O’nyong-nyong the Second Time Around
Abstracts & commentary
Synopsis: The second identified outbreak of O’nyong-nyong fever is described.
Sources: Sanders EJ, et al. O’nyong-nyong fever in south-central Uganda, 1996-1997: Description of the epidemic and results of a household-based seroprevalence survey. J Infect Dis 1999;180:1463-1443; Kiwanuka N, et al. O’nyong-nyong fever in south-central Uganda, 1996-1997: Clinical features and validation of a clinical case definition for surveillance purposes. Clin Infect Dis 1999;29:1243-1250.
An epidemic of self-limited febrile illness as-sociated with often severe polyarthralgia in Uganda in 1996-1997 was demonstrated to be due to O’nyong-nyong fever. In an active case finding and serological and laboratory survey performed at the time the epidemic was waning, 40 cases of confirmed and 21 of presumptive infection were detected among 391 individuals evaluated. The febrile illness was characterized by the presence of arthralgia for a median of six days (range, 2-21 days) and, in a majority, a generalized skin eruption. Lymphadenopathy, predominantly cervical, was reported by nearly one-half. Viremia was detected in 16 subjects, some of whom were afebrile, during the first three days of illness. A clinical case definition consisting of the presence of fever, arthralgia, and lymphadenopathy was found to have a sensitivity of 61% and specificity of 83% during the epidemic.
Using the presence of an acute febrile illness with polyarthralgia and serologic or virologic evidence of infection, the attack rate in two areas affected by the epidemic was 45%. In addition, approximately one-third of infections were asymptomatic.
Comment by stan deresinski, md
O’nyong-nyong, in the language of the Acholi, is variously reported to mean "joint breaker" or "very painful and weak." However, Sanders and associates point out that in northern Uganda, the illness is called kyikutiiya or kiyikonyogo; the meaning of the latter approximates "beaten on the joints with a stick." Whatever the actual meaning, it is easy to get the point that patients with symptomatic infection with this virus suffer great discomfort. The illness, clinically indistinguishable from that caused by chikungunya virus infection, is characterized by fever, often severe arthralgias, skin rash, and lymphadenopathy. Fortunately, infection is self-limited and recovery is complete.
O’nyong-nyong virus was first identified during an epidemic that affected an estimated 2 million individuals in Uganda, Kenya, Tanzania, Mozambique, Malawi, and Senegal from 1959-1962. Anopheles funestus and A. gambiae were implicated as the vectors at that time (O’nyong-nyong is the only alphavirus transmitted by Anopheles mosquitoes). During the recent outbreak, the virus was most commonly isolated from, among more than 10,000 trapped mosquitoes, A. funestus.1
No cases of illness due to infection with this virus had been identified after 1962, although serological evidence indicated that new infections were occurring. Attempts to identify the natural reservoirs of the virus have failed; recent attempts to isolate the virus from small wild vertebrates in Uganda have proven unsuccessful.2
Analysis of the sequence of the entire genome and deduced amino acid sequence of an isolate from this epidemic found it to be closely related to an isolate of O’nyong-nyong virus obtained in 1959.3 This study also found that the Igbo Ora virus, thought by some to be a distinct organism, is a strain of O’nyong-nyong.
At least seven different mosquito-borne virus infections, including that due to O’nyong-nyong, are associated with severe polyarthralgia. The other six are Chi-kungunya, Mayaro, Ross River, Barmah Forest, Sindbis, and dengue viruses.4 All but the last are alphaviruses (Family Togaviridae), suggesting a common pathogenic mechanism.
References
1. Lutwama JJ, et al. Epidemic O’nyong-nyong fever in southcentral Uganda, 1996-1997: Entomologic studies in Bbaale village, Rakai District. Am J Trop Med Hyg 1999;61:158-162.
2. Ogen-Odoi A, et al. Isolation of thogoto virus (Orthomyxoviridae) from the banded mongoose, Mongos mungo (Herpestidae), in Uganda. Am J Trop Med Hyg 1999;60:439-440.
3. Lanciotti RS, et al. Emergence of epidemic O’nyong-nyong fever in Uganda after a 35-year absence; genetic characterization of the virus. Virology 1998; 252:258-268.
4. McGill PE. Viral infections: Alpha-viral arthropathy. Baillieres Clin Rheumatol 1995;9:145-150.
Which of the following is correct?
a. O’nyong-nyong virus is a flavivirus.
b. Most alphaviruses are transmitted by anopheline mosquitoes.
c. O’nyong-nyong infection can be distingushed from chikungunya because the latter seldom causes polyarthralgia.
d. Rash and lymphadenopathy are commonly seen in patients with symptomatic O’nyong-nyong virus infection.
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