oa Southern African Journal of Epidemiology and Infection - The outbreak of poliomyelitis in Namibia : editorial
The outbreak of poliomyelitis in Namibia in June 2006 is undoubtedly an unfortunate setback to the global polio eradication initiative. To date (8th of July 2006) 17 cases of paralytic disease of whom two died have been laboratory-confirmed as due to type 1 polio virus. The virus belongs to the SOAS genotype which is endemic in India. Analysis of the sequence homology between these isolates as well as those responsible for the outbreak of eight cases in Angola in 2005 and those of the parental Indian isolates, indicate a molecular distance equivalent to 2½ years of virus circulation. Whether the Namibian virus was imported from Angola, or whether from India is not clear. However, what the molecular clock tells us is that the virus had been circulating for upwards of 2½ years before it was manifest as the Angola epidemic last year and the Namibian outbreak this year. Rather disturbingly, this reveals significant gaps in the acute flaccid paralysis (AFP) surveillance which is used as the marker to detect circulation of polio in the population. An unusual feature of the Namibian outbreak is the age distribution of cases : with the exception of one case (aged 14 years), all but one case (a 51-year-old female) occurred in young adults (up to 39 years of age) older than the 15-year-old age used as the upper age limit for AFP surveillance. This unusual age distribution could possibly be the result of the late introduction of routine polio immunisation in Namibia and a consequent accumulation of susceptible adults. Routine polio immunisation as part of the EPI programme was only introduced into Namibia after its independence in the early nineties.
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