Life history correlates of adult size in the malaria vector Anopheles darlingi

Adult dry weights of laboratory-reared Anopheles darlingi were highly correlated with wing lengths, which were used to estimate size variation in natural populations of this species. Significant differences in mean wing lengths of females trapped at baits were detected among collections in the same week at one site, but not between three sites in Brazil and Boliva. Relatively higher variability of wing lengths, compared to collections of other Anopheles (Nyssorhynchus), and platykurtic size distributions in large, single-night collections suggested that An. darlingi females caught at baits emerged from heterogenous larval habitats. No relationship was detected between parous state and the body size of wild-caught females. Adult males and females of laboratory-reared An. darlingi did not differ in body size. This absence of sexual size dimorphism is rare among mosquitoes and has not been noted previously in the genus Anopheles.

The epidemiology of malaria in Prábis, Guinea-Bissau

This article reports upon a community survey of malaria in Prábis, Guinea-Bissau. A house to house census of the population was initially carried out from August to December 1991(rainy season). After completing the census of each village, the population was invited to come, a week later, to a central point, where they were medically examined and finger-prick blood samples were collected for epidemiological characterization of the malaria situation in the area. The blood films of the one single village were used to compare the sensitivity and specificity of Polymerase Chain Reaction (PCR) with optical microscopy detection of parasites. In another village, the occurrence of parasitaemia was compared in children with and without fever. During the dry season, from March to June 1992, the population in each village was again invited to come to a central point. Some of the field procedures were repeated. The study revealed Prábis as an administrative Sector of Guinea-Bissau with endemic malaria, mostly due to Plasmodium falciparum, but with a significant rate of mixed infections. Active transmission occurred throughout the year, but it was more intensive during the rainy season and in the northwestern quadrant of the Sector. The level of endemicity of the villages varied from hypo to holoendemic. The factors associated with the differences among villages included village size and predominant economic activity (closeness to rice fields). The transmission paradigm was, most likely, a mixture of malaria of the African wet Savannah and malaria associated with irrigated paddy fields. PCR proved to be a sensitive method with low specificity during the dry season. Pyraexia of 37.4ºC or higher in children aged 2-9 years is not a sensitive indicator of parasitaemia but, it is highly specific and it has a clinically useful predictive value.

Diagnosis of malaria by acridine orange fluorescent microscopy in an endemic area of Venezuela

Fluorescent (acridine orange) microscopical examination of capillary centrifuged blood (quantitative buffy coat [QBC®] analysis) and Giemsa stained thick blood smears (GTS) were compared for diagnosis of malaria in blood specimens from adults living in malaria transmission areas of the States of Bolivar and Amazonas in southeastern and south Venezuela, respectively. Of a total of 198 GTS examined, 95 subjects (48%) showed parasitaemia. Among the 95 blood films with a positive GTS, 94 were judged positive by the QBC. However, positive QBC tubes were found in 29 out of 103 blood specimens with a negative GTS. Thus, relative to a GTS standard, the sensitivity and specificity of the QBC-test was 99.2% and 72%, respectively. Young trophozoites of Plasmodium vivax and P. falciparum could not be distinguished with certainty. It is confirmed that the QBC offers many advantages compared with the standard diagnosis of malaria parasites, specifically in the speed of staining and ease of interpretation. However, in places where P. falciparum and P. vivax occur, species and stage differentiation should be confirmed with the GTS.

A research agenda for malaria eradication: vaccines.

Vaccines could be a crucial component of efforts to eradicate malaria. Current attempts to develop malaria vaccines are primarily focused on Plasmodium falciparum and are directed towards reducing morbidity and mortality. Continued support for these efforts is essential, but if malaria vaccines are to be used as part of a repertoire of tools for elimination or eradication of malaria, they will need to have an impact on malaria transmission. We introduce the concept of "vaccines that interrupt malaria transmission" (VIMT), which includes not only "classical" transmission-blocking vaccines that target the sexual and mosquito stages but also pre-erythrocytic and asexual stage vaccines that have an effect on transmission. VIMT may also include vaccines that target the vector to disrupt parasite development in the mosquito. Importantly, if eradication is to be achieved, malaria vaccine development efforts will need to target other malaria parasite species, especially Plasmodium vivax, where novel therapeutic vaccines against hypnozoites or preventive vaccines with effect against multiple stages could have enormous impact. A target product profile (TPP) for VIMT is proposed and a research agenda to address current knowledge gaps and develop tools necessary for design and development of VIMT is presented.

