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Letters to the Editor
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Athena
Challenging statement regarding mosquitoes
From Mr J. A. Parry, MRPharmS
Your columnist, Athena, has made the most incredibly challenging statement
(PJ, 21 July, p78) asserting that the mosquito Culex pipiens “is
the most common transmitter of malaria”. It is, to my mind, essential
that this serious allegation should be repudiated immediately. If it
were true, then malaria would be endemic throughout the UK, because Culex
pipiens is overall the most abundant mosquito of our land, being overtaken
only by Aedes cantans and Aedes rustica in some wooded areas.
Malaria is caused by species of the protozoon genus Plasmodium, of which
there are many species. These parasites each have two hosts, one of which
is a bloodsucking insect and the other a vertebrate, such as an anthropoid,
bird, lizard or other. In anthropoid (ie, human, simian) malaria the
parasite is carried only by one or more of the many species of anopheles
mosquito. The parasite is passed between the two hosts alternately.
Anopheles mosquitoes may be recognised by their characteristic resting
position in which the body, wings and proboscis are aligned in a forward-sloping
position as opposed to the horizontal stance of culicines. The only British
species, Anopheles maculipennis, does occur commonly in this country,
most frequently in salt marshes, where in earlier times sporadic outbreaks
of malaria (then known as “ague”) did occur. The wings of
A maculipennis are dark-spotted, the only other indigenous mosquito that
has spotted wings being Theobaldia annulata (and sometimes in the Scottish
Highlands T alaskaensis). Both these are much larger.
Culex species, including Culex pipiens, have never been implicated in
the transmission of anthropoid malaria. A telephone call to the London
School of Hygiene and Tropical Medicine will confirm this.
This mistake would not in itself appear to be important, but journalists
from the tabloids do peruse professional journals for juicy titbits and
if the statement should be taken seriously, every open stretch of water
from garden water butts to Windermere might be covered by a thin film
of liquid paraffin or engine oil in order to kill all mosquito larvae
and eradicate this “pest”. This of course has happened in
areas of Africa such as Gambia (where the worst form of malaria, quaternary
malaria, caused by Plasmodium falciparum is endemic), with catastrophic
consequences for the local aquatic wildlife. It is important, therefore,
that the statement is refuted at once.
There is a form of malaria called avian malaria, also caused by a plasmodium,
which is indeed carried by culicine mosquitoes. It does not appear to
be endemic in the UK, but it could explain how this misunderstanding
may have occurred.
I am much surprised that this error was not noticed by The Journal‘s
editorial team, or by any other pharmacist on the staff, because I should
have thought that by now all pharmacists would have become aware of the
causal organisms and vectors of malaria.
John Parry
Tenterden,
Kent
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ATHENA responds:
Ronald Ross won a Nobel Prize (1902)
for demonstrating the existence of plasmodium in the wall of the midgut
and salivary glands
of a culex or common house mosquito (1898). Indeed the life cycle
of the plasmodium was researched extensively in this species.
However
since
then, research has
shown that the anopheles mosquito is the most common transmitter of malaria
in humans. It has been suggested that the increasing numbers of
culex in the domestic
environment could lead to an increase in feeding on humans (as adverse to
birds, their preferred targets) and transmission of disease. Culex is
also a transmitter
of West Nile virus, filariasis and Japanese encephalitis.
I offer my apologies
for the wording in the article, which may have misled readers. |
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The
Pharmaceutical Journal