Rift Valley Fever (RVF) is a viral disease that primarily targets animals like cattle, buffalo, goats, sheep, and camels in Sub-Saharan Africa. However, humans can also get infected, though it’s less common and usually less severe. When humans do get RVF, it can sometimes lead to serious health issues.
Humans can contract RVF through direct contact with the blood, fluids, or tissues of infected animals or through the bite of a mosquito carrying the virus. There haven’t been any documented cases of RVF spreading from person to person.
The incubation period for RVF is typically between 2 to 6 days. Many people who get the virus either don’t show symptoms or only experience mild fever-like symptoms such as fever, headache, and muscle pain. However, around 8-10% of those infected might develop severe symptoms like hemorrhaging, brain inflammation (encephalitis), or eye disease, which can significantly affect their health.
The RVF virus, part of the Phlebovirus family, was first identified in 1931 during an investigation of a sheep epidemic in Kenya’s Rift Valley. Since then, it has caused several outbreaks in Sub-Saharan Africa and beyond, including a significant outbreak in Egypt in 1977 due to the trade of infected livestock. Another major outbreak occurred in 1997-98 in Kenya, Tanzania, and Somalia, and in 2000, the virus spread to Saudi Arabia and Yemen from the Horn of Africa via livestock trade.
**How RVF Spreads to Humans**
Humans usually get RVF through direct or indirect contact with the blood or tissues of infected animals, often during butchering, slaughtering, or handling animal birth or carcasses. This makes certain occupations like farming, herding, veterinary work, and slaughterhouse duties particularly high-risk. Infection can occur through wounds from contaminated tools, broken skin, or inhaling aerosols produced during slaughtering. There are also instances where people have been infected by consuming unpasteurized or uncooked milk from infected animals. Additionally, bites from infected mosquitoes, especially Aedes and Culex species, can spread RVF to humans.
**Signs and Symptoms**
After being exposed to the RVF virus, symptoms can take 2 to 6 days to appear. Most people show no symptoms or only mild ones like fever, fatigue, and back pain, usually recovering within a week.
In severe cases, which represent about 8-10% of infections, symptoms can be more serious:
– **Ocular Disease**: Eye disease may develop, causing blurry vision, and sometimes leading to permanent vision loss if it affects the central part of the retina.
– **Hemorrhagic Fever**: This severe form is very rare, with symptoms like jaundice, bleeding, and liver impairment, and has a high fatality rate.
– **Encephalitis**: This brain inflammation can lead to headaches, seizures, and in rare instances, coma. While death is rare, long-term neurological impacts may occur.
In animals, RVF causes severe symptoms such as fever, weakness, and spontaneous abortions, especially in young animals. The disease’s fatality rate is much lower in adult livestock.
**Diagnosis**
Diagnosing RVF can be challenging due to its non-specific symptoms, especially early on, and it requires laboratory tests, which are only available in specialized labs. The virus can be identified through tests such as Reverse Transcriptase Polymerase Chain Reaction (RT-PCR) assays, ELISA for antibodies, or virus isolation via cell cultures.
**Treatment**
Most human cases of RVF do not need specific treatment, as symptoms are generally mild and short-lived. Severe cases, making up about 8-10% of infections, require supportive therapy in hospitals. Although an inactivated vaccine exists, it is not yet licensed for general use and is currently reserved for high-risk groups like laboratory and veterinary workers.
**Prevention**
For animals, sustained vaccination programs using either modified live vaccines or inactivated virus vaccines are crucial. These should be administered before outbreaks occur to prevent epizootics. Movement restrictions on livestock, especially during international trade, can help contain the spread.
For humans, increasing awareness through public health education about the risks and how the virus spreads can significantly reduce infection rates. Important preventive measures include safe animal handling practices, proper cooking of animal products, protective clothing, and mosquito control.
Healthcare workers should follow standard precautions when handling specimens from suspected or confirmed RVF cases to minimize any risk of transmission.
**Vector Control**
Controlling mosquito populations through measures like larviciding around breeding sites can help reduce RVF spread. Effective vector control, combined with climate forecasting to predict favorable conditions for RVF outbreaks, is essential in preventing and managing outbreaks.