WHO Report on Global Surveillance of Epidemic-prone Infectious Diseases - Meningococcal disease
Background of the disease
Meningococcal disease is a contagious bacterial disease caused by the meningococcus (Neisseria meningitidis) with high case fatality rates. It is spread by person-to-person contact through respiratory droplets of infected people.
N. meningitidis is a common inhabitant of the mucosal membranes of the nose and throat, where it usually causes no harm. Up to 5-10% of a population may be asymptomatic carriers. These carriers are crucial to the spread of the disease; most cases are acquired through exposure to asymptomatic carriers. A small minority of the persons who contract the disease will develop an acute inflammation of the meninges, the membranes covering the brain and the spinal cord. The disease is mainly affecting young children, but is also common in older children and young adults.
There are two clinical forms of meningococcal disease. Meningococcal meningitis is the more common entity, especially during epidemics, and the less common entity is meningococcal septicaemia. Meningococcal meningitis is the only form of bacterial meningitis which causes epidemics. The data presented in this report refer to both clinical forms of meningococcal disease.
Meningococcal disease occurs as both an endemic and epidemic disease, and both forms cause substantial illness, and death, as well as persistent neurological defects, particularly deafness. Other consequences of the disease are loss of limbs, mental retardation and paralysis. Because of the severe consequences of meningococcal disease, access to treatment with antimicrobials as early as possible is very important. In the case of epidemics, mass vaccination campaigns are used to control epidemics.
Three serogroups, A, B and C, account for up to 90% of all disease. All three serogroups may cause epidemics, however the risk of epidemic meningococcal meningitis differs between serogroups. Serogroup A meningococcus has historically been the main cause of epidemic meningococcal disease and still dominates in Africa during both endemic and epidemic periods.
The highest number of cases and the highest burden of disease occur in sub-Saharan Africa in an area that is referred to as the meningitis belt. This is the area between Senegal and Ethiopia (Map 5.1). Epidemics occur in seasonal cycles between the end of November and the end of June, depending on the location and climate of the country, and decline rapidly with the arrival of the rainy season. Within the meningitis belt, meningococcal disease occurs in epidemic cycles which last between 8 to 15 years. The mechanisms that cause these cycles are not well understood, but are thought to be related to variations in herd immunity.
Although the highest burden of disease is currently in Africa, epidemics can occur in any part of the world. Asia has had some major epidemics of meningococcal disease in the last 30 years (China 1979 and 1980, Viet Nam 1977, Mongolia 1973-1974 and 1994-1995, Saudi Arabia 1987, Yemen 1988). There have also been epidemics in Europe and in the Americas during the last 30 years, but they have not reached the very high incidence levels of epidemics in other parts of the world.
In January 1997, the International Coordinating Group on Vaccine Provision for Epidemic Meningitis Control (ICG) was developed to regulate and coordinate the procurement of meningococcal disease vaccine, after large epidemics in sub-Saharan Africa in 1995-1996 largely exhausted global vaccine stocks. In order for the ICG to function properly, timely information on meningococcal disease from each country is required. This has accelerated improvements in the surveillance system in African countries - which now have an increased incentive to report cases.
Map 5.1 Meningococcal disease in Africa, 1995-1999