Modelling the distribution and transmission intensity of lymphatic filariasis in sub-Saharan Africa prior to scaling up interventions: integrated use of geostatistical and mathematical modelling.
BACKGROUND
Lymphatic filariasis (LF) is one of the neglected tropical diseases targeted for global elimination. The ability to interrupt transmission is, partly, influenced by the underlying intensity of transmission and its geographical variation. This information can also help guide the design of targeted surveillance activities. The present study uses a combination of geostatistical and mathematical modelling to predict the prevalence and transmission intensity of LF prior to the implementation of large-scale control in sub-Saharan Africa.


METHODS
A systematic search of the literature was undertaken to identify surveys on the prevalence of Wuchereria bancrofti microfilaraemia (mf), based on blood smears, and on the prevalence of antigenaemia, based on the use of an immuno-chromatographic card test (ICT). Using a suite of environmental and demographic data, spatiotemporal multivariate models were fitted separately for mf prevalence and ICT-based prevalence within a Bayesian framework and used to make predictions for non-sampled areas. Maps of the dominant vector species of LF were also developed. The maps of predicted prevalence and vector distribution were linked to mathematical models of the transmission dynamics of LF to infer the intensity of transmission, quantified by the basic reproductive number (R0).


RESULTS
The literature search identified 1267 surveys that provide suitable data on the prevalence of mf and 2817 surveys that report the prevalence of antigenaemia. Distinct spatial predictions arose from the models for mf prevalence and ICT-based prevalence, with a wider geographical distribution when using ICT-based data. The vector distribution maps demonstrated the spatial variation of LF vector species. Mathematical modelling showed that the reproduction number (R0) estimates vary from 2.7 to 30, with large variations between and within regions.


CONCLUSIONS
LF transmission is highly heterogeneous, and the developed maps can help guide intervention, monitoring and surveillance strategies as countries progress towards LF elimination.
Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, UK. paula.moraga-serrano@lshtm.ac.uk.
Paula
P
Moraga
Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, UK. jcano.ortega@lshtm.ac.uk.
Jorge
J
Cano
Faculty of Epidemiology and Population Health, London School of Hygiene & Tropical Medicine, London, UK. rebecca.baggaley@lshtm.ac.uk.
Rebecca F
RF
Baggaley
School of Public Health, College of Health Sciences, University of Ghana, Legon, Accra, Ghana. jgyapong@ug.edu.gh.
John O
JO
Gyapong
Eastern and Southern Africa Centre of International Parasite Control, Kenya Medical Research Institute, Nairobi, Kenya. SNjenga@kemri.org.
Sammy M
SM
Njenga
Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, UK. birgit.nikolay@lshtm.ac.uk.
Birgit
B
Nikolay
Ministry of Health, Abuja, Nigeria. enimed2003@yahoo.com.
Emmanuel
E
Davies
NTD Support Center, Task Force for Global Health, Emory University, Atlanta, USA. mrebollo@taskforce.org.
Maria P
MP
Rebollo
Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, UK. Rachel.Pullan@lshtm.ac.uk.
Rachel L
RL
Pullan
Department of Vector Biology, Liverpool School for Tropical Medicine, Liverpool, UK. Moses.Bockarie@liverpool.ac.uk.
Moses J
MJ
Bockarie
Warwick Infectious Disease Epidemiology Research, Warwick Mathematics Institute, University of Warwick, Coventry, UK. deirdre.hollingsworth@warwick.ac.uk.|School of Life Sciences, University of Warwick, Coventry, UK. deirdre.hollingsworth@warwick.ac.uk.
T Déirdre
TD
Hollingsworth
Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Australia. manoj.gambhir@monash.edu.
Manoj
M
Gambhir
Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, UK. Simon.Brooker@lshtm.ac.uk.
Simon J
SJ
Brooker
D017954:Africa South of the Sahara / Q000453:epidemiology; D000818:Animals; D003140:Communicable Disease Control / Q000379:methods; D004605:Elephantiasis, Filarial / Q000453:epidemiology* / Q000635:transmission*; D062665:Epidemiological Monitoring; D008962:Models, Theoretical; D015995:Prevalence; D062211:Spatio-Temporal Analysis; D019371:Topography, Medical; D014958:Wuchereria bancrofti / Q000302:isolation & purification*