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Article Dans Une Revue Scientific Reports Année : 2024

Ability of a dynamical climate sensitive disease model to reproduce historical Rift Valley Fever outbreaks over Africa

Résumé

Rift Valley Fever (RVF) is a zoonosis transmitted by Aedes and Culex mosquitoes, and is considered a priority pathogen by the WHO. RVF epidemics mostly occur in Africa and can decimate livestock herds, causing significant economic losses and posing health risks for humans. RVF transmission is associated with the occurrence of El Niño events that cause floods in eastern Africa and favour the emergence of mosquitoes in wetlands. Different risk models have been developed to forecast RVF transmission risk but very few studies have validated models at pan-African scale. This study aims to validate the skill of the Liverpool Rift Valley Fever model (LRVF) in reproducing RVF epidemics over Africa and to explore the relationship between simulated climatic suitability for RVF transmission and large-scale climate modes of variability such as the El Niño Southern Oscillation (ENSO) and the Dipole Mode Index (DMI). Our results show that the LRVF model correctly simulates RVF transmission hotspots and reproduces large epidemics that affected African countries. LRVF was able to correctly reproduce major RVF epidemics in Somalia, Kenya, Zambia and to a lesser extent for Mauritania and Senegal. The positive phases of ENSO and DMI are associated with an increased risk of RVF over the Horn of Africa, with important time lags. Following research activities should focus on the development of predictive modelling systems at different time scales. Rift Valley fever (RVF) is a zoonotic mosquito-borne disease that was first isolated and discovered in Kenya in 1931 1. Rift Valley fever virus (RVFV) belongs to the genus Phlebovirus in the family Bunyaviridae 2. Rift Valley Fever is a vector-borne disease that primarily affects goats and sheep but can also infect cattle, camels, other wildlife animals (antelopes and wildebeest) and humans 3. Epizootics of RVF are characterized by abortion storms, increased mortality rates in livestock and significant economic losses. Infection experiments showed that the mortality rate in newborn lambs can reach 95-100% while it usually ranges between 20 and 30% in adult sheep 4. Abortion rate in pregnant ewes can be as high as 100%. Recovered animals usually maintain lifelong immunity 5. RVF virus is primarily transmitted to animals by the bite of infected Aedes or Culex mosquitoes 6. Humans can also be infected by mosquito bites and by direct contact with infected animal materials (viraemic blood, infected organs, foetuses, consumption of raw meat and to a lesser extent unpasteurized milk). Slaughterhouse and abattoir personnel, herders and veterinarians usually face a greater risk of infection. The human symptoms are characterized by high fever, headaches, dizziness, back pain and liver abnormalities. In some cases (8-10%), a severe and often a fatal haemorrhagic form of the disease can occur with ocular complications, meningoencephalitis and haemorrhagic fever 7. Currently, there are commercially available vaccines (mostly live-attenuated and inactivated) for animals and an unlicensed human vaccine has been clinically tested on most at-risk professionals such as veterinarians, livestock farmers and slaughterhouse personnel 8. One of the first well-documented RVF epidemic occurred in western provinces of South Africa in autumn 1951 and affected sheep, cattle, probably wild bucks, and humans 9. In 1977-1978, a large RVF epidemic caused about 600 human deaths in Egypt. Imported livestock from the Horn of Africa might have triggered this epidemic and increased abundance of mosquito vectors from the flooded Nile might have played an amplification role 10. The 1997-1998 RVF epidemic that caused thousands of livestock deaths and about 500 human unexplained
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hal-04488428 , version 1 (04-03-2024)

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Alizée Chemison, Gilles Ramstein, Anne Jones, Andy Morse, Cyril Caminade. Ability of a dynamical climate sensitive disease model to reproduce historical Rift Valley Fever outbreaks over Africa. Scientific Reports, 2024, 14 (1), pp.3904. ⟨10.1038/s41598-024-53774-x⟩. ⟨hal-04488428⟩
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