Meningococcal Meningitis in Africa:Overview
Response strategiesand Current challenges
Eric Bertherat
What is Meningitis ?What is Meningitis ?
Meningitis is an inflammation of the meninges, the thin lining that surrounds the brain and the spinal cord.
Different origins:– Mechanical: eg. tumours– Infectious: Cerebrospinal fluid (CSF) found infected
• Viruses• Fungi• Parasites• BACTERIA
Bacterial causes of MeningitisBacterial causes of Meningitis
Many bacteria but some are of specific importance in public health:
Streptococcus pneumoniaeHaemophilus influenza
Neisseria meningitidis (Nm)
The meningococcusThe meningococcus
ADNSequence Type ST
Polysaccharideserogroups A, B, C, W135, Y..
Source: IMTSSA, Marseilles
Meningococcal meningitisMeningococcal meningitis
• Worldwide distribution
• Sporadic, cluster or large epidemic
• 12 serogroups:
•Europe, Americas: B, C
•Asia: A
•Africa: A, C, W135, X
• Africa: 80 % of the burden
Transmission:Transmission:
Strictly a human disease
Direct transmission, person to person
Close and prolonged contact.
Average incubation period 4 days, ranging between 2 and 10 days.
Carried in the pharynx – can overwhelm the body’s defenses allowing infection to spread through the bloodstream and to the meninges.
1-10% of asymptomatic carriers. Up to 10- 25% during epidemics.
The Meningitis BeltThe Meningitis Belt
21 countries and 300 million people at risk
700 000 cases in the past 10 years
10-50 % case fatality rates
10-20 % of survivors suffer permanent brain damage
Impact of meningitis epidemics the example of Burkina Faso, 2006
Impact of meningitis epidemics the example of Burkina Faso, 2006
Duration of the oubreak : 5 months
N° of cases/deaths: 19,000 / 1,500
N° of districts affected: 35
N° of vaccinated: 4 million (3 months)
N° health workers mobilized: 9,000
Direct cost : 4 million USD (5% of total health expenditure)
How to reduce the burden of meningitis ?The WHO strategy in the Belt
How to reduce the burden of meningitis ?The WHO strategy in the Belt
Based on:
Characteristics of meningitis in the Belt
Technical and financial capacities of the concerned countries
Performance and Availability of vaccines
The Meningitis Belt: a region presenting distinct epidemiological features
The Meningitis Belt: a region presenting distinct epidemiological features
Hyper incidence– 10-150 per 100,000 in non-epidemic yrs
– 250-1000 per 100,000 in epidemic yrs
(Europe-USA: 1-3 per 100,000)
Seasonal increase
Large epidemics during the dry season
N0 1000 2000 Kilometers
Average annual rates per 100,000
0 - 2.93 - 9.910 - 24.925 - 120
Meningitis belt 4.5
WHO strategy:Capacities of the concerned countries
WHO strategy:Capacities of the concerned countries
Multiple endemic and epidemic diseases
Limited resources
Lack of laboratory capacities
WHO strategy:Performance and Availability of vaccines
WHO strategy:Performance and Availability of vaccines PS vaccines
Poorly immunogenic in children < 2y
Immunity short lived: requires multiple doses
Does not protect from carriage
Routine immunization not feasible in the Belt countries
Limited supply, affordability
bivalent AC
trivalent ACW
tetravalent ACWY
Outbreak control: 2 Core ComponentsOutbreak control: 2 Core Components
To prevent the lethality = case management• Presumptive treatment• Cheap and efficient on the most probable
causative agent
Ceftriaxone / Oily chloramphenicol: single dose IM
To prevent the cases = reactive vaccination
Reactive VaccinationReactive Vaccination
District level
Targeted on the high risk population: usually < 30yrs
Targeted on the responsible Nm serogroup: A, C, W
Timely
60% of cases averted when vaccination is implemented
within 2-4 weeks (Leake et al)
Reactive vaccination: the good timing Reactive vaccination: the good timing
0
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wk1 wk8 wk15 wk20
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Too early !
Too late !
