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XXVI. The part played by insects in the epidemiology of plague

  • D. T. Verjbitski (a1)
Extract

(1) All fleas and bugs which have sucked the blood of animals dying from plague contain plague1 microbes.

(2) Fleas and bugs which have sucked the blood of animals which are suffering from plague only contain plague microbes when the bites have been inflicted from 12 to 26 hours before the death of the animals, that is, during that period of their illness when their blood contains plague bacilli.

(3) The vitality and virulence of the plague microbes are preserved in these insects.

(4) Plague bacilli may be found in fleas from four to six days after they have sucked the blood of an animal dying with plague. In bugs, not previously starved or starved only for a short time (one to seven days), the plague microbes disappear on the third day; in those that have been starved for 4 to 4½ months, after eight or nine days.

(5) The numbers of plague microbes in the infected fleas and bugs increase during the first few days.

(6) The faeces of infected fleas and bugs contain virulent plague microbes as long as they persist in the alimentary canal of these insects.

(7) Animals could not be infected by the bites of fleas and bugs which had been infected by animals whose own infection had been occasioned by a culture of small virulence, notwithstanding the fact that the insects may be found to contain abundant plague microbes.

(8) Fleas and bugs that have fed upon animals which have been infected by cultures of high virulence convey infection by means of bites, and the more certainly so the more virulent the culture with which the first animal was inoculated.

(9) The local inflammatory reaction in animals which have died from plague occasioned by the bites of infected insects is either very slight or absent. In the latter case it is only by the situation of the primary bubo that one can approximately identify the area through which the plague infection entered the organism.

(10) Infected fleas communicate the disease to healthy animals for three days after infection. Infected bugs have the power of doing so for five days.

(11) It was not found possible for more than two animals to be infected by the bites of the same bugs.

(12) The crushing of infected bugs in situ during the process of biting, occasioned in the majority of cases the infection of the healthy animal with plague.

(13) The injury to the skin occasioned by the bite of bugs or fleas offers a channel through which plague microbes can easily enter the body and occasion death from plague.

(14) Crushed infected bugs and fleas and their faeces, like other plague material, can infect through the small punctures of the skin caused by the bites of bugs and fleas, but only for a short time after the infliction of these bites.

(15) In the case of linen and other fabrics soiled by crushing infected fleas and bugs on them, or by the faeces of these insects, the plague microbes can under favourable conditions remain alive and virulent during more than five months.

(16) Chemical disinfectants do not in the ordinary course of application kill plague microbes in infected fleas and bugs.

(17) The rat flea Typhlopsylla musculi does not bite human beings.

(18) Human fleas do bite rats.

(19) Fleas found on dogs and cats bite both human beings and rats.

(20) Human fleas and fleas found on cats and dogs can live on rats as casual parasites, and therefore can under certain conditions play a part in the transmission of plague from rats to human beings, and vice versa.

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page 162 note 1 The attention of the Committee was drawn to the work by a short abstract in the Journal de Physiologie et de Pathologie générale, vol. VIII. 1906, p. 387.

page 163 note 1 Dr Verjbitski is presumably referring to his experience in Cronstadt. The commonest rat flea in most parts of Europe is Ceratophyllus fasciatus, and in India and most subtropical countries Pulex cheopis of Rothschild (see Journal of Hygiene, vol. VI. 1906, p. 483). Ed.

page 187 note 1 In Nuttall's experiments (Centralbl. f. Bakt. XXII. (1897), p. 92)Cimex lectularius which had starved for three months were fed on septicaemic plague mice. The bugs were kept at 20°C. and their contents injected at intervals into mice. Virulent bacilli survived for 72 hours (but not for 120 hours) in the bugs. Smear preparations of the gut contents of the bugs made 24 hours after feeding on infected blood revealed an almost pure culture of B. pestis, but after 48 hours they appeared to be distinctly fewer in number and more saprophytes were present. The longer survival found by Dr Verjbitski is doubtless due to the lower temperature at which he kept his bugs.—Ed.

page 190 note 1 Materials for the Study of Relapsing Fever, Dissertation, 1898.

page 194 note 1 Nuttall (1897, p. 92) made four experiments with mice with negative results: two to ten bugs were applied at the root of the tail.—Ed.

page 205 note 1 That is, if a septicaemia is present. Dr Verjbitski does not appear to have had the experience that rats may die of plague without developing a septicaemia sufficiently extensive to infect the flea: this not infrequently occurs especially in cool climates.—Ed.

page 207 note 1 Dr Verjbitski presumably means in his experience. This was not by any means the case with the observations of the Commission.—Ed.

page 207 note 2 This is of course not true for the Indian rat flea (P. cheopis): see these reports Journal of Hygiene, vol. VII. (1897), p. 472.—Ed.

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Epidemiology & Infection
  • ISSN: 0950-2688
  • EISSN: 1469-4409
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