Random distribution of mixed species malaria infections in Papua New Guinea.
(17/1293)
Plasmodium falciparum (Pf), P. vivax (Pv), P. malariae (Pm), and P. ovale (Po) infections are endemic in coastal areas of Papua New Guinea. Here 2,162 individuals living near Dreikikir, East Sepik Province, have been analyzed for complexity of malaria infection by blood smear and polymerase chain reaction (PCR) diagnoses. According to blood smear, the overall prevalence of Plasmodium infection was 0.320. Most individuals (0.283) were infected with a single species only. The prevalence of mixed species infections was low (0.037). Further analysis of a 173-sample subset by nested PCR of small subunit ribosomal DNA resulted in an overall 3.0-fold increase in prevalence of infection, with a 17.5-fold increase in the frequency of mixed species infections. Among mixed species infections detected by PCR, the frequency of double species was 0.364, and that of triple species was 0.237. Nine individuals (0.052) were infected with all 4 species. To determine if infection status (uninfected, single, and multiple infections) deviates from an independent random distribution (null hypothesis), observed versus expected frequencies of all combinations of Plasmodium species infections, or assemblages (Pf-, Pv-, Pm-, Po-, to Pf+, Pv+, Pm+, Po+), were compared using a multiple-kind lottery model. All 4 species were randomly distributed whether diagnosed by blood smear or PCR in the overall population and when divided into age group categories. These findings suggest that mixed species malaria infections are common, and that Plasmodium species appear to establish infection independent of one another. (+info)
Life history of a malaria parasite (Plasmodium mexicanum): independent traits and basis for variation.
(18/1293)
Plasmodium mexicanum, a malaria parasite of lizards, exhibits substantial variation among infections in the life-history traits which define its blood-dwelling stages. Such variation in life histories among infections is common in Plasmodium and may influence the ecology and evolution of the parasite's transmission success and virulence. Insight into these issues requires identification of independent traits (some traits may be bound by developmental trade-offs) and the importance of genetic versus host effects producing the variation. We studied 11 life-history traits in 120 induced infections of P. mexicanum in its natural lizard host (20 each from six donor infections). The traits varied among infections and fell into three clusters: rate/peak (rate of increase and peak parasitaemia of asexuals and gametocytes), time (duration of pre-patent period and the infection's growth) and maturity (timing of first gametocytes). Thus, few life-history traits define an infection in the lizard's blood. Donor effects were significant for ten traits and two trait clusters (maturity was the exception) suggesting genetic differences among infections may influence the rate of increase and peak parasitaemia, but not the timing of the first production of gametocytes. (+info)
Immunopathology of nephropathies associated with malaria.
(19/1293)
Immune complexes play an important role in the pathogenesis of malaria-associated nephropathies. Two main types of lesion are demonstrable: (a) acute (transient-reversible) lesions typical of falciparum infections in man, with mild clinical symptoms developing a week or two after infection. Renal biopsies at that time show deposits of immunoglobulins, complement, and sometimes antigen. The lesions respond to antimalarials. (b) Chronic (progressive) lesions characteristic of quartan infections in man, developing slowly into a chronic stage with persistent proteinuria and gradually deteriorating renal function and hypertension. Renal biopsies at the onset of the disease show deposits of immunoglobulins, complement, and P. malariae antigens in glomerular capillary walls. Antimalarial therapy has no effect. Recent immunochemical findings confirm that these lesions are of the immune-complex type and are associated with malaria infection. However, several questions remain to be solved. (+info)
Parasite cultivation in relation to research on the chemotherapy of malaria.
