Prevention of malaria epidemics by vector control in Burundi highlands

MSF UK Scientific day, 2007

Natacha Protopopoff, Dismas Baza, Michel Van Herp, Peter Maes, Wim Van Bortel, Tanguy Marcotty, Umberto D’Alessandro, Marc Coosemans

Introduction (1) Background

2000 malaria epidemics (In Karuzi : 500 000 cases over a population of 300 000 people)

After the epidemics: 4 years vector control activities

implemented by MOH, MSF-B and ITM-Antwerp in Karuzi.

Evaluation by cross sectional surveys

Introduction (2)

Intervention description 2002-2005: One round IRS/ year targeted in

the valleys before the transmission period (More than 90% coverage).

Limit

Intervention non Treated Hill top+/-700 m +/-700 m

Intervention Treated Valley

Introduction (3) Intervention description

2002: 2 LLIN distributed/household (total: 24000)

High net retention after distribution but quick decreased during following years.

2002 2003 2004 2005

Net used 78.8% 65.2% 53.4% 31.2%

Introduction (4) Objectives

Reduction vectors density & transmission Reduction of malaria prevalence Protective effect of treated valleys on non

treated hill topsLimit

Intervention non Treated Hill top+/-700 m +/-700 m

Intervention Treated Valley

Material and Methods (1)

Study design

Areas Valleys Hill tops

Intervention Treated Non treated

Control Non treated

Non treated

Material and Methods (2) Study design

2002-2006: 2 cross sectional surveys/year (3 and 9 months after IRS): total 9 surveys

Sample size: 25 clusters by area, 8 houses by cluster

Anopheles mosquitoes: indoor resting collection

Human population: blood slide collection (age group 1-9 y and >9)

0

2

4

6

8

10

12

14

1 2 3 4 5 6 7 8 9

2002 2003 2004 2005 2006

Survey

Anophel

es d

ensi

ty

.

C-Valley

I-Valley

Results Anopheles density (1)

-96%**-85%**

-91%**

-93%**

-89%*

-60%*

-90%**

-68%*

% reduction between Intervention and Control valleys. * p<0.05, ** p<0.001

Results Anopheles density (2)

Additional benefit of using net in the sprayed houses: reduction in Anopheles density of 77% (CI95%: 35-83, p=0.001)

No significant difference in Anopheles density between hill tops of intervention and control areas despite a high reduction in the intervention treated valleys

Results malaria transmission The overall reduction on the infectious bites is

91.1% (CI95%: 67.9-97.6, p=0.001) in intervention valleys compared to control valleys. Reduction of vectors density Reduction of sporozoite rates among vectors in

intervention valley (1.0%) compared to control valley (2.4%) (OR: 0.4 (CI95%: 0.2-0.8) p=0004)

No significant difference in malaria transmission between control and intervention hill tops

0

10

20

30

40

50

60

70

80

1 2 3 4 5 6 7 8 9

2002 2003 2004 2005 2006

Survey

Prev

alenc

e (%

) .

C-Valley

I-Valley

Results malaria prevalence (1)

-12% -57%*-49%

-64%*

-43%-49%

-38%

-53%*

• % reduction ((1-OR)*100) between Intervention and Control valleys.

• * p<0.05

Age group 1 to 9 years old

Results malaria prevalence (2)

Areas N Prevalence OR* (95%CI) P value

Control 161 10.6% 1 0.004

Intervention 189 1.6% 0.14 (0.04-0.52)

•Prevalence of malaria infection in infants (1 to 11 months) during survey 6 in the valleys

* OR adjusted for age

Surveys conclusions• IRS feasible in unstable political context• High impact on vectors with additional

protective effect of nets• High impact on transmission• Moderate impact on prevalence• No reduction on intervention hill tops Intervention focus on the higher risk areas:

Higher anopheles density and malaria prevalence in the valleys than hill tops

From 2002-2006: Malaria cases didn’t reach epidemic threshold in Karuzi

Lessons learnt Collaboration with WHO, MOH & local authorities Expertise product purchase, quality control Standard tools (LLIN, pre-pack dose ready to use,

Sprayers) Implementation methodology (HR training, IRS, LLIN

distribution vs dumping) MSF internal precursor,

Other MSF large scale intervention (e.g.:Malaria: Sierra Leone, Kenya (Wadjir), Tchad, Indonesia ; Chagas: Nicaragua)

Essential VC requirement in medical infrastructures Networking with specialists and suppliers