Rift Valley Fever

Fig: Annual number of immediate notifications (green lines) and number of outbreaks (blue bars) reported to the OIE from 2005 – 2020 (WAHIS, May 2020)

More recently, in 2009 and 2010, the Republic of South Africa reported close to 500 outbreaks of RVF to the OIE and suffered 18 human losses, amongst which a young lady-veterinarian. In 2010, an unprecedented outbreak of RVF was reported in Mauritania causing loss of human life and killing cattle.

In west Africa, more outbreaks, though relatively reduced in scale, occurred in Mauritania (2013, 2015), Senegal (2013), Niger (2016) and Mali (2017). In eastern Africa, after an inter-epizootic period of some 8 years (2011 – 2017), outbreaks were again reported from 2018 onwards, with immediate notifications being submitted by Kenya, Rwanda, South Sudan, Sudan, and Uganda, in addition to Chad and South Africa (and lately – January 2020 – Libya).

Global warming is likely to lead to a modified and possibly enlarged distribution of the main disease vectors, the Culex and Aedes mosquitos, which has already proven to survive in previously unaffected countries, such as Portugal, Spain and Italy. This threat to the developed world has triggered accelerated research in prevention and control of RVF. Several vaccines for use in animals are available but are not used on a wide scale since RVF outbreaks tend to be unpredictable (but often related to floods) and follow an approximate 10-year cycle. This epidemiological feature also makes the establishment of vaccine banks cost-inefficient, at least with the current set of vaccines. Also, few sufficiently sensitive pen-side tests are widely available.