Prophylactic activity of atovaquone against Plasmodium falciparum in humans.
(17/1919)
The prophylactic antimalarial activity of atovaquone was determined in a randomized, double-blind, placebo-controlled study of healthy volunteers who were challenged by the bite of Plasmodium falciparum-infected Anopheles stephensi. Subjects were randomly assigned to one of three groups: six received seven daily doses of 750 mg of atovaquone, starting the day before challenge; six received a single dose of 250 mg of atovaquone the day before challenge; and four received placebo. Polymerase chain reaction- and culture-confirmed parasitemia developed in all four placebo recipients, but in none of the drug recipients, indicating that either of the atovaquone regimens provides effective prophylaxis (P = 0.005). However, in low-dose recipients, the drug levels by day 6.5 were profoundly subtherapeutic, indicating that parasites were eliminated prior to the establishment of erythrocytic infection. Atovaquone thus protects non-immune subjects against mosquito-transmitted falciparum malaria, and has causal prophylactic activity. (+info)
Cytogenetic evidence for a species complex within Anopheles pseudopunctipennis theobald (Diptera: Culicidae).
(18/1919)
Anopheles pseudopunctipennis was collected from Acapulco, Mexico and Sallee River, Grenada, West Indies and used in cross-mating experiments. Larvae from the cross, Mexico female X Grenada male, died in the third instar. However, adult progeny were obtained from the reciprocal cross Grenada female x Mexico male. These hybrid males had testes with apparently normal appearance but some without viable sperm. Polytene chromosomes obtained from hybrid females exhibited extensive asynapsis of the X chromosomes. Previously undescribed fixed inversion differences between the two populations were noted on the X chromosome. It is concluded that the two populations belong to different species. The Grenada population is designated An. pseudopunctipennis species C, since it is the third taxon recognized in this species complex. (+info)
Gender-related efficacy difference to an extended duration formulation of topical N,N-diethyl-m-toluamide (DEET).
(19/1919)
A clinical trial (n = 120, 60 males and 60 females) was conducted to assess the efficacy of an extended duration tropical insect/arthropod repellent (EDTIAR) topical formulation of N,N-diethyl-m-toluamide (DEET). The amount of EDTIAR (mean +/- confidence interval), applied by participants in accordance with label directions, was not significantly different between females (3.66 +/- 0.32 mg/cm2) and males (3.45 +/- 0.33 mg/cm2). There also was no significant difference in the number of Anopheles stephensi mosquitoes biting the control arm of females or males at 0, 3, 6, 9, and 12 hr. While gender had no effect on feeding, the time of day did effect mosquito feeding with fewer mosquitoes feeding in the afternoon than in the morning or evening. The percent protective efficacy at 0, 3, 6, 9, and 12 hr was 100.0, 99.3, 92.8, 79.7 and 66.3 for females, and 100.0, 100.0, 97.6, 91.9, and 77.5 for males. These data are inconsistent with the EDTIAR label claim that the repellent provides 95% or greater protection against mosquitoes for 12 hr or more under normal use conditions. The results of a multivariate regression analysis indicated that 1) protection decreased linearly as time after application of repellent increased (P < 0.001), 2) individuals who applied higher doses of repellent were better protected against mosquito bites (P < 0.001), 3) females experienced significantly less protection over time than did males (P = 0.005), and 4) the estradiol concentration in the blood had no effect on efficacy of the repellent (P = 0.110). (+info)
High amounts of genetic differentiation between populations of the malaria vector Anopheles arabiensis from West Africa and eastern outer islands.
(20/1919)
Polymorphism at nine microsatellite loci was examined to assess the level of genetic differentiation between four Anopheles arabiensis populations from Senegal, the high plateau of Madagascar, and Reunion and Mauritius islands. Eight of nine loci showed great polymorphism (2-16 alleles/locus) and significant genetic differentiation was revealed between all four populations by F- and R-statistics, with Fst estimates ranging from 0.080 to 0.215 and equivalent Rst values ranging between 0.022 and 0.300. These high amounts of genetic differentiation are discussed in relation to geographic distance including large bodies of water, and history of mosquito settlement, and insecticide use on the islands. The results suggest that historical events of drift rather than mutation are probably the forces generating genetic divergence between these populations, with homogenization of the gene pool by migration being drastically restricted across the ocean. (+info)
Population structure and genetic divergence in Anopheles nuneztovari (Diptera: Culicidae) from Brazil and Colombia.
(21/1919)
Anopheles nuneztovari is considered an important vector of human malaria in several localities in Venezuela and Colombia. Its status as a vector of human malaria is still unresolved in areas of the Brazilian Amazon, in spite of have been found infected with Plasmodium sp.. For a better understanding of the genetic differentiation of populations of A. nuneztovari, electrophoretic analysis using 11 enzymes was performed on four populations from Brazil and two from Colombia. The results showed a strong differentiation for two loci: alpha-glycerophosphate dehydrogenase (alpha-Gpd) and malate dehydrogenase (Mdh) from 16 loci analyzed. Diagnostic loci were not detected. The populations of A. nuneztovari from the Brazilian Amazon showed little genetic structure and low geographic differentiation, based on the F(IS) (0.029), F(ST) (0.070), and genetic distance (0.001-0.032) values. The results of the isozyme analysis do not coincide with the indication of two lineages in the Amazon Basin by analysis of mitochondrial DNA, suggesting that this evolutionary event is recent. The mean F(ST) value (0.324) suggests that there is considerable genetic divergence among populations from the Brazilian Amazon and Colombia. The genetic distance among populations from the Brazilian Amazon and Colombia is ranges from 0.047 to 0.148, with the highest values between the Brazilian Amazon and Sitronela (SIT) (0.125-0.148). These results are consistent with those observed among members of anopheline species complexes. It is suggested that geographic isolation has reduced the gene flow, resulting in the genetic divergence of the SIT population. Dendrogram analysis showed three large groups: one Amazonian and two Colombia, indicating some genetic structuring. The present study is important because it attempted to clarify the taxonomic status of A. nuneztovari and provide a better understanding of the role of this mosquito in transmission of human malaria in northern South America. (+info)
Detection and characterization of a mannan-binding lectin from the mosquito, Anopheles stephensi (Liston).
