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

BACKGROUND: Simian 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. METHODS: Parasites 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. RESULTS: An 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. CONCLUSION: The 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.

Plasmodium falciparum rhoptry protein RSP2 triggers destruction of the erythroid lineage.

The destruction of erythrocytes and defects in erythropoiesis are among the most frequently observed causes of morbidity in severe Plasmodium falciparum malaria. The molecular mechanisms involved remain unclear, despite extensive investigation. We show here, for the first time, that tagging with the parasite rhoptry protein ring surface protein 2 (RSP2) is not restricted to the surfaces of normal erythrocytes, as previously reported, but that it extends to erythroid precursor cells in the bone marrow of anemic malaria patients. Monoclonal mouse antibodies and human sera from patients with severe anemia, reacting with RSP2-tagged erythrocytes, induced cell destruction by phagocytosis and complement activation in vitro. Our observations reveal a new parasite mechanism implicated in the destruction of normal erythrocytes and probably dyserythropoiesis in malaria patients. These data suggest that the tagging of host cells with RSP2 may trigger anemia in falciparum malaria.

High prevalence of asymptomatic Plasmodium vivax and Plasmodium falciparum infections in native Amazonian populations.

The epidemiology of malaria in 2 riverine localities in Rondjnia, Brazilian western Amazjnia, was assessed by a 1-year study at Portuchuelo, and a cross-sectional survey at riverine communities at Rio Machado (= Ji-Parana). Plasmodium spp. infections were diagnosed by light microscopy and by polymerase chain reaction (PCR) amplification of ribosomal DNA. PCR was 6-7 times more efficient than microscopy for detecting plasmodial infections. Both Plasmodium vivax and Plasmodium falciparum infections occurred as asymptomatic and symptomatic forms of the disease. The relation between symptomatic and asymptomatic clinical forms was roughly similar for both species of Plasmodium. Symptomless patients were monitored for 2 months. The prevalence of symptomless infections was 4-5 times higher than the symptomatic ones--respectively, 20% and 4.6% for Portuchuelo and 49.5% and 10% for Ji-Parana. Symptomatic malaria occurred mostly in patients in younger age groups. In contrast, there was a significant association of symptomless malaria with older age groups (medians of 26.5 and 21 years, respectively, for Portuchuelo and Ji-Parana), whereas the age medians for symptomatic malaria were 14 and 8 years, respectively, in the 2 regions. Symptomatic malaria also was more prevalent in groups living for shorter times in Amazjnia (13 and 4 years, respectively, for Portuchuelo and Ji-ParanA) as compared with symptomless malaria, which was more prevalent in groups living for longer periods in the region (medians of 25.5 and 18 years, respectively, for Portuchuelo and Ji-Paraná). The high prevalence of symptomless malaria may pose new problems for the currently adopted strategy for the control of malaria in the Amazonian region, which is essentially based on the treatment of symptomatic patients.

Malaria control in an agro-industrial settlement of Rondônia (Western Amazon region, Brazil)

A malaria control pilot project was developed in the Urupá agro-industrial farm that is situated in the State of Rondônia (Western Amazon Region, Brazil). Around 180 inhabitants had been surveyed for the past five years. The control measures were based on (1) training a community agent to perform on the spot microscopical diagnosis of malaria and to treat the uncomplicated cases of malaria; (2) limiting the use of insecticides to a short period before the high transmission season. This resulted in a significant reduction in the time between the onset of clinical symptoms and specific chemotherapy which fell from 3.5 to 1.3 days. In relation to the previous three reference years the total number of malaria cases was reduced to 50 in the first year and to 25 in the second year. The introduction of these measures coincided with pronounced reduction in the frequency of Plasmodium falciparum infections but this was less marked for P. vivax infections. In the second year of the pilot experiment there was no P. falciparum transmission on the farm. During the last decade there was a general decrease in the endemicity of malaria in the State of Rondônia. The linear regression coefficient values indicate that the decline was more pronounced in Urupá than in the general municipality and that the falciparum malaria API in Urupá farm is significantly lower than in the general municipality of Candeias were the farm is situated.