Assessment of asymptomatic Plasmodium spp. infection by detection of parasite DNA in residents of an extra Amazonian region of Brazil

The hypotheses put forward to explain the malaria transmission cycle in extra-Amazonian Brazil, an area of very low malaria incidence, are based on either a zoonotic scenario involving simian malaria, or a scenario inwhich asymptomatic carriers play an important role. Objectives: To determine the incidence of asymptomatic infection by detecting Plasmodium spp. DNA and its role inresidual malaria transmission in a non-Amazonian region of Brazil. Methods: Upon the report of the first malaria case in 2010 in the Atlantic Forest region of the state of Espírito Santo, inhabitants within a 2 km radius were invited to participate in a follow-up study. After providing signed informed consent forms, inhabitants filled out a questionnaire and gave blood samples for PCR, and thick and thin smears. Follow up visits were performed every 3 months over a 21 month period, when new samples were collected and information was updated. Results: Ninety-two individuals were initially included for follow-up. At the first collection, all of them were clearly asymptomatic. One individual was positive for Plasmodium vivax, one for Plasmodium malariae and one for both P.vivax and P. malariae, corresponding to a prevalence of 3.4% (2.3% for each species). During follow-up, four new PCR positive cases (two for each species) were recorded, corresponding to an incidence of 2.5 infections per 100 person years or 1.25 infections per 100 person-years for each species...

Merozoite surface protein-1 genetic diversityin Plasmodium malariae and Plasmodium brasilianum from Brazil

The merozoite surface protein 1 (MSP1) gene encodes the major surface antigen of invasive forms of the Plasmodium erythrocytic stages and is considered a candidate vaccine antigen against malaria. Due to its polymorphisms, MSP1 is also useful for strain discrimination and consists of a good genetic marker. Sequence diversity in MSP1 has been analyzed in field isolates of three human parasites: P. falciparum, P. vivax, and P. ovale. However, the extent of variation in another human parasite, P. malariae, remains unknown. This parasite shows widespread, uneven distribution in tropical and subtropical regions throughout South America, Asia, and Africa. Interestingly, it is genetically indistinguishable from P. brasilianum, a parasite known to infect New World monkeys in Central and South America. Methods: Specific fragments (1 to 5) covering 60 % of the MSP1 gene (mainly the putatively polymorphic regions), were amplified by PCR in isolates of P. malariae and P. brasilianum from different geographic origin and hosts. Sequencing of the PCR-amplified products or cloned PCR fragments was performed and the sequences were used to construct a phylogenetic tree by the maximum likelihood method. Data were computed to give insights into the evolutionary and phylogenetic relationships of these parasites...

The genetic diversity of Plasmodium malariae and Plasmodium brasilianum from human, simian and mosquito hosts in Brazil

Plasmodium malariae is a protozoan parasite that causes malaria in humans and is genetically indistinguish able from Plasmodium brasilianum, a parasite infecting New World monkeys in Central and South America. P. malariae has a wide and patchy global distribution in tropical and subtropical regions, being found in South America, Asia, and Africa. However, little is known regarding the genetics of these parasites and the similarity between them could be because until now there are only a very few genomic sequences available from simian Plasmodium species. This study presents the first molecular epidemiological data for P. malariae and P. brasilianum from Brazil obtained from different hosts and uses them to explore the genetic diversity in relation to geographical origin and hosts. By using microsatellite genotyping, we discovered that of the 14 human samples obtained from areas of the Atlantic forest, 5 different multilocus genotypes were recorded, while in a sample from an infected mosquito from the same region a different haplo type was found. We also analyzed the longitudinal change of circulating plasmodial genetic profile in two untreated non-symptomatic patients during a 12-months interval...

Survivorship of Anopheles darlingi (Diptera: Culicidae) in relation with malaria incidence in the Brazilian Amazon.

We performed a longitudinal study of adult survival of Anopheles darlingi, the most important vector in the Amazon, in a malarigenous frontier zone of Brazil. Survival rates were determined from both parous rates and multiparous dissections. Anopheles darlingi human biting rates, daily survival rates and expectation of life where higher in the dry season, as compared to the rainy season, and were correlated with malaria incidence. The biting density of mosquitoes that had survived long enough for completing at least one sporogonic cycle was related with the number of malaria cases by linear regression. Survival rates were the limiting factor explaining longitudinal variations in Plasmodium vivax malaria incidence and the association between adult mosquito survival and malaria was statistically significant by logistic regression (P<0.05). Survival rates were better correlated with malaria incidence than adult mosquito biting density. Mathematical modeling showed that P. falciparum and P. malariae were more vulnerable to changes in mosquito survival rates because of longer sporogonic cycle duration, as compared to P. vivax, which could account for the low prevalence of the former parasites observed in the study area. Population modeling also showed that the observed decreases in human biting rates in the wet season could be entirely explained by decreases in survival rates, suggesting that decreased breeding did not occur in the wet season, at the sites where adult mosquitoes were collected. For the first time in the literature, multivariate methods detected a statistically significant inverse relation (P<0.05) between the number of rainy days per month and daily survival rates, suggesting that rainfall may cause adult mortality.

Presencia de Plasmodium brasilianum (Apicomplexa, Plasmodidae) en el mono congo (Alouatta palliata, Primates: Cebidae) de Costa Rica: importancia epidemiológica en relación con el ser humano / Plasmodium brasilianum (Apicomplexa, Plasmodidae) in the congo monkey Alouatta brasilianum (Primate: Cebidae) of Costa Rica: epidemiological importance related to human

La especie productora de malaria en primates, Plasmodium brasilianum, fue encontrada por primera vez en Costa Rica en 6 de 104 ejemplares de monos congo o aulladores (Alouatta palliata). Los animales fueron capturados y anestesiados por medio de dardos que contenían hidrocloruro de tiletamina y zolazepam (Zoletil®) combinados en partes iguales. Para estudiar estos animales por parásitos sanguíneos, se prepararon frotis sanguíneos que luego se tiñeron y se estudiaron en el laboratorio, encontrándose las formas de trofozoitos jóvenes o avanzados así como gametocitos y esquizontes. La morfología característica de algunos estados evolutivos, como por ejemplo, las formas en banda de trofozoitos avanzados y los esquizontes en forma de margarita o "rosetta" permitieron el diagnóstico de la especie. Puesto que se han encontrado casos humanos infectados con este organismo y éste es casi indiferenciable de Plasmodium malariae, una especie parásita del ser humano, se discute el hallazgo de este parásito desde un punto de vista epidemiológico en el área de la salud.

Studies on the Uganda I/CDC strain of Plasmodium malariae in bolivian Aotus monkeys and various anophelines.

A strain of Plasmodium malariae (Uganda I/CDC) was isolated from an infant who had been infected via blood transfusion from a donor who had entered the United States 8 yr previously. After passage through a splenectomized chimpanzee, the parasite was studied in 29 splenectomized Aotus azarae boliviensis monkeys. Maximum parasitemias were higher in Aotus monkeys without previous Plasmodium infection than in Aotus monkeys with a history of P. vivax infection. Animals with a history of infection with both P. vivax and P. falciparum had lower maximum parasitemias than did monkeys in either of the 2 preceding groups. The highest rates of mosquito infection were most often obtained during the 10-day period just after the parasite count rose above 500/mm3 of blood. The most susceptible mosquito was Anopheles freeborni followed by An. stephensi, An. gambiae, An. dirus, and An. maculatus. Two attempts to transmit the Uganda I/CDC strain of P. malariae to other monkeys by sporozoite inoculation were unsuccessful.