ee
dl
aegis
.
SNle
as hie
5
ead
oe te
on
De at
de at
mts
Table 2. Comparison of number of reported
infections with number of viruses handled by
laboratories. Numbers in parentheses represent total number of laboratories checked.
Viruses
handled
(No.)
1-5
6-10
11-20
21-30
31-40
41
Unknown
Laboratories
reporting cases
TT
Percent
No.
29
9 (31)
43
6 (14)
I
(6)
19
100
23
33
(3)
16
32
42
67
4 (6)
0.
40
64
8 (20)
7 (11)
6
Ne)
were probably also acquired
by the
respiratory route.
Although many pathogens decrease
in their virulence for the natural host
after several passages, a number of
overt infections have been acquired
in the laboratory by individuals working with “laboratory-adapted” strains
of
various
arboviruses;
hence,
virus
strains that have been passed through
animals many times may bestill pathogenic for man (/4, 17). A serious laboratory infection with St. Louis en-
9
1
igo
£23] ARBOVIRUSES
RECOGNIZED
ES|IOVERT
40LABORATORY
INFECTIONS
20+
160+
that had been passed through mice
many times over a period of 16 years.
Disease occurred in an individual who
had worked with a strain of Rift Valley
ly acquired infection, but yet they have
fever virus that had undergone over
to cause disease in man through naturalproduced infections in the laboratory.
Acquisition of laboratory infections
is not always similar to transmission
of the disease when it occurs naturally.
For example,
none
of the cases
of
encephalitis was believed to be trans-
mitted by an arthropod, and only one
case of yellow fever was thought to
be due to the bite of an infected mosquito. Many persons have become infected while working with dried virus
preparations which provide ideal circumstances for aerosol transmission.
A case of St. Louis encephalitis and a
fatal case of Russian spring-summer
encephalitis apparently resulted from
aerosol transmission of such materials
(14, 15), Contaminated dust from
mouse cages was apparently responsi-
150 mouse passages, and Japanese B
encephalitis occurred in an individual
who had worked with a strain that
had been through six passages in a
mouse brain and one passage in chickembryo cell cultures.
The intensity of activity of the reporting laboratories may be indicated
by the number of viruses with which
they had been working (Table 2). The
percentage of laboratories reporting infections increased directly with the number of viruses being studied in the
laboratory. This was the only apparent
relation between a characteristic of the
laboratory (size of staff, length of operation, and number of viruses handled)
listed on the questionnaire and number of infections {including subclini-
ble for several infections with the virus
cal) reported.
litis (76) and for a fatal infection with
Machupo virus; thus, these infections
directly related to the number of ac-
of Venezuelan equine encephalomye-
Failure of the size of staff to be
quired infections may be due to the
increase in the proportion of supportive
personnel
Table 3. Proved or probable sources of labOratory-acquired arbovirus infections. Cases
are distributed according to the one most
probable source.
Probable source
Experimentally infected
animals
Not indicated
Aerosol
Agent handled
Accidents
Preparation of vaccines,
antigens, and other
Experimentally infected
chick embryos
Discarded glassware
Autopsy (including
known accidents)
Clinical specimens
8 DECEMBER 1967
Infec-
Percent-
(No.)
total
tions
age of
93
84
74
70
43
21.7
19.6
17.3
16.4
10.0
35
8.2
9
9
2.1
2.1
8
3
1.9
0.7
in
such
lJaboratories—indi-
viduals who have less exposure to infection. Unless the maintenance of records of acquired infection is an ad-
7
7
4
loot
4
80+
4
60}
4
40h
20
4
23
22
ge
cephalitis virus occurred in an investigator who had worked: with a strain
infection (13). Several additional arboviruses (Germiston, Kunjin, Piry, and
Nairobi sheep disease) are not known
§
13 Fes
5 [ BS.
98 82 23
a
oO
i
oa
‘
SES
7
$8
or
Fig. 1. Number of overt laboratory infections and recognition of new arboviruses by decade. In addition, 12 arboviruses have been added to the ACAV
catalog; one virus, Canjam, was respon-
sible for an overt mild febrile illness.
in the number of overt infections acquired in the laboratory correlates with
the increase in the recognition of new
arboviruses (Fig. 1). Changes in the
kinds of agents involved in laboratory
infections and in the circumstances
resulting in infection to some extent
reflect trends in areas of research and
interest in certain agents (/8). Prior
to 1950, bacterial infections accounted
for over one-half of known overt cases
of laboratory-acquired infections, while
viruses were responsible for about 20
percent of the total. Since 1950, there
has been an increasing number of laboratory-acquired infections due to viruses, with more than half due to arbo-
viruses, This is probably the result of
the marked acceleration in research and
diagnosis in connection with arboviruses and a consequent increase in the
number of persons and laboratories
handling such agents. A large propor-
tion of the total number of infections
due to arboviruses occurred since 1950
ministrative routine of the laboratory
(Fig. 1). Relatively few laboratories
worked with these viruses prior to
changing, one would not expect a ret-
tory infections at that time reflect the
and unless surveillance has been un-
rospective query to obtain as many early
as later cases of infection. The lack
of relationship between numberof infections and length of operation of lab-
oratories may be ascribed in part to
an inadequacy of reporting and in
part to changing methodologies. Because of these variables, a man-year
exposure index was not presented for
any virus.
1941, and the agents causing labora-
area of interest prevailing then.
The exact source of a laboratoryacquired infection is frequently obscure, Often it is known only that an
individual had been working with a
particular agent or that he had been
in contact with infected animals. In
other situations, it is known that the
atmosphere of the laboratory had become contaminated. That an aerosol
Over 80 percent of the currently
may be unwittingly produced by a va-
nized since 1950. The steady increase
dures has been conyinginghy: dérion-
classified arboviruses have been recog-
tiety
of common
laboratory _proce1285