Simian malaria at two sites in the Brazilian Amazon - II: Vertical distribution and frequency of anopheline species inside and outside the forest

An anopheline survey was carried out in two simian malaria areas in the Brazilian Amazon, Balbina and Samuel, to determine the potential vectors of Plasmodium brasilianum. The most abundant and/or acrodendrophilic anophelines in the forest and the most likely vector were Anopheles mediopunctatus, An. nuneztovari, An. oswaldoi, An. triannulatus and An. shannoni. An. darlingi and An. marajoara were captured essentially in anthropic habitats outside the forest and are unlikely to be involved in the transmission of P. brasilianum among monkeys within the forests and from monkeys to man in their surroundings in the Amazon.

Antibodies anti Bloodstream and Circumsporozoite Antigens (Plasmodium vivax and Plasmodium malariae/P. brasilianum) in Areas of Very Low Malaria Endemicity in Brazil

During 1992-1994, 33 malaria cases were reported in two regions in Brazil where few sporadic atypical cases occur, most of them in home owners, who are weekenders, while home caretakers live there permanently. Indirect Fluorescent Antibody Test (IFAT), with Plasmodium vivax, and Enzime Linked Immunosorbent Assay (ELISA) with repeat peptides of the circumsporozoite (CS) proteins of the 3 known P. vivax variants and P. malarie/P. brasilianum, were performed on 277 sera, obtained within a 5 to 10 km range of malaria cases. Very rarely did any of these donors recall typical malaria episodes. Blood smears of all but 5 were negative. One of the 5 malaria cases included in our serology was of a home owner, 1 of a permanent resident, 3 from Superintendência de Controle de Endemias employees who went there to capture mosquitoes. In Region 1 the prevalence of IFAT positive sera was 73% and 28% among caretakers, 18% and 9.6% among home owners. In Region 2 (3 localities) no distinction was possible between caretakers and home owners, IFAT positivity being 38%, 28% and 7%. The relative percentage of positive anti-CS repeats ELISA, differed for each of the peptides among localities. Dwellings are in the vicinity of woods, where monkeys are frequently seen. The origin of these malaria cases, geographical differences and high seropositivity is discussed

Humoral Immune Response to the Anti-malaria Vaccine SPf66 in the Colombian Atrato River Region

The immunogenicity of anti-malaria synthetic vaccine SPf66 was tested in a region of the Colombian middle Atrato river. The specific serum antibodies against SPf66 were quantified in vaccinees and placebo injected controls for a two-years period post-immunization. The frequency of individuals showing seroconversion of anti-SPf66 antibodies three months after completion of the immunization schedule was higher in vaccinees than in controls (52.7% and 25.5%, respectively, p<0.01). However, an over than four-fold increase of the specific anti-SPf66 antibody titers was observed only in 1.4% of vaccinees and 0.2% of the controls (p<0.01). The anti-SPf66 antibody titers augmented in vaccinees from first dose application to three months after the third dose, continuously decreasing thereafter to reach below baseline values two years after completion of the immunization schedule. The results show that SPf66 has very low immunogenicity and induces a short term humoral immune response (six months).