(20/1293)
Attempts to develop techniques for the continuous in vitro cultivation of the malaria parasite have not yet proved successful. It has not been possible to obtain the complete sporogonic development of the parasite in vitro although some progress was made with Plasmodium relictum and P. berghei. Exoerythrocytic stages of P. gallinaceum have been successfully cultivated in vitro in tissue explants and those of P. fallax have been grown in turkey primary embryo tissue cells. With the recent development of mammalian liver cell lines, prospects for the in vitro cultivation of exoerythrocytic stages of mammalian plasmodia are greatly improved. While it is still not possible to cultivate erythrocytic stages of plasmodia serially in vitro some species have been successfully grown through one asexual cycle. This progress has led to a number of applications of parasite cultivation to chemotherapeutic studies, to the testing of new antimalarial drugs, and especially to the testing of the susceptibility of P. falciparum to chloroquine. Cultivation technique is greatly improved by an appropriate choice of culture media. The addition of fresh red cells to the subculture system permits relatively high rates of invasion and multiplication of the parasite to be obtained. As well as its application in the screening and evaluation of antimalarial compounds, the in vitro cultivation technique is also very suitable for studying the entry mechanism of the parasite into red blood cells. (+info)
Frequent umbilical cord-blood and maternal-blood infections with Plasmodium falciparum, P. malariae, and P. ovale in Kenya.
(21/1293)
The prevalence of malaria infection in 102 paired maternal-blood and umbilical cord-blood samples was assessed by microscopy and polymerase chain reaction (PCR) in a holoendemic area in Kenya. Plasmodium falciparum single-species infection was detected in maternal peripheral blood (3.4%), whereas microscopy indicated that no Plasmodium species were in cord blood. In contrast, maternal-blood samples showed a PCR prevalence of 48% for P. falciparum, 25% for P. malariae, and 24% for P. ovale, and cord-blood samples showed a PCR prevalence of 32%, 23%, and 21%, respectively. Although mothers with mixed-species infections were more likely to have offspring infected with mixed species, the specific malaria species were discordant in paired maternal- and cord-blood samples. Triple-species infections were observed in 11 cord- and maternal-blood samples at a 5.5-fold greater frequency than expected. These findings indicate that Plasmodium species infections in cord blood are common, occur at lower densities, and may be acquired before parturition. (+info)
Malaria transmission model for different levels of acquired immunity and temperature-dependent parameters (vector).
(22/1293)
OBJECTIVE: Describe the overall transmission of malaria through a compartmental model, considering the human host and mosquito vector. METHODS: A mathematical model was developed based on the following parameters: human host immunity, assuming the existence of acquired immunity and immunological memory, which boosts the protective response upon reinfection; mosquito vector, taking into account that the average period of development from egg to adult mosquito and the extrinsic incubation period of parasites (transformation of infected but non-infectious mosquitoes into infectious mosquitoes) are dependent on the ambient temperature. RESULTS: The steady state equilibrium values obtained with the model allowed the calculation of the basic reproduction ratio in terms of the model's parameters. CONCLUSIONS: The model allowed the calculation of the basic reproduction ratio, one of the most important epidemiological variables. (+info)
New serological test for malaria antibodies.
(23/1293)
In an enzyme-linked immunosorbent assay test for malaria antibodies, antibodies to Plasmodium vivax and P. falciparum in man are detected using a crude antigen prepared from the simian malaria parasite P. knowlesi. The test may be suitable for epidemiological studies. (+info)
Estimation of the sporozoite rate of malaria vectors using the polymerase chain reaction and a mathematical model.
(24/1293)
We developed a sensitive polymerase chain reaction (PCR) method for the detection of Plasmodium falciparum DNA from mosquitoes collected in the field. Plasmodium falciparum was detected from 15.2% of 1-parous mosquitoes, Anopheles farauti, in the Solomon Islands through use of the PCR method. A novel mathematical model was developed to estimate the sporozoite rate based on the malaria-positive rate of 1-parous mosquitoes. Using this model, the sporozoite rate of Anopheles farauti in the Solomon Islands was calculated to be 0.09%. This method enables estimation of the sporozoite rate based on a relatively small number (100-200) of mosquitoes compared with the number needed for the ELISA method. (+info)