Clinically silent Plasmodium vivax infections in native Amazonians of northwestern Brazil: acquired immunity or low parasite virulence?

Barros, Luiza Barbosa; Calil, Priscila Rodrigues; Rodrigues, Priscila T.; Tonini, Juliana; Fontoura, Pablo S.; Sato, Priscila de Morais; Cardoso, Marly Augusto; Russo, Marina Werneck de Almeida Avellar; Cavasini, Carlos Eduardo; Fernandes, Anderson; Ferreira, Marcelo U.

doi:10.1590/0074-02760220175

Cited by 4 publications

(1 citation statement)

References 38 publications

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“…It has not been possible to confirm if this case was acquired through autochthonous transmission or was imported because the patient was lost to follow up. P. vivax can produce asymptomatic or clinically silent infections in endemic regions and these patients may present with AUFI caused by a different pathogen [52,53]. Considering that Villeta municipality is not endemic for malaria this possibility is less likely.…”

Section: Diagnostic Results (N) Positive Tests (N)mentioning

confidence: 99%

Etiological characterization of acute undifferentiated febrile illness in Apartadó and Villeta municipalities, Colombia, during COVID-19 pandemic

2023

Infez Med

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Background: Acute undifferentiated febrile illness (AUFI) is one of the leading causes of illness in tropical regions. Although malaria is the most important cause, other pathogens such as Dengue (DENV), Leptospira and recently, Coronavirus Disease 2019 (COVID-19) have gained importance. In Colombia, few studies aimed to identify the etiology of AUFI. Most of them performed in Apartadó and Villeta municipalities, identifying the active circulation of several pathogens. Thus, we conducted a cross-sectional study in these municipalities to characterize the etiologies of AUFI during COVID-19 pandemic. Methods: An active surveillance was conducted between September and December 2021 in local hospitals of Apartadó and Villeta municipalities. Febrile patients were enrolled after voluntarily agreeing to participate in the study. Ten different etiologies were evaluated through direct, serological, molecular and rapid diagnostic methods.Results: In Apartadó a confirmed etiology was found in 60% of subjects, DENV (25%) being the most frequent, followed by leptospirosis (16.7%), malaria (10%), CO-VID-19 (8.3%), spotted fever group (SFG) rickettsiosis (6.7%) and Chikungunya (1.7%). In Villeta, a specific etiology was confirmed in 55.4% of patients, of which SFG rickettsiosis (39.3%) was the most frequent, followed by leptospirosis (21.4%), DENV (3.6%) and malaria (1.8%). No cases due to Mayaro, Yellow Fever, Oropouche and Venezuelan Equine Encephalitis viruses were detected. Conclusion:We confirm the relevance of dengue fever, leptospirosis, SFG rickettsiosis, COVID-19 and malaria as causes of AUFI in the municipality of Apartadó, and highlight the great importance of SFG rickettsiosis as the main cause of AUFI in the municipality of Villeta.

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Section: Diagnostic Results (N) Positive Tests (N)mentioning

confidence: 99%

Etiological characterization of acute undifferentiated febrile illness in Apartadó and Villeta municipalities, Colombia, during COVID-19 pandemic

2023

Infez Med

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Changing Clinical Epidemiology of Plasmodium vivax Malaria as Transmission Decreases: Population-Based Prospective Panel Survey in the Brazilian Amazon

Fontoura,

Macedo,

Calil

et al. 2024

The Journal of Infectious Diseases

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Background Malarial infections are often missed by microscopy, and most parasite carriers are asymptomatic in low-endemicity settings. Whether parasite detectability and its ability to elicit symptoms change as transmission declines remains unclear. Methods We performed a prospective panel survey with repeated measurements on the same participants over 12 months to investigate whether Plasmodium vivax detectability by microscopy and risk of symptoms upon infection varied during a community-wide larviciding intervention in the Amazon basin of Brazil that markedly reduced vector density. We screened 1096 to 1400 residents in the intervention site for malaria by microscopy and quantitative TaqMan assays at baseline and twice during intervention. Results We found that more P vivax infections than expected from their parasite densities measured by TaqMan assays were missed by microscopy as transmission decreased. At lower transmission, study participants appeared to tolerate higher P vivax loads without developing symptoms. We hypothesize that changes in the ratio between circulating parasites and those that accumulate in the bone marrow and spleen, by avoiding peripheral blood microscopy detection, account for decreased parasite detectability and lower risk of symptoms under low transmission. Conclusions P vivax infections are more likely to be subpatent and remain asymptomatic as malaria transmission decreases.

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Profiling vivax malaria incidence, residual transmission, and risk factors using reactive case detection in low transmission settings of Ethiopia

Abossie,

Getachew,

Demissew

et al. 2024

Malar J

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Clinically silent Plasmodium vivax infections in native Amazonians of northwestern Brazil: acquired immunity or low parasite virulence?

Cited by 4 publications

References 38 publications

Etiological characterization of acute undifferentiated febrile illness in Apartadó and Villeta municipalities, Colombia, during COVID-19 pandemic

Etiological characterization of acute undifferentiated febrile illness in Apartadó and Villeta municipalities, Colombia, during COVID-19 pandemic

Changing Clinical Epidemiology of Plasmodium vivax Malaria as Transmission Decreases: Population-Based Prospective Panel Survey in the Brazilian Amazon

Profiling vivax malaria incidence, residual transmission, and risk factors using reactive case detection in low transmission settings of Ethiopia

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