Intercontinental spread of an epidemic group A Neisseria meningitidis strain.

Electrophoretic enzyme typing revealed that a single group A Neisseria meningitidis clonal complex, designated III-1, was responsible for recent epidemics in Nepal, Saudi Arabia, and Chad. Epidemiological investigations and enzyme typing profiles indicated that this clone was brought from South Asia to the Middle East by Muslims making their pilgrimage (haj) to Mecca, Saudi Arabia, in 1987. Pilgrims who became group A carriers introduced this clonal group into sub-Saharan Africa on their return from the haj. The introduction of this clonal group into sub-Saharan Africa may be responsible for the current wave of epidemics affecting the region. Although the findings suggest that clonal virulence is an important factor in the development of epidemics of meningococcal disease, other factors also seem to be necessary for the development of an epidemic.