Recently, the World Health Organization (WHO) confirmed an outbreak of Rift Valley Fever (RVF) affecting Mauritania and Senegal in Western Africa.

About Rift Valley Fever

Rift Valley fever(RVF) is a viral zoonotic disease that primarily affects domesticated animals (cattle, sheep, goats, camels) but can also infect humans. It is a mosquito-borne illness that causes significant economic losses in livestock and a range of symptoms in humans, from a mild flu-like illness to a potentially fatal hemorrhagic fever. 

Cause and Transmission

The disease is caused by the Rift Valley fever virus (RVFV), a Phlebovirus that is part of the Bunyavirales order. The transmission cycle involves mosquitoes and vertebrate hosts: 

• Animal-to-animal transmission: Primarily through infected mosquitoes, mainly Aedes species, which can also transmit the virus to their eggs (vertical transmission), allowing the virus to persist for years in dry conditions. During heavy rainfall and flooding, these eggs hatch, leading to outbreaks in livestock.
• Animal-to-human transmission: The majority of human infections result from direct or indirect contact with the blood, organs, or other body fluids of infected animals. This risk is particularly high for occupational groups like herders, farmers, slaughterhouse workers, and veterinarians. Inhalation of viral particles (aerosol transmission) during animal slaughter and the consumption of unpasteurized milk or undercooked meat/blood from infected animals are also potential transmission routes.
• Mosquito-to-human transmission: Humans can also be infected through the bites of infected Aedes and Culex mosquitoes.
• Human-to-human transmission: Has not been documented to date. 

Symptoms

In Animals

• RVF is most severe in sheep and goats, with high mortality rates (90-100%) in young animals and near 100% abortion rates in pregnant females. Other symptoms include fever, weakness, anorexia, and bloody diarrhea. Adult cattle and camels are more resistant to severe illness but can still experience abortion. 

In Humans

Most human infections are asymptomatic or result in a mild, self-limiting flu-like illness characterized by: 

• Fever, headache, muscle and joint pain.
• General weakness, back pain, and dizziness.
• Sensitivity to light (photophobia), neck stiffness, and loss of appetite. 

In a small percentage of cases (less than 2%), the disease can progress to more severe forms: 

• Ocular form: Retinal lesions can lead to blurred or decreased vision, which may be permanent in about half of the affected patients.
• Meningoencephalitis form: Inflammation of the brain can cause severe headache, hallucinations, confusion, disorientation, and other neurological deficits, which can be permanent in survivors.
• Hemorrhagic fever form: Begins with signs of severe liver impairment (jaundice) followed by spontaneous bleeding (vomiting blood, bloody stool, bleeding gums, rash). This form has a high case fatality rate of approximately 50%. 

Treatment and Prevention

There is no specific treatment for RVF in humans; medical care is primarily supportive, including fluid replacement and pain management. Antiviral drugs are being investigated. 

Prevention and control measures focus on breaking the transmission cycle through a "One Health" approach integrating human and animal health efforts: 

• In animals: A sustained program of preventive vaccination for livestock is a key measure. Vaccination should be done before an outbreak, as doing so during one can intensify the spread through multi-use vials/needles. Restricting animal movement during outbreaks is also important.
• In humans:
  • Avoid contact with potentially infected animal tissues or fluids by using personal protective equipment (gloves, masks, boots) when handling sick animals, assisting with births, or during slaughter/butchering.
  • Ensure food safety by thoroughly cooking all animal products (meat, milk, blood) before consumption in endemic areas.
  • Protect against mosquito bites using repellents, insecticide-treated nets, and protective clothing, and by eliminating mosquito breeding sites. 

An inactivated human vaccine is available but is not licensed for commercial use and is restricted to high-risk laboratory and veterinary personnel. Several other human vaccine candidates are under investigation. 

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