After introduction of Rift Valley fever virus (RVFV) in the Netherlands, the virus may cause an outbreak and persist in several areas of the Netherlands. Counter-intuitively, the areas at risk of Rift Valley Fever (RVF) outbreaks are not the densely populated livestock areas.
The virus is not effectively transmitted in densely populated livestock areas due to a low number of vectors per host. This was shown in a study using a mathematical model by experts of the Central Veterinary Institute.
Rift Valley Fever
RVF is a zoonotic vector-borne infection. RVFV infection in humans is generally mild or unapparent, but occasionally severe and potentially fatal complications occur. Infection in pregnant cattle, sheep and goats can cause abortions and causes high mortality rates of new-borns.
Vectors and hosts
Mosquito species present in the Netherlands are related to those that transmit Rift Valley fever virus in Africa. An introduction in the Netherlands might therefore lead to an outbreak. A mathematical model can be used to determine the potential of spread and persistence of RVFV. This study showed that areas with a low livestock density are most likely to experience an outbreak and persistence of the infection, as they are the areas with the highest vector-to-host ratio.
Many aspects of Rift Valley Fever Virus transmission are uncertain. The mathematical model developed in the study provides insight into the importance of uncertainties and gaps in knowledge for the potential risk of a RVF outbreak and persistence. The main uncertainty is knowledge of the potential vectors: a lack of accurate vector abundance estimates in the Netherlands, and the uncertainties whether Dutch mosquitoes can actually transmit the virus and whether the virus can survive during winter. Another uncertain factor is whether the virus can reproduce and be transmitted by animals other than the above mentioned livestock species. For instance, the susceptibility of deer-species is unknown at this moment.
An outbreak of RVFV potentially has a large impact on public health, animal welfare and economy. Further research into the potential vectors is needed: the mosquito abundance and the association with host species, as well as survival potential of the virus during winter.