(22/1919)
Two lectins from the serum of the mosquito, Anopheles stephensi (Liston), with distinct characteristics, were detected by agglutination of various animal erythrocytes. The lectins were developmental stage-specific and/or sex-related. One adult female-specific lectin was identified as mannan-specific, and named mosquito mannan-binding lectin (MBL). MBL cross-reacted immunologically with antibodies against a previously characterized cockroach lectin, Blaberus discoidalis lectin (BDL1), and its activity was almost completely blocked by the antibodies. Mosquito MBL agglutinated erythrocytes from human, sheep, goat and rabbit, but not chicken or mouse, and agglutination was inhibited by mannan and nitrophenol-modified sugar derivatives, but not by simple sugars. Using affinity chromatography with immobilized mannan on Sepharose 6B, the mosquito MBL was partially purified. Purified mosquito MBL shared biochemical properties with BDL1, containing two subunits of molecular mass of 28 and 30 kDa under reducing conditions in SDS/PAGE. Its activity is dependent on Ca(2+), and it is stable at pH 7-9 and at temperatures less than 30 degrees C. (+info)
A retrospective examination of sporozoite- and trophozoite-induced infections with Plasmodium falciparum: development of parasitologic and clinical immunity during primary infection.
(23/1919)
A retrospective analysis was made of the parasitologic and fever records of 318 patients who had been infected with the El Limon, Santee Cooper, or McLendon strains of Plasmodium falciparum for treatment of neurosyphilis between 1940 and 1963 to determine the development of parasitologic and clinical immunity during primary infection. The presence of fever > or = 101 degrees F and > or = 104 degrees F, asexual parasite counts > or = 1,000 and > or = 10,000/microl, and gametocyte counts > or = 100/microl and > or = 1,000/microl are presented. The frequency of fever (number of patients with fever/number of patients remaining in study) for the first 100 days of patent parasitemia, the frequency of parasite counts > or = 1,000 and > or = 10,000/microl during the first 100 days of patent parasitemia, and the frequency of gametocyte counts > or = 100 and > or = 1,000/microl during the first 100 days of patent parasitemia are presented for 4 groups of patients: 1) sporozoite-induced and 2) trophozoite-induced infections requiring treatment during their primary attack, and 3) sporozoite-induced and 4) trophozoite-induced infections not requiring treatment during the primary attack. For each sporozoite-induced infection, the route of inoculation (bites or syringe), the species of mosquito used, the number of mosquito glands or bites, the intensity of salivary gland infection, and the length of the prepatent period are recorded. Prepatent periods for 109 sporozoite-induced infections ranged from 6 to 28 days. Patients with parasitologic or clinical findings that required suppressive, but non-curative treatment, during the primary attack had higher frequency of fever, parasitemia, and gametocytemia than patients not so treated. Fever was concentrated in the first 2 weeks of patent parasitemia although instances of fever were reported >100 days after infection. High-density parasitemia was also concentrated early in the infection; instances of parasite counts > or = 10,000/microl occurred > 75 days after infection. In conclusion, immunity to infection with P. falciparum was shown to develop rapidly. Following primary infection, clinical and parasitologic immunity was evident within 2-3 weeks following the detection of parasites in the peripheral circulation. (+info)
A retrospective examination of secondary sporozoite- and trophozoite-induced infections with Plasmodium falciparum: development of parasitologic and clinical immunity following secondary infection.
(24/1919)
A retrospective study was made of clinical records to determine parasitemia and episodes of fever of 59 patients reinfected with Plasmodium falciparum for treatment of neurosyphilis, which was considered standard medical care at the time. Records were collected at the National Institutes of Health laboratories in Columbia, South Carolina and Milledgeville, Georgia during the period 1940 to 1963. Nineteen patients were infected via the bites of Anopheles albimanus, An. quadrimaculatus, or An. freeborni mosquitoes; the median prepatent period was 11.5 days. It was evident that clinical immunity, as measured by the frequency of fever, particularly high intensity fever (> or = 104 degrees F), was increased following reinfection. The parasitologic immunity, as measured by the frequency of asexual parasite counts and gametocyte counts, was also evident. In general, in secondary infections with homologous and/or heterologous strains of P. falciparum, fever episodes > or = 101 degrees F and > or = 104 degrees F were reduced in number, parasitemia was reduced, and gametocyte production was reduced. However, despite long courses of parasitemia during their primary infections, most patients developed fever and, in some cases, high-density parasitemia and gametocytemia following reinfection. The intensity of the secondary response did not appear to be associated with the length of the previous course of parasitemia. In addition, current infection with heterologous strain parasites did not prevent the development of fever or higher density parasite counts following imposition of the new strain of parasite. (+info)