Increased Plasmodium falciparum gametocyte production in mixed infections with P. malariae

Plasmodium falciparum and P. malariae occur endemically in many parts of Africa. Observations from malariotherapy patients suggest that co-infection with P. malariae may increase P. falciparum gametocyte production. We determined P. falciparum gametocyte prevalence and density by quantitative nucleic acid sequence-based amplification (QT-NASBA) after antimalarial treatment of Kenyan children with either P. falciparum mono-infection or P. falciparum and P. malariae mixed infection. In addition, we analyzed the relationship between mixed species infections and microscopic P. falciparum gametocyte prevalence in three datasets from previously published studies. In Kenyan children, QT-NASBA gametocyte density was increased in mixed species infections (P = 0.03). We also observed higher microscopic prevalences of P. falciparum gametocytes in mixed species infections in studies from Tanzania and Kenya (odds ratio = 2.15, 95% confidence interval = 0.99-4.65 and 2.39, 1.58-3.63) but not in a study from Nigeria. These data suggest that co-infection with P. malariae is correlated with increased P. falciparum gametocytemia.     

Prospective risk of morbidity in relation to malaria infection in an area of high endemicity of multiple species of Plasmodium.

In an area of Papua New Guinea with high prevalence of Plasmodium falciparum (39.6%), Plasmodium vivax (18.3%), and Plasmodium malariae (13.8%), cross-sectional analysis found P. falciparum infection to be independent of the other species despite heterogeneities in transmission. Plasmodium vivax and P. malariae infections were negatively correlated. Plasmodium malariae infection was positively associated with homologous infection four months previously and with prior P. falciparum, but not P. vivax infection. There were no other indications that any Plasmodium species protected against heterologous infection. Prospective analysis of health-center morbidity supported the idea that P. malariae infection protects against disease, but indicated greater protection against non-malaria than P. falciparum-associated fevers. Plasmodium vivax appeared to protect against P. falciparum disease but not against other forms of morbidity. Covariate adjustment had considerable effects on estimated relationships between species, and confounding variables may account for many differences among reports of inter-species interactions in human malaria.     

Transmission of mixed Plasmodium species and Plasmodium falciparum genotypes

We studied malaria transmission by comparing parasite populations in humans and mosquito vectors at the household level. Blood samples were collected from all inhabitants for microscopic detection of gametocytes and polymerase chain reaction analysis. The next morning, blood-fed resting mosquitoes were collected inside the bed nets used by the individuals surveyed the previous afternoon. After 8 days of maintenance, mosquitoes were dissected, and midguts and salivary glands were recovered for polymerase chain reaction analysis. Results showed that parasite distribution was the same in the 2 hosts when compared at each household but was different when whole populations were analyzed. Different associations of Plasmodium species seem to occur in humans (Plasmodium falciparum/Plasmodium malariae) and mosquitoes (P. falciparum/Plasmodium ovale). Regarding P. falciparum infections, a higher proportion of single-genotype infections and less allele diversity are observed in mosquitoes than in humans.     

巢式PCR扩增SSU rRNA基因确诊1例三日疟原虫感染

目的 通过巢式PCR扩增18SSU rRNA基因片段确诊三日疟原虫的感染,减少三日疟的漏诊和误诊.方法 采用18SSU rRNA基因片段,通过巢式PCR方法,用镜检确诊的间日疟和恶性疟滤纸血样本进行对照,检测1例可疑疟疾患者滤纸血样本.结果 通过种间特异性引物的巢式PCR扩增后,间日疟及恶性疟确诊样本均扩增出相应的12...     

Plasmodium malariae in East Timor

A community-based rainy-season malaria prevalence survey was conducted in Bobonaro district, in recently independent East Timor, in 2001. Although the survey was primarily aimed at defining the prevalence of Plasmodium falciparum and P. vivax, six individuals with P. malariae infection were identified (prevalence 0.57%). We believe these are the first reported cases of P. malariae from the island of Timor.     

Short report: increased susceptibility to Plasmodium malariae in pregnant alpha(+)-thalassemic women.

The influence of alpha(+)-thalassemia on malaria in pregnancy was assessed in a cross-sectional study of 530 women in Ghana. Plasmodial infections, alpha(+)-thalassemia, serum levels of C-reactive protein, and antimalarial drugs in urine were determined. The alpha-globin genotypes did not correlate with the prevalence of Plasmodium falciparum-infection and parasite densities. However, Plasmodium malariae tended to be more frequent in alpha(+)-thalassemic women (P = 0.05). Excluding women with residual antimalarials, a significant excess of P. malariae was observed in alpha(+)-thalassemic individuals. Febrile responses (P = 0.05) and inflammation (CRP > 0.6 mg/dl, P = 0.06) appeared to be less common in infected alpha(+)-thalassemic women and were also comparatively rare in parasitemic individuals who harbored double species infections with P. falciparum and P. malariae. Plasmodium malariae may influence the pathogenesis of falciparum malaria leading to a low prevalence of inflammation and febrile responses in alpha(+)-thalassemic women.     

