Why do we need to know more about mixed Plasmodium species infections in humans?

Abstract

Four Plasmodium species cause malaria in humans. Most malaria-endemic regions feature mixed infections involving two or more of these species. Factors contributing to heterogeneous parasite species and disease distribution include differences in genetic polymorphisms underlying parasite drug resistance and host susceptibility, mosquito vector ecology and transmission seasonality. It is suggested that unknown factors limit mixed Plasmodium species infections, and that mixedspecies infections protect against severe Plasmodium falciparum malaria. Careful examination of methods used to detect these parasites and interpretation of individual-and population-based data are necessary to understand the influence of mixed Plasmodium species infections on malarial disease. This should ensure that deployment of future antimalarial vaccines and drugs will be conducted in a safe and timely manner. Although novel exceptions have been reported [1], it is commonly agreed that Plasmodium falciparum, Plasmodium vivax, Plasmodium malariae and Plasmodium ovale are the four species that cause human malaria. Factors underlying mixed infections involving these parasite species have been discussed since 1930, when Knowles and White acknowledged difficulties that microscopists might encounter in accurately documenting their findings from examinations of blood smears [2]. Humans often harbor multiple Plasmodium species [3][4][5][6], and varying patterns in species-specific parasitemia and mixed-species prevalence characterize malaria infections in different endemic regions ([7-10]; reviewed in Refs [11,12]). Data from malaria fever therapy patients involving different Plasmodium species [13][14][15], and naturally infected study volunteers, have illustrated a range of observations from orderly to turbulent species-specific patterns (Figure 1) of parasitemia in infected individuals [13][14][15][16][17]. Antimalarial treatment studies have also contributed insight regarding mixed Plasmodium species infections by revealing undocumented infection of a second species following successful treatment of a first species (reviewed in Ref. [18]). These varied patterns of parasitemia observed in individuals infected by multiple Plasmodium species are surely influenced by a complex array of host factors [19] acting to constrain the infection before the parasites completely over-run the available erythrocyte population. Evidence that the four Plasmodium parasites of humans antagonize one another seems less clear.Conflicting results suggesting the presence or absence of mixed-species interactions from one study to the next are seldom resolved. If direct interaction between Plasmodium species occurs within an infected individual to any significant level, these interactions would then be expected to influence the distribution of species within the endemic population. A common theme discussed in the context of Plasmodium species interactions has focused on

Diagnosis of Malaria by Magnetic Deposition Microscopy

“…4,11 PCR-based diagnosis (individual diagnosis ≈ US$0.50-1.00) 4 requires a laboratory with electricity and expensive equipment and is most expedient when analysis is performed on large numbers of samples in a 96-well plate format. 12 In an attempt to overcome some problems inherent to blood smear microscopy, we have developed a magnet-based approach to concentrate malaria parasites and augment detection of malaria-infected erythrocytes by microscopy. This system, malaria magnetic deposition microscopy (MDM), exploits the fact that Plasmodium species parasites produce a crystalline by-product, hemozoin, from heme liberated during hemoglobin digestion.…”

Can mosquitoes help to unravel the community structure of Plasmodium species?

“…A series of recent articles in Trends in Parasitology was dedicated to the neglected problem of Plasmodium vivax and it reignited the debate about the importance of mixedspecies infections in the epidemiology of malaria [1][2][3][4]. Most of the reviews in the series concern Asia, where P. vivax is particularly abundant, and they pinpoint particular clinical and biological outcomes of mixedspecies infections.…”

Trombosis axilar y embolismo pulmonar tras implantación de marcapasos

“…El EP sintomático es sin embargo muy infrecuente, con una incidencia menor al 4% (1,2,5). La mayoría de casos de EP asociado a marcapasos están relacionados con trombosis a nivel del cable de marcapasos y con extensión intracavitaria de la misma (6)(7)(8).…”

“…En nuestro caso no se constató trombosis en el electrodo ni en las cavidades cardiacas, sino sólo a nivel de la vena axilar izquierda, relacionado obviamente con el procedimiento de colocación del marcapasos. La existencia de un catéter venoso central, además de ser portador de enfermedades neoplásicas, es el factor de riesgo más invocado para el desarrollo de trombosis venosa y EP en estos pacientes (3)(4)(5)9), no existiendo sin embargo aparente relación entre la localización de la trombosis y la probabilidad de sufrir un EP (5). Estos fenó-menos tromboembólicos pueden aparecer en cualquier momento tras la implantación del marcapasos (2,5,9), si bien un estudio reciente ha encontrado que la mayoría de casos ocurrieron en los primeros 3 meses desde su colocación (4), al igual que en el caso aportado.…”

“…La existencia de un catéter venoso central, además de ser portador de enfermedades neoplásicas, es el factor de riesgo más invocado para el desarrollo de trombosis venosa y EP en estos pacientes (3)(4)(5)9), no existiendo sin embargo aparente relación entre la localización de la trombosis y la probabilidad de sufrir un EP (5). Estos fenó-menos tromboembólicos pueden aparecer en cualquier momento tras la implantación del marcapasos (2,5,9), si bien un estudio reciente ha encontrado que la mayoría de casos ocurrieron en los primeros 3 meses desde su colocación (4), al igual que en el caso aportado. El tratamiento de la trombosis venosa profunda de extremidades superiores y del EP asociado a la implantación de marcapasos puede requerir diferentes medidas como la anticoagulación convencional, trombolisis, angioplastia o cirugía (2,6-8, si bien las últimas publicaciones sobre el tema aconsejan realizar fibrinolisis (6).…”