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Background 

Rift Valley Fever (RVF)is caused by RFV virus, a zoonotic virus (family Bunyaviridae and genus Phlebovirus) transmitted by mosquitoes and blood feeding flies that usually affects animals (commonly cattle and sheep) but can also involve humans. Some infected people have no symptoms or mild symptoms such as fever, headache, fatigue, arthralgia and myalgia. Some develop neck stiffness, sensitivity to light, loss of appetite and vomiting. The symptoms usually last from 4 to 7 days. Typically, patients recover within two days to one week after illness onset. However, some patients develop severe symptoms, including ocular disease, meningoencephalitis, hemorrhagic fever, shock, hepatic damage or even death. The case fatality rate is 1%. As most human cases of RVF experience relatively mild symptoms of short duration, no specific treatment is required for these patients. For severe cases, the predominant treatment is general supportive therapy. 

Epidemiology

The outbreaks have been reported in sub-Saharan Africa, and in recent years the disease has spread to Sudan, Kenya, Somalia, Tanzania, South Africa, Mauritania, Saudi Arabia and Yemen. In 2000, the outbreaks in Saudi Arabia and Yemen marked the first reported occurrence of the disease outside the African continent, raising concerns that it could extend to other parts of Asia and Europe. RVF virus primarily infects livestock, causing epizootics. The most notable RVF epizootic occurred in Kenya in 1950-1951, resulting in the death of an estimated 100,000 sheep. Another example of RVF spillover into human populations occurred in West Africa in 1987, and was linked to the construction of the Senegal River Project. The project caused flooding in the lower Senegal River area, altering ecological systems and interactions between animals and humans. So far, no confirmed case has been reported in Taiwan. 

RVF Surveillance in Taiwan

1. Taiwan National Infectious Disease Statistics System- RVF
2. Fever screening at international airports and seaports.
3. Self–reporting through the toll–free 1922 hotline or local public health authority. 

Prevention and Control

1. Clean and remove vector breeding sites and avoid mosquito bites. Effective prevention methods include the use of screen door/window, bed net, and mosquito repellents, and wearing protective garments. 
2. Animal immunization. Avoid contact with the blood, body fluids, or tissues of the infected animals or products in the RVF-affected areas. 
3. In laboratory and healthcare settings, staff should be properly trained and always follow standard infection prevention and control precautions.
4. One inactivated vaccine has been in development, which is not licensed and commercially available. It has been used experimentally to protect veterinarians and laboratory workers at high risk of exposure to RVF. 

FAQs

1. Who is the most at risk of RVF infection?
   • People who have contact with sick animals, including animal health workers, herders, abattoir workers, people involved in slaughtering sick animals, people who may touch the bodies of sick or dead animals, and those who may handle uncooked meat or drink raw milk of sick animals.
2. What is the treatment of RVF infection?
   • As most human cases of RVF experience relatively mild symptoms of short duration, no specific treatment is required for these patients. For severe cases, the predominant treatment is general supportive therapy.
3.  What are the symptoms of RVF infection?
   • Some infected people have no symptoms or mild symptoms such as fever, headache, fatigue, arthralgia and myalgia. Some develop neck stiffness, sensitivity to light, loss of appetite and vomiting. The symptoms usually last from 4 to 7 days. Typically, patients recover within two days to one week after illness onset. However, some patients develop severe symptoms, including ocular disease, meningoencephalitis, hemorrhagic fever, shock, hepatic damage or even death.
4. How to prevent infect RVF?
   • (1) Clean and remove vector breeding sites and avoid mosquito bites. Effective prevention methods include the use of screen door/window, bed net, and mosquito repellents, and wearing protective garments.
   • (2) Animal immunization. Avoid contact with the blood, body fluids, or tissues of infected animals or products in RVF-affected areas.
   • (3) In laboratory and health­care settings, staff should be properly trained and always follow standard infection prevention and control precautions.
   • (4) One inactivated vaccine has been in development, which is not licensed and commercially available. It has been used experimentally to protect veterinarians and laboratory workers at high risk of exposure to RVF. 

More information

• WHO/Rift Valley fever
• USA CDC/ Rift Valley Fever (RVF)