Antimalarial Drug Resistance: Surveillance and Molecular Methods for National Malaria Control Programmes

National malaria control programmes have the responsibility to develop a policy for malaria disease management based on a set of defined criteria as efficacy, side effects, costs and compliance. These will fluctuate over time and national guidelines will require periodic re-assessment and revision. Changing a drug policy is a major undertaking that can take several years before being fully operational. The standard methods on which a decision can be taken are the in vivo and the in vitro tests. The latter allow a quantitative measurement of the drug response and the assessment of several drugs at once. However, in terms of drug policy change its results might be difficult to interpret although they may be used as an early warning system for 2nd or 3rd line drugs. The new WHO 14-days in vivo test addresses mainly the problem of treatment failure and of haematological parameters changes in sick children. It gives valuable information on whether a drug still `works'. None of these methods are well suited for large-scale studies. Molecular methods based on detection of mutations in parasite molecules targeted by antimalarial drugs could be attractive tools for surveillance. However, their relationship with in vivo test results needs to be established

Anopheline Species Complexes in Brazil. Current Knowledge of Those Related to Malaria Transmission

A summary of the problems related to the systematics of primary and secondary Brazilian anophelines vectors of malaria is presented.

The separate and combined effects of MHC genotype, parasite clone, and host gender on the course of malaria in mice.

BACKGROUND: The link between host MHC (major histocompatibility complex) genotype and malaria is largely based on correlative data with little or no experimental control of potential confounding factors. We used an experimental mouse model to test for main effects of MHC-haplotypes, MHC heterozygosity, and MHC x parasite clone interactions. We experimentally infected MHC-congenic mice (F2 segregants, homo- and heterozygotes, males and females) with one of two clones of Plasmodium chabaudi and recorded disease progression. RESULTS: We found that MHC haplotype and parasite clone each have a significant influence on the course of the disease, but there was no significant host genotype by parasite genotype interaction. We found no evidence for overdominance nor any other sort of heterozygote advantage or disadvantage. CONCLUSION: When tested under experimental conditions, variation in the MHC can significantly influence the course of malaria. However, MHC heterozygote advantage through overdominance or dominance of resistance cannot be assumed in the case of single-strain infections. Future studies might focus on the interaction between MHC heterozygosity and multiple-clone infections.

Population pharmacokinetics and clinical response for artemether-lumefantrine in pregnant and nonpregnant women with uncomplicated Plasmodium falciparum malaria in Tanzania.

Artemether-lumefantrine (AL) is the first-line treatment for uncomplicated malaria in the second and third trimesters of pregnancy. Its efficacy during pregnancy has recently been challenged due to altered pharmacokinetic (PK) properties in this vulnerable group. The aim of this study was to determine the PK profile of AL in pregnant and nonpregnant women and assess their therapeutic outcome. Thirty-three pregnant women and 22 nonpregnant women with malaria were treated with AL (80/480 mg) twice daily for 3 days. All patients provided five venous plasma samples for drug quantification at random times over 7 days. Inter- and intraindividual variability was assessed, and the effects of covariates were quantified using a nonlinear mixed-effects modeling approach (NONMEM). A one-compartment model with first-order absorption and elimination with linear metabolism from drug to metabolite fitted the data best for both arthemether (AM) and lumefantrine (LF) and their metabolites. Pregnancy status and diarrhea showed a significant influence on LF PK. The relative bioavailability of lumefantrine and its metabolism rate into desmethyl-lumefantrine were, respectively, 34% lower and 78% higher in pregnant women than in nonpregnant patients. The overall PCR-uncorrected treatment failure rates were 18% in pregnant women and 5% in nonpregnant women (odds ratio [OR] = 4.04; P value of 0.22). A high median day 7 lumefantrine concentration was significantly associated with adequate clinical and parasitological response (P = 0.03). The observed reduction in the relative bioavailability of lumefantrine in pregnant women may explain the higher treatment failure in this group, mostly due to lower posttreatment prophylaxis. Hence, a modified treatment regimen of malaria in pregnancy should be considered.

