Environmental limits of Rift Valley fever revealed using ecoepidemiological mechanistic models.

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Lo Iacono, Giovanni  ORCID logo  https://orcid.org/0000-0002-6150-2843
Cunningham, Andrew A 
Bett, Bernard 
Grace, Delia 
Redding, David W 

Vector-borne diseases (VBDs) of humans and domestic animals are a significant component of the global burden of disease and a key driver of poverty. The transmission cycles of VBDs are often strongly mediated by the ecological requirements of the vectors, resulting in complex transmission dynamics, including intermittent epidemics and an unclear link between environmental conditions and disease persistence. An important broader concern is the extent to which theoretical models are reliable at forecasting VBDs; infection dynamics can be complex, and the resulting systems are highly unstable. Here, we examine these problems in detail using a case study of Rift Valley fever (RVF), a high-burden disease endemic to Africa. We develop an ecoepidemiological, compartmental, mathematical model coupled to the dynamics of ambient temperature and water availability and apply it to a realistic setting using empirical environmental data from Kenya. Importantly, we identify the range of seasonally varying ambient temperatures and water-body availability that leads to either the extinction of mosquito populations and/or RVF (nonpersistent regimens) or the establishment of long-term mosquito populations and consequently, the endemicity of the RVF infection (persistent regimens). Instabilities arise when the range of the environmental variables overlaps with the threshold of persistence. The model captures the intermittent nature of RVF occurrence, which is explained as low-level circulation under the threshold of detection, with intermittent emergence sometimes after long periods. Using the approach developed here opens up the ability to improve predictions of the emergence and behaviors of epidemics of many other important VBDs.

Floquet analysis, cross-species transmission, stability analysis, vector-borne diseases, zoonosis, Aedes, Animals, Environment, Humans, Models, Theoretical, Mosquito Vectors, Rift Valley Fever, Seasons, Temperature
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Proc Natl Acad Sci U S A
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Proceedings of the National Academy of Sciences
NERC (via Institute of Development Studies) (KN/0929)
NERC (via Institute of Zoology (IoZ)) (EE505 loZ(N575))
NERC (via University College London (UCL)) (CDAGG)
European Commission (278976)
The work was partially supported by the National Institute for Health Research (NIHR) Health Protection Research Unit in Environmental Change and Health at the London School of Hygiene and Tropical Medicine in partnership with Public Health England (PHE) and in collaboration with the University of Exeter, University College London, and the Met Office. European Union FP7 Project ANTIGONE (Contract 278976). Royal Society Wolfson Research Merit Award. The Alborada Trust.