Evening star. [volume] (Washington, D.C.) 1854-1972, 1932-05-29
GERMS MULTIPLY
RAPIDLY IN FLEAS
Hundred Th0uSandth Part OF
Insect Transmits Deadly
Typhus.
BY THOMAS r. HENRY.

A deadly disease can be transmitted
by less than hundred-thousandth OF
flea.
i. This is established by experiments
just reported from the National Insti
tute OF Health laboratories here in the
transmission of endemic typhus, the
American form of this dreaded malady
which is carried by rat fieas instead Of
.he body lice responsible for the old
world form Of typhus.
Having established the fact that the
disease is caused by filterable virus
! which exists in rats and is transmitted
and his assistants set out to determine
the progress Of the virus between ami
NAL and man. They worked with
guinea pigs, which readily contract the
disease They wanted to know especial
ly whether the flea merely transmits
what it gets from the rat or whether
the virus multiplies in the insects body.
Three Days Required.
Il The fleas were allowed to feed on
infected rats. Then they were ground
| up In preparation and injected into the
guinea pigs 1t required an amount Of
the preparation equivalent to the bodies
of two fieaS to transmit the disease
| ed rats for only one day. A half-fiea
| injection did not invariably produce the
the disease until after three days feed
| ing After that the result could be pro-
| duced by an amount of the preparation
| equivalent to one thirty second OF a
| flea Up to about the sixth day the
| guinea pigs could be infected with in
| creasingly smaller amounts, and the in
cubation period, the time between the
injection and the development of the
disease by the animal, became pro-
| gressively shorter.
All the fleas used fed for the same
! time. "a hours, on the infected rats.
! Then they were removed into disease
free surroundings, Numbers OF them
were killed each day and made up into
| found that the virus in the insects
reached its height about tn sixth day.
Dr. Dyer and his assistants continued
| to experiment with smaller and smaller
amounts of the flea preparation. An
amount equivalent to l6-thouSandth
| of a hea produced the disease in the
guinea pigs 20 days after the feeding.
| Similar results were obtained with a
32-thousandth and 64-thousandth.
The final experiment was with an
amount of the preparation equivalent
to a 128-thousandth 40 days after the
insects had fed on the sick rats. This
| infinitely minute amount produced the
| disease in minimum of eight days.
Months Increase Is Large.
In slightly over a month, with no
! fresh source Of supply, the virus in the
body of the flea obtained originally
! from the infected rat had increased to
somewhat more than 100000 times its
original amount or potency. Probably
this increase came in a few days, after
which the amount remained stable
The findings are expected to prove of
considerable importance in measures
for the control of this native American
disease which breaks out in spots and
reaches its height during the late
Summer and Fall. The rat apparently
harbors only very minute amount
of the virus. 1t needs the body of
flea in which to grow before it reaches
its disease-producing potency.
Previous experiments by DR.. Dyer
and his associates had shown that f1eas
retain the infection for at least So days
after a single feeding on infected rats.
Apparently infected f1eas cannot trans
nit the virus to their young through
the eggs. 1t is also indicated by DR.
Dyer's experiments that the virus is
I not transmitted through the bites of
the infected f1eas, but it can be trans
mitted by rubbing the crushed bodies
of these insects against scratches in
the skin Of the guinea pig.
The discovery that the mysterious
filterable virus-presumably a living
organism, but SO small that it cannot
be detected by the most powerful
microscopes in the bodies of
insects is believed to be Of considerable
Importance in understanding the basic
biology of these living substances which
are responsible for so many human and
animal diseases
Associated with Dr. Dyer in the
experiment were Assistant Surgeons
w. G. Workman and E. r Ceder, and
Past Assistant Surgeons L. F. Badger
and A. Rumreich.