mitigation of the impacts of rift valley fever through targeted vaccination strategies
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Mi#ga#on of the impacts of Ri2 Valley fever through targeted vaccina#on strategies John Gachohi and Bernard Be.
• Ri# Valley fever (RVF) virus (RVFV) is a mosquito-‐borne pathogen that causes explosive outbreaks of severe human and livestock disease in Africa and Arabian Peninsula. The rapid evoluDon of RVF outbreaks generates excepDonal challenges in its miDgaDon and control.
• A decision-‐support tool (DST) for prevenDon and control of RVF in the Greater Horn of Africa idenDfies a series of events that indicates increasing risk of an outbreak and matches intervenDons to each event (RVF-‐DST, 2010).
• This study assessed the effecDveness of targeted vaccinaDon in miDgaDng the impacts of RVF outbreaks.
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John Gachohi j.gachohi@cgiar.org ● P.O. Box 30709-‐00100 Nairobi, Kenya ● +254 20 422 3000 h]p://aghealth.wordpress.com ● www.ilri.org Acknowledgements: The CGIAR Research Program on Agriculture for NutriDon and Health (A4NH) and the InternaDonal Livestock Research InsDtute (ILRI) Funding: European Community’s Seventh Framework Programme (FP7/2007-‐2013) under grant agreement no 266327.
This document is licensed for use under a CreaDve Commons A]ribuDon –Non commercial-‐Share Alike 3.0 Unported License September 2014
• We used a 2-‐host (ca]le and sheep) and 2-‐ vector (Aedes and Culex species) RVFV transmission model to assess the impact of vaccinaDng either 50% or 75% of each host species populaDon at different Dme points idenDfied in the DST.
• The impact is measured by esDmaDng the area under incidence curve (AUC) for the different scenarios.
IntroducDon
Materials and methods
Results
Research into use
DST #me points included in the model and their lead #mes based on recent outbreak in 2006/2007 in Kenya
1. Issuance of RVF early warning based on naDonal meteorological forecasts -‐-‐ 11 weeks to the outbreak.
2. Onset of heavy rains -‐-‐ 6 weeks to the outbreak.
3. Occurrence of mosquito swarms and first RVF cases in livestock -‐-‐ at outbreak onset.
4. Laboratory RVF virus confirmaDon -‐-‐ 3 weeks following outbreak onset.
• Targeted vaccinaDon can be effecDve in miDgaDng the impacts of RVF outbreaks.
• However, challenges associated with predicDon of the outbreak, availability and delivery of vaccines need to be addressed.
• Impacts appear to depend on host diversity, with sheep potenDally requiring more intensive vaccinaDon coverage.
Figure 1: Incidence curves upon vaccina#ng 50% and 75% of each host species at different #me points iden#fied in the RVF-‐DST.
Table 1: Impact of caOle and sheep vaccina#on measured as propor#onal reduc#on (%) in the area under incidence curves rela#ve to baseline (no interven#on)
• Predicted impacts higher in ca]le relaDve to sheep (Fig.1)
• No major differences in vaccinaDng hosts during the period prior to and at outbreak onset parDcularly in ca]le.
• VaccinaDng hosts 3 weeks a#er outbreak onset has li]le or no impact parDcularly in sheep.
• Similar pa]erns in both scenario with moderate reducDons in the AUC upon vaccinaDng 75% of hosts (Table 1).
• Differences in impacts dependent on species is a]ributed to higher populaDon turn-‐over and higher disease suscepDbility among sheep relaDve to ca]le.
Reference Decision-‐Support Tool for PrevenDon and Control of Ri# Valley Fever EpizooDcs in the Greater Horn of Africa. Am. J. Trop. Med. Hyg., 83(Suppl 2), 2010, pp. 75–85
September 2014
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