Epidemics in Africa
Periodic waves of meningitis epidemics occur across sub-Saharan Africa, wreaking havoc in the region.
Studies indicate that epidemic meningitis has been present in Africa since the mid-1800s. The disease is most common in the sub-Saharan meningitis belt, an area that stretches from Senegal and Gambia in the West to Ethiopia in the East and has an at-risk population of about 430 million. Epidemics typically occur in the dry season (December through June), and periodic epidemic waves can last two to three years, dying out during the intervening rainy seasons.
The African meningitis belt
Source: Control of epidemic meningococcal disease, WHO practical guidelines, World Health Organization, 1998, 2nd edition, WHO/EMC/BAC/98.3
Size of Epidemics
The size of these epidemics can be enormous and place an immediate and great burden on the health systems of meningitis belt countries. In major epidemics, the attack rate ranges from 100 to 800 per 100,000 population, but individual communities have reported rates as high as 1 per 100 people.
More than one million cases of meningitis have been reported in Africa since 1988. In 1996 to 1997, the largest epidemic wave ever recorded in history swept across Africa causing more than 250,000 cases and 25,000 deaths. However, the true disease burden is likely higher. Routine reporting systems often break down during epidemics and many people with meningitis remain unreported, dying before reaching a health center.
Since the 1940s, epidemic cycles have been detected every 5 to 12 years, but two troubling trends have been observed since the early 1980s:
- Intervals between epidemics have become shorter and more irregular
- The meningitis belt seems to be extending further south
At this point, it is not possible to tell with certainty if these changes are real or if they result from enhanced disease surveillance in the region.
Although the pattern of these epidemic cycles is not entirely understood, several risk factors have been associated with the development of epidemics in the meningitis belt. They include:
- Medical conditions: immunological susceptibility of the population
- Demographic conditions: travel and large population displacements due to pilgrimages and traditional markets at regional level
- Socioeconomic conditions: overcrowding and poor living conditions
- Climatic conditions: drought and dust storms
- Concurrent infections: acute respiratory infection
Bacteria Groups Associated with Epidemics
Historically, serogroup A meningococci have been the main cause of meningitis epidemics in Africa and account for about 80 to 85 percent of all cases. Since the introduction of meningococcal A conjugate vaccine (MACV/PsA–TT; MenAfriVac™ Serum Institute of India, Ltd), cases of serogroup A meningococcal meningitis have declined drastically in sub-Saharan Africa. However, cases of meningitis and outbreaks from other serogroups, such as W, X, and C, continue to occur. For example, major epidemics of serogroup W meningococcal meningitis occurred in Burkina Faso in 2002 and 2012.
In 2015, there was an unprecedented epidemic of serogroup C meningococcal meningitis in Niger and Nigeria that resulted in approximately 11,000 cases and 800 deaths. Since this epidemic was caused by a unique strain of meningococcus and populations have limited immunity to non-serogroup A meningococcus, the regional risk of subsequent epidemics of serogroup C meningococcal meningitis will continue into 2016.