Luiz Herman Soares Gil

Asymptomatic Carriers of Plasmodium spp. as Infection Source for Malaria Vector Mosquitoes in the Brazilian Amazon

Abstract We have described the existence of asymptomatic carriers of Plasmodium vivax and Plasmodium falciparum infections in native Amazon populations. Most of them had low parasitemias, detected only by polymerase chain reaction (PCR). Because they remain symptomless and untreated, we wanted to determine whether they could infect Anopheles darlingi Root, the main Brazilian vector, and act as disease reservoirs. Fifteen adult asymptomatic patients (PCR positive only) were selected, and experimental infections of mosquitoes were performed by direct feeding and by a membrane-feeding system. Seventeen adult symptomatic patients with high parasitemias were used as controls. We found an infection rate in An. darlingi of 1.2% for the asymptomatic carriers and 22% for the symptomatic carriers. Although the asymptomatic group infected mosquitoes at a much lower rate, these patients remain infective longer than treated, symptomatic patients. Also, the prevalence of asymptomatic infections is 4 to 5 times higher than symptomatic infections among natives. These results have implications for the malaria control program in Brazil, which focuses essentially on the treatment of symptomatic patients.

Urban and suburban malaria in Rondônia (Brazilian Western Amazon) II: perennial transmissions with high anopheline densities are associated with human environmental changes

Longitudinal entomological surveys were performed in Vila Candelária and adjacent rural locality of Bate Estaca concomitantly with a clinical epidemiologic malaria survey. Vila Candelária is a riverside periurban neighborhood of Porto Velho, capital of the state of Rondônia in the Brazilian Amazon. High anopheline densities were found accompanying the peak of rainfall, as reported in rural areas of the region. Moreover, several minor peaks of anophelines were recorded between the end of the dry season and the beginning of the next rainy season. These secondary peaks were related to permanent anopheline breeding sites resulting from human activities. Malaria transmission is, therefore, observed all over the year. In Vila Candelária, the risk of malaria infection both indoors and outdoors was calculated as being 2 and 10/infecting bites per year per inhabitant respectively. Urban malaria in riverside areas was associated with two factors: (1) high prevalence of asymptomatic carriers in a stable human population and (2) high anopheline densities related to human environmental changes. This association is probably found in other Amazonian urban and suburban communities. The implementation of control measures should include environmental sanitation and better characterization of the role of asymptomatic carriers in malaria transmission.

Larval food quantity affects development time, survival and adult biological traits that influence the vectorial capacity of Anopheles darlingi under laboratory conditions.

BackgroundThe incidence of malaria in the Amazon is seasonal and mosquito vectorial capacity parameters, including abundance and longevity, depend on quantitative and qualitative aspects of the larval diet. Anopheles darlingi is a major malaria vector in the Amazon, representing >95% of total Anopheles population present in the Porto Velho region. Despite its importance in the transmission of the Plasmodium parasite, knowledge of the larval biology and ecology is limited. Studies regarding aspects of adult population ecology are more common than studies on larval ecology. However, in order develop effective control strategies and laboratory breeding conditions for this species, more data on the factors affecting vector biology is needed. The aim of the present study is to assess the effects of larval food quantity on the vectorial capacity of An. darling under laboratory conditions.MethodsAnopheles darlingi was maintained at 28°C, 80% humidity and exposed to a daily photoperiod of 12 h. Larvae were divided into three experimental groups that were fed either a low, medium, or high food supply (based on the food amounts consumed by other species of culicids). Each experiment was replicated for six times. A cohort of adults were also exposed to each type of diet and assessed for several biological characteristics (e.g. longevity, bite frequency and survivorship), which were used to estimate the vectorial capacity of each experimental group.ResultsThe group supplied with higher food amounts observed a reduction in development time while larval survival increased. In addition to enhanced longevity, increasing larval food quantity was positively correlated with increasing frequency of bites, longer blood meal duration and wing length, resulting in greater vectorial capacity. However, females had greater longevity than males despite having smaller wings.ConclusionsOverall, several larval and adult biological traits were significantly affected by larval food availability. Greater larval food supply led to enhance larval and production and larger mosquitoes with longer longevity and higher biting frequency. Thus, larval food availability can alter important biological traits that influence the vectorial capacity of An. darlingi.

