LASSA FEVER, PREDICTIVE MAPS - WEST AFRICA
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A ProMED-mail post
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http://www.promedmail.org>
ProMED-mail is a program of the
International Society for Infectious Diseases
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http://www.isid.org>
Date: Tue 28 Apr 2009
From: Elisabeth Fichet-Calvet, PhD and David J. Rogers, PhD
We were struck by the remarks of the ProMED moderator following the
report of Lassa fever cases originating in Nigeria but treated in
both the UK (a returning UK national) and South Africa (a Nigerian
medical doctor, presumed to have been treating Lassa fever patients
from around Abuj-a, [see: Lassa fever - South Africa ex Nigeria
20090425.1554. Please note that this report actually referred to an
incident that occurred in 2007 and has since been corrected in report
20090428.1603], although one wonders in this case why the paramedics,
pilot and 2 co-pilots -- now placed under quarantine -- who flew him
from Nigeria were not adequately protected against risk of infection
during their flight to South Africa). The ProMED Moderator commented:
"the Lassa fever outbreaks provide a unique opportunity for teams of
health professions to work together to understand the epidemiology of
Lassa fever better when outbreaks occur.
"We have recently made predictive risk maps of Lassa Fever in West
Africa using all available information on the location of past human
cases, serological surveys of rodents, and environmental data derived
from both satellites and ground-based measures of climate. (See:
<
http://www.plosntds.org/article/info%3A ... 95CF9E71CB>).
The disease occurs within high rainfall areas of West Africa, a
subset of the very much wider environmental range of its multimammate
rat host, _Mastomys natalensis_, which extends into many biotic zones
in West, Central, Eastern and Southern Africa. Maps in the
publication may be used to identify high risk areas within which
especial care should be taken to avoid contact with rats, their urine
and faeces. Travellers expecting to visit countries from which Lassa
fever has been reported could also be given more precise information
about high risk zones within those countries. Such risk maps can be
produced from records of past outbreaks without necessarily fully
understanding the epidemiology of the disease in question. The past
is a useful, though never perfect, guide to the future. Our eventual
aim, however, is to translate the statistical analyses involved in
risk map production into a fuller biological understanding of
crucial, limiting environmental variables that should inform future
epidemiological studies.
Risk maps of the sort we have produced will be much improved by
adding precise geographical locations of past and new disease
outbreaks, and we encourage much clearer identification and reporting
of the locations where infection is most likely to have taken place.
Lassa fever was in fact 1st described from NorthEast Nigeria, but
very few data-points in our database came from Nigeria because of a
lack of clear reporting of past cases from that country. Controlling
diseases certainly involves teamwork of nurses, medics and
clinicians, as these reports of Lassa outbreaks have shown. Such
teams are used to working together. However, understanding diseases
involves cross-disciplinary teams (medics, biologists, geographers,
sociologists, etc.) which do not necessarily 'self-assemble'
themselves in quite the same way, and thus may require new
initiatives from those involved in national and global health.
--
Elisabeth Fichet-Calvet, PhD
Evolutionary Biology Group, Universiteit Antwerpen
Groenenborgerlaan 171, B-2020 Antwerpen, Belgium
<
Elisabeth.Fichet-Calvet@ua.ac.be>
<
ecalvet@club-internet.fr>
and,
David J. Rogers, PhD
Professor of Ecology,
Oxford University,
TALA Research Group,
Dept. of Zoology,
South Parks Rd.,
Oxford OX1 3PS, UK.
<
david.rogers@zoo.ox.ac.uk>
[Pro-MED-mail welcomes this opportunity to draw attention to the work
of Drs Fichet-Calvet and Rogers, which has resulted in the production
of Lassa fever risk maps. These maps indicate the strong influence of
rainfall, and a lesser influence of temperature in defining high risk
areas. The area of greatest risk is located between Guinea and
Cameroon. - Mod.CP]
HIER