Biology Reference
In-Depth Information
highland malaria during brief warm periods above 2000 m. If such warmth
is maintained for a few weeks, then those mosquitoes carrying malaria para-
sites can support development of infective sporozoites. This is true of areas
in high latitudes as well as tropical countries with mountains. Transmission
can also occur in warmer than ambient conditions such as inside houses or
animal shelters which can result in highly focal transmission as occurred
in England before elimination. Despite global warming, reintroduction of
malaria into previously eliminated areas is not primarily dependant on tem-
perature changes (
Gething et al., 2010
). Movement of gametocyte-carrying
individuals is much more important than climate in terms of reintroduction
of vivax malaria into eliminated areas such as the United States and Europe,
where the Anopheline mosquito vectors have never been absent. Rare cases
of autochthonous malaria transmission continue to be reported in the USA
and Europe but represent little threat to malaria control if they remain iso-
lated instances without secondary cases (
Danis et al., 2011
).
1.2. Different Types of Vivax Malaria
Whether
P. vivax
consists of separate species or not will be left to those with
greater taxonomic knowledge and interest. From a public health viewpoint,
however, different vivax types certainly exist and the variability of relapses
and drug sensitivity have important control and elimination implications
(
White, 2011
;
Baird, 2009
). As explained in chapter 2, volume 80, tropical
vivax is much more likely to repeatedly relapse as well as demonstrate greater
resistance to chloroquine treatment than those types found away from the
equator, such as in China and the Korean peninsula. This is probably due
respectively to lack of evolutionary drive to adapt to limited transmission sea-
sons and wide-spread use of chloroquine in tropical areas. The circumstances
that encourage chloroquine resistance are continuously circulating blood par-
asites under consistent drug pressure, which occurs mostly in tropical areas.
Institution of polymerase chain reactions (PCR) for malaria diagnosis has
determined that the number of mixed falciparum/vivax infections as well as
asymptomatic parasitaemic persons is much larger than was appreciated from
traditional microscopic diagnosis (
Mayxay et al., 2004
). A malaria control
program that depends largely on symptomatic persons coming to a clinic for
microscopic diagnosis may be adequate for malaria control, but it certainly
will not be for malaria elimination as there will remain a reservoir of parasites
to continue transmission in the absence of ill persons (
Harris et al., 2010
). It is
unclear if molecular diagnostic methods can be practically transferred to the
field situation, but the requirement of a much more complete degree of case
