London's Pulse: Medical Officer of Health reports 1848-1972

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City of London 1932

[Report of the Medical Officer of Health for Port of London]

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27
Species of "Rats.—Under the heading "Black Eat" are included the different
varieties of Mus rattus, and under that of "Brown Rat" are included all varieties of
Mus norvegicus.
Observations on Rats.—During the investigation 728 rats were examined.
This number was comprised of 497 black and 231 brown rats. Of the total, 242 rats
were found not to be harbouring fleas.
The greatest number of fleas obtained from a single rat was 61. This host was an
old brown rat trapped at Tilbury Dock in November, 1932. All the fleas were
C. fasciatus.
A small number (10 per cent.) of all the rats were autopsied with a view to
ascertaining the presence of any microscopical lesions in the viscera which might seem
to indicate a "plague carrier," but in none of these rats was any suspicious lesion
noticed.
Observations on Fleas.—The average number of fleas per rat for the whole
period was 3.08. C. fasciatus appears to be the predominating flea throughout the
year, the number encountered being 83.09 per cent. of the total flea count for the year.
The C. fasciatus Index for all zones reached its highest in November, when it was
3.6. The G. fasciatus index for all zones for the whole period under review is 2.55.
Leptopsylla musculi.—During the winter months occasional specimens of this
flea were met with. With the onset of warmer weather its numbers increased so that
in June, 1932. it constituted 18.3 per cent. of the total fleas examined. In July, this
figure rose to 20 per cent., and this percentage was maintained throughout August.
A rise to 34 per cent. of the total fleas examined was recorded in September. During
October the figure reverted to 20 per cent. and this was followed by a sudden decline
in the numbers encountered during the months of November and December. The
period of its maximum incidence would appear to correspond fairly closely to that of
C. fasciatus.
Ctenophthalmus agyrtes.—Only nine specimens of this flea were obtained from
two hosts. Seven were obtained from a brown rat trapped at Tilbury Dock in
February, 1932, and two were obtained from a brown male rat caught in the Royal
Albert Dock in May, 1932.
Ctenocephalus felis was encountered on four occasions only. Five in number,
they were obtained from four black rats during the months of June, July, October,
1932, and January, 1933. The hosts of four of those fleas came from B. Zone and
the host of one from A. Zone (St. Katharine Dock).
Xenopsylla, C. londiniensis, P. irritans.—A noteworthy feature was the failure
to discover a single representative of either of the above genera. All fleas examined
were submitted to the Department of Entomology, London School of Hygiene and
Tropical Medicine, for confirmation of identifications.


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