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Wipasa J.,Chiang Mai University | Suphavilai C.,Chiang Mai University | Okell L.C.,London School of Hygiene and Tropical Medicine | Cook J.,London School of Hygiene and Tropical Medicine | And 5 more authors.
PLoS Pathogens | Year: 2010

Antibodies constitute a critical component of the naturally acquired immunity that develops following frequent exposure to malaria. However, specific antibody titres have been reported to decline rapidly in the absence of reinfection, supporting the widely perceived notion that malaria infections fail to induce durable immunological memory responses. Currently, direct evidence for the presence or absence of immune memory to malaria is limited. In this study, we analysed the longevity of both antibody and B cell memory responses to malaria antigens among individuals who were living in an area of extremely low malaria transmission in northern Thailand, and who were known either to be malaria naïve or to have had a documented clinical attack of P. falciparum and/or P. vivax in the past 6 years. We found that exposure to malaria results in the generation of relatively avid antigen-specific antibodies and the establishment of populations of antigen-specific memory B cells in a significant proportion of malaria-exposed individuals. Both antibody and memory B cell responses to malaria antigens were stably maintained over time in the absence of reinfection. In a number of cases where antigenspecific antibodies were not detected in plasma, stable frequencies of antigen-specific memory B cells were nonetheless observed, suggesting that circulating memory B cells may be maintained independently of long-lived plasma cells. We conclude that infrequent malaria infections are capable of inducing long-lived antibody and memory B cell responses. © 2010 Wipasa et al.

Wipasa J.,Chiang Mai University | Okell L.,London School of Hygiene and Tropical Medicine | Okell L.,Imperial College London | Sakkhachornphop S.,Chiang Mai University | And 5 more authors.
PLoS Pathogens | Year: 2011

Immunity to malaria is widely believed to wane in the absence of reinfection, but direct evidence for the presence or absence of durable immunological memory to malaria is limited. Here, we analysed malaria-specific CD4+ T cell responses of individuals living in an area of low malaria transmission in northern Thailand, who had had a documented clinical attack of P. falciparum and/or P. vivax in the past 6 years. CD4+ T cell effector memory (CD45RO+) IFN-γ (24 hours ex vivo restimulation) and cultured IL-10 (6 day secretion into culture supernatant) responses to malaria schizont antigens were detected only in malaria-exposed subjects and were more prominent in subjects with long-lived antibodies or memory B cells specific to malaria antigens. The number of IFN-γ-producing effector memory T cells declined significantly over the 12 months of the study, and with time since last documented malaria infection, with an estimated half life of the response of 3.3 (95% CI 1.9-10.3) years. In sharp contrast, IL-10 responses were sustained for many years after last known malaria infection with no significant decline over at least 6 years. The observations have clear implications for understanding the immunoepidemiology of naturally acquired malaria infections and for malaria vaccine development. © 2011 Wipasa et al.

Kim M.,Centers for Disease Control and Prevention | Holt J.B.,Centers for Disease Control and Prevention | Eisen R.J.,Centers for Disease Control and Prevention | Padgett K.,Vector Borne Disease Section | And 2 more authors.
Photogrammetric Engineering and Remote Sensing | Year: 2011

The recent economic crisis in United States has led to an increase in home foreclosures and subsequent abandonments. A by-product of this trend has been an associated rise in the number of neglected swimming pools, which provide new habitats for the larval stages of the Culex mosquito vectors of West Nile Virus (WNV) in urban and suburban environments. WNV has been major concern related to neglected swimming pools in California. Our research focused on using very high spatial resolution (VHR) satellite imagery and processing techniques, including image pansharpening, normalized difference water index, and geographic object-based image analysis (GEOBIA), to develop a geographic information system (GIS) database of swimming pool locations. This research demonstrated that GEOBIA with VHR imagery could produce a GIS database of swimming pools with the high accuracy of 94 percent. The analytic approach of this research is expected to economically facilitate the location of swimming pools for ground inspection and mosquito control. © 2011 American Society for Photogrammetry and Remote Sensing.

Geraghty E.M.,University of California at Davis | Margolis H.G.,University of California at Davis | Kjemtrup A.,Vector Borne Disease Section | Reisen W.,University of California at Davis | Franks P.,University of California at Davis
Public Health Reports | Year: 2013

Objectives. Insecticides reduce vector-borne pathogen transmission but also pose health risks. In August 2005, Sacramento County, California, underwent emergency aerial ultralow-volume (ULV) application of pyrethrin insecticide to reduce the population of West Nile virus (WNV)-infected mosquitoes and thereby interrupt enzootic and tangential transmission. We assessed the association between aerially applied pyrethrin insecticide and patterns of emergency department (ED) visit diagnoses. Methods. We used geographic information systems software to determine ZIP Code-level exposure to pyrethrin. We used logistic regression models to examine the relationship between exposure status and three-digit International Classification of Diseases, Ninth Edition, Clinical Modification (ICD-9-CM) codes (785 in total) for all ED visits (n=5253,648) within Sacramento County in 2005 and for specific diagnostic clusters (e.g., respiratory, gastrointestinal, skin, eye, and neurologic). All models were adjusted for age, gender, race/ethnicity (individual level), median income, ozone, and temperature (ZIP Code level). Results. Exposure to aerially applied insecticide was not associated with clusters of respiratory, gastrointestinal, skin, eye, and neurologic complaints in adjusted models but was inversely associated with ICD-9-CM code 799 ("other ill-defined morbidity and mortality"), with adjusted odds ratios (AORs) ranging from 0.31 to 0.36 for 0-3 lag days (95% confidence interval 0.17, 0.68). Spraying was also directly associated with ICD-9-CM code 553 ("other abdominal hernia"), with AORs ranging from 2.34 to 2.96 for 2-3 lag days. Conclusions. The observed significant ICD-9-CM code associations likely represented chance findings. Aerial ULV pyrethrin applications were not associated with ED visits for specific diagnoses or clusters of diagnoses. © 2013 Association of Schools of Public Health.

Salkeld D.J.,Stanford University | Padgett K.A.,Vector Borne Disease Section | Jones J.H.,Stanford University
Ecology Letters | Year: 2013

Zoonotic pathogens are significant burdens on global public health. Because they are transmitted to humans from non-human animals, the transmission dynamics of zoonoses are necessarily influenced by the ecology of their animal hosts and vectors. The 'dilution effect' proposes that increased species diversity reduces disease risk, suggesting that conservation and public health initiatives can work synergistically to improve human health and wildlife biodiversity. However, the meta-analysis that we present here indicates a weak and highly heterogeneous relationship between host biodiversity and disease. Our results suggest that disease risk is more likely a local phenomenon that relies on the specific composition of reservoir hosts and vectors, and their ecology, rather than patterns of species biodiversity. © 2013 Blackwell Publishing Ltd/CNRS.

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