The Dynamics of Transmission and Spatial Distribution of Malaria in Riverside Areas of Porto Velho, Rondônia, in the Amazon Region of Brazil

The study area in Rondônia was the site of extensive malaria epidemic outbreaks in the 19th and 20th centuries related to environmental impacts, with large immigration flows. The present work analyzes the transmission dynamics of malaria in these areas to propose measures for avoiding epidemic outbreaks due to the construction of two Hydroelectric Power Plants. A population based baseline demographic census and a malaria prevalence follow up were performed in two river side localities in the suburbs of Porto Velho city and in its rural vicinity. The quantification and nature of malaria parasites in clinical patients and asymptomatic parasite carriers were performed using microscopic and Real Time PCR methodologies. Anopheles densities and their seasonal variation were done by monthly captures for defining HBR (hourly biting rate) values. Main results: (i) malaria among residents show the riverside profile, with population at risk represented by children and young adults; (ii) asymptomatic vivax and falciparum malaria parasite carriers correspond to around 15% of adults living in the area; (iii) vivax malaria relapses were responsible for 30% of clinical cases; (iv) malaria risk for the residents was evaluated as 20–25% for vivax and 5–7% for falciparum malaria; (v) anopheline densities shown outdoors HBR values 5 to 10 fold higher than indoors and reach 10.000 bites/person/year; (vi) very high incidence observed in one of the surveyed localities was explained by a micro epidemic outbreak affecting visitors and temporary residents. Temporary residents living in tents or shacks are accessible to outdoors transmission. Seasonal fishermen were the main group at risk in the study and were responsible for a 2.6 fold increase in the malaria incidence in the locality. This situation illustrates the danger of extensive epidemic outbreaks when thousands of workers and secondary immigrant population will arrive attracted by opportunities opened by the Hydroelectric Power Plants constructions.

Natural Plasmodium infection in monkeys in the state of Rondônia (Brazilian Western Amazon)

BackgroundSimian malaria is still an open question concerning the species of Plasmodium parasites and species of New World monkeys susceptible to the parasites. In addition, the lingering question as to whether these animals are reservoirs for human malaria might become important especially in a scenario of eradication of the disease. To aid in the answers to these questions, monkeys were surveyed for malaria parasite natural infection in the Amazonian state of Rondônia, Brazil, a state with intense environmental alterations due to human activities, which facilitated sampling of the animals.MethodsParasites were detected and identified in DNA from blood of monkeys, by PCR with primers for the 18S rRNA, CSP and MSP1 genes and sequencing of the amplified fragments. Multiplex PCR primers for the 18S rRNA genes were designed for the parasite species Plasmodium falciparum and Plasmodium vivax, Plasmodium malariae/Plasmodium brasilianum and Plasmodium simium.ResultsAn overall infection rate of 10.9% was observed or 20 out 184 monkey specimens surveyed, mostly by P. brasilianum. However, four specimens of monkeys were found infected with P. falciparum, two of them doubly infected with P. brasilianum and P. falciparum. In addition, a species of monkey of the family Aotidae, Aotus nigriceps, is firstly reported here naturally infected with P. brasilianum. None of the monkeys surveyed was found infected with P. simium/P. vivax.ConclusionThe rate of natural Plasmodium infection in monkeys in the Brazilian state of Rondônia is in line with previous surveys of simian malaria in the Amazon region. The fact that a monkey species was found that had not previously been described to harbour malaria parasites indicates that the list of monkey species susceptible to Plasmodium infection is yet to be completed. Furthermore, finding monkeys in the region infected with P. falciparum clearly indicates parasite transfer from humans to the animals. Whether this parasite can be transferred back to humans and how persistent the parasite is in monkeys in the wild so to be efficient reservoirs of the disease, is yet to be evaluated. Finding different species of monkeys infected with this parasite species suggests indeed that these animals can act as reservoirs of human malaria.

Malaria and hematological aspects among residents to be impacted by reservoirs for the Santo Antônio and Jirau Hydroelectric Power Stations, Rondônia State, Brazil

In Rondônia State, Brazil, two new hydroelectric plants, Santo Antônio and Jirau, are scheduled for construction on the Madeira River, upriver from the State capital, Porto Velho. The current study analyzes malaria prevalence before the construction and provides information on the possible impacts of malaria burden related to the influx of thousands of persons attracted by direct and indirect employment opportunities. According to the findings, malaria is present throughout the region, with varying prevalence rates. The existence of potential asymptomatic malaria carriers among the local population may be epidemiologically relevant and should be considered in the malaria control programs organized by public authorities and companies responsible for building the power plants, aimed at early diagnosis and treatment, vector control, water supply, and infrastructure in the urban areas.

Endemias e epidemias na Amazônia: malária e doenças emergentes em áreas ribeirinhas do Rio Madeira. Um caso de escola

Apos fazer uma analise da evolucao da malaria na Amazonia brasileira, detalhando em particular a situacao em Rondonia e no municipio de Porto Velho, onde ocorreram episodios dramaticos de epidemias de malaria no passado, os autores apresentam o quadro atual da prevalencia de malaria nas areas do Vale do Rio Madeira, que sofrerao impactos com a construcao das hidreletricas de Santo Antonio e Jirau, e alertam sobre a situacao particular da malaria em areas ribeirinhas. Nessas areas, observam-se alta incidencia de malaria vivax e falciparum, a presenca de grande numero de portadores assintomaticos de parasitas e altas densidades do vetor Anopheles darlingi o ano todo. Esses elementos, associados a provavel chegada de migrantes oriundos de areas nao-endemicas de Rondonia e de outros Estados do pais, atraidos pela possibilidade de trabalho nessas hidreletricas e oportunidades de comercio, lazer, educacao e atividades domesticas, criam condicoes favoraveis a ocorrencia de epidemias de malaria e de outras doencas tropicais se nao forem realizadas intervencoes adequadas de controle, em particular no dominio do saneamento.

Seasonal genetic partitioning in the neotropical malaria vector, Anopheles darlingi.

BackgroundAnopheles darlingi is the main malaria mosquito vector in the Amazonia region. In spite of being considered a riverine, forest-dwelling species, this mosquito is becoming more abundant in peri-urban areas, increasing malaria risk. This has been associated with human-driven environmental changes such as deforestation.MethodsMicrosatellites were used to characterize A. darlingi from seven localities along the Madeira River, Rondônia (Brazil), collected in the early and late periods of the rainy season.ResultsTwo genetically distinct subpopulations were detected: one (subpopulation A) was associated with the late rainfall period and seems to be ecologically closer to the typical forest A. darlingi; the other (subpopulation B) was associated with the early rainfall period and is probably more adapted to drier conditions by exploiting permanent anthropogenic breeding sites. Results suggest also a pattern of asymmetric introgression, with more subpopulation A alleles introgressed into subpopulation B. Both subpopulations (and admixed mosquitoes) presented similar malaria infection rates, highlighting the potential for perennial malaria transmission in the region.ConclusionsThe co-occurrence of two genetically distinct subpopulations of A. darlingi adapted to different periods of rainfall may promote a more perennial transmission of malaria throughout the year. These findings, in a context of strong environmental impact due to deforestation and dam construction, have serious implications for malaria epidemiology and control in the Amazonian region.

Mosquito abundance and behavior in the influence area of the hydroelectric complex on the Madeira River, Western Amazon, Brazil

Malaria is currently highly prevalent and restricted to the north of Brazil, and its dynamics are severely affected by human environmental changes, such as the large dam construction recently approved by the Brazilian Government in Rondônia. We studied the mosquito fauna and behavior before hydroelectric construction. Mosquitoes were captured by human landing catches on the riversides of the Madeira River in Porto Velho, Rondônia. A total of 3121 mosquitoes from eight different genera were collected; only Mansonia and Anopheles darlingi were found in all 21 collection sites throughout the night. These results suggest that the riverines of the study area are exposed to malaria.

Avaliação da incidência da deficiência de Glicose-6-Fosfato Desidrogenase (G6PD) e perfil hematológico em indivíduos de uma região de Rondônia

This study consisted of evaluations of glucose-6-phosphate dehydrogenase (G6PD) deficiency and the hematologic profile of 122 individuals (69 men and 53 women) with ages varying between 3 and 83 years old. The individuals, all of whom were residents of the rural and urban areas of Porto Velho, Rondonia, Brazil, were selected according to their acceptance to participate in the study. The data of this study were collected in the period from July 2003 to August 2004. The analyses consisted of using the glucose NaNO2 method and complete Blood Cell count. Four men had G6PD deficiency (5.8% among the men and 3.3% of the total cases analyzed). None of the individuals with G6PD deficiency presented malaria tested using a thick smear stained with Giemsa stain 20. Among the men, 19 individuals (27.5%) presented malaria with 15 infected by Plasmodium vivax and 4 infected by Plasmodium falciparum. Forty-eight men (69.5%) presented with haemoglobin values of less than 14.0 g/dL and 26 (37.6%) presented erythrocytary values of less than 4.5 millions/mm3. Among the women, just 2 (3.2%) presented with malaria, caused by Plasmodium vivax and 24 (45.2%) presented haemoglobin values less than 12.0 g/dL. Twelve (22.6%) presented erithrocytary values less than 4.0 millions/mm3. Eosinophilia was seen in 47 (68.1%) men and 34 (64.1%) women. The incidence of G6PD deficiency was significant among the male population who sought medical assistance due to fever. As primaquine is used in the radical treatment of malaria caused by both vivax and falciparum infections, the risk of serious intravascular hemolysis is significant among these individuals. The test used is very simple and has a low cost so we suggest its adoption in routine public service laboratories in endemic areas.