Signs and Symptoms

RVFV has an incubation period of 2-6 days following exposure to the virus and can cause several different disease syndromes if symptoms do appear. Most commonly, people with RVF have either no symptoms or a mild illness that includes fever, weakness, back pain, and dizziness at the onset of illness. Typically, patients recover within two days to one week after symptoms start.

A small percentage (8-10%) of people infected with RVFV develop much more severe symptoms, including:

• Ocular disease (disease of the eye), which sometimes accompanies the mild symptoms described above. Lesions on the eyes may occur 1-3 weeks after onset of initial symptoms with patients reporting blurred and decreased vision. For many patients, lesions disappear after 10-12 weeks; however, for those with lesions occurring in the macula (the center of the retina), about half will have permanent vision loss.
• Encephalitis, or inflammation of the brain, which can lead to headaches, coma, or seizures. This occurs in less than 1% of patients and presents 1-4 weeks after first symptoms appear. Death from encephalitis in RVF patients is rare, but neurological deficits may be severe and long-lasting.
• Hemorrhagic fever, which occurs in less than 1% of all RVF patients. Symptoms of hemorrhaging may begin with jaundice and other signs of liver impairment, followed by vomiting blood, bloody stool, or bleeding from gums, skin, nose, and injection sites. These symptoms appear 2-4 days after onset of illness. Fatality for those who do develop symptoms of hemorrhagic fever is around 50% and death usually occurs 3-6 days after symptoms start.

RVF causes severe disease in animals that is characterized by fever, weakness, abortions (loss of pregnancy), and a high rate of severe illness and death, particularly among young animals. RVFV infection causes abortion in nearly 100% of livestock pregnancies and most young animals that are infected will die, whereas fatality among adult animals is significantly lower.