Rift Valley fever (RVF) is a mosquito-borne zoonotic disease primarily affecting livestock such as sheep, goats, camels, and can also infect humans.

Traditionally found in certain regions of Africa, RVF has increasingly shown a concerning pattern of outbreaks in unexpected locations.

This shift poses new challenges for public health and livestock management, as the virus's spread is influenced by complex environmental, ecological, and human factors.

<h3>Origins and Traditional Epidemiology of Rift Valley Fever</h3>

RVF was first identified in Kenya's Rift Valley in the early 20th century following a series of livestock deaths and abortions. Historically, outbreaks were primarily associated with specific cycles of heavy rainfall and flooding, conditions which favor the breeding of mosquito vectors—mainly Aedes and Culex species that transmit the virus.

The virus mainly circulates among animals, but humans can become infected through mosquito bites or direct contact with fluids and tissues of infected animals, especially during slaughtering or veterinary procedures. While most human cases are mild or asymptomatic, severe disease and even fatal hemorrhagic fever can occur, posing considerable health risks.

<h3>Expansion Beyond Traditional Hotspots</h3>

Recently, RVF has been increasingly reported outside its usual endemic areas. For example, the East African Community countries have experienced a rise in outbreak frequency and geographical spread between 2010 and 2024.

Countries like Rwanda and Burundi, which had limited prior documented outbreaks, have reported significant RVF events in the past decade. This expansion reflects a wider distribution of the mosquito vectors and suitable environmental conditions, possibly accelerated by climate change.

<h3>Contributing Factors to New Outbreak Patterns</h3>

Several intertwined factors contribute to the shifting landscape of RVF outbreaks:

<b>Climate Variability and Change:</b> Extreme weather events like flooding, heavy rainfalls, and droughts create variable mosquito breeding habitats. Climate change intensifies these phenomena, promoting more frequent and widespread outbreaks.

<b>Ecological Changes:</b> Modifications in land use, deforestation, water management, and agricultural practices alter vector and host habitats. Such ecological disruptions can facilitate the virus's migration to new zones.

<b>Animal Movement and Trade:</b> The nomadic nature of pastoralist communities and growing livestock trade increase the chance of virus dissemination across regions and borders.

<b>Surveillance and Reporting Improvements:</b> Better detection and data collection may reveal outbreaks previously undetected, contributing to the impression of virus expansion.

<h3>Impacts on Human and Animal Health</h3>

RVF outbreaks severely impact both livestock and human populations. In affected regions, livestock face high morbidity and mortality, particularly pregnant animals experiencing abortions, causing significant economic losses and food security concerns for dependent communities. Human infections range from mild flu-like symptoms to severe viral hemorrhagic fever, with mortality rates reaching up to 50% in critical cases.

Mitigation is complicated by low vaccination coverage in livestock, often due to the nomadic lifestyle of herders, insufficient awareness, and vaccine side effects concerns. Mosquito control remains difficult given the widespread vector habitats and environmental conditions.

<h3>Measures and Future Directions</h3>

Addressing RVF's evolving threat requires multifaceted strategies:

<b>Strengthening Surveillance:</b> Enhanced epidemiological monitoring and rapid response capabilities are crucial for timely detection and containment of outbreaks.

<b>Vaccination:</b> Expanding vaccination coverage among livestock can reduce the viral reservoir, though vaccine safety and logistical challenges persist.

<b>Community Education:</b> Improving awareness among at-risk populations about transmission risks and protective measures—such as avoiding contact with infected animals and using mosquito nets—is vital.

<b>Research and Innovation:</b> Development of more effective and safer vaccines, better diagnostic tools, and vector control methods are priorities.

"This groundbreaking research will shed new light on a disease that has been neglected for far too long. The learnings will tell us whether large-scale vaccine efficacy trials are feasible, where they should take place, and how long they are expected to take."— Dr. Kent Kester.

Rift Valley fever is no longer confined to traditional endemic areas but is increasingly causing outbreaks in unexpected regions, driven by climatic variability, ecological changes, and socio-economic dynamics. Understanding the complex and shifting nature of RVF is critical for protecting vulnerable populations and preserving livestock health as the virus's reach continues to widen.