EVALUATION OF THE ASYMPTOMATIC CARRIERS OF PLASMODIUM SP DNA IN AN ENDEMIC AREA OF MALARIA IN THE STATE OF ESPÍRITO SANTO
Name: FILOMENA EURIDICE CARVALHO DE ALENCAR
Type: PhD thesis
Publication date: 11/12/2017
Advisor:
Name |
Role |
|---|---|
| ANGELICA ESPINOSA BARBOSA MIRANDA | Advisor * |
Examining board:
| Name |
Role |
|---|---|
| ALOÍSIO FALQUETO | Internal Examiner * |
| ANGELICA ESPINOSA BARBOSA MIRANDA | Advisor * |
| ETHEL LEONOR NOIA MACIEL | External Examiner * |
| PATRÍCIA DUARTE DEPS | Internal Examiner * |
Summary: The behavior of residual malaria in the extra-Amazonian differs from that in the Amazon region, not only due to the small number of recorded cases, but also due to their dispersion in geographic areas within the Atlantic Forest biome. Understanding the role of the symptomatic Plasmodium DNA carrier in the transmission cycle in these areas is important for the improvement of policies focused in the elimination and control of this endemic disease. Two
cohorts were conducted in the mountainous region of Espírito Santo state. One to evaluate the persistence of Plasmodium DNA positivity in individuals detected in a previous study and another to estimate the incidence of Plasmodium DNA among residents in the vicinity of a detected case. In the first, of the 48 patients detected in a study conducted between 2001 and
2004, 37 were located and reassessed between 2010 and 2011, by three collections at three months interval. In this cohort, only two residents had positive results on the PCR, revealing Plasmodium malariae as in the first survey. In the second cohort, after the occurrence of the first malaria case in 2010, residents living within a radius of 2 km around their house, invited
to participate in a follow-up study, answered a questionnaire and provided blood samples for PCR and thick and thin smears initially and at each follow-up visit, every three months for 21 months. Ninety-two subjects were initially included for follow-up. At the first collection, all of them were asymptomatic. One individual was positive for Plasmodium vivax, one for Plasmodium malariae and one for P. vivax and P. malariae, corresponding to a prevalence of
3.3% (2.2% for each species). During the follow-up, four new PCR-positive cases (two for each species) were recorded, corresponding to an incidence of 2.5 infections/100 person-years or 1.25 infections/100 person-years for each species. The mathematical transmission model analysis, using a low frequency of human carriers and the vector density in the region, calculated from previous studies in the same locality, whose results were submitted to a linear
regression, suggests that the transmission cycle probably is not based only on human carriers, regardless of whether they are symptomatic or not. Findings from the first cohort suggest that untreated residents of this extra-Amazon region, initially positive for Plasmodium DNA, may become negative without developing symptoms of the disease. Although the possibility of reinfection cannot be ruled out, the positivity for P. malariae in two individuals in the first and in the second survey may be matching with a long-term carriage of this species. Since most of the symptomatic cases of malaria in the area are caused by P. vivax, the epidemiological impact of long-term carriage of P. malariae would be limited. The low incidence of cases and low frequency of asymptomatic malaria carriers detected on these surveys make it unlikely that the transmission cycle in the region could be based solely on human hosts since cases are isolated one from another by hundreds of kilometers and frequently by long periods of time, reinforcing instead the hypothesis of zoonotic transmission