Plasmodium falciparum malaria: rosettes are disrupted by quinine, artemisinin, mefloquine, primaquine, pyrimethamine, chloroquine and proguanil

An assay was developed measuring the disruption of rosettes between Plasmodium falciparuminfected (trophozoites) and uninfected erythrocytes by the antimalarial drugs quinine, artemisinin mefloquine, primaquine, pyrimethamine, chloroquine and proguanil. At 4 hr incubation rosettes were disrupted by all the drugs in a dose dependent manner. Artemisinin and quinine were the most effective anti-malarials at disrupting rosettes at their therapeutic concentrations with South African RSA 14, 15, 17 and The Gambian FCR-3 P. falciparum strains. The least effective drugs were proguanil and chloroquine. A combination of artemisinin and mefloquine was more effective than each drug alone. The combinations of pyrimethamine or primaquine, with quinine disrupted more rosettes than quinine alone. Quinine may be an effective drug in the treatment of severe malaria because the drug efficiently reduces the number of rosettes.

Role of Anopheles (Kerteszia) bellator as malaria vector in Southeastern Brazil (Diptera: Culicidae)

New research concerning Anopheles bellator in the southeast of the State of São Paulo, Brazil, are reported. Adult females of this mosquito showed remarkable endophily and endophagy which was even greater than An. cruzii. The epidemiological role of this anopheline as a malaria vector is discussed.

Delayed mortality and attenuated thrombocytopenia associated with severe malaria in urokinase- and urokinase receptor-deficient mice.

We explored the role of urokinase and tissue-type plasminogen activators (uPA and tPA), as well as the uPA receptor (uPAR; CD87) in mouse severe malaria (SM), using genetically deficient (-/-) mice. The mortality resulting from Plasmodium berghei ANKA infection was delayed in uPA(-/-) and uPAR(-/-) mice but was similar to that of the wild type (+/+) in tPA(-/-) mice. Parasitemia levels were similar in uPA(-/-), uPAR(-/-), and +/+ mice. Production of tumor necrosis factor, as judged from the plasma level and the mRNA levels in brain and lung, was markedly increased by infection in both +/+ and uPAR(-/-) mice. Breakdown of the blood-brain barrier, as evidenced by the leakage of Evans Blue, was similar in +/+ and uPAR(-/-) mice. SM was associated with a profound thrombocytopenia, which was attenuated in uPA(-/-) and uPAR(-/-) mice. Administration of aprotinin, a plasmin antagonist, also delayed mortality and attenuated thrombocytopenia. Platelet trapping in cerebral venules or alveolar capillaries was evident in +/+ mice but absent in uPAR(-/-) mice. In contrast, macrophage sequestration in cerebral venules or alveolar capillaries was evident in both +/+ and uPAR(-/-) mice. Polymorphonuclear leukocyte sequestration in alveolar capillaries was similar in +/+ and uPAR(-/-) mice. These results demonstrate that the uPAR deficiency attenuates the severity of SM, probably by its important role in platelet kinetics and trapping. These results therefore suggest that platelet sequestration contributes to the pathogenesis of SM.

Malaria control in an agro-industrial settlement of Rondônia (Western Amazon Region, Brazil)

A malaria control pilot project was developed in the Urupá agro-industrial farm that is situated in the State of Rondônia (Western Amazon Region, Brazil). Around 180 inhabitants had been surveyed for the past five years. The control measures were based on (1) training a community agent to perform on the spot microscopical diagnosis of malaria and to treat the uncomplicated cases of malaria; (2) limiting the use of insecticides to a short period before the high transmission season. This resulted in a significant reduction in the time between the onset of clinical symptoms and specific chemotherapy which fell from 3.5 to 1.3 days. In relation to the previous three reference years the total number of malaria cases was reduced to 50% in the first year and to 25% in the second year. The introduction of these measures coincided with pronounced reduction in the frequency of Plasmodium falciparum infections but this was less marked for P. vivax infections. In the second year of the pilot experiment there was no P. falciparum transmission on the farm. During the last decade there was a general decrease in the endemicity of malaria in the State of Rondônia. The linear regression coefficient values indicate that the decline was more pronounced in Urupá than in the general municipality and that the falciparum malaria API in Urupá farm is significantly lower than in the general municipality of Candeias were the farm is situated.