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Rift Valley fever

Rift Valley fever

16 January 2026

Causative agent

Rift Valley fever (RVF) is a viral zoonosis that primarily affects animals (such as cattle, buffalo, sheep, goats, and camels) but can also infect humans. The disease is caused by an arbovirus belonging to the Phlebovirus genus. The virus was first identified in 1931 during an outbreak among sheep in the Rift Valley of Kenya. The RVF virus is mainly found in eastern and southern Africa, as well as Madagascar, Saudi Arabia, and Yemen.

Clinical features

Most human infections present with mild symptoms such as fever, weakness, back pain, and dizziness. Patients usually recover without treatment within two to seven days. However, in rare cases, some individuals may develop a severe form of infection:

  • Eye disease (0.5–2%): Patients may have reduced vision or even permanent vision loss.
  • Inflammation of the brain (less than 1%): Patients may have headache, coma, or seizure. Significant residual neurological deficits are commonly observed.
  • Haemorrhagic fever (less than 1%): Patients may present with severe liver impairment, vomiting of blood, bloody stool, bleeding from gums, skin, nose, and injection sites. Mortality can be up to 50%.

Mode of transmission

The RVF virus is mainly spread among animals through bites from infected mosquitoes, particularly those of the Aedes species.

Human infections are primarily caused by direct or indirect contact with the blood or organs of infected animals. People may contract RVF by consuming milk from infected animals that has not been pasteurized or cooked. Furthermore, people can contract the infection through bites from infected mosquitoes.

No human-to-human transmission of RVF has been documented.

Incubation period

The incubation period ranges from 2 to 6 days.

Management

There is no specific treatment for RVF. Treatment is mainly supportive.

Prevention

Currently, no RVF vaccine is commercially available for human use. To reduce the risk of human infection, it is important to avoid contact with the blood, body fluids, or tissues of potentially infected animals and to prevent mosquito bites.

Prevention of mosquito bites

1. Wear loose, light-coloured, long-sleeved tops and trousers.

2. Use DEET-containing insect repellent on exposed parts of the body and clothing.

  • Pregnant women and children of 6 months or older can use DEET-containing insect repellent. In general, use DEET of up to 30% for pregnant women and up to 10% for children. For children who travel to countries or areas where mosquito-borne diseases are endemic or epidemic and where exposure is likely, children aged 2 months or above can use DEET-containing insect repellents with a concentration of DEET up to 30%

3. Take additional preventive measures when engaging in outdoor activities:

  • Avoid using fragrant cosmetics or skin care products
  • Re-apply insect repellents according to instructions
  • If both insect repellents and sunscreen are used, apply insect repellents after sunscreen

Prevention of mosquito proliferation

1. Prevent accumulation of stagnant water

  • Change the water in vases once a week
  • Avoid using saucers underneath flower pots
  • Cover water containers tightly
  • Ensure air-conditioner drip trays are free of stagnant water
  • Put all used cans and bottles into covered dustbins

2. Control vectors and reservoir of the diseases

  • Store food and dispose of garbage properly

For more information about control and prevention of mosquito breeding, please visit the website of the Food and Environmental Hygiene Department (FEHD) at https://www.fehd.gov.hk/english/pestcontrol/handbook_prev_mos_breeding.html

Advice for travellers

1. Take preventive measures to avoid mosquito bites. For details about the use of insect repellents and the key points to be observed, please refer to 'Tips for using insect repellents'.

2. If going to affected areas or countries, arrange medical consultation at least 6 weeks before the trip and take extra preventive measures to avoid mosquito bites.

3. If travelling in endemic rural areas, carry a portable bed net and apply permethrin (an insecticide) on it. Permethrin should NOT be applied to the skin. Seek medical attention promptly if feeling unwell.