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Anyamba A, Damoah R, Kemp A, Small JL, Rostal MK, Bagge W, Cordel C, Brand R, Karesh WB, Paweska JT. Climate Conditions During a Rift Valley Fever Post-epizootic Period in Free State, South Africa, 2014–2019. Front Vet Sci 2022; 8:730424. [PMID: 35187137 PMCID: PMC8848741 DOI: 10.3389/fvets.2021.730424] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2021] [Accepted: 12/20/2021] [Indexed: 11/13/2022] Open
Abstract
Rift Valley fever virus (RVFV) activity in Southern Africa tends to occur during periods of sustained elevated rainfall, cooler than normal conditions, and abundant vegetation cover creating ideal conditions for the increase and propagation of populations of RVFV mosquito vectors. These climatic and ecological conditions are modulated by large-scale tropical-wide El Niño–Southern Oscillation (ENSO) phenomena. The aim of this 5-year study was to investigate climatic conditions during Rift Valley fever “post-epizootic” period in Free State province of the Republic of South Africa, which historically experienced the largest RVF outbreaks in this country. We collected satellite-derived rainfall, land surface temperature (LST), and normalized difference vegetation index (NDVI) data since 2014 to understand broad environmental conditions in the years following a period of sustained and widespread large RVF outbreaks (2008–2011) in the region. We found this post-epizootic/interepizootic period to be characterized by below-normal rainfall (~-500 mm), above LSTs (~+12°C), depressed NDVI (60% below normal), and severe drought as manifested particularly during the 2015–2016 growing season. Such conditions reduce the patchwork of appropriate habitats available for emergence of RVFV vectors and diminish chances of RVFV activity. However, the 2016–2017 growing season saw a marked return to somewhat wetter conditions without any reported RVFV transmission. In general, the aggregate vector collections during this 5-year period follow patterns observed in climate measurements. During the 2017–2018 growing season, late and seasonally above average rainfall resulted in a focal RVF outbreak in one location in the study region. This unanticipated event is an indicator of cryptic RVF activity during post-epizootic period and may be a harbinger of RVFV activity in the coming years.
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Affiliation(s)
- Assaf Anyamba
- Universities Space Research Association, Columbia, MD, United States
- Biospheric Sciences Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, United States
- *Correspondence: Assaf Anyamba
| | - Richard Damoah
- Biospheric Sciences Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, United States
- Physics Department and Goddard Earth Sciences Technology and Research, Morgan State University, Baltimore, MD, United States
| | - Alan Kemp
- Center for Emerging and Zoonotic Diseases, Johannesburg, South Africa
| | - Jennifer L. Small
- Biospheric Sciences Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, United States
- Science Systems and Applications, Inc., Lanham, MD, United States
| | | | | | | | - Robert Brand
- Cuyahoga County Board of Health, Parma, OH, United States
- Department of Soil, Crop and Climate Sciences, University of the Free State, Bloemfontein, South Africa
| | | | - Janusz T. Paweska
- Center for Emerging and Zoonotic Diseases, Johannesburg, South Africa
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Nosrat C, Altamirano J, Anyamba A, Caldwell JM, Damoah R, Mutuku F, Ndenga B, LaBeaud AD. Impact of recent climate extremes on mosquito-borne disease transmission in Kenya. PLoS Negl Trop Dis 2021; 15:e0009182. [PMID: 33735293 PMCID: PMC7971569 DOI: 10.1371/journal.pntd.0009182] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2020] [Accepted: 01/26/2021] [Indexed: 01/12/2023] Open
Abstract
