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In places where rats are very numerous plague may develop when
climatic conditions are adverse, i.e., when rat-fleas are scarce, but
plague tends to disappear with the advent of hot dry weather.
It cannot be too strongly emphasized that anti-rat measures, directed
towards the eradication of plague infection, can be prosecuted with
most chance of success in the hot dry months when plague cases and
foci of infection are fewest. The relatively plague-free season should
synchronize with maximum anti-plague effort and not be regarded as a
suitable time for a cessation of anti-plague measures.
Anti-plague measures can be grouped under four heads:-
(a) Rat elimination or the prevention of rat infestation. This
comprises such modifications in the habits, customs, and dwellings of
a community as will result in a diminished rat infestation in the homes
of the people and make the association between rats and men less
intimate than at present.
(b) Measures designed to protect the rat population of any given
town or village from plague infection. These entail a clear under-
standing of the manner in which plague infection is carried from
place to place.
(c) Rat destruction designed, as is (a), to diminish the chances
of infection, and to keep the rat population at so low a level that is
plague be introduced the severity of the resulting epidemic will be
appreciably diminished.
(d) If our efforts under these three heads fail to keep plague out
it is left to try and render the human population immune to attacks
of the disease by means of inoculation, or to remove the population
at risk from close association with infected rats. The latter involves
the evacuation of infected dwellings and the provision of temporary
accommodation outside the rat-infested, plague-infected area.
Measures included under (a), (b) and (c) can be carried out at any
season of the year; measures under (d) are generally applicable only
in the plague season.
Segregation of the sick is not essential. For all practical purposes
the patient suffering from bubonic plague is not capable of infecting
those in close attendance on him. Such a statement is not true of
pneumonic plague. Small outbreaks of this disease, which is extremely
infectious, are occasionally experienced in India. These are, however,
of infrequent occurrence and of small moment when compared with
the incidence of bubonic plague.
It will be noted that of the four 'components' of a plague
epidemic, viz., the plague bacillus, the rat-flea, the rat, and man, only
the rat and man have been specifically mentioned in this preliminary
discussion of preventive measures. The plague bacillus is so short-
lived outside the body of either the rat-flea, the rat, or man, that
for practical purposes it need not be considered as possessing an
independent existence. Similarly, the welfare of the rat-flea is so
dependent on the plentiful supply of rats which they parasitize, and
has so short a life apart from its proper host, especially if it be infected
with plague, that 'anti-flea' measures received no specific mention.
Such measures will be referred to when (b) is under detailed consi-
deration: they have very decided value and should in no wise be
overlooked.