A Rift Valley Fever Outbreak in Western Uganda, 2023

Rift Valley fever (RVF) is a viral hemorrhagic fever spread by mosquitoes and shared between animals and people. Caused by Rift Valley fever virus, it is endemic across most of Africa and the Arabian Peninsula and sickens and kills many domestic livestock. People catch it from infected animals or animal products, or from the bites of infected mosquitoes, mainly Aedes and Culex species. Most human infections cause no symptoms or a mild flu-like illness, but about 10% become severe, with bleeding, and 10%–20% of those are fatal. Because of its economic impact and epidemic potential, Uganda counts RVF among its priority diseases that spread between animals and people.

The first case

On February 4, 2023, Uganda's National Public Health Emergency Operations Center was alerted to a suspected viral hemorrhagic fever in a 42-year-old man from Mbarara City, Uganda's second-largest city, who worked at an abattoir and roasted meat.

• January 30: he visited a private clinic after two days of flu-like illness, got antimalarial medicine and was sent home.
• February 1: worse — fever, vomiting, diarrhea, fatigue, loss of appetite, trouble breathing and pain in his abdomen, chest, muscles and joints — he went to Mbarara Regional Referral Hospital.
• February 3: he began bleeding from the nose and gums and in his urine and stool, and left for another private facility. Clinicians there suspected a viral hemorrhagic fever, isolated him and sent him back to the regional hospital.
• February 4: he died.

A blood sample taken after death and tested at the Uganda Virus Research Institute was positive for Rift Valley fever virus on February 5.

Finding more cases

The Mbarara District Task Force began coordinating the response on February 7, later joined by the National Rapid Response Team. Reports of cattle aborting or dying suddenly had begun in December 2022, after unusually heavy rains from September to November.

Searching the community turned up 102 suspected cases and one probable case from January to March 2023. Twenty-four were confirmed by laboratory tests, and with the probable case they came from 11 villages in five subcounties of Mbarara District. Symptoms began between January 11 and March 1, 2023.

Rift Valley fever cases by date of symptom onset, Mbarara District, 2023 (MMWR).

• Patients: median age 36; four of the 25 (16%) died.
• Symptoms: everyone had fever; 72% had general weakness, 64% loss of appetite and 60% joint pain.
• The link: cases traced to six cattle farms and three abattoirs. Every patient had contact with cattle that had died suddenly or recently aborted, and 60% worked on a farm where cattle abortions were reported.
• Care: 17 patients sought care, three of them at two or more facilities before being diagnosed, and eight were hospitalized. Illness lasted an average of 9 days (range 5–29) in the 21 survivors and 6 days (range 4–7) in those who died. All known survivors recovered.

Prevention

No RVF vaccine is licensed for people. Protecting humans depends on controlling the disease in animals and on:

• thoroughly cooking meat and milk;
• wearing protective equipment to avoid contact with the blood or tissues of infected animals;
• protecting against mosquitoes and other bloodsucking insects.

Vaccinating animals is essential, but although an animal vaccine is approved in neighboring Kenya, Rwanda and Tanzania, it had not yet been approved in Uganda. The investigators called for better mosquito control and more education for health workers, veterinarians and communities, to strengthen surveillance and awareness of the continuing threat of viral hemorrhagic fevers in Uganda's people and animals.

Sources

• Kabami Z, Ario AR, Migisha R, et al. "Notes from the Field: Rift Valley Fever Outbreak — Mbarara District, Western Uganda, January–March 2023," MMWR Vol. 72, No. 23, CDC; a work of the United States government in the public domain.