Climate change and variability influence temperature and rainfall, which impact vector abundance and the dynamics of vector-borne disease transmission. Climate change is projected to increase the frequency and intensity of extreme climate events. Mosquito-borne diseases, such as dengue fever, are primarily transmitted by Aedes aegypti mosquitoes. Freshwater availability and temperature affect dengue vector populations via a variety of biological processes and thus influence the ability of mosquitoes to effectively transmit disease. However, the effect of droughts, floods, heat waves, and cold waves is not well understood. Using vector, climate, and dengue disease data collected between 2013 and 2019 in Kenya, this retrospective cohort study aims to elucidate the impact of extreme rainfall and temperature on mosquito abundance and the risk of arboviral infections. To define extreme periods of rainfall and land surface temperature (LST), we calculated monthly anomalies as deviations from long-term means (1983–2019 for rainfall, 2000–2019 for LST) across four study locations in Kenya. We classified extreme climate events as the upper and lower 10% of these calculated LST or rainfall deviations. Monthly Ae. aegypti abundance was recorded in Kenya using four trapping methods. Blood samples were also collected from children with febrile illness presenting to four field sites and tested for dengue virus using an IgG enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR). We found that mosquito eggs and adults were significantly more abundant one month following an abnormally wet month. The relationship between mosquito abundance and dengue risk follows a non-linear association. Our findings suggest that early warnings and targeted interventions during periods of abnormal rainfall and temperature, especially flooding, can potentially contribute to reductions in risk of viral transmission. Dengue is a rapidly spreading mosquito-borne disease transmitted primarily by Aedes aegypti mosquitoes. As climate change leads to extremes in rainfall and temperature, the abundance and populations of these vectors will be affected, thus influencing transmission of dengue. Using satellite-derived climate data for Kenya, we classified months that experienced highly abnormal rainfall and temperature as extreme climate events (floods, droughts, heat waves, or cold waves). We compared the average monthly Ae. aegypti abundance and confirmed dengue counts following extreme climate months using lag periods of one month and two months, respectively. This study utilized several statistical models to account for differences among study sites and time. Floods resulted in significantly increased egg and adult abundance. Our results contributed to a better understanding of the effect of climate variability and change on dengue. As suggested by our observed increase in vector counts yet a relatively unchanged dengue infection risk, human behavior can help reduce viral transmission. Targeted interventions should be focused on both reducing vector populations and limiting human-vector contact, especially during these climate anomalies.
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Affiliation(s)
- Cameron Nosrat
- Program in Human Biology, Stanford University, Stanford, California, United States of America
- * E-mail:
| | - Jonathan Altamirano
- Department of Pediatrics, Stanford University School of Medicine, Stanford, California, United States of America
| | - Assaf Anyamba
- Universities Space Research Association & NASA Goddard Space Flight Center, Greenbelt, Maryland, United States of America
| | - Jamie M. Caldwell
- Department of Biology, Stanford University, Stanford, California, United States of America
| | - Richard Damoah
- Morgan State University & NASA Goddard Space Flight Center, Greenbelt, Maryland, United States of America
| | | | - Bryson Ndenga
- Centre for Global Health Research, Kenya Medical Research Institute, Kisumu, Kenya
| | - A. Desiree LaBeaud
- Department of Pediatrics, Stanford University School of Medicine, Stanford, California, United States of America
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Shah MM, Krystosik AR, Ndenga BA, Mutuku FM, Caldwell JM, Otuka V, Chebii PK, Maina PW, Jembe Z, Ronga C, Bisanzio D, Anyamba A, Damoah R, Ripp K, Jagannathan P, Mordecai EA, LaBeaud AD. Malaria smear positivity among Kenyan children peaks at intermediate temperatures as predicted by ecological models. Parasit Vectors 2019; 12:288. [PMID: 31171037 PMCID: PMC6555721 DOI: 10.1186/s13071-019-3547-z] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2019] [Accepted: 06/01/2019] [Indexed: 11/11/2022] Open
Abstract