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Too late !
expected incidence rise or beginning of an outbreak?
the principle of the thresholds the principle of the thresholds
Alert threshold5/100 000/week
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ases
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wk1 wk8 wk15 wk20
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5
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Epidemic threshold10/100 000/week
Immediately conduct district mass vaccinationStrengthen case management
Clinical samples + lab confirmation
To immunize with the right vaccine: a rational choice
To immunize with the right vaccine: a rational choice
Mainly Nm identified 3
yes no
laboratory test results available
epidemic threshold reached 2
Conduct active fieldinvestigation andobtain specimens
Specimensobtained
at least one W135identified
> 30% of W135 out of 10-19Nm positive samples,
OR> 20% of W135 out of 20 ormore Nm positive samples
ACW PS AC PSVaccine
W135 epidemic in aneighboring district
in less than 10 samplesin 10 or more samples
W135 not identified
W135 not identified
yes no
AC PSVaccine
Meningitis Surveillance in the BeltMeningitis Surveillance in the Belt
•Early detection = weekly AR
•Identification of the target population = AR/age group
•Identification of responsible germs = confirmation + serogrouping
Enhanced surveillance
(epid./lab).
Countries implementing enhanced meningitis surveillance, 2003-2007.
Countries implementing enhanced meningitis surveillance, 2003-2007.
Niger
Chad
Nigeria
Mali
Burkina Faso
Ghana Togo Bénin
Ivory Coast
Ethiopia
From the reaction to the prevention..
Ziniare 2006
0
10
20
30
40
50
60
70
1 3 5 7 9 11 13 15 17 19
semaines
taux
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Seuil épidémique
Vaccination
Ziniare 2006
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10
20
30
40
50
60
70
1 3 5 7 9 11 13 15 17 19
semaines
taux
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Seuil épidémique
Vaccination
The reactive vaccination: a frustrant strategy
Toward a true prevention: a conjugate vaccine for Africa…
Bogande 2007
0
10
20
30
40
50
1 3 5 7 9 11 13 15 17 19
semaines
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Seuil épidémique
Vaccination
Bogande 2007
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10
20
30
40
50
1 3 5 7 9 11 13 15 17 19
semaines
taux
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Seuil épidémique
Vaccination
Figure 1. Trends of epidemic meningitis diisease in the African Belt, 1970-2006
020,00040,00060,00080,000
100,000120,000140,000160,000180,000200,000
19
70
19
73
19
76
19
79
19
82
19
85
19
88
19
91
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94
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97
20
00
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03
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Years
Cas
es
Country-Level Attack Rate - NIGER
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60
1986
1987
1988
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Year
Cas
es/1
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Meningitis weekly ARs Meningitis weekly ARs /100,000 Niger/100,000 Niger
Meningitis weekly ARs Meningitis weekly ARs /100,000 Burkina Faso/100,000 Burkina Faso
Country-level Attack Rates - Burkina Faso, 1997-2006
0
5
10
15
20
25
30
35
1997 1998 1999 2000 2001 2002 2003 2004 2005 2006
Year
Cas
es/1
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0
Periodicity of Epidemics
Number of meningitis cases per year. Sudan 1977-2007
0
5000
10000
15000
20000
25000
30000
35000
40000
1977
1978
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2007
Years
N°
Cas
es
Meningitis weekly cases Meningitis weekly cases SudanSudan
1 4 7
10
13
16
19
0
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20
30
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100
Ars/100,000
Weeks
District Epidemic Curves, Burkina Faso, 2001
Weekly attack rates , Banfora District, Burkina Faso 1997
0102030405060708090
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29
Weeks
AR
/100,0
00
6-8 weeks
Classical Epidemic Curve at District level
Meningitis outbreaks dynamicsMeningitis outbreaks dynamics
Magnitud of the outbreak determined by simultaneous occurrence of multi-focal outbreaks geographically not related
– A given community/district can be affected while contiguous communities/districts are not
Meningitis outbreaks in the African belt do not "spread "
Transmission is likely to occur through out the year (rainy and dry seasons) (Blakebrough,1979 – Greenwood 1985)
Relation of seasonal climatic factors to meningococcal meningitis cases
Relation of seasonal climatic factors to meningococcal meningitis cases
* Grenwood et al, Trans Roy Trop Med 1987
Cases start increasing at beginning of the dry season (January)
Sharp decrease with the beginning of rains, May-June
Causes of meningitis epidemics still poorly understood
Causes of meningitis epidemics still poorly understood
Introduction of new epidemic strains– 1996-1997 epidemic associated to spread of Nm A of the ST-5
complex
Accumulation of susceptible cohorts
Environmental factors – Low absolute humidity– Land cover – Atmospheric dust…
….and millions of doses of vaccine injected
From a public health view…From a public health view…
Knowledge of the natural history of the disease:
What can we expect from the research community (environment, socio-demography, mathematical analysis..) ?
From a public health view…From a public health view…
How much this added knowledge can improve the control strategy (reactive response / preventive vaccination) ?
From a public health view…From a public health view…
Long term strategy: What will be the Belt in the coming decades ?
XA
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