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Travel health information for people travelling abroad from the UK

Rift Valley Fever

Introduction

Rift Valley fever (RVF) is a viral infection that is harboured in ruminant animals such as cattle, goats and sheep. Animals are mainly affected by this virus but humans can also become infected. The virus was first identified in 1931, in the Rift Valley of Kenya, in Africa, where an outbreak among sheep on a farm was being investigated. Outbreaks of the disease have since been reported from sub-Saharan and North Africa.

In 2000, RVF was identified in Saudi Arabia and Yemen in the Middle East for the first time, causing concern that the disease could spread further to other parts of Asia and Europe.

Transmission

  • Most human infections are acquired through direct contact with blood, tissue or organs from infected animals eg during butchering, slaughtering or assisting with animal births. The virus can also be transmitted through inhalation of aerosols produced during the slaughter of infected animals. Those at highest risk are farmers, herders, veterinarians and slaughterhouse workers.
  • Humans can also be infected by a bite from an infected mosquito. This mode of transmission usually results in the milder form of the disease in humans. 
  • Consumption of unpasteurised or uncooked milk from an infected animal has also shown to cause RVF infection in humans.
  • To date there have been no cases of infection transmitted between humans. 

The Illness

Most human cases of RVF tend to be of the mild form of the illness, however some individuals may go on to develop a much more severe form of the disease.

Mild RVF in humans: the incubation period is between two to six days. Some of those infected may suffer no symptoms at all while others go on to develop a feverish illness with acute onset of flu-like symptoms, including high temperature, muscle aches, headache and joint pains. In the early stages, the illness may be mistaken for meningitis as some individuals may complain of neck stiffness, dislike of light, loss of appetite and vomiting. The symptoms of mild RVF generally last from four to seven days.

Severe RVF in humans: most human cases of RVF are mild, however a small number may progress to a much more severe form of the disease. They may present with symptoms of one or more of three different illnesses:

  • Eye disease: lesions on the retina of the eye appear one to three weeks after  the symptoms of mild RVF begin. These lesions cause blurred or poor vision which may resolve itself with no permanent damage within 10-12 weeks. In some instances however, permanent loss of vision may occur. 
  • Meningoencephalitis: the onset of meningoencephalitis is usually one to four weeks after the first symptoms begin. Signs and symptoms include severe headache, memory loss, hallucinations, vertigo, disorientation, convulsions and coma. Neurological complications can also develop later (around 60 days). The number who die from this illness is low, however permanent severe neurological damage is common.
  • Haemorrhagic fever: between two to four days after the onset of RVF, the signs of haemorrhagic fever may appear, beginning with severe liver damage such as jaundice. Signs of bleeding follow eg vomiting blood, passing blood in the stool, a purpuric rash, nose bleeds, bleeding from the gums and vaginal bleeding. Once these signs appear, death usually follows in 3-6 days. A few may survive and recover after a long slow convalescence.

Treatment

No specific treatment is required for most human cases as they are often mild and short lasting.

For the more severe form of the illness, the main treatment is supportive care.

Recommendations for Travellers

There is no commercially available human vaccine against this infection at present.

  • Travellers should be aware of the risk from livestock such as cattle, goats and sheep and avoid contact with ruminant animals, particularly if slaughter, butchering and birthing is taking place.
  • Travellers should avoid mosquito bites (particularly in rural and farming areas) by covering skin with clothing, using insect repellent on exposed skin and sleeping under a mosquito net impregnated with insecticide. 
  • Travellers should always refrain from consuming unpasteurised or uncooked milk and not partake of raw or undercooked meat that has not been properly verified. 

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