Rift Valley fever virus: Movement of infected humans threatens global public health and agriculture

Abstract

Rift Valley fever (RVF) is an acute disease of ungulate livestock and wildlife as well as humans caused by the Rift Valley fever virus (RVFV), which can be transmitted by arthropod vectors such as mosquitoes as well as by direct contact with infected tissues. Outbreaks of this virus may lead to widespread mortality and morbidity in susceptible ungulates and humans, with pronounced economic and agricultural impacts. Humans infected with RVFV can develop extremely high viremias capable of infecting vectors such as mosquitoes. Critically, RVFV has potential for globalization resulting from the movement of infected humans into non-endemic regions containing populations of potentially competent mosquito vectors and susceptible livestock and wildlife hosts that include the US, Asia, and parts of southern Europe. In this review, we explore scenarios of escape of RVFV from its endemic range that could be caused by the movement of infected humans. The risks of globalization of the RVFV pathogen into Europe, Asia, and the Americas is high and increasing each year because of climate change, redistribution and expanding ranges of vector and host species, lack of an approved human vaccine, insecticide resistance, and international travel and commerce. We discuss approaches that could be used to mitigate these avenues of spread that include surveillance targeted by environmental modeling coupled with decisive vector control.

The increasing threat of Rift Valley fever virus globalization: strategic guidance for protection and preparation

“…Within the last 25 yr, however, RVFV has spread to the Arabian Peninsula (Balkhy and Memish 2003) and now shows increasing patterns of interepizootic activity in areas of historic large scale epizootic transmission, as well as emergence and re-emergence in adjoining regions in Africa, on the annual scale. This virus is poised to escape from its expanding range on the African continent, western Indian Ocean, and Arabian Peninsula and spread to Europe, the Americas, Asia, and further (Gibson et al 2022). Globalization of this virus will likely cause rapid, severe, and lasting negative consequences to public and veterinary health and the economy (Peyre et al 2015, Pendell et al 2016) for each region in which it emerges.…”

“…Rift Valley fever virus vaccines for human use are not approved but are approved and in use for veterinary applications in endemic regions but must be targeted in space and time to be effective and affordable (Anyamba et al 2010). In emerging regions, however, this may not be a realistic solution, especially if the virus enters wild ungulate populations or is unrecognized before quickly spreading in livestock (Gibson et al 2022).…”

“…Models of the risk of spread of RVFV into new regions overwhelmingly focus on movement of infective livestock over movement of infective humans (Drouin et al 2022). However, a strong case can be made that the massive daily international movement of humans, combined with the extremely high viremias of RVFV that humans can produce, create the most vulnerable route for spread of RVFV (Gibson et al 2022). Reports of circulation of RVFV in humans (e.g., Sanderson et al 2020, Mhamadi et al 2023, Satapathy et el.…”

“…In addition to the capability of the virus to be transmitted by aerosols and direct contact with infected tissues, there exists a very large diversity of known putative potential mosquito and other arthropod vectors of RVFV in the United States, Europe, and Australia, and likely worldwide, that could readily transfer the virus from an infected traveler or domestic livestock into other humans, livestock, and wildlife (Golnar et al 2014, Linthicum et al 2016, Gibson et al 2022). Enough public and veterinary health care practitioners in nonendemic regions are not sufficiently trained to recognize symptoms or consider diagnostics for RVF infections, and mosquitoes collected by mosquito and vector control districts are routinely tested for select pathogens that do not include RVFV or orthobunyaviruses in general with which there may be some cross reactivity.…”

Mechanistic models of Rift Valley fever virus transmission: A systematic review

“…Nevertheless, some data, while scarce, suggest they could develop a high viremia [144][145][146][147], which would be sufficient to infect mosquitoes. Under this hypothesis, humans could have a role in the long distance spread of the virus [148]. Considering this knowledge gap and the difficulty to obtain direct observations on that matter, it would seem relevant for future models to evaluate whether human-to-mosquito transmission is necessary to explain observed transmission dynamics.…”