Summary An outbreak of Ebola disease was reported from Gulu district, Uganda, on 8 October 2000. The outbreak was characterized by fever and haemorrhagic manifestations, and affected health workers and the general population of Rwot‐Obillo, a village 14 km north of Gulu town. Later, the outbreak spread to other parts of the country including Mbarara and Masindi districts. Response measures included surveillance, community mobilization, case and logistics management. Three coordination committees were formed: National Task Force (NTF), a District Task Force (DTF) and an Interministerial Task Force (IMTF). The NTF and DTF were responsible for coordination and follow‐up of implementation of activities at the national and district levels, respectively, while the IMTF provided political direction and handled sensitive issues related to stigma, trade, tourism and international relations. The international response was coordinated by the World Health Organization (WHO) under the umbrella organization of the Global Outbreak and Alert Response Network. A WHO/CDC case definition for Ebola was adapted and used to capture four categories of cases, namely, the ‘alert’, ‘suspected’, ‘probable’ and ‘confirmed cases’. Guidelines for identification and management of cases were developed and disseminated to all persons responsible for surveillance, case management, contact tracing and Information Education Communication (IEC). For the duration of the epidemic that lasted up to 16 January 2001, a total of 425 cases with 224 deaths were reported countrywide. The case fatality rate was 53%. The attack rate (AR) was highest in women. The average AR for Gulu district was 12.6 cases/10 000 inhabitants when the contacts of all cases were considered and was 4.5 cases/10 000 if limited only to contacts of laboratory confirmed cases. The secondary AR was 2.5% when nearly 5000 contacts were followed up for 21 days. Uganda was finally declared Ebola free on 27 February 2001, 42 days after the last case was reported. The Government's role in coordination of both local and international support was vital. The NTF and the corresponding district committees harmonized implementation of a mutually agreed programme. Community mobilization using community‐based resource persons and political organs, such as Members of Parliament was effective in getting information to the public. This was critical in controlling the epidemic. Past experience in epidemic management has shown that in the absence of regular provision of information to the public, there are bound to be deleterious rumours. Consequently rumour was managed by frank and open discussion of the epidemic, providing daily updates, fact sheets and press releases. Information was regularly disseminated to communities through mass media and press conferences. Thus all levels of the community spontaneously demonstrated solidarity and response to public health interventions. Even in areas of relative insecurity, rebel abductions diminished considerably.

O'nyong-nyong (ONN) virus is an alphavirus (family Togaviridae, genus Alphavirus) classified in the Semliki Forest virus (SFV) antigenic complex. ONN was initially isolated in northern Uganda in 1959 during the early stages of an explosive arbovirus epidemic in which > 2 million cases were reported. No additional epidemics or human isolations of ONN were reported until 1996, when it was isolated from an epidemic in southern Uganda. We report the complete nucleotide and deduced amino acid sequence of one of these 1996-1997 ONN isolates (SG650) and that of the related alphavirus Igbo Ora virus. The data indicate that the recent ONN virus isolate is closely related to the previously published ONN strain isolated in 1959. In addition, phylogenetic analysis of the sequence data reveals that Igbo Ora virus, previously thought to be a separate virus closely related to ONN and Chikungunya (CHIK), clearly is a strain of ONN. The sequence data also reveal that unlike the published ONN (1959) sequence, all ONN strains from the 1996-1997 epidemic possess a stop codon at the nsp3-nsp4 junction.

O'nyong-nyong (ONN) fever, caused by infection with a mosquito-borne central African alphavirus, is an acute, nonfatal illness characterized by polyarthralgia. During 1996-1997, south-central Uganda experienced the second ONN fever epidemic ever recognized. Among 391 persons interviewed and sampled, 40 cases of confirmed and 21 of presumptive, well-characterized acute, recent, or previous ONN fever were identified through active case-finding efforts or during a household serosurvey and by the application of clinical and laboratory criteria. Among confirmed cases, the knees and ankles were the joints most commonly affected. The median duration of arthralgia was 6 days (range, 2-21 days) and of immobilization was 4 days (range, 1-14 days). In the majority, generalized skin rash was reported, and nearly half had lymphadenopathy, mainly of the cervical region. Viremia was documented in 16 cases, primarily during the first 3 days of illness, and in some of these, body temperature was normal. During this epidemic, the combination of fever, arthralgia, and lymphadenopathy had a specificity of 83% and a sensitivity of 61% in the identification of cases of ONN fever and thus could be useful for surveillance purposes.

O'nyong-nyong (ONN) fever, an acute, nonfatal illness characterized by polyarthralgia, is caused by infection with a mosquito-borne central African alphavirus. During 1996-1997, south-central Uganda experienced the second ONN fever epidemic ever recognized. During January and early February 1997, active case-finding and a household cluster serosurvey were conducted in two affected and two comparison areas. A confirmed case was defined as an acute febrile illness with polyarthralgia occurring within the previous 9 months plus serologic confirmation or isolation of ONN virus from blood. In affected (n=129) and comparison (n=115) areas, the estimated infection rates were 45% and 3%, respectively, and the estimated attack rates were 29% and 0%, respectively, for an apparent:inapparent infection ratio of nearly 2 in affected areas. In villages sampled near Lake Kijanebalola, Rakai District, the estimated infection and attack rates were 68% and 41%, respectively, and 55% of sampled households had >/=1 case of ONN fever. In conclusion, this epidemic was focused near lakes and swamps, where it was associated with high infection and attack rates.

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