Plasmodium malariae--a report of three cases.

Kasaragod District of Kerala state has never reported cases of Plasmodium malariae. During September 1999-March 2000 a total of 52 slides were reported as positive for P. vivax, P. falciparum and mixed infection. The expert team cross-checked these positive slides and three were found positive for P. malariae which were reported as P. vivax. All these had similar clinical features and were either imported cases from endemic areas or local population who visited endemic areas or by persons who came in as construction workers.     

Treatment of an acute case of Plasmodium malariae malaria with mefloquine

Mefloquine, a new antimalarial which has been effective in curing malaria due to Plasmodium falciparum and P. vivax, was used for the first time in a patient infected with P. malariae. Treatment was successful, and the relatively long parasite clearance time and fever clearance time were probably characteristic of P. malariae rather than true drug resistance.     

Ultrastructure of human erythrocytes infected with Plasmodium ovale

Ultrastructural changes of the human erythrocytes infected with Plasmodium ovale were studied, and differences of P. ovale from other human malarial parasites were discussed. Four characteristic morphological alterations were observed on the host cells: caveola-vesicle complex, excrescence, nodule, and cytoplasmic cleft. Caveola-vesicle complexes consisted of caveolae surrounded by vesicles in an alveolar fashion and were formed along the host cell plasmalemma. Similar complexes have been reported previously in P. vivax but not in P. falciparum and P. malariae. This complex probably corresponds to a Schüffner's dot. Excrescences similar to those observed by others on the host cell membrane in P. falciparum and P. malariae were observed also in P. ovale. The excrescences in P. ovale, as in P. falciparum, were limited to the erythrocytes infected by asexual parasites, whereas the excrescences in P. malariae have been demonstrated on erythrocytes with asexual parasites and gametocytes. Nodules were observed on the erythrocytes infected with asexual parasites of P. ovale. Structures such as the nodule have not been described previously in the erythrocytes infected with any other species of malarial parasite. Clefts within the cytoplasm of the host erythrocytes were present in P. ovale, as in all other malarial parasites.     

Rapid diagnostic devices for malaria: field evaluation of a new prototype immunochromatographic assay for the detection of Plasmodium falciparum and non-falciparum Plasmodium

The NOW ICT Malaria P.f./P.v. for Whole Blood (Binax, Inc., Portland, ME) is a new malaria rapid diagnostic device that represents a technical advance over previous assays, such as ICT Malaria P.f./P.v. and ICT Malaria P.f.. We evaluated this device in March 2001 in symptomatic patients at malaria clinics in Maesod, Thailand. Microscopic examination of Giemsa-stained blood smears was the reference standard. In 246 patients, microscopy showed 32 (13.0%) infected with Plasmodium falciparum, 63 (25.6%) with P. vivax, 6 (2.4%) with mixed infections of P. falciparum and P. vivax, 5 (2.0%) with P. malariae, and 140 (56.9%) negative. Sensitivity for P. falciparum was 100% and specificity was 96.2% (200 of 208; 95% confidence interval [CI] = 92-98). For P. vivax, sensitivity was 87.3% (55 of 63; 95% CI = 77-93) and specificity was 97.7% (173 of 177; 95% CI = 95-99), but all the four false-positive results were microscopically positive for P. malariae; thus, specificity for non-falciparum Plasmodium was 100%. These results suggest improved performance over NOW ICT predecessors.     

Significance of circumsporozoite-specific antibody in the natural transmission of Plasmodium falciparum, Plasmodium vivax, and Plasmodium malariae in an aboriginal (Orang Asli) population of central peninsula Malaysia

Two hundred and seventy-five Orang Asli volunteers living in nine villages in the Pos Legap Valley of Perak State, peninsular Malaysia, participated in a prospective study designed to characterize the epidemiological, parasitological, and entomological characteristics of Plasmodium falciparum, P. vivax, and P. malariae malaria transmission. Prevalence rates for the three plasmodial species at initiation of the study ranged from 56% in the 0-4-year-old age group to 0% in individuals over the age of 40. Entomological surveys were conducted, enabling us to determine mosquito salivary gland-positive rates and entomological inoculation rates of 1.2 infectious mosquito bites per person per month for P. falciparum, 2.4 for P. vivax, and 0.3 for P. malariae. Cumulative incidence rates over the 16 weeks of the study, following radical cure of all volunteers, were 22.5% for P. falciparum, 12.7% for P. vivax, and 1.5% for P. malariae. The median baseline antibody titer against the immunodominant repetitive B cell epitope of P. falciparum or P. vivax circumsporozoite protein was significantly higher for volunteers who did not become parasitemic. Volunteers were selected for further study if they had evidence of being challenged with P. falciparum sporozoites during the study, based on a two-fold or greater increase in antibody titer against the immunodominant repetitive B cell epitope of the circumsporozoite protein. Resistance to infection was seen in six of 10 individuals who had high (greater than 25 OD units) baseline ELISA titers, compared with only three of 24 individuals who had low baseline ELISA titers (chi 2 P less than 0.02). A similar analysis for P. vivax did not show a significant correlation.     

