Investigation of suspected O’nyong nyong fever Outbreak in Kampala District, Uganda, February 2019

Summary

On 21st February 2019, Ministry of Health received an alert on suspected O’nyong nyong fever outbreak in Kampala by a private hospital. We conducted investigations to confirm the outbreak and identify potential exposure factors. We identified one confirmed female case-patient resid-ing in Kampala District. She had travel history to Kitgum District with a stopover in Gulu District. She reportedly had mosquito bites in Kitgum and did not sleep under a mosquito net in Gulu. We concluded that mosquito bites in Kitgum and not sleeping under a mosquito net were the potential exposure factor for infection. We recommend sleeping under a mosquito net and wearing long-sleeved clothes when outside in the evening to reduce exposure to mosquito bites.

Background

O’nyong nyong Fever is a neglected mosquito-borne disease caused by O’nyong nyong virus (ONNV), which is an Alphavirus (1). The name ‘O’nyong nyong’ was derived from Acholi tribe meaning ‘joint break-er’ (2). The virus was first isolated during a 1959–1962 epidemic that affected 2 million people in Uganda, Kenya, Tanzania, Mozambique, Malawi and Senegal (3, 4). An estimated 1 million cases were affected during a 1996 outbreak in south-western Uganda and northern Tanza-nia (5, 6) approximately 34 years after the first confirmed outbreak.
Anopheles funestus and Anopheles gambiae mosquitoes primarily transmit ONNV though aedes and culex mosquitoes can spread this virus as well (3, 7, 8). O’nyong nyong infection presents with fever, joint pains (without effusions); primarily in the large joints, headache, generalized maculopapular skin rash (often itchy), posterior cervical lymphadenopathy, and conjunctivitis (red eyes); bleeding gums or nosebleeds are rarely reported (6). The incubation period of O’nyong nyong is estimated to be 8 days.

On 21st February 2019, Ministry of Health was notified on suspected O’nyong nyong fever outbreak following 2 suspected case-patients that were reported at a private hospital in Kampala. We conducted investigations to confirm the outbreak and identify potential exposure factors.

Methods

We reviewed medical records of the private hospital and interviewed medical staff for more details regarding the diagnosis. We took two serum samples from the case-patient for laboratory testing at Uganda Virus Research Institute (UVRI). We later interviewed the case-patient to identify potential exposure factors.

Findings

We identified one confirmed case-patient. The case-patientwas a 35-year old female residing in Bunga, Kampala District. She had travelled to Padibe, Kitgum District between 23 and 25 January 2019. She reportedly had painful mosquito bites in Padibe as she sat outdoors one evening. She spent the night in Gulu on the 25 January 2019 before traveling back to Kampala on 26 January 2019. She reportedly did not sleep under a mosquito net while in Gulu. On 30 January 2019, she experienced excruciating joint pains that started from the lower limbs and slowly moved to upper limbs and also had on and off fevers. She later presented with chest pain and difficulty in breathing. She developed an itchy rash on her trunk 4 days after symptom onset. She was diagnosed with urinary tract infection from the first private hospital she visited.

The symptoms persisted and she went to another private hospital where a provisional diagnosis of O’nyong nyong fever was made. She was negative for brucellosis, dengue, shistosomiasis, and typhoid fever. Her white blood cell count was low with elevated C-reactive protein of 71.9mg/l (Normal =<10mg/l). She tested positive for O’nyong nyong virus by IgM serological tests (Titres 10,240) done at UVRI.

Discussion

This was a confirmed case of a recent Onyong nyong fever infection based on the serological tests taken with high titres. We suspected that the case-person had the exposure to infection in Kitgum based on the minimum incubation period of O’nyong nyong. Our assumption is backed by the proximity between Kitgum and Gulu; which has a history of O’nyong nyong outbreaks (3, 4). The reports of Case-patient experiencing mosquito bites in Kitgum while outdoors in the evening and not sleeping under mosquito net in Gulu were potential exposure factors.
O’nyong nyong disease surveillance is not adequate in the country. A sero-survey on healthy Ugandan blood bank donors concluded that ONNV disease could be a more likely cause of febrile illness with ar-thralgia (10). Definitive diagnosis O’nyong nyong fever is difficult with-out appropriate diagnostic tests because of similar clinical presenta-tions with other illnesses including Chikungunya fever.

Limitations of the study

Previous o’nyong nyong fever outbreaks in Uganda were prolonged and affected a large number of people. We did not conduct further investigations in Kitgum District to establish whether there was an on-going outbreak in the area.

Conclusions and Recommendations

An outbreak of O’nyong nyong fever occurred in Kampala District. One case-patient of O’nyong nyong fever was identified and was likely ex-posed in Kitgum District. The potential exposure factors were mosquito bites in the evening and not sleeping under a mosquito net. We recommended reducing exposure to mosquito bites through sleeping under mosquito nets and wearing long-sleeved clothes when outdoors during evening time. We recommend strengthening of surveillance for O’n-yong nyong fever in Kitgum District and surrounding areas by Ministry of Health. An epidemiological investigation in Kitgum District would also determine whether other people were affected since the disease is known to cause prolonged outbreaks.

References

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