P. falciparum 37% of the infections (10% were mixed), but whereas P. vivax was most common in young children, with a decline in incidence with increasing age, P. falciparum incidence rates rose with age to a peak incidence between 20 and 29 years, although the risk of developing a severe malaria decreased with increasing age. There was no death from malaria during the study. P. falciparum infections were more common in males, subjects with a history of malaria before the study, and in those who had travelled outside their village. These findings suggest a higher transmission rate for P. vivax than P. falciparum, although adults still suffered symptomatic malaria due to both species. The 2 malaria parasites found in this area contribute approximately 50% of infections each, but their clinical epidemiology is very different.

Dengue is the most important mosquito-borne, human viral disease in many tropical and sub-tropical areas. In India the disease has been essentially described in the form of case series. We reviewed the epidemiology of dengue in India to improve understanding of its evolution in the last 50 years and support the development of effective local prevention and control measures. Early outbreak reports showed a classic epidemic pattern of transmission with sporadic outbreaks, with low to moderate numbers of cases, usually localized to urban centres and neighbouring regions, but occasionally spreading and causing larger epidemics. Trends in recent decades include: larger and more frequent outbreaks; geographic expansion of endemic transmission; spread of the disease from urban to peri-urban and rural areas; an increasing proportion of severe cases and deaths; and progression to hyperendemicity, particularly in large urban areas. The global picture of dengue in India is currently that of a largely endemic country. Understanding demographic differences in infection rates and severity of dengue has important implications for the planning and implementation of effective public health prevention and control measures and targeting of future vaccination campaigns.