Biology Reference
In-Depth Information
Plasmodium vivax
makes up the vast majority of malaria transmission that
occurs in the Americas (
Arevalo-Herrera et al., 2010
). Survey data from this
region were relatively sparse and records represent a picture of heteroge-
neous transmission levels. The Americas contributed a small fraction (5.5%)
of global PAR of
P. vivax
, but comprised nearly a quarter (22%) of the global
area at risk. Areas of high transmission in highly dispersed populations may
present unique challenges to malaria control. To advance elimination efforts,
high-resolution mapping will be needed to accurately illustrate the degree
of heterogeneity in this region and areas that require the greatest resources.
This will demand more data from areas with high predicted prevalence
and uncertainty, such as Honduras and Nicaragua in Central America and
northwest Brazil in South America. Although Brazil is a large and populous
country, its areas of stable transmission occur in sparsely populated regions
of the Amazon basin. In 2010, Brazil had the seventh largest PAR of
P. vivax
globally (45 million), the largest area at risk (4.90 million km
2
) as well as the
largest area at stable risk (4.40 million km
2
) and, therefore, has an important
role to play in the region's future of malaria control and elimination.
4.4. Africa+
The estimates for endemicity and populations at risk of
P. vivax
malaria in
Africa+ (defined here as Africa, Saudi Arabia and Yemen) are mitigated by
the high prevalence of Duffy negativity in these populations, and the vector
situation in this region is relatively straightforward.
Defining the limits of transmission.
High
P. falciparum
endemicity in Africa,
coupled with high prevalences of Duffy negativity, has meant that collection
of
P. vivax
-specific data has not been a priority in the past. The data available
from which to estimate the limits of
P. vivax
transmission is, therefore, limited.
Plasmodium vivax
annual parasite incidence (
Pv
API) data were only available
from six Africa+ countries (13%). The last year of reporting available was
2009 for four countries (Dijbouti, Namibia, South Africa and Swaziland);
whilst for the remaining two countries (Saudi Arabia and Yemen) the last
available reports were from 2006. Based on the limited
Pv
API and
Pv
PR data
available for Africa+, and the presence of suitable vectors and climatic condi-
tions, forty-six countries are assumed to be
P. vivax
endemic in this region.
The area at risk was estimated to span over 22 million km
2
of Africa,
Yemen and Saudi Arabia. Despite the historical misconception that
P. vivax
is absent from the African continent, 84% of the 22.46 million km
2
of land
in the region was at some risk of
P. vivax
transmission (
Fig. 1.3
D2). How-
ever, the vast majority (92%; 20.60 million km
2
) of total area at risk was
estimated to house unstable transmission.