An antigenic determinant which is variant in a population of Plasmodium falciparum is present in isolates of Plasmodium malariae

A monoclonal antibody that is directed against an antigenic determinant which is variant in a population of Plasmodium falciparum also reacts with Plasmodium malariae.     

Monoclonal antibody-based enzyme-linked immunosorbent assay (ELISA) for detection of Plasmodium malariae sporozoites in mosquitoes

A monoclonal antibody specific for a repeated epitope of the circumsporozoite protein of Plasmodium malariae sporozoites has been used to develop a two-site, single antibody-based enzyme-linked immunosorbent assay that can detect P. malariae sporozoites in mosquitoes. The assay uses a purified monoclonal antibody produced against sporozoites of the Uganda I/CDC strain of P. malariae to capture the antigen and the same monoclonal antibody labeled with horseradish peroxidase as the detector. Sporozoites have been detected in laboratory-infected mosquitoes stored at room temperature in the presence of a desiccant for as long as 18 months. The detection limit of the assay is approximately 50 P. malariae sporozoites per test well. Cross-reaction has not been observed with mosquitoes infected with P. falciparum, P. vivax, or P. ovale sporozoites.     

Transfusion-transmitted malaria: case report of asymptomatic donor harboring Plasmodium malariae

Malaria in Brazil is endemic in the Amazon region, but autochthonous cases with low parasitaemia occur in the Atlantic Forest area of the country. According to Brazilian legislation no test is mandatory for blood donors from non-endemic areas. However if they have traveled to malaria transmission regions they are deferred for six months before they can donate. This report describes a transfusion-transmitted malaria case in Sao Paulo, Brazil, where one recipient received infected blood and developed the disease. He lived in Sao Paulo and had no previous transfusion or trips to endemic areas, including those of low endemicity, such as Atlantic Forest. Thick blood smears confirmed Plasmodium malariae. All donors lived in Sao Paulo and one of them (Donor 045-0) showed positive hemoscopy and PCR. This asymptomatic donor had traveled to Juquia, in the Atlantic Forest area of S ao Paulo State, where sporadic cases of autochthonous malaria are described. DNA assay revealed P. malariae in the donor's (Donor 045-0) blood. Serum archives of the recipient and of all blood donors were analyzed by ELISA using both P. vivax and P. falciparum antigens, and IFAT with P. malariae. Donor 045-0's serum was P. malariae IFAT positive and the P. vivax ELISA was reactive. In addition, two out of 44 donors' archive sera were also P. vivax ELISA reactive. All sera were P. falciparum ELISA negative. This case suggests the need of reviewing donor selection criteria and deferral strategies to prevent possible cases of transfusion-transmitted malaria.     

Plasmodium brasilianum antigen for use in the indirect hemagglutination test.

Antigen was prepared from Plasmodium brasilianum harvested from an infected spider monkey. This antigen was attached to aldehyde-fixed, human type O cells, and was tested against sera from human cases of P. malaria, P. vivax, P. falciparum, and P. ovale infection, and sera from noninfected persons. At dilutions of 1:16 or greater the antigen failed to react in sera from noninfected persons. It reacted at titers of 16 or above with sera from 85% of the persons with P. malariae infection, 83% with P. vivax infection, 70% with P. falciparum infection, and 70% with P. ovale infection.     

Extended clearance time after treatment of infections with Plasmodium malariae may not be indicative of resistance to chloroquine

A retrospective examination was made of archival data on the response of Plasmodium malariae infections in humans to chloroquine. The clearance time for P. malariae was longer than that for P. falciparum and P. vivax. Of 100 P. malariae-infected patients treated with 1,500 mg of chloroquine given over 3 days, 15 had detectable parasites for 7 days, 4 for 10 days, and 1 for 15 days after treatment. Of 17 patients treated intramuscularly with 450 mg of dihydrochloroquine, parasites persisted in 1 patient for 11 days. Of patients with chloroquine-sensitive P. falciparum. 44 cleared parasites by 6 days after treatment; 37 patients with P. vivax infections cleared parasites by day 5. The confirmation of chloroquine resistance may depend on the adaptation of isolates to nonhuman primates in which controlled drug trials can be made.     

Plasmodium knowlesi malaria in humans is widely distributed and potentially life threatening.

