Biology Reference
In-Depth Information
Estimating endemicity
. There were 1640 records of prevalence data from
97 sources obtained for Africa+, 79% of which reported an absence of
P. vivax
. Approximately 16% of the global
Pv
PR data records used in
the modelling were from surveys conducted in Africa, Yemen and Saudi
Arabia. Ethiopia, Zambia and Sudan were the most data rich countries,
contributing 50% (
n
= 826), 18% (
n
= 295) and 18% (
n
= 290) of the
total data, respectively.
The predicted prevalence estimates were uniformly low for areas at
stable risk in Africa, Yemen and Saudi Arabia as shown in
Fig. 1.3
D2. The
point estimates of predicted
Pv
PR
1-99
rarely exceeded 2%. The uncertainty
of the predictions in this region was also very low (
Fig. 1.4
D). The incor-
poration of information regarding the proportion of Duffy negative indi-
viduals strengthened the predictions in this area and compensated for the
sparse parasite rate data available from this region (
Fig. 1.3
D1,
Fig. 1.4
D and
Fig. 1.7
D). Areas with higher
Pv
PR
1-99
(Ethiopia, South Sudan and Mada-
gascar) predictions were also found to have the highest uncertainty, likely
because these areas were outside the range of high Duffy negativity and
could not borrow from the certainty conferred by that restriction. As with
the Americas, the uncertainty in Africa+ was reduced in the population-
weighted predictions because of the low population density found in parts of
the continent, particularly Madagascar (
Fig. 1.4
D2). Uncertainty remained
relatively high in the highlands of Ethiopia, which are more densely popu-
lated and are therefore important targets for control.
Population at risk
. The PAR in Africa+ was low given the large geo-
graphic coverage of the region because of the high prevalence of Duffy
negativity (
Fig. 1.3
D1 and
Fig. 1.7
D). There were an estimated 86 million
people living at risk of
P. vivax
in Africa, Yemen and Saudi Arabia in 2010,
which was 3.5% of the global total. More than half (56%), or 48.72 million,
of the PAR were those living in unstable transmission and the remaining
37.66 million (44%) lived in areas at the level of stable transmission. Nine
countries had an estimated PAR of zero, all of which are located in West
Africa: Côte d'Ivoire, Ghana, Guinea, The Gambia, Guinea-Bissau, Senegal,
Sierra Leone and São Tomé and Príncipe. Togo, Equatorial Guinea, Gabon
and Burkina Faso also had a total PAR of less than one thousand individuals.
Thirty-four countries in the Africa+ region had zero individuals at risk of
stable transmission. Of the 12 countries with stable transmission, Madagas-
car was the only country where the entire PAR (5.23 million) experienced
stable transmission. Madagascar has the fourth highest PAR in the region;
the highest were Ethiopia, Sudan and Yemen with 35.19 million (41% of
