RESUMO
BACKGROUND: 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 in which asymptomatic carriers play an important role. OBJECTIVES: To determine the incidence of asymptomatic infection by detecting Plasmodium spp. DNA and its role in residual 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. A mathematical transmission model was applied, using a low frequency of human carriers and the vector density in the region, and calculated based on previous studies in the same locality whose results were subjected to a linear regression. This analysis suggests that the transmission chain is unlikely to be based solely on human carriers, regardless of whether they are symptomatic or not. CONCLUSION: The low incidence of cases and the low frequency of asymptomatic malaria carriers investigated make it unlikely that the transmission chain in the region is based solely on human hosts, as cases are isolated one from another by hundreds of kilometers and frequently by long periods of time, reinforcing instead the hypothesis of zoonotic transmission.
Assuntos
DNA de Protozoário/sangue , Malária/epidemiologia , Malária/parasitologia , Plasmodium/isolamento & purificação , Adolescente , Adulto , Brasil/epidemiologia , Portador Sadio , Feminino , Humanos , Incidência , Malária/transmissão , Masculino , Pessoa de Meia-Idade , Modelos Biológicos , Prevalência , Adulto JovemRESUMO
BACKGROUND: Regions with residual transmission are potential obstacles to the elimination of malaria. It is, therefore, essential to understand the factors associated with the maintenance of endemic malaria in these areas. The objective was to investigate whether the status of asymptomatic carriers of Plasmodium spp. DNA is maintained in the long term in an extra-Amazonian region of Brazil with low incidence, residual malaria transmission. METHODS: Asymptomatic carriers of Plasmodium DNA detected in a survey carried out between 2001 and 2004 were reassessed between 2010 and 2011 using questionnaires, PCR and thick and thin blood smear tests three times at 3-month intervals. RESULTS: Of the 48 carriers detected between 2001 and 2004, 37 were located. Of these, only two had positive PCR results and, as in the first survey, Plasmodium malariae DNA was detected. CONCLUSION: The findings suggest that untreated dwellers from this extra-Amazonian region, who initially harbour malaria parasites, may become negative without ever developing apparent symptoms of the disease. Although the possibility of re-infection cannot be ruled out, the finding of two individuals harbouring P. malariae, both in the first and in the second survey, may be compatible with a long-term carrier state for this parasite. Since most clinical cases of malaria in the region are a consequence of infection by Plasmodium vivax, the epidemiological impact of such long-term carriage would be limited.
Assuntos
Infecções Assintomáticas/epidemiologia , Malária/epidemiologia , Plasmodium/isolamento & purificação , Adolescente , Adulto , Brasil/epidemiologia , Criança , Estudos de Coortes , Feminino , Humanos , Incidência , Malária/parasitologia , Masculino , Pessoa de Meia-Idade , Adulto JovemRESUMO
The protozoan parasite Cryptosporidium has emerged as one of the most important water contaminants, causing outbreaks of waterborne diarrhea worldwide. In order to assess the importance for public health of this pathogens presence in environmental samples, several methods have been developed to isolate and detect Cryptosporidium oocysts. In the present study, a reliable and reproducible method has been standardized for detecting and identifying Cryptosporidium oocysts in water samples in the State of São Paulo, Brazil as the first step for future genotyping studies. Water samples were concentrated by filtration, and then subjected to ultrasound in Tween 80 0.1%, the obtained sediment was transferred into micro tubes containing 1.0 ml of distilled water and stored at -20ºC. DNA was extracted with the addition of 1% PVP in lysis buffer, the organic extraction was performed in Phase Lock Gel Heavy®. There was a 214 bp amplification on the expected fragment in five out of the 11 water samples analyzed. The results of this study demonstrated the application usefulness of the standardized test in epidemiological studies and surveillance programs because the technology allowed to increase significantly the amount of amplified product.
O protozoário parasito Cryptosporidium tem emergido como um dos mais importantes contaminantes da água, causando surtos de diarreia de veiculação hídrica em todo mundo. Para avaliar o significado, para a saúde pública, da presença desse agente patogênico em amostras ambientais, vários métodos têm sido desenvolvidos para isolar e detectar oocistos de Cryptosporidium. No presente estudo foi padronizado um método confiável e reprodutível para detectar e identificar oocistos de Cryptosporidium em amostras de água no Estado de São Paulo, Brasil, como o primeiro passo para futuros estudos de genotipagem. Amostras de água foram concentradas por filtração, submetidas a ultrasom em solução de Tween 80 a 0.1%; o sedimento obtido foi transferido para microtubos contendo 1,0 ml de água destilada e conservado a -20ºC. O DNA foi extraído com adição de 1% de PVP no tampão de lise; a extração foi realizada em tubo Phase Lock Gel Heavy®. Houve amplificação do fragmento esperado de 214 bp em cinco das 11 amostras de água analisadas. Os resultados deste estudo demonstraram a utilidade de aplicação do teste padronizado em estudos epidemiológicos e em programas de vigilância, em virtude da técnica ter apresentado sensibilidade para incrementar significativamente a quantidade de produto amplificado.