Biology Reference
In-Depth Information
break the malaria transmission cycle (
Greenwood, 2008a
). A short intense
program (attack phase) of residual insecticide spray during the GMEP
was often sufficient to nearly eliminate falciparum in areas without year-
round transmission. Vivax malaria's ability to reappear from the liver fol-
lowing intense control efforts, often meant control but not elimination was
achieved. This window of vulnerability for malaria elimination failure dur-
ing which programs must maintain intensive anti-transmission measures is
uncertain but is at least 3 years and probably as long as 5 years. Over time,
the failure to achieve the promised eradication of malaria despite impres-
sive decreases in malaria mortality and morbidity doomed the GMEP. This
historical lesson is important to current elimination efforts such that initial
success does not create unrealistic expectations that malaria elimination will
be easy or cheap.
Furthermore, relapses of vivax malaria from hypnozoites make it much
more likely that it will be this species which is reintroduced into eliminated
areas. This was seen in the USA when autochthonous cases occurred prob-
ably from persons travelling from Mexico and Central America while car-
rying parasites either in their blood or liver (
Rodriguez et al., 2009
;
Zucker,
1996
). This was also demonstrated by vivax malaria epidemics in the south-
ern (now independent) republics of the former Soviet Union likely from
soldiers returning from Afghanistan (
Sergiev et al., 1993
).
1.4.
P. vivax
in Africa
One does not associate
P. vivax
with Africa because the population is largely
Duffy antigen negative (
Howes et al. 2011
), which deprives the parasite of
one of its most important cellular receptors on the erythrocyte. The related
parasite
P. ovale
is often seen as a vivax equivalent in Africa due to its abil-
ity to cause mixed infections with falciparum and relapse, presumably from
hypnozoites. These two factors mean that in much of sub-Saharan Africa
no vivax malaria is reported (further discussed in chapter 1, volume 80),
but the parasite is not absent as travellers do on occasion return from Africa
with documented vivax infections (
Blossom et al., 2005
;
Guerra et al. 2010
;
PLoS NTDs). When groups of people with Duffy antigen have been brought
to Africa, they have brought
P. vivax
with them. An example would be the
Indian labourers used to construct the Mombasa to Lake Victoria railway in
the early part of the twentieth century. Peoples in the Horn of Africa (Soma-
lia, Ethiopia) have Duffy antigen on their erythrocytes so vivax malaria is
quite common in that corner of Africa (
Ashton et al., 2011
). This includes
highland areas as well as tourist destinations such as the Omo River. Duffy
