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

Abstract

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.

The Global Public Health Significance of Plasmodium vivax

“…Relatively low parasite densities in blood (arising from its strict preference for reticulocytes) may lead to high rates of false-negative diagnoses by microscopy or rapid diagnostic tests (RDTs) (Mueller et al, 2009a). Microscopic diagnoses very often underestimate the true prevalence of P. vivax in blood in both high-and low-transmission settings (Mueller et al, 2009b;da Silva et al, 2010;Harris et al, 2010;Katsuragawa et al, 2010;Steenkeste et al, 2010). Further details regarding the diagnosis of P. vivax may be found in a review elsewhere in this thematic volume of Advances in Parasitology (Chapter 4, Volume 80).…”

Asymptomatic infection with Plasmodium falciparum and Plasmodium vivax in the Brazilian Amazon Basin: to treat or not to treat?

“…1) (all localities have been described in previous studies) (Gil et al 2007, Katsuragawa et al 2008, 2010: Vila Candelária (VC), Engenho Velho (EV), Santo Antônio (SA), Cachoeira do Teotônio (CT) and Vila Amazonas (VA). VC and EV are suburban, whereas CT and VA are rural localities approximately 30 km from the urban area.…”

“…Epidemiological surveys of the suburban and rural communities near the city of Porto Velho, the capital of RO (Fig. 1), also reported a relatively high prevalence of asymptomatic infections in the riverside areas (Gil et al 2007, Katsuragawa et al 2008, 2010. More detailed studies conducted in rural communities in the vicinity of the urban area of Porto Velho showed that asymptomatic infections were limited to long-term residents.…”

“…More detailed studies conducted in rural communities in the vicinity of the urban area of Porto Velho showed that asymptomatic infections were limited to long-term residents. By contrast, clinical malaria cases from the area were more frequent in nonresidents on short stays for fishing or tourism who slept in tents or shacks that rendered them more susceptible to Anopheles bites (Katsuragawa et al 2010).…”

Cross-reactive anti-PfCLAG9 antibodies in the sera of asymptomatic parasite carriers of Plasmodium vivax

“…This characteristic of the population due to a high density of the Anopheles darlingi vector (Gil et al 2003(Gil et al , 2007. Annual parasite index levels found for residents of these localities were 200-800, in association with the development of natural immunity among long time residents and a prevalence of asymptomatic malaria parasite carriers in the adult population varying from 15-30% for Plasmodium vivax and 5-10% for P. falciparum (Katsuragawa et al 2009(Katsuragawa et al , 2010. Control measures developed in recent years, based on new formulations of drugs against P. falciparum malaria, have reduced the risk of P. falciparum infections in the studied areas to less than 10% (Epidemiologic Surveillance of Information System/ Brazilian Health Ministry) (portalweb04.saude.gov.br/ sivep_malaria/default.asp).…”