Background Ambient temperature is an important determinant of malaria transmission and suitability, affecting the life-cycle of the Plasmodium parasite and Anopheles vector. Early models predicted a thermal malaria transmission optimum of 31 °C, later revised to 25 °C using experimental data from mosquito and parasite biology. However, the link between ambient temperature and human malaria incidence remains poorly resolved. Methods To evaluate the relationship between ambient temperature and malaria risk, 5833 febrile children (<18 years-old) with an acute, non-localizing febrile illness were enrolled from four heterogenous outpatient clinic sites in Kenya (Chulaimbo, Kisumu, Msambweni and Ukunda). Thick and thin blood smears were evaluated for the presence of malaria parasites. Daily temperature estimates were obtained from land logger data, and rainfall from National Oceanic and Atmospheric Administration (NOAA)’s Africa Rainfall Climatology (ARC) data. Thirty-day mean temperature and 30-day cumulative rainfall were estimated and each lagged by 30 days, relative to the febrile visit. A generalized linear mixed model was used to assess relationships between malaria smear positivity and predictors including temperature, rainfall, age, sex, mosquito exposure and socioeconomic status. Results Malaria smear positivity varied between 42–83% across four clinic sites in western and coastal Kenya, with highest smear positivity in the rural, western site. The temperature ranges were cooler in the western sites and warmer in the coastal sites. In multivariate analysis controlling for socioeconomic status, age, sex, rainfall and bednet use, malaria smear positivity peaked near 25 °C at all four sites, as predicted a priori from an ecological model. Conclusions This study provides direct field evidence of a unimodal relationship between ambient temperature and human malaria incidence with a peak in malaria transmission occurring at lower temperatures than previously recognized clinically. This nonlinear relationship with an intermediate optimal temperature implies that future climate warming could expand malaria incidence in cooler, highland regions while decreasing incidence in already warm regions with average temperatures above 25 °C. These findings support efforts to further understand the nonlinear association between ambient temperature and vector-borne diseases to better allocate resources and respond to disease threats in a future, warmer world. Electronic supplementary material The online version of this article (10.1186/s13071-019-3547-z) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Melisa M Shah
- Infectious Diseases and Geographic Medicine, Stanford University School of Medicine, Stanford, CA, USA.
| | - Amy R Krystosik
- Department of Pediatrics, Division of Infectious Disease, Stanford University School of Medicine, Stanford, CA, USA
| | - Bryson A Ndenga
- Centre for Global Health Research, Kenya Medical Research Institute, Kisumu, Kenya
| | - Francis M Mutuku
- Department of Environment and Health Sciences, Technical University of Mombasa, Mombasa, Kenya
| | | | - Victoria Otuka
- Centre for Global Health Research, Kenya Medical Research Institute, Kisumu, Kenya
| | - Philip K Chebii
- Department of Pediatrics, Msambweni County Referral Hospital, Msambweni, Kenya
| | - Priscillah W Maina
- Department of Pediatrics, Msambweni County Referral Hospital, Msambweni, Kenya
| | - Zainab Jembe
- Department of Pediatrics, Diani Health Center, Ukunda, Kenya
| | - Charles Ronga
- Centre for Global Health Research, Kenya Medical Research Institute, Kisumu, Kenya
| | - Donal Bisanzio
- RTI International, Washington, DC, USA.,Epidemiology and Public Health Division, University of Nottingham, Nottingham, UK
| | - Assaf Anyamba
- Universities Space Research Association (USRA), & NASA Goddard Space Flight, Biospheric Science Laboratory, Greenbelt, MD, USA
| | - Richard Damoah
- Morgan State University & NASA Goddard Space Flight, Biospheric Science Laboratory, Greenbelt, MD, USA
| | - Kelsey Ripp
- Department of Medicine, Hospital of the University of Pennsylvania, Philadelphia, USA.,Department of Pediatrics, Children's Hospital of Philadelphia, Children's Hospital of Philadelphia, USA
| | - Prasanna Jagannathan
- Infectious Diseases and Geographic Medicine, Stanford University School of Medicine, Stanford, CA, USA
| | - Erin A Mordecai
- Department of Biology, Stanford University, Stanford, CA, USA
| | - A Desiree LaBeaud
- Department of Pediatrics, Division of Infectious Disease, Stanford University School of Medicine, Stanford, CA, USA
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