BACKGROUND: Until recently, Plasmodium knowlesi malaria in humans was misdiagnosed as Plasmodium malariae malaria. The objectives of the present study were to determine the geographic distribution of P. knowlesi malaria in the human population in Malaysia and to investigate 4 suspected fatal cases. METHODS: Sensitive and specific nested polymerase chain reaction was used to identify all Plasmodium species present in (1) blood samples obtained from 960 patients with malaria who were hospitalized in Sarawak, Malaysian Borneo, during 2001-2006; (2) 54 P. malariae archival blood films from 15 districts in Sabah, Malaysian Borneo (during 2003-2005), and 4 districts in Pahang, Peninsular Malaysia (during 2004-2005); and (3) 4 patients whose suspected cause of death was P. knowlesi malaria. For the 4 latter cases, available clinical and laboratory data were reviewed. RESULTS: P. knowlesi DNA was detected in 266 (27.7%) of 960 of the samples from Sarawak hospitals, 41 (83.7%) of 49 from Sabah, and all 5 from Pahang. Only P. knowlesi DNA was detected in archival blood films from the 4 patients who died. All were hyperparasitemic and developed marked hepatorenal dysfunction. CONCLUSIONS: Human infection with P. knowlesi, commonly misidentified as the more benign P. malariae, are widely distributed across Malaysian Borneo and extend to Peninsular Malaysia. Because P. knowlesi replicates every 24 h, rapid diagnosis and prompt effective treatment are essential. In the absence of a specific routine diagnostic test for P. knowlesi malaria, we recommend that patients who reside in or have traveled to Southeast Asia and who have received a "P. malariae" hyperparasitemia diagnosis by microscopy receive intensive management as appropriate for severe falciparum malaria.     

Antibody responses to malarial antigens in the Wopkaimin population of the Star Mountains, Papua New Guinea

Antibody responses to malarial antigens were determined in 614 serum samples collected from the Wopkaimin population of the Star Mountains of Papua New Guinea. In point prevalence surveys made in 1982-1983, 33.7% of the persons examined were infected with Plasmodium falciparum, P. vivax, or P. malariae. Of these, 72.9% were infected with P. falciparum. In a standard fluorescent antibody test, highest level responses were to P. falciparum, followed by P. malariae, P. vivax, and P. ovale. A strong correlation was found between results of the fluorescent antibody tests and those obtained in an enzyme-linked immunosorbent assay using P. falciparum antigens. The failure of immune responses to eliminate these species of Plasmodium in this highly isolated population is discussed.     

Factors influencing resistance to reinfection with Plasmodium falciparum

A treatment-reinfection study design was used to investigate the relationships between host immunologic and/or genetic factors and resistance to reinfection with Plasmodium falciparum. Sixty-one children in Gabon were enrolled in a cross-sectional study to measure the prevalence of each human plasmodial species. All were given amodiaquine for radical cure of parasites, and 40 were subsequently followed-up for 30 weeks. Successive blood smears were examined to measure the delay of reappearance in blood of asexual stages of P. falciparum parasites. Presence of infection during the cross-sectional survey was associated with male sex, non-deficient glucose-6-phosphate dehydrogenase activity, plasma interleukin-10 level, and anti-LSA-Rep antibody concentration. Resistance to reinfection was related to the presence of anti-LSA-J antibodies, and the absence of anti-LSA-Rep antibodies. Moreover, P. malariae-infected subjects were usually co-infected with P. falciparum, and were also more rapidly reinfected with P. falciparum after treatment, compared with those without P. malariae infection.     

Wide distribution of Plasmodium ovale in Myanmar

The presence of Plasmodium ovale has never been previously reported in Myanmar. Using blood samples obtained in many villages across the country between 1996 and 2000, molecular diagnosis of Plasmodium species was made with semi- or full-nested polymerase chain reaction (PCR) with species-specific primers, followed by agarose gel electrophoresis to detect amplification products. The presence of P. ovale was also confirmed with the another PCR-based diagnosis, the microtiterplate hybridization (MPH) method using species-specific probes. Both methods target the A type of the small subunit ribosomal RNA gene of the four human malaria parasites. Plasmodium ovale DNA was amplified in samples from 65 (4.9%) of 1323 PCR-positive patients, with perfect agreement between results obtained by nested PCR and MPH. Only four P. ovale-infected patients had single-species infection; all others were coinfected with P. falciparum, P. vivax and/or P. malariae. Quadruple infections were observed in six subjects. Parasites with typical P. ovale morphology were found in only 19 patients by conventional microscopy of Giemsa-stained thin smears or fluorescence microscopy of acridine orange-stained thin smears. Plasmodium ovale infections were found in villages situated in the southern, central and western regions of Myanmar, suggesting that P. ovale may be widely distributed in this country.