MALARIA, MOSQUITOES AND THE ESSEX MARSHES 35
Malaria, Mosquitoes and the Essex Marshes*
By T. H. C. Bartrop, F.R.S.H.
The choice of a subject for my first Presidential Address has
not been an easy one. My final choice was made because of a
number of circumstances, among them being my war-time
experiences in anti—malarial measures, my easy access to the
Essex Record Office and to certain specialised libraries, my
interest in the affairs of the World Health Organisation (whose
main theme for 1962 is, by a coincidence, 'The World United
Against Malaria') and the idea that I thought it would be of in-
terest to bring together earlier Essex records of the disease.
It is now well known that malaria is a disease caused by the
malarial parasite which is transferred from man to man by mos-
quitoes; in England, as in Essex, indigenous (or locally con-
tracted) malaria is now almost a thing of the past. The purpose
of this paper is to give an historical survey from published records
of the disease in our own county of Essex, but before doing this
it seems essential to give general descriptions of the disease, the
causal organism, the insect vector and the method of transmission.
The female mosquito—and it is only the female which is able
to puncture the skin and suck blood—needs a meal of blood to
allow the ovaries to develop. The mosquito punctures the skin
and drives in her proboscis, draws blood and continues to do so
unless disturbed!) until she is full. She then withdraws her
proboscis and flies away to a quiet spot to rest and digest the
meal. If her victim was suffering from malaria, then the malarial
parasites in the red blood cells will be taken into the mosquito's
body and development, as described later, will take place, and
parasites will eventually reach her salivary glands.
The mosquito feeds every two or three days, but as it takes
about fourteen days for the parasites to complete their life cycle
in the mosquito, it will be at a later blood meal that the mosquito,
when driving in her proboscis (together with saliva), will inject
malarial parasites before she begins to draw blood—and so a new
victim is infected. The object of injecting saliva is not definitely
known. It may have a retarding influence on the coagulation of
the blood; it may reduce the capillary resistance to the flow of
the blood up the proboscis; it may mingle with the blood and
aid digestion; or it may be the means of washing out any film of
blood left in the tube.
The period of fourteen days for the parasites to complete their
life cycle in the mosquito is a very important one from the point
of view of malaria control It also means that only the relatively
elderly mosquito is dangerous.
The main causal organism so far as indigenous malaria in this
country is concerned, is Plasmodium vivax (Fig. 5), one of four
*Presidential Address—24th March 1962.