Health > Housing and malaria

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CONCLUSIONS.
The matter may be summed up thus :
The anopheles associated by experience in the transmission of malaria are in the
main house-haunters and night-biters, circumstances which make it likely that the
house is important in the transmission of malaria. This likelihood is increased by the
consideration that throughout that part of the world where malaria can be transmitted
there are “malarious houses”, houses where inhabitant after inhabitant acquires
malaria. These houses have certain characteristics, at least in Europe ; they possess
dark, dirty and often damp portions. In parts of Europe and in indigenous dwellings
in the tropics, a chimneyless fire is efficient in driving away anopheles from places which
would otherwise suit them, and it is suggested that this condition in the past must
widely have influenced the incidence of malaria in Europe ; with the invention of the
chimney it needed the further institution of ample lighting before houses again became
distasteful to anopheles. There is slight, though disputed, evidence that A. maculi-
pennis may actually breed inside houses ; it appears established that A. stephensi w\W
do so in Bombay. It is the case that infected anopheles may be particularly associated
with certain houses, and the question has been considered as to whether these
mosquitoes have an instinct to return to a pleasant hospice after they have left it to
oviposit. Such evidence as exists for an instinct of this kind is questionable ; the facts
are perhaps explicable as showing a tropism towards food, and, if so, they emphasise
the importance of abolishing breeding-places near houses, so that no house shall
become established as a malarious one by virtue of being near enough to a breeding-
place to exercise a food taxis on an infected ovipositing anopheles looking for her next
meal. Certain species of anopheles leave the house where they have fed immediately
after feeding, others remain in it for some hours. There is, however, at least in Europe,
Northern America and Brazil, a condition of gonotropic dissociation, when the need
to oviposit ceases, while the need to feed does not. Mosquitoes in this condition remain
in the house where they have fed, and they are capable of becoming malarious and of
transmitting malaria. There is some evidence too that anopheles may become sick
of malaria, an added reason for their failure to leave the house where they became
infected. The effects of aestivation in this direction are unknown. The kind of blood
meal which has been consumed by anopheles caught in houses shows that they are not
tied to any particular feeding-place, and an anopheles caught in a house has often had
her previous meal from some animal outside it ; as to the converse, there appears to be
little evidence, though that is the point which